Science.gov

Sample records for quaking neutron star

  1. Alfvn seismic vibrations of crustal solid-state plasma in quaking paramagnetic neutron star

    NASA Astrophysics Data System (ADS)

    Bastrukov, S.; Molodtsova, I.; Takata, J.; Chang, H.-K.; Xu, R.-X.

    2010-11-01

    Magneto-solid-mechanical model of two-component, core-crust, paramagnetic neutron star responding to quake-induced perturbation by differentially rotational, torsional, oscillations of crustal electron-nuclear solid-state plasma about axis of magnetic field frozen in the immobile paramagnetic core is developed. Particular attention is given to the node-free torsional crust-against-core vibrations under combined action of Lorentz magnetic and Hooke's elastic forces; the damping is attributed to Newtonian force of shear viscose stresses in crustal solid-state plasma. The spectral formulas for the frequency and lifetime of this toroidal mode are derived in analytic form and discussed in the context of quasiperiodic oscillations of the x-ray outburst flux from quaking magnetars. The application of obtained theoretical spectra to modal analysis of available data on frequencies of oscillating outburst emission suggests that detected variability is the manifestation of crustal Alfvn's seismic vibrations restored by Lorentz force of magnetic field stresses.

  2. Alfven seismic vibrations of crustal solid-state plasma in quaking paramagnetic neutron star

    SciTech Connect

    Bastrukov, S.; Xu, R.-X.; Molodtsova, I.; Takata, J.; Chang, H.-K.

    2010-11-15

    Magneto-solid-mechanical model of two-component, core-crust, paramagnetic neutron star responding to quake-induced perturbation by differentially rotational, torsional, oscillations of crustal electron-nuclear solid-state plasma about axis of magnetic field frozen in the immobile paramagnetic core is developed. Particular attention is given to the node-free torsional crust-against-core vibrations under combined action of Lorentz magnetic and Hooke's elastic forces; the damping is attributed to Newtonian force of shear viscose stresses in crustal solid-state plasma. The spectral formulas for the frequency and lifetime of this toroidal mode are derived in analytic form and discussed in the context of quasiperiodic oscillations of the x-ray outburst flux from quaking magnetars. The application of obtained theoretical spectra to modal analysis of available data on frequencies of oscillating outburst emission suggests that detected variability is the manifestation of crustal Alfven's seismic vibrations restored by Lorentz force of magnetic field stresses.

  3. Neutron Stars

    NASA Technical Reports Server (NTRS)

    Cottam, J.

    2007-01-01

    Neutron stars were discovered almost 40 years ago, and yet many of their most fundamental properties remain mysteries. There have been many attempts to measure the mass and radius of a neutron star and thereby constrain the equation of state of the dense nuclear matter at their cores. These have been complicated by unknown parameters such as the source distance and burning fractions. A clean, straightforward way to access the neutron star parameters is with high-resolution spectroscopy. I will present the results of searches for gravitationally red-shifted absorption lines from the neutron star atmosphere using XMM-Newton and Chandra.

  4. Dibaryons in neutron stars

    NASA Technical Reports Server (NTRS)

    Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.

    1991-01-01

    The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.

  5. Neutron skins and neutron stars

    SciTech Connect

    Piekarewicz, J.

    2013-11-07

    The neutron-skin thickness of heavy nuclei provides a fundamental link to the equation of state of neutron-rich matter, and hence to the properties of neutron stars. The Lead Radius Experiment ('PREX') at Jefferson Laboratory has recently provided the first model-independence evidence on the existence of a neutron-rich skin in {sup 208}Pb. In this contribution we examine how the increased accuracy in the determination of neutron skins expected from the commissioning of intense polarized electron beams may impact the physics of neutron stars.

  6. Introduction to neutron stars

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2015-02-01

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  7. Introduction to neutron stars

    SciTech Connect

    Lattimer, James M.

    2015-02-24

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  8. General relativity and neutron stars

    NASA Astrophysics Data System (ADS)

    Yakovlev, D. G.

    2016-01-01

    General Relativity affects all major aspects of neutron star structure and evolution including radiation from the surface, neutron star models, evolution in compact binaries. It is widely used for neutron star mass measurements and for studying properties of superdense matter in neutron stars. Observations of neutron stars help testing General Relativity and planning gravitational wave experiments. No deviations from Einstein Theory of Gravity have been detected so far from observations of neutron stars.

  9. STAR RNA-binding protein Quaking suppresses cancer via stabilization of specific miRNA.

    PubMed

    Chen, An-Jou; Paik, Ji-Hye; Zhang, Hailei; Shukla, Sachet A; Mortensen, Richard; Hu, Jian; Ying, Haoqiang; Hu, Baoli; Hurt, Jessica; Farny, Natalie; Dong, Caroline; Xiao, Yonghong; Wang, Y Alan; Silver, Pamela A; Chin, Lynda; Vasudevan, Shobha; Depinho, Ronald A

    2012-07-01

    Multidimensional cancer genome analysis and validation has defined Quaking (QKI), a member of the signal transduction and activation of RNA (STAR) family of RNA-binding proteins, as a novel glioblastoma multiforme (GBM) tumor suppressor. Here, we establish that p53 directly regulates QKI gene expression, and QKI protein associates with and leads to the stabilization of miR-20a; miR-20a, in turn, regulates TGF?R2 and the TGF? signaling network. This pathway circuitry is substantiated by in silico epistasis analysis of its components in the human GBM TCGA (The Cancer Genome Atlas Project) collection and by their gain- and loss-of-function interactions in in vitro and in vivo complementation studies. This p53-QKI-miR-20a-TGF? pathway expands our understanding of the p53 tumor suppression network in cancer and reveals a novel tumor suppression mechanism involving regulation of specific cancer-relevant microRNAs. PMID:22751500

  10. STAR RNA-binding protein Quaking suppresses cancer via stabilization of specific miRNA

    PubMed Central

    Chen, An-Jou; Paik, Ji-Hye; Zhang, Hailei; Shukla, Sachet A.; Mortensen, Richard; Hu, Jian; Ying, Haoqiang; Hu, Baoli; Hurt, Jessica; Farny, Natalie; Dong, Caroline; Xiao, Yonghong; Wang, Y. Alan; Silver, Pamela A.; Chin, Lynda; Vasudevan, Shobha; DePinho, Ronald A.

    2012-01-01

    Multidimensional cancer genome analysis and validation has defined Quaking (QKI), a member of the signal transduction and activation of RNA (STAR) family of RNA-binding proteins, as a novel glioblastoma multiforme (GBM) tumor suppressor. Here, we establish that p53 directly regulates QKI gene expression, and QKI protein associates with and leads to the stabilization of miR-20a; miR-20a, in turn, regulates TGFβR2 and the TGFβ signaling network. This pathway circuitry is substantiated by in silico epistasis analysis of its components in the human GBM TCGA (The Cancer Genome Atlas Project) collection and by their gain- and loss-of-function interactions in in vitro and in vivo complementation studies. This p53–QKI–miR-20a–TGFβ pathway expands our understanding of the p53 tumor suppression network in cancer and reveals a novel tumor suppression mechanism involving regulation of specific cancer-relevant microRNAs. PMID:22751500

  11. Probing Neutron Star Physics with Quasi-Periodic Oscillations in Magnetar Bursts

    NASA Astrophysics Data System (ADS)

    Huppenkothen, Daniela

    2015-04-01

    Neutron stars, the remnants of massive stellar explosions, are prime candidates for studying dense matter physics in conditions not accessible in the laboratory. Among the zoo of neutron star phenomena, magnetars, neutron stars with an extremely high magnetic field, are of particular interest for their spectacular bursting behaviour in X-rays and gamma-rays. They show thousands of recurrent short, bright bursts as well as some of the brightest gamma-ray events, called giant flares, ever observed on earth. The detection of quasi-periodic oscillations (QPOs) in giant flares and, more recently, in small recurrent bursts, is generally interpreted as the observable signature of global oscillations of the neutron star following a star quake. This detection has opened up the potential of neutron star seismology: probing the physical conditions in the interior of the star via the information conveyed in star quakes. In this talk, I will give an overview of observational studies of these sources, focusing on recent detections of QPOs in smaller bursts as well as results from the giant flares. I will then tie these observational results to theoretical models of the star quakes that tie observations to the neutron star interior and crust, and I will finish with an outlook of the future of magnetar seismology. DH is supported by the Moore-Sloan Data Science Environment at NYU.

  12. Neutron star models

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Bowers, R. L.

    1981-01-01

    The current state of neutron star structure calculations is reviewed. Uncertainties in the equation of state for matter at and above nuclear density remain. The role of the delta resonance, pion condensates, and quark matter is reviewed. It is found that recent models yield stable neutron star masses which are consistent with observational estimates.

  13. Neutron Star Cooling: II

    NASA Astrophysics Data System (ADS)

    Tsuruta, Sachiko

    It was more than 70 years ago when Baade and Zwicky [3] speculated that an exotic star consisting mostly of neutrons, now known as a neutron star, may be formed when a normal star collapses through a supernova explosion. During the subsequent years in the 1930s several theorists, including Oppenheimer and Volkoff [35], discussed the properties of neutron stars. However, it was not until the late 1950s to the early 1960s, when curiosity on such a hypothetical object revived [11,73]. As far as I am aware Cameron [11] is the first author who discussed thermodynamic problems of neutron stars. This article's author chose to explore this problem as one of the projects on neutron stars as her PhD thesis [59]. The research started as a purely theoretical endeavor, but before the calculations were completed we learned of the discovery of the first Galactic X-ray source Sco X-1, which was soon followed by the second such Galactic X-ray source detection, this time in the Crab supernova remnant [15]. It was immediately suggested by several theorists [19, 59, 66] that these strong X-ray sources might be neutron stars, because if these X-rays are blackbody radiation as expected, the radius of the emitting region has to be as small as 10 km (because the temperature is so high), just the correct size predicted for a neutron star.1

  14. Converting neutron stars into strange stars

    NASA Technical Reports Server (NTRS)

    Olinto, A. V.

    1991-01-01

    If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

  15. Hyperons in neutron stars

    NASA Astrophysics Data System (ADS)

    Katayama, Tetsuya; Saito, Koichi

    2015-07-01

    Using the Dirac-Brueckner-Hartree-Fock approach, the properties of neutron-star matter including hyperons are investigated. In the calculation, we consider both time and space components of the vector self-energies of baryons as well as the scalar ones. Furthermore, the effect of negative-energy states of baryons is partly taken into account. We obtain the maximum neutron-star mass of 2.08M?, which is consistent with the recently observed, massive neutron stars. We discuss a universal, repulsive three-body force for hyperons in matter.

  16. Cooling of neutron stars

    NASA Technical Reports Server (NTRS)

    Pethick, C. J.

    1992-01-01

    It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.

  17. The elastic energy and character of quakes in solid stars and planets

    NASA Technical Reports Server (NTRS)

    Pines, D.; Shaham, J.

    1972-01-01

    The quadrupolar mechanical energy of a rotating axially symmetric solid planet (with or without a liquid interior) is calculated using methods previously developed for neutron stars in which an elastic reference tensor is introduced to describe the build-up of elastic energy in the star. The basic parameters of the theory (the gravitational energy A and elastic energy B) depend upon the internal structure of the planet and may be calculated from specific planetary models. Explicit expressions are obtained for the Love numbers, and for the planetary wobble frequency. The theory provides a simple relationship between changes in shape or axis of figure of the planet and elastic energy release. The theory is extended to describe the Earth by taking into account isostasy, triaxiality and the observed lithospheric configuration.

  18. Planets Around Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wolszczan, Alexander; Kulkarni, Shrinivas R; Anderson, Stuart B.

    2003-01-01

    The objective of this proposal was to continue investigations of neutron star planetary systems in an effort to describe and understand their origin, orbital dynamics, basic physical properties and their relationship to planets around normal stars. This research represents an important element of the process of constraining the physics of planet formation around various types of stars. The research goals of this project included long-term timing measurements of the planets pulsar, PSR B1257+12, to search for more planets around it and to study the dynamics of the whole system, and sensitive searches for millisecond pulsars to detect further examples of old, rapidly spinning neutron stars with planetary systems. The instrumentation used in our project included the 305-m Arecibo antenna with the Penn State Pulsar Machine (PSPM), the 100-m Green Bank Telescope with the Berkeley- Caltech Pulsar Machine (BCPM), and the 100-m Effelsberg and 64-m Parkes telescopes equipped with the observatory supplied backend hardware.

  19. Neutrinos from neutron stars

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.

    1979-01-01

    A calculation of the flux of ultra-high energy neutrinos from galactic neutron stars is presented. The calculation is used to determine the number of point sources detectable at the sensitivity threshold of a proposed deep underwater muon and neutrino detector array. The detector array would have a point source detection threshold of about 100 eV/sq cm-sec. Analysis of neutrino luminosities and the number of detectable sources suggests that the deep underwater detector may make a few discoveries. In particular, a suspected neutron star in the Cyg X-3 source seems a promising target for the deep underwater array.

  20. Neutron Star Phenomena

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin

    1998-01-01

    Various phenomena involving neutron stars are addressed. Electron-positron production in the near magnetosphere of gamma-ray pulsars is discussed along with magnetic field evolution in spun-up and spinning-down pulsars. Glitches and gamma-ray central engines are also discussed.

  1. Hyperons and neutron stars

    SciTech Connect

    Vidaña, Isaac

    2015-02-24

    In this lecture I will briefly review some of the effects of hyperons on the properties of neutron and proto-neutron stars. In particular, I will revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a puzzle which has become more intringuing and difficult to solve due the recent measurements of the unusually high masses of the millisecond pulsars PSR J1903+0327 (1.667±0.021M{sub ⊙}), PSR J1614–2230 (1.97±0.04M{sub ⊙}), and PSR J0348+0432 (2.01±0.04M{sub ⊙}). Finally, I will also examine the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

  2. Hyperons in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Vidaña, Isaac

    2016-01-01

    In this work I briefly review some of the effects of hyperons on the properties of neutron and proto-neutron stars. In particular, I revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a puzzle which has become more intringuing and difficult to solve because of the recent measurements of the unusually high masses of the millisecond pulsars PSR J1903+0327 (1.667 ± 0.021M⊙), PSR J1614-2230 (1.97 ± 0.04M⊙), and PSR J0348+0432 (2.01 ± 0.04M⊙). Some of the solutions proposed to tackle this problem are discussed. Finally, I re-examine also the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

  3. Neutron Stars and NuSTAR

    NASA Astrophysics Data System (ADS)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses among all classes of neutron star binaries. Intrigued by this diversity - which points to diverse birth masses - we undertook a systematic survey to measure the masses of neutron stars in nine high-mass X-ray binaries. In this thesis, I present results from this ongoing project. While neutron stars formed the primary focus of my work, I also explored other topics in compact objects. Appendix A describes the discovery and complete characterization of a 1RXS J173006.4+033813, a polar cataclysmic variable. Appendix B describes the discovery of a diamond planet orbiting a millisecond pulsar, and our search for its optical counterpart.

  4. Neutron matter, symmetry energy and neutron stars

    NASA Astrophysics Data System (ADS)

    Gandolfi, S.; Steiner, A. W.

    2016-01-01

    Recent progress in quantum Monte Carlo with modern nucleon-nucleon interactions have enabled the successful description of properties of light nuclei and neutron- rich matter. Of particular interest is the nuclear symmetry energy, the energy cost of creating an isospin asymmetry, and its connection to the structure of neutron stars. Combining these advances with recent observations of neutron star masses and radii gives insight into the equation of state of neutron-rich matter near and above the saturation density. In particular, neutron star radius measurements constrain the derivative of the symmetry energy.

  5. Compactness of Neutron Stars.

    PubMed

    Chen, Wei-Chia; Piekarewicz, J

    2015-10-16

    Recent progress in the determination of both masses and radii of neutron stars is starting to place stringent constraints on the dense matter equation of state. In particular, new theoretical developments together with improved statistical tools seem to favor stellar radii that are significantly smaller than those predicted by models using purely nucleonic equations of state. Given that the underlying equation of state must also account for the observation of 2M⊙ neutron stars, theoretical approaches to the study of the dense matter equation of state are facing serious challenges. In response to this challenge, we compute the underlying equation of state associated with an assumed mass-radius template similar to the "common radius" assumption used in recent studies. Once such a mass-radius template is adopted, the equation of state follows directly from the implementation of Lindblom's algorithm; assumptions on the nature or composition of the dense stellar core are not required. By analyzing mass-radius profiles with a maximum mass consistent with observation and common radii in the 8-11 km range, a lower limit on the stellar radius of a 1.4M⊙ neutron star of RNS≳10.7  km is required to prevent the equation of state from violating causality. PMID:26550859

  6. The physics of neutron stars.

    PubMed

    Lattimer, J M; Prakash, M

    2004-04-23

    Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics, and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near 10(10) kelvin, opaqueness to neutrinos, and magnetic fields in excess of 10(13) Gauss. Here, we describe the formation, structure, internal composition, and evolution of neutron stars. Observations that include studies of pulsars in binary systems, thermal emission from isolated neutron stars, glitches from pulsars, and quasi-periodic oscillations from accreting neutron stars provide information about neutron star masses, radii, temperatures, ages, and internal compositions. PMID:15105490

  7. On magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Lopes, Luiz; Menezes, Debora

    2015-08-01

    In this work we review the formalism normally used in the literature about the effects of density-dependent magnetic fields on the properties of neutron and quark stars, expose some ambiguities that arise and propose a way to solve the related problem. Our approach explores more deeply the concept of pressure, yielding the so called chaotic magnetic field formalism for the stress tensor. We also use a different way of introducing a variable magnetic field, which depends on the energy density rather than on the baryonic density, which allows us to build a parameter free model.

  8. QCD in Neutron Stars and Strange Stars

    SciTech Connect

    Weber, Fridolin; Negreiros, Rodrigo

    2011-05-24

    This paper provides an overview of the possible role of Quantum Chromo Dynamics (QCD) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than even the most stable atomic nucleus, {sup 56}Fe. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

  9. Structure of neutron star cores

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Datta, B.; Lodenquai, J.

    1975-01-01

    After reviewing the outer and central regions of a neutron star, we discuss the central region and the possibility that the core has a solid structure. We present the work of different groups on the solidification problem, suggesting that the neutron star-cores are indeed solid.

  10. KAON CONDENSATION IN NEUTRON STARS.

    SciTech Connect

    RAMOS,A.; SCHAFFNER-BIELICH,J.; WAMBACH,J.

    2001-04-24

    We discuss the kaon-nucleon interaction and its consequences for the change of the properties of the kaon in the medium. The onset of kaon condensation in neutron stars under various scenarios as well its effects for neutron star properties are reviewed.

  11. Axion emission from neutron stars

    NASA Technical Reports Server (NTRS)

    Iwamoto, N.

    1984-01-01

    It is shown that axion emission from neutron stars is the dominant energy-loss mechanism for a range of values of the Peccei-Quinn symmetry-breaking scale (F) not excluded by previous constraints. This gives the possibility of obtaining a better bound on F from measurements of surface temperature of neutron stars.

  12. QPO Constraints on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Miller, M. Coleman

    2005-01-01

    The kilohertz frequencies of QPOs from accreting neutron star systems imply that they are generated in regions of strong gravity, close to the star. This suggests that observations of the QPOs can be used to constrain the properties of neutron stars themselves, and in particular to inform us about the properties of cold matter beyond nuclear densities. Here we discuss some relatively model-insensitive constraints that emerge from the kilohertz QPOs, as well as recent developments that may hint at phenomena related to unstable circular orbits outside neutron stars.

  13. Grand unification of neutron stars

    PubMed Central

    Kaspi, Victoria M.

    2010-01-01

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical grand unification of this wealth of observational phenomena, and comment on possibilities for Chandras next decade in this field. PMID:20404205

  14. Neutron Star Physics and EOS

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2016-02-01

    Neutron stars are important because measurement of their masses and radii will determine the dense matter equation of state. They will constrain the nuclear matter symmetry energy, which controls the neutron star matter pressure and the interior composition, and will influence the interpretation of nuclear experiments. Astrophysical observations include pulsar timing, X-ray bursts, quiescent low-mass X-ray binaries, pulse profiles from millisecond pulsars, neutrino observations from gravitational collapse supernovae,and gravitational radiation from compact object mergers. These observations will also constrain the neutron star interior, including the properties of superfluidity there, and determine the existence of a possible QCD phase transition.

  15. Neutron star evolution and emission

    SciTech Connect

    Epstein, R.I.; Edwards, B.C.; Haines, T.J.

    1997-08-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors investigated the evolution and radiation characteristics of individual neutron stars and stellar systems. The work concentrated on phenomena where new techniques and observations are dramatically enlarging the understanding of stellar phenomena. Part of this project was a study of x-ray and gamma-ray emission from neutron stars and other compact objects. This effort included calculating the thermal x-ray emission from young neutron stars, deriving the radio and gamma-ray emission from active pulsars and modeling intense gamma-ray bursts in distant galaxies. They also measured periodic optical and infrared fluctuations from rotating neutron stars and search for high-energy TeV gamma rays from discrete celestial sources.

  16. Neutron StarsThermal Emitters

    NASA Astrophysics Data System (ADS)

    Potekhin, Alexander Y.; De Luca, Andrea; Pons, Jos A.

    2015-10-01

    Confronting theoretical models with observations of thermal radiation emitted by neutron stars is one of the most important ways to understand the properties of both, superdense matter in the interiors of the neutron stars and dense magnetized plasmas in their outer layers. Here we review the theory of thermal emission from the surface layers of strongly magnetized neutron stars, and the main properties of the observational data. In particular, we focus on the nearby sources for which a clear thermal component has been detected, without being contaminated by other emission processes (magnetosphere, accretion, nebulae). We also discuss the applications of the modern theoretical models of the formation of spectra of strongly magnetized neutron stars to the observed thermally emitting objects.

  17. Children's Literature on Neutron Stars

    NASA Astrophysics Data System (ADS)

    Struck, James

    Children's literature is simple discussion of complicated issues. Neutron stars are discussed in several children's books. Using libraries in Chicago, I will review children's books on neutron stars and compare the literature to literature from scientific discussions of neutron stars on sites like the Chandra site, Hubble Space Telescope site and NASA site. The result will be a discussion of problems and issues involved in discussion of neutron stars. Do children's books leave material out? Do children's books discuss recent observations? Do children's books discuss anything discredited or wrong? How many children's books are in resources like World Cat, the Library of Congress catalog, and the Chicago Public Library catalog? Could children's books be useful to present some of your findings or observations or projects? Children's books are useful for both children and scientist as they present simplified discussion of topics, although sometimes issues are simplified too much.

  18. The Neutron Star Zoo

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2014-01-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not clear how effective it is or on what timescale a buried field might re-emerge. One piece of evidence in favor of accretion-driven field reduction is the fact that NSs in LMXBs, which are older systems (> 108 yr), have mostly low fields and NSs in HMXBs, which are younger systems (107 - 108 yr), have higher fields. This may be an indication that accretion-driven field reduction or decay has not had enough time to operate in HMXBs but has in LMXBs. However, there does not seem to be any evidence of decaying fields in either the LMXB or HMXB populations; e.g. smaller magnetic fields in older systems. On the other hand, CCOs are very young so if they acquired their low fields through mass fallback accretion, the field submergence would have had to operate on much faster timescales than it apparently does in LMXBs. But as we continue to find new species in the NS zoo, one of these may someday be the "Rosetta Stone" that will give us the clues for solving these puzzles.

  19. Delta isobars in neutron stars

    NASA Astrophysics Data System (ADS)

    Pagliara, Giuseppe; Drago, Alessandro; Lavagno, Andrea; Pigato, Daniele

    2015-05-01

    The appearance of delta isobars in beta-stable matter is regulated by the behavior of the symmetry energy at densities larger than saturation density. We show that by taking into account recent constraints on the density derivative of the symmetry energy and the theoretical and experimental results on the excitations of delta isobars in nuclei, delta isobars are necessary ingredients for the equations of state used for studying neutron stars. We analyze the effect of the appearance of deltas on the structure of neutron stars: as in the case of hyperons, matter containing delta is too soft for allowing the existence of 2M⊙ neutron stars. Quark stars on the other hand, could reach very massive configurations and they could form from a process of conversion of hadronic stars in which an initial seed of strangeness appears through hyperons.

  20. Neutron star news and puzzles

    NASA Astrophysics Data System (ADS)

    Prakash, Madappa

    2014-08-01

    Gerry Brown has had the most influence on my career in Physics, and my life after graduate studies. This article gives a brief account of some of the many ways in which Gerry shaped my research. Focus is placed on the significant strides on neutron star research made by the group at Stony Brook, which Gerry built from scratch. Selected puzzles about neutron stars that remain to be solved are noted.

  1. Neutron star moments of inertia

    NASA Technical Reports Server (NTRS)

    Ravenhall, D. G.; Pethick, C. J.

    1994-01-01

    An approximation for the moment of inertia of a neutron star in terms of only its mass and radius is presented, and insight into it is obtained by examining the behavior of the relativistic structural equations. The approximation is accurate to approximately 10% for a variety of nuclear equations of state, for all except very low mass stars. It is combined with information about the neutron-star crust to obtain a simple expression (again in terms only of mass and radius) for the fractional moment of inertia of the crust.

  2. WIMP annihilation and cooling of neutron stars

    SciTech Connect

    Kouvaris, Chris

    2008-01-15

    We study the effect of WIMP annihilation on the temperature of a neutron star. We shall argue that the released energy due to WIMP annihilation inside the neutron stars might affect the temperature of stars older than 10x10{sup 6} years, flattening out the temperature at {approx}10{sup 4} K for a typical neutron star.

  3. The nuclear physics of neutron stars

    SciTech Connect

    Piekarewicz, J.

    2014-05-09

    We explore the unique and fascinating structure of neutron stars. Although neutron stars are of interest in many areas of Physics, our aim is to provide an intellectual bridge between Nuclear Physics and Astrophysics. We argue against the naive perception of a neutron star as a uniform assembly of neutrons packed to enormous densities. Rather, by focusing on the many exotic phases that are speculated to exist in a neutron star, we show how the reality is different and far more interesting.

  4. The nuclear physics of neutron stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, J.

    2014-05-01

    We explore the unique and fascinating structure of neutron stars. Although neutron stars are of interest in many areas of Physics, our aim is to provide an intellectual bridge between Nuclear Physics and Astrophysics. We argue against the naive perception of a neutron star as a uniform assembly of neutrons packed to enormous densities. Rather, by focusing on the many exotic phases that are speculated to exist in a neutron star, we show how the reality is different and far more interesting.

  5. Old and new neutron stars

    SciTech Connect

    Ruderman, M.

    1984-09-01

    The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10/sup 38/s/sup -1/ of 10/sup 12/ eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10/sup 8/ old dead pulsars in the Galaxy are the most probable source for the isotropically distributed ..gamma..-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables.

  6. Neutron stars and black holes

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1991-01-01

    The radiation of neutron stars is powered by accretion, rotation, or internal heat; accreting black holes are thought to be the central engines of AGNs and of a handful of binary X-ray sources in the Galaxy. The evolution of a neutron star depends on the coupling between the rotating neutron and proton fluids in the interior, and between these fluids and the crust; it also depends on the magnetic and thermal properties of the star. Significant progress has been made in recent years in the understanding of radial and disk accretion by black holes. Radiation from pair plasmas may make an important contribution to the X- and gamma-ray spectra of AGNs and black holes in binary systems.

  7. Nuclear Physics of neutron stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, Jorge

    2015-04-01

    One of the overarching questions posed by the recent community report entitled ``Nuclear Physics: Exploring the Heart of Matter'' asks How Does Subatomic Matter Organize Itself and What Phenomena Emerge? With their enormous dynamic range in both density and neutron-proton asymmetry, neutron stars provide ideal laboratories to answer this critical challenge. Indeed, a neutron star is a gold mine for the study of physical phenomena that cut across a variety of disciplines, from particle physics to general relativity. In this presentation--targeted at non-experts--I will focus on the essential role that nuclear physics plays in constraining the dynamics, structure, and composition of neutron stars. In particular, I will discuss some of the many exotic states of matter that are speculated to exist in a neutron star and the impact of nuclear-physics experiments on elucidating their fascinating nature. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics under Award Number DE-FD05-92ER40750.

  8. Neutrino Processes in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kolomeitsev, E. E.; Voskresensky, D. N.

    2010-10-01

    The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities). The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Green’s function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Green’s functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong interaction effects can be included within the Green’s function formalism. Softening of the pion mode with an baryon density increase is explicitly incorporated. We show examples of inconsistencies in calculations without inclusion of medium effects. Then we demonstrate calculations of different reaction rates in non-superfluid nuclear matter with taking into account medium effects. Many new reaction channels are open up in the medium and should be analyzed. Part IV: We discuss the neutrino production reactions in superfluid nuclear systems. The reaction rates of processes associated with the pair breaking and formation are calculated. Special attention is focused on the gauge invariance and the exact fulfillment of the Ward identities for the vector current. Finally we present comparison of calculations of neutron star cooling performed within nuclear medium cooling scenario with the available data.

  9. Chandra Observations of Neutron Stars: An Overview

    NASA Technical Reports Server (NTRS)

    Weisskopf, M. C.; Six, N. Frank (Technical Monitor)

    2002-01-01

    We present a brief review of Chandra observations of neutron stars, with a concentration on neutron stars in supernova remnants. The early Chandra results clearly demonstrate how critical the angular resolution has been in order to separate the neutron star emission from the surrounding nebulosity.

  10. Holographic neutron stars

    NASA Astrophysics Data System (ADS)

    de Boer, Jan; Papadodimas, Kyriakos; Verlinde, Erik

    2010-10-01

    We construct in the context of the AdS/CFT correspondence degenerate composite operators in the conformal field theory that are holographically dual to degenerate stars in anti de Sitter space. We calculate the effect of the gravitational back-reaction using the Tolman-Oppenheimer-Volkoff equations, and determine the Chandrasekhar limit beyond which the star undergoes gravitational collapse towards a black hole.

  11. Isolated neutron stars as seen by Athena

    NASA Astrophysics Data System (ADS)

    Posselt, Bettina; Pavlov, George

    2015-09-01

    The X-ray emission from the surfaces of isolated neutron stars and from the neutron star's immediate surroundings is not well understood. Partly, this is due to a lack of spectral resolution and sensitivity of current X-ray detectors. In our poster, we present simulations of neutron star X-ray emission as Athena may see it. We employ the latest Athena instrument response and up-to-date neutron star atmosphere models. This will allow us to evaluate the impact Athena can have on the investigations of neutron star properties, such as the composition of their surface layers, their magnetic fields, and the physics of their magnetospheres and ambient matter.

  12. Neutron StarsCooling and Transport

    NASA Astrophysics Data System (ADS)

    Potekhin, Alexander Y.; Pons, Jos A.; Page, Dany

    2015-10-01

    Observations of thermal radiation from neutron stars can potentially provide information about the states of supranuclear matter in the interiors of these stars with the aid of the theory of neutron-star thermal evolution. We review the basics of this theory for isolated neutron stars with strong magnetic fields, including most relevant thermodynamic and kinetic properties in the stellar core, crust, and blanketing envelopes.

  13. Induced gravitational collapse in FeCO Core-Neutron star binaries and Neutron star-Neutron star binary mergers

    NASA Astrophysics Data System (ADS)

    Ruffini, R.; Aimuratov, Y.; Bianco, C. L.; Enderli, M.; Kovacevic, M.; Moradi, R.; Muccino, M.; Penacchioni, A. V.; Pisani, G. B.; Rueda, J. A.; Wang, Y.

    2015-10-01

    We review the recent progress in understanding the nature of gamma-ray bursts (GRBs). The occurrence of GRB is explained by the Induced Gravitational Collapse (IGC) in FeCO Core-Neutron star binaries and Neutron star-Neutron star binary mergers, both processes occur within binary system progenitors. Making use of this most unexpected new paradigm, with the fundamental implications by the neutron star (NS) critical mass, we find that different initial configurations of binary systems lead to different GRB families with specific new physical predictions confirmed by observations.

  14. Gravitational Redshift of Deformed Neutron Stars

    NASA Astrophysics Data System (ADS)

    Romero, Alexis; Zubairi, Omair; Weber, Fridolin

    2015-04-01

    Non-rotating neutron stars are generally treated in theoretical studies as perfect spheres. Such a treatment, however, may not be correct if strong magnetic fields are present and/or the pressure of the matter in the cores of neutron stars is non-isotropic, leading to neutron stars which are deformed. In this work, we investigate the impact of deformation on the gravitational redshift of neutron stars in the framework of general relativity. Using a parameterized metric to model non-spherical mass distributions, we derive an expression for the gravitational redshift in terms of the mass, radius, and deformity of a neutron star. Numerical solutions for the redshifts of sequences of deformed neutron stars are presented and observational implications are pointed out. This research is funded by the NIH through the Maximizing Access to Research Careers (MARC), under Grant Number: 5T34GM008303-25 and through the National Science Foundation under grant PHY-1411708.

  15. Neutron Stars and Pulsars (IAU S291)

    NASA Astrophysics Data System (ADS)

    van Leeuwen, Joeri

    2013-04-01

    1. Pulsar discovery I; 2. Pulsar genesis - neutron-star formation and birth properties; 3. Pulsar discovery II; 4. Pulsar diversity; 5. Binary pulsars; 6. Neutron star vibration and emission; 7. Pulsar timing and testing gravitational theories; 8. Pulsar timing; 9. Pulsars and the interstellar medium; 10. Galactic distribution and evolution of neutron stars; 11. Pulsar magnetosphere and emission mechanisms; 12. Emission mechanisms; 13. Future facilities; Summary; Posters; Author index.

  16. White Dwarfs, Neutron Stars and Black Holes

    ERIC Educational Resources Information Center

    Szekeres, P.

    1977-01-01

    The three possible fates of burned-out stars: white dwarfs, neutron stars and black holes, are described in elementary terms. Characteristics of these celestial bodies, as provided by Einstein's work, are described. (CP)

  17. Burst Oscillations: Watching Neutron Stars Spin

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2010-01-01

    It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.

  18. Magnetic fields in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Viganò, D.; Pons, J. A.; Miralles, J. A.; Rea, N.

    2015-05-01

    Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.

  19. On the conversion of neutron stars into quark stars

    NASA Astrophysics Data System (ADS)

    Pagliara, Giuseppe

    2014-03-01

    The possible existence of two families of compact stars, neutron stars and quark stars, naturally leads to a scenario in which a conversion process between the two stellar objects occurs with a consequent release of energy of the order of 1053 erg. We discuss recent hydrodynamical simulations of the burning process and neutrino diffusion simulations of cooling of a newly formed strange star. We also briefly discuss this scenario in connection with recent measurements of masses and radii of compact stars.

  20. Planetary Systems Around Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wolszczan, Alexander

    1997-01-01

    This project was initiated in 1993, about one year after the announcement of two planets around PSR B1257+12. Its goal was to investigate planetary systems around neutron stars using high precision timing of radio pulsars as a tool. A microsecond precision of the pulse timing analysis, which is equivalent to a millimeter-per-second radial velocity resolution, makes it possible to detect asteroid-mass bodies in orbit around pulsars and to study the dynamics of pulsar planetary systems. The project originally consisted of two longterm efforts: (i) routine observations and timing analysis of the millisecond pulsar PSR B1257+12 which was found to be orbited by at least two earth-mass bodies (Wolszczan and Frail, Nature, 355, 145) and (ii) a sensitive all-sky search for millisecond pulsars to detect further examples of neutron stars with planetary systems. In the third year of the project, it was expanded to include long-term timing observations of slow pulsars in search for planetary systems around these younger neutron stars. The instrumentation used to conduct these investigations included the 305-m Arecibo antenna with the Penn State Pulsar Machine (PSPM-1), the 100-m Effelsberg telescope with the local pulse timing hardware, and the 32-m paraboloid of the Torun Centre for Astronomy in Torun, Poland (TCFA) with the PSPM-2, the second pulsar machine built at Penn State. The PI's collaborators included pulsar groups led by D. Backer (Berkeley), R. Foster (NRL), S. Kulkarni (Caltech), J. Taylor (Princeton) and R. Wielebinski (Bonn). One postdoc (Stuart Anderson), one graduate student (Brian Cadwell) and several undergraduates have been engaged in various aspects of research related to this project.

  1. The Nuclear Physics of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, Jorge

    2007-10-01

    The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties in the reaction mechanism. The finite nucleus - a system that is 18 order of magnitude smaller and 55 orders of magnitude lighter than a neutron star - may be used as a miniature surrogate to establish important correlations between its neutron skin and several neutron-star properties. Indeed, a nearly model-independent correlation develops between the neutron skin of ^208Pb and the transition density between the liquid mantle and the solid crust in the neutron star. The implications of the proposed purely electroweak Parity Radius EXperiment (PREX) at the Jefferson Laboratory on neutron-star structure will be reviewed and connections to other fields, such as atomic and condensed-matter physics, will be established.

  2. The Lives of the Neutron Stars

    NASA Astrophysics Data System (ADS)

    Alpar, M. A.; Kiziloglu, U.; van Paradijs, Jan

    The book covers many aspects of current research on neutron stars in an evolutionary perspective, such as supernovae and supernova remnants, radio pulsars, X-ray binaries, cooling of neutron stars, magnetic-field decay, optical counterparts and populations (statistics and birth rates).

  3. Neutron Star Interior Composition Explorer (NICE)

    NASA Technical Reports Server (NTRS)

    Gendreau, Keith C.; Arzoumanian, Zaven

    2008-01-01

    This viewgraph presentation contains an overview of the mission of the Neutron Star Interior Composition Explorer (NICE), a proposed International Space Station (ISS) payload dedicated ot the study of neutron stars. There are also reviews of the Science Objectives of the payload,the science measurements, the design and the expected performance for the instruments for NICE,

  4. Where a Neutron Star's Accretion Disk Ends

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    In X-ray binaries that consist of a neutron star and a companion star, gas funnels from the companion into an accretion disk surrounding the neutron star, spiraling around until it is eventually accreted. How do the powerful magnetic fields threading through the neutron star affect this accretion disk? Recent observations provide evidence that they may push the accretion disk away from the neutron stars surface.Truncated DisksTheoretical models have indicated that neutron star accretion disks may not extend all the way in to the surface of a neutron star, but may instead be truncated at a distance. This prediction has been difficult to test observationally, however, due to the challenge of measuring the location of the inner disk edge in neutron-star X-ray binaries.In a new study, however, a team of scientists led by Ashley King (Einstein Fellow at Stanford University) has managed to measure the location of the inner edge of the disk in Aquila X-1, a neutron-star X-ray binary located 17,000 light-years away.Iron line feature detected by Swift (red) and NuSTAR (black). The symmetry of the line is one of the indicators that the disk is located far from the neutron star; if the inner regions of the disk were close to the neutron star, severe relativistic effects would skew the line to be asymmetric. [King et al. 2016]Measurements from ReflectionsKing and collaborators used observations made by NuSTAR and Swift/XRT both X-ray space observatories of Aquila X-1 during the peak of an X-ray outburst. By observing the reflection of Aquila X-1s emission off of the inner regions of the accretion disk, the authors were able to estimate the location of the inner edge of the disk.The authors find that this inner edge sits at ~15 gravitational radii. Since the neutron stars surface is at ~5 gravitational radii, this means that the accretion disk is truncated far from the stars surface. In spite of this truncation, material still manages to cross the gap and accrete onto the neutron star as evidenced by X-ray flaring (almost certainly caused by accretion) that occurred during the authors observations.Magnetic EffectsWhat could cause the truncation of the disk? The authors believe the most likely factor is pressure from the neutron stars sizable magnetic field, pushing the inner edge of the disk out. They calculate that a field strength of roughly 5*108 Gauss (for comparison, a typical refrigerator magnet has a field strength of ~100 G!) would be necessary to hold the inner edge this far out. This is consistent with previous estimates for the field of the neutron star in Aquila X-1.The authors point out that magnetic field lines could also explain how the neutron star is still accreting material despite the gap between it and its disk: gas could be channeled along field lines from the inner edge of the disk which is roughly co-rotating with the neutron star onto the neutron star poles.The observations of Aquila X-1s truncated disk are an important step toward confirming models of how neutron stars magnetic fields interact with their accretion disks in X-ray binaries.CitationAshley L. King et al 2016 ApJ 819 L29. doi:10.3847/2041-8205/819/2/L29

  5. Collective excitations in neutron-star crusts

    NASA Astrophysics Data System (ADS)

    Chamel, N.; Page, D.; Reddy, S.

    2016-01-01

    We explore the spectrum of low-energy collective excitations in the crust of a neutron star, especially in the inner region where neutron-proton clusters are immersed in a sea of superfluid neutrons. The speeds of the different modes are calculated systematically from the nuclear energy density functional theory using a Skyrme functional fitted to essentially all experimental atomic mass data.

  6. Neutron Star Science with the NuSTAR

    SciTech Connect

    Vogel, J. K.

    2015-10-16

    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

  7. Magnetic fields in superconducting neutron stars.

    PubMed

    Lander, S K

    2013-02-15

    The interior of a neutron star is likely to be predominantly a mixture of superfluid neutrons and superconducting protons. This results in the quantization of the star's magnetic field into an array of thin flux tubes, producing a macroscopic force very different from the Lorentz force of normal matter. We show that in an axisymmetric superconducting equilibrium the behavior of a magnetic field is governed by a single differential equation. Solving this, we present the first self-consistent superconducting neutron star equilibria with poloidal and mixed poloidal-toroidal fields and also give the first quantitative results for the corresponding magnetically induced distortions to the star. The poloidal component is dominant in all our configurations. We suggest that the transition from normal to superconducting matter in a young neutron star may cause a large-scale field rearrangement. PMID:25166363

  8. The breaking strain of neutron star crust

    SciTech Connect

    Kadau, Kai; Horowitz, C J

    2009-01-01

    Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Due to the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gTavitational wave radiation could limit the spin periods of some stars and might be detectable in large scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in Magnetar Giant and Micro Flares.

  9. The many lives of magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Perna , R.; Pons, J. A.; Vigan, D.; Rea, N.

    2014-09-01

    The magnetic field strength at birth is arguably one of the most important properties to determine the evolutionary path of a neutron star. Objects with very high fields, collectively known as magnetars, are characterized by high X-ray quiescent luminosities, occurrence of outbursts, and, for some of them, sporadic giant flares. While the magnetic field strength is believed to drive their collective behaviour, however, the diversity of their properties, and, especially, the observation of magnetar-like bursts from ``low-field'' pulsars, has been a theoretical puzzle. In this review, we discuss results of long-term simulations following the coupled evolution of the X-ray luminosity and the timing properties for a large, homogeneous sample of X-ray emitting isolated neutron stars, accounting for a range of initial magnetic field strengths, envelope compositions, and neutron star masses. In addition, by following the evolution of magnetic stresses within the neutron star crust, we can also relate the observed magnetar phenomenology to the physical properties of neutron stars, and in particular to their age and magnetic field strength and topology. The dichotomy of ``high-B'' field pulsars versus magnetars is naturally explained, and occasional outbursts from old, low B-field neutron stars are predicted. We conclude by speculating on the fate of old magnetars, and by presenting observational diagnostics of the neutron star crustal field topology.

  10. Experimental approach to neutron stars

    SciTech Connect

    Leifels, Yvonne

    2014-05-09

    The equation of state (EOS) of nuclear matter is of fundamental importance in many areas of nuclear physics and astrophysics In the laboratory, there are different means to study the nuclearmatter equation of state and its density dependence in particular: nuclear masses, neutron skins, pygmy resonance, and nuclear structure at the drip line give access to nuclear matter properties at densities lower than and at saturation density ρ0. Heavy ion reactions at energies above 0.1 AGeV are the only means to study nuclear matter at densities larger than normal nuclear matter density ρ0. In the beamenergy range of 0.1 to 2A GeV nuclear matter is compressed upto three times ρ0. Access to nuclear matter properties is achieved by simulating nuclear collisions by means of microscopic transport codes, or statistical or hydrodynamicalmodels. Characteristics of heavy-ion collisions are discussed, and experimental observables which allow to constrain nuclear matter properties by comparing experimental results with those of transport codes are presented. Special emphasis will be given to the density dependence of the symmetry energy which is the most relevant connection between neutron stars and heavy ion collisions.

  11. Gravitational waves from low mass neutron stars

    SciTech Connect

    Horowitz, C. J.

    2010-05-15

    Low mass neutron stars may be uniquely strong sources of gravitational waves. The neutron star crust can support large deformations for low mass stars. This is because of the star's weaker gravity. We find maximum ellipticities {epsilon} (fractional difference in moments of inertia) that are 1000 times larger, and maximum quadrupole moments Q{sub 22} over 100 times larger, for low mass stars than for 1.4M{sub {center_dot}}neutron stars. Indeed, we calculate that the crust can support an {epsilon} as large as 0.005 for a minimum mass neutron star. A 0.12M{sub {center_dot}}star, that is maximally strained and rotating at 100 Hz, will produce a characteristic gravitational wave strain of h{sub 0}=2.1x10{sup -24} at a distance of 1 kpc. The gravitational wave detector Advanced LIGO should be sensitive to such objects through out the Milky Way Galaxy. A low mass neutron star could be uniquely identified from a large observed spin down rate and its discovery would have important implications for general relativity, supernova mechanisms, and possibly nucleosynthesis.

  12. Gravitational Waves from Neutron Stars: A Review

    NASA Astrophysics Data System (ADS)

    Lasky, Paul D.

    2015-09-01

    Neutron stars are excellent emitters of gravitational waves. Squeezing matter beyond nuclear densities invites exotic physical processes, many of which violently transfer large amounts of mass at relativistic velocities, disrupting spacetime and generating copious quantities of gravitational radiation. I review mechanisms for generating gravitational waves with neutron stars. This includes gravitational waves from radio and millisecond pulsars, magnetars, accreting systems, and newly born neutron stars, with mechanisms including magnetic and thermoelastic deformations, various stellar oscillation modes, and core superfluid turbulence. I also focus on what physics can be learnt from a gravitational wave detection, and where additional research is required to fully understand the dominant physical processes at play.

  13. LARGE-MASS NEUTRON STARS WITH HYPERONIZATION

    SciTech Connect

    Jiang Weizhou; Li Baoan; Chen Liewen

    2012-09-01

    Within a density-dependent relativistic mean-field model and using in-medium meson-hadron coupling constants and meson masses, we explore the effects of in-medium hyperon interactions on the properties of neutron stars. We found that hyperonic constituents in large-mass neutron stars cannot be simply ruled out, while the recently measured mass of the millisecond pulsar J1614-2230 can significantly constrain in-medium hyperon interactions. In addition, we discuss the effects of nuclear symmetry energy on hyperonization in neutron stars.

  14. DYNAMICAL CAPTURE BINARY NEUTRON STAR MERGERS

    SciTech Connect

    East, William E.; Pretorius, Frans

    2012-11-20

    We study dynamical capture binary neutron star mergers as may arise in dense stellar regions such as globular clusters. Using general-relativistic hydrodynamics, we find that these mergers can result in the prompt collapse to a black hole or in the formation of a hypermassive neutron star, depending not only on the neutron star equation of state but also on impact parameter. We also find that these mergers can produce accretion disks of up to a tenth of a solar mass and unbound ejected material of up to a few percent of a solar mass. We comment on the gravitational radiation and electromagnetic transients that these sources may produce.

  15. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Supid

    2007-01-01

    This viewgraph presentation describes neutron stars and thermonuclear x ray bursts. The contents include: 1) Neutron Stars: why do we care?; 2) Thermonuclear Bursts: why do we care?; 3) Neutron Stars: Mass, Radius and Spin: a. Continuum Spectroscopy of Bursts b. Spectral Lines from Bursts c. Timing Properties of Bursts; 4) Neutron Star Atmosphere: Thermonuclear Flame Spreading; and 5) Future Prospects and Conclusions.

  16. Plasma physics of accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Ghosh, Pranab; Lamb, Frederick K.

    1991-01-01

    Plasma concepts and phenomena that are needed to understand X- and gamma-ray sources are discussed. The capture of material from the wind or from the atmosphere or envelope of a binary companion star is described and the resulting types of accretion flows discussed. The reasons for the formation of a magnetosphere around the neutron star are explained. The qualitative features of the magnetospheres of accreting neutron stars are then described and compared with the qualitative features of the geomagnetosphere. The conditions for stable flow and for angular and linear momentum conservation are explained in the context of accretion by magnetic neutron stars and applied to obtain rough estimates of the scale of the magnetosphere. Accretion from Keplerian disks is then considered in some detail. The radial structure of geometrically thin disk flows, the interaction of disk flows with the neutron star magnetosphere, and models of steady accretion from Keplerian disks are described. Accretion torques and the resulting changes in the spin frequencies of rotating neutron stars are considered. The predicted behavior is then compared with observations of accretion-powered pulsars. Magnetospheric processes that may accelerate particles to very high energies, producing GeV and, perhaps, TeV gamma-rays are discussed. Finally, the mechanisms that decelerate and eventually stop accreting plasma at the surfaces of strongly magnetic neutron stars are described.

  17. Neutron-star matter within the energy-density functional theory and neutron-star structure

    SciTech Connect

    Fantina, A. F.; Chamel, N.; Goriely, S.; Pearson, J. M.

    2015-02-24

    In this lecture, we will present some nucleonic equations of state of neutron-star matter calculated within the nuclear energy-density functional theory using generalized Skyrme functionals developed by the Brussels-Montreal collaboration. These equations of state provide a consistent description of all regions of a neutron star. The global structure of neutron stars predicted by these equations of state will be discussed in connection with recent astrophysical observations.

  18. Neutron Star Compared to Manhattan - Duration: 11 seconds.

    NASA Video Gallery

    A pulsar is a neutron star, the crushed core of a star that has exploded. Neutron stars crush half a million times more mass than Earth into a sphere no larger than Manhattan, as animated in this s...

  19. The Neutron Star Interior Composition Explorer

    NASA Technical Reports Server (NTRS)

    Gendreau, Keith C.

    2008-01-01

    The Neutron star Interior Composition Explorer (NICE) will be a Mission of Opportunity dedicated to the study of neutron stars, the only places in the universe where all four fundamental forces of nature are simultaneously in play. NICE will explore the exotic states of matter within neutron stars, revealing their interior and surface compositions through rotation resolved X-ray spectroscopy. Absolute time-referenced data will allow NICE to probe the extreme physical environments associated with neutron stars, leveraging observations across the electromagnetic spectrum to answer decades-old questions about one of the most powerful cosmic accelerators known. Finally, NICE will definitively measure stabilities of pulsars as clocks, with implications for navigation, a pulsar-based timescale, and gravitational-wave detection. NICE will fly on the International Space Station, while GLAST is on orbit and post-RXTE, and will allow for the discovery of new high-energy pulsars and provide continuity in X-ray timing astrophysics.

  20. Theoretical Studies of Accreting Neutron Stars

    NASA Technical Reports Server (NTRS)

    Taam, Ronald E.

    2003-01-01

    Among the newly discovered classes of X-ray sources which have attracted wide attention are close binary systems in which mass is transferred via Roche lobe overflow from a low mass donor star to its neutron star companion. Many of these sources exhibit intense bursts of X-ray radiation as well as periodic and quasi-periodic phenomena. Intensive analysis of these sources as a class has provided insight into the accretion process in binary star systems and into the magnetic field, rotational, and nuclear evolution of the underlying neutron star. In this proposal we have focused on theoretical studies of the hydrodynamical and nuclear processes that take place on the surface of accreting neutron stars in these systems. The investigation of these processes is critical for providing an understanding of a number of outstanding problems related to their transient behavior and evolution.

  1. Direct URCA process in neutron stars

    NASA Technical Reports Server (NTRS)

    Lattimer, James M.; Prakash, Madappa; Pethick, C. J.; Haensel, Pawel

    1991-01-01

    It is shown that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11-15 percent. The proton concentration, which is determined by the poorly known symmetry energy of matter above nuclear density, exceeds the critical value in many current calculations. If it occurs, the direct URCA process enhances neutrino emission and neutron star cooling rates by a large factor compared to any process considered previously.

  2. Chandra Observations of Isolated Neutron Stars

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin

    2006-01-01

    We present a review of the first six years of Chandra X-ray Observatory observations of isolated neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present a (biased) overview of six years of these observations, highlighting new discoveries made possible by the Observatory's unique capabilities.

  3. Neutron stars as laboratories for gravity physics

    SciTech Connect

    Deliduman, Cemsinan

    2014-01-01

    We study the structure of neutron stars in R+αR² gravity model with perturbative method. We obtain mass-radius relations for four representative equations of state (EoS). We find that, for |α|~10⁹ cm², the results differ substantially from the results of general relativity. The effects of modified gravity are seen as mimicking a stiff or soft EoS for neutron stars depending upon whether α is negative or positive, respectively. Some of the soft EoS that are excluded within the framework of general relativity can be reconciled for certain values of α of this order with the 2 solar mass neutron star recently observed. Indeed, if the EoS is ever established to be soft, modified gravity of the sort studied here may be required to explain neutron star masses as large as 2 M{sub ⊙}. The associated length scale √(α)~10⁵ cm is of the order of the the typical radius of neutron stars implying that this is the smallest value we could find by using neutron stars as a probe. We thus conclude that the true value of α is most likely much smaller than 10⁹ cm².

  4. Carbon Atmosphere Discovered On Neutron Star

    NASA Astrophysics Data System (ADS)

    2009-11-01

    Evidence for a thin veil of carbon has been found on the neutron star in the Cassiopeia A supernova remnant. This discovery, made with NASA's Chandra X-ray Observatory, resolves a ten-year mystery surrounding this object. "The compact star at the center of this famous supernova remnant has been an enigma since its discovery," said Wynn Ho of the University of Southampton and lead author of a paper that appears in the latest issue of Nature. "Now we finally understand that it can be produced by a hot neutron star with a carbon atmosphere." By analyzing Chandra's X-ray spectrum - akin to a fingerprint of energy - and applying it to theoretical models, Ho and his colleague Craig Heinke, from the University of Alberta, determined that the neutron star in Cassiopeia A, or Cas A for short, has an ultra-thin coating of carbon. This is the first time the composition of an atmosphere of an isolated neutron star has been confirmed. The Chandra "First Light" image of Cas A in 1999 revealed a previously undetected point-like source of X-rays at the center. This object was presumed to be a neutron star, the typical remnant of an exploded star, but researchers were unable to understand its properties. Defying astronomers' expectations, this object did not show any X-ray or radio pulsations or any signs of radio pulsar activity. By applying a model of a neutron star with a carbon atmosphere to this object, Ho and Heinke found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because -- like a lightbulb that shines consistently in all directions -- this neutron star would be unlikely to display any changes in its intensity as it rotates. Scientists previously have used a neutron star model with a hydrogen atmosphere giving a much smaller emission area, corresponding to a hot spot on a typical neutron star, which should produce X-ray pulsations as it rotates. Interpreting the hydrogen atmosphere model without pulsations would require a tiny size, consistent only with exotic stars made of strange quark matter. "Our carbon veil solves one of the big questions about the neutron star in Cas A," said Craig Heinke. "People have been willing to consider some weird explanations, so it's a relief to discover a less peculiar solution." Unlike most astronomical objects, neutron stars are small enough to understand on a human scale. For example, neutron stars typically have a diameter of about 14 miles, only slightly longer than a half-marathon. The atmosphere of a neutron star is on an even smaller scale. The researchers calculate that the carbon atmosphere is only about 4 inches thick, because it has been compressed by a surface gravity that is 100 billion times stronger than on Earth. "For people who are used to hearing about immense sizes of things in space, it might be a surprise that we can study something so small," said Ho. "It's also funny to think that such a thin veil over this star played a key role in frustrating researchers." In Earth's time frame, the estimated age of the neutron star in Cas A is only several hundred years, making it about ten times younger than other neutron stars with detected surface emission. Therefore, the Cas A neutron star gives a unique window into the early life of a cooling neutron star. The carbon itself comes from a combination of material that has fallen back after the supernova, and nuclear reactions on the hot surface of the neutron star which convert hydrogen and helium into carbon. The X-ray spectrum and lack of pulsar activity suggest that the magnetic field on the surface of this neutron star is relatively weak. Similarly low magnetic fields are implied for several other young neutron stars by study of their weak X-ray pulsations. It is not known whether these neutron stars will have low magnetic fields for their entire lives, and never become radio pulsars, or whether processes in their interior will lead to the development of stronger magnetic fields as they age. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

  5. Accreting neutron stars by QFT

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Guang

    I deduce the new gravitational formula from the variance in mass of QFT and GR (H05-0029-08, E15-0039 -08, E14-0032-08, D31-0054-10) in the partial differential: f (QFT) = f (GR) = delta∂ (m v)/delta∂ t = f _{P} + f _{C} , f _{P} = m delta∂ v / delta∂ t = - ( G m M /r (2) ) r / r, f _{C} = v delta∂ m / delta∂ t = - ( G mM / r (2) ) v / c (1). f (QFT) is the quasi-Casimir pressure of net virtual neutrinos nuν _{0} flux (after counteract contrary direction nuν _{0}). f (GR) is equivalent to Einstein’s equation as a new version of GR. GR can be inferred from Eq.(1) thereby from QFT, but QFT cannot be inferred from Eq.(1) or GR. f (QFT) is essential but f (GR) is phenomenological. Eq.(1) is obtained just by to absorb the essence of corpuscule collided gravitation origin ism proposed by Fatio in 1690 and 1920 Majorana’s experiment concept about gravitational shield effect again fuse with QFT. Its core content is that the gravity produced by particles collide cannot linear addition, i.e., Eq.(1) with the adding nonlinearity caused by the variable mass to replace the nonlinearity of Einstein’s equation. The nonlinear gravitation problems can be solved using the classical gradual approximation of alone f _{P} and alone f _{C}. Such as the calculation of advance of the perihelion of QFT, let the gravitational potential U = - G M /r which is just the distribution density of net nuν _{0} flux. From SR we again get Eq.(1): f (QFT) = f _{P} + f _{C}, f _{P} = - m ( delta∂ U / delta∂ r) r / r, f _{C} = - m ( delta∂U / delta∂ r) v / c , U = (1 - betaβ (2) )V, V is the Newtonian gravitational potential. f_{ P} correspond the change rate of three-dimensional momentum p, f_{C} correspond the change rate of fourth dimensional momentum i m c which show directly as a dissipative force of mass change. In my paper ‘To cross the great gap between the modern physics and classic physics, China Science &Technology Overview 129 85-91 (2011)’ with the measuring value of one-way velocity of light (H05-0020-08) to replace the infinity value of light speed measured by Galileo in 1607, thereby the mass m in NM will become variable m. Or else, the energy of electron in accelerator should not larger than 0.51Mev which conflict with the experimental fact. According to the variable mass and the definition of force we again get Eq.(1) from NM without hypothesis, i.e., NM is generalized in which Galileo coordinates transformation and the action at a distance will be of no effect. Eq.(1) has more reliable experimental base and generalized NM may be applied to the high-speed and the microscopic conditions. Because of the result of a test of GR with use of a hydrogen-maser frequency standard in a spacecraft launched nearly vertically upward to 10000 km (R. F. C. Vessot et.al., Phys. Rev. Lett. 45, 2081(1980)), the isotropy of one-way velocity of light had been validated at the 1*10 (-10) level (D2.4-0030-12, H0.1-0009-12, H0.2-0008-12). Again from the Lorentz transformation (H01-0006 -08) and the uncertainty principle (H05-0036-10) deduced from the metrical results of Doppler effects, SR and QM, thereby QFT and GR all become the inferential theorems from generalized NM. Eq.(1) is as a bridge to join the modern physics and classical physics. In my paper ‘Basal electric and magnetic fields of celestial bodies come from positive-negative charge separation caused by gravitation of quasi-Casimir pressure in weak interaction’ (D31-0054-10): According to QFT the gravitation is the statistic average pressure collided by net virtual neutrinos nuν _{0} flux, the net nuν _{0} flux can press a part freedom electrons in plasma of ionosphere into the surface of celestial bodies. The static electric force of redundant positive ions prevents electrons further falling and till reach the equilibrium of stable spatial charge distribution, which is just the cause of the geomagnetic field and the geo-electric field. In the solar surface plasma add the negative charge from ionosphere electrons again rotate, thereby come into being the solar basal magnetic field. The solar surface plasma with additional electrons get the dynamic balance between the upwards force of stable positive charge distribution in the solar upside gas and the downwards force of the vacuum net nuν _{0} flux pressure (solar gravity). When the Jupiter enter into the connecting line of the Sun and the center of the Galaxy, the pressure (solar gravity) observed from earth will weaken because of the Jupiter stop (shield) the net nuν _{0} flux which shoot to Sun from the center of Galaxy. The dynamic balance of forces on the solar surface plasma at once is broken and the plasma will upwards eject as the solar wind with redundant negative charge. At the same time, the solar surface remain a cavity as a sunspot whorl with the positive electric potential relative to around plasma. The whorl is caused by the reaction of plasma eject front and upwards with the different velocity at different latitude of solar rotation, it leads to the cavity around in the downwards and backwards helix movement. The solar rotation more slow, when the cavity is filled by around plasma in the reverse turn direction and return to carry-over negative charge, the Jupiter at front had been produced a new cavity carry-over positive charge, so we had observe the sunspot pair with different whorl directions and different magnetic polarity. Jupiter possess half mass of all planets in solar system, its action to stop net nuν _{0} flux is primary, so that Jupiter’s period of 11.8 sidereal years accord basically with the period of sunspot eruptions. In my paper ‘Nonlinear superposition of strong gravitational field of compact stars’(E15-0039-08), according to QFT it is deduced that: let q is a positive shielding coefficient, 1- q show the gravity weaken degree, the earth (104 km) as a obstructing layer q = 4.6*10 (-10) . A spherical shell of neutron star as obstructing layer with thickness of 1 km then q = 1 (N1S1), the gravity from N1S1 inside and exterior will be completely shielded. Because of net nuν _{0} flux is the medium to produce and transmit gravity, q obstructed by the shielding layer lie on the density of layer matter and the section of single nucleon to electronic neutrino obtained by nuclear physics experiments is about 1.1*10 ({-) 43} cm (2) . The mass inside N1S1 for exterior has not gravity interaction, it equivalent to has not inertia as the mass vanish. The neutron star is as a empty shell thereby may rapidly rotating and has not upper limit of mass and radii by the gravity accretion of N1S1, which will influence the mechanisms of pulsars, quasars and X-rays generated. At N1S1 interior the mass for exterior has not gravity which is just we searching dark matter. The mass each part will each other shielding and gravity decrease to less than the pressure of the degenerate neutron gas. The neutron star cannot collapse into a singular point with infinite density, i.e., the black hole with infinite gravity cannot be formed or the neutron star is jest the black hole in observational meaning. By the gravity accrete of N1S1 the neutron star may enlarge its shell radii but thickness keep. Only a shell gravity may be not less than any a observed value which to be deemed as black hole. The neutron star has powerful gravity certainly accompany with great surface negative charge and it may rapidly to rotate, so that there is a powerful magnetic field surround it. The accreting neutron star is as a slowly expand empty shell with fixed thickness of 1 km, its spin period depend on its radii or total accretion mass.

  6. Neutron Stars and the Discovery of Pulsars.

    ERIC Educational Resources Information Center

    Greenstein, George

    1985-01-01

    Part one recounted the story of the discovery of pulsars and examined the Crab Nebula, supernovae, and neutron stars. This part (experts from the book "Frozen Star") shows how an understanding of the nature of pulsars allowed astronomers to tie these together. (JN)

  7. The decompression of cold neutron star matter

    NASA Technical Reports Server (NTRS)

    Lattimer, J. M.; Mackie, F.; Ravenhall, D. G.; Schramm, D. N.

    1977-01-01

    The ejection of cold neutron-star matter is examined, and an attempt is made to determine whether the final composition of this matter may be similar to that normally associated with the hot high-neutron-flux r-process. A semiempirical liquid-drop model is used for the nucleus, and the equilibrium composition of the matter is determined by assuming it to be in its absolute ground state at a given density. Physical mechanisms operating during the expansion are analyzed, and the composition of the ejected matter is found as a function of its density during expansion. The results indicate that it is virtually impossible for deuterium to form, that neutrons can be captured only after beta decay increases the atomic numbers of nuclei, and that no free neutrons can escape. It is concluded that neutron-star ejecta can produce heavy neutron-rich nuclei and may produce somewhat heavier nuclei than a standard r-process.

  8. Forecasting Neutron Star Temperatures: Predictability and Variability

    NASA Astrophysics Data System (ADS)

    Page, Dany; Reddy, Sanjay

    2013-12-01

    It is now possible to model thermal relaxation of neutron stars after bouts of accretion during which the star is heated out of equilibrium by nuclear reactions in its crust. Major uncertainties in these models can be encapsulated in modest variations of a handful of control parameters that change the fiducial crustal thermal conductivity, specific heat, and heating rates. Observations of thermal relaxation constrain these parameters and allow us to predict longer term variability in terms of the neutron star core temperature. We demonstrate this explicitly by modeling ongoing thermal relaxation in the neutron star XTE J1701-462. Its future cooling, over the next 5 to 30 years, is strongly constrained and depends mostly on its core temperature, uncertainties in crust physics having essentially been pinned down by fitting to the first three years of observations.

  9. Determining neutron star masses using weak microlensing

    NASA Astrophysics Data System (ADS)

    Tian, Lanlan; Mao, Shude

    2012-12-01

    The masses of stars, including stellar remnants, are almost exclusively known from binary systems. In this paper, we study the gravitational microlensing of faint background galaxies caused by isolated neutron stars (pulsars). We show that the resulting distortions in the surface brightness can be used to determine the masses of neutron stars. Because of their different evolutionary histories, isolated neutron stars might have different masses from those in binary systems, which can thus provide a unique insight into their equation of states under extreme physical conditions. Having searched the existing pulsar catalogues, we have found one promising pair, consisting of a nearby pulsar and a background galaxy. This method will become more practical for the next-generation optical and radio surveys and telescopes.

  10. Forecasting neutron star temperatures: predictability and variability.

    PubMed

    Page, Dany; Reddy, Sanjay

    2013-12-13

    It is now possible to model thermal relaxation of neutron stars after bouts of accretion during which the star is heated out of equilibrium by nuclear reactions in its crust. Major uncertainties in these models can be encapsulated in modest variations of a handful of control parameters that change the fiducial crustal thermal conductivity, specific heat, and heating rates. Observations of thermal relaxation constrain these parameters and allow us to predict longer term variability in terms of the neutron star core temperature. We demonstrate this explicitly by modeling ongoing thermal relaxation in the neutron star XTE J1701-462. Its future cooling, over the next 5 to 30 years, is strongly constrained and depends mostly on its core temperature, uncertainties in crust physics having essentially been pinned down by fitting to the first three years of observations. PMID:24483640

  11. The oscillations of superfluid neutron stars

    NASA Technical Reports Server (NTRS)

    Lindblom, Lee; Mendell, Gregory

    1994-01-01

    The effects of superfluid hydrodynamics on the oscillations of neutron stars are investigated. The equations describing the small-amplitude pulsations of a neutron star's neutron-proton superfluid mixture are reduced to a system of three second-order equations for three scalar potentials. A variational principle is developed from which the frequencies of the modes of these superfluid oscillations may be estimated. These pulsations are studied by finding analytical solutions to the equations for simple uniform models of nonrotating neutron stars and numerical solutions for realistic models (including rotation). These solutions reveal that the lowest frequency modes are almost indistinguishable from those based on ordinary-fluid hydrodynamics. The analytical solutions also reveal the existence of a new set of modes having no ordinary-fluid counterpart.

  12. Limiting rotational period of neutron stars

    NASA Astrophysics Data System (ADS)

    Glendenning, Norman K.

    1992-11-01

    We seek an absolute limit on the rotational period for a neutron star as a function of its mass, based on the minimal constraints imposed by Einstein's theory of relativity, Le Chatelier's principle, causality, and a low-density equation of state, uncertainties in which can be evaluated as to their effect on the result. This establishes a limiting curve in the mass-period plane below which no pulsar that is a neutron star can lie. For example, the minimum possible Kepler period, which is an absolute limit on rotation below which mass shedding would occur, is 0.33 ms for a M=1.442Msolar neutron star (the mass of PSR1913+16). A still lower curve, based only on the structure of Einstein's equations, limits any star whatsoever to lie in the plane above it. Hypothetical stars such as strange stars, if the matter of which they are made is self-bound in bulk at a sufficiently large equilibrium energy density, can lie in the region above the general-relativistic forbidden region, and in the region forbidden to neutron stars.

  13. Hyperaccreting Neutron Star Disks and Neutrino Annihilation

    NASA Astrophysics Data System (ADS)

    Zhang, Dong; Dai, Z. G.

    2009-09-01

    Newborn neutron stars surrounded by hyperaccreting and neutrino-cooled disks may exist in some gamma-ray bursts and/or supernovae. In this paper, we further study the structure of such a neutron star disk based on the two-region (i.e., inner & outer) disk scenario following our previous work, and calculate the neutrino annihilation luminosity from the disk in various cases. We investigate the effects of the viscosity parameter ?, energy parameter ? (measuring the neutrino cooling efficiency of the inner disk), and outflow strength on the structure of the entire disk as well as the effect of emission from the neutron star surface boundary emission on the total neutrino annihilation rate. The inner disk satisfies the entropy-conservation self-similar structure for the energy parameter ? sime 1 and the advection-dominated structure for ? < 1. An outflow from the disk decreases the density and pressure but increases the thickness of the disk. Moreover, compared with the black hole disk, the neutrino annihilation luminosity above the neutron star disk is higher, and the neutrino emission from the boundary layer could increase the neutrino annihilation luminosity by about one order of magnitude higher than the disk without boundary emission. The neutron star disk with the advection-dominated inner disk could produce the highest neutrino luminosity while the disk with an outflow has the lowest. Although a heavily mass-loaded outflow from the neutron star surface at early times of neutron star formation prevents the outflow material from being accelerated to a high bulk Lorentz factor, an energetic ultrarelativistic jet via neutrino annihilation can be produced above the stellar polar region at late times if the disk accretion rate and the neutrino emission luminosity from the surface boundary layer are sufficiently high.

  14. Binary neutron stars with arbitrary spins in numerical relativity

    NASA Astrophysics Data System (ADS)

    Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Haas, Roland; Ossokine, Serguei; Kaplan, Jeff; Muhlberger, Curran; Duez, Matt D.; Kidder, Lawrence E.; Scheel, Mark A.; Szilgyi, Bla

    2015-12-01

    We present a code to construct initial data for binary neutron star systems in which the stars are rotating. Our code, based on a formalism developed by Tichy, allows for arbitrary rotation axes of the neutron stars and is able to achieve rotation rates near rotational breakup. We compute the neutron star angular momentum through quasilocal angular momentum integrals. When constructing irrotational binary neutron stars, we find a very small residual dimensionless spin of 2 10-4 . Evolutions of rotating neutron star binaries show that the magnitude of the stars' angular momentum is conserved, and that the spin and orbit precession of the stars is well described by post-Newtonian approximation. We demonstrate that orbital eccentricity of the binary neutron stars can be controlled to 0.1 % . The neutron stars show quasinormal mode oscillations at an amplitude which increases with the rotation rate of the stars.

  15. The neutron star mass distribution

    SciTech Connect

    Kiziltan, Blent; Kottas, Athanasios; De Yoreo, Maria; Thorsett, Stephen E.

    2013-11-20

    In recent years, the number of pulsars with secure mass measurements has increased to a level that allows us to probe the underlying neutron star (NS) mass distribution in detail. We critically review the radio pulsar mass measurements. For the first time, we are able to analyze a sizable population of NSs with a flexible modeling approach that can effectively accommodate a skewed underlying distribution and asymmetric measurement errors. We find that NSs that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. NSs in double NS and NS-white dwarf (WD) systems show consistent respective peaks at 1.33 M {sub ?} and 1.55 M {sub ?}, suggesting significant mass accretion (?m ? 0.22 M {sub ?}) has occurred during the spin-up phase. The width of the mass distribution implied by double NS systems is indicative of a tight initial mass function while the inferred mass range is significantly wider for NSs that have gone through recycling. We find a mass cutoff at ?2.1 M {sub ?} for NSs with WD companions, which establishes a firm lower bound for the maximum NS mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for NS matter. The lack of truncation close to the maximum mass cutoff along with the skewed nature of the inferred mass distribution both enforce the suggestion that the 2.1 M {sub ?} limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare supermassive NSs is possible.

  16. Encounters between binaries and neutron stars

    NASA Technical Reports Server (NTRS)

    Davies, M. B.; Benz, W.; Hills, J. G.

    1993-01-01

    We simulated encounters between a neutron star and primordial and tidal-capture binaries. In the case of encounters involving a tidal-capture binary, comprising a white dwarf and a main-sequence star, we find that most exchange encounters will produce a single merged object with the white dwarf and neutron star engulfed in a common envelope of gas donated by the main-sequence primary of the original binary. A small fraction of exchanges induce a merger of the white dwarf and main-sequence star, with this object being unbound to the neutron star, and the two objects having a large relative speed at infinity. For encounters involving a primordial binary, fewer encounters require the inclusion of hydrodynamical effects. Those involving collisions or close encounters tend to produce a binary comprised of the two merged stars (now forming one star) and the third star. The binaries produced typically have large enough separations to prevent the formation of a single merged object until subsequent stellar evolution of one of the components causes it to fill its Roche lobe. Clean exchanges produce binaries with large eccentricities; they are typically sufficiently wide to avoid circularization.

  17. Improved microphysics in neutron star merger simulations

    NASA Astrophysics Data System (ADS)

    Foucart, Francois

    2014-09-01

    Neutron star mergers are expected to be among the main sources of gravitational waves detectable by the Advance LIGO/VIRGO/KAGRA detector network. In many cases, these mergers are also likely to power bright electromagnetic transients, including short gamma-ray bursts and ``kilonovae,'' the optical/infrared emission due to the radioactive decay of neutron rich elements in material unbound by the merger. These EM counterparts can provide important information on the environment in which the merger takes place and the nature of the binary, and their detection could shed a light on the origin of short gamma-ray bursts and of r-process elements. Numerical simulations of neutron star mergers using general relativistic codes are required to understand the merger dynamics, the impact of the equation of state of the neutron star on the gravitational wave signal, and the potential of a given binary to power electromagnetic counterparts to that signal. Until recently, however, general relativistic codes used very simple models for the neutron star - often a simple gamma-law equation of state without any additional microphysics. Although sufficient to model the gravitational wave signal before merger, this cannot be used to follow the post-merger evolution of the system, or even some aspects of the disruption of the neutron star. To do so, nuclear-theory based equations of state with temperature and composition dependence have to be used, and the effects of neutrinos and magnetic fields should be taken into account. In this talk, I will discuss current efforts to include more advanced microphysics in general relativistic simulations, what we can do so far, and what the remaining computational challenges are. I will also show how existing numerical simulations have helped us constrain the outcome of neutron star mergers, and what remains to be done in order to extract as much information as possible from upcoming gravitational wave and electromagnetic observations. Neutron star mergers are expected to be among the main sources of gravitational waves detectable by the Advance LIGO/VIRGO/KAGRA detector network. In many cases, these mergers are also likely to power bright electromagnetic transients, including short gamma-ray bursts and ``kilonovae,'' the optical/infrared emission due to the radioactive decay of neutron rich elements in material unbound by the merger. These EM counterparts can provide important information on the environment in which the merger takes place and the nature of the binary, and their detection could shed a light on the origin of short gamma-ray bursts and of r-process elements. Numerical simulations of neutron star mergers using general relativistic codes are required to understand the merger dynamics, the impact of the equation of state of the neutron star on the gravitational wave signal, and the potential of a given binary to power electromagnetic counterparts to that signal. Until recently, however, general relativistic codes used very simple models for the neutron star - often a simple gamma-law equation of state without any additional microphysics. Although sufficient to model the gravitational wave signal before merger, this cannot be used to follow the post-merger evolution of the system, or even some aspects of the disruption of the neutron star. To do so, nuclear-theory based equations of state with temperature and composition dependence have to be used, and the effects of neutrinos and magnetic fields should be taken into account. In this talk, I will discuss current efforts to include more advanced microphysics in general relativistic simulations, what we can do so far, and what the remaining computational challenges are. I will also show how existing numerical simulations have helped us constrain the outcome of neutron star mergers, and what remains to be done in order to extract as much information as possible from upcoming gravitational wave and electromagnetic observations. Einstein Fellow.

  18. Boundary layers of accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Revnivtsev, Mikhail

    I would like to present an overview of observational results of studies of X-ray emission of boundary/spreading layer on neutron stars. The boundary/spreading layer is a part of the accretion flow in X-ray binaries with neutron stars, where the rapidly rotating matter of the accretion disk decelerates and settles to the neutron star surface. It was shown that in spite of complexity of physical conditions in the boundary layer, properties of its emission can be effectively used to put constrains on physical parameters of neutron stars. This ensures a rising level of interest in measurements of the boundary layer emission. In spite of that, during long period of time it was hardly possible to measure its energy spectrum in a model independent way. I will demonstrate that it is possible to do with the help of combined spectral timing information on X-ray emission of neutron stars. It will be shown that the emission of the boundary/spreading layer has virtually constant shape over large variations of its total luminosity which supports existing theoretical ideas of its structue in radiation pressure dominated regime.

  19. Dissipative processes in superfluid neutron stars

    SciTech Connect

    Mannarelli, Massimo; Colucci, Giuseppe; Manuel, Cristina

    2011-05-23

    We present some results about a novel damping mechanism of r-mode oscillations in neutron stars due to processes that change the number of protons, neutrons and electrons. Deviations from equilibrium of the number densities of the various species lead to the appearance in the Euler equations of the system of a dissipative mechanism, the so-called rocket effect. The evolution of the r-mode oscillations of a rotating neutron star are influenced by the rocket effect and we present estimates of the corresponding damping timescales. In the description of the system we employ a two-fluid model, with one fluid consisting of all the charged components locked together by the electromagnetic interaction, while the second fluid consists of superfluid neutrons. Both components can oscillate however the rocket effect can only efficiently damp the countermoving r-mode oscillations, with the two fluids oscillating out of phase. In our analysis we include the mutual friction dissipative process between the neutron superfluid and the charged component. We neglect the interaction between the two r-mode oscillations as well as effects related with the crust of the star. Moreover, we use a simplified model of neutron star assuming a uniform mass distribution.

  20. The spin evolution of nascent neutron stars

    NASA Astrophysics Data System (ADS)

    Watts, Anna L.; Andersson, Nils

    2002-07-01

    The loss of angular momentum owing to unstable r-modes in hot young neutron stars has been proposed as a mechanism for achieving the spin rates inferred for young pulsars. One factor that could have a significant effect on the action of the r-mode instability is fallback of supernova remnant material. The associated accretion torque could potentially counteract any gravitational-wave-induced spin-down, and accretion heating could affect the viscous damping rates and hence the instability. We discuss the effects of various external agents on the r-mode instability scenario within a simple model of supernova fallback on to a hot young magnetized neutron star. We find that the outcome depends strongly on the strength of the magnetic field of the star. Our model is capable of generating spin rates for young neutron stars that accord well with initial spin rates inferred from pulsar observations. The combined action of r-mode instability and fallback appears to cause the spin rates of neutron stars born with very different spin rates to converge, on a time-scale of approximately 1 year. The results suggest that stars with magnetic fields <=1013G could emit a detectable gravitational wave signal for perhaps several years after the supernova event. Stars with higher fields (magnetars) are unlikely to emit a detectable gravitational wave signal via the r-mode instability. The model also suggests that the r-mode instability could be extremely effective in preventing young neutron stars from going dynamically unstable to the bar-mode.

  1. Neutron star dynamics and gravitational waves

    NASA Astrophysics Data System (ADS)

    Kokkotas, Kostas D.; Gaertig, Erich; Colaiuda, Antonella

    2010-04-01

    As several large scale interferometers are beginning to take data at sensitivities where astrophysical sources are predicted, the direct detection of gravitational waves may well be imminent. This would open the gravitational-wave window to our Universe and should lead to a much improved understanding of the most violent processes imaginable; the formation of black holes and neutron stars following core collapse supernovae and the merger of compact objects at the end of binary inspiral. Among the best candidate sources for gravitational waves are the oscillations, but mainly the rotational instabilities of neutron stars which can emit quite strong gravitational wave signals via which one may reveal the details of their structure. Magnetars also are neutron stars with ultra strong magnetic field whose periodic flaring activity is associated with starquakes. They are also a potential source of gravitational waves while even the quasi-periodic oscillations (QPOs) observed in the electromagnetic spectrum can reveal the details of their structure.

  2. Neutron Star Dynamics and Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Kokkotas, K. D.; Colaiuda, A.; Gaertig, E.

    2010-07-01

    As several large scale interferometers are beginning to take data at sensitivities where astrophysical sources are predicted, the direct detection of gravitational waves may well be imminent. This would open the gravitational-wave window to our Universe and should lead to a much improved understanding of the most violent processes imaginable; the formation of black holes and neutron stars following core collapse supernovae and the merger of compact objects at the end of binary inspiral. Among the best candidate sources for gravitational waves are the oscillations, but mainly the rotational instabilities of neutron stars which can emit quite strong gravitational wave signals via which one may reveal the details of their structure. Magnetars also are neutron stars with ultra strong magnetic field whose periodic flaring activity is associated with starquakes. They are also a potential source of gravitational waves while even the quasi-periodic oscillations (QPOs) observed in the electromagnetic spectrum can reveal the details of their structure.

  3. Ultrahigh energy neutrinos from galactic neutron stars

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.

    1979-01-01

    An attempt is made to estimate the production rate of ultrahigh energy (UHE) neutrinos from galactic neutron stars. The statistics of various stellar populations are reviewed as well as an evolutionary scheme linking several neutron star environments. An observational test for predicting stellar evolution is made using two mass ratio intervals of less than 0.3 and greater than or approximately equal to 0.3, which is supported by kinematical evidence. Attention is given to the problem of the target material that is required by UHE protons accelerated from the pulsar's surface to their rotational kinetic energy, and to the detectability of neutron stars in the UHE neutrinos by employing the deep underwater muon and neutrino detector (DUMAND) array.

  4. Remarks concerning kaon condensation in neutron stars

    SciTech Connect

    Wang Guohua; Fu Weijie; Liu Yuxin

    2007-12-15

    We reanalyze the existence of antikaon condensation phase in neutron stars with large mass and high gravitational redshift with not only the Glendenning-Moszkowski (GM) model but also the Zimanyi-Moszkowski (ZM) model in the framework of relativistic mean field (RMF) approximation theory. We find that even in the large mass and high redshift neutron stars, there are still some stiff enough equations of state of neutron star matter so that the pure antikaon condensation phase and the mixed phase of normal baryons and antikaon condensation can exist. By comparing the result given in the GM model and that in the ZM model, we notice that the existence of antikaon condensation phase does not depend on the details of the models.

  5. Remarks concerning kaon condensation in neutron stars

    NASA Astrophysics Data System (ADS)

    Wang, Guo-Hua; Fu, Wei-Jie; Liu, Yu-Xin

    2007-12-01

    We reanalyze the existence of antikaon condensation phase in neutron stars with large mass and high gravitational redshift with not only the Glendenning-Moszkowski (GM) model but also the Zimanyi-Moszkowski (ZM) model in the framework of relativistic mean field (RMF) approximation theory. We find that even in the large mass and high redshift neutron stars, there are still some stiff enough equations of state of neutron star matter so that the pure antikaon condensation phase and the mixed phase of normal baryons and antikaon condensation can exist. By comparing the result given in the GM model and that in the ZM model, we notice that the existence of antikaon condensation phase does not depend on the details of the models.

  6. The Neutron Star Interior Composition Explorer (NICER)

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Gendreau, K.; Arzoumanian, Z.

    2014-01-01

    The Neutron Star Interior Composition Explorer (NICER) is an approved NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. Scheduled to be launched in 2016 as an International Space Station payload, NICER will explore the exotic states of matter, using rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2-12 keV) X-ray band. Grazing-incidence "concentrator" optics coupled with silicon drift detectors, actively pointed for a full hemisphere of sky coverage, will provide photon-counting spectroscopy and timing registered to GPS time and position, with high throughput and relatively low background. The NICER project plans to implement a Guest Observer Program, which includes competitively selected user targets after the first year of flight operations. I will describe NICER and discuss ideas for potential Be/X-ray binary science.

  7. Towards a metallurgy of neutron star crusts.

    PubMed

    Kobyakov, D; Pethick, C J

    2014-03-21

    In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic lattice of nuclei immersed in an essentially uniform electron gas. We show that, at densities above that for neutron drip (∼ 4 × 1 0(11)  g cm(-3) or roughly one-thousandth of nuclear matter density), the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO3. As a consequence, the properties of matter in the inner crust are expected to be much richer than previously appreciated, and we mention possible consequences for observable neutron star properties. PMID:24702357

  8. Magnetic field evolution in superconducting neutron stars

    NASA Astrophysics Data System (ADS)

    Graber, Vanessa; Andersson, Nils; Glampedakis, Kostas; Lander, Samuel K.

    2015-10-01

    The presence of superconducting and superfluid components in the core of mature neutron stars calls for the rethinking of a number of key magnetohydrodynamical notions like resistivity, the induction equation, magnetic energy and flux-freezing. Using a multifluid magnetohydrodynamics formalism, we investigate how the magnetic field evolution is modified when neutron star matter is composed of superfluid neutrons, type-II superconducting protons and relativistic electrons. As an application of this framework, we derive an induction equation where the resistive coupling originates from the mutual friction between the electrons and the vortex/fluxtube arrays of the neutron and proton condensates. The resulting induction equation allows the identification of two time-scales that are significantly different from those of standard magnetohydrodynamics. The astrophysical implications of these results are briefly discussed.

  9. Bulk viscosity of superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Gusakov, Mikhail E.

    2007-10-01

    The hydrodynamics describing dynamical effects in superfluid neutron stars essentially differs from the standard one-fluid hydrodynamics. In particular, we have four bulk viscosity coefficients in the theory instead of one. In this paper we calculate these coefficients, for the first time, assuming they are due to nonequilibrium beta processes (such as modified or direct Urca process). The results of our analysis are used to estimate characteristic damping times of sound waves in superfluid neutron stars. It is demonstrated that all four bulk viscosity coefficients lead to comparable dissipation of sound waves and should be considered on the same footing.

  10. An instability in neutron stars at birth

    NASA Technical Reports Server (NTRS)

    Burrows, Adam; Fryxell, Bruce A.

    1992-01-01

    Calculations with a two-dimensional hydrodynamic simulation show that a generic Raleigh-Taylor-like instability occurs in the mantles of nascent neutron stars, that it is possibly violent, and that the standard spherically symmetric models of neutron star birth and supernova explosion may be inadequate. Whether this 'convective' instability is pivotal to the supernova mechanism, pulsar nagnetic fields, or a host of other important issues that attend stellar collapse remains to be seen, but its existence promises to modify all questions concerning this most energetic of astronomical phenomena.

  11. Chandra Observations of Neutron Stars: An Overview

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; Karovska, M.; Pavlov, G. G.; Zavlin, V. E.; Clarke, Tracy

    2006-01-01

    We present a brief review of Chandra X-ray Observatory observations of neutron stars. The outstanding spatial and spectral resolution of this great observatory have allowed for observations of unprecedented clarity and accuracy. Many of these observations have provided new insights into neutron star physics. We present an admittedly biased and overly brief overview of these observations, highlighting some new discoveries made possible by the Observatory's unique capabilities. We also include our analysis of recent multiwavelength observations of the putative pulsar and its pulsar-wind nebula in the IC 443 SNR.

  12. Physics in Strong Magnetic Fields Near Neutron Stars.

    ERIC Educational Resources Information Center

    Harding, Alice K.

    1991-01-01

    Discussed are the behaviors of particles and energies in the magnetic fields of neutron stars. Different types of possible research using neutron stars as a laboratory for the study of strong magnetic fields are proposed. (CW)

  13. Constraining Neutron Star Matter with Quantum Chromodynamics

    NASA Astrophysics Data System (ADS)

    Kurkela, Aleksi; Fraga, Eduardo S.; Schaffner-Bielich, Jrgen; Vuorinen, Aleksi

    2014-07-01

    In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amountor even presenceof quark matter inside the stars.

  14. Constraining neutron star matter with quantum chromodynamics

    SciTech Connect

    Kurkela, Aleksi; Fraga, Eduardo S.; Schaffner-Bielich, Jürgen; Vuorinen, Aleksi

    2014-07-10

    In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount—or even presence—of quark matter inside the stars.

  15. PULSE PROFILES FROM THERMALLY EMITTING NEUTRON STARS

    SciTech Connect

    Turolla, R.; Nobili, L.

    2013-05-10

    The problem of computing the pulse profiles from thermally emitting spots on the surface of a neutron star in general relativity is reconsidered. We show that it is possible to extend Beloborodov's approach to include (multiple) spots of finite size in different positions on the star surface. The results for the pulse profiles are expressed by comparatively simple analytical formulae which involve only elementary functions.

  16. Merger of Magnetized Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Anderson, Matthew; Lehner, Luis; Liebling, Steven L.; Hirschmann, Eric; Neilsen, David; Palenzuela, Carlos

    2016-01-01

    We present simulations of the merger of binary neutron star systems calculated with full general relativity and incorporating the global magnetic field structure for the stars evolved with resistive magnetohydrodynamics. We also incorporate the effects of neutrino transport and tabular equations of state to describe the degenerate matter. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  17. Neutron Star Observations and the Equation of State

    SciTech Connect

    Lattimer, James M.

    2009-05-07

    This talk reviews limits to the properties of neutron stars established from physical considerations such as causality and stability. In addition, it summarizes recent attempts to determine realistic bounds to the equation of state (EOS) from a simultaneous measurement of a neutron star's mass and radius. Observational constraints on the neutron star radius from thermal emission, seismology, spin-orbit coupling, and tidal effects in mergers are discussed. Possible constraints from neutron star cooling, including neutrino emissions, are discussed.

  18. Chandra Observations of Supernova Remnants and Neutron Stars: An Overview

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.

    2002-01-01

    We present a brief overview of Chandra observations of supernova remnants and neutron stars, with emphasis on neutron stars in supernova remnants. The Chandra images demonstrate the importance of angular resolution in separating the neutron star emission from the surrounding nebulosity.

  19. Neutron Stars and Pulsar: Three Years of Chandra Operations

    NASA Technical Reports Server (NTRS)

    Weisskopf, M. C.; Six, N. Frank (Technical Monitor)

    2002-01-01

    We present a brief review of Chandra Observations of neutron stars, with a concentration on neutron stars in supernova remnants. Three years of Chandra results clearly demonstrate how critical the angular resolution has been in order to separate the neutron star emission from the surrounding nebulosity.

  20. Generalized equation of state for cold superfluid neutron stars

    SciTech Connect

    Chamel, N.; Goriely, S.; Pearson, J. M.

    2011-09-21

    Mature neutron stars are expected to contain various kinds of superfluids in their interiors. Modeling such stars requires the knowledge of the mutual entrainment couplings between the different condensates. We present a unified equation of state describing the different regions of a neutron star with superfluid neutrons and superconducting protons in its core.

  1. Strange Stars, Neutron Stars and Pulsar Emission

    NASA Astrophysics Data System (ADS)

    Benvenuto, O. G.; Horvath, J. E.

    1990-11-01

    RESUMEN. Se ha conjeturado que una partlecula de dieciocho quarks, sin Carga, sin espi'n y sin colar (quark-alfa) podri'a ser estable a ba5as tern peraturas y presiones aiTh COfl respecto a materia extrafla. Presentamos en este trabajo la estmctura de estrellas extraflas incluyendo los efectos y apariencia de parti'culas uark-alfa en las capas exteriores. La estruc tura interna ya no es hoinogenea del centro a la superficie, sino que muestra un centro de materia extrafla, capas s6lidas y una costra delgada de materia normal en la superficie. La superficie de materia nonnal permite la fornaci6n de una magnetosfera, la que se piensa sea el sitlo en donde ocurre la emisi6n del pulsar. La superficie de superflui'do ayuda a explicar el fen6rneno de `glitch', el cual ba sido observado en muchos pulsares. Se discute la ecuaci6n de estado para rnateria quark-alfa relevante en este regimen. ABSTIZACT:It has been conjectured that an quark, uncharged, spinless and colorless particle Cquark-alpha) could be stable at low pressures and temperatures even with respect to strange matter. We present in work tlie structure of stars including the effects of the appearance of quark-alpi' particles ii their outer layers. The internal structure is no longer from tlie center to the surface, but show a strange matter core, a solid and superfluid layers and a thin crust of normal matter at the surface. The normal matter surface allows tlie fon tion of a magnetosphere, whicl is to be tl place where pulsar emission occurs. A superfluid layer helps to explain tlie glitch , wlflch has been observed in . equation of state for quark-alpha matter relevant in regime is also discussed. Keq LA)OtL : ARY S - OF STATF - ?.ACT

  2. The Mystery of the Lonely Neutron Star

    NASA Astrophysics Data System (ADS)

    2000-09-01

    The VLT Reveals Bowshock Nebula around RX J1856.5-3754 Deep inside the Milky Way, an old and lonely neutron star plows its way through interstellar space. Known as RX J1856.5-3754 , it measures only ~ 20 km across. Although it is unusually hot for its age, about 700,000 °C, earlier observations did not reveal any activity at all, contrary to all other neutron stars known so far. In order to better understand this extreme type of object, a detailed study of RX J1856.5-3754 was undertaken by Marten van Kerkwijk (Institute of Astronomy of the University of Utrecht, The Netherlands) and Shri Kulkarni (California Institute of Technology, Pasadena, California, USA). To the astronomers' delight and surprise, images and spectra obtained with the ESO Very Large Telescope (VLT) now show a small nearby cone-shaped ("bowshock") nebula. It shines in the light from hydrogen atoms and is obviously a product of some kind of interaction with this strange star. Neutron stars - remnants of supernova explosions Neutron stars are among the most extreme objects in the Universe. They are formed when a massive star dies in a "supernova explosion" . During this dramatic event, the core of the star suddenly collapses under its own weight and the outer parts are violently ejected into surrounding space. One of the best known examples is the Crab Nebula in the constellation Taurus (The Bull). It is the gaseous remnant of a star that exploded in the year 1054 and also left behind a pulsar , i.e., a rotating neutron star [1]. A supernova explosion is a very complex event that is still not well understood. Nor is the structure of a neutron star known in any detail. It depends on the extreme properties of matter that has been compressed to incredibly high densities, far beyond the reach of physics experiments on Earth [2]. The ultimate fate of a neutron star is also unclear. From the observed rates of supernova explosions in other galaxies, it appears that several hundred million neutron stars must have formed in our own galaxy, the Milky Way. However, most of these are now invisible, having since long cooled down and become completely inactive while fading out of sight. An unsual neutron star - RX J1856.5-3754 Some years ago, the X-ray source RX J1856.5-3754 was found by the German ROSAT X-ray satellite observatory. Later observations with the Hubble Space Telescope (cf. STScI-PR97-32 ) detected extremely faint optical emission from this source and conclusively proved that it is an isolated neutron star [3]. There is no sign of the associated supernova remnant and it must therefore be at least 100,000 years "old". Most interestingly, and unlike younger isolated neutron stars or neutron stars in binary stellar systems, RX J1856.5-3754 does not show any sign of activity whatsoever, such as variability or pulsations. As a unique member of its class, RX J1856.5-3754 quickly became the centre of great interest among astronomers. It apparently presented the first, very welcome opportunity to perform detailed studies of the structure of a neutron star, without the disturbing influence of ill-understood activity. One particular question arose immediately. The emission of X-rays indicates a very high temperature of RX J1856.5-3754 . However, from the moment of their violent birth, neutron stars are thought to lose energy and to cool down continuously. But then, how can an old neutron star like this one be so hot? One possible explanation is that some interstellar material, gas and/or dust grains, is being captured by its strong gravitational field. Such particles would fall freely towards the surface of the neutron star and arrive there with about half the speed of light. Since the kinetic energy of these particles is proportionate to the second power of the velocity, even small amounts of matter would deposit much energy upon impact, thereby heating the neutron star. The spectrum of RX J1856.5-3754 The new VLT study by van Kerkwijk and Kulkarni of RX J1856.5-3754 was first aimed at taking optical spectra, in order to study its structure. The astronomers hoped to find in its spectrum some "signatures", i.e., emission or absorption lines and/or bands, that might provide information about the physical conditions on its surface. While the chances for this were admittedly rather slim, a detection of such spectral features would be a real break-through in the study of neutron stars. If present in the spectrum, they could for instance be used to measure directly the immense strength of the gravitational field on the surface, expected to be about 10 12 times stronger than that on the surface of the Earth. Moreover, it might be possible to determine the gravitational redshift , a relativistic effect whereby the light quanta (photons) that are emitted from the surface lose about 20% of their energy as they escape from the neutron star. Their wavelength is consequently red-shifted by that amount. The spectral observations were difficult, first of all because of the extreme faintness of RX J1856.5-3754 . But even though an excellent spectrum was obtained with the multi-mode FORS1 instrument at VLT ANTU, it was indeed quite featureless and no spectral features were seen. Surprises from RX J1856.5-3754 Nevertheless, as it often happens in astronomy, these observations did bring surprises. The first was that the neutron star had obviously moved on the sky since the HST had observed it in 1997. From positional measurements and the assumed distance, approx. 200 light-years, RX J1856.5-3754 was found to be moving with a velocity of about 100 km/s [4]. However, at such a high speed, it is hard to imagine how it would be able to catch much interstellar matter, whose infall might heat the surface as described above. The puzzle was deepening! Another surprise was that the spectra showed very faint emission from the neighbourhood of the neutron star. The measured wavelengths identified these emission lines as H-alpha and H-beta , two of the so-called Balmer lines that originate in hydrogen atoms. Most likely, the strong radiation from the very hot surface of the neutron star is ionizing hydrogen atoms (separating them in a proton and an electron) in the surroundings, a process that also takes place near very hot, normal stars. The observed emission is then produced when, at a later time, the protons and electrons again (re)combine into hydrogen atoms. Interestingly, a simple estimate of the hydrogen density near the neutron star that is needed to produce the observed glow indicates the presence of about one hundred hydrogen atoms per cubic centimetre. This is no less than one hundred times the usual density in the interstellar medium. So maybe the surface of RX J1856.5-3754 could still be heated by infalling hydrogen atoms? VLT images of the RX J1856.5-3754 region With the inferred hydrogen density near the neutron star, about one thousand years on the average will elapse between the moment of ionization by the passing neutron star and the subsequent re-unification of a proton with an electron to form a hydrogen atom. During this time, however, the fast-moving neutron star will have covered a substantial distance. For this reason, it is expected that much of the hydrogen emission will not be seen very close to the neutron star, but rather along its "recent" trajectory in space. ESO PR Photo 23a/00 ESO PR Photo 23a/00 [Preview - JPEG: 400 x 474 pix - 192k] [Normal - JPEG: 800 x 948 pix - 622k] [Full-Res - JPEG: 1975 x 2340 pix - 2.2Mb] ESO PR Photo 23b/00 ESO PR Photo 23b/00 [Preview - JPEG: 400 x 472 pix - 184k] [Normal - JPEG: 800 x 944 pix - 424k] Caption : False-colour composite photo of the sky field with the lonely neutron star RX J1856.5-3754 and the related cone-shaped nebula. It is based on a series of exposures obtained with the multi-mode FORS2 instrument at VLT KUEYEN through three different optical filters: R (29 exposures of 136 sec each; ~1.1 hrs total; here rendered as green); H-alpha (19; 1020 sec; ~5.5 hrs; red); and B (10; 138 sec; ~0.4 hrs; blue). The seeing was good to excellent during the exposures (0.66 arcsec on average). The trails of some moving objects, most likely asteroids in the solar system, are seen in the field with intermittent blue, green and red colours. The large field ( PR Photo 23a/00 ) measures 6.6 x 6.7 arcmin 2 , with 0.2 arcsec/pixel. For clarity, a smaller area around the neutron star and the cone ("bowshock") nebula has been enlarged in PR Photo 23b/00 . The object is at the centre of the circle and the neutron star is indicated with an arrow; the field measures 80 x 80 arcsec 2. North is to the lower right and East is upper right. The motion of the neutron star as seen on the sky (see the text) is towards East, exactly in the direction indicated by the nebula. In order to test these ideas, additional observing time was granted on the VLT to obtain very "deep", direct images that would attempt to map the hydrogen glow. They were carried out by ESO staff astronomers at Paranal in "service mode". Exposures lasting more than five hours in total were taken through a narrow optical filter that isolates the H-alpha hydrogen emission. In addition, shorter exposures were taken through B(lue) and R(ed) filters. The exposures have been combined into the false-colour PR Photos 23a-b/00 . Legions of stars are seen in the photos. This is partly because of the extraordinary light sensitivity of the VLT, and partly because a star-forming region is located in this direction. Stars like our Sun appear whitish, relatively cool stars emit little blue light and appear more reddish, while hot stars appear blue. The photos clearly show a lot of diffuse light, especially in the lower left area. This is most likely starlight reflected off interstellar dust grains. The cone-shaped nebula near RX J1856.5-3754 A small area, just a little above and to the right of the centre of PR Photo 23a/00 , has been enlarged in PR Photo 23b/00 . It shows a small, cone-shaped nebula never seen before - this is the emission from hydrogen atoms near the neutron star RX J1856.5-3754 . The star itself is the very faint, blue object very close to the top of the cone. The shape of the cone is like that of a "bowshock" from a ship, plowing through water. Similarly shaped cones have been found around fast-moving radio pulsars and massive stars, cf. e.g., ESO PR 01/97. However, for those objects, the bowshock forms because of a strong outflow of particles from the star or the pulsar (a "stellar wind"), that collides with the interstellar matter. Because of this analogy, one may think that a "wind" also blows from RX J1856.5-3754 . However, for this a new hypothesis would have to be invoked. An alternative, perhaps more plausible possibility is that when the surrounding hydrogen atoms are ionized, the resulting electrons and protons acquire substantial velocities, heating the interstellar gas near the passing neutron star. The heated gas expands and pushes aside the surrounding cooler gas. In the end, this process may lead to a geometrical shape similar to that caused by a stellar wind. Whither RX J1856.5-3754? At present, it is still uncertain whether the observed density of the surrounding interstellar matter is sufficient to heat RX J1856.5-3754 to the observed temperature. However, it is possible that sometimes in the past the neutron star managed to collect more matter during its travel through interstellar space, was heated, and is now slowly cooling down. In another million years or so, it will become undetectable, until it happens to pass through another dense interstellar region. And so on... Notes [1]: Images of the Crab Nebula and its pulsar from VLT KUEYEN and FORS2 are available in ESO PR 17/99. [2]: In fact, a neutron star is like one big atom with a diameter of 10-20 kilometres, and weighing about as much as the Sun. The mean density is an unimaginable 10 15 g/cm 3. Thus, a pinhead of neutron star material (1 millimetre across) weighs almost 1 million tons, or about as much as the largest oil carrier ever built, fully loaded. [3]: The apparent visual magnitude of RX J1856.5-3754 is 25.6, or nearly 100 million times fainter than what can be perceived with the unaided eye in a dark sky. [4]: The motion of RX J1856.5-3754 was also found by Frederick M. Walter (Stony Brook, New York, USA), who also determined the distance, cf. the corresponding research article that is now available on the web.

  3. Neutron Star Structure, Neutron-rich Matter, and Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Steiner, Andrew

    2014-03-01

    In addition to opening a new window on the universe, the detection of gravitational waves will have important implications for nuclear physics. In particular, gravitational waves from neutron star mergers contain important information about the structure of neutron stars - which are our best probes of QCD at non-perturbative densities. I will briefly review what we can learn about neutron star structure from gravitational waves and compare that with what we have learned recently from electromagnetic observations. A careful combination of these two types of data will bring us closer to answering one of the fundamental questions about high-density QCD: what are the best degrees of freedom for describing matter above the nuclear saturation density? Also, neutron star mergers are promising sites of r-process nucleosynthesis, and gravitational waves signals may help us understand how much r-process material comes from mergers as opposed to neutrino driven winds. R-process material in mergers originates near the neutrinosphere, a region very sensitive to the nuclear physics input. AWS is supported by DOE Grant No. DEFG02-00ER41132.

  4. Neutron star solutions in perturbative quadratic gravity

    SciTech Connect

    Deliduman, Cemsinan; Ek?i, K.Y.; Kele?, Vildan E-mail: eksi@itu.edu.tr

    2012-05-01

    We study the structure of neutron stars in R+?R{sup ??}R{sub ??} gravity model with perturbative method. We obtain mass-radius relations for six representative equations of state (EoSs). We find that, for |?| ? 10{sup 11} cm{sup 2}, the results differ substantially from the results of general relativity. Some of the soft EoSs that are excluded within the framework of general relativity can be reconciled for certain values of ? of this order with the 2 solar mass neutron star recently observed. For values of ? greater than a few 10{sup 11} cm{sup 2} we find a new solution branch allowing highly massive neutron stars. By referring some recent observational constraints on the massradius relation we try to constrain the value of ? for each EoS. The associated length scale (?){sup 1/2} ? 10{sup 6} cm is of the order of the the typical radius of neutron stars, the probe used in this test. This implies that the true value of ? is most likely much smaller than 10{sup 11} cm{sup 2}.

  5. Nuclear physics problems for accreting neutron stars

    SciTech Connect

    Wallace, R.K.; Woosley, S.E.

    1983-01-01

    The importance of p(e/sup -/nu)n and of (p,..gamma..) reactions on /sup 56/Ni during a thermonuclear runaway on a neutron star surface is pointed out. A fast 16-isotope approximate nuclear reaction network is developed that is suitable for use in hydrodynamic calculations of such events.

  6. Temperature effects in pulsating superfluid neutron stars

    SciTech Connect

    Kantor, Elena M.; Gusakov, Mikhail E.

    2011-05-15

    We study the effects of finite stellar temperatures on the oscillations of superfluid neutron stars. The importance of these effects is illustrated with a simple example of a radially pulsating general relativistic star. Two main effects are taken into account: (i) temperature dependence of the entrainment matrix and (ii) the variation of the size of superfluid region with temperature. Four models are considered, which include either one or both of these two effects. Pulsation spectra are calculated for these models, and asymptotes for eigenfrequencies at temperatures close to critical temperature of neutron superfluidity are derived. It is demonstrated that models that allow for the temperature effect (ii) but disregard the effect (i), yield unrealistic results. Eigenfunctions for the normal- and superfluid-type pulsations are analyzed. It is shown that superfluid pulsation modes practically do not appear at the neutron-star surface and, therefore, can hardly be observed by measuring the modulation of the electromagnetic radiation from the star. The e-folding times for damping of pulsations due to the shear viscosity and nonequilibrium modified Urca processes are calculated and their asymptotes at temperatures close to the neutron critical temperature, are obtained. It is demonstrated that superfluid pulsation modes are damped by 1-3 orders of magnitude faster than normal modes.

  7. Tidal Love Numbers of Neutron Stars

    SciTech Connect

    Hinderer, Tanja

    2008-04-20

    For a variety of fully relativistic polytropic neutron star models we calculate the star's tidal Love number k{sub 2}. Most realistic equations of state for neutron stars can be approximated as a polytrope with an effective index n {approx} 0.5-1.0. The equilibrium stellar model is obtained by numerical integration of the Tolman-Oppenheimer-Volkhov equations. We calculate the linear l = 2 static perturbations to the Schwarzschild spacetime following the method of Thorne and Campolattaro. Combining the perturbed Einstein equations into a single second-order differential equation for the perturbation to the metric coefficient g{sub tt} and matching the exterior solution to the asymptotic expansion of the metric in the star's local asymptotic rest frame gives the Love number. Our results agree well with the Newtonian results in the weak field limit. The fully relativistic values differ from the Newtonian values by up to {approx}24%. The Love number is potentially measurable in gravitational wave signals from inspiralling binary neutron stars.

  8. General relativistic neutron stars with twisted magnetosphere

    NASA Astrophysics Data System (ADS)

    Pili, A. G.; Bucciantini, N.; Del Zanna, L.

    2015-03-01

    Soft gamma-ray repeaters and anomalous X-ray pulsars are extreme manifestations of the most magnetized neutron stars: magnetars. The phenomenology of their emission and spectral properties strongly support the idea that the magnetospheres of these astrophysical objects are tightly twisted in the vicinity of the star. Previous studies on equilibrium configurations have so far focused on either the internal or the external magnetic field configuration, without considering a real coupling between the two fields. Here, we investigate numerical equilibrium models of magnetized neutron stars endowed with a confined twisted magnetosphere, solving the general relativistic Grad-Shafranov equation both in the interior and in the exterior of the compact object. A comprehensive study of the parameters space is provided, to investigate the effects of different current distributions on the overall magnetic field structure.

  9. Oscillations of dissipative superfluid neutron stars

    SciTech Connect

    Andersson, N.; Haskell, B.; Glampedakis, K.

    2009-05-15

    We investigate the oscillations of slowly rotating superfluid stars, taking into account the vortex-mediated mutual friction force that is expected to be the main damping mechanism in mature neutron star cores. Working to linear order in the rotation of the star, we consider both the fundamental f-modes and the inertial r-modes. In the case of the (polar) f-modes, we work out an analytic approximation of the mode which allows us to write down a closed expression for the mutual friction damping time scale. The analytic result is in good agreement with previous numerical results obtained using an energy integral argument. We extend previous work by considering the full range of permissible values for the vortex drag, e.g. the friction between each individual vortex and the electron fluid. This leads to the first ever results for the f-mode in the strong drag regime. Our estimates provide useful insight into the dependence on, and relevance of, various equation of state parameters. In the case of the (axial) r-modes, we confirm the existence of two classes of modes. However, we demonstrate that only one of these sets remains purely axial in more realistic neutron star models. Our analysis lays the foundation for companion studies of the mutual friction damping of the r-modes at second order in the slow-rotation approximation, the first time evolutions for superfluid neutron star perturbations and also the first detailed attempt at studying the dynamics of superfluid neutron stars with both a relative rotation between the components and mutual friction.

  10. Population synthesis of young neutron stars

    NASA Astrophysics Data System (ADS)

    Igoshev, Andrei P.; Kholtygin, Alexander F.

    2013-03-01

    We investigate the fortune of young neutron stars (NS) in the whole volume of the Milky Way with new code for population synthesis. We start our modeling from the birth of massive OB stars and follow their motion in the Galaxy up to the Supernova explosion. Next we integrate the equations of motion of NS in the averaged gravitational potential of the Galaxy. We estimate the mean kick velocities from a comparison the model Z and R-distributions of radio emitting NS with that for galactic NS accordingly ATNF pulsar catalog. We follow the history of the rotational velocity and the surface magnetic field of NS taking into account the significant magnetic field decay during the first million year of a neutron star's life. The derived value for the mean time of ohmic decay is 2.3?105 years. We model the subsample of galactic radio pulsars which can be detected with available radio telescopes, using a radio beaming model with inhomogeneous distribution of the radio emission in the cone. The distributions functions of the pulsar periods P, period derivatives ? and surface magnetic fields B appear to be in a close agreement with those obtained from an ensemble of neutron stars in the ATNF catalogue.

  11. Constraining the neutron star equation of state with gravitational wave signals from coalescing binary neutron stars

    NASA Astrophysics Data System (ADS)

    Agathos, M.; Meidam, J.; Del Pozzo, W.; Li, T. G. F.; Tompitak, M.; Veitch, J.; Vitale, S.; Van Den Broeck, C.

    2015-07-01

    Recently exploratory studies were performed on the possibility of constraining the neutron star equation of state (EOS) using signals from coalescing binary neutron stars, or neutron star-black hole systems, as they will be seen in upcoming advanced gravitational wave detectors such as Advanced LIGO and Advanced Virgo. In particular, it was estimated to what extent the combined information from multiple detections would enable one to distinguish between different equations of state through hypothesis ranking or parameter estimation. Under the assumption of zero neutron star spins both in signals and in template waveforms and considering tidal effects to 1 post-Newtonian (1PN) order, it was found that O (20 ) sources would suffice to distinguish between a stiff, moderate, and soft equation of state. Here we revisit these results, this time including neutron star tidal effects to the highest order currently known, termination of gravitational waveforms at the contact frequency, neutron star spins, and the resulting quadrupole-monopole interaction. We also take the masses of neutron stars in simulated sources to be distributed according to a relatively strongly peaked Gaussian, as hinted at by observations, but without assuming that the data analyst will necessarily have accurate knowledge of this distribution for use as a mass prior. We find that especially the effect of the latter is dramatic, necessitating many more detections to distinguish between different EOSs and causing systematic biases in parameter estimation, on top of biases due to imperfect understanding of the signal model pointed out in earlier work. This would get mitigated if reliable prior information about the mass distribution could be folded into the analyses.

  12. Relativistic simulations of eccentric binary neutron star mergers: One-arm spiral instability and effects of neutron star spin

    NASA Astrophysics Data System (ADS)

    East, William E.; Paschalidis, Vasileios; Pretorius, Frans; Shapiro, Stuart L.

    2016-01-01

    We perform general-relativistic hydrodynamical simulations of dynamical capture binary neutron star mergers, emphasizing the role played by the neutron star spin. Dynamical capture mergers may take place in globular clusters, as well as other dense stellar systems, where most neutron stars have large spins. We find significant variability in the merger outcome as a function of initial neutron star spin. For cases where the spin is aligned with the orbital angular momentum, the additional centrifugal support in the remnant hypermassive neutron star can prevent the prompt collapse to a black hole, while for antialigned cases the decreased total angular momentum can facilitate the collapse to a black hole. We show that even moderate spins can significantly increase the amount of ejected material, including the amount unbound with velocities greater than half the speed of light, leading to brighter electromagnetic signatures associated with kilonovae and interaction of the ejecta with the interstellar medium. Furthermore, we find that the initial neutron star spin can strongly affect the already rich phenomenology in the postmerger gravitational wave signatures that arise from the oscillation modes of the hypermassive neutron star. In several of our simulations, the resulting hypermassive neutron star develops the one-arm (m =1 ) spiral instability, the most pronounced cases being those with small but non-negligible neutron star spins. For long-lived hypermassive neutron stars, the presence of this instability leads to improved prospects for detecting these events through gravitational waves, and thus may give information about the neutron star equation of state.

  13. Why neutron stars have three hairs

    NASA Astrophysics Data System (ADS)

    Stein, Leo; Yagi, Kent; Pappas, George; Yunes, Nicolas; Apostolatos, Theocharis

    2015-04-01

    Neutron stars have recently been found to enjoy a certain `baldness' in their multipolar structure which is independent of the equation of state (EoS) of dense nuclear matter. This is reminiscent of the black hole no-hair relations, and in stark contrast to regular stars. Why is this? Is it because realistic EoSs are sufficiently similar, or because GR effects are especially important, or because the nuclear matter is `cold'? We explore the physics behind these and more hypotheses, and give a convincing explanation for the true origin of the three-hair relations.

  14. Gravitational Radiation from Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Melatos, Andrew; Payne, D. J.; Peralta, C.

    2006-09-01

    Accreting neutron stars spinning at near-kHz frequencies are thought to be strong gravitational wave (GW) emitters. X-ray timing experiments reveal a dearth of such objects spinning near break up, suggesting that GW emission stalls recycling by accretion. We present recent numerical modeling of two new GW emission mechanisms in this class of sources: (i) hydromagnetic oscillations of a magnetically confined polar mountain on the stellar surface, and (ii) nonaxisymmetric internal motions caused by high-Reynolds-number superfluid spherical Couette flow in the outer core of the star. GW amplitudes and spectra are computed for both processes, which are potentially detectable by LIGO II.

  15. Strong Quake Strikes Japan

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2011-03-01

    As Eos was about to go to press, a powerful earthquake with a preliminary estimated magnitude of 8.9 shook the northeast coast of Japan on 11 March at 05:46:23 UTC. It is the largest known earthquake along the Japan Trench subduction zone since 869 A.D. or earlier, Brian Atwater, geologist with the U.S. Geological Survey (USGS), told Eos. The quake's magnitude would place it fifth in terms of any earthquake magnitude worldwide since at least 1900, according to information from the USGS Earthquake Hazards Program. The amount of energy released in the quake—which occurred 130 kilometers east of Sendai, Honshu, at a depth of 24.4 kilometers—was equivalent to the energy from 30 earthquakes the size of the 1906 quake in San Francisco, Calif., according to David Applegate, USGS senior science advisor for earthquake and geologic hazards. He said the economic losses from the shaking are estimated to be in the tens of billions of dollars.

  16. Electromagnetic multipole fields of neutron stars

    NASA Technical Reports Server (NTRS)

    Roberts, W. J.

    1979-01-01

    A formalism is developed for treating general multipole electromagnetic fields of neutron stars. The electric multipoles induced in a neutron star by its rotation with an arbitrary magnetic multipole at its center are presented. It is shown how to express a family of off-centered multipoles having the same l weight as an infinite array of centered multipoles of increasing l weight referred to the rotational axis. General expressions are given for the linear momentum present in the superposition of arbitrary multipole fields, and the results are combined to compute the radiation rate of linear momentum by an off-centered dipole to zeroth order in the parameter Omega x R/c. The general Deutsch (1955) solution is then rederived in a clear consistent manner, and some minor additions and corrections are provided.

  17. 'Tertiary' nuclear burning - Neutron star deflagration?

    NASA Technical Reports Server (NTRS)

    Michel, F. Curtis

    1988-01-01

    A motivation is presented for the idea that dense nuclear matter can burn to a new class of stable particles. One of several possibilities is an 'octet' particle which is the 16 baryon extension of alpha particle, but now composed of a pair of each of the two nucleons, (3Sigma, Delta, and 2Xi). Such 'tertiary' nuclear burning (here 'primary' is H-He and 'secondary' is He-Fe) may lead to neutron star explosions rather than collapse to a black hole, analogous to some Type I supernovae models wherein accreting white dwarfs are pushed over the Chandrasekhar mass limit but explode rather than collapse to form neutron stars. Such explosions could possibly give gamma-ray bursts and power quasars, with efficient particle acceleration in the resultant relativistic shocks. The new stable particles themselves could possibly be the sought-after weakly interacting, massive particles (WIMPs) or 'dark' matter.

  18. FAST FOSSIL ROTATION OF NEUTRON STAR CORES

    SciTech Connect

    Melatos, A.

    2012-12-10

    It is argued that the superfluid core of a neutron star super-rotates relative to the crust, because stratification prevents the core from responding to the electromagnetic braking torque, until the relevant dissipative (viscous or Eddington-Sweet) timescale, which can exceed {approx}10{sup 3} yr and is much longer than the Ekman timescale, has elapsed. Hence, in some young pulsars, the rotation of the core today is a fossil record of its rotation at birth, provided that magnetic crust-core coupling is inhibited, e.g., by buoyancy, field-line topology, or the presence of uncondensed neutral components in the superfluid. Persistent core super-rotation alters our picture of neutron stars in several ways, allowing for magnetic field generation by ongoing dynamo action and enhanced gravitational wave emission from hydrodynamic instabilities.

  19. Cyclotron Lines of Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Wilms, Joern

    2012-07-01

    In the strong magnetic fields at the poles of accreting neutron stars, the motion of electrons around the field lines is quantized into discrete energy levels. Interactions between photons generated in the accretion column at the magnetic poles and these quantized electrons lead to absorption line like features, so-called cyclotron scattering features or cyclotron lines. Since the energy of the cyclotron lines is proportional to the magnetic field in the region where they are formed, observations of cyclotron lines allow the direct determination of neutron star magnetic fields. The aim of this talk is to review recent observational and theoretical work on cyclotron lines and to give an outlook on cyclotron line observations with the next generation of X-ray satellites.

  20. Particle acceleration in axisymmetric, magnetized neutron stars

    NASA Technical Reports Server (NTRS)

    Baker, K. B.; Sturrock, P. A.

    1977-01-01

    The potential drop in the polar cap region of a rotating, magnetized neutron star is found assuming that the magnetic field is dipolar, with the field aligned (or anti-aligned) with the rotation axis. The curvature of the field lines is of critical importance. Charge flow is assumed to be along magnetic field lines. The electric field has a maximum at radius 1.5 R and the magnitude and functional form of the current is determined.

  1. Physics of systems containing neutron stars

    NASA Technical Reports Server (NTRS)

    Shaham, Jacob

    1989-01-01

    The following is a summary of work done during the period of Mar. to Oct. 1989. Three major topics were extensively looked into during this time: the reported 2,000 Hz optical signal from the direction of SNR1987A, the possibility that neutron stellar surface magnetic fields do not decay except when the star is accreting, and the 6 Hz QPOs of LMXBs.

  2. Topological characterization of neutron star crusts

    NASA Astrophysics Data System (ADS)

    Dorso, C. O.; Giménez Molinelli, P. A.; López, J. A.

    2012-11-01

    Neutron star crusts are studied using a classical molecular dynamics model developed for heavy-ion reactions. After the model is shown to produce a plethora of the so-called pasta shapes, a series of techniques borrowed from nuclear physics, condensed matter physics, and topology is used to craft a method that can be used to characterize the shape of the pasta structures in an unequivocal way.

  3. Magnetic field evolution of accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Istomin, Y. N.; Semerikov, I. A.

    2016-01-01

    The flow of a matter, accreting on to a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the superconducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transverse conductivity. As a result, the current begins to flow mainly in the toroidal direction, creating a strong longitudinal magnetic field, far exceeding an initial dipole field. This field exists only in the narrow polar tube of r width, narrowing with the depth, i.e. with increasing of the crust density ?, r ? ?-1/4. Accordingly, the magnetic field B in the tube increases with the depth, B??1/2, and reaches the value of about 1017 Gauss in the core. It destroys superconducting vortices in the core of a star in the narrow region of the size of the order of 10 cm. Because of generated density gradient of vortices, they constantly flow into this dead zone and the number of vortices decreases, the magnetic field of a star decreases as well. The attenuation of the magnetic field is exponential, B = B0(1 + t/?)-1. The characteristic time of decreasing of the magnetic field ? is equal to ? ? 103 yr. Thus, the magnetic field of accreted neutron stars decreases to values of 108-109 Gauss during 107-106 yr.

  4. Radiation drag near slowly rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Miller, M. Coleman; Lamb, Frederick K.

    1994-05-01

    In a previous paper (Miller & Lamb 1993) we showed that radiation forces are more important than general relativistic corrections to Newtonian gravitational forces in determining the motion of particles accreting onto a nonrotating, isotropically emitting neutron star if the luminosity is greater than ~ 1% of the Eddington critical luminosity L_E(infty ) , even if the radius of the star is less than the radius of the innermost stable orbit. We also showed that at luminosities greater than ~ 0.2L_E(infty ) , a substantial fraction of the accreting matter can transfer most of its angular momentum and gravitational binding energy to the radiation field before reaching the stellar surface. Here we extend this work to include slow rotation of the gravitating mass and radiation source, as well as radiation from ring-like boundary layers. By ``slow rotation" we mean that the azimuthal velocity of the radiating source is v/c<< 1 and that the dimensionless angular momentum of the gravitating mass is jequiv cJ/GM(2<<) 1; for all neutron stars with measured rotation periods j<1, so this is a good approximation. We find that, compared to particle motion around nonrotating stars, the rate of radiation drag is decreased for prograde motion around rotating sources. However, because the drag time is increased, the total energy and angular momentum transfered from the particle to the radiation field can actually be increased compared to the nonrotating case. We conclude that in any disk-accreting neutron star source, radiation drag will have a significant qualitative effect on particle motion. This work was supported in part by NASA grant NAGW 830 at the University of Chicago and by NSF grant PHY 91-00283 and NASA grant NAGW 1583 at the University of Illinois.

  5. Magnetically driven crustquakes in neutron stars

    NASA Astrophysics Data System (ADS)

    Lander, S. K.; Andersson, N.; Antonopoulou, D.; Watts, A. L.

    2015-05-01

    Crustquake events may be connected with both rapid spin-up `glitches' within the regular slowdown of neutron stars, and high-energy magnetar flares. We argue that magnetic-field decay builds up stresses in a neutron star's crust, as the elastic shear force resists the Lorentz force's desire to rearrange the global magnetic-field equilibrium. We derive a criterion for crust-breaking induced by a changing magnetic-field configuration, and use this to investigate strain patterns in a neutron star's crust for a variety of different magnetic-field models. Universally, we find that the crust is most liable to break if the magnetic field has a strong toroidal component, in which case the epicentre of the crustquake is around the equator. We calculate the energy released in a crustquake as a function of the fracture depth, finding that it is independent of field strength. Crust-breaking is, however, associated with a characteristic local field strength of 2.4 1014 G for a breaking strain of 0.001, or 2.4 1015 G at a breaking strain of 0.1. We find that even the most luminous magnetar giant flare could have been powered by crustal energy release alone.

  6. Charged Ising model of neutron star matter

    NASA Astrophysics Data System (ADS)

    Hasnaoui, K. H. O.; Piekarewicz, J.

    2013-08-01

    Background: The inner crust of a neutron star is believed to consist of Coulomb-frustrated complex structures known as nuclear pasta that display interesting and unique low-energy dynamics.Purpose: To elucidate the structure and composition of the neutron-star crust as a function of temperature, density, and proton fraction.Methods: A new lattice-gas model, the charged Ising model (CIM), is introduced to simulate the behavior of neutron-star matter. Preliminary Monte Carlo simulations on 303 lattices are performed for a variety of temperatures, densities, and proton fractions.Results: Results are obtained for the heat capacity, pair-correlation function, and static structure factor for a variety of conditions appropriate to the inner stellar crust.Conclusions: Although relatively simple, the CIM captures the essence of Coulomb frustration that is required to simulate the subtle dynamics of the inner stellar crust. Moreover, the computationally demanding long-range Coulomb interactions have been precomputed at the appropriate lattice sites prior to the start of the simulation, resulting in enormous computational gains. This work demonstrates the feasibility of future CIM simulations involving a large number of particles as a function of density, temperature, and proton fraction.

  7. On the cooling of globally-neutral neutron stars

    NASA Astrophysics Data System (ADS)

    de Carvalho, Sheyse M.; Rueda, Jorge A.; Ruffini, Remo

    2014-09-01

    We compute the thermal evolution of neutron stars by taking into account the strong, weak, electromagnetic and gravitational interactions within the framework of general relativity and by satisfying the condition of global, but not local, charge neutrality. We focus on the isothermal phase following the thermal relaxation of the star and compare the result with observational data from isolated neutron stars.

  8. Mesoscopic pinning forces in neutron star crusts

    NASA Astrophysics Data System (ADS)

    Seveso, S.; Pizzochero, P. M.; Grill, F.; Haskell, B.

    2016-02-01

    The crust of a neutron star is thought to be comprised of a lattice of nuclei immersed in a sea of free electrons and neutrons. As the neutrons are superfluid, their angular momentum is carried by an array of quantized vortices. These vortices can pin to the nuclear lattice and prevent the neutron superfluid from spinning down, allowing it to store angular momentum which can then be released catastrophically, giving rise to a pulsar glitch. A crucial ingredient for this model is the maximum pinning force that the lattice can exert on the vortices, as this allows us to estimate the angular momentum that can be exchanged during a glitch. In this paper, we perform, for the first time, a detailed and quantitative calculation of the pinning force per unit length acting on a vortex immersed in the crust and resulting from the mesoscopic vortex-lattice interaction. We consider realistic vortex tensions, allow for displacement of the nuclei and average over all possible orientations of the crystal with respect to the vortex. We find that, as expected, the mesoscopic pinning force becomes weaker for longer vortices and is generally much smaller than previous estimates, based on vortices aligned with the crystal. Nevertheless, the forces we obtain still have maximum values of the order of fpin ≈ 1015 dyn cm-1, which would still allow for enough angular momentum to be stored in the crust to explain large Vela glitches, if part of the star is decoupled during the event.

  9. Many faces of young neutron stars

    NASA Astrophysics Data System (ADS)

    Vasisht, Gautam

    The hardware aspect of this thesis consists in the design, fabrication and assembly of twin analog Flexible Filter Banks at Caltech. These are user-friendly, workhorse, radio-pulsar search and timing instruments. Novel features include the flexibility in configuring channel center-frequencies and widths, the rapid sampling down to 25 ?s and a total instrument bandwidth ranging from a narrow 0.2 MHz to a mammoth 100 MHz. Frequency synthesis is used to downconvert, detect and sample the telescope receiver bandpass as 32 separate time-series in each polarization. The collected data are later subjected to standard pulsar search and timing algorithms in software.The vital scientific issue addressed here is the nature of young neutron stars. In the standard picture, young neutron stars are rapidly spinning radio-luminous pulsars, which may also display pulsed emission at high X-ray and ?-ray energies. However there is no evidence that all neutron stars are born according to this standard picture. We present radio or X-ray investigations of steady nebular emission produced by three clearly non-standard and ill-understood objects. In all likelihood, these are young neutron stars, a notion upheld by their association with young Galactic supernova remnants.Based on its display of high energy transients, the soft ?-ray repeater SGR 1806-20 is posited to be a seismically active "magnetar", i.e., a neutron star with a super-strong magnetic field (10[superscript 15] G) nearly three orders of magnitude greater than pulsar dipolar fields. Our VLA observations of fleeting small-scale structure around SGR 1806-20 provide intriguing, although preliminary, support for the magnetar model. In time, similar observations could unravel the riddle of soft ?-ray repeaters and possibly establish the reality of magnetars.X-ray observations of the remnant of the historical supernova of 386 A.D., SNR G 11.2-0.3 are presented. The nature of an embedded underlumnious plerion discovered in these observations argues for a central neutron star very different from the prototypical Crab pulsar. The urgency to undertake a large scale study of young and hollow Galactic shells in broadband X-rays with fine spatial resolution is elucidated.X-ray spectroscopy of the object 1E 1207.4-5209 at the core of the large remnant PKS 1209-51/52 has revealed a non-thermal source with a very steep spectrum. After considering various scenarios for lE 1207.4-5209, we conclude that its spectral signature, its lack of optical emission and its position at the center of a supernova remnant make it a source similar to the mysterious anomalous X-ray pulsars.A large and sensitive search for radio pulsar companions of massive stars was undertaken. Primary motivation stems from the recent discovery of binary radio pulsar B 1259-63 as the first member of such a population and a "missing link" in the current models of evolution. Prevalent expectations, based on binary evolution scenarios, suggested that many more such systems should exist and would be uncovered in sensitive targeted searches. Together with other smaller searches, this survey uncovered no pulsars orbiting early-type stars. We conclude that such binary systems must be rare.

  10. Accretion Acceleration of Neutron Stars and Effects of Gravitational Radiation

    NASA Astrophysics Data System (ADS)

    Fu, Yan-yan; Zhang, Yue-zhu; Wei, Yi-huan; Zhang, Cheng-min; Yu, Shao-hua; Pan, Yuan-yue; Guo, Yuan-qi; Wang, De-hua

    2016-01-01

    In this paper we studied the neutron star's spin acceleration in the accretion process of the neutron star binary system, and the relation how the spin period changes with the accreted mass. We analyzed further the evolutions of both magnetic field and spin period of a neutron star, and compared the modeled results with the observational data of pulsars, to show that they are consistent with each other. Based on above studies, we investigated the effect of gravitational radiation on the spin-up process of a neutron star, and derived the change rate of the neutron star's spin period in the accretion process. We also estimated the critical angular velocity ?cr, at which the accretion torque is balanced by that of gravitational radiation, and discussed the influence of gravitational radiation on the neutron star's spin evolution.

  11. Relativistic density functional theory for finite nuclei and neutron stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, Jorge

    In 1939 Oppenheimer and Volkoff demonstrated using Einstein's theory of general relativity that a neutron star supported exclusively by neutron degeneracy pressure will collapse into a black hole if its mass exceeds seven tenths of a solar mass. Seventy five years after such a pioneering prediction the existence of neutron stars with masses as large as two solar masses has been firmly established. This fact alone highlights the critical role that nuclear interactions play in explaining the structure of neutron stars. Indeed, a neutron star is a gold mine for the study of nuclear phenomena that span an enormous range of densities and neutron-proton asymmetries. Physical phenomena over such diverse scales are best described by a formalism based on Relativistic Density Functional Theory. In this contribution I focus on the synergy between theory, experiment, and observation that is needed to elucidate the myriad of exotic states of matter that are believed to exist in a neutron star.

  12. Neutron stars in f(R) gravity with perturbative constraints

    SciTech Connect

    Cooney, Alan; DeDeo, Simon; Psaltis, Dimitrios

    2010-09-15

    We study the structure of neutron stars in f(R) gravity theories with perturbative constraints. We derive the modified Tolman-Oppenheimer-Volkov equations and solve them for a polytropic equation of state. We investigate the resulting modifications to the masses and radii of neutron stars and show that observations of surface phenomena alone cannot break the degeneracy between altering the theory of gravity versus choosing a different equation of state of neutron-star matter. On the other hand, observations of neutron-star cooling, which depends on the density of matter at the stellar interior, can place significant constraints on the parameters of the theory.

  13. Burst Oscillations: A New Spin on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2007-01-01

    Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have shown that the X-ray flux during thermonuclear X-ray bursts fr-om accreting neutron stars is often strongly pulsed at frequencies as high as 620 Hz. We now know that these oscillations are produced by spin modulation of the thermonuclear flux from the neutron star surface. In addition to revealing the spin frequency, they provide new ways to probe the properties and physics of accreting neutron stars. I will briefly review our current observational and theoretical understanding of these oscillations and discuss what they are telling us about neutron stars.

  14. A SECOND NEUTRON STAR IN M4?

    SciTech Connect

    Kaluzny, J.; Rozanska, A.; Rozyczka, M.; Krzeminski, W.; Thompson, Ian B.

    2012-05-01

    We show that the optical counterpart of the X-ray source CX 1 in M4 is a {approx}20th magnitude star, located in the color-magnitude diagram on (or very close to) the main sequence of the cluster, and exhibiting sinusoidal variations of the flux. We find the X-ray flux to be also periodically variable, with X-ray and optical minima coinciding. Stability of the optical light curve, lack of UV-excess, and unrealistic mean density resulting from period-density relation for semidetached systems speak against the original identification of CX 1 as a cataclysmic variable. We argue that the X-ray active component of this system is a neutron star (probably a millisecond pulsar).

  15. Tidal polarizability effects in neutron star mergers

    NASA Astrophysics Data System (ADS)

    Bernuzzi, S.; Nagar, A.; Balmelli, S.; Dietrich, T.; Ujevic, M.

    2015-05-01

    Using the analytical effective-one-body model and nonlinear 3+1 numerical relativity simulations, we investigate binary neutron star mergers. It is found that, for nonspinning binaries, both the mass-rescaled gravitational wave frequency at merger and the specific binding energy at merger almost uniquely depend on the tidal coupling constants κT2, which are functions of the stars’ Love numbers, compactnesses and mass ratio. These relations are quasiuniversal in the sense that there is an additional dependence on the spins, which is linear for realistic spins values χ ≲ 0.1. In the effective-one-body model, the quasiuniversality is a direct consequence of the conservative dynamics of tidally interacting bodies. In the context of gravitational wave astronomy, our findings may be used to constrain the neutron stars’ equation of state using waveforms that accurately model the merger.

  16. Spectral Models of Neutron Star Magnetospheres

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.

    1997-01-01

    We revisit the association of unidentified Galactic plane EGRET sources with tracers of recent massive star formation and death. Up-to-date catalogs of OB associations, SNR's, young pulsars, H2 regions and young open clusters were used in finding counterparts for a recent list of EGRET sources. It has been argued for some time that EGRET source positions are correlated with SNR's and OB associations as a class; we extend such analyses by finding additional counterparts and assessing the probability of individual source identifications. Among the several scenarios relating EGRET sources to massive stars, we focus on young neutron stars as the origin of the gamma-ray emission. The characteristics of the candidate identifications are compared to the known gamma-ray pulsar sample and to detailed Galactic population syntheses using our outer gap pulsar model of gamma-ray emission. Both the spatial distribution and luminosity function of the candidates are in good agreement with the model predictions; we infer that young pulsars can account for the bulk of the excess low latitude EGRET sources. We show that with this identification, the gamma-ray point sources provide an important new window into the history of recent massive star death in the solar neighborhood.

  17. Light curves from binary neutron star coalescence

    NASA Astrophysics Data System (ADS)

    Ortiz, Nestor; Green, Stephen; Lehner, Luis; Ponce, Marcelo; HAD Collaboration

    2015-04-01

    Evolution of binary neutron stars, and the extraction of associated gravitational waveforms, have acquired certain maturity using numerical simulations. In this work we look to augment the observational predictions by extracting electromagnetic counterparts. That is, given results from a merger simulation, we produce a photon emission sky map. Our ray-tracing algorithm employ the two-pole caustic model of gamma-ray emission from the binary system's magnetosphere. The combined measurement of both gravitational and electromagnetic wave signals provides additional information to characterize the merger.

  18. Neutron star cooling and pion condensation

    NASA Technical Reports Server (NTRS)

    Umeda, Hideyuki; Nomoto, Ken'ichi; Tsuruta, Sachiko; Muto, Takumi; Tatsumi, Toshitaka

    1994-01-01

    The nonstandard cooling of a neutron star with the central pion core is explored. By adopting the latest results from the pion condensation theory, neutrino emissivity is calulated for both pure charged pions and a mixture of charged and neutral pions, and the equations of state are constructed for the pion condensate. The effect of superfluidity on cooling is investigated, adopting methods more realistic than in previous studies. Our theoretical models are compared with the currently updated observational data, and possible implications are explored.

  19. Neutron star coupling to its environment

    NASA Technical Reports Server (NTRS)

    Salvati, Marco; Pacini, Franco

    1987-01-01

    A discussion is undertaken of the outward flow generated by rotation-powered neutron stars, giving attention to the identification of particle, wave, and time-steady EMF components of the flow, the estimation of their densities, and the assessment of their contributions to the global energetics. It is concluded that a firm qualitative understanding of pulsar behavior has been achieved in the matters of magnetospheric structure, pair-production, the fate of large-amplitude waves, and the asymptotic behavior of the wind.

  20. Quark matter droplets in neutron stars

    NASA Technical Reports Server (NTRS)

    Heiselberg, H.; Pethick, C. J.; Staubo, E. F.

    1993-01-01

    We show that, for physically reasonable bulk and surface properties, the lowest energy state of dense matter consists of quark matter coexisting with nuclear matter in the presence of an essentially uniform background of electrons. We estimate the size and nature of spatial structure in this phase, and show that at the lowest densities the quark matter forms droplets embedded in nuclear matter, whereas at higher densities it can exhibit a variety of different topologies. A finite fraction of the interior of neutron stars could consist of matter in this new phase, which would provide new mechanisms for glitches and cooling.

  1. HYDROMAGNETIC INSTABILITIES IN RELATIVISTIC NEUTRON STARS

    SciTech Connect

    Lasky, Paul D.; Zink, Burkhard; Kokkotas, Kostas D.; Glampedakis, Kostas

    2011-07-01

    We model the nonlinear ideal magnetohydrodynamics of poloidal magnetic fields in neutron stars in general relativity assuming a polytropic equation of state. We identify familiar hydromagnetic modes, in particular the 'sausage/varicose' mode and 'kink' instability inherent to poloidal magnetic fields. The evolution is dominated by the kink instability, which causes a cataclysmic reconfiguration of the magnetic field. The system subsequently evolves to new, non-axisymmetric, quasi-equilibrium end states. The existence of this branch of stable quasi-equilibria may have consequences for magnetar physics, including flare generation mechanisms and interpretations of quasi-periodic oscillations.

  2. Accretion of matter onto highly magnetized neutron stars: Final report, July 1-September 30, 1985

    SciTech Connect

    Hernquist, L.

    1986-06-01

    A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns. (DWL)

  3. Probing dense matter in neutron stars with axial w modes

    SciTech Connect

    Chatterjee, Debarati; Bandyopadhyay, Debades

    2009-07-15

    We study the problem of extracting information about composition and equation of state of dense matter in neutron star interior using axial w modes. We determine complex frequencies of axial w modes for a set of equations of state involving hyperons as well as Bose-Einstein condensates of antikaons adopting the continued fraction method. Hyperons and antikaon condensates result in softer equations of state leading to higher frequencies and lower damping times of first axial w modes than those of the nuclear matter case. The presence of condensates may lead to the appearance of a new stable branch of superdense stars beyond the neutron star branch called the third family. The existence of the same mass compact stars in both branches is known as neutron star twins. Further investigation of twins reveals that first axial w-mode frequencies of superdense stars in the third family are higher than those of the corresponding twins in the neutron star branch.

  4. Theory of Radiation Transfer in Neutron Star Atmospheres

    NASA Technical Reports Server (NTRS)

    Zavlin, Vyacheslav

    2006-01-01

    The possibility for direct investigation of thermal emission from isolated neutron stars opened about a quarter of century ago with the launch of the first X-ray observatories Einstein and EXOSAT stimulated developing models of the neutron star surface radiation which began at the end of 80's. Confronting observational data with theoretical models of thermal emission allows one to infer the surface temperatures, magnetic fields, chemical composition, and neutron star masses and radii. This information, supplemented with the model equations of state and neutron star cooling models, provides an opportunity to understand the fundamental properties of the superdense matter in the stars' interiors. Almost all available models are based on the assumption that thermal radiation emitted by a neutron star is formed in the superficial star's layers--atmosphere. The neutron star atmospheres are very different from those of usual stars due to the immense gravity and huge magnetic fields. In this presentation we review the current status of the neutron star atmosphere modeling, present most important results, discuss problems and possible future developments.

  5. Anisotropic pressure and hyperons in neutron stars

    NASA Astrophysics Data System (ADS)

    Sulaksono, A.

    2015-01-01

    We study the effects of anisotropic pressure (AI-P) on properties of the neutron stars (NSs) with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of AI-P on NS matter is to increase the stiffness of the equation of state EOS, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of AI-P model h ≤ 0.8 [L. Herrera and W. Barreto, Phys. Rev. D 88 (2013) 084022.] and Λ ≤ -1.15 [D. D. Doneva and S. S. Yazadjiev, Phys. Rev. D 85 (2012) 124023.]. The radius of the corresponding NS at M = 1.4 M⊙ is more than 13 km, while the effect of AI-P on the minimum mass of NS is insignificant. Furthermore, due to the AI-P in the NS, the maximum mass limit of higher than 2.1 M⊙ cannot rule out the presence of hyperons in the NS core.

  6. Constraining decaying dark matter with neutron stars

    NASA Astrophysics Data System (ADS)

    Pérez-García, M. Ángeles; Silk, Joseph

    2015-05-01

    The amount of decaying dark matter, accumulated in the central regions in neutron stars together with the energy deposition rate from decays, may set a limit on the neutron star survival rate against transitions to more compact objects provided nuclear matter is not the ultimate stable state of matter and that dark matter indeed is unstable. More generally, this limit sets constraints on the dark matter particle decay time, τχ. We find that in the range of uncertainties intrinsic to such a scenario, masses (mχ /TeV) ≳ 9 ×10-4 or (mχ /TeV) ≳ 5 ×10-2 and lifetimes τχ ≲1055 s and τχ ≲1053 s can be excluded in the bosonic or fermionic decay cases, respectively, in an optimistic estimate, while more conservatively, it decreases τχ by a factor ≳1020. We discuss the validity under which these results may improve with other current constraints.

  7. Physics of systems containing neutron stars

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin

    1996-01-01

    This grant dealt with several topics related to the dynamics of systems containing a compact object. Most of the research dealt with systems containing Neutron Stars (NS's), but a Black Hole (BH) or a White Dwarf (WD) in situations relevant to NS systems were also addressed. Among the systems were isolated regular pulsars, Millisecond Pulsars (MSP's) that are either Single (SMP's) or in a binary (BMP's), Low Mass X-Ray Binaries (LMXB's) and Cataclysmic Variables (CV's). Also dealt with was one aspect of NS structure, namely NS superfluidity. A large fraction of the research dealt with irradiation-driven winds from companions which turned out to be of importance in the evolution of LMXB's and MSP's, be they SMP's or BMP's. While their role during LMXB evolution (i.e. during the accretion phase) is not yet clear, they may play an important role in turning BMP's into SMP's and also in bringing about the formation of planets around MSP's. Work was concentrated on the following four problems: The Windy Pulsar B197+20 and its Evolution; Wind 'Echoes' in Tight Binaries; Post Nova X-ray Emission in CV's; and Dynamics of Pinned Superfluids in Neutron Stars.

  8. Transition density and pressure in hot neutron stars

    SciTech Connect

    Xu Jun; Chen Liewen; Ko, Che Ming; Li Baoan

    2010-05-15

    Using the momentum-dependent effective interaction (MDI) for nucleons, we have studied the transition density and pressure at the boundary between the inner crust and the liquid core of hot neutron stars. We find that their values are larger in neutrino-trapped neutron stars than in neutrino-free neutron stars. Furthermore, both are found to decrease with increasing temperature of a neutron star as well as increasing slope parameter of the nuclear symmetry energy, except that the transition pressure in neutrino-trapped neutron stars for the case of small symmetry energy slope parameter first increases and then decreases with increasing temperature. We have also studied the effect of the nuclear symmetry energy on the critical temperature above which the inner crust in a hot neutron star disappears and found that with increasing value of the symmetry energy slope parameter, the critical temperature decreases slightly in neutrino-trapped neutron stars but first decreases and then increases in neutrino-free neutron stars.

  9. Neutron Star Structure in the Presence of Scalar Fields

    NASA Technical Reports Server (NTRS)

    Kazanas, Demosthenes

    2004-01-01

    Motivated by the possible presence of scalar fields on astrophysical scales, suggested by the apparent acceleration of the universe implied by the supernovae surveys, we present models of neutron star structure including the contribution of a (massless) scalar field to the stress energy momentum tensor, in addition to that made by the normal matter. To that end we solve the coupled Einstein -- scalar field -- hydrostatic balance equations to compute the effect of the presence of the scalar field on the neutron star structure. We find that the presence of the scalar field does change the structure of the neutron star, especially in cases of strong coupling between the scalar field and the matter density. We present the neutron star radius as a function of the matter--scalar field coupling constant for different values of the neutron star central density. The presence of the scalar field affects both the maximum neutron star mass and Its radius, the latter increasing with the value of the above coupling constant. We also compute particle and photon geodesics in the geometry of these neutron stars as well as to the geometry of black holes with different values of the scalar field. Our results may be testable with timing observations of accreting neutron stars.

  10. Geminga: A cooling superfluid neutron star

    NASA Technical Reports Server (NTRS)

    Page, Dany

    1994-01-01

    We compare the recent temperature estimate for Geminga with neutron star cooling models. Because of its age (approximately 3.4 x 10(exp 5) yr), Geminga is in the photon cooling era. We show that its surface temperature (approximately 5.2 x 10(exp 5) K) can be understood by both types of neutrino cooling scenarios, i.e., slow neutrino cooling by the modified Urca process or fast neutrino cooling by the direct Urca process or by some exotic matter, and thus does not allow us to discriminate between these two competing schemes. However, for both types of scenarios, agreement with the observed temperature can only be obtained if baryon pairing is present in most, if not all, of the core of the star. Within the slow neutrino cooling scenario, early neutrino cooling is not sufficient to explain the observed low temperature, and extensive pairing in the core is necessary to reduce the specific heat and increase the cooling rate in the present photon cooling era. Within all the fast neutrino cooling scenarios, pairing is necessary throughout the whole core to control the enormous early neutrino emission which, without pairing suppression, would result in a surface temperature at the present time much lower than observed. We also comment on the recent temperature estimates for PSR 0656+14 and PSR 1055-52, which pertain to the same photon cooling era. If one assumes that all neutron stars undergo fast neutrino cooling, then these two objects also provide evidence for extensive baryon pairing in their core; but observational uncertainties also permit a more conservative interpretation, with slow neutrino emission and no pairing at all. We argue though that observational evidence for the slow neutrino cooling model (the 'standard' model) is in fact very dim and that the interpretation of the surface temperature of all neutron stars could be done with a reasonable theoretical a priori within the fast neutrino cooling scenarios only. In this case, Geminga, PSR 0656+14, and PSR 1055-52 all show evidence of baryon pairing down to their very centers.

  11. Do hyperons exist in the interior of neutron stars?

    NASA Astrophysics Data System (ADS)

    Chatterjee, Debarati; Vidaña, Isaac

    2016-02-01

    In this work we review the role of hyperons on the properties of neutron and proto-neutron stars. In particular, we revise the so-called "hyperon puzzle", go over some of the solutions proposed to tackle it, and discuss the implications that the recent measurements of unusually high neutron star masses have on our present knowledge of hypernuclear physics. We re-examine also the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

  12. NARROW ATOMIC FEATURES FROM RAPIDLY SPINNING NEUTRON STARS

    SciTech Connect

    Bauboeck, Michi; Psaltis, Dimitrios; Oezel, Feryal E-mail: dpsaltis@email.arizona.edu

    2013-04-01

    Neutron stars spinning at moderate rates ({approx}300-600 Hz) become oblate in shape and acquire a nonzero quadrupole moment. In this paper, we calculate the profiles of atomic features from such neutron stars using a ray-tracing algorithm in the Hartle-Thorne approximation. We show that line profiles acquire cores that are much narrower than the widths expected from pure Doppler effects for a large range of observer inclinations. As a result, the effects of both the oblateness and the quadrupole moments of neutron stars need to be taken into account when aiming to measure neutron-star radii from rotationally broadened lines. Moreover, the presence of these narrow cores substantially increases the likelihood of detecting atomic lines from rapidly spinning neutron stars.

  13. Gravitational wave afterglow in binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Doneva, Daniela D.; Kokkotas, Kostas D.; Pnigouras, Pantelis

    2015-11-01

    We study in detail the f -mode secular instability for rapidly rotating neutron stars, putting emphasis on supramassive models which do not have a stable nonrotating counterpart. Such neutron stars are thought to be the generic outcome of the merger of two standard-mass neutron stars. In addition, we take into account the effects of a strong magnetic field and r -mode instability, that can drain a substantial amount of angular momentum. We find that the gravitational wave signal emitted by supramassive neutron stars can reach above the Advanced LIGO sensitivity at distance of about 20 Mpc, and the detectability is substantially enhanced for the Einstein Telescope. The event rate will be of the same order as the merging rates, while the analysis of the signal will carry information for the equation of state of the postmerging neutron stars and the strength of the magnetic fields.

  14. The EOS of neutron matter, and the effect of Lambda hyperons to neutron star structure

    SciTech Connect

    Gandolfi, Stefano

    2015-01-13

    The following topics are addressed: the model and the method; equation of state of neutron matter, role of three-neutron force; symmetry energy; Λ-hypernuclei; Λ-neutron matter; and neutron star structure. In summary, quantum Monte Carlo methods are useful to study nuclear systems in a coherent framework; the three-neutron force is the bridge between Esym and neutron star structure; and neutron star observations are becoming competitive with experiments. Λ-nucleon data are very limited, but ΛNN is very important. The role of Λ in neutron stars is far from understood; more ΛN data are needed. The author's conclusion: We cannot conclude anything with present models.

  15. Energy Density Functional for Nuclei and Neutron Stars

    SciTech Connect

    Erler, J.

    2013-01-01

    Background: Recent observational data on neutron star masses and radii provide stringent constraints on the equation of state of neutron rich matter [ Annu. Rev. Nucl. Part. Sci. 62 485 (2012)]. Purpose: We aim to develop a nuclear energy density functional that can be simultaneously applied to finite nuclei and neutron stars. Methods: We use the self-consistent nuclear density functional theory (DFT) with Skyrme energy density functionals and covariance analysis to assess correlations between observables for finite nuclei and neutron stars. In a first step two energy functionals a high density energy functional giving reasonable neutron properties, and a low density functional fitted to nuclear properties are matched. In a second step, we optimize a new functional using exactly the same protocol as in earlier studies pertaining to nuclei but now including neutron star data. This allows direct comparisons of performance of the new functional relative to the standard one. Results: The new functional TOV-min yields results for nuclear bulk properties (energy, rms radius, diffraction radius, and surface thickness) that are of the same quality as those obtained with the established Skyrme functionals, including SV-min. When comparing SV-min and TOV-min, isoscalar nuclear matter indicators vary slightly while isovector properties are changed considerably. We discuss neutron skins, dipole polarizability, separation energies of the heaviest elements, and proton and neutron drip lines. We confirm a correlation between the neutron skin of 208Pb and the neutron star radius. Conclusions: We demonstrate that standard energy density functionals optimized to nuclear data do not carry information on the expected maximum neutron star mass, and that predictions can only be made within an extremely broad uncertainty band. For atomic nuclei, the new functional TOV-min performs at least as well as the standard nuclear functionals, but it also reproduces expected neutron star data within assumed error bands. This functional is expected to yield more reliable predictions in the region of very neutron rich heavy nuclei.

  16. Relativistic tidal properties of neutron stars

    SciTech Connect

    Damour, Thibault; Nagar, Alessandro

    2009-10-15

    We study the various linear responses of neutron stars to external relativistic tidal fields. We focus on three different tidal responses, associated to three different tidal coefficients: (i) a gravito-electric-type coefficient G{mu}{sub l}=[length]{sup 2l+1} measuring the lth-order mass multipolar moment GM{sub a{sub 1}}{sub ...a{sub I}} induced in a star by an external lth-order gravito-electric tidal field G{sub a{sub 1}}{sub ...a{sub I}}; (ii) a gravito-magnetic-type coefficient G{sigma}{sub l}=[length]{sup 2l+1} measuring the lth spin multipole moment GS{sub a{sub 1}}{sub ...a{sub I}} induced in a star by an external lth-order gravito-magnetic tidal field H{sub a{sub 1}}{sub ...a{sub I}}; and (iii) a dimensionless 'shape' Love number h{sub l} measuring the distortion of the shape of the surface of a star by an external lth-order gravito-electric tidal field. All the dimensionless tidal coefficients G{mu}{sub l}/R{sup 2l+1}, G{sigma}{sub l}/R{sup 2l+1}, and h{sub l} (where R is the radius of the star) are found to have a strong sensitivity to the value of the star's 'compactness'c{identical_to}GM/(c{sub 0}{sup 2}R) (where we indicate by c{sub 0} the speed of light). In particular, G{mu}{sub l}/R{sup 2l+1}{approx}k{sub l} is found to strongly decrease, as c increases, down to a zero value as c is formally extended to the 'black hole (BH) limit'c{sup BH}=1/2. The shape Love number h{sub l} is also found to significantly decrease as c increases, though it does not vanish in the formal limit c{yields}c{sup BH}, but is rather found to agree with the recently determined shape Love numbers of black holes. The formal vanishing of {mu}{sub l} and {sigma}{sub l} as c{yields}c{sup BH} is a consequence of the no-hair properties of black holes. This vanishing suggests, but in no way proves, that the effective action describing the gravitational interactions of black holes may not need to be augmented by nonminimal worldline couplings.

  17. Journey to the Center of a Neutron Star

    NASA Technical Reports Server (NTRS)

    Wanjek, Christopher

    2003-01-01

    A neutron star is not a place most would want to visit. This dense remnant of a collapsed star has a magnetic field billions of times stronger than Earth's, enough to shuffle your body's molecules long before you even land. The featureless surface is no fun either. Crushing gravity ensures that the star is a near perfect sphere, compressing all matter so that a sand-grain-sized scoop of neutron star material would weigh as much as a battleship on Earth. At least black holes offer the promise of funky singularity, time warps, and the Odyssean temptation to venture beyond a point of no return. What s a journey to a neutron star good for, one might ask? Well, for starters, it offers the possibility of confirming a theorized state of matter called quark-gluon plasma, which likely existed for a moment after the Big Bang and now might only exist in the superdense interiors of neutron stars. Beneath the neutron star crust, a kilometer-thick plate of crystalline matter, lies the great unknown. The popular theory is that the neutron star interior is made up of a neutron superfluid - a fluid without friction. With the help of two NASA satellites - the Rossi X-Ray Timing Explorer and the Chandra X-Ray Observatory - scientists are journeying to the center of a neutron star. Matter might be so compressed there that it breaks down into quarks, the building blocks of protons and neutrons, and gluons, the carrier of the strong nuclear force. To dig inside a neutron star, no simple drill bit will do. Scientists gain insight into the interior through events called glitches, a sudden change in the neutron star s precise spin rate. 'Glitches are one of the few ways we have to study the neutron star interior,' says Frank Marshall of NASA s Goddard Space Flight Center, who has used the Rossi Explorer to follow the escapades of the glitchiest of all neutron stars, dubbed the Big Glitcher and known scientifically as PSR J0537-6910.

  18. I-Love-Q: unexpected universal relations for neutron stars and quark stars.

    PubMed

    Yagi, Kent; Yunes, Nicolás

    2013-07-26

    Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star's internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure-independent fashion. PMID:23888033

  19. Neutron Star Discovered Where a Black Hole Was Expected

    NASA Astrophysics Data System (ADS)

    2005-11-01

    A very massive star collapsed to form a neutron star and not a black hole as expected, according to new results from NASA's Chandra X-ray Observatory. This discovery shows that nature has a harder time making black holes than previously thought. Scientists found this neutron star -- a dense whirling ball of neutrons about 12 miles in diameter -- in an extremely young star cluster. Astronomers were able to use well-determined properties of other stars in the cluster to deduce that the progenitor of this neutron star was at least 40 times the mass of the Sun. ESO Optical Image of Westerlund 1 ESO Optical Image of Westerlund 1 "Our discovery shows that some of the most massive stars do not collapse to form black holes as predicted, but instead form neutron stars," said Michael Muno, a UCLA postdoctoral Hubble Fellow and lead author of a paper to be published in The Astrophysical Journal Letters. When very massive stars make neutron stars and not black holes, they will have a greater influence on the composition of future generations of stars. When the star collapses to form the neutron star, more than 95% of its mass, much of which is metal-rich material from its core, is returned to the space around it. "This means that enormous amounts of heavy elements are put back into circulation and can form other stars and planets," said J. Simon Clark of the Open University in the United Kingdom. Animation: Dissolve from Optical to X-ray Image of Westerlund 1 Animation: Dissolve from Optical to X-ray Image of Westerlund 1 Astronomers do not completely understand how massive a star must be to form a black hole rather than a neutron star. The most reliable method for estimating the mass of the progenitor star is to show that the neutron star or black hole is a member of a cluster of stars, all of which are close to the same age. Because more massive stars evolve faster than less massive ones, the mass of a star can be estimated from if its evolutionary stage is known. Neutron stars and black holes are the end stages in the evolution of a star, so their progenitors must have been among the most massive stars in the cluster. Muno and colleagues discovered a pulsing neutron star in a cluster of stars known as Westerlund 1. This cluster contains a hundred thousand or more stars in a region only 30 light years across, which suggests that all the stars were born in a single episode of star formation. Based on optical properties such as brightness and color some of the normal stars in the cluster are known to have masses of about 40 suns. Since the progenitor of the neutron star has already exploded as a supernova, its mass must have been more than 40 solar masses. 2MASS Infrared Image of Westerlund 1 2MASS Infrared Image of Westerlund 1 Introductory astronomy courses sometimes teach that stars with more than 25 solar masses become black holes -- a concept that until recently had no observational evidence to test it. However, some theories allow such massive stars to avoid becoming black holes. For example, theoretical calculations by Alexander Heger of the University of Chicago and colleagues indicate that extremely massive stars blow off mass so effectively during their lives that they leave neutron stars when they go supernovae. Assuming that the neutron star in Westerlund 1 is one of these, it raises the question of where the black holes observed in the Milky Way and other galaxies come from. Other factors, such as the chemical composition of the star, how rapidly it is rotating, or the strength of its magnetic field might dictate whether a massive star leaves behind a neutron star or a black hole. The theory for stars of normal chemical composition leaves a small window of initial masses - between about 25 and somewhat less than 40 solar masses - for the formation of black holes from the evolution of single massive stars. The identification of additional neutron stars or the discovery of black holes in young star clusters should further constrain the masses and properties of neutron star and black hole progenitors. T

  20. QuakeSim Project Networking

    NASA Astrophysics Data System (ADS)

    Kong, D.; Donnellan, A.; Pierce, M. E.

    2012-12-01

    QuakeSim is an online computational framework focused on using remotely sensed geodetic imaging data to model and understand earthquakes. With the rise in online social networking over the last decade, many tools and concepts have been developed that are useful to research groups. In particular, QuakeSim is interested in the ability for researchers to post, share, and annotate files generated by modeling tools in order to facilitate collaboration. To accomplish this, features were added to the preexisting QuakeSim site that include single sign-on, automated saving of output from modeling tools, and a personal user space to manage sharing permissions on these saved files. These features implement OpenID and Lightweight Data Access Protocol (LDAP) technologies to manage files across several different servers, including a web server running Drupal and other servers hosting the computational tools themselves.

  1. Proton acceleration in neutron star magnetospheres

    NASA Technical Reports Server (NTRS)

    Smith, I. A.; Katz, J. I.; Diamond, P. H.

    1992-01-01

    To explain the emission of TeV and PeV gamma rays from accreting X-ray binary sources, protons must be accelerated to several times the gamma-ray energy. It is shown here that at certain times, the plasma in the accretion column of the neutron star may form a deep enough pool that the top portion becomes unstable to convective motions in spite of the strong magnetic field. The resulting turbulence produces fluctuations in the strength of the magnetic field that travel up the accretion column, taking energy out to the region of the energetic protons. The protons resonantly absorb this energy and are accelerated to high energies. Including the synchrotron radiation losses of the protons, it is shown that they can be accelerated to energies that are high enough to explain the gamma-ray observations.

  2. Deterministic chaos in accreting neutron star systems

    NASA Astrophysics Data System (ADS)

    Morfill, G. E.; Atmanspacher, H.; Demmel, V.; Scheingraber, H.; Voges, W.

    This review contains a brief introduction to the terminology of deterministic chaos, and a summary of important properties and definitions of strange attractors. A method is described how to reconstruct the attractor from experimental data. Using synthetic data, the specific problems associated with the reconstruction are examined. As an observational example, analysis of data from the accreting neutron star system Her X-1 is described. Finally, the authors discuss the physical interpretation of these observations, the possible implications for the description of the system from a general point of view, the specific implication for the pulse shape and pulse to pulse variations, and possible approaches towards a better understanding of both accretion disc and accretion column.

  3. Shear viscosity in magnetized neutron star crust

    NASA Astrophysics Data System (ADS)

    Ofengeim, D. D.; Yakovlev, D. G.

    2015-12-01

    The electron shear viscosity due to Coulomb scattering of degenerate electrons by atomic nuclei throughout a magnetized neutron star crust is calculated. The theory is based on the shear viscosity coefficient calculated neglecting magnetic fields but taking into account gaseous, liquid and solid states of atomic nuclei, multiphonon scattering processes, and finite sizes of the nuclei albeit neglecting the effects of electron band structure. The effects of strong magnetic fields are included in the relaxation time approximation with the effective electron relaxation time taken from the field-free theory. The viscosity in a magnetized matter is described by five shear viscosity coefficients. They are calculated and their dependence on the magnetic field and other parameters of dense matter is analyzed. Possible applications and open problems are outlined.

  4. Cosmic rays from binary neutron stars

    NASA Astrophysics Data System (ADS)

    Kundt, W.

    1983-02-01

    The acceleration mechanism of cosmic rays is discussed. Parker's (1965, 1979) suggestion that buoyant reordering of magnetic flux tubes is the dominant transport mechanism of cosmic rays out of the galactic disk is reinforced. Arguments that the cosmic ray sources are located inside the molecular cloud layer are presented, and the shock accretion model as the primary mechanism of cosmic ray acceleration is argued against. A model of cosmic ray acceleration is presented in which the ionic component of the rays is injected by young binary neutron stars whose rotating magnetospheres act like grindstones in the wind of their companion. The model appears versatile enough to be consistent with the observed abundance anomalies. While pulsars are probably not the dominant source of cosmic ray nuclei, they may be the dominant source of cosmic ray electrons and positrons above about 30 GeV.

  5. Breaking Strain of Neutron Star Crust and Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Horowitz, C. J.; Kadau, Kai

    2009-05-01

    Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of the neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Because of the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large-scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in magnetar giant flares and microflares.

  6. Neutron star dynamos and the origins of pulsar magnetism

    NASA Technical Reports Server (NTRS)

    Thompson, Christopher; Duncan, Robert C.

    1993-01-01

    Neutron star convection is a transient phenomenon and has an extremely high magnetic Reynolds number. In this sense, a neutron star dynamo is the quintessential fast dynamo. The convective motions are only mildly turbulent on scales larger than the approximately 100 cm neutrino mean free path, but the turbulence is well developed on smaller scales. Several fundamental issues in the theory of fast dynamos are raised in the study of a neutron star dynamo, in particular the possibility of dynamo action in mirror-symmetric turbulence. It is argued that in any high magnetic Reynolds number dynamo, most of the magnetic energy becomes concentrated in thin flux ropes when the field pressure exceeds the turbulent pressure at the smallest scale of turbulence. In addition, the possibilities for dynamo action during the various (pre-collapse) stages of convective motion that occur in the evolution of a massive star are examined, and the properties of white dwarf and neutron star progenitors are contrasted.

  7. Towards real neutron star seismology: accounting for elasticity and superfluidity

    NASA Astrophysics Data System (ADS)

    Passamonti, A.; Andersson, N.

    2012-01-01

    We study the effects of an elastic crust on the oscillation spectrum of superfluid neutron stars. Within the two-fluid formalism, we consider Newtonian stellar models that include the relevant constituents of a mature neutron star. The core is formed by a mixture of superfluid neutrons and a conglomerate of charged particles, while the inner crust is described by a lattice of nuclei permeated by superfluid neutrons. We linearize the Poisson and the conservation equations of non-rotating superfluid stars and study the effects of elasticity, entrainment and composition stratification on the shear and acoustic modes. In both the core and the crust, the entrainment is derived from recent results for the nucleon effective mass. Solving the perturbation equations as an eigenvalue problem, we find that the presence of superfluid neutrons in the crust and their large effective mass may have significant impact on the star's oscillation spectrum.

  8. Superfluid heat conduction and the cooling of magnetized neutron stars.

    PubMed

    Aguilera, Deborah N; Cirigliano, Vincenzo; Pons, Jos A; Reddy, Sanjay; Sharma, Rishi

    2009-03-01

    We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superfluid neutron matter, called superfluid phonons, can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to the magnetic field when the magnetic field B> approximately 10(13) G. At a density of rho approximately 10(12)-10(14) g/cm3, the conductivity due to superfluid phonons is significantly larger than that due to lattice phonons and is comparable to electron conductivity when the temperature approximately 10(8) K. This new mode of heat conduction can limit the surface anisotropy in highly magnetized neutron stars. Cooling curves of magnetized neutron stars with and without superfluid heat conduction could show observationally discernible differences. PMID:19392503

  9. Superfluid heat conduction and the cooling of magnetized neutron stars

    SciTech Connect

    Cirigliano, Vincenzo; Reddy, Sanjay; Sharma, Rishi; Aguilera, Deborah N

    2008-01-01

    We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superftuid neutron matter, called superfiuid phonons (sPhs), can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to magnetic field when the magnetic field B {approx}> 10{sup 13} C. At density p {approx_equal} 10{sup 12}--10{sup 14} g/cm{sup 3} the conductivity due to sPhs is significantly larger than that due to lattice phonons and is comparable to electron conductivity at when temperature {approx_equal} 10{sup 8} K. This new mode of heat conduction can limit the surface anisotropy in highly magnetized neutron stars. Cooling curves of magnetized neutron stars with and without superfluid heat conduction show observationally discernible differences.

  10. Rotational and magnetic field instabilities in neutron stars

    SciTech Connect

    Kokkotas, Kostas D.

    2014-01-14

    In this short review we present recent results on the dynamics of neutron stars and their magnetic fields. We discuss the progress that has been made, during the last 5 years, in understanding the rotational instabilities with emphasis to the one due to the f-mode, the possibility of using gravitational wave detection in constraining the parameters of neutron stars and revealing the equation of state as well as the detectability of gravitational waves produced during the unstable phase of a neutron star’s life. In addition we discuss the dynamics of extremely strong magnetic fields observed in a class of neutron stars (magnetars). Magnetic fields of that strength are responsible for highly energetic phenomena (giant flares) and we demonstrate that the analysis of the emitted electromagnetic radiation can lead in constraining the parameters of neutron stars. Furthermore, we present our results from the study of such violent phenomena in association with the emission of gravitational radiation.

  11. Superfluid Heat Conduction and the Cooling of Magnetized Neutron Stars

    SciTech Connect

    Aguilera, Deborah N.; Cirigliano, Vincenzo; Reddy, Sanjay; Sharma, Rishi; Pons, Jose A.

    2009-03-06

    We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superfluid neutron matter, called superfluid phonons, can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to the magnetic field when the magnetic field B > or approx. 10{sup 13} G. At a density of {rho}{approx_equal}10{sup 12}-10{sup 14} g/cm{sup 3}, the conductivity due to superfluid phonons is significantly larger than that due to lattice phonons and is comparable to electron conductivity when the temperature {approx_equal}10{sup 8} K. This new mode of heat conduction can limit the surface anisotropy in highly magnetized neutron stars. Cooling curves of magnetized neutron stars with and without superfluid heat conduction could show observationally discernible differences.

  12. Measuring the basic parameters of neutron stars using model atmospheres

    NASA Astrophysics Data System (ADS)

    Suleimanov, V. F.; Poutanen, J.; Klochkov, D.; Werner, K.

    2016-02-01

    Model spectra of neutron star atmospheres are nowadays widely used to fit the observed thermal X-ray spectra of neutron stars. This fitting is the key element in the method of the neutron star radius determination. Here, we present the basic assumptions used for the neutron star atmosphere modeling as well as the main qualitative features of the stellar atmospheres leading to the deviations of the emergent model spectrum from blackbody. We describe the properties of two of our model atmosphere grids: i) pure carbon atmospheres for relatively cool neutron stars (1-4MK) and ii) hot atmospheres with Compton scattering taken into account. The results obtained by applying these grids to model the X-ray spectra of the central compact object in supernova remnant HESS 1731-347, and two X-ray bursting neutron stars in low-mass X-ray binaries, 4U 1724-307 and 4U 1608-52, are presented. Possible systematic uncertainties associated with the obtained neutron star radii are discussed.

  13. Astrophysical observations and future projects of neutron stars and magnetars

    NASA Astrophysics Data System (ADS)

    Enoto, Teruaki

    2014-09-01

    Neutron stars are enigmatic compact objects characterized by dense nuclear matter, rapid stellar rotation, and strong magnetic fields. Such an extreme environment has provided an accessible astrophysical laboratory to test fundamental physics. Recent astronomical observations from radio to gamma-rays have revealed a remarkable diversity of neutron stars: e.g., rotation-powered pulsars, accretion-powered pulsars, and magnetically-powered sources. Among important physical parameters of neutron stars, a wide range of magnetic field from 104 T to 1011 T is thought to be one principal cause of the diversity. Especially, enigmatic X-ray sources, Soft Gamma Repeater (SGRs) and Anomalous X-ray Pulsar (AXPs), are now considered to have extremely strong magnetic field reaching 1010-1011 T, and thus, dubbed as ``magnetars.'' They emerge mainly in the X-ray frequency with intense giant flares, short bursts, and X-ray outbursts. Unlike for rotation-powered or accretion-powered pulsars, the bulk of their X-ray emission appears to be powered by their super-strong magnetic fields. At this talk, I will review recent high energy astrophysical observations of strongly-magnetized neutron stars, and also overview approved future missions to approach the neutron star science, for example, Astro-H (launch in 2015) which realizes the high energy resolution and the Neutron star Interior Composition ExploreR Mission (NICER, launch in late 2016) mission which is dedicated to determine the equation of state of neutron stars.

  14. Neutron Star Structure In The Presence of Scalar Fields

    NASA Technical Reports Server (NTRS)

    Crawford, James P.; Kazanas, Demosthenes

    2004-01-01

    Motivated by the possible presence of scalar fields on astrophysical scales, suggested by the recent measurement of the deceleration parameter by supernovae surveys, we present models of neutron star structure under the assumption that a scalar field makes a significant contribution to the stress energy momentum tensor, in addition to that made by the normal matter. To that end we solve the coupled Einstein - scalar field - hydrostatic balance equations to compute the effect of the presence of the scalar field on the neutron star structure. We find that the presence of the scalar field does change the structure of the neutron star, especially in cases of strong coupling between the scalar field and the matter density. We present the neutron star radius as a function of the matter-scalar field coupling constant for different values of the neutron star central density. The presence of the scalar field does affect both the maximum neutron star mass and its radius, the latter increasing with the value of the above coupling constant. Our results may be testable with the recent timing observations of accreting neutron stars.

  15. Spin paramagnetic deformation of a neutron star

    NASA Astrophysics Data System (ADS)

    Suvorov, A. G.; Mastrano, A.; Melatos, A.

    2016-02-01

    Quantum mechanical corrections to the hydromagnetic force balance equation, derived from the microscopic Schrödinger-Pauli theory of quantum plasmas, modify the equilibrium structure and hence the mass quadrupole moment of a neutron star. It is shown here that the dominant effect - spin paramagnetism - is most significant in a magnetar, where one typically has μ _B|B|≳ k_B T_e, where μB is the Bohr magneton, B is the magnetic field, and Te is the electron temperature. The spin paramagnetic deformation of a non-barotropic magnetar with a linked poloidal-toroidal magnetic field is calculated to be up to ˜10 times greater than the deformation caused solely by the Lorentz force. It depends on the degree of Pauli blocking by conduction electrons and the propensity to form magnetic domains, processes which are incompletely modelled at magnetar field strengths. The star becomes more oblate, as the toroidal field component strengthens. The result implies that existing classical predictions underestimate the maximum strength of the gravitational wave signal from rapidly spinning magnetars at birth. Turning the argument around, future gravitational-wave upper limits of increasing sensitivity will place ever-stricter constraints on the physics of Pauli blocking and magnetic domain formation under magnetar conditions.

  16. Lev Landau and the concept of neutron stars

    NASA Astrophysics Data System (ADS)

    Yakovlev, Dmitrii G.; Haensel, Pawel; Baym, Gordon; Pethick, Christopher

    2013-03-01

    We review Lev Landau's role in the history of neutron star physics in the 1930s. According to the recollections of Rosenfeld (Proc. 16th Solvay Conference on Physics, 1974, p. 174), Landau improvised the concept of neutron stars in a discussion with Bohr and Rosenfeld just after the news of the discovery of the neutron reached Copenhagen in February 1932. We present arguments that the discussion must have taken place in March 1931, before the discovery of the neutron, and that they, in fact, discussed the paper written by Landau in Zurich in February 1931 but not published until February 1932 (Phys. Z. Sowjetunion 1, 285). In this paper, Landau mentioned the possible existence of dense stars that look like one giant nucleus; this could be regarded as an early theoretical prediction or anticipation of neutron stars, albeit prior to the discovery of the neutron. The coincidence of the dates of the neutron discovery and the publication of the paper has led to an erroneous association of Landau's paper with the discovery of the neutron. In passing, we outline Landau's contribution to the theory of white dwarfs and to the hypothesis of stars with neutron cores.

  17. MAGNETIC INTERACTIONS IN COALESCING NEUTRON STAR BINARIES

    SciTech Connect

    Piro, Anthony L.

    2012-08-10

    It is expected on both evolutionary and empirical grounds that many merging neutron star (NS) binaries are composed of a highly magnetized NS in orbit with a relatively low magnetic field NS. I study the magnetic interactions of these binaries using the framework of a unipolar inductor model. The electromotive force generated across the non-magnetic NS as it moves through the magnetosphere sets up a circuit connecting the two stars. The exact features of this circuit depend on the uncertain resistance in the space between the stars R{sub space}. Nevertheless, I show that there are interesting observational and/or dynamical effects irrespective of its exact value. When R{sub space} is large, electric dissipation as great as {approx}10{sup 46} erg s{sup -1} (for magnetar-strength fields) occurs in the magnetosphere, which would exhibit itself as a hard X-ray precursor in the seconds leading up to merger. With less certainty, there may also be an associated radio transient. When R{sub space} is small, electric dissipation largely occurs in the surface layers of the magnetic NS. This can reach {approx}10{sup 49} erg s{sup -1} during the final {approx}1 s before merger, similar to the energetics and timescales of short gamma-ray bursts. In addition, for dipole fields greater than Almost-Equal-To 10{sup 12} G and a small R{sub space}, magnetic torques spin up the magnetized NS. This drains angular momentum from the binary and accelerates the inspiral. A faster coalescence results in less orbits occurring before merger, which would impact matched-filtering gravitational-wave searches by ground-based laser interferometers and could create difficulties for studying alternative theories of gravity with compact inspirals.

  18. Magnetic Interactions in Coalescing Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Piro, Anthony L.

    2012-08-01

    It is expected on both evolutionary and empirical grounds that many merging neutron star (NS) binaries are composed of a highly magnetized NS in orbit with a relatively low magnetic field NS. I study the magnetic interactions of these binaries using the framework of a unipolar inductor model. The electromotive force generated across the non-magnetic NS as it moves through the magnetosphere sets up a circuit connecting the two stars. The exact features of this circuit depend on the uncertain resistance in the space between the stars {R}_space. Nevertheless, I show that there are interesting observational and/or dynamical effects irrespective of its exact value. When {R}_space is large, electric dissipation as great as ~1046 erg s-1 (for magnetar-strength fields) occurs in the magnetosphere, which would exhibit itself as a hard X-ray precursor in the seconds leading up to merger. With less certainty, there may also be an associated radio transient. When {R}_space is small, electric dissipation largely occurs in the surface layers of the magnetic NS. This can reach ~1049 erg s-1 during the final ~1 s before merger, similar to the energetics and timescales of short gamma-ray bursts. In addition, for dipole fields greater than ?1012 G and a small {R}_space, magnetic torques spin up the magnetized NS. This drains angular momentum from the binary and accelerates the inspiral. A faster coalescence results in less orbits occurring before merger, which would impact matched-filtering gravitational-wave searches by ground-based laser interferometers and could create difficulties for studying alternative theories of gravity with compact inspirals.

  19. The spin evolution of neutron stars with the superfluid core

    NASA Astrophysics Data System (ADS)

    Barsukov, D. P.; Goglichidze, O. A.; Tsygan, A. I.

    2013-06-01

    We investigate the neutron stars spin evolution (breaking, inclination angle evolution and radiative precession), taking into account the superfluidity of the neutrons in the star core. The neutron star is treated as a two-component system consisting of a `charged' component (including the crust and the core protons, electrons and normal neutrons) and a core superfluid neutron component. The components are supposed to interact through the mutual friction force. We assume that the `charged' component rotates rigidly. The neutron superfluid velocity field is calculated directly from linearized hydrodynamical equations. It is shown that the superfluid core accelerates the evolution of inclination angle and makes all pulsars evolve to either the orthogonal or coaxial state. However, rapid evolution seems to contradict the observation data. Obtained results together with the observations may allow us to examine the superfluid models.

  20. Neutron Stars and Black Holes Seen with the Rossi X-Ray Timing Explorer (RXTE)

    NASA Technical Reports Server (NTRS)

    Swank, Jean

    2008-01-01

    Astrophysical X-rays bring information about location, energy, time, and polarization. X-rays from compact objects were seen in the first explorations to vary in time. Eclipses and pulsations have simple explanations that identified the importance of X-ray binaries and magnetic neutron stars in the first decade of X-ray astronomy. The dynamics of accretion onto stellar and supermassive black holes and onto neutron stars with relatively low magnetic fields shows up as more complex variations, quasi-periodic oscillations, noise with characteristic frequency spectra, broad-band changes in the energy spectra. To study these variations, RXTE instruments needed to have large area and operational flexibility to find transient activity and observe when it was present. Proportional counters and Phoswich scintillators provided it in a modest mission that has made textbook level contributions to understanding of compact objects. The first seen, and the brightest known, X-ray binary, Sco X-1 is one of a class of neutron stars with low mass companions. Before RXTE, none of these had been seen to show pulsations, though they were hypothesized to be the precursors of radio pulsars with millisecond periods and low magnetic fields. RXTE's large area led to identifying coherent millisecond pulsars in a subset which are relatively faint transients. It also led to identifying short episodes of pulsation during thermonuclear bursts, in sources where a steady signal is not seen. The X-ray stage verifies the evolution that produces millisecond radio pulsars.Masses and radii of neutron stars are being determined by various techniques, constraining the equation of state of matter at nuclear densities. Accretion should lead to a range of neutron star masses. An early stage of superstrong magnetic field neutron stars is now known to produce X-ray and gamma-ray bursts in crust quakes and magnetic field reconnection releases of energy. Soft Gamma Repeaters, Anomolous X-ray Pulsars, and high magnetic field rotation-powered pulsars are all now called magnetars, because they have pulse periods indicating they are slowing down as they would with magnetic dipole radiation for a surface field above 5x1013 gauss. The accretion disk has been connected to the launching of radio jets from black holes, and even from neutron stars. Estimates of the angular momenta of black holes are being made from different approaches, modelling a high frequency oscillation that may be related to how close the inner part of the accretion disk is to the black hole, modelling the continua spectra of the X-ray emission, and modeling the emission of red-shifted iron that may be emitted from the accretion disk. These investigations require early discovery of the black hole transient with the All Sky Monitor on RXTE or other monitoring information, frequent extended observations, and coordinated observations with missions that give higher energy resolution, or radio and infrared information.

  1. High Velocity Neutron Stars and Gamma-Ray Bursts Proceedings

    SciTech Connect

    Rothschild, R.E.; Lingenfelter, R.E.

    1996-08-01

    These proceedings represent papers from the workshop on gamma{minus}ray bursters. The workshop was inspired by a major breakthrough in the understanding of gamma{minus}ray bursters. This advance was the linking of soft gamma{minus}ray repeaters with high velocity neutron stars. Topics discussed included supernovae, soft gamma{minus}ray repeaters, origins of high velocity neutron stars and radio observations of high velocity neutron stars. There are 48 papers presented at the workshop and 5 have been abstracted for the Energy Science and Technology database.(AIP)

  2. Composition temperature-dependent g modes in superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Kantor, E. M.; Gusakov, M. E.

    2014-07-01

    We demonstrate a possibility of existence of peculiar temperature-dependent composition g modes in superfluid neutron stars. We calculate the Brunt-Visl frequency for these modes, as well as their eigenfrequencies. The latter turn out to be rather large, up to 500 Hz for a chosen model of a neutron star. This result indicates, in particular, that use of the barotropic equation of state may be not a good approximation for calculation of inertial modes even in most rapidly rotating superfluid neutron stars.

  3. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip

    2007-01-01

    Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star approaching EOS model of high density cold matter in the neutron star cores. +k Extensive observation and analysis of the data from the rising portions of the bursts - modeling of burst oscillations and thermonuclear flame spreading. +k Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

  4. Understanding Neutron Stars using Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.

    2007-01-01

    Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star = EOS model of high density cold matter in the neutron star cores. Extensive observation and analysis of the data from the rising portions of the bursts = modeling of burst oscillations and thermonuclear flame spreading. Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

  5. Does mass accretion lead to field decay in neutron stars

    NASA Technical Reports Server (NTRS)

    Shibazaki, N.; Murakami, T.; Shaham, Jacob; Nomoto, K.

    1989-01-01

    The recent discovery of cyclotron lines from gamma-ray bursts indicates that the strong magnetic fields of isolated neutron stars might not decay. The possible inverse correlation between the strength of the magnetic field and the mass accreted by the neutron star suggests that mass accretion itself may lead to the decay of the magnetic field. The spin and magnetic field evolution of the neutron star was calculated under the hypothesis of the accretion-induced field decay. It is shown that the calculated results are consistent with the observations of binary and millisecond radio pulsars.

  6. Neutron-capture nucleosynthesis in the first stars

    SciTech Connect

    Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Sneden, Christopher

    2014-04-01

    Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars.

  7. Solar flare leaves sun quaking

    NASA Astrophysics Data System (ADS)

    1998-05-01

    Dr. Alexander G. Kosovichev, a senior research scientist from Stanford University, and Dr. Valentina V. Zharkova from Glasgow (United Kingdom) University found the tell-tale seismic signature in data on the Sun's surface collected by the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory (SOHO) spacecraft immediately following a moderate-sized flare on July 9, 1996. "Although the flare was a moderate one, it still released an immense amount of energy," said Dr. Craig Deforest, a researcher with the SOHO project. "The energy released is equal to completely covering the Earth's continents with a yard of dynamite and detonating it all at once." SOHO is a joint project of the European Space Agency and NASA. The finding is reported in the May 28 issue of the journal Nature, and is the subject of a press conference at the spring meeting of the American Geophysical Union in Boston, Mass., May 27. The solar quake that the science team recorded looks much like ripples spreading from a rock dropped into a pool of water. But over the course of an hour, the solar waves traveled for a distance equal to 10 Earth diameters before fading into the fiery background of the Sun's photosphere. Unlike water ripples that travel outward at a constant velocity, the solar waves accelerated from an initial speed of 22,000 miles per hour to a maximum of 250,000 miles per hour before disappearing. "People have looked for evidence of seismic waves from flares before, but they didn't have a theory so they didn't know where to look," says Kosovichev. Several years ago Kosovichev and Zharkova developed a theory that can explain how a flare, which explodes in space above the Sun's surface, can generate a major seismic wave in the Sun's interior. According to the currently accepted model of solar flares, the primary explosion creates high-energy electrons (electrically charged subatomic particles). These are funneled down into a magnetic flux tube, an invisible tube of magnetic energy, and produce X-rays, microwaves and a shock wave that heats the solar surface. Kosovichev and Zharkova developed a theory that predicts the nature and magnitude of the shock waves that this beam of energetic electrons should create when they slam down into the solar atmosphere. Although their theory directed them to the right area to search for the seismic waves, the waves that they found were 10 times stronger than they had predicted. "They were so strong that you can see them in the raw data," Kosovichev says. The solar seismic waves appear to be compression waves like the "P" waves generated by an earthquake. They travel throughout the Sun's interior. In fact, the waves should recombine on the opposite side of the Sun from the location of the flare to create a faint duplicate of the original ripple pattern, Kosovichev predicts. Now that they know how to find them, the SOHO scientists say that the seismic waves generated by solar flares should allow them to verify independently some of the conditions in the solar interior that they have inferred from studying the pattern of waves that are continually ruffling the Sun's surface. SOHO is part of the International Solar-Terrestrial Physics (ISTP) program, a global effort to observe and understand our star and its effects on our environment. The ISTP mission includes more than 20 satellites, coupled with with ground-based observatories and modeling centers, that allow scientists to study the Sun, the Earth, and the space between them in unprecedented detail. ISTP is a joint program of NASA, ESA, Japan's Institute for Astronautical Science, and Russia's Space Research Institute. Still images of the solar quake can be found at the following internet address: FTP://PAO.GSFC.NASA.GOV/newsmedia/QUAKE/ For further information, please contact : ESA Public Relations Division Tel:+33(0)1.53.69.71.55 Fax: +33(0)1.53.69.76.90 3

  8. Gamow's calculation of the neutron star's critical mass revised

    NASA Astrophysics Data System (ADS)

    Ludwig, Hendrik; Ruffini, Remo

    2014-09-01

    It has at times been indicated that Landau introduced neutron stars in his classic paper of 1932. This is clearly impossible because the discovery of the neutron by Chadwick was submitted more than one month after Landau's work. Therefore, and according to his calculations, what Landau really did was to study white dwarfs, and the critical mass he obtained clearly matched the value derived by Stoner and later by Chandrasekhar. The birth of the concept of a neutron star is still today unclear. Clearly, in 1934, the work of Baade and Zwicky pointed to neutron stars as originating from supernovae. Oppenheimer in 1939 is also well known to have introduced general relativity (GR) in the study of neutron stars. The aim of this note is to point out that the crucial idea for treating the neutron star has been advanced in Newtonian theory by Gamow. However, this pioneering work was plagued by mistakes. The critical mass he should have obtained was 6.9 M ?, not the one he declared, namely, 1.5 M ?. Probably, he was taken to this result by the work of Landau on white dwarfs. We revise Gamow's calculation of the critical mass regarding calculational and conceptual aspects and discuss whether it is justified to consider it the first neutron-star critical mass. We compare Gamow's approach to other early and modern approaches to the problem.

  9. Neutron Stars as a Source of the Short-Lived Nuclides in Ap-star Atmospheres

    SciTech Connect

    Gopka, Vera F.; Andrievsky, Sergey M.; Ulyanov, Oleg M.

    2008-05-21

    We propose a new explanation of some magnetic chemically peculiar (MCP) star anomalies, which is based on an assumption that such stars be the close binary systems with a secondary component being a neutron star. Within this hypothesis one can naturally explain the main anomalous features of MCP stars: first of all, an existence of the short-lived radioactive isotopes detected in some stars (like Przybylski's star (PS) and HR465), and some others peculiarities. Also we can assume the presence of the electron-positron annihilation emission lines (0.511 MeV) in the gamma spectrum of some MCP stars.

  10. Chandra Captures Neutron Star Action - Duration: 61 seconds.

    NASA Video Gallery

    This movie from NASA's Chandra X-ray Observatory shows a fast moving jet of particles produced by a rapidly rotating neutron star, and may provide new insight into the nature of some of the densest...

  11. Probing the faint end of the isolated neutron star population

    NASA Astrophysics Data System (ADS)

    Posselt, Bettina

    2010-09-01

    Isolated neutron stars are of supreme value but are extremely difficult to find, mainly due to the problem of source confusion in the usually large X-ray positional errors. This proposal aims to take advantage of the superb spatial resolution of Chandra to search for isolated neutron stars with thermal X-ray emission in the Chandra archive. Applying our latest population synthesis model we estimate that several such objects are lurking in the archive, with the highest likelihood for faint sources. Such objects will allow to probe the unexplored faint population of cooling isolated neutron stars. The initial candidates from the Chandra Source Catalogue are also faint enough to tap the expected elusive population of ISM-accreting neutron stars.

  12. Hadron-quark crossover and hot neutron stars at birth

    NASA Astrophysics Data System (ADS)

    Masuda, Kota; Hatsuda, Tetsuo; Takatsuka, Tatsuyuki

    2016-02-01

    We construct a new isentropic equation of state (EOS) at finite temperature, "Rover," on the basis of the hadron-quark crossover at high density. By using the new EOS, we study the structure of hot neutron stars at birth with typical lepton fraction (Y_l=0.3-0.4) and typical entropy per baryon (hat {S}=1{-}2). Due to the gradual appearance of quark degrees of freedom at high density, the temperature T and the baryon density ρ at the center of hot neutron stars with hadron-quark crossover are found to be smaller than those without the crossover by a factor of two or more. Typical energy release due to the contraction of a hot neutron star to a cold neutron star with mass M=1.4 M_{⊙} is shown to be about 0.04 M_{⊙}, with a spin-up rate of about 14%.

  13. Properties of Dense Matter in Neutron Stars and Supernovae

    SciTech Connect

    Shen, H.; Wang, Y. N.; Wen, W.

    2010-08-12

    We study the equation of state (EOS) of nuclear matter at finite temperature density with various proton fractions for use in supernova simulations. The properties of nuclear matter with both uniform and non-uniform distributions are studied consistently. We also discuss the EOS of neutron star matter at zero temperature in a wide density range including hyperons antikaons quarks. The EOS of neutron star matter could be softened by incorporating these new degrees of freedom.

  14. Static and rotating neutron stars fulfilling all fundamental interactions

    NASA Astrophysics Data System (ADS)

    Belvedere, Riccardo; Rueda, Jorge A.; Ruffini, Remo

    2014-09-01

    We summarize the key ingredients of a new neutron star model fulfilling global, but not local, charge neutrality. The model is described by what we have called the Einstein-Maxwell-Thomas-Fermi equations, which account for the strong, weak, electromagnetic, and gravitational interactions, as well as thermodynamical equilibrium, within the framework of general relativity and relativistic nuclear mean field theory. We show the results for both static and uniformly-rotating neutron stars and discuss some astrophysical implications.

  15. Searching for substellar companions of young isolated neutron stars

    NASA Astrophysics Data System (ADS)

    Posselt, B.; Neuhuser, R.; Haberl, F.

    2009-03-01

    Context: Only two planetary systems orbiting old ms-pulsars have been discovered. Young radio pulsars and radio-quiet neutron stars cannot be analysed by the usually-applied radio-pulse-timing technique. However, finding substellar companions orbiting these neutron stars would be of significant importance: the companion may have had an exotic formation, its observation may also enable us to study neutron-star physics. Aims: We investigate the closest young neutron stars to Earth to search for orbiting substellar companions. Methods: Young, thus warm substellar companions are visible in the Near infrared, in which the neutron star itself is much fainter. Four young neutron stars are at sufficient speed to enable a common proper-motion search for substellar companions within few years. Results: For Geminga, RX J0720.4-3125, RX J1856.6-3754, and PSR J1932+1059 we found no comoving companion of masses as low as 12, 15, 11, and 42 Jupiter masses, respectively, for assumed ages of 1, 1, 1, and 3.1 Myr, and distances of 250, 361, 167, and 361 pc, respectively. Near infrared limits are presented for these four and five additional neutron stars for which we have observations for only one epoch. Conclusions: We conclude that young, isolated neutron stars rarely have brown-dwarf companions. Based on observations made with ESO Telescopes at the La Silla or Paranal Observatories under programme IDs: 66.D-0135, 71.C-0189, 72.C-0051, 74.C-0596, 077.C-0162, 78.C-0686, 79.C-0570.

  16. MHD Stability of Polar Caps of Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Litwin, C.; Brown, E. F.; Rosner, R.

    2000-12-01

    We assess the stability of magnetic Rayleigh-Taylor type modes driven by the overpressure of magnetically confined accreted matter on the surface of a neutron star. We employ the magnetohydrodynamic (MHD) energy principle to analyze the stability of short-wavelength (ballooning) modes subject to line-tying in the neutron star crust. Research supported by ASCI/Alliances Center for Astrophysical Thermonuclear Flashes at the University of Chicago.

  17. ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS

    SciTech Connect

    Oezel, Feryal; Psaltis, Dimitrios; Santos Villarreal, Antonio; Narayan, Ramesh

    2012-09-20

    We investigate the distribution of neutron star masses in different populations of binaries, employing Bayesian statistical techniques. In particular, we explore the differences in neutron star masses between sources that have experienced distinct evolutionary paths and accretion episodes. We find that the distribution of neutron star masses in non-recycled eclipsing high-mass binaries as well as of slow pulsars, which are all believed to be near their birth masses, has a mean of 1.28 M{sub Sun} and a dispersion of 0.24 M{sub Sun }. These values are consistent with expectations for neutron star formation in core-collapse supernovae. On the other hand, double neutron stars, which are also believed to be near their birth masses, have a much narrower mass distribution, peaking at 1.33 M{sub Sun }, but with a dispersion of only 0.05 M{sub Sun }. Such a small dispersion cannot easily be understood and perhaps points to a particular and rare formation channel. The mass distribution of neutron stars that have been recycled has a mean of 1.48 M{sub Sun} and a dispersion of 0.2 M{sub Sun }, consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed {approx}2 M{sub Sun} suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.

  18. Phase separation in the crust of accreting neutron stars

    SciTech Connect

    Horowitz, C. J.; Berry, D. K.; Brown, E. F.

    2007-06-15

    Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus.

  19. R-mode constraints from neutron star equation of state

    NASA Astrophysics Data System (ADS)

    Papazoglou, M. C.; Moustakidis, C. C.

    2016-03-01

    The gravitational radiation has been proposed a long time before, as an explanation for the observed relatively low spin frequencies of young neutron stars and of accreting neutron stars in low-mass X-ray binaries as well. In the present work we studied the effects of the neutron star equation of state on the r-mode instability window of rotating neutron stars. Firstly, we employed a set of analytical solution of the Tolman-Oppenheimer-Volkoff equations with special emphasis on the Tolman VII solution. In particular, we tried to clarify the effects of the bulk neutron star properties (mass, radius, density distribution, crust size and elasticity) on the r-mode instability window. We found that the critical angular velocity \\varOmegac depends mainly on the neutron star radius. The effects of the gravitational mass and the mass distribution are almost negligible. Secondly, we studied the effect of the elasticity of the crust, via to the slippage factor S and also the effect of the nuclear equation of state, via the slope parameter L, on the instability window. We found that the crust effects are more pronounced, compared to those originated from the equation of state. Moreover, we proposed simple analytical expressions which relate the macroscopic quantity \\varOmegac to the radius, the parameter L and the factor {S}. We also investigated the possibility to measure the radius of a neutron star and the factor {S} with the help of accurate measures of \\varOmegac and the neutron star temperature. Finally, we studied the effects of the mutual friction on the instability window and discussed the results in comparison with previous similar studies.

  20. Phase separation in the crust of accreting neutron stars.

    PubMed

    Horowitz, C J; Berry, D K; Brown, E F

    2007-06-01

    Nucleosynthesis, on the surface of accreting neutron stars, produces a range of chemical elements. We perform molecular dynamics simulations of crystallization to see how this complex composition forms new neutron star crust. We find chemical separation, with the liquid ocean phase greatly enriched in low atomic number elements compared to the solid crust. This phase separation should change many crust properties such as the thermal conductivity and shear modulus. PMID:17677319

  1. From ultracold Fermi Gases to Neutron Stars

    NASA Astrophysics Data System (ADS)

    Salomon, Christophe

    2012-02-01

    Ultracold dilute atomic gases can be considered as model systems to address some pending problem in Many-Body physics that occur in condensed matter systems, nuclear physics, and astrophysics. We have developed a general method to probe with high precision the thermodynamics of locally homogeneous ultracold Bose and Fermi gases [1,2,3]. This method allows stringent tests of recent many-body theories. For attractive spin 1/2 fermions with tunable interaction (^6Li), we will show that the gas thermodynamic properties can continuously change from those of weakly interacting Cooper pairs described by Bardeen-Cooper-Schrieffer theory to those of strongly bound molecules undergoing Bose-Einstein condensation. First, we focus on the finite-temperature Equation of State (EoS) of the unpolarized unitary gas. Surprisingly, the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory [3] and we localize the superfluid phase transition. A detailed comparison with theories including recent Monte-Carlo calculations will be presented. Moving away from the unitary gas, the Lee-Huang-Yang and Lee-Yang beyond-mean-field corrections for low density bosonic and fermionic superfluids are quantitatively measured for the first time. Despite orders of magnitude difference in density and temperature, our equation of state can be used to describe low density neutron matter such as the outer shell of neutron stars. [4pt] [1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, Nature 463, 1057 (2010) [0pt] [2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon, Science 328, 729 (2010) [0pt] [3] S. Nascimbène, N. Navon, S. Pilati, F. Chevy, S. Giorgini, A. Georges, and C. Salomon, Phys. Rev. Lett. 106, 215303 (2011)

  2. Structure of neutron stars in tensor-vector-scalar theory

    SciTech Connect

    Lasky, Paul D.; Sotani, Hajime; Giannios, Dimitrios

    2008-11-15

    Bekenstein's tensor-vector-scalar (TeVeS) theory has had considerable success in explaining various phenomena without the need for dark matter. However, it is difficult to observationally discern the differences between TeVeS and predictions made within the {lambda}-cold dark matter concordance model. This implies that alternative tests are required that independently verify which theory is correct. For this we turn to the strong-field regime of TeVeS. In particular, we solve the spherically symmetric equations of hydrostatic equilibrium for a perfect fluid with a realistic equation of state to build models of neutron stars in TeVeS. We show that causality within the neutron star is only maintained for certain cosmological values of the scalar field, which allows us to put constraints on this value independently of cosmological observations. We also discuss in detail the internal structure of neutron stars and how each of the free parameters in the theory affects the overall size and mass of the neutron stars. In particular, the radii of neutron stars in TeVeS can significantly differ from those in general relativity for certain values of the vector field coupling, which allows us to also place extra constraints on this parameter. Finally, we discuss future observations of neutron stars using both the electromagnetic and gravitational wave spectrums that will allow for tests of the appropriate theory of gravity.

  3. Instability windows and evolution of rapidly rotating neutron stars.

    PubMed

    Gusakov, Mikhail E; Chugunov, Andrey I; Kantor, Elena M

    2014-04-18

    We consider an instability of rapidly rotating neutron stars in low-mass x-ray binaries (LMXBs) with respect to excitation of r modes (which are analogous to Earth's Rossby waves controlled by the Coriolis force). We argue that finite temperature effects in the superfluid core of a neutron star lead to a resonance coupling and enhanced damping (and hence stability) of oscillation modes at certain stellar temperatures. Using a simple phenomenological model we demonstrate that neutron stars with high spin frequency may spend a substantial amount of time at these "resonance" temperatures. This finding allows us to explain puzzling observations of hot rapidly rotating neutron stars in LMXBs and to predict a new class of hot, nonaccreting, rapidly rotating neutron stars, some of which may have already been observed and tentatively identified as quiescent LMXB candidates. We also impose a new theoretical limit on the neutron star spin frequency, which can explain the cutoff spin frequency ∼730  Hz, following from the statistical analysis of accreting millisecond x-ray pulsars. In addition to explaining the observations, our model provides a new tool to constrain superdense matter properties by comparing measured and theoretically predicted resonance temperatures. PMID:24785021

  4. Spin Crystals may be commonly formed from Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kriske, Richard

    2015-04-01

    Neutron Stars may be a Crystal of Neutrons. One has to consider what would happen to this matter if Neutron Stars do not commonly collapse into Black Holes, but rather tear apart. One idea is that the Neutrons would separate and become single Neutrons, or lose an Electron and become Hydrogen with one or more Neutrons or Heavy and Super Heavy water. Perhaps the Graviton plays a role in crushing and packing the matter together, and there is another particle that keeps track of the Crystal structure of the packed Neutrons. We could call this particle the Neutron Crystal Particle. We may know something about it already, in that the Nuclei as we know them have what are know as Magic Numbers of stability. Are there other series that occur but are very rare here? Magic Number series that occur around Black Holes and perhaps in Comets or other bodies that seem to be made of water. When the Neutrons from Neutron Stars break up perhaps they form Spin Crystals, which are like Crystals but are not localized, they fly off in all directions, but are connected through the NCP. One way to test this would be to irradiate a Comet with an X-ray laser since this sort of Crystal could be forced to Fission. Perhaps Comet tails are the result of a Nuclear Reaction with the Sun.

  5. Measuring neutron-star properties via gravitational waves from neutron-star mergers.

    PubMed

    Bauswein, A; Janka, H-T

    2012-01-01

    We demonstrate by a large set of merger simulations for symmetric binary neutron stars (NSs) that there is a tight correlation between the frequency peak of the postmerger gravitational-wave (GW) emission and the physical properties of the nuclear equation of state (EoS), e.g., expressed by the radius of the maximum-mass Tolman-Oppenheimer-Volkhoff configuration. Therefore, a single measurement of the peak frequency of the postmerger GW signal will constrain the NS EoS significantly. For optimistic merger-rate estimates a corresponding detection with Advanced LIGO is expected to happen within an operation time of roughly a year. PMID:22304250

  6. Electromagnetic Counterparts of Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Metzger, Brian

    2011-09-01

    The most promising astrophysical sources of gravitational waves (GWs) for ground-based interferometers such as Advanced LIGO are the inspiral and merger of binary neutron star (NS) and black hole systems. Maximizing the benefits of a GW detection will require identifying a coincident electromagnetic (EM) counterpart. One possible source of bright EM emission is a gamma-ray burst (GRB), powered by accretion following the merger. However, for typical viewers outside the opening angle of the GRB jet, prompt emission may be difficult to detect. Another source of isotropic EM emission from NS mergers is a supernova-like optical transient (`kilo-nova'), powered by the radioactive decay of heavy elements synthesized in the ejecta . I will present the first calculations of the optical transients from NS mergers that self consistently determine the radioactive heating using a nuclear reaction network and which determine the resulting light curve with a Monte Carlo radiation transfer calculation. I will compare the predicted brightness and duration of the kilo-nova to the expected off-axis (`orphan') afterglow emission, in order to assess the optimal EM follow-up strategy following a future GW detection.

  7. Gravitational radiation during coalescence of neutron stars

    NASA Astrophysics Data System (ADS)

    Aksenov, A. G.; Chechetkin, V. M.

    2013-07-01

    The coalescence of components of a binary star with equal masses ( M 1 = M 2 = M ?) and moving in circular orbits is considered. The equation of state for degenerate neutrons is used, leading to the equation of state for an ideal gas. The initial model has zero temperature, corresponding to a polytrope with n = 1.5. To reduce the required computational time, the initial close binary is constructed using the self-consistent field method. The computations use Newtonian gas dynamics, but the back reaction of the gravitational radiation is taken into account in a PN2.5 post-Newton approximation, obtained using ADM formalism. This makes it possible to apply previous experienceof constructing high-order Godunov-type difference schemes, which are suitable for end-to-end calculations of discontinuous solutions of the gas-dynamics equations on a fixed Eulerian grid. The Poisson equations were solved using an original spherical-function expansion method. The 3D computations yielded the parameters of the gravitational signal. Near the radiation maximum, the strain amplitude is rh 4 104 cm, the power maximum is 4 1054 erg/s, and the typical radiation frequency is ?1 kHz. The energy carried away by gravitational waves is ?1052 erg. These parameters are of interest, since they form an inherent part of a rotational mechanism for the supernova explosion. They are also of interest for the planning of gravitational-wave detection experiments.

  8. Hydrodynamical Neutron Star Kicks in Three Dimensions

    NASA Astrophysics Data System (ADS)

    Wongwathanarat, Annop; Janka, Hans-Thomas; Mller, Ewald

    2010-12-01

    Using three-dimensional (3D) simulations of neutrino-powered supernova explosions, we show that the hydrodynamical kick scenario proposed by Scheck et al. on the basis of two-dimensional (2D) models can yield large neutron star (NS) recoil velocities also in 3D. Although the shock stays relatively spherical, standing accretion-shock and convective instabilities lead to a globally asymmetric mass and energy distribution in the post-shock layer. An anisotropic momentum distribution of the ejecta is built up only after the explosion sets in. Total momentum conservation implies the acceleration of the NS on a timescale of 1-3 s, mediated mainly by long-lasting, asymmetric accretion downdrafts and the anisotropic gravitational pull of large inhomogeneities in the ejecta. In a limited set of 15 M sun models with an explosion energy of about 1051 erg, this stochastic mechanism is found to produce kicks from <100 km s-1 to gsim500 km s-1, and kicks gsim1000 km s-1 seem possible. Strong rotational flows around the accreting NS do not develop in our collapsing, non-rotating progenitors. The NS spins therefore remain low with estimated periods of ~500-1000 ms and no alignment with the kicks.

  9. Resonant shattering of neutron star crusts.

    PubMed

    Tsang, David; Read, Jocelyn S; Hinderer, Tanja; Piro, Anthony L; Bondarescu, Ruxandra

    2012-01-01

    The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (SGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ∼10{46}-10{47}  erg of energy seconds before the merger of a NS-NS or NS-black-hole binary. Such properties are consistent with Swift/BAT detections of SGRB precursors, and we use the timing of the observed precursors to place weak constraints on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state. PMID:22304251

  10. Physics of systems containing neutron stars

    NASA Technical Reports Server (NTRS)

    Shaham, Jacob

    1995-01-01

    This grant deals with several topics related to the dynamics of systems containing a compact object. Most of our research in 1994 dealt with systems containing Neutron Stars (NS's), but we also addressed systems containing a Black Hole (BH) or a White Dwarf (WD) in situations relevant to NS systems. Among the systems were isolated regular pulsars, Millisecond Pulsars (MSP's) that are either Single (SMP's) or in a binary (BMP's) Low Mass X-Ray Binaries (LMX's) and Cataclysmic Variables (CV's). We also dealt with one aspect of NS structure, namely NS superfluidity. A large fraction of our research dealt with irradiation-driven winds from companions. These winds turned out to be of some importance in the evolution of LMXB's and MSP's, be they SMP's or BMP's. While their role during LMXB evolution (i.e. during the accretion phase) is not yet clear, they may play an important role in turning BMP's into SMP's and also in bringing about the formation of planets around MSP's.

  11. Astronomers Discover Most Massive Neutron Star Yet Known

    NASA Astrophysics Data System (ADS)

    2010-10-01

    Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered the most massive neutron star yet found, a discovery with strong and wide-ranging impacts across several fields of physics and astrophysics. "This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out," said Paul Demorest, of the National Radio Astronomy Observatory (NRAO). "This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics," he added. Neutron stars are the superdense "corpses" of massive stars that have exploded as supernovae. With all their mass packed into a sphere the size of a small city, their protons and electrons are crushed together into neutrons. A neutron star can be several times more dense than an atomic nucleus, and a thimbleful of neutron-star material would weigh more than 500 million tons. This tremendous density makes neutron stars an ideal natural "laboratory" for studying the most dense and exotic states of matter known to physics. The scientists used an effect of Albert Einstein's theory of General Relativity to measure the mass of the neutron star and its orbiting companion, a white dwarf star. The neutron star is a pulsar, emitting lighthouse-like beams of radio waves that sweep through space as it rotates. This pulsar, called PSR J1614-2230, spins 317 times per second, and the companion completes an orbit in just under nine days. The pair, some 3,000 light-years distant, are in an orbit seen almost exactly edge-on from Earth. That orientation was the key to making the mass measurement. As the orbit carries the white dwarf directly in front of the pulsar, the radio waves from the pulsar that reach Earth must travel very close to the white dwarf. This close passage causes them to be delayed in their arrival by the distortion of spacetime produced by the white dwarf's gravitation. This effect, called the Shapiro Delay, allowed the scientists to precisely measure the masses of both stars. "We got very lucky with this system. The rapidly-rotating pulsar gives us a signal to follow throughout the orbit, and the orbit is almost perfectly edge-on. In addition, the white dwarf is particularly massive for a star of that type. This unique combination made the Shapiro Delay much stronger and thus easier to measure," said Scott Ransom, also of NRAO. The astronomers used a newly-built digital instrument called the Green Bank Ultimate Pulsar Processing Instrument (GUPPI), attached to the GBT, to follow the binary stars through one complete orbit earlier this year. Using GUPPI improved the astronomers' ability to time signals from the pulsar severalfold. The researchers expected the neutron star to have roughly one and a half times the mass of the Sun. Instead, their observations revealed it to be twice as massive as the Sun. That much mass, they say, changes their understanding of a neutron star's composition. Some theoretical models postulated that, in addition to neutrons, such stars also would contain certain other exotic subatomic particles called hyperons or condensates of kaons. "Our results rule out those ideas," Ransom said. Demorest and Ransom, along with Tim Pennucci of the University of Virginia, Mallory Roberts of Eureka Scientific, and Jason Hessels of the Netherlands Institute for Radio Astronomy and the University of Amsterdam, reported their results in the October 28 issue of the scientific journal Nature. Their result has further implications, outlined in a companion paper, scheduled for publication in the Astrophysical Journal Letters. "This measurement tells us that if any quarks are present in a neutron star core, they cannot be 'free,' but rather must be strongly interacting with each other as they do in normal atomic nuclei," said Feryal Ozel of the University of Arizona, lead author of the second paper. There remain several viable hypotheses for the internal composition of neutron stars, but the new results put limits on those, as well as on the maximum possible density of cold matter. The scientific impact of the new GBT observations also extends to other fields beyond characterizing matter at extreme densities. A leading explanation for the cause of one type of gamma-ray burst -- the "short-duration" bursts -- is that they are caused by colliding neutron stars. The fact that neutron stars can be as massive as PSR J1614-2230 makes this a viable mechanism for these gamma-ray bursts. Such neutron-star collisions also are expected to produce gravitational waves that are the targets of a number of observatories operating in the United States and Europe. These waves, the scientists say, will carry additional valuable information about the composition of neutron stars. "Pulsars in general give us a great opportunity to study exotic physics, and this system is a fantastic laboratory sitting out there, giving us valuable information with wide-ranging implications," Ransom explained. "It is amazing to me that one simple number -- the mass of this neutron star -- can tell us so much about so many different aspects of physics and astronomy," he added.

  12. Hydromagnetic Equilibria and their Evolution in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Reisenegger, Andreas

    2014-08-01

    The strongest known magnetic fields are found in neutron stars. I briefly discuss how they are inferred from observations, as well as the evidence for their time-evolution. I go on to show how these extremely strong fields are actually weak in terms of their effects on the stellar structure. This is also the case for magnetic stars on the upper main sequence and magnetic white dwarfs, which have similar total magnetic fluxes, perhaps pointing to an evolutionary connection. I suggest that a stable hydromagnetic equilibrium (containing a poloidal and a toroidal field component) could be established soon after the birth of the neutron star, aided by the strong compositional stratification of neutron star matter, and this state is slowly eroded by non-ideal magnetohydrodynamic processes such as beta decays and ambipolar diffusion in the core of the star and Hall drift and breaking of the solid in its crust. Over sufficiently long time scales, the fluid in the neutron star core will behave as if it were barotropic, because, depending on temperature and magnetic field strength, beta decays will keep adjusting the composition to the chemical equilibrium state, or ambipolar diffusion will decouple the charged component from the neutrons. Therefore, the still open question regarding stable hydromagnetic equilibria in barotropic fluids will become relevant for the evolution, at least for magnetar fields, which are likely too strong to be stabilized by the solid crust.

  13. HUBBLE SEES A NEUTRON STAR ALONE IN SPACE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    his is the first direct look, in visible light, at a lone neutron star, as seen by NASA's Hubble Space Telescope. The Hubble results show the star is very hot (1.2 million degrees Fahrenheit at the surface), and can be no larger than 16.8 miles (28 kilometers) across. These results prove that the object must be a neutron star, because no other known type of object can be this hot, small, and dim (below 25th magnitude). The first clue that there was a neutron star at this location came in 1992, when the ROSAT (the Roentgen Satellite) found a bright X-ray source without any optical counterpart in optical sky surveys. Hubble's Wide Field Planetary Camera 2 was used in October 1996 to undertake a sensitive search for the optical object, and found a stellar pinpoint of light within only 2 arc seconds (1/900th the diameter of the Moon) of the X-ray position. Astronomers haven't directly measured the neutron star's distance, but fortunately the neutron star lies in front of a molecular cloud known to be about 400 light-years away in the southern constellation Corona Australis. Credit: Fred Walter (State University of New York at Stony Brook), and NASA

  14. Limits on self-interacting dark matter from neutron stars.

    PubMed

    Kouvaris, Chris

    2012-05-11

    We impose new severe constraints on the self-interactions of fermionic asymmetric dark matter based on observations of nearby old neutron stars. Weakly interacting massive particle (WIMP) self-interactions mediated by Yukawa-type interactions can lower significantly the number of WIMPs necessary for gravitational collapse of the WIMP population accumulated in a neutron star. Even nearby neutron stars located at regions of low dark matter density can accrete a sufficient number of WIMPs that can potentially collapse, form a mini black hole, and destroy the host star. Based on this, we derive constraints on the WIMP self-interactions which in some cases are by several orders of magnitude stricter than the ones from the bullet cluster. PMID:23003023

  15. Quark matter in neutron stars and core-collapse supernovae

    NASA Astrophysics Data System (ADS)

    Sagert, Irina; Fischer, Tobias; Hempel, Matthias; Pagliara, Giuseppe; Schaffner-Bielich, Juergen; Rauscher, Thomas; Thielemann, Friedrich-K.; Kaeppeli, Roger; Martinez-Pinedo, Gabriel; Liebendoerfer, Matthias

    2011-10-01

    Recent neutron star mass measurements point to compact star maximum masses of at least 1.970.04 solar masses and represent thereby a challenge for soft nuclear equations of state, which often go hand in hand with the presence of hyperons or quarks. In this talk I will discuss such high neutron star masses regarding the nuclear equation of state from heavy ion experiments. Furthermore, I will introduce equations of state for core-collapse supernova and binary merger simulations, which include a phase transition to strange quark matter. As was recently shown, neutrino signals from supernova explosions can provide a probe for the low density appearance of quark matter. The compatibility of the latter with high neutron star masses is an interesting and important question and will be addressed in the talk.

  16. Fast radio bursts: the last sign of supramassive neutron stars

    NASA Astrophysics Data System (ADS)

    Falcke, Heino; Rezzolla, Luciano

    2014-02-01

    Context. Several fast radio bursts have been discovered recently, showing a bright, highly dispersed millisecond radio pulse. The pulses do not repeat and are not associated with a known pulsar or gamma-ray burst. The high dispersion suggests sources at cosmological distances, hence implying an extremely high radio luminosity, far larger than the power of single pulses from a pulsar. Aims: We suggest that a fast radio burst represents the final signal of a supramassive rotating neutron star that collapses to a black hole due to magnetic braking. The neutron star is initially above the critical mass for non-rotating models and is supported by rapid rotation. As magnetic braking constantly reduces the spin, the neutron star will suddenly collapse to a black hole several thousand to million years after its birth. Methods: We discuss several formation scenarios for supramassive neutron stars and estimate the possible observational signatures making use of the results of recent numerical general-relativistic calculations. Results: While the collapse will hide the stellar surface behind an event horizon, the magnetic-field lines will snap violently. This can turn an almost ordinary pulsar into a bright radio "blitzar": accelerated electrons from the travelling magnetic shock dissipate a significant fraction of the magnetosphere and produce a massive radio burst that is observable out to z > 0.7. Only a few per cent of the neutron stars need to be supramassive in order to explain the observed rate. Conclusions: We suggest the intriguing possibility that fast radio bursts might trace the solitary and almost silent formation of stellar mass black holes at high redshifts. These bursts could be an electromagnetic complement to gravitational-wave emission and reveal a new formation and evolutionary channel for black holes and neutron stars that are not seen as gamma-ray bursts. If supramassive neutron stars are formed at birth and not by accretion, radio observations of these bursts could trace the core-collapse supernova rate throughout the universe.

  17. Supergiant pulses from extragalactic neutron stars

    NASA Astrophysics Data System (ADS)

    Cordes, J. M.; Wasserman, Ira

    2016-03-01

    We consider radio bursts that originate from extragalactic neutron stars (NSs) by addressing three questions about source distances. What are the physical limitations on coherent radiation at GHz frequencies? Do they permit detection at cosmological distances? How many bursts per NS are needed to produce the inferred burst rate ˜103-104sky-1 d-1? The burst rate is comparable to the NS formation rate in a Hubble volume, requiring only one per NS if they are bright enough. Radiation physics suggests a closer population, requiring more bursts per NS and increasing the chances for repeats. Bursts comprise sub-ns, coherent shot pulses superposed incoherently to produce ms-duration ˜1 Jy amplitudes; each shot pulse can be much weaker than 1 Jy, placing less restrictive requirements on the emission process. None the less, single shot pulses are similar to the extreme, unresolved (<0.4 ns) MJy shot pulse seen from the Crab pulsar, consistent with coherent curvature radiation emitted near the light cylinder by an almost neutral clump with net charge ˜± 1021e and total energy ≳ 1023 erg. Bursts from Gpc distances require incoherent superposition of {˜ } 10^{12}d_Gpc^2 shot pulses or a total energy ≳ 10^{35} d_Gpc^2 erg. The energy reservoir near the light cylinder limits the detection distance to ≲ few × 100 Mpc for a fluence ˜1 Jy ms unless conditions are more extreme than for the Crab pulsar, such as in magnetars. We discuss contributions to dispersion measures from galaxy clusters and we propose tests for the overall picture presented.

  18. NASA'S Chandra Finds Superfluid in Neutron Star's Core

    NASA Astrophysics Data System (ADS)

    2011-02-01

    NASA's Chandra X-ray Observatory has discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the core of a neutron star. Superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers. The finding has important implications for understanding nuclear interactions in matter at the highest known densities. Neutron stars contain the densest known matter that is directly observable. One teaspoon of neutron star material weighs six billion tons. The pressure in the star's core is so high that most of the charged particles, electrons and protons, merge resulting in a star composed mostly of uncharged particles called neutrons. Two independent research teams studied the supernova remnant Cassiopeia A, or Cas A for short, the remains of a massive star 11,000 light years away that would have appeared to explode about 330 years ago as observed from Earth. Chandra data found a rapid decline in the temperature of the ultra-dense neutron star that remained after the supernova, showing that it had cooled by about four percent over a 10-year period. "This drop in temperature, although it sounds small, was really dramatic and surprising to see," said Dany Page of the National Autonomous University in Mexico, leader of a team with a paper published in the February 25, 2011 issue of the journal Physical Review Letters. "This means that something unusual is happening within this neutron star." Superfluids containing charged particles are also superconductors, meaning they act as perfect electrical conductors and never lose energy. The new results strongly suggest that the remaining protons in the star's core are in a superfluid state and, because they carry a charge, also form a superconductor. "The rapid cooling in Cas A's neutron star, seen with Chandra, is the first direct evidence that the cores of these neutron stars are, in fact, made of superfluid and superconducting material," said Peter Shternin of the Ioffe Institute in St Petersburg, Russia, leader of a team with a paper accepted in the journal Monthly Notices of the Royal Astronomical Society. Both teams show that this rapid cooling is explained by the formation of a neutron superfluid in the core of the neutron star within about the last 100 years as seen from Earth. The rapid cooling is expected to continue for a few decades and then it should slow down. "It turns out that Cas A may be a gift from the Universe because we would have to catch a very young neutron star at just the right point in time," said Page's co-author Madappa Prakash, from Ohio University. "Sometimes a little good fortune can go a long way in science." The onset of superfluidity in materials on Earth occurs at extremely low temperatures near absolute zero, but in neutron stars, it can occur at temperatures near a billion degrees Celsius. Until now there was a very large uncertainty in estimates of this critical temperature. This new research constrains the critical temperature to between one half a billion to just under a billion degrees. Cas A will allow researchers to test models of how the strong nuclear force, which binds subatomic particles, behaves in ultradense matter. These results are also important for understanding a range of behavior in neutron stars, including "glitches," neutron star precession and pulsation, magnetar outbursts and the evolution of neutron star magnetic fields. Small sudden changes in the spin rate of rotating neutron stars, called glitches, have previously given evidence for superfluid neutrons in the crust of a neutron star, where densities are much lower than seen in the core of the star. This latest news from Cas A unveils new information about the ultra-dense inner region of the neutron star. "Previously we had no idea how extended superconductivity of protons was in a neutron star," said Shternin's co-author Dmitry Yakovlev, also from the Ioffe Institute. The cooling in the Cas A

  19. Electrodynamics of disk-accreting magnetic neutron stars

    NASA Technical Reports Server (NTRS)

    Miller, M. Coleman; Lamb, Frederick K.; Hamilton, Russell J.

    1994-01-01

    We have investigated the electrodynamics of magnetic neutron stars accreting from Keplerian disks and the implications for particle acceleration and gamma-ray emission by such systems. We argue that the particle density in the magnetospheres of such stars is larger by orders of magnitude than the Goldreich-Julian density, so that the formation of vacuum gaps is unlikely. We show that even if the star rotates slowly, electromotive forces (EMFs) of order 10(exp 15) V are produced by the interaction of plasma in the accretion disk with the magnetic field of the neutron star. The resistance of the disk-magnetosphere-star circuit is small, and hence these EMFs drive very large conduction currents. Such large currents are likely to produce magnetospheric instabilities, such as relativistic double layers and reconnection events, that can accelerate electrons or ions to very high energies.

  20. The Case of the Neutron Star With a Wayward Wake

    NASA Astrophysics Data System (ADS)

    2006-06-01

    A long observation with NASA's Chandra X-ray Observatory has revealed important new details of a neutron star that is spewing out a wake of high-energy particles as it races through space. The deduced location of the neutron star on the edge of a supernova remnant, and the peculiar orientation of the neutron star wake, pose mysteries that remain unresolved. "Like a kite flying in the wind, the behavior of this neutron star and its wake tell us what sort of gas it must be plowing through," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., and lead author of a paper accepted to The Astrophysical Journal. "Yet we're still not sure how the neutron star got to its present location." Animation: Sequence of images of J0617 in IC 443 Animation: Sequence of images of J0617 in IC 443 The neutron star, known as CXOU J061705.3+222127, or J0617 for short, appears to lie near the outer edge of an expanding bubble of hot gas associated with the supernova remnant IC 443. Presumably, J0617 was created at the time of the supernova -- approximately 30,000 years ago -- and propelled away from the site of the explosion at about 500,000 miles per hour. However, the neutron star's wake is oriented almost perpendicularly to the direction expected if the neutron star were moving away from the center of the supernova remnant. This apparent misalignment had previously raised doubts about the association of the speeding neutron star with the supernova remnant. Gaensler and his colleagues provide strong evidence that J0617 was indeed born in the same explosion that created the supernova remnant. First, the shape of the neutron star's wake indicates it is moving a little faster than the speed of sound in Composite Images of SNR IC 443 Composite Images of SNR IC 443 the remnant's multimillion-degree gas. The velocity that one can then calculate from this conclusion closely matches the predicted pace of the neutron star. In contrast, if the neutron star were outside the confines of the remnant, its inferred speed would be a sluggish 20,000 miles per hour. Also, the measured temperature of the neutron star matches that of one born at the same time of the supernova remnant. What then, could cause the misaligned, or wayward, neutron star wake? The authors speculate that perhaps the doomed progenitor star was moving at a high speed before it exploded, so that the explosion site was not at the observed center of the supernova remnant. Fast moving gusts of gas inside the supernova remnant have further pushed the neutron star's wake out of alignment. Observations of J0617 in the next 10 years should put this idea to the test. "If the neutron star was born off-center and if the wake is being pushed around by cross-winds, the neutron star should be moving close to vertically, away from the center of the supernova remnant. Now we wait and see," said Gaensler. Chandra X-ray Image of J0617 in IC 443 Chandra X-ray Image of J0617 in IC 443 Another group, led by Margarita Karovska, also of the CfA, has concentrated on other, previously unnoticed intriguing features of J0617. At a recent conference on neutron stars in London, England, they announced their findings, which include a thin filament of cooler gas that appears to extend from the neutron star along the long axis of its wake, and a second point-like feature embedded in the X-ray nebula around the neutron star. "There are a number of puzzling observational features associated with this system crying out for longer observations," said Karovska. Other members of the Gaensler team were S. Chatterjee and P. O. Slane (CfA), E. van der Swaluw (Royal Netherlands Meteorological Institute), F. Camilo (Columbia University), and J. P. Hughes (Rutgers University). Karovska's team included T. Clarke (Naval Research Laboratory), G. Pavlov (Penn State University), and M.C. Weisskopf and V. Zavlin of the Marshall Space Flight Center, Huntsville, Ala. which also manages the Chandra program for NASA's Science Mission Directorate. The Smithsonian Astrophysical Observatory provides science support and controls flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images can be found at: http://chandra.harvard.edu and http://chandra.nasa.gov For information about NASA and agency programs on the Web, visit: http://www.nasa.gov

  1. Discriminating strange star mergers from neutron star mergers by gravitational-wave measurements

    SciTech Connect

    Bauswein, A.; Oechslin, R.; Janka, H.-T.

    2010-01-15

    We perform three-dimensional relativistic hydrodynamical simulations of the coalescence of strange stars and explore the possibility to decide on the strange matter hypothesis by means of gravitational-wave measurements. Self-binding of strange quark matter and the generally more compact stars yield features that clearly distinguish strange star from neutron star mergers, e.g. hampering tidal disruption during the plunge of quark stars. Furthermore, instead of forming dilute halo structures around the remnant as in the case of neutron star mergers, the coalescence of strange stars results in a differentially rotating hypermassive object with a sharp surface layer surrounded by a geometrically thin, clumpy high-density strange quark matter disk. We also investigate the importance of including nonzero temperature equations of state in neutron star and strange star merger simulations. In both cases we find a crucial sensitivity of the dynamics and outcome of the coalescence to thermal effects, e.g. the outer remnant structure and the delay time of the dense remnant core to black hole collapse depend on the inclusion of nonzero temperature effects. For comparing and classifying the gravitational-wave signals, we use a number of characteristic quantities like the maximum frequency during inspiral or the dominant frequency of oscillations of the postmerger remnant. In general, these frequencies are higher for strange star mergers. Only for particular choices of the equation of state the frequencies of neutron star and strange star mergers are similar. In such cases additional features of the gravitational-wave luminosity spectrum like the ratio of energy emitted during the inspiral phase to the energy radiated away in the postmerger stage may help to discriminate coalescence events of the different types. If such characteristic quantities could be extracted from gravitational-wave signals, for instance with the upcoming gravitational-wave detectors, a decision on the strange matter hypothesis and the existence of strange stars should be possible.

  2. SPINDOWN OF ISOLATED NEUTRON STARS: GRAVITATIONAL WAVES OR MAGNETIC BRAKING?

    SciTech Connect

    Staff, Jan E.; Jaikumar, Prashanth; Chan, Vincent; Ouyed, Rachid

    2012-05-20

    We study the spindown of isolated neutron stars from initially rapid rotation rates, driven by two factors: (1) gravitational wave emission due to r-modes and (2) magnetic braking. In the context of isolated neutron stars, we present the first study including self-consistently the magnetic damping of r-modes in the spin evolution. We track the spin evolution employing the RNS code, which accounts for the rotating structure of neutron stars for various equations of state. We find that, despite the strong damping due to the magnetic field, r-modes alter the braking rate from pure magnetic braking for B {<=} 10{sup 13} G. For realistic values of the saturation amplitude {alpha}{sub sat}, the r-mode can also decrease the time to reach the threshold central density for quark deconfinement. Within a phenomenological model, we assess the gravitational waveform that would result from r-mode-driven spindown of a magnetized neutron star. To contrast with the persistent signal during the spindown phase, we also present a preliminary estimate of the transient gravitational wave signal from an explosive quark-hadron phase transition, which can be a signal for the deconfinement of quarks inside neutron stars.

  3. The Fate of the Compact Remnant in Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Fryer, Chris L.; Belczynski, Krzysztoff; Ramirez-Ruiz, Enrico; Rosswog, Stephan; Shen, Gang; Steiner, Andrew W.

    2015-10-01

    Neutron star (binary neutron star and neutron star-black hole) mergers are believed to produce short-duration gamma-ray bursts (GRBs). They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and advanced VIRGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of Newtonian merger calculations and equation of state studies to determine the fate of the cores of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3-2.4 solar masses. If quick black hole formation is essential in producing GRBs, LIGO/Virgo observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.

  4. Discovery of a Neutron Star Oscillation Mode During a Superburst

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod; Mahmoodifar, Simin

    2014-10-01

    Neutron stars are among the most compact objects in the universe and provide a unique laboratory for the study of cold ultra-dense matter. While asteroseismology can provide a powerful probe of the interiors of stars, for example, helioseismology has provided unprecedented insights about the interior of the Sun, comparable capabilities for neutron star seismology have not yet been achieved. Here, we report the discovery of a coherent X-ray modulation from the neutron star 4U 1636-536 during the 2001 February 22 thermonuclear superburst seen with NASA's Rossi X-Ray Timing Explorer (RXTE) that is very likely produced by a global oscillation mode. The observed frequency is 835.6440 0.0002 Hz (1.43546 times the stellar spin frequency of 582.14323 Hz) and the modulation is well described by a sinusoid (A + Bsin (phi - phi0)) with a fractional half-amplitude of B/A = 0.19 0.04% (4-15 keV). The observed frequency is consistent with the expected inertial frame frequency of a rotationally modified surface g-mode, an interfacial mode in the ocean-crust interface, or perhaps an r-mode. Observing an inertial frame frequencyas opposed to a co-rotating frame frequencyappears consistent with the superburst's thermal emission arising from the entire surface of the neutron star, and the mode may become visible by perturbing the local surface temperature. We briefly discuss the implications of the mode detection for the neutron star's projected velocity and mass. Our results provide further strong evidence that global oscillation modes can produce observable modulations in the X-ray flux from neutron stars.

  5. DISCOVERY OF A NEUTRON STAR OSCILLATION MODE DURING A SUPERBURST

    SciTech Connect

    Strohmayer, Tod; Mahmoodifar, Simin

    2014-10-01

    Neutron stars are among the most compact objects in the universe and provide a unique laboratory for the study of cold ultra-dense matter. While asteroseismology can provide a powerful probe of the interiors of stars, for example, helioseismology has provided unprecedented insights about the interior of the Sun, comparable capabilities for neutron star seismology have not yet been achieved. Here, we report the discovery of a coherent X-ray modulation from the neutron star 4U 1636–536 during the 2001 February 22 thermonuclear superburst seen with NASA's Rossi X-Ray Timing Explorer (RXTE) that is very likely produced by a global oscillation mode. The observed frequency is 835.6440 ± 0.0002 Hz (1.43546 times the stellar spin frequency of 582.14323 Hz) and the modulation is well described by a sinusoid (A + Bsin (φ – φ{sub 0})) with a fractional half-amplitude of B/A = 0.19 ± 0.04% (4-15 keV). The observed frequency is consistent with the expected inertial frame frequency of a rotationally modified surface g-mode, an interfacial mode in the ocean-crust interface, or perhaps an r-mode. Observing an inertial frame frequency—as opposed to a co-rotating frame frequency—appears consistent with the superburst's thermal emission arising from the entire surface of the neutron star, and the mode may become visible by perturbing the local surface temperature. We briefly discuss the implications of the mode detection for the neutron star's projected velocity and mass. Our results provide further strong evidence that global oscillation modes can produce observable modulations in the X-ray flux from neutron stars.

  6. A debris disk around an isolated young neutron star.

    PubMed

    Wang, Zhongxiang; Chakrabarty, Deepto; Kaplan, David L

    2006-04-01

    Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of the order of 10 Earth masses, and its lifetime (> or = 10(6) years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars. PMID:16598251

  7. Neutron stars, strange stars, and the nuclear equation of state

    SciTech Connect

    Weber, F.; Glendenning, N.K.

    1992-11-02

    This article consists of three parts. In part one we review the present status of dense nuclear matter calculations, and introduce a representative collection of realistic nuclear equations of state which are derived for different assumptions about the physical behavior of dense matter (baryon population, pion condensation,.possible transition of baryon matter to quark matter). In part two we review recently performed non-rotating and rotating compact star calculations performed for these equations of state. The minimum stable rotational periods of compact stars, whose knowledge is of decisive importance for the interpretation of rapidly rotating pulsars, axe determined. For this purpose two different limits on stable rotation are studied: rotation at the general relativistic Kepler period (below which mass shedding at the star`s equator sets in), and, secondly, rotation at the gravitational radiation-reaction instability (at which emission of gravitational waves set in which slows the star down). Part three of this article deals with the properties of hypothetical strange stars. Specifically we investigate the amount of nuclear solid crust that can be carried by a rotating strange star, and answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

  8. Neutron star matter in an effective model

    SciTech Connect

    Jha, T. K.; Raina, P. K.; Panda, P. K.; Patra, S. K.

    2006-11-15

    We study an equation of state (EOS) for dense matter in the core of a compact star with hyperons and calculate the star's structure in an effective model using a mean-field approach. With varying incompressibility and effective nucleon mass, we analyze the resulting EOS with hyperons in {beta} equilibrium and their underlying effect on the gross properties of the compact star sequences. The results obtained in our analysis are compared with predictions of other theoretical models and observations. The maximum mass of a compact star lies in the range 1.21-1.96M{sub {center_dot}} for the different EOS obtained in the model.

  9. Modelling the magnetic field configuration of neutron stars

    NASA Astrophysics Data System (ADS)

    Ciolfi, R.

    2014-09-01

    The properties of the extremely strong magnetic fields of neutron stars affect in a unique way their evolution and the associated phenomenology. Due to the lack of constraints from direct observations, our understanding of the magnetic field configuration in neutron star interiors depends on the progress in theoretical modelling. Here we discuss the effort in building models of magnetized neutron stars focussing on some of the recent results. In particular, we comment on the instability of purely poloidal and purely toroidal magnetic field configurations and on the evidence in favour of the so-called twisted-torus solutions. We conclude with an outlook on the present status of the field and future directions.

  10. Persistent crust-core spin lag in neutron stars

    NASA Astrophysics Data System (ADS)

    Glampedakis, Kostas; Lasky, Paul D.

    2015-06-01

    It is commonly believed that the magnetic field threading a neutron star provides the ultimate mechanism (on top of fluid viscosity) for enforcing long-term corotation between the slowly spun-down solid crust and the liquid core. We show that this argument fails for axisymmetric magnetic fields with closed field lines in the core, the commonly used `twisted torus' field being the most prominent example. The failure of such magnetic fields to enforce global crust-core corotation leads to the development of a persistent spin lag between the core region occupied by the closed field lines and the rest of the crust and core. We discuss the repercussions of this spin lag for the evolution of the magnetic field, suggesting that, in order for a neutron star to settle to a stable state of crust-core corotation, the bulk of the toroidal field component should be deposited into the crust soon after the neutron star's birth.

  11. Physics in strong magnetic fields near neutron stars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    1991-01-01

    Electromagnetic phenomena occurring in the strong magnetic fields of neutron stars are currently of great interest in high-energy astrophysics. Observations of rotation rate changes and cyclotron lines in pulsars and gamma-ray bursts indicate that surface magnetic fields of neutron stars often exceed a trillion gauss. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes, and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: energies perpendicular to the field are quantized, transverse momentum is not conserved, and electron-positron spin is important. Neutron stars therefore provide a unique laboratory for the study of physics in extremely high fields that cannot be generated on earth.

  12. Ultrarelativistic electromagnetic counterpart to binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Kyutoku, Koutarou; Ioka, Kunihito; Shibata, Masaru

    2014-01-01

    We propose a possibility of ultrarelativistic electromagnetic counterparts to gravitational waves from binary neutron star mergers at nearly all the viewing angles. Our proposed mechanism relies on the merger-shock propagation accelerating a smaller mass in the outer parts of the neutron star crust to a larger Lorentz factor ? with smaller energy 1047?-1 erg. This mechanism is difficult to resolve by current 3D numerical simulations. The outflows emit synchrotron flares for seconds to days by shocking the ambient medium. Ultrarelativistic flares shine at an early time and in high-energy bands, potentially detectable by current X-ray to radio instruments, such as Swift XRT and Pan-STARRS, and even in low ambient density 10-2 cm-3 by EVLA. The flares probe the merger position and time, and the merger types as black hole-neutron star outflows would be non-/mildly relativistic.

  13. Accreting Millisecond Pulsars: Neutron Star Masses and Radii

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2004-01-01

    High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries. The recent discovery of X-ray burst oscillations from two accreting millisecond pulsars has confirmed this basic picture and provided a new route to measuring neutron star properties and constraining the dense matter equation of state. I will briefly summarize the current observational understanding of accreting millisecond pulsars, and describe recent attempts to determine the mass and radius of the neutron star in XTE J1814-338.

  14. Effects of hyperons in binary neutron star mergers.

    PubMed

    Sekiguchi, Yuichiro; Kiuchi, Kenta; Kyutoku, Koutarou; Shibata, Masaru

    2011-11-18

    Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling. It is found that even for the hyperonic EOS, a hypermassive neutron star is first formed after the merger for the typical total mass ≈2.7M(⊙), and subsequently collapses to a black hole (BH). It is shown that hyperons play a substantial role in the postmerger dynamics, torus formation around the BH, and emission of gravitational waves (GWs). In particular, the existence of hyperons is imprinted in GWs. Therefore, GW observations will provide a potential opportunity to explore the composition of neutron star matter. PMID:22181867

  15. Thermonuclear Burning as a Probe of Neutron Star

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2008-01-01

    Thermonuclear fusion is a fundamental process taking place in the matter transferred onto neutron stars in accreting binary systems. The heat deposited by nuclear reactions becomes readily visible in the X-ray band when the burning is either unstable or marginally stable, and results in the rich phenomenology of X-ray bursts, superbursts, and mHz quasiperiodic oscillations. Fast X-ray timing observations with NASA's Rossi X-ray Timing Explorer (RXTE) over the past decade have revealed a wealth of new phenomena associated with thermonuclear burning on neutron stars, including the discovery of nuclear powered pulsations during X-ray bursts and superbursts. I will briefly review our current observational and theoretical understanding of these new phenomena, with an emphasis on recent findings, and discuss what they are telling us about the structure of neutron stars.

  16. Scientific goals of SCHOOLS & QUAKES

    NASA Astrophysics Data System (ADS)

    Brckl, Ewald; Kberl, Christian; Lenhardt, Wolfgang; Mertl, Stefan; Rafeiner-Magor, Walter; Stark, Angelika; Stickler, Gerald; Weber, Robert

    2015-04-01

    In many countries around the world seismometers are used in schools to broaden the knowledge in seismology in a vivid way and to take part in the observation of the current worldwide seismic activity. SCHOOLS & QUAKES is a project within the Sparkling Science program (http://www.sparklingscience.at), which not only pursues the given educational goals but also integrates scholars in seismological research permitting their own contributions. Research within SCHOOLS & QUAKES concentrates on the seismic activity of the Mrz Valley - Semmering - Vienna Basin transfer fault system in Austria because of its relatively high earthquake hazard and risk. The detection of low magnitude local earthquakes (magnitude ? 2), precise location of hypocenters, determination of the focal mechanisms, and correlation of hypocenters with active geological structures are the main scientific goals in this project. Furthermore, the long term build-up of tectonic stress, slip deficit and aseismic slip, and the maximum credible earthquake in this area are issues to be addressed. The scientific efforts of SCHOOLS & QUAKES build on the work of the Seismological Service of Austria at the Zentralanstalt fr Meteorologie und Geodynamik (ZAMG), and benefit from the findings on the lithospheric structure of the Eastern Alps gained by the CELEBRATION 2000 and ALP 2002 projects. Regional Vp and Vs-models were derived from this data covering the SCHOOLS & QUAKES target area. Within the ALPAACT project (Seismological and geodetic monitoring of ALpine-PAnnonian ACtive Tectonics) the seismic network of the target area was densified by 7 broadband und 2 short period stations. Relocations based on a 3D-velocity model and the densified seismic network yielded substantially higher spatial resolution of seismically active structures. A new method based on waveform stacking (GRA, 16, EGU2014-5722) allowed for focal mechanism solutions of low magnitude (Ml ~2.5) events. Data from 22 GNSS stations have been reprocessed and yield continuous time series since 2008. The research within SCHOOLS & QUAKES is a consequent continuation of the ALPAACT initiatives. It is coordinated with the ZAMG efforts to keep the routine seismological work on a high scientific standard. Three polytechnic schools in Vienna and the southern Vienna Basin (Mdling and Wiener Neustadt) take part in SCHOOLS & QUAKES. So-called school seismometers as well as high performance short period stations have been installed at these locations. In addition to routine maintenance and site optimization of the seismic stations, scholars and teachers of these schools contribute to research by their unprejudiced approach to interactive event detection and travel time picking as well as by their expertise in electronics, informatics, and civil engineering. The development of low cost short period stations which meet the requirements of medium to high noise locations, or the generation of shake maps and their conversion into maps of potential source locations are work in progress in cooperation with graduate students.

  17. R-mode instability of strange stars and observations of neutron stars in LMXBs

    NASA Astrophysics Data System (ADS)

    Pi, Chun-Mei; Yang, Shu-Hua; Zheng, Xiao-Ping

    2015-06-01

    Using a realistic equation of state (EOS) of strange quark matter, namely, the modified bag model, and considering the constraints on the parameters of EOS by the observational mass limit of neutron stars, we investigate the r-mode instability window of strange stars, and find the same result as in the brief study of Haskell, Degenaar and Ho in 2012 that these instability windows are not consistent with the spin frequency and temperature observations of neutron stars in low mass X-ray binaries. Supported by the National Natural Science Foundation of China.

  18. The magnetosphere of oscillating neutron stars in general relativity

    NASA Astrophysics Data System (ADS)

    Abdikamalov, Ernazar B.; Ahmedov, Bobomurat J.; Miller, John C.

    2009-05-01

    Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment.

  19. Microscopic calculations of nuclear and neutron matter, symmetry energy and neutron stars

    DOE PAGESBeta

    Gandolfi, S.

    2015-02-01

    We present Quantum Monte Carlo calculations of the equation of state of neutron matter. The equation of state is directly related to the symmetry energy and determines the mass and radius of neutron stars, providing then a connection between terrestrial experiments and astronomical observations. As a result, we also show preliminary results of the equation of state of nuclear matter.

  20. Neutron stars, strange stars, and the nuclear equation of state

    SciTech Connect

    Weber, F.; Glendenning, N.K.

    1992-11-02

    This article consists of three parts. In part one we review the present status of dense nuclear matter calculations, and introduce a representative collection of realistic nuclear equations of state which are derived for different assumptions about the physical behavior of dense matter (baryon population, pion condensation,.possible transition of baryon matter to quark matter). In part two we review recently performed non-rotating and rotating compact star calculations performed for these equations of state. The minimum stable rotational periods of compact stars, whose knowledge is of decisive importance for the interpretation of rapidly rotating pulsars, axe determined. For this purpose two different limits on stable rotation are studied: rotation at the general relativistic Kepler period (below which mass shedding at the star's equator sets in), and, secondly, rotation at the gravitational radiation-reaction instability (at which emission of gravitational waves set in which slows the star down). Part three of this article deals with the properties of hypothetical strange stars. Specifically we investigate the amount of nuclear solid crust that can be carried by a rotating strange star, and answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

  1. X-ray spectra from convective photospheres of neutron stars

    SciTech Connect

    Zavlin, V.E.; Pavlov, G.G. |; Shibanov, Yu.A.; Rogers, F.J.; Iglesias, C.A.

    1996-01-17

    We present first results of modeling convective photospheres of neutron stars. We show that in photospheres composed of the light elements convection arises only at relatively low effective temperatures ({le}3 - 5 x 10{sup 4} K), whereas in the case of iron composition it arises at T{sub eff}{le} 3 x 10{sup 5}K. Convection changes the depth dependence of the photosphere temperature and the shapes of the emergent spectra. Thus, it should be taken into account for the proper interpretation of EUV/soft-X-ray observations of the thermal radiation from neutron stars.

  2. Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars

    NASA Technical Reports Server (NTRS)

    Starrfield, S. G.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

    1981-01-01

    A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to evolve thermonuclear runaways in the accreted hydrogen rich envelopes of 1.0 Msub solar neutron stars with radii of 10 km and 20 km. Simulations produce outbursts which last from about 750 seconds to about one week. Peak effective temeratures and luninosities were 26 million K and 80 thousand Lsub solar for the 10 km study and 5.3 millison and 600 Lsub solar for the 20 km study. Hydrodynamic expansion on the 10 km neutron star produced a precursor lasting about one ten thousandth seconds.

  3. Evolutions of eccentric binary neutron stars with improved initial data

    NASA Astrophysics Data System (ADS)

    Johnson-McDaniel, Nathan; Moldenhauer, Niclas; Markakis, Charalampos; Brgmann, Bernd; Tichy, Wolfgang

    2014-03-01

    We describe the first evolutions of eccentric binary neutron stars using initial data constructed with a new method that solves the Einstein constraints and Euler equation self-consistently, which previously had only been done in the quasicircular case. We show that these data indeed lead to considerable improvement in the initial spurious oscillation of the neutron stars, compared with the superposed data used in previous evolutions. We also consider the convergence of the constraints, the gravitational wave signal (including the tidally induced oscillations), and the properties of the final remnant and ejecta, again comparing the evolutions of the new data with those of the old, superposed data.

  4. On the spreading layer emission in luminous accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Revnivtsev, Mikhail G.; Suleimanov, Valery F.; Poutanen, Juri

    2013-09-01

    Emission of the neutron star surface potentially contains information about its size and thus of vital importance for high-energy astrophysics. In spite of the wealth of data on the emission of luminous accreting neutron stars, the emission of their surfaces is hard to disentangle from their time-averaged spectra. A recent X-ray transient source XTE J1701-462 has provided a unique data set covering the largest ever observed luminosity range for a single source and showing type I (thermonuclear) X-ray bursts. In this paper, we extract the spectrum of the neutron star surface (more specifically, the spectrum of the boundary layer between the inner part of the accretion disc and the neutron star surface) with the help of maximally spectral model-independent method. We show compelling evidences that the energy spectrum of the boundary layer stays virtually the same over factor of 20 variations of the source luminosity. It is rather wide and cannot be described by a single-temperature blackbody spectrum, probably because of the inhomogeneity of the boundary layer and a spread in the colour temperature. The observed maximum colour temperature of the boundary/spreading layer emission of kT ≈ 2.4-2.6 keV is very close to the maximum observed colour temperature in the photospheric radius expansion X-ray bursts, which is set by the limiting Eddington flux at the neutron star surface. The observed stability of the boundary layer spectrum and its maximum colour temperature strongly supports theoretical models of the boundary/spreading layers on surfaces of luminous accreting neutron stars, which assume the presence of a region emitting at the local Eddington limit. Variations in the luminosity in that case lead to changes in the size of this region, but affect less the spectral shape. Elaboration of this model will provide solid theoretical grounds for measurements of the neutron star sizes using the emission of the boundary/spreading layers of luminous accreting neutron stars.

  5. Observing quantum vacuum lensing in a neutron star binary system.

    PubMed

    Dupays, Arnaud; Robilliard, Ccile; Rizzo, Carlo; Bignami, Giovanni F

    2005-04-29

    In this Letter we study the propagation of light in the neighborhood of magnetized neutron stars. Because of the optical properties of quantum vacuum in the presence of a magnetic field, the light emitted by background astronomical objects is deviated, giving rise to a phenomenon of the same kind as the gravitational one. We give a quantitative estimation of this effect, and we discuss the possibility of its observation. We show that this effect could be detected by monitoring the evolution of the recently discovered double neutron star system J0737-3039. PMID:15904205

  6. The Many Faces - and Phases - of Neutron Stars

    SciTech Connect

    Piekarewicz, J.

    2007-10-26

    Understanding the equation of state (EOS) of nuclear matter is a central goal of nuclear physics that cuts across a variety of disciplines. Indeed, the limits of nuclear existence, the collision of heavy ions, the structure of neutron stars, and the dynamics of core-collapse supernova, all depend critically on the equation of state of hadronic matter. In this contribution I will concentrate on the EOS of cold baryonic matter with special emphasis on its impact on the structure and dynamics of neutron stars. In particular, I will discuss the many fascinating phases that one encounters as one travels from the low-density crust to the high-density core.

  7. Gravitational radiation from dual neutron star elliptical binaries

    NASA Technical Reports Server (NTRS)

    Hils, Dieter

    1991-01-01

    General expressions are derived for the gravitational radiation incident on earth due to elliptical binary systems in the Galaxy. These results are applied to dual neutron star elliptical binaries. Calculations show that eccentric dual neutron star binaries lead to a moderate increase in gravitational flux density compared with circular systems for frequencies above approximately 0.0001 Hz. Tables of various quantities such as average gravitational luminosity, number of sources per unit bandwidth, energy spectral flux density, and gravitational wave strain density are given.

  8. GRAVITATIONAL WAVES AND THE MAXIMUM SPIN FREQUENCY OF NEUTRON STARS

    SciTech Connect

    Patruno, Alessandro; Haskell, Brynmor; D'Angelo, Caroline

    2012-02-10

    In this paper, we re-examine the idea that gravitational waves are required as a braking mechanism to explain the observed maximum spin frequency of neutron stars. We show that for millisecond X-ray pulsars, the existence of spin equilibrium as set by the disk/magnetosphere interaction is sufficient to explain the observations. We show as well that no clear correlation exists between the neutron star magnetic field B and the X-ray outburst luminosity L{sub X} when considering an enlarged sample size of millisecond X-ray pulsars.

  9. Hydrogen molecules and chains in a magnetic neutron star atmosphere.

    NASA Astrophysics Data System (ADS)

    Dong, Lai; Salpeter, E. E.; Shapiro, S. L.

    The authors study the electronic structures of different forms of hydrogen in a typical superstrong magnetic field (B ≡ 1012G) found on the surface of a neutron star, including atoms, poly-molecules Hn (n = 2,3,4,...), molecular ions (H+2) and negative ions (H-). They also consider the excitations of H2 molecules. They estimate the equilibrium abundances of different forms of H in a neutron star atmosphere and find that H atoms and molecules will be present if the atmosphere is cool (Teff ≡ 105-106K).

  10. Decoupling of superfluid and normal modes in pulsating neutron stars

    SciTech Connect

    Gusakov, Mikhail E.; Kantor, Elena M.

    2011-04-15

    We show that equations governing pulsations of superfluid neutron stars can be split into two sets of weakly coupled equations, one describing the superfluid modes and another one, the normal modes. The coupling parameter s is small, |s|{approx}0.01-0.05, for realistic equations of state. Already an approximation s=0 is sufficient to calculate the pulsation spectrum within the accuracy of a few percent. Our results indicate, in particular, that emission of gravitational waves from superfluid pulsation modes is suppressed in comparison to that from normal modes. The proposed approach allows to drastically simplify modeling of pulsations of superfluid neutron stars.

  11. Inertial modes in stratified rotating neutron stars: An evolutionary description

    NASA Astrophysics Data System (ADS)

    Villain, L.; Bonazzola, S.; Haensel, P.

    2005-04-01

    With (nonbarotropic) equations of state valid even when the neutron, proton, and electron content of neutron star cores is not in beta equilibrium, we study inertial and composition gravity modes of relativistic rotating neutron stars. We solve the relativistic Euler equations in the time domain with a three dimensional numerical code based on spectral methods, in the slow rotation, relativistic Cowling and anelastic approximations. Principally, after a short description of the gravity modes due to smooth composition gradients, we focus our analysis on the question of how the inertial modes are affected by nonbarotropicity of the nuclear matter. In our study, the deviation with respect to barotropicity results from the frozen composition of nonsuperfluid matter composed of neutrons, protons, and electrons, when beta equilibrium is broken by millisecond oscillations. We show that already for moderately fast rotating stars the increasing coupling between polar and axial modes makes those two cases less different than for very slowly rotating stars. In addition, as we directly solve the Euler equations, without coupling only a few number of spherical harmonics, we always find, for the models that we use, a discrete spectrum for the l=m=2 inertial mode. Finally, we conclude that, for nonbarotropic stars, the frequency of this mode, which is our main focus, decreases in a non-negligible way, whereas the time dependence of the energy transfer between polar and axial modes is substantially different due to the existence of low-frequencies gravity modes.

  12. X-Ray Emission from Pulsars and Neutron Stars

    NASA Astrophysics Data System (ADS)

    Becker, Werner

    The idea of neutron stars can be traced back to the early 1930s, when Subrahmanyan Chandrasekhar discovered that there is no way for a collapsed stellar core with a mass more than 1.4 times the solar mass, M, to hold itself up against gravity once its nuclear fuel is exhausted. This implies that a star left with M 1.4 M (the Chandrasekhar limit) would keep collapsing and eventually disappear from view.

  13. Probing the internal composition of neutron stars with gravitational waves

    NASA Astrophysics Data System (ADS)

    Chatziioannou, Katerina; Yagi, Kent; Klein, Antoine; Cornish, Neil; Yunes, Nicols

    2015-11-01

    Gravitational waves from neutron star binary inspirals contain information about the as yet unknown equation of state of supranuclear matter. In the absence of definitive experimental evidence that determines the correct equation of state, a number of diverse models that give the pressure inside a neutron star as function of its density have been constructed by nuclear physicists. These models differ not only in the approximations and techniques they employ to solve the many-body Schrdinger equation, but also in the internal neutron star composition they assume. We study whether gravitational wave observations of neutron star binaries in quasicircular inspirals up to contact will allow us to distinguish between equations of state of differing internal composition, thereby providing important information about the properties and behavior of extremely high density matter. We carry out a Bayesian model selection analysis, and find that second generation gravitational wave detectors can heavily constrain equations of state that contain only quark matter, but hybrid stars containing both normal and quark matter are typically harder to distinguish from normal matter stars. A gravitational wave detection with a signal-to-noise ratio of 20 and masses around 1.4 M? would provide indications of the existence or absence of strange quark stars, while a signal-to-noise ratio 30 detection could either detect or rule out strange quark stars with a 20 to 1 confidence. The presence of kaon condensates or hyperons in neutron star inner cores cannot be easily confirmed. For example, for the equations of state studied in this paper, even a gravitational wave signal with a signal-to-noise ratio as high as 60 would not allow us to claim a detection of kaon condensates or hyperons with confidence greater than 5 to 1. On the other hand, if kaon condensates and hyperons do not form in neutron stars, a gravitational wave signal with similar signal-to-noise ratio would be able to constrain their existence with an 11 to 1 confidence for high-mass systems. We, finally, find that combining multiple lower signal-to-noise ratio detections (stacking) must be handled with caution since it could fail in cases where the prior information dominates over new information from the data.

  14. Extreme neutron stars from Extended Theories of Gravity

    SciTech Connect

    Astashenok, Artyom V.; Capozziello, Salvatore; Odintsov, Sergei D. E-mail: capozziello@na.infn.it

    2015-01-01

    We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M{sub ☉} can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρ{sub c} ∼ 1.5–2.0 GeV/fm{sup 3}) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 10{sup 18} G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.

  15. The galactic population of binaries containing neutron stars

    NASA Astrophysics Data System (ADS)

    Pfahl, Eric D.

    2002-11-01

    The research presented herein is a theoretical investigation of the formation, evolution, and ultimate fate of low-, intermediate-, and high-mass X-ray binaries (L/I/HMXBs). The primary theoretical tool used throughout is binary population synthesis. Results of these calculations are used to account for the numbers and properties of observed X-ray binaries and their descendants, as well as to direct future observational and theoretical work. Combining binary population synthesis and binary stellar evolution calculations, I present a systematic population study of L/IMXBs in the Galactic plane. Since full stellar evolution calculations are used to model the X- ray binary phase, it is possible to make detailed comparisons between the theoretical models and observations. It is demonstrated quantitatively that IMXBs probably play a crucial role in shaping the population of LMXBs observed at the current epoch, as well as their descendant binary millisecond radio pulsars. Recently, a new class of HMXBs has emerged, distinguished from other HMXBs by their wide, nearly circular orbits. I show that the discovery of a significant number of such systems is at odds with the conventional wisdom that most neutron stars receive very large kick speeds at birth. This problem may be rectified in a self- consistent way if the kick speed depends on the rotation rate of the pre-collapse core, which I propose is strongly influenced by the evolution of the neutron-star progenitor in a binary system. The reasonable suggestion that certain globular clusters contain nearly 1000 neutron stars conflicts with the large mean kick speeds estimated from observations of isolated radio pulsars, which are 5 to 10 times the present cluster escape speeds. Therefore, most neutron stars born from single progenitors should have been ejected from their host clusters. I show that many more neutron stars are retained if a significant fraction are formed with massive stellar companions, but that the retained fraction is still too small to account for the inferred large numbers of neutron stars at the current epoch. Several alternative hypotheses are discussed, including the intriguing possibility that globular clusters we see today were ten times more massive in the distant past. The Chandra X-ray Observatory has revealed hundreds of previously undetected point sources in a small field about the Galactic center. I show that the majority of these sources may be neutron stars accreting from the winds of unevolved companion stars. Infrared observations are proposed to search for the stellar counterparts of the X-ray sources. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.)

  16. Gamma-burst emission from neutron-star accretion

    NASA Technical Reports Server (NTRS)

    Colgate, S. A.; Petschek, A. G.; Sarracino, R.

    1983-01-01

    A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge separation is required to drag electrons into the star with the nuclei against the flux of photons leaking out through the accreting matter. The photon number is not increased substantially by Bremsstrahlung or any other process. It is suggested that instability in an accretion disc might provide the infalling matter required.

  17. Perturbative approach to the structure of rapidly rotating neutron stars

    SciTech Connect

    Benhar, Omar; Ferrari, Valeria; Gualtieri, Leonardo; Marassi, Stefania

    2005-08-15

    We construct models of rotating stars using the perturbative approach introduced by J. Hartle in 1967, and a set of equations of state proposed to model hadronic interactions in the inner core of neutron stars. We integrate the equations of stellar structure to third order in the angular velocity and show, comparing our results to those obtained with fully nonlinear codes, to what extent third order corrections are needed to accurately reproduce the moment of inertia of a star which rotates at rates comparable to that of the fastest isolated pulsars.

  18. Evolution of Proto-Neutron Stars with Quarks

    SciTech Connect

    Pons, Jose A.; Steiner, Andrew W.; Prakash, Madappa; Lattimer, James M.

    2001-06-04

    Neutrino fluxes from proto-neutron stars with and without quarks are studied. Observable differences become apparent after 10{endash}20s of evolution. Sufficiently massive stars containing negatively charged, strongly interacting, particles collapse to black holes during the first minute of evolution. Since the neutrino flux vanishes when a black hole forms, this is the most obvious signal that quarks (or other types of strange matter) have appeared. The metastability time scales for stars with quarks are intermediate between those containing hyperons and kaon condensates.

  19. Dark matter, neutron stars, and strange quark matter.

    PubMed

    Perez-Garcia, M Angeles; Silk, Joseph; Stone, Jirina R

    2010-10-01

    We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos. PMID:21230823

  20. Role of Nucleonic Fermi Surface Depletion in Neutron Star Cooling

    NASA Astrophysics Data System (ADS)

    Dong, J. M.; Lombardo, U.; Zhang, H. F.; Zuo, W.

    2016-01-01

    The Fermi surface depletion of beta-stable nuclear matter is calculated to study its effects on several physical properties that determine the neutron star (NS) thermal evolution. The neutron and proton Z factors measuring the corresponding Fermi surface depletions are calculated within the Brueckner-Hartree-Fock approach, employing the AV18 two-body force supplemented by a microscopic three-body force. Neutrino emissivity, heat capacity, and in particular neutron 3PF2 superfluidity, turn out to be reduced, especially at high baryonic density, to such an extent that the cooling rates of young NSs are significantly slowed.

  1. Neutron Star Population Dynamics. I. Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Cordes, J. M.; Chernoff, David F.

    1997-06-01

    We study the field millisecond pulsar (MSP) population to infer its intrinsic distribution in spin period and luminosity and to determine its spatial distribution within the Galaxy. Our likelihood analysis on data from extant surveys (22 pulsars with periods less than 20 ms) accounts for the following important selection effects: (1) the survey sensitivity as a function of direction, spin period, and sky coverage; (2) interstellar scintillation, which modulates the pulsed flux and causes a net increase in search volume of ~30% and (3) errors in the pulsar distance scale. Adopting power-law models (with cutoffs) for the intrinsic distributions, the analysis yields a minimum-period cutoff Pmin > 0.65 ms (99% confidence), a period distribution proportional to P-2.0+/-0.33, and a pseudoluminosity distribution proportional to L-2.0+/-0.2p (where Lp is the product of the flux density and the square of the distance, for Lp >= 1.1 mJy kpc2). We find that the column density of MSPs (uncorrected for beaming effects) is ~50+30-20 kpc-2 in the vicinity of the solar system. For a Gaussian model, the z scale height is 0.65+0.16-0.12 kpc, corresponding to the local number density 29+17-11 kpc-3. (For an exponential model, the scale height becomes 0.50+0.19-0.13 kpc, and the number density 44+25-16 kpc-3.) Estimates of the total number of MSPs in the disk of the Galaxy and for the associated birthrate are given. The contribution of a diffuse halo-like component (tracing the Galactic spheroid, the halo, or the globular cluster density profile) to the local number density of MSPs is limited to <~1% of the midplane value. We consider a kinematic model for the MSP spatial distribution in which objects in the disk are kicked once at birth and then orbit in a smooth Galactic potential, becoming dynamically well-mixed. The analysis yields a column density 49+27-17 kpc-2 (comparable to the above), a birth z kick velocity 52+17-11 km s-1, and a three-dimensional velocity dispersion of ~84 km s-1. MSP velocities are smaller than those of young, long-period pulsars by about a factor of 5. The kinematic properties of the MSP population are discussed, including expected transverse motions, the occurrence of asymmetric drift, the shape of the velocity ellipsoid, and the z scale height at birth. If MSPs are long-lived, then a significant contribution to observed MSP z velocities is the result of diffusive processes that increase the scale height of old stellar populations; our best estimate of the one-dimensional velocity kick that is unique to MSP evolution is ~40 km s-1 if such diffusion is taken into account. The scale heights of millisecond pulsars and low-mass X-ray binaries are consistent, suggesting a common origin and that the primary channel for forming both classes of objects imparts only low velocities. Binaries involving a common envelope phase and a neutron star-forming supernova explosion can yield such objects, even with explosion asymmetries like those needed to provide the velocity distribution of isolated, nonspun-up radio pulsars. Future searches for MSPs may be optimized using the model results. As an example, we give the expected number of detectable MSPs per beam area and the volumes of the Galaxy sampled per beam area for a hypothetical Green Bank Telescope all sky survey. Estimates for the volume that must be surveyed to find a pulsar faster than 1.5 ms are given. We also briefly discuss how selection effects associated with fast binaries influence our results.

  2. Further stable neutron star models from f(R) gravity

    SciTech Connect

    Astashenok, Artyom V.; Capozziello, Salvatore; Odintsov, Sergei D. E-mail: capozziello@na.infn.it

    2013-12-01

    Neutron star models in perturbative f(R) gravity are considered with realistic equations of state. In particular, we consider the FPS, SLy and other equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for f(R) = R+R(e{sup −R/R{sub 0}}−1) model and for R{sup 2} models with logarithmic and cubic corrections are obtained. In the case of R{sup 2} gravity with cubic corrections, we obtain that at high central densities (ρ > 10ρ{sub ns}, where ρ{sub ns} = 2.7 × 10{sup 14} g/cm{sup 3} is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ∼ 1.9M{sub ⊙} (SLy equation). A similar situation takes place for AP4 and BSK20 EoS. Such an effect can give rise to more compact stars than in General Relativity. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level. Another interesting result can be achieved in modified gravity with only a cubic correction. For some EoS, the upper limit of neutron star mass increases and therefore these EoS can describe realistic star configurations (although, in General Relativity, these EoS are excluded by observational constraints)

  3. Post-AGB stars in the Magellanic Clouds and neutron-capture processes in AGB stars

    NASA Astrophysics Data System (ADS)

    Lugaro, M.; Campbell, S. W.; Van Winckel, H.; De Smedt, K.; Karakas, A. I.; Käppeler, F.

    2015-11-01

    Aims: We explore modifications to the current scenario for the slow neutron-capture process (the s-process) in asymptotic giant branch (AGB) stars to account for the Pb deficiency observed in post-AGB stars of low metallicity ([Fe/H] ≃-1.2) and low initial mass (≃ 1-1.5 M⊙) in the Large and Small Magellanic Clouds. Methods: We calculated the stellar evolution and nucleosynthesis for a 1.3 M⊙ star with [Fe/H] = -1.3 and tested different amounts and distributions of protons leading to the production of the main neutron source within the 13C-pocket and proton ingestion scenarios. Results: No s-process models can fully reproduce the abundance patterns observed in the post-AGB stars. When the Pb production is lowered, the abundances of the elements between Eu and Pb, such as Er, Yb, W, and Hf, are also lowered to below those observed. Conclusions: Neutron-capture processes with neutron densities intermediate between the s and the rapid neutron-capture processes may provide a solution to this problem and be a common occurrence in low-mass, low-metallicity AGB stars.

  4. Quark deconfinement in high-mass neutron stars

    NASA Astrophysics Data System (ADS)

    Orsaria, M.; Rodrigues, H.; Weber, F.; Contrera, G. A.

    2014-01-01

    In this paper, we explore whether or not quark deconfinement may occur in high-mass neutron stars such as J1614 - 2230 (1.970.04M?) and J0348 + 0432 (2.010.04M?). Our study is based on a nonlocal extension of the SU(3) Nambu-Jona-Lasinio (n3NJL) model with repulsive vector interactions among the quarks. This model goes beyond the frequently used local version of the Nambu-Jona-Lasinio (NJL) model by accounting for several key features of QCD which are not part of the local model. Confined hadronic matter is treated in the framework of nonlinear relativistic mean field theory. We find that both the local as well as the nonlocal NJL model predict the existence of extended regions of mixed quark-hadron (quark-hybrid) matter in high-mass neutron stars with masses of 2.1 to 2.4M?. Pure quark matter in the cores of neutron stars is obtained for certain parametrizations of the hadronic lagrangian and choices of the vector repulsion among quarks. The radii of high-mass neutron stars with quark-hybrid matter and/or pure quark matter cores in their centers are found to lie in the canonical range of 12 to 13 km.

  5. Very massive neutron stars in Ni's theory of gravity

    NASA Technical Reports Server (NTRS)

    Mikkelsen, D. R.

    1977-01-01

    It is shown that in Ni's theory of gravity, which is identical to general relativity in the post-Newtonian limit, neutron stars of arbitrarily large mass are possible. This result is independent, within reasonable bounds, of the equation of state of matter at supernuclear densities.

  6. Velocity-induced collapses of stable neutron stars

    NASA Astrophysics Data System (ADS)

    Novak, J.

    2001-09-01

    The collapse of spherical neutron stars is studied in General Relativity. The initial state is a stable neutron star to which an inward radial kinetic energy has been added through some velocity profile. For two different equations of state and two different shapes of velocity profiles, it is found that neutron stars can collapse to black holes for high enough inward velocities, provided that their masses are higher than some minimal value, depending on the equation of state. For a polytropic equation of state of the form p=Krho gamma, with gamma = 2 it is found to be 1.16 ( (K)/(0.1) right )0.5 Msun, whereas for a more realistic one (described in Pons et al. \\cite{PonREPL00}), it is 0.36 Msun . In some cases of collapse forming a black hole, part of the matter composing the initial neutron star can be ejected through a shock, leaving only a fraction of the initial mass to form a black hole. Therefore, black holes of very small masses can be formed and, in particular, the mass scaling relation, as a function of initial velocity, takes the form discovered by Choptuik (\\cite{Cho93}) for critical collapses.

  7. Magnetar activity mediated by plastic deformations of neutron star crust

    NASA Astrophysics Data System (ADS)

    Lyutikov, Maxim

    2015-02-01

    We advance a `solar flare' model of magnetar activity, whereas a slow evolution of the magnetic field in the upper crust, driven by electron magnetohydrodynamic flows, twists the external magnetic flux tubes, producing persistent emission, bursts, and flares. At the same time, the neutron star crust plastically relieves the imposed magnetic field stress, limiting the strain ɛt to values well below the critical strain ɛcrit of a brittle fracture, ɛt ˜ 10-2ɛcrit. Magnetar-like behaviour, occurring near the magnetic equator, takes place in all neutron stars, but to a different extent. The persistent luminosity is proportional to cubic power of the magnetic field (at a given age), and hence is hardly observable in most rotationally powered neutron stars. Giant flares can occur only if the magnetic field exceeds some threshold value, while smaller bursts and flares may take place in relatively small magnetic fields. Bursts and flares are magnetospheric reconnection events that launch Alfvén shocks which convert into high-frequency whistlers upon hitting the neutron star surface. The resulting whistler pulse induces a strain that increases with depth both due to the increasing electron density (and the resulting slowing of the waves), and due to the increasing coherence of a whistler pulse with depth. The whistler pulse is dissipated on a time-scale of approximately a day at shallow depths corresponding to ρ ˜ 1010 g cm-3; this energy is detected as enhanced post-flare surface emission.

  8. Testing general metric theories of gravity with bursting neutron stars

    SciTech Connect

    Psaltis, Dimitrios

    2008-03-15

    I show that several observable properties of bursting neutron stars in metric theories of gravity can be calculated using only conservation laws, Killing symmetries, and the Einstein equivalence principle, without requiring the validity of the general relativistic field equations. I calculate, in particular, the gravitational redshift of a surface atomic line, the touchdown luminosity of a radius-expansion burst, which is believed to be equal to the Eddington critical luminosity, and the apparent surface area of a neutron star as measured during the cooling tails of bursts. I show that, for a general metric theory of gravity, the apparent surface area of a neutron star depends on the coordinate radius of the stellar surface and on its gravitational redshift in the exact same way as in general relativity. On the other hand, the Eddington critical luminosity depends also on an additional parameter that measures the degree to which the general relativistic field equations are satisfied. These results can be used in conjunction with current and future high-energy observations of bursting neutron stars to test general relativity in the strong-field regime.

  9. Successive X-ray bursts from accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Taam, Ronald E.; Woosley, S. E.; Weaver, T. A.; Lamb, D. Q.

    1993-01-01

    The evolution of a neutron star undergoing a series of thermonuclear flashes in its accreted hydrogen-rich layer has been numerically followed to determine the effects of the history of the neutron star's thermal and compositional structure on the properties of the emitted X-ray bursts. Burst characteristics are studied for a range of mass accretion rates, CNO abundances in the accreted matter, and initial thermal states of the underlying neutron star core; the bursts exhibit erratic behavior for low CNO metal abundances and cool neutron star cores, with the burst recurrence time scales varying by 1-2 orders of magnitude. There is typically a continued presence of a substantial amount of unburnt hydrogen in the accreted layer throughout the series of the X-ray burst events. Convective mixing during the quiescent phase leads to the inward transport of helium to high densities and eventually to the initiation of the next outburst. The resulting bursts can be weak and, in such cases, are characterized by short recurrence time scales (1-2 hr), low peak luminosities (0.1-0.2 times the Eddington value), and low alpha-values (about 20).

  10. Gamma-ray bursts from neutron star mergers

    NASA Technical Reports Server (NTRS)

    Piran, Tsvi

    1993-01-01

    Binary neutron stars merger (NS(sup 2)M) at cosmological distances is probably the only gamma-ray bursts model based on an independently observed phenomenon which is known to be taking place at a comparable rate. We describe this model, its predictions and some open questions.

  11. Neutron stars in a class of nonlinear relativistic models

    NASA Astrophysics Data System (ADS)

    Taurines, A. R.; Vasconcellos, C. A.; Malheiro, M.; Chiapparini, M.

    2001-06-01

    In this work we introduce a class of relativistic models for nuclear matter and neutron stars which exhibits a parametrization, through mathematical constants, of the nonlinear meson-baryon couplings. For appropriate choices of the parameters, it recovers current quantum hadrodynamics models found in the literature: the Walecka model and Zimanyi-Moszkowski models (ZM and ZM3). For other choices of parameters, the models give very interesting and new physical results. The phenomenology of neutron stars in ZM models is presented and compared to the phenomenology obtained in other versions of the Walecka model. We have found that the ZM3 model is too soft, and predicts a very small maximum neutron star mass, ~0.72Msolar. A strong similarity between the results of ZM-like models and those with exponential couplings is noted. The sensibility of the results to the specific choice of the values for the binding energy and saturation density is pointed out. Finally, we discuss the very intense scalar condensates found in the interior of neutron stars, which may lead to negative effective masses.

  12. Dense Matter in the Crust of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Yao, C. C.; Cheng, K. S.

    1996-05-01

    With the relativistic extended Thomas-Fermi method, we study the dense matter in the inner crust of neutron stars based on the Zimanyi & Moszkowski (1990, ZM) model in the relativistic mean field theory. We also compare these results with those based on the Boguta & Bodmer (1977, BB) model with a resent satisfactory parameter set.

  13. Old isolated neutron stars - Fire burns and cauldron bubbles

    NASA Astrophysics Data System (ADS)

    Treves, A.; Colpi, M.; Lipunov, V. M.

    1993-03-01

    Isolated magnetic neutron stars are considered at the end of the phase of coherent pulsar emission when accretion from the interstellar medium becomes important but rotation affects the inflow dynamics. When the centrifugal acceleration at the Alfven radius exceeds the gravitational one, a process of piling up of matter is expected to take place, yielding the compression of the magnetospheric boundary. Prompt matter infall to the neutron star surface occurs when the gravitational energy density has increased with time to overcome the centrifugal barrier. Recurrence times are estimated, and it is suggested that the aging neutron star can undergo accretion with intermittent or quasi-cycling behavior when passing from the isolated radio pulsar phase to quiescent steady accretion over the life time of the Galaxy. An analogous process of build up of the magnetodipole energy is envisaged and it is proposed that a relativistic jet may form. Although on energetic scales much more modest, the picture has some resemblance to the cauldron model of SS 433. The consequences for the detectability of old isolated neutron stars are briefly discussed.

  14. Constraints on perturbative f(R) gravity via neutron stars

    SciTech Connect

    Arapoğlu, Savaş; Ekşi, K. Yavuz; Deliduman, Cemsinan E-mail: cemsinan@msgsu.edu.tr

    2011-07-01

    We study the structure of neutron stars in perturbative f(R) gravity models with realistic equations of state. We obtain mass-radius relations in a gravity model of the form f(R) = R+αR{sup 2}. We find that deviations from the results of general relativity, comparable to the variations due to using different equations of state (EoS'), are induced for |α| ∼ 10{sup 9} cm{sup 2}. Some of the soft EoS' that are excluded within the framework of general relativity can be reconciled with the 2 solar mass neutron star recently observed for certain values of α within this range. For some of the EoS' we find that a new solution branch, which allows highly massive neutron stars, exists for values of α greater than a few 10{sup 9} cm{sup 2}. We find constraints on α for a variety of EoS' using the recent observational constraints on the mass-radius relation. These are all 5 orders of magnitude smaller than the recent constraint obtained via Gravity Probe B for this gravity model. The associated length scale √(alpha)approx 10{sup 5} cm is only an order of magnitude smaller than the typical radius of a neutron star, the probe used in this test. This implies that real deviations from general relativity can be even smaller.

  15. Many-particle theory of nuclear systems with application to neutron star matter

    NASA Technical Reports Server (NTRS)

    Chakkalakal, D. A.; Yang, C. H.

    1974-01-01

    The energy-density relation was calculated for pure neutron matter in the density range relevant for neutron stars, using four different hard-core potentials. Calculations are also presented of the properties of the superfluid state of the neutron component, along with the superconducting state of the proton component and the effects of polarization in neutron star matter.

  16. Extended quark mean-field model for neutron stars

    NASA Astrophysics Data System (ADS)

    Hu, J. N.; Li, A.; Toki, H.; Zuo, W.

    2014-02-01

    We extend the quark mean-field (QMF) model to strangeness freedom to study the properties of hyperons (? ,?,?) in infinite baryon matter and neutron star properties. The baryon-scalar meson couplings in the QMF model are determined self-consistently from the quark level, where the quark confinement is taken into account in terms of a scalar-vector harmonic oscillator potential. The strength of such confinement potential for u ,d quarks is constrained by the properties of finite nuclei, while that for an s quark is limited by the properties of nuclei with a ? hyperon. These two strengths are not the same, which represents the SU(3) symmetry breaking effectively in the QMF model. Also, we use an enhanced ? coupling with the vector meson, and both ? and ? hyperon potentials can be properly described in the model. The effects of the SU(3) symmetry breaking on the neutron star structures are then studied. We find that the SU(3) breaking shifts the hyperon onset density earlier and makes hyperons more abundant in the star, in comparison with the results of the SU(3) symmetry case. However, it has little effect on the star's maximum mass. The maximum masses are found to be 1.62M? with hyperons and 1.88M? without hyperons. The present neutron star model is shown to have limitations in explaining the recently measured heavy pulsars around 2M?.

  17. Correlation energy of nuclear matter and neutron star masses

    SciTech Connect

    Trojan, Ernst; Vlasov, George V.

    2010-04-15

    We consider nuclear matter in the frames of the sigma model and find the role of correlation energy in the determination of the parameters of neutron stars. The response-function formalism is used for calculations within the Hartree-Fock approach and beyond. When electrons and muons are present in the neutron-rich matter, the maximal mass of the star is M{sub *}=1.64 (in the unit of the solar mass M{sub c}entre dot). The correlation energy becomes very important for the stars with M{sub *}approx0.7 divide 1.5M{sub c}entre dot and its effect is estimated as 0.3 divide 0.4M{sub c}entre dot extracted from the relevant values obtained in the frames of the Hartree-Fock approximation. On the whole, the nuclear equation of state is definitely 'softened'.

  18. A Theoretical Analysis of Thermal Radiation from Neutron Stars

    NASA Technical Reports Server (NTRS)

    Applegate, James H.

    1993-01-01

    As soon as it was realized that the direct URCA process is allowed by many modern nuclear equation of state, an analysis of its effect on the cooling of neutron stars was undertaken. A primary study showed that the occurrence of the direct URCA process makes the surface temperature of a neutron star suddenly drop by almost an order of magnitude when the cold wave from the core reaches the surface when the star is a few years old. The results of this study are published in Page and Applegate. As a work in progress, we are presently extending the above work. Improved expressions for the effect of nucleon pairing on the neutrino emissivity and specific heat are now available, and we have incorporated them in a recalculation of rate of the direct URCA process.

  19. Prompt merger collapse and the maximum mass of neutron stars.

    PubMed

    Bauswein, A; Baumgarte, T W; Janka, H-T

    2013-09-27

    We perform hydrodynamical simulations of neutron-star mergers for a large sample of temperature-dependent nuclear equations of state and determine the threshold mass above which the merger remnant promptly collapses to form a black hole. We find that, depending on the equation of state, the threshold mass is larger than the maximum mass of a nonrotating star in isolation by between 30 and 70 percent. Our simulations also show that the ratio between the threshold mass and maximum mass is tightly correlated with the compactness of the nonrotating maximum-mass configuration. We speculate on how this relation can be used to derive constraints on neutron-star properties from future observations. PMID:24116763

  20. Deep crustal heating in a multicomponent accreted neutron star crust

    NASA Astrophysics Data System (ADS)

    Steiner, Andrew W.

    2012-05-01

    A quasistatistical equilibrium model is constructed to simulate the multicomponent composition of the crust of an accreting neutron star. The ashes of rp-process nucleosynthesis are driven by accretion through a series of electron captures, neutron emissions, and pycnonuclear fusions up to densities near the transition between the neutron star crust and core. A liquid droplet model which includes nuclear shell effects is used to provide nuclear masses far from stability. Reaction pathways are determined consistently with the nuclear mass model. The nuclear symmetry energy is an important uncertainty in the masses of the exotic nuclei in the inner crust and varying the symmetry energy changes the amount of deep crustal heating by as much as a factor of two.

  1. Thermal evolution of neutron stars with global and local neutrality

    NASA Astrophysics Data System (ADS)

    de Carvalho, S. M.; Negreiros, R.; Rueda, Jorge A.; Ruffini, Remo

    2014-11-01

    Globally neutral neutron stars, obtained from the solution of the called Einstein-Maxwell-Thomas-Fermi equations that account for all the fundamental interactions, have been recently introduced. These configurations have a more general character than the ones obtained with the traditional Tolman-Oppenheimer-Volkoff equations, which impose the condition of local charge neutrality. The resulting configurations have a less massive and thinner crust, leading to a new mass-radius relation. Signatures of this new structure of the neutron star on the thermal evolution might be a potential test for this theory. We compute the cooling curves by integrating numerically the energy balance and transport equations in general relativity, for globally neutral neutron stars with crusts of different masses and sizes, according to this theory for different core-crust transition interfaces. We compare and contrast our study with known results for local charge neutrality. We found a new behavior for the relaxation time, depending upon the density at the base of the crust, ?crust. In particular, we find that the traditional increase of the relaxation time with the crust thickness holds only for configurations whose density of the base of the crust is greater than ?5 1013 g cm -3. The reason for this is that neutron star crusts with very thin or absent inner crust have some neutrino emission processes blocked, which keeps the crust hotter for longer times. Therefore, accurate observations of the thermal relaxation phase of neutron stars might give crucial information on the core-crust transition which may aid us in probing the inner composition and structure of these objects.

  2. Neutron star equation of state and QPO observations

    NASA Astrophysics Data System (ADS)

    Urbanec, Martin; Stuchlk, Zden?k; Trk, Gabriel; Bakala, Pavel; ?ermk, Petr

    2007-12-01

    Assuming a resonant origin of the twin peak quasiperiodic oscillations observed in the X-ray neutron star binary systems, we apply a genetic algorithm method for selection of neutron star models. It was suggested that pairs of kilohertz peaks in the X-ray Fourier power density spectra of some neutron stars reflect a non-linear resonance between two modes of accretion disk oscillations. We investigate this concept for a specific neutron star source. Each neutron star model is characterized by the equation of state (EOS), rotation frequency ? and central energy density rho_{c}. These determine the spacetime structure governing geodesic motion and position dependent radial and vertical epicyclic oscillations related to the stable circular geodesics. Particular kinds of resonances (KR) between the oscillations with epicyclic frequencies, or the frequencies derived from them, can take place at special positions assigned ambiguously to the spacetime structure. The pairs of resonant eigenfrequencies relevant to those positions are therefore fully given by KR, rho_{c}, ?, EOS and can be compared to the observationally determined pairs of eigenfrequencies in order to eliminate the unsatisfactory sets (KR, rho_{c}, ?, EOS). For the elimination we use the advanced genetic algorithm. Genetic algorithm comes out from the method of natural selection when subjects with the best adaptation to assigned conditions have most chances to survive. The chosen genetic algorithm with sexual reproduction contains one chromosome with restricted lifetime, uniform crossing and genes of type 3/3/5. For encryption of physical description (KR, rho_{c}, ?, EOS) into the chromosome we use the Gray code. As a fitness function we use correspondence between the observed and calculated pairs of eigenfrequencies.

  3. QPO observations related to neutron star equations of state

    NASA Astrophysics Data System (ADS)

    Stuchlik, Zdenek; Urbanec, Martin; Trk, Gabriel; Bakala, Pavel; Cermak, Petr

    We apply a genetic algorithm method for selection of neutron star models relating them to the resonant models of the twin peak quasiperiodic oscillations observed in the X-ray neutron star binary systems. It was suggested that pairs of kilo-hertz peaks in the X-ray Fourier power density spectra of some neutron stars reflect a non-linear resonance between two modes of accretion disk oscillations. We investigate this concept for a specific neutron star source. Each neutron star model is characterized by the equation of state (EOS), rotation frequency ? and central energy density ?c . These determine the spacetime structure governing geodesic motion and position dependent radial and vertical epicyclic oscillations related to the stable circular geodesics. Particular kinds of resonances (KR) between the oscillations with epicyclic frequencies, or the frequencies derived from them, can take place at special positions assigned ambiguously to the spacetime structure. The pairs of resonant eigenfrequencies relevant to those positions are therefore fully given by KR,?c , ?, EOS and can be compared to the observationally determined pairs of eigenfrequencies in order to eliminate the unsatisfactory sets (KR,?c , ?, EOS). For the elimination we use the advanced genetic algorithm. Genetic algorithm comes out from the method of natural selection when subjects with the best adaptation to assigned conditions have most chances to survive. The chosen genetic algorithm with sexual reproduction contains one chromosome with restricted lifetime, uniform crossing and genes of type 3/3/5. For encryption of physical description (KR,?, ?, EOS) into chromosome we used Gray code. As a fitness function we use correspondence between the observed and calculated pairs of eigenfrequencies.

  4. Gamma-ray bursts from fast, Galactic neutron stars

    SciTech Connect

    Colgate, S.A.; Leonard, P.J.T.

    1995-07-01

    What makes a Galacic model of gamma-ray bursts (GBs) feasible is the observation of a new population of objects, fast neutron stars, that are isotropic with respect to the Galaxy following a finite period, {approximately}30My, after their formation. Our Galactic model for the isotropic component of (GBs) is based upon these high-velocity neutron stars (NSs) that have accretion disks. The fast NSs are formed in tidally locked binaries, where tidal locking occurs due to the meridional circulation caused by the conservation of angular momentum of the tidal lobes. These same lobes perturb the subsequent collapse to a supernova and forming a slowly rotating NS. Following the collapse to a NS and explosion, subsequent accretion occurs on the rear side of the initially perturbed NS, resulting in a run-away acceleration of the neutron star by neutrino emission from the hot accreted matter. The recoil momentum of the relativistic neutrino emission from the localized, down flowing matter far exceeds the momentum drag of the accreted matter. The recoil of the NS may be oriented towards the companion, but misses because of the initial orbital motion. The near miss captures matter from the companion and forms a disk around the NS. Accretion onto the neutron star from this initially gaseous disk due to the ``alpha`` viscosity results initially in the soft gamma-ray repeater phase, {approximately}10{sup 4} yr. After the neutron star has moved {approximately}30 kpc from its birthplace, solid bodies form in the disk, and accrete to planetoid size bodies after {approximately}3 {times} 10{sup 7} years. Some of these planetoid bodies, with a mass of {approximately}10{sup 21to22} g, are perturbed into being captured by the magnetic field of the NS to create GBs. The high velocity and millions of years delay in forming planetoids, results in isotropy.

  5. Parity violation, the neutron radius of lead, and neutron stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, J.

    2007-06-01

    The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties in the reaction mechanism. The parity radius experiment at the Jefferson Laboratory offers an attractive electro-weak alternative to the hadronic program and promises to measure the neutron radius of 208Pb accurately and model independently via parity-violating electron scattering. In this contribution we examine the far-reaching implications that such a determination will have in areas as diverse as nuclear structure, atomic parity violation, and astrophysics.

  6. Fusion of neutron-rich oxygen isotopes in the crust of accreting neutron stars

    SciTech Connect

    Horowitz, C. J.; Dussan, H.; Berry, D. K.

    2008-04-15

    Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge Z. Nuclei with Z{<=}6 can fuse at low densities in a liquid ocean. However, nuclei with Z=8 or 10 may not burn until higher densities where the crust is solid and electron capture has made the nuclei neutron rich. We calculate the S factor for fusion reactions of neutron rich nuclei including {sup 24}O+{sup 24}O and {sup 28}Ne+{sup 28}Ne. We use a simple barrier penetration model. The S factor could be further enhanced by dynamical effects involving the neutron rich skin. This possible enhancement in S should be studied in the laboratory with neutron rich radioactive beams. We model the structure of the crust with molecular dynamics simulations. We find that the crust of accreting neutron stars may contain micro-crystals or regions of phase separation. Nevertheless, the screening factors that we determine for the enhancement of the rate of thermonuclear reactions are insensitive to these features. Finally, we calculate the rate of thermonuclear {sup 24}O+{sup 24}O fusion and find that {sup 24}O should burn at densities near 10{sup 11} g/cm{sup 3}. The energy released from this and similar reactions may be important for the temperature profile of the star.

  7. Fusion of neutron-rich oxygen isotopes in the crust of accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Horowitz, C. J.; Dussan, H.; Berry, D. K.

    2008-04-01

    Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge Z. Nuclei with Z?6 can fuse at low densities in a liquid ocean. However, nuclei with Z=8 or 10 may not burn until higher densities where the crust is solid and electron capture has made the nuclei neutron rich. We calculate the S factor for fusion reactions of neutron rich nuclei including O24+O24 and Ne28+Ne28. We use a simple barrier penetration model. The S factor could be further enhanced by dynamical effects involving the neutron rich skin. This possible enhancement in S should be studied in the laboratory with neutron rich radioactive beams. We model the structure of the crust with molecular dynamics simulations. We find that the crust of accreting neutron stars may contain micro-crystals or regions of phase separation. Nevertheless, the screening factors that we determine for the enhancement of the rate of thermonuclear reactions are insensitive to these features. Finally, we calculate the rate of thermonuclear O24+O24 fusion and find that O24 should burn at densities near 1011 g/cm3. The energy released from this and similar reactions may be important for the temperature profile of the star.

  8. The Fermi Gamma-Ray Space Telescope, Exploding Stars, Neutron Stars, and Black Holes

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2010-01-01

    Since August, 2008, the Fermi Gamma-ray Space Telescope has been scanning the sky, producing a full-sky image every three hours. These cosmic gamma-rays come from extreme astrophysical phenomena, many related to exploding stars (supernovae) or what these explosions leave behind: supernova remnants, neutron stars, and black holes. This talk uses sample Fermi results, plus simple demonstrations, to illustrate the exotic properties of these endpoints of stellar evolution.

  9. One-arm spiral instability in hypermassive neutron stars formed by dynamical-capture binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Paschalidis, Vasileios; East, William E.; Pretorius, Frans; Shapiro, Stuart L.

    2015-12-01

    Using general-relativistic hydrodynamical simulations, we show that merging binary neutron stars can form hypermassive neutrons stars that undergo the one-arm spiral instability. We study the particular case of a dynamical capture merger where the stars have a small spin, as may arise in globular clusters, and focus on an equal-mass scenario where the spins are aligned with the orbital angular momentum. We find that this instability develops when postmerger fluid vortices lead to the generation of a toroidal remnanta configuration whose maximum density occurs in a ring around the center-of-masswith high vorticity along its rotation axis. The instability quickly saturates on a time scale of 10 ms , with the m =1 azimuthal density multipole mode dominating over higher modes. The instability also leaves a characteristic imprint on the postmerger gravitational wave signal that could be detectable if the instability persists in long-lived remnants.

  10. Molecular Dynamics of Nuclear Pasta in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Briggs, Christian; da Silva Schneider, Andre

    2014-09-01

    During a core collapse supernova, a massive star undergoes rapid contraction followed by a massive explosion on the order of a hundred trillion trillion nuclear bombs in less than a second. While most matter is expelled at high speeds, what remains can form a neutron star. The bulk of a neutron star does not contain separate nuclei but is itself a single nucleus of radius ~10 km. In the crust of a neutron star, density is low enough that some matter exists as distinct nuclei arranged into crystalline lattice dominated by electromagnetic forces. Between the crust and core lies an interesting interface where matter is neither a single nucleus nor separate nuclei. It exists in a frustrated phase; competition between electromagnetic and strong nuclear forces causes exotic shapes to emerge, referred to as nuclear pasta. We use Molecular Dynamics (MD) to simulate nuclear pasta, with densities between nuclear saturation density and approximately one-tenth saturation density. Using MD particle trajectories, we compute the static structure factor S(q) and dynamical response function to describe both electron-pasta and neutrino-pasta scattering. We relate the structure and properties of nuclear pasta phases to features in S(q). Finally, one can integrate over S(q) to determine transport properties such as the electrical and thermal conductivity. This may help provide a better understanding of X-ray observations of neutron stars. During a core collapse supernova, a massive star undergoes rapid contraction followed by a massive explosion on the order of a hundred trillion trillion nuclear bombs in less than a second. While most matter is expelled at high speeds, what remains can form a neutron star. The bulk of a neutron star does not contain separate nuclei but is itself a single nucleus of radius ~10 km. In the crust of a neutron star, density is low enough that some matter exists as distinct nuclei arranged into crystalline lattice dominated by electromagnetic forces. Between the crust and core lies an interesting interface where matter is neither a single nucleus nor separate nuclei. It exists in a frustrated phase; competition between electromagnetic and strong nuclear forces causes exotic shapes to emerge, referred to as nuclear pasta. We use Molecular Dynamics (MD) to simulate nuclear pasta, with densities between nuclear saturation density and approximately one-tenth saturation density. Using MD particle trajectories, we compute the static structure factor S(q) and dynamical response function to describe both electron-pasta and neutrino-pasta scattering. We relate the structure and properties of nuclear pasta phases to features in S(q). Finally, one can integrate over S(q) to determine transport properties such as the electrical and thermal conductivity. This may help provide a better understanding of X-ray observations of neutron stars. This research was supported in part by DOE Grants DE-FG02-87ER40365 (Indiana University) and DE-SC0008808 (NUCLEI SciDAC Collaboration).

  11. Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

    NASA Technical Reports Server (NTRS)

    Lai, Dong; Shapiro, Stuart L.

    1995-01-01

    We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set of coupled ordinary differential equations for the evolution of the principal axes of the ellipsoids, the internal velocity parameters, and the binary orbital parameters. Gravitational radiation reaction and viscous dissipation are both incorporated. We set up exact initial binary equilibrium configurations and follow the transition from the quasi-static, secular decay of the orbit at large separation to the rapid dynamical evolution of the configurations just prior to contact. A hydrodynamical instability resulting from tidal interactions significantly accelerates the coalescence at small separation, leading to appreciable radial infall velocity and tidal lag angles near contact. This behavior is reflected in the gravitational waveforms and may be observable by gravitational wave detectors under construction. In cases where the neutron stars have spins which are not aligned with the orbital angular momentum, the spin-induced quadrupole moment can lead to precession of the orbital plane and therefore modulation of the gravitational wave amplitude even at large orbital radius. However, the amplitude of the modulation is small for typical neutron star binaries with spins much smaller than the orbital angular momentum.

  12. On neutron star structure and the millisecond pulsar

    NASA Technical Reports Server (NTRS)

    Harding, A. K.

    1983-01-01

    The recently discovered millisecond pulsar (PSR1937-214) is observed to be rotating close to the limit of dynamical instability for a neutron star. Despite its extremely rapid rotation, measurements of the period derivative put a stringent upper limit on the energy loss from gravitational radiation, thus requiring that the quadrupole moment be quite small. The pulsar must also be rotating below the critical frequency at which its equilibrium configuration would become non-axisymmetric, since the lifetime of this configuration against decay by gravitational radiation is very short. This critical frequency, given by the theory of rotating ellipsoids, imposes a restriction on the rotation rate more severe than the break-up frequency and may be used to set a lower limit, rho 2 x 10 to the 14th power g/cu cm, on the density of the star. If the mass is 0.5 - 1.5 solar mass, several of the stiffer neutron star equations of state may be ruled out, and the radius should be less than 16 km. The condition for axisymmetry also imposes an upper limit on the rotation rate to which neutron stars may be spun up by accretion disks in binary systems, a model recently proposed for the evolution of the millisecond pulsar.

  13. Supernova Explosions and the Birth of Neutron Stars

    SciTech Connect

    Janka, H.-Thomas; Marek, Andreas; Mueller, Bernhard; Scheck, Leonhard

    2008-02-27

    We report here on recent progress in understanding the birth conditions of neutron stars and the way how supernovae explode. More sophisticated numerical models have led to the discovery of new phenomena in the supernova core, for example a generic hydrodynamic instability of the stagnant supernova shock against low-mode nonradial deformation and the excitation of gravity-wave activity in the surface and core of the nascent neutron star. Both can have supportive or decisive influence on the inauguration of the explosion, the former by improving the conditions for energy deposition by neutrino heating in the postshock gas, the latter by supplying the developing blast with a flux of acoustic power that adds to the energy transfer by neutrinos. While recent two-dimensional models suggest that the neutrino-driven mechanism may be viable for stars from {approx}8M{sub {center_dot}} to at least 15M{sub {center_dot}}, acoustic energy input has been advocated as an alternative if neutrino heating fails. Magnetohydrodynamic effects constitute another way to trigger explosions in connection with the collapse of sufficiently rapidly rotating stellar cores, perhaps linked to the birth of magnetars. The global explosion asymmetries seen in the recent simulations offer an explanation of even the highest measured kick velocities of young neutron stars.

  14. PSR J1840-1419: A VERY COOL NEUTRON STAR

    SciTech Connect

    Keane, E. F.; Kramer, M.; McLaughlin, M. A.; Stappers, B. W.; Bassa, C. G.; Purver, M. B.; Weltevrede, P.

    2013-02-20

    We present upper limits on the X-ray emission for three neutron stars. For PSR J1840-1419, with a characteristic age of 16.5 Myr, we calculate a blackbody temperature upper limit (at 99% confidence) of kT {sup {infinity}} {sub bb} < 24{sup +17} {sub -10} eV, making this one of the coolest neutron stars known. PSRs J1814-1744 and J1847-0130 are both high magnetic field pulsars, with inferred surface dipole magnetic field strengths of 5.5 Multiplication-Sign 10{sup 13} and 9.4 Multiplication-Sign 10{sup 13} G, respectively. Our temperature upper limits for these stars are kT {sup {infinity}} {sub bb} < 123{sup +20} {sub -33} eV and kT {sup {infinity}} {sub bb} < 115{sup +16} {sub -33} eV, showing that these high magnetic field pulsars are not significantly hotter than those with lower magnetic fields. Finally, we put these limits into context by summarizing all temperature measurements and limits for rotation-driven neutron stars.

  15. Improved universality in the neutron star three-hair relations

    NASA Astrophysics Data System (ADS)

    Majumder, Barun; Yagi, Kent; Yunes, Nicols

    2015-07-01

    No-hair-like relations between the multipole moments of the exterior gravitational field of neutron stars have recently been found to be approximately independent of the star's internal structure. This approximate equation-of-state universality arises after one adimensionalizes the multipole moments appropriately, which then begs the question of whether there are better ways to adimensionalize the moments to obtain stronger universality. We here investigate this question in detail by considering slowly rotating neutron stars to quartic order in spin, an approximation that is valid for spin frequencies roughly below 500 Hz, both in the nonrelativistic limit and in full general relativity. We find that there exist normalizations that lead to stronger equation-of-state universality in the relations among the moment of inertia and the quadrupole, octopole and hexadecapole moments of neutron stars. We determine the optimal normalization that minimizes the equation-of-state dependence in these relations. The results found here may have applications in the modeling of x-ray pulses and atomic line profiles from millisecond pulsars with NICER and LOFT.

  16. HOW CAN NEWLY BORN RAPIDLY ROTATING NEUTRON STARS BECOME MAGNETARS?

    SciTech Connect

    Cheng, Quan; Yu, Yun-Wei

    2014-05-10

    In a newly born (high-temperature and Keplerian rotating) neutron star, r-mode instability can lead to stellar differential rotation, which winds the seed poloidal magnetic field (∼10{sup 11} G) to generate an ultra-high (∼10{sup 17} G) toroidal field component. Subsequently, by succumbing to the Tayler instability, the toroidal field could be partially transformed into a new poloidal field. Through such dynamo processes, the newly born neutron star with sufficiently rapid rotation could become a magnetar on a timescale of ∼10{sup 2} {sup –} {sup 3} s, with a surface dipolar magnetic field of ∼10{sup 15} G. Accompanying the field amplification, the star could spin down to a period of ∼5 ms through gravitational wave radiation due to the r-mode instability and, in particular, the non-axisymmetric stellar deformation caused by the toroidal field. This scenario provides a possible explanation for why the remnant neutron stars formed in gamma-ray bursts and superluminous supernovae could be millisecond magnetars.

  17. A NEW CODE FOR PROTO-NEUTRON STAR EVOLUTION

    SciTech Connect

    Roberts, L. F.

    2012-08-20

    A new code for following the evolution and emissions of proto-neutron stars during the first minute of their lives is developed and tested. The code is one dimensional, fully implicit, and general relativistic. Multi-group, multi-flavor neutrino transport is incorporated that makes use of variable Eddington factors obtained from a formal solution of the static general relativistic Boltzmann equation with linearized scattering terms. The timescales of neutrino emission and spectral evolution obtained using the new code are broadly consistent with previous results. Unlike other recent calculations, however, the new code predicts that the neutrino-driven wind will be characterized, at least for part of its existence, by a neutron excess. This change, potentially consequential for nucleosynthesis in the wind, is due to an improved treatment of the charged current interactions of electron-flavored neutrinos and anti-neutrinos with nucleons. A comparison is also made between the results obtained using either variable Eddington factors or simple equilibrium flux-limited diffusion. The latter approximation, which has been frequently used in previous studies of proto-neutron star cooling, accurately describes the total neutrino luminosities (to within 10%) for most of the evolution, until the proto-neutron star becomes optically thin.

  18. A new class of g-modes in neutron stars

    NASA Technical Reports Server (NTRS)

    Reisenegger, Andreas; Goldreich, Peter

    1992-01-01

    Because a neutron star is born hot, its internal composition is close to chemical equilibrium. In the fluid core, this implies that the ratio of the number densities of charged particles (protons and electrons) to neutrons is an increasing function of the mass density. This composition gradient stably stratifies the matter giving rise to a Brunt-Vaisala frequency N of about 500/s. Consequently, a neutron star core provides a cavity that supports gravity modes (g-modes). These g-modes are distinct from those previously identified with the thermal stratification of the surface layers and the chemical stratification of the crust. We compute the lowest-order, quadrupolar, g-modes for cold, Newtonian, neutron star models with M/solar M = 0.581 and M/solar M = 1.405, and show that the crustal and core g-modes have similar periods. We also discuss damping mechanisms and estimate damping rates for the core g-modes. Particular attention is paid to damping due to the emission of gravitational radiation.

  19. INVESTIGATING SUPERCONDUCTIVITY IN NEUTRON STAR INTERIORS WITH GLITCH MODELS

    SciTech Connect

    Haskell, B.; Pizzochero, P. M.; Seveso, S.

    2013-02-20

    The high-density interior of a neutron star is expected to contain superconducting protons and superfluid neutrons. Theoretical estimates suggest that the protons will form a type II superconductor in which the stellar magnetic field is carried by flux tubes. The strong interaction between the flux tubes and the neutron rotational vortices could lead to strong ''pinning'', i.e., vortex motion could be impeded. This has important implications especially for pulsar glitch models as it would lead to a large part of the vorticity of the star being decoupled from the ''normal'' component to which the electromagnetic emission is locked. In this Letter, we explore the consequences of strong pinning in the core on the ''snowplow'' model for pulsar glitches, making use of realistic equations of state and relativistic background models for the neutron star. We find that, in general, a large fraction of the pinned vorticity in the core is not compatible with observations of giant glitches in the Vela pulsar. Thus, the conclusion is that either most of the core is in a type I superconducting state or the interaction between vortices and flux tubes is weaker than previously assumed.

  20. Discovery of a Neutron Star Oscillation Mode During a Superburst

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod E.; Mahmoodifar, Simin

    2014-08-01

    Neutron stars are among the most compact objects in the universe and provide a unique laboratory for the study of cold ultra-dense matter. Asteroseismology can provide a powerful probe of the interiors of stars. For example, helioseismology has provided unprecedented insights about the interior of the Sun, but comparable capabilities for neutron star seismology have not yet been achieved. Here we report the discovery of a coherent X-ray modulation from the neutron star 4U 1636-536 during the February 22, 2001 thermonuclear superburst seen with NASA's Rossi X-ray Timing Explorer (RXTE) that is very likely a global oscillation mode. The observed frequency is 835.6440 ± 0.0002 Hz (1.43546 times the stellar spin frequency of 582.14323 Hz) and the modulation is well described by a sinusoid with an amplitude of 0.19 ± 0.04 %. The observed frequency is consistent with the expected inertial frame frequency of an m=2 rotationally-modified g-mode or perhaps an r-mode, where m is the mode's azimuthal wavenumber. Interestingly, this frequency is within 1.5 % of the candidate oscillation frequency recently identified in the accreting millisecond X-ray pulsar XTE J1751-305 assuming that the relevant mode has m=2, and the observed frequency is indeed the mode's inertial frame frequency. If this is correct, it is conceivable that the same oscillation mode is detected in both 4U 1636-536 and XTE J1751-305, but we observe the mode's inertial frame frequency in the former, and the co-rotating frame frequency in the latter. Our results provide further strong evidence that global oscillation modes can indeed produce observable modulations in the X-ray flux from neutron stars.

  1. Slowly rotating superfluid Newtonian neutron star model with entrainment

    NASA Astrophysics Data System (ADS)

    Prix, R.; Comer, G. L.; Andersson, N.

    2002-01-01

    We develop a formalism that can be used to model slowly rotating superfluid Newtonian neutron stars. A simple two-fluid model is used to describe the matter, where one fluid consists of the superfluid neutrons that are believed to exist in the inner crust and core of mature neutron stars, while the other fluid is a charge neutral conglomerate of the remaining constituents (crust nuclei, core superconducting protons, electrons, etc.). We include the entrainment effect, which is a non-dissipative interaction between the two fluids whereby a momentum induced in one of the fluids will cause part of the mass of the other fluid to be carried along. The equations that describe rotational equilibria (i.e. axisymmetric and stationary configurations) are approximated using the slow-rotation approximation; an expansion in terms of the rotation rates of the two fluids where only terms up to second-order are kept. Our formalism allows the neutrons to rotate at a rate different from that of the charged constituents. For a particular equation of state that is quadratic in the two mass-densities and relative velocities of the fluids, we find an analytic solution to the slow-rotation equations. This result provides an elegant generalisation to the two-fluid problem of the standard expressions for the one-fluid polytrope E propto rho 2. The model equation of state includes entrainment and is general enough to allow for realistic values for, say, mass and radius of the star. It also includes a mixed term in the mass densities that can be related to ``symmetry energy'' terms that appear in more realistic equations of state. We use the analytic solution to explore how relative rotation between the two fluids, the ``symmetry energy'' term, and entrainment affect the neutron star's local distribution of particles, as well as global quantities as the Kepler limit, ellipticity, and moments of inertia.

  2. Kaon condensation in proto-neutron star matter

    SciTech Connect

    Pons, Jose A.; Departament d'Astronomia i Astrofisica, Universitat de Valencia, E-46100 Burjassot, ; Reddy, Sanjay; Ellis, Paul J.; Prakash, Madappa; Lattimer, James M.

    2000-09-01

    We study the equation of state of kaon-condensed matter including the effects of temperature and trapped neutrinos. Several different field-theoretical models for the nucleon-nucleon and kaon-nucleon interactions are considered. It is found that the order of the phase transition to a kaon-condensed phase, and whether or not Gibbs' rules for phase equilibrium can be satisfied in the case of a first order transition, depend sensitively on the choice of the kaon-nucleon interaction. To avoid the anomalous high-density behavior of previous models for the kaon-nucleon interaction, a new functional form is developed. For all interactions considered, a first order phase transition is possible only for magnitudes of the kaon-nucleus optical potential (greater-or-similar sign)100 MeV. The main effect of finite temperature, for any value of the lepton fraction, is to mute the effects of a first order transition, so that the thermodynamics becomes similar to that of a second order transition. Above a critical temperature, found to be at least 30-60 MeV depending upon the interaction, the first order transition disappears. The phase boundaries in baryon density versus lepton number and baryon density versus temperature planes are delineated, which is useful in understanding the outcomes of proto-neutron star simulations. We find that the thermal effects on the maximum gravitational mass of neutron stars are as important as the effects of trapped neutrinos, in contrast to previously studied cases in which the matter contained only nucleons or in which hyperons and/or quark matter were considered. Kaon-condensed equations of state permit the existence of metastable neutron stars, because the maximum mass of an initially hot, lepton-rich proto-neutron star is greater than that of a cold, deleptonized neutron star. The large thermal effects imply that a metastable proto-neutron star's collapse to a black hole could occur much later than in previously studied cases that allow metastable configurations. (c) 2000 The American Physical Society.

  3. X-Ray Bursts from Accreting Magnetic Neutron Stars

    NASA Astrophysics Data System (ADS)

    Lamb, D. Q.; Miller, M. Coleman; Taam, R. E.

    1996-05-01

    We investigate the mass accretion rate per unit area dot ? and magnetic field strength B for which nuclear burning in the envelope of an accreting neutron star is unstable. When B=0, high dot ? leads to very high temperatures T in the neutron star envelope, due to compressional heating. This stabilizes the nuclear burning. When Bnot =0, the electron scattering cross section becomes sigma_ {e gamma } ~ (omega /omega_c )(2) sigma_T ~ 10(-2) sigma_T for all photons traveling along the magnetic field and for photons in the extraordinary mode traveling at large angles to the field with energies hbar omega << hbar omega_C . Thus a very strong magnetic field can dramatically reduce the electron scattering cross section, which is the dominant radiative opacity in the envelope, for radiation escaping outward from the accreted matter. For B < 3 x 10(12) G, the peak of the blackbody photon number spectrum for T ~ 1 x 10(8) K (a temperature typical of the neutron star envelope) lies at an energy hbar omega > hbar omega_C , and the surface magnetic field has little effect on the radiative opacity. Under these conditions, compressional heating again produces very high temperatures in the neutron star envelope, which stabilizes the nuclear burning. Consequently, we do not expect most accretion-powered pulsars to produce Type I X-ray bursts. In contrast, for B >> 3 x 10(12) G, the peak of the blackbody photon number spectrum for T ~ 1 x 10(8) K lies at an energy hbar omega << hbar omega_C for which the electron scattering opacity is dramatically reduced. The enhanced radiative energy transport prevents the neutron star envelope from reaching the very high T otherwise expected for high dot ?. Analytic calculations indicate that under these conditions hydrogen and helium burning can be highly unstable, and consequently that strongly magnetic accreting neutron stars can produce Type I X-ray bursts. MCM acknowledges the support of a Compton Fellowship.

  4. NUCLEAR CONSTRAINTS ON PROPERTIES OF NEUTRON STAR CRUSTS

    SciTech Connect

    Xu Jun; Chen Liewen; Ma Hongru; Li Baoan E-mail: hrma@sjtu.edu.cn E-mail: Bao-An_Li@tamu-commerce.edu

    2009-06-01

    The transition density {rho} {sub t} and pressure P{sub t} at the inner edge separating the liquid core from the solid crust of neutron stars are systematically studied using a modified Gogny (MDI) and 51 popular Skyrme interactions within well established dynamical and thermodynamical methods. First of all, it is shown that the widely used parabolic approximation to the full equation of state (EOS) of isospin asymmetric nuclear matter may lead to huge errors in estimating the transition density and pressure, especially for stiffer symmetry energy functionals E {sub sym}({rho}), compared to calculations using the full EOS within both the dynamical and thermodynamical methods mainly because of the energy curvatures involved. Thus, fine details of the EOS of asymmetric nuclear matter are important for locating accurately the inner edge of the neutron star crust. Second, the transition density and pressure decrease roughly linearly with increasing slope parameter L of E {sub sym}({rho}) at normal nuclear matter density using the full EOS within both the dynamical and thermodynamical methods. It is also shown that the thickness, fractional mass, and moment of inertia of the neutron star crust are all very sensitive to the parameter L through the transition density {rho} {sub t} whether one uses the full EOS or its parabolic approximation. Moreover, it is shown that E {sub sym}({rho}) constrained in the same subsaturation density range as the neutron star crust by the isospin diffusion data in heavy-ion collisions at intermediate energies limits the transition density and pressure to 0.040 fm{sup -3} {<=}{rho} {sub t} {<=} 0.065 fm{sup -3} and 0.01 MeV fm{sup -3} {<=}P{sub t} {<=} 0.26 MeV fm{sup -3}, respectively. These constrained values for the transition density and pressure are significantly lower than their fiducial values currently used in the literature. Furthermore, the mass-radius relation and several other properties closely related to the neutron star crust are studied by using the MDI interaction. It is found that the newly constrained {rho} {sub t} and P{sub t} together with the earlier estimate of {delta}I/I>0.014 for the crustal fraction of the moment of inertia of the Vela pulsar impose a more stringent constraint of R {>=} 4.7 + 4.0M/M {sub sun} km for the radius R and mass M of neutron stars compared to previous studies in the literature.

  5. Buoyancy and g-modes in young superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Passamonti, A.; Andersson, N.; Ho, W. C. G.

    2016-01-01

    We consider the local dynamics of a realistic neutron-star core, including composition gradients, superfluidity and thermal effects. The main focus is on the gravity g-modes, which are supported by composition stratification and thermal gradients. We derive the equations that govern this problem in full detail, paying particular attention to the input that needs to be provided through the equation of state and distinguishing between normal and superfluid regions. The analysis highlights a number of key issues that should be kept in mind whenever equation of state data is compiled from nuclear physics for use in neutron-star calculations. We provide explicit results for a particular stellar model and a specific nucleonic equation of state, making use of cooling simulations to show how the local wave spectrum evolves as the star ages. Our results show that the composition gradient is effectively dominated by the muons whenever they are present. When the star cools below the superfluid transition, the support for g-modes at lower densities (where there are no muons) is entirely thermal. We confirm the recent suggestion that the g-modes in this region may be unstable, but our results indicate that this instability will be weak and would only be present for a brief period of the star's life. Our analysis accounts for the presence of thermal excitations encoded in entrainment between the entropy and the superfluid component. Finally, we discuss the complete spectrum, including the normal sound waves and, in superfluid regions, the second sound.

  6. Nuclear reactions in the crust of accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Lau, Kit Yu

    There have been many discoveries from observations of accreting neutron stars in X-ray binaries. Many of the observed phenomena such as superbursts or the cooling of quasi-persistent transients during their quiescent state are affected by the thermal properties and the composition of the crust. To model the nuclear energy release and crust composition, we build up a first complete network with pycnonuclear fusion. We run a consistent nuclear reaction network that follows the evolution of an accreted fluid element from the atmosphere down to the inner crust. We take into account a majority of the most important nuclear processes including electron capture, neutron capture, neutron emissions, beta- decay, and pycnonuclear fusion reactions. The result of the model shows that there is nuclear reaction path splitting in the crust of accreting neutron stars due to the usage of finite electron capture rates. The pycnonuclear fusion reactions can occur at a shallower depth than previously thought. The composition deep inside the inner crust is mainly 40Mg, independent of the initial composition of the ashes of the outer crust. The inner crust is found to be very pure no matter what the initial abundance of the ashes is in the outer crust. The neutron drip locates at a higher density in our model. In general, the nuclear reaction path and the heat energy generation in the inner crust are significantly different from the previous work.

  7. Neutron-star formation in the carbon-detonation supernova.

    NASA Technical Reports Server (NTRS)

    Wheeler, J. C.; Buchler, J.-R.; Barkat, Z. K.

    1973-01-01

    Neutrino losses, such as those driven by the convective Urca process, may affect the evolution of stars in the mass range from 4 to 8 solar masses so as to lead to collapse of their degenerate carbon/oxygen cores. A corresponding hydrodynamic model is computed which leads to the formation of a 1.3 to 1.4 solar mass neutron star with the expulsion of a small fraction of the mass, about 0.l solar mass at about 20,000 km/sec into the overlying hydrogen envelope. This sets the stage for the Ostriker-Gunn mechanism in which Type II supernovae and pulsars are formed.

  8. Merger of a Neutron Star with a Newtonian Black Hole

    NASA Technical Reports Server (NTRS)

    Lee, William H.; Kluzniak, Wlodzimierz

    1995-01-01

    Newtonian smooth particle hydro simulations are presented of the merger of a 1.4 solar mass neutron star with a black hole of equal mass. The initial state of the system is modeled with a stiff polytrope orbiting a point mass. Dynamical instability sets in when the orbital separation is equal to about three stellar radii. The ensuing mass transfer occurs on the dynamical timescale. No accretion torus is formed. At the end of the computation a corona of large extent shrouds an apparently stable binary system of a 0.25 solar mass star orbiting a 2.3 solar mass black hole.

  9. Magnetic fields in mixed neutron-star-plus-wormhole systems

    NASA Astrophysics Data System (ADS)

    Aringazin, Ascar; Dzhunushaliev, Vladimir; Folomeev, Vladimir; Kleihaus, Burkhard; Kunz, Jutta

    2015-04-01

    We consider mixed configurations consisting of a wormhole filled by a strongly magnetized isotropic or anisotropic neutron fluid. The nontrivial topology of the spacetime is allowed by the presence of exotic matter. By comparing these configurations with ordinary magnetized neutron stars, we clarify the question of how the presence of the nontrivial topology influences the magnetic field distribution inside the fluid. In the case of an anisotropic fluid, we find new solutions describing configurations, where the maximum of the fluid density is shifted from the center. A linear stability analysis shows that these mixed configurations are unstable.

  10. Strangeness in neutron star matter: a challenging puzzle

    NASA Astrophysics Data System (ADS)

    Lonardoni, Diego; Lovato, Alessandro; Gandolfi, Stefano; Pederiva, Francesco

    2014-09-01

    The onset of strange baryons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions about the predicted maximum mass and the recent astrophysical observations are the grounds of the so called hyperon puzzle. We attempt to give our contribution to the discussion by studying the general problem of the hyperon-nucleon interaction by means of Auxiliary Field Diffusion Monte Carlo calculations. We employ a phenomenological approach showing that a three-body hyperon-nucleon force provides the strong repulsive contribution needed to correctly describe the systematics of medium-light ? hypernuclei. The same potential has been used to determine the equation of state and the mass-radius relation of an infinite systems of neutrons and ? particles. We find that the three-body hyperon-nucleon force has a dramatic effect on the equation of state and the predicted maximum mass. Our results suggest that more constraints on the nature of hyperon-neutron forces are needed before drawing any conclusion on the role played by hyperons in neutron stars. The onset of strange baryons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions about the predicted maximum mass and the recent astrophysical observations are the grounds of the so called hyperon puzzle. We attempt to give our contribution to the discussion by studying the general problem of the hyperon-nucleon interaction by means of Auxiliary Field Diffusion Monte Carlo calculations. We employ a phenomenological approach showing that a three-body hyperon-nucleon force provides the strong repulsive contribution needed to correctly describe the systematics of medium-light ? hypernuclei. The same potential has been used to determine the equation of state and the mass-radius relation of an infinite systems of neutrons and ? particles. We find that the three-body hyperon-nucleon force has a dramatic effect on the equation of state and the predicted maximum mass. Our results suggest that more constraints on the nature of hyperon-neutron forces are needed before drawing any conclusion on the role played by hyperons in neutron stars. D. Lonardoni is supported by the U.S. Department of Energy, Office of Nuclear Physics, under the NUCLEI SciDAC-3 grant.

  11. Will black hole-neutron star binary inspirals tell us about the neutron star equation of state?

    NASA Astrophysics Data System (ADS)

    Pannarale, Francesco; Rezzolla, Luciano; Ohme, Frank; Read, Jocelyn S.

    2011-11-01

    The strong tidal forces that arise during the last stages of the life of a black hole-neutron star binary may severely distort, and possibly disrupt, the star. Both phenomena will imprint signatures about the stellar structure in the emitted gravitational radiation. The information from the disruption, however, is confined to very high frequencies, where detectors are not very sensitive. We thus assess whether the lack of tidal distortion corrections in data-analysis pipelines will affect the detection of the inspiral part of the signal and whether these may yield information on the equation of state of matter at nuclear densities. Using recent post-Newtonian expressions and realistic equations of state to model these scenarios, we find that point-particle templates are sufficient for the detection of black hole-neutron star inspiralling binaries, with a loss of signals below 1% for both second- and third-generation detectors. Such detections may be able to constrain particularly stiff equations of state, but will be unable to reveal the presence of a neutron star with a soft equation of state.

  12. Properties of Neutron Stars in the Relativistic Mean-Field Theory

    NASA Astrophysics Data System (ADS)

    Cheng, K. S.; Dai, Z. G.; Yao, C. C.

    1996-06-01

    We study the properties of dense matter in neutron stars and calculate the structure of the stars based on the Zimanyi & Moszkowski (ZM) model in the relativistic mean-field theory. We also compare these results with those based on the Boguta & Bodmer (BB) model with a recent satisfactory parameter set. The two models satisfy the requirements from the observations of the masses of binary radio pulsars, the rotation frequencies of millisecond pulsars, the redshifts of the e+ annihilation lines of some ?-ray bursts if they are neutron stars, and the crustal moment of inertia of neutron stars deduced from the glitch events. Other observations may provide a way to discriminate between the two models. We suggest that the most important observational discriminant between these two models is found by observing the surface radiation of neutron stars, since the BB model leads to a large photon fraction of neutron star matter and rapid cooling of neutron stars, but the ZM model does not.

  13. Quark matter in neutron stars within the field correlator method

    NASA Astrophysics Data System (ADS)

    Plumari, S.; Burgio, G. F.; Greco, V.; Zappal, D.

    2013-10-01

    We discuss the appearance of quark matter in neutron star cores, focusing on the possibility that the recent observation of a very heavy neutron star could constrain free parameters of quark matter models. For that, we use the equation of state derived with the field correlator method, extended to the zero temperature limit, whereas for the hadronic phase we use the equation of state obtained within both the nonrelativistic and the relativistic Brueckner-Hartree-Fock many-body theory. We find a strong dependence of the maximum mass both on the value of the qq interaction V1 and on the gluon condensate G2, for which we introduce a dependence on the baryon chemical potential ?B. We find that the maximum masses are consistent with the observational limit for not too small values of V1.

  14. Tkachenko waves, glitches and precession in neutron stars

    NASA Astrophysics Data System (ADS)

    Popov, S. B.

    2008-10-01

    Here I discuss possible relations between free precession of neutron stars, Tkachenko waves inside them and glitches. I note that the proposed precession period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is consistent with the period of Tkachenko waves for the spin period 8.4 s. Based on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al. 2007), I propose a simple model, in which long period precession is powered by Tkachenko waves generated by a glitch. The period of free precession, determined by a NS oblateness, should be equal to the standing Tkachenko wave period for effective energy transfer from the standing wave to the precession motion. A similar scenario can be applicable also in the case of the PSR B1828-11.

  15. Micropulses, drifting subpulses, and nonradial oscillations of neutron stars

    NASA Astrophysics Data System (ADS)

    van Horn, H. M.

    1980-03-01

    Rotating, magnetized neutron stars can support a rich variety of oscillation modes. The periods of the modes are estimated and compared with periodicities found in the pulsars. The millisecond time scale quasi-periodic micropulsations observed in PSR 2016+28 and PSR 1133+16 can be identified as nonradial l = 0 or 1 p-mode oscillations, if mode-beating or internal noise broadening can account for the apparent rapid variability of amplitude and frequency. Torsional oscillations of the neutron star crusts have periods in the range of the pulsar subpulses; and rotational splitting of modes with l = 2, 3, or 4 can account qualitatively for subpulse drift. Long-period Alfvn modes, as well as Tkachenko oscillations, should be excited by pulsar glitches, and postglitch data may contain direct evidence of these modes.

  16. Electromagnetic and gravitational outputs from binary-neutron-star coalescence.

    PubMed

    Palenzuela, Carlos; Lehner, Luis; Ponce, Marcelo; Liebling, Steven L; Anderson, Matthew; Neilsen, David; Motl, Patrick

    2013-08-01

    The late stage of an inspiraling neutron-star binary gives rise to strong gravitational wave emission due to its highly dynamic, strong gravity. Moreover, interactions between the stellar magnetospheres can produce considerable electromagnetic radiation. We study this scenario using fully general relativistic, resistive magnetohydrodynamic simulations. We show that these interactions extract kinetic energy from the system, dissipate heat, and power radiative Poynting flux, as well as develop current sheets. Our results indicate that this power can (i) outshine pulsars in binaries, (ii) display a distinctive angular- and time-dependent pattern, and (iii) radiate within large opening angles. These properties suggest that some binary neutron-star mergers are ideal candidates for multimessenger astronomy. PMID:23971553

  17. Modeling the Complete Gravitational Wave Spectrum of Neutron Star Mergers.

    PubMed

    Bernuzzi, Sebastiano; Dietrich, Tim; Nagar, Alessandro

    2015-08-28

    In the context of neutron star mergers, we study the gravitational wave spectrum of the merger remnant using numerical relativity simulations. Postmerger spectra are characterized by a main peak frequency f2 related to the particular structure and dynamics of the remnant hot hypermassive neutron star. We show that f(2) is correlated with the tidal coupling constant κ(2)^T that characterizes the binary tidal interactions during the late-inspiral merger. The relation f(2)(κ(2)^T) depends very weakly on the binary total mass, mass ratio, equation of state, and thermal effects. This observation opens up the possibility of developing a model of the gravitational spectrum of every merger unifying the late-inspiral and postmerger descriptions. PMID:26371635

  18. Systematic parameter errors in inspiraling neutron star binaries.

    PubMed

    Favata, Marc

    2014-03-14

    The coalescence of two neutron stars is an important gravitational wave source for LIGO and other detectors. Numerous studies have considered the precision with which binary parameters (masses, spins, Love numbers) can be measured. Here I consider the accuracy with which these parameters can be determined in the presence of systematic errors due to waveform approximations. These approximations include truncation of the post-Newtonian (PN) series and neglect of neutron star (NS) spin, tidal deformation, or orbital eccentricity. All of these effects can yield systematic errors that exceed statistical errors for plausible parameter values. In particular, neglecting spin, eccentricity, or high-order PN terms causes a significant bias in the NS Love number. Tidal effects will not be measurable with PN inspiral waveforms if these systematic errors are not controlled. PMID:24679276

  19. Does SN 1987A contain a rapidly vibrating neutron star

    NASA Technical Reports Server (NTRS)

    Wang, Q.; Chen, K.; Hamilton, T. T.; Ruderman, M.; Shaham, Jacob

    1989-01-01

    If the recently reported 0.5 ms-period pulsed optical signal from the direction of Supernova 1987A originated in a young neutron star, its interpretation as a rotational period has difficulties. The surface magnetic field would have to be much lower than expected, and the high rotation rate may rule out preferred nuclear equations of state. It is pointed out here that a remnant radial vibration of a neutron star, excited in the supernova event, may survive for several years with about the observed (gravitationally redshifted) period. Heavy ions at the low-density stellar surface, periodically shocked by the vibration, may efficiently produce narrow pulses of optical cyclotron radiation in a surface field of about a trillion gauss.

  20. Neutron-Rich Nuclei and Neutron Stars: A New Accurately Calibrated Interaction for the Study of Neutron-Rich Matter

    SciTech Connect

    Todd-Rutel, B.G.; Piekarewicz, J.

    2005-09-16

    An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars. While similar in spirit to the successful NL3 parameter set, it produces an equation of state that is considerably softer--both for symmetric nuclear matter and for the symmetry energy. This softening appears to be required for an accurate description of several collective modes having different neutron-to-proton ratios. Among the predictions of this model are a symmetric nuclear-matter incompressibility of K=230 MeV and a neutron skin thickness in {sup 208}Pb of R{sub n}-R{sub p}=0.21 fm. The impact of such a softening on various neutron-star properties is also examined.

  1. Multi-messenger observations and exotic physics of neutron star oscillations

    NASA Astrophysics Data System (ADS)

    Ho, Wynn

    2015-08-01

    Neutron stars are the end-products of high mass stars. Being primarily composed of degenerate matter at supranuclear densities, the oscillation spectrum of neutron stars is determined by physics at extreme regimes. Here I discuss the detection of neutron star oscillations at X-ray energies and the potential for their detection through gravitational wave observations. I briefly describe what these observations can tell us about the fundamental physics that govern neutron stars and their various modes of oscillation, including General Relativity, the nuclear equation of state, and superfluidity.

  2. Neutron star mergers and gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Narayan, Ramesh

    1993-01-01

    Under the support of grant NAG 5-1904, we have carried out research on several topics related to gamma-ray bursts (GRB's). In our proposal, we stated that we would study three topics: (1) fireball evolution; (2) neutron star mergers; and (3) statistics of bursts. We have completed a significant amount of work in each of these areas. Resulting papers from this work are presented.

  3. Tidal Love numbers of a slowly spinning neutron star

    NASA Astrophysics Data System (ADS)

    Pani, Paolo; Gualtieri, Leonardo; Ferrari, Valeria

    2015-12-01

    By extending our recent framework to describe the tidal deformations of a spinning compact object, we compute for the first time the tidal Love numbers of a spinning neutron star to linear order in the angular momentum. The spin of the object introduces couplings between electric and magnetic distortions, and new classes of spin-induced ("rotational") tidal Love numbers emerge. We focus on stationary tidal fields, which induce axisymmetric perturbations. We present the perturbation equations for both electric-led and magnetic-led rotational Love numbers for generic multipoles and explicitly solve them for various tabulated equations of state and for a tidal field with an electric (even parity) and magnetic (odd parity) component with ℓ=2 , 3, 4. For a binary system close to the merger, various components of the tidal field become relevant. In this case we find that an octupolar magnetic tidal field can significantly modify the mass quadrupole moment of a neutron star. Preliminary estimates, assuming a spin parameter χ ≈0.05 , show modifications ≳10 % relative to the static case, at an orbital distance of five stellar radii. Furthermore, the rotational Love numbers as functions of the moment of inertia are much more sensitive to the equation of state than in the static case, where approximate universal relations at the percent level exist. For a neutron-star binary approaching the merger, we estimate that the approximate universality of the induced mass quadrupole moment deteriorates from 1% in the static case to roughly 6% when χ ≈0.05 . Our results suggest that spin-tidal couplings can introduce important corrections to the gravitational waveforms of spinning neutron-star binaries approaching the merger.

  4. Uncovering the Properties of Young Neutron Stars and Their Surroundings

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald (Technical Monitor); Slane, Patrick

    2005-01-01

    The subject grant provides funding through the NASA LTSA program. This five-year grant involves the study of young neutron stars, particularly those in supernova remnants. In the fifth year of this program, the following studies have been undertaken in support of this effort and are discussed in this report. 1) 3C 58; 2) Chandra Survey for Compact Objects in Supernova Remnants; 3) G327.1-1.1; 4) Infrared Emission from Pulsar Wind Nebulae; and Cas A.

  5. On the capture of dark matter by neutron stars

    SciTech Connect

    Güver, Tolga; Erkoca, Arif Emre; Sarcevic, Ina; Reno, Mary Hall E-mail: aeerkoca@gmail.com E-mail: ina@physics.arizona.edu

    2014-05-01

    We calculate the number of dark matter particles that a neutron star accumulates over its lifetime as it rotates around the center of a galaxy, when the dark matter particle is a self-interacting boson but does not self-annihilate. We take into account dark matter interactions with baryonic matter and the time evolution of the dark matter sphere as it collapses within the neutron star. We show that dark matter self-interactions play an important role in the rapid accumulation of dark matter in the core of the neutron star. We consider the possibility of determining an exclusion region of the parameter space for dark matter mass and dark matter interaction cross section with the nucleons as well as dark matter self-interaction cross section, based on the observation of old neutron stars. We show that for a dark matter density of 10{sup 3} GeV/cm{sup 3}and dark matter mass m{sub χ} ∼< 10 GeV, there is a potential exclusion region for dark matter interactions with nucleons that is three orders of magnitude more stringent than without self-interactions. The potential exclusion region for dark matter self-interaction cross sections is many orders of magnitude stronger than the current Bullet Cluster limit. For example, for high dark matter density regions, we find that for m{sub χ} ∼ 10 GeV when the dark matter interaction cross section with the nucleons ranges from σ{sub χn} ∼ 10{sup −52} cm{sup 2} to σ{sub χn} ∼ 10{sup −57} cm{sup 2}, the dark matter self-interaction cross section limit is σ{sub χχ} ∼< 10{sup −33} cm{sup 2}, which is about ten orders of magnitude stronger than the Bullet Cluster limit.

  6. Electric and thermal conductivities of quenched neutron star crusts

    NASA Technical Reports Server (NTRS)

    Ogata, Shuji; Ichimaru, Setsuo

    1990-01-01

    The electric and thermal conductivities in the outer crustal matter of a neutron star quenched into a solid state by cooling are estimated using a Monte Carlo simulation of freezing transition for dense plasmas. The conductivities are calculated by the precise evaluation of the scattering integrals, using the procedure of Ichimaru et al. (1983) and Iyetomi and Ichimaru (1983). The results predict the conductivities lower, by a factor of about 3, than those with the single-phonon approximation.

  7. SHATTERING FLARES DURING CLOSE ENCOUNTERS OF NEUTRON STARS

    SciTech Connect

    Tsang, David

    2013-11-10

    We demonstrate that resonant shattering flares can occur during close passages of neutron stars in eccentric or hyperbolic encounters. We provide updated estimates for the rate of close encounters of compact objects in dense stellar environments, which we find are substantially lower than given in previous works. While such occurrences are rare, we show that shattering flares can provide a strong electromagnetic counterpart to the gravitational wave bursts expected from such encounters, allowing triggered searches for these events to occur.

  8. Dragging of inertial frames inside the rotating neutron stars

    SciTech Connect

    Chakraborty, Chandrachur; Modak, Kamakshya Prasad; Bandyopadhyay, Debades E-mail: kamakshya.modak@saha.ac.in

    2014-07-20

    We derive the exact frame-dragging rate inside rotating neutron stars. This formula is applied to show that the frame-dragging rate monotonically decreases from the center to the surface of the neutron star along the pole. In the case of the frame-dragging rate along the equatorial distance, it decreases initially away from the center, becomes negligibly small well before the surface of the neutron star, rises again, and finally approaches to a small value at the surface. The appearance of a local maximum and minimum in this case is the result of the dependence of frame-dragging frequency on the distance and angle. Moving from the equator to the pole, it is observed that this local maximum and minimum in the frame-dragging rate along the equator disappear after crossing a critical angle. It is also noted that the positions of the local maximum and minimum of the frame-dragging rate along the equator depend on the rotation frequency and central energy density of a particular pulsar.

  9. Dynamical mass ejection from black hole-neutron star binaries

    NASA Astrophysics Data System (ADS)

    Kyutoku, Koutarou; Ioka, Kunihito; Okawa, Hirotada; Shibata, Masaru; Taniguchi, Keisuke

    2015-08-01

    We investigate properties of material ejected dynamically in the merger of black hole-neutron star binaries by numerical-relativity simulations. We systematically study the dependence of ejecta properties on the mass ratio of the binary, spin of the black hole, and equation of state of the neutron-star matter. Dynamical mass ejection is driven primarily by tidal torque, and the ejecta is much more anisotropic than that from binary neutron star mergers. In particular, the dynamical ejecta is concentrated around the orbital plane with a half opening angle of 10-20 and often sweeps out only a half of the plane. The ejecta mass can be as large as 0.1 M?, and the velocity is subrelativistic with 0.2 - 0.3 c for typical cases. The ratio of the ejecta mass to the bound mass (disk and fallback components) is larger, and the ejecta velocity is larger, for larger values of the binary mass ratio, i.e., for larger values of the black-hole mass. The remnant black hole-disk system receives a kick velocity of O (100 ) km s-1 due to the ejecta linear momentum, and this easily dominates the kick velocity due to gravitational radiation. Structures of postmerger material, velocity distribution of the dynamical ejecta, fallback rates, and gravitational waves are also investigated. We also discuss the effect of ejecta anisotropy on electromagnetic counterparts, specifically a macronova/kilonova and synchrotron radio emission, developing analytic models.

  10. The Neutron Star Interior Composition Explorer Mission of Opportunity

    NASA Astrophysics Data System (ADS)

    Gendreau, Keith

    2014-08-01

    The Neutron Star Interior Composition ExploreR (NICER) is an X-ray astrophysics mission of opportunity (MoO) that will reveal the inner workings of neutron stars, cosmic lighthouses that embody unique gravitational, electromagnetic, and nuclear-physics environments. NICER achieves this objective by deploying a high-heritage instrument as an attached payload on a zenith-side ExPRESS Logistics Carrier (ELC) aboard the International Space Station (ISS). NICER offers order-of-magnitude improvements in time-coherent sensitivity and timing resolution beyond the capabilities of any X-ray observatory flown to date.Through a cost-sharing opportunity between the NASA Science Mission Directorate (SMD) and NASA Space Technology Mission Directorate (STMD) NICER will also demonstrate how neutron stars can serve as deep-space navigation beacons to guide humankind out of Earth orbit, to destinations throughout the Solar System and beyond.I will overview the NICER mission, discuss our experience working with the ISS, and describe the process of forging a partnership between SMD and STMD.

  11. UNIVERSALITY IN OSCILLATION MODES OF SUPERFLUID NEUTRON STARS?

    SciTech Connect

    Wong, K. S.; Lin, L. M.; Leung, P. T.

    2009-07-10

    It has been well established that the f-mode of relativistic ordinary fluid neutron stars displays a universal scaling behavior. Here, we study whether the 'ordinary' f{sub o}- and 'superfluid' f{sub s}-modes of superfluid neutron stars also show similar universal behavior. We first consider a simple case where the neutron superfluid and normal fluid are decoupled, and with each fluid modeled by a polytropic equation of state. We find that the f{sub o}-mode obeys the same scaling laws as established for the f-mode of ordinary fluid stars. However, the oscillation frequency of the f{sub s}-mode obeys a different scaling law, which can be derived analytically from a homogenous two-fluid stellar model in Newtonian gravity. Next the coupling effect between the two fluids is studied via a parameterized model of entrainment. We find that the coupling in general breaks the universal behavior seen in the case of decoupled fluids. Based on a relativistic variational principle, an approximated expression is derived for the first-order shift of the f{sub s}-mode squared frequency due to the entrainment.

  12. MAGNETIC ENERGY PRODUCTION BY TURBULENCE IN BINARY NEUTRON STAR MERGERS

    SciTech Connect

    Zrake, Jonathan; MacFadyen, Andrew I.

    2013-06-01

    The simultaneous detection of electromagnetic and gravitational wave emission from merging neutron star binaries would greatly aid in their discovery and interpretation. By studying turbulent amplification of magnetic fields in local high-resolution simulations of neutron star merger conditions, we demonstrate that magnetar-level ({approx}> 10{sup 16} G) fields are present throughout the merger duration. We find that the small-scale turbulent dynamo converts 60% of the randomized kinetic energy into magnetic fields on a merger timescale. Since turbulent magnetic energy dissipates through reconnection events that accelerate relativistic electrons, turbulence may facilitate the conversion of orbital kinetic energy into radiation. If 10{sup -4} of the {approx}10{sup 53} erg of orbital kinetic available gets processed through reconnection and creates radiation in the 15-150 keV band, then the fluence at 200 Mpc would be 10{sup -7} erg cm{sup -2}, potentially rendering most merging neutron stars in the advanced LIGO and Virgo detection volumes detectable by Swift BAT.

  13. The Oscillations and Stability of Differentially Rotating Neutron Stars

    NASA Technical Reports Server (NTRS)

    Watts, A.

    2004-01-01

    Studies of the oscillations and stability of neutron stars are motivated by the fact that vibrating neutron stars are a promising source of gravitational waves. One important factor is the influence of differential rotation, which is likely to arise in a neutron star at times, such as the immediate aftermath of the supernova, when we expect strong vibrations. I will discuss two phenomena unique to differentially rotating systems: dynamical shear instabilities, and the existence of a co-rotation band (a frequency band in which mode pattern speed matches the local angular velocity). Using a simple model, we have found dynamical shear instabilities that arise where modes cross into the co-rotation band, if the degree of differential rotation exceeds a certain threshold. We are currently investigating whether this mechanism operates in more realistic stellar models, and whether it is responsible for the dynamical instabilities occurring at low ratios of kinetic to potential energy that have been observed by several authors. I will present the latest results of these studies. Another topic of investigation is the nature of oscillations within the co-rotation band. The band gives rise to a continuous spectrum whose collective physical perturbation exhibits complicated temporal behaviour. I will also discuss the existence of modes within the continuous spectrum that appear physically indistinguishable from the discrete modes outside the band, despite the apparently singular nature of their eigenfunctions.

  14. The hydrodynamic origin of neutron star kicks

    NASA Astrophysics Data System (ADS)

    Nordhaus, J.; Brandt, T. D.; Burrows, A.; Almgren, A.

    2012-06-01

    We present results from a suite of axisymmetric, core-collapse supernova simulations in which hydrodynamic recoil from an asymmetric explosion produces large protoneutron star (PNS) velocities. We use the adaptive mesh refinement code CASTRO to self-consistently follow core collapse, the formation of the PNS and its subsequent acceleration. We obtain recoil velocities of up to 620 km s-1 at 1 s after bounce. These velocities are consistent with the observed distribution of pulsar kicks and with PNS velocities obtained in other theoretical calculations. Our PNSs are still accelerating at several hundred km s-1 at the end of our calculations, suggesting that even the highest velocity pulsars may be explained by hydrodynamic recoil in generic, core-collapse supernovae.

  15. Symmetry energy from nuclear masses and neutron-star observations using generalised Skyrme functionals

    NASA Astrophysics Data System (ADS)

    Chamel, N.; Fantina, A. F.; Pearson, J. M.; Goriely, S.

    2016-01-01

    We study the constraints imposed by nuclear mass measurements and neutron-star observations on the symmetry energy. For this purpose, we use a family of unified equations of state of neutron-star interiors, based on generalised Skyrme functionals that were fitted to essentially all the experimental nuclear mass data while ensuring a realistic neutron-matter equation of state.

  16. Can very compact and very massive neutron stars both exist?

    NASA Astrophysics Data System (ADS)

    Drago, Alessandro; Lavagno, Andrea; Pagliara, Giuseppe

    2014-02-01

    The existence of neutron stars with masses of 2M? requires a stiff equation of state at high densities. On the other hand, the necessary appearance also at high densities of new degrees of freedom, such as hyperons and ? resonances, can lead to a strong softening of the equation of state with resulting maximum masses of 1.5M? and radii smaller than 10 km. Hints for the existence of compact stellar objects with very small radii have been found in recent statistical analyses of quiescent low-mass X-ray binaries in globular clusters. We propose an interpretation of these two apparently contradicting measurements, large masses and small radii, in terms of two separate families of compact stars: hadronic stars, whose equation of state is soft, can be very compact, while quark stars, whose equation of state is stiff, can be very massive. In this respect an early appearance of ? resonances is crucial to guarantee the stability of the branch of hadronic stars. Our proposal could be tested by measurements of radii with an error of 1 km, which is within reach of the planned Large Observatory for X-ray Timing satellite, and it would be further strengthened by the discovery of compact stars heavier than 2M?.

  17. Relativistic structure, stability, and gravitational collapse of charged neutron stars

    SciTech Connect

    Ghezzi, Cristian R.

    2005-11-15

    Charged stars have the potential of becoming charged black holes or even naked singularities. We present a set of numerical solutions of the Tolman-Oppenheimer-Volkov equations that represents spherical charged compact stars in hydrostatic equilibrium. The stellar models obtained are evolved forward in time integrating the Einstein-Maxwell field equations. We assume an equation of state of a neutron gas at zero temperature. The charge distribution is taken as being proportional to the rest mass density distribution. The set of solutions present an unstable branch, even with charge-to-mass ratios arbitrarily close to the extremum case. We perform a direct check of the stability of the solutions under strong perturbations and for different values of the charge-to-mass ratio. The stars that are in the stable branch oscillate and do not collapse, while models in the unstable branch collapse directly to form black holes. Stars with a charge greater than or equal to the extreme value explode. When a charged star is suddenly discharged, it does not necessarily collapse to form a black hole. A nonlinear effect that gives rise to the formation of a shell of matter (in supermassive stars), is negligible in the present simulations. The results are in agreement with the third law of black hole thermodynamics and with the cosmic censorship conjecture.

  18. Levitating atmospheres of Eddington-luminosity neutron stars

    NASA Astrophysics Data System (ADS)

    Wielgus, Maciek; Sądowski, Aleksander; Kluźniak, Włodek; Abramowicz, Marek; Narayan, Ramesh

    2016-03-01

    We construct models of static, spherically symmetric shells supported by the radiation flux of a luminous neutron star in the Schwarzschild metric. The atmospheres are disconnected from the star and levitate above its surface. Gas pressure and density inversion appear in the inner region of these atmospheres, which is a purely relativistic phenomenon. We account for the scattering opacity dependence on temperature green by using the Klein-Nishina formula. The relativistic M1 closure scheme for the radiation tensor provides a GR-consistent treatment of the photon flux and radiation tensor anisotropy. In this way we are able to address atmospheres of both large and moderate/low optical depths with the same set of equations. We discuss properties of the levitating atmospheres and find that they may indeed be optically thick, with the distance between star surface and the photosphere expanding as luminosity increases. These results may be relevant for the photosphereric radius expansion X-ray bursts.

  19. Galactic Center Minispiral: Interaction Modes of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Zajacek, Michal; Karas, Vladimir; Kunneriath, Devaky

    2015-06-01

    Streams of gas and dust in the inner parsec of the Galactic center form a distinct feature known as the Minispiral, which has been studied in radio waveband as well as in the infrared wavebands. A large fraction of the Minispiral gas is ionized by radiation of OB stars present in the Nuclear Star Cluster (NSC). Based on the inferred mass in the innermost parsec ( ~10^6 solar masses), over ~10^3-10^4 neutron stars should move in the sphere of gravitational influence of the SMBH. We estimate that a fraction of them propagate through the denser, ionized medium concentrated mainly along the three arms of the Minispiral. Based on the properties of the gaseous medium, we discuss different interaction regimes of magnetised neutron stars passing through this region. Moreover, we sketch expected observational effects of these regimes. The simulation results may be applied to other galactic nuclei hosting NSC, where the expected distribution of the interaction regimes is different across different galaxy types.

  20. Glitches induced by the core superfluid in a neutron star

    NASA Astrophysics Data System (ADS)

    Jahan-Miri, M.

    2002-02-01

    The long-term evolution of the relative rotation of the core superfluid in a neutron star with respect to the rest of the star, at different radial distances from the rotation axis, is determined through model calculations. The core superfluid rotates at a different rate (faster, in young pulsars), while spinning down at the same steady-state rate as the rest of the star, because of the assumed pinning between the superfluid vortices and the superconductor fluxoids. We find that the magnitude of this rotational lag changes with time and also depends on the distance from the rotation axis; the core superfluid supports an evolving pattern of differential rotation. We argue that the predicted change of the lag might occur as discrete events which could result in a sudden rise of the spin frequency of the crust of a neutron star, as is observed at glitches in radio pulsars. This new possibility for the triggering cause of glitches in radio pulsars is further supported by an estimate of the total predicted excess angular momentum reservoir of the core superfluid. The model seems also to offer resolutions for some other aspects of the observational data on glitches.

  1. Neutron stars and white dwarfs in galactic halos

    NASA Technical Reports Server (NTRS)

    Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

    1989-01-01

    The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

  2. Neutron stars and white dwarfs in galactic halos?

    NASA Technical Reports Server (NTRS)

    Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

    1990-01-01

    The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

  3. Diversity of neutron star properties at the fixed neutron-skin thickness of 208Pb

    NASA Astrophysics Data System (ADS)

    Alam, N.; Sulaksono, A.; Agrawal, B. K.

    2015-07-01

    We study the diversities in the properties of the neutron stars arising due to the different choices for the cross coupling between various mesons, which governs the density dependence of the nuclear symmetry energy in the extended relativistic mean-field (RMF) model. For this purpose, we obtain two different families of the extended RMF model corresponding to different nonlinear cross-coupling terms in the isovector part of the effective Lagrangian density. The lowest-order contributions for the ? mesons are also included. The different models within the same family yield wide variation in the value of neutron-skin thickness in the 208Pb nucleus. These models are employed to compute the neutron-star properties such as core-crust transition density, radius and red shift at canonical mass ( 1.4 M?) , tidal polarizability parameter, and threshold mass required for the enhanced cooling through the direct Urca process. Most of the neutron-star properties considered are significantly different(10-40%) for the different families of models at a smaller neutron-skin thickness (0.15 fm ) in the 208Pb nucleus.

  4. A Christmas comet falling onto a neutron star

    NASA Astrophysics Data System (ADS)

    Campana, S.

    The Sun and the planets are the main, but not the only, bodies of the Solar System. There are thousands of asteroids and several tens of comets, many of which are still unknown. They are the remnants of the planetesimals that formed at the origin of our Solar System, and they are rocky objects of different dimensions and irregular shape. Sometimes these minor bodies fall onto the Sun or onto planets, like Jupiter. Less dramatic events occur when the infalling bodies do not directly impact onto the target but are tidally disrupted. The tidal disruption of solar mass stars around supermassive black holes has been extensively studied analytically and numerically. In these events the star, as it approaches the black hole, develops into an elongated banana-shaped structure, the most tightly bound debris being at the closer end to the compact object. After completing an (few) eccentric orbit(s), these bound debris fall onto the black hole, emitting energy. Orbital precession may lead to the crossing of the debris orbits producing an accretion disk. Observationally, these events will give rise to luminous events with different temporal decays in different energy bands. Tidal break-up events occur also in planetary systems around normal stars but these events are too faint to be detected. Things change when the star is a compact object. Indeed planets have been discovered around radio pulsars, making likely the existence also of orbiting minor bodies. The direct impact of minor bodies onto neutron stars has been studied in the past and it has been envisaged as a possible (local) explanation for Gamma-Ray Bursts (GRBs), producing short-duration (˜ seconds) events. To explain the peculiarities of GRB 101225A (Christmas burst) we propose that it resulted from the tidal disruption event of a minor body around a neutron star in our Galaxy.

  5. HERSCHEL AND SPITZER OBSERVATIONS OF SLOWLY ROTATING, NEARBY ISOLATED NEUTRON STARS

    SciTech Connect

    Posselt, B.; Pavlov, G. G.; Popov, S.; Wachter, S.

    2014-11-01

    Supernova fallback disks around neutron stars have been suspected to influence the evolution of the diverse neutron star populations. Slowly rotating neutron stars are the most promising places to find such disks. Searching for the cold and warm debris of old fallback disks, we carried out Herschel PACS (70 μm, 160 mu m) and Spitzer IRAC (3.6 μm, 4.5 μm) observations of eight slowly rotating (P ≈ 3-11 s) nearby (<1 kpc) isolated neutron stars. Herschel detected 160 μm emission (>5σ) at locations consistent with the positions of the neutron stars RX J0806.4-4123 and RX J2143.0+0654. No other significant infrared emission was detected from the eight neutron stars. We estimate probabilities of 63%, 33%, and 3% that, respectively, none, one, or both Herschel PACS 160 μm detections are unrelated excess sources due to background source confusion or an interstellar cirrus. If the 160 μm emission is indeed related to cold (10-22 K) dust around the neutron stars, this dust is absorbing and re-emitting ∼10% to ∼20% of the neutron stars' X-rays. Such high efficiencies would be at least three orders of magnitude larger than the efficiencies of debris disks around nondegenerate stars. While thin dusty disks around the neutron stars can be excluded as counterparts of the 160 μm emission, dusty asteroid belts constitute a viable option.

  6. Bulk viscosity coefficients due to phonons in superfluid neutron stars

    SciTech Connect

    Manuel, Cristina; Tolos, Laura; Tarrs, Jaume E-mail: tarrus@ecm.ub.edu

    2013-07-01

    We calculate the three bulk viscosity coefficients as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state of the system. The solution of the dynamical evolution of the phonon number density allows us to calculate the bulk viscosity coefficients as function of the phonon collisional rate and the phonon dispersion law, which depends on the neutron pairing gap. Our method of computation is rather general, and could be used for different superfluid systems, provided they share the same underlying symmetries. We find that the behavior with temperature of the bulk viscosity coefficients is dominated by the contributions coming from the collinear regime of the 2?3 phonon processes. For typical star radial pulsation frequencies of ? ? 10{sup 4}s{sup ?1}, we obtain that the bulk viscosity coefficients at densities n?>4n{sub 0} are within 10% from its static value for T?<10{sup 9} K and for the case of strong neutron superfluidity in the core with a maximum value of the {sup 3}P{sub 2} gap above 1 MeV, while, otherwise, the static solution is not a valid approximation to the bulk viscosity coefficients. Compared to previous results from Urca and modified Urca reactions, we conclude that at T ? 10{sup 9}K phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars, except for n ? 2n{sub 0} when the opening of the Urca processes takes place.

  7. Advection of magnetic flux by accretion disks around neutron stars

    NASA Astrophysics Data System (ADS)

    Flores-Tulian, S.; Reisenegger, A.

    The aim of our research is to address why millisecond pulsars have relatively weak surface magnetic fields, of about 10^8 G, with a narrow spread. We propose that the accretion of plasma from the companion star fully screens the original neutron star field, but the accretion disk carries additional magnetic flux from the companion star, or itself can generate field by means of dynamo processes. For a strongly magnetized star, the field prevents the disk from approaching the star. The accretion is along the field lines and deposits the matter on the polar cap. Then, the accreted plasma flows, dragging with itself the magnetic field lines, from the pole to the equator (Payne & Melatos 2004). In a following stage, when the star becomes non-magnetic, because the field has been buried, the disk touches the star. We suggest that some effective mechanism of magnetic flux transport such as that proposed by Spruit & Uzdensky 2005 (or Bisnovatyi-Kogan & Lovelace 2007), operates and necessarily leads to a "strongly magnetized disk''. It becomes laminar because the magneto-rotational instability saturates (it is considered to be responsible for turbulence in the disk), and the magnetic difussivity is negligible. Then, the loss of angular momentum allowing the accretion is only caused by the magneto-centrifugal disk-wind (Blandford & Payne 1982). Meanwhile, the wind-driven transport of the magnetic flux by the disk re-magnetizes the star. This process continues until the Lorentz force due to the star's magnetic field forbids any further accretion of matter and magnetic flux, in the Ideal Magneto-Hydro-Dynamics approach. Additional of material can fall onto the star (but at lower rate) if some instability process sets in, allowing the diffusion of mass through the magnetic field lines (e.g the Interchange Instability, Spruit & Taam 1990). All these processes might lead to an asymptotic magnetic field of 10^8 G,as is inferred from observations. We are developing a self-consistent theoretical model to describe the above dynamical processes taking into account the interaction among the star, the strongly magnetized disk, and the disk-wind, justifying our hypothesis.

  8. Determining the nuclear equation of state from neutron-star masses and radii

    NASA Technical Reports Server (NTRS)

    Lindblom, Lee

    1992-01-01

    A method is developed for determining the nuclear equation of state directly from a knowledge of the masses and radii of neutron stars. This analysis assumes only that equilibrium neutron-star matter has the stress-energy tensor of an isotropic fluid with a barotropic equation of state, and that general relativity describes a neutron star's internal gravitational field. We present numerical examples which illustrate how well this method will determine the equation of state when the appropriate observational data become available.

  9. Short-range nucleon correlations and neutrino emission by neutron stars

    SciTech Connect

    Frankfurt, Leonid; Strikman, Mark

    2008-10-13

    We argue that significant probability of protons with momenta above their Fermi surface leads for proton concentrations p/n{>=}1/8 to the enhancement of termally excited direct and modified URCA processes within a cold neutron star, and to a nonzero probability of direct URCA processes for small proton concentrations (p/n{<=}1/8). We evaluate high momentum tails of neutron, proton and electrons distributions within a neutron star. We expect also significantly faster neutrino cooling of hyperon stars.

  10. Many-particle theory of nuclear systems with application to neutron star matter

    NASA Technical Reports Server (NTRS)

    Chakkalakal, D. A.; Yang, C.

    1973-01-01

    The research is reported concerning energy-density relation for the normal state of neutron star matter, and the effects of superfluidity and polarization on neutron star matter. Considering constraints on variation, and the theory of quantum fluids, three methods for calculating the energy-density range are presented. The effects of polarization on neutron star structure, and polarization effects on condensation and superfluid-state energy are discussed.

  11. Coalescing neutron stars - A step towards physical models. III. Improved numerics and different neutron star masses and spins

    NASA Astrophysics Data System (ADS)

    Ruffert, M.; Janka, H.-Th.

    2001-12-01

    In this paper we present a compilation of results from our most advanced neutron star merger simulations. Special aspects of these models were refered to in earlier publications (Ruffert & Janka \\cite{ruf99}; Janka et al. \\cite{jan99}), but a description of the employed numerical procedures and a more complete overview over a large number of computed models are given here. The three-dimensional hydrodynamic simulations were done with a code based on the Piecewise Parabolic Method (PPM), which solves the discretized conservation laws for mass, momentum, energy and, in addition, for the electron lepton number in an Eulerian frame of reference. Up to five levels of nested cartesian grids ensure higher numerical resolution (about 0.6 km) around the center of mass while the evolution is followed in a large computational volume (side length between 300 and 400 km). The simulations are basically Newtonian, but gravitational-wave emission and the corresponding back-reaction on the hydrodynamic flow are taken into account. The use of a physical nuclear equation of state allows us to follow the thermodynamic history of the stellar medium and to compute the energy and lepton number loss due to the emission of neutrinos. The computed models differ concerning the neutron star masses and mass ratios, the neutron star spins, the numerical resolution expressed by the cell size of the finest grid and the number of grid levels, and the calculation of the temperature from the solution of the entropy equation instead of the energy equation. The models were evaluated for the corresponding gravitational-wave and neutrino emission and the mass loss which occurs during the dynamical phase of the merging. The results can serve for comparison with smoothed particle hydrodynamics (SPH) simulations. In addition, they define a reference point for future models with a better treatment of general relativity and with improvements of the complex input physics. Our simulations show that the details of the gravitational-wave emission are still sensitive to the numerical resolution, even in our highest-quality calculations. The amount of mass which can be ejected from neutron star mergers depends strongly on the angular momentum of the system. Our results do not support the initial conditions of temperature and proton-to-nucleon ratio needed according to recent work for producing a solar r-process pattern for nuclei around and above the A~ 130 peak. The improved models confirm our previous conclusion that gamma-ray bursts are not powered by neutrino emission during the dynamical phase of the merging of two neutron stars.

  12. Self-similar Hot Accretion Flow onto a Neutron Star

    NASA Astrophysics Data System (ADS)

    Medvedev, Mikhail V.; Narayan, Ramesh

    2001-06-01

    We consider hot, two-temperature, viscous accretion onto a rotating, unmagnetized neutron star. We assume Coulomb coupling between the protons and electrons, as well as free-free cooling from the electrons. We show that the accretion flow has an extended settling region that can be described by means of two analytical self-similar solutions: a two-temperature solution that is valid in an inner zone, r<~102.5, where r is the radius in Schwarzschild units; and a one-temperature solution that is valid in an outer zone, r>~102.5. In both zones the density varies as ?~r-2 and the angular velocity as ?~r-3/2. We solve the flow equations numerically and confirm that the analytical solutions are accurate. Except for the radial velocity, all gas properties in the self-similar settling zone, such as density, angular velocity, temperature, luminosity, and angular momentum flux, are independent of the mass accretion rate; these quantities do depend sensitively on the spin of the neutron star. The angular momentum flux is outward under most conditions; therefore, the central star is nearly always spun down. The luminosity of the settling zone arises from the rotational energy that is released as the star is braked by viscosity, and the contribution from gravity is small; hence, the radiative efficiency, ?=Lacc/Mc2, is arbitrarily large at low M. For reasonable values of the gas adiabatic index ?, the Bernoulli parameter is negative; therefore, in the absence of dynamically important magnetic fields, a strong outflow or wind is not expected. The flow is also convectively stable but may be thermally unstable. The described solution is not advection dominated; however, when the spin of the star is small enough, the flow transforms smoothly to an advection-dominated branch of solution.

  13. Studies of neutron star X-ray binaries

    NASA Astrophysics Data System (ADS)

    Thompson, Thomas W. J.

    Neutron stars represent the endpoint in stellar evolution for stars with initial masses between ~3 and 8 solar masses. They are the densest non- singularities in the universe, cramming more than a solar mass of matter into a sphere with a radius of about 10 km. Such a large mass-to-radius ratio implies deep potential wells, so that when mass transfer is taking place ~10% of the rest-mass is liberated as gravitational binding energy, resulting in prodigious amounts of X-ray emission that contains valuable information on the physical characteristics in accreting binary systems. Much of my research in this dissertation focuses on the spectroscopic and timing properties of the canonical thermonuclear bursting source GS 1826-238. By measuring the relationship between the X-ray flux (which is assumed to trace the accretion rate onto the stellar surface) and the time intervals between subsequent bursts, I find that although the intervals usually decreased proportionately as the persistent flux increased, a few measurements of the flux-recurrence time relationship were significant outliers. Accompanying spectral and timing changes strongly suggest that the accretion disk extends down to smaller radial distances from the source during these atypical episodes. This result is important for understanding the nature of accretion flows around neutron stars because it indicates that accretion disks probably evaporate at some distance from the neutron star surface at lower accretion rates. I also contribute to our understanding of two newly discovered and heavily- absorbed pulsars (neutron stars with strong magnetic fields) by determining the orbital parameters of the systems through pulse timing analysis. Orbital phase- resolved spectroscopy of one source revealed evidence for an "accretion wake" trailing the pulsar through its orbit, showing that X-rays emanating from the surface can ionize the stellar wind in its vicinity. Finally, I develop an innovative application of dust scattering halos (diffuse emission surrounding X-ray sources, resulting from photons scattering from dust grains) to geometrically determine the distance and the distribution of dust along the line of sight to X-ray sources. The distance is clearly important for inferring the absolute luminosities of systems from measured fluxes, and knowledge of the distribution of dust can further understanding of the interstellar medium.

  14. EUV/soft x-ray spectra for low B neutron stars

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.; Rajagopal, Mohan; Rogers, Forrest J.; Iglesias, Carlos A.

    1995-01-01

    Recent ROSAT and EUVE detections of spin-powered neutron stars suggest that many emit 'thermal' radiation, peaking in the EUV/soft X-ray band. These data constrain the neutron stars' thermal history, but interpretation requires comparison with model atmosphere computations, since emergent spectra depend strongly on the surface composition and magnetic field. As recent opacity computations show substantial change to absorption cross sections at neutron star photospheric conditions, we report here on new model atmosphere computations employing such data. The results are compared with magnetic atmosphere models and applied to PSR J0437-4715, a low field neutron star.

  15. EUV/soft x-ray spectra for low B neutron stars

    SciTech Connect

    Romani, R.W.; Rajagopal, M.; Rogers, F.J.; Iglesias, C.A.

    1995-05-23

    Recent ROSAT and EUVE detections of spin-powered neutron stars suggest that many emit ``thermal`` radiation, peaking in the EUV/soft X-ray band. These data constrain the neutron stars` thermal history, but interpretation requires comparison with model atmosphere computations, since emergent spectra depend strongly on the surface composition and magnetic field. As recent opacity computations show substantial change to absorption cross sections at neutron star photospheric conditions, we report here on new model atmosphere computations employing such data. The results are compared with magnetic atmosphere models and applied to PSR J0437-4715, a low field neutron star.

  16. Prediction of Black Hole and Neutron Star Mesolensing Events

    NASA Astrophysics Data System (ADS)

    Harding, Alex; Di Stefano, Rosanne; Urama, Johnson; Pham, Dang

    2016-01-01

    Black holes and neutron stars are ideal gravitational lenses because they have large masses and dim optical magnitudes. Lensing induced by nearby stellar objects, typically within a few kpc, is known as mesolensing. We report on our study of the spatial paths of more than 200 compact objects with measured proper motions. We predict their close approaches on the sky to background stars whose positions and magnitudes have been drawn from the Hubble Source Catalog, and from the 2MASS and USNO-A catalogs. By plotting the paths of the stellar remnants many years into the future we make predictions on when detectable events will occur. The observations provide a way of measuring the masses of the neutron star/black hole lenses. We also investigate possible future lensing events that would be caused if the compact object is orbited by dark companions, including exoplanets. Mesolensing events may be caused by exoplanets even if the compact object is unlikely to produce its own event. Constraints can be derived for planet masses and orbits both in cases with event detections and in cases in which no detection is achieved.

  17. Hydrodynamics of black hole-neutron star coalescence

    NASA Astrophysics Data System (ADS)

    Lee, William H.

    2001-09-01

    We present a numerical study of the hydrodynamics in the final stages of inspiral in a black hole-neutron star binary, when the separation becomes comparable to the stellar radius. We use a Newtonian 3D Smooth Particle Hydrodynamics (SPH) code and model the neutron star with a stiff equation of state. The black hole is modeled as a point mass with an absorbing boundary at the Schwarzschild radius. The initial conditions correspond to irrotational binaries in equilibrium, and we follow the evolution of the system for approximately 23 ms. We find that the result of the initial interaction between the stars is an intense episode of mass transfer, and the details of the subsequent evolution depend greatly on the assumed stiffness of the equation of state. We find that an accretion disk containing a few tenths of a solar mass is formed around the black hole, and that up to 0.1 solar masses of material may be dynamically ejected from the system. Our results show that these systems are promising candidates for the production of short gamma-ray bursts.

  18. Strangeness content of neutron stars with strong ?--hyperon repulsion

    NASA Astrophysics Data System (ADS)

    Razeira, M.; Mesquita, A.; Vasconcellos, C. A. Z.; Ruffini, R.; Rueda, J. A.; Gomes, R. O.

    2014-09-01

    A new constraint on the equation of state and composition of the matter on neutron stars has been provided by the measurement of the mass 2.01 0.04 M? for PSR J0348 +0432. In this contribution we investigate the role of many-body correlations in the maximum mass of neutron stars using the effective relativistic QHD-model with parameterized couplings. The complete expression of our QHD interaction Lagrangian exhausts the whole fundamental baryon octet (n, p, ?-, ?0, ?+, ?, ?-, ?0) and includes many-body forces simulated by nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (?, ?*), vector-isoscalar (?, ?), vector-isovector (?rrho), and scalar-isovector (?). We study the behavior of the asymmetry parameter, which describes the relative neutron excess in the system as well as the behavior of the strangeness asymmetry parameter, which specifies the strangeness content in the system and is strictly connected with the appearance of a particular hyperon species in the extreme case where the ?- experiences such a strong repulsion that it does not appear at all in nuclear matter.

  19. Entrainment coefficient and effective mass for conduction neutrons in neutron star crust: simple microscopic models

    NASA Astrophysics Data System (ADS)

    Carter, Brandon; Chamel, Nicolas; Haensel, Pawel

    2005-02-01

    In the inner crust of a neutron star, at densities above the "drip" threshold, unbound "conduction" neutrons can move freely past through the ionic lattice formed by the nuclei. The relative current density ni=nvi of such conduction neutrons will be related to the corresponding mean particle momentum pi by a proportionality relation of the form ni=Kpi in terms of a physically well defined mobility coefficient K whose value in this context has not been calculated before. Using methods from ordinary solid state and nuclear physics, a simple quantum mechanical treatment based on the independent particle approximation, is used here to formulate K as the phase space integral of the relevant group velocity over the neutron Fermi surface. The result can be described as an "entrainment" that changes the ordinary neutron mass m to a macroscopic effective mass per neutron that will be givensubject to adoption of a convention specifying the precise number density n of the neutrons that are considered to be "free"by m?=n/K. The numerical evaluation of the mobility coefficient is carried out for nuclear configurations of the "lasagna" and "spaghetti" type that may be relevant at the base of the crust. Extrapolation to the middle layers of the inner crust leads to the unexpected prediction that m? will become very large compared with m.

  20. Gamma-ray bursts from colliding neutron stars

    NASA Technical Reports Server (NTRS)

    Paczynski, Bohdan

    1992-01-01

    Three distance scales to gamma-ray bursters are discussed: about 300 pc, about 2 - 50 kpc, and about 1 Gpc, corresponding to the Galactic disk, Galactic halo, and extragalactic origin. No compelling evidence is found in favor of any of them. The BATSE experiment on GRO should determine the distance scale by determining the angular distribution of very weak bursts. The rate of collisions between the neutron stars is about 0.0001/yr in our Galaxy, and about 10 exp 5/yr within the Hubble distance. The collisions are the final phases of binary orbit decay driven by gravitational radiation, and may produce gamma-ray bursts detectable at extra-galactic distances. If strange stars exist then their collisions must release about 10 exp 49 erg in gamma-rays over about 10 seconds. Such events should be detectable out to about 1 Gpc with the current instruments.

  1. Gravitational wave asteroseismology with fast rotating neutron stars

    SciTech Connect

    Gaertig, Erich; Kokkotas, Kostas D.

    2011-03-15

    We investigate damping and growth times of the quadrupolar f mode for rapidly rotating stars and a variety of different polytropic equations of state in the Cowling approximation. This is the first study of the damping/growth time of these types of oscillations for fast-rotating neutron stars in a relativistic treatment where the spacetime degrees of freedom of the perturbations are neglected. We use these frequencies and damping/growth times to create robust empirical formulae which can be used for gravitational-wave asteroseismology. The estimation of the damping/growth time is based on the quadrupole formula and our results agree very well with Newtonian ones in the appropriate limit.

  2. Realistic electrostatic potentials in a neutron star crust

    NASA Astrophysics Data System (ADS)

    Ebel, Claudio; Mishustin, Igor; Greiner, Walter

    2015-10-01

    We study the electrostatic properties of inhomogeneous nuclear matter which can be formed in the crusts of neutron stars or in supernova explosions. Such matter is represented by Wigner-Seitz cells of different geometries (spherical, cylindrical, cartesian), which contain nuclei, free neutrons and electrons under the conditions of electrical neutrality. Using the Thomas-Fermi approximation, we have solved the Poisson equation for the electrostatic potential and calculated the corresponding electron density distributions in individual cells. The calculations are done for different shapes and sizes of the cells and different average baryon densities. The electron-to-baryon fraction was fixed at 0.3. Using realistic electron distributions leads to a significant reduction in electrostatic energy and electron chemical potential.

  3. Neutron star models in frames of f (R) gravity

    SciTech Connect

    Astashenok, Artyom V.

    2009-01-01

    Neutron star models in perturbative f (R) gravity are considered with realistic equations of state. In particular, we consider the FPS and SLy equations of state. The mass-radius relations for f(R)=R+βR(e{sup -R/R₀}₋1) model and for R² models with cubic corrections are obtained. In the case of R2 gravity with cubic corrections, we obtain that at high central densities (ρ > 10 ρ{sub ns} = 2.7 × 10¹⁴ g/cm³ is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ~ 1.9M{sub ⊙}(SLy equation) or to 8.5 km with mass ~ 1.7M{sub ⊙} (FPS equation). This effect can give rise to more compact stars than in GR. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level.

  4. Strong, Weak, Electromagnetic, and Gravitational Interactions in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Rueda, Jorge A.; Ruffini, Remo

    2015-01-01

    The traditional Tolman-Oppenheimer-Volkoff (TOV) equations of NSs assume local charge neutrality and electromagnetic structure is not accounted for. We show that such an assumption is inconsistent when all known interactions in NS equilibrium equations are present, including electromagnetism. We present the new Einstein-Maxwell-Thomas-Fermi (EMTF) set of equations, which must be solved under the constraint of global, but not local, charge neutrality. We discuss new gravito-electrodynamic effects and present their implications on the mass-radius relation and observational properties of neutron stars.

  5. Magneto-rotational and thermal evolution of young neutron stars

    NASA Astrophysics Data System (ADS)

    Popov, S. B.

    2015-11-01

    After a brief review of population synthesis of close-by cooling neutron stars, I focus on the interpretation of the dichotomy of spin periods of near-by coolers. The existence of two well separated groups - short period ( 0.1-0.3 s) radio pulsars and long period ( 3-10 s) radio quiet sources, aka the Magnificent Seven, - can not easily be explained by unified models developed recently (Popov et al. 2010; Gulln et al. 2014). I speculate that the most natural solution of the problem can be in the bimodal initial magnetic-field distribution related to the existence of an additional mechanism of field generation in magnetars.

  6. Soft gamma rays from black holes versus neutron stars

    NASA Technical Reports Server (NTRS)

    Liang, Edison P.

    1992-01-01

    The recent launches of GRANAT and GRO provide unprecedented opportunities to study compact collapsed objects from their hard x ray and gamma ray emissions. The spectral range above 100 keV can now be explored with much higher sensitivity and time resolution than before. The soft gamma ray spectral data is reviewed of black holes and neutron stars, radiation, and particle energization mechanisms and potentially distinguishing gamma ray signatures. These may include soft x ray excesses versus deficiencies, thermal versus nonthermal processes, transient gamma ray bumps versus power law tails, lines, and periodicities. Some of the highest priority future observations are outlines which will shed much light on such systems.

  7. CONSTRAINTS ON NATAL KICKS IN GALACTIC DOUBLE NEUTRON STAR SYSTEMS

    SciTech Connect

    Wong, Tsing-Wai; Willems, Bart; Kalogera, Vassiliki E-mail: b-willems@northwestern.ed

    2010-10-01

    Since the discovery of the first double neutron star (DNS) system in 1975 by Hulse and Taylor, there are currently eight confirmed DNS in our galaxy. For every system, the masses of both neutron stars, the orbital semimajor axis, and eccentricity are measured, and proper motion is known for half of the systems. Using the orbital parameters and kinematic information, if available, as constraints for all systems, we investigate the immediate progenitor mass of the second-born neutron star (NS2) and the magnitude of the supernova kick it received at birth, with the primary goal to understand the core-collapse mechanism leading to neutron star formation. Compared to earlier studies, we use a novel method to address the uncertainty related to the unknown radial velocity of the observed systems. For PSR B1534+12 and PSR B1913+16, the kick magnitudes are 150-270 km s{sup -1} and 190-450 km s{sup -1} (with 95% confidence), respectively, and the progenitor masses of the NS2 are 1.3-3.4 M{sub sun} and 1.4-5.0 M{sub sun} (95%), respectively. These suggest that the NS2 was formed by an iron core-collapse supernova in both systems. For PSR J0737 - 3039, on the other hand, the kick magnitude is only 5-120 km s{sup -1} (95%), and the progenitor mass of the NS2 is 1.3-1.9 M{sub sun} (95%). Because of the relatively low progenitor mass and kick magnitude, the formation of the NS2 in PSR J0737 - 3039 is potentially connected to an electron capture supernova of a massive O-Ne-Mg white dwarf. For the remaining five Galactic DNS, the kick magnitude ranges from several tens to several hundreds of km s{sup -1}, and the progenitor mass of the NS2 can be as low as {approx}1.5 M{sub sun} or as high as {approx}8 M{sub sun}. Therefore, in these systems it is not clear which type of supernova is more likely to form the NS2.

  8. Photoneutrino reactions in a superstrong magnetoactive plasma. [neutron stars

    NASA Technical Reports Server (NTRS)

    Chou, C. K.; Fassio-Canuto, L.; Canuto, V.

    1979-01-01

    The neutrino luminosity due to the photoneutrino process in the presence of a superstrong magnetoactive electron plasma appropriate for neutron stars is computed. The results indicate that for relatively low temperatures, between 100 million and 500 million K, the energy loss rate is significantly reduced both in the low-density regime below about 10 million g/cu cm (by the magnetic field) and in the high-density regime above that value (by plasmon excitations). These effects are temperature dependent, and they are less pronounced when the temperature is in the range from 500 million to 1 billion K.

  9. Atmospheres of Quiescent Low-Mass Neutron Stars

    NASA Astrophysics Data System (ADS)

    Karpov, Platon; Medin, Zachary; Calder, Alan; Lattimer, James M.

    2016-01-01

    Observations of the neutron stars in quiescent low-mass X-ray binaries are important for determining their masses and radii which can lead to powerful constraints on the dense matter nuclear equation of state. The interpretation of these sources is complex and their spectra differ appreciably from blackbodies. Further progress hinges on reducing the uncertainties stemming from models of neutron star atmospheres. We present a suite of low-temperature neutron star atmospheres of different chemical compositions (pure H and He). Our models are constructed over a range of temperatures [log(T/1 K)=5.3, 5.6, 5.9, 6.2, 6.5] and surface gravities [log(g/1 cm/s2)=14.0, 14.2, 14.4, 14.6]. We generated model atmospheres using zcode - a radiation transfer code developed at Los Alamos National Laboratory. In order to facilitate analytic studies, we developed three-parameter fits to our models, and also compared them to diluted blackbodies in the energy range of 0.4-5 keV (CXO/MGE). From the latter, we extract color-correction factors (fc), which represent the shift of the spectra as compared to a blackbody with the same effective temperature. These diluted blackbodies are also useful for studies of photspheric expansion X-ray bursts. We provide a comparison of our models to previous calculations using the McGill Planar Hydrogen Atmosphere Code (McPHAC). These results enhance our ability to interpret thermal emission from neutron stars and to constrain the mass-radius relationship of these exotic objects.This research was supported in part by the U.S. Department of Energy under grant DE-FG02-87ER40317 and by resources at the Institute for Advanced Computational Science at Stony Brook University. This research was carried out in part under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory and supported by Contract No. DE-AC52-06NA25396.

  10. Cyclotron harmonics in opacities of isolated neutron star atmospheres

    NASA Astrophysics Data System (ADS)

    Potekhin, A. Y.

    2010-07-01

    Some X-ray dim isolated neutron stars (XDINS) and central compact objects in supernova remnants (CCO) contain absorption features in their thermal soft X-ray spectra. It has been hypothesized that this absorption may relate to periodic peaks in free-free absorption opacities, caused by either Landau quantization of electron motion in magnetic fields B ? 1011 G or analogous quantization of ion motion in magnetic fields B > 1013 G. Here, I review the physics behind cyclotron quantum harmonics in free-free photoabsorption, discuss different approximations for their calculation, and explain why the ion cyclotron harmonics (beyond the fundamental) cannot be observed.

  11. Constraints on Natal Kicks in Galactic Double Neutron Star Systems

    NASA Astrophysics Data System (ADS)

    Wong, Tsing-Wai; Willems, Bart; Kalogera, Vassiliki

    2010-10-01

    Since the discovery of the first double neutron star (DNS) system in 1975 by Hulse and Taylor, there are currently eight confirmed DNS in our galaxy. For every system, the masses of both neutron stars, the orbital semimajor axis, and eccentricity are measured, and proper motion is known for half of the systems. Using the orbital parameters and kinematic information, if available, as constraints for all systems, we investigate the immediate progenitor mass of the second-born neutron star (NS2) and the magnitude of the supernova kick it received at birth, with the primary goal to understand the core-collapse mechanism leading to neutron star formation. Compared to earlier studies, we use a novel method to address the uncertainty related to the unknown radial velocity of the observed systems. For PSR B1534+12 and PSR B1913+16, the kick magnitudes are 150-270 km s-1 and 190-450 km s-1 (with 95% confidence), respectively, and the progenitor masses of the NS2 are 1.3-3.4 M sun and 1.4-5.0 M sun (95%), respectively. These suggest that the NS2 was formed by an iron core-collapse supernova in both systems. For PSR J0737 - 3039, on the other hand, the kick magnitude is only 5-120 km s-1 (95%), and the progenitor mass of the NS2 is 1.3-1.9 M sun (95%). Because of the relatively low progenitor mass and kick magnitude, the formation of the NS2 in PSR J0737 - 3039 is potentially connected to an electron capture supernova of a massive O-Ne-Mg white dwarf. For the remaining five Galactic DNS, the kick magnitude ranges from several tens to several hundreds of km s-1, and the progenitor mass of the NS2 can be as low as ~1.5 M sun or as high as ~8 M sun. Therefore, in these systems it is not clear which type of supernova is more likely to form the NS2.

  12. Relativistic outflow from two thermonuclear shell flashes on neutron stars

    NASA Astrophysics Data System (ADS)

    in't Zand, J. J. M.; Keek, L.; Cavecchi, Y.

    2014-08-01

    We study the exceptionally short (32-43 ms) precursors of two intermediate-duration thermonuclear X-ray bursts observed with the Rossi X-ray Timing Explorer from the neutron stars in 4U 0614+09 and 2S 0918-549. They exhibit photon fluxes that surpass those at the Eddington limit later in the burst by factors of 2.6 to 3.1. We are able to explain both the short duration and the super-Eddington flux by mildly relativistic outflow velocities of 0.1c to 0.3c subsequent to the thermonuclear shell flashes on the neutron stars. These are the highest velocities ever measured from any thermonuclear flash. The precursor rise times are also exceptionally short: about 1 ms. This is inconsistent with predictions for nuclear flames spreading laterally as deflagrations and suggests detonations instead. This is the first time that a detonation is suggested for such a shallow ignition column depth (yign ? 1010 g cm-2). The detonation would possibly require a faster nuclear reaction chain, such as bypassing the ?-capture on 12C with the much faster 12C(p,?)13N(?,p)16O process previously proposed. We confirm the possibility of a detonation, albeit only in the radial direction, through the simulation of the nuclear burning with a large nuclear network and at the appropriate ignition depth, although it remains to be seen whether the Zel'dovich criterion is met. A detonation would also provide the fast flame spreading over the surface of the neutron star to allow for the short rise times. This needs to be supported by future two-dimensional calculations of flame spreading at the relevant column depth. As an alternative to the detonation scenario, we speculate on the possibility that the whole neutron star surface burns almost instantly in the auto-ignition regime. This is motivated by the presence of 150 ms precursors with 30 ms rise times in some superexpansion bursts from 4U 1820-30 at low ignition column depths of ~108 g cm-2.

  13. Quantifying Neutron Star Spins from Spiral SASI Modes

    NASA Astrophysics Data System (ADS)

    Fernandez, Rodrigo

    2011-01-01

    The stalled accretion shock in core-collapse supernovae is unstable to non-spherical perturbations. In three-dimensions, this instability can develop spiral modes that torque the nascent neutron star. I'll report work that quantifies the angular momentum redistribution caused by these modes, and the feasibility of their excitation. Maximum spin periods of the order of 60ms can be obtained out of a non-rotating progenitor. The bulk of the angular momentum redistribution occurs during the exponential growth of unstable modes, and operates through non-oscillatory torques that are second order in the peturbation amplitude.

  14. Reactions on the surface and inside of neutron stars

    NASA Astrophysics Data System (ADS)

    Rehm, K. E.

    2016-02-01

    Measurements from orbiting X-ray satellites during the last decades have provided us with a wealth of information about nuclear reactions thought to occur in the extreme, highdensity environment of neutron stars. With radioactive ion beams from first-generation facilities we have begun to study some of these processes in the laboratory. In this contribution I report on experiments performed with radioactive beams from the ATLAS accelerator at Argonne. I will discuss the nuclear physics of X-ray bursts and super-bursts, the production of in-flight radioactive beams, as well as novel detectors which are used in these experiments.

  15. Hypernuclei and the hyperon problem in neutron stars

    NASA Astrophysics Data System (ADS)

    Bedaque, Paulo F.; Steiner, Andrew W.

    2015-08-01

    The likely presence of Λ baryons in dense hadronic matter tends to soften the equation of state to an extent that the observed heaviest neutron stars are difficult to explain. We analyze this "hyperon problem" with a phenomenological approach. First, we review what can be learned about the interaction of Λ particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on nonstrange dense matter, including its uncertainties, to conclude that the interaction between Λ 's and dense matter has to become repulsive at densities below three times the nuclear saturation density.

  16. Binary-binary collisions involving main-sequence stars, white dwarfs and neutron stars in globular clusters

    SciTech Connect

    Leonard, P.J.T.; Davies, M.B.

    1993-12-31

    We consider collisions between dynamically-evolved primordial binaries consisting of main-sequence stars, white dwarfs and neutron stars in globular clusters. In our four-body binary-binary scattering experiments, we allow stars to ``stick`` if they pass close enough to each other, which leads to the formation of a wide variety of exotic objects. Most of these objects have binary companions. Also, relatively clean exchange interactions can produce binaries containing neutron stars that eventually receive material from their companions. Such systems will be observable as X-ray binaries.

  17. Stellar neutron sources and s-process in massive stars

    NASA Astrophysics Data System (ADS)

    Talwar, Rashi

    The s-process or the slow neutron capture process is a nucleosynthesis process taking place at relatively low neutron densities in stars. It runs along the valley of beta stability since the neutron capture rate is much slower compared to the beta decay rate. The s-process occurs mainly during core helium burning and shell carbon burning phase in massive stars and during thermally pulsing helium burning phase in asymptotic giant-branch stars. The potential stellar neutron source for the s-process is associated with alpha-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the build-up of22Ne neutron source during the heliumburning phase in these stars. The low energy 26Mg resonances at stellar energies below 800 keV are predicted to have a critical influence on the alpha-capture rates on 22Ne. Some of these resonances may also correspond to pronounced alpha cluster structure near the alpha-threshold. However, these resonances have remained elusive during direct alpha capture measurements owing to the high Coulomb barrier and background from cosmic rays and beam induced reactions. Hence, in the present work, alpha-inelastic scattering and alpha- transfer measurements have been performed to probe the level structure of 26Mg nucleus in order to determine the 22Ne+alpha-capture rates. Both experiments have been performed using the high-resolution Grand Raiden Spectrometer at the Research Center for Nuclear Physics (RCNP), Osaka, Japan. For the alpha-inelastic scattering measurement, a self-supporting solid 26Mg target was used and for the alpha-transfer study via the (6Li,d) reaction, 22Ne gas enclosed in a gas cell with Aramid windows was used. The reaction products were momentum analysed by the spectrometer and detected at the focal plane equipped with two multi-wire drift chambers and two plastic-scintillation detectors. The focal plane detection system provided information on the position, the angle, the time of flight and the energy of the particles enabling the reconstruction of the kinematics at the target. The focal plane energy calibration allowed for the study of 26 Mg levels from Ex = 7.69 - 12.06 MeV in the (alpha; alpha0) measurement and Ex = 7.36 - 11.32 MeV in the (6Li,d) measurement. Six levels (Ex = 10717 (9) keV , 10822 (10) keV, 10951 (21) keV, 11085 (8) keV, 11167 (8) keV and 11317 (18) keV) were observed above the alpha-threshold in the region of interest (10.61 - 11.32 MeV). The Ex = 10717 keV had a negligible contribution to the alpha-capture rates. The Ex = 10951, 11167 and 11317 keV exhibited pronounced alpha-cluster structure and hence, dominated the alpha-capture rates. The Ex = 11167 keV had the most appreciable impact on the (alpha; gamma ) rate increasing it by 2 orders of magnitude above Longland et al. [58] and Bisterzo et al. [8] rates and by a factor of 3 above NACRE [2] rate. Hence, the recommended 22Ne(alpha,n) + 22Ne(alpha; ) rates, from the present work, strongly favour the reduction of s-process over-abundances associated with massive stars as well as AGB stars of intermediate initial mass. Also, the uncertainty range corresponding to the present rates suggest the need for a more refined measurement of the associated resonance parameters.

  18. Prospects for gravitational-wave observations of neutron-star tidal disruption in neutron-star-black-hole binaries.

    PubMed

    Vallisneri, M

    2000-04-17

    For an inspiraling neutron-star-black-hole (NS-BH) binary, we estimate the gravity-wave frequency f(td) at the onset of NS tidal disruption. We model the NS as a tidally distorted, homogeneous, Newtonian ellipsoid on a circular, equatorial geodesic around a Kerr BH. We find that f(td) depends strongly on the NS radius R, and estimate that LIGO-II (ca. 2006-2008) might measure R to 15% precision at 140 Mpc ( approximately 1 event/yr under current estimates). This suggests that LIGO-II might extract valuable information about the NS equation of state from tidal-disruption waves. PMID:11019135

  19. Gravitational Waves from Fallback Accretion onto Neutron Stars

    NASA Astrophysics Data System (ADS)

    Piro, Anthony L.; Thrane, Eric

    2012-12-01

    Massive stars generally end their lives as neutron stars (NSs) or black holes (BHs), with NS formation typically occurring at the low-mass end and collapse to a BH more likely at the high-mass end. In an intermediate regime, with a mass range that depends on the uncertain details of rotation and mass loss during the star's life, an NS is initially formed, which then experiences fallback accretion and collapse to a BH. The electromagnetic consequence of such an event is not clear. Depending on the progenitor's structure, possibilities range from a long gamma-ray burst to a Type II supernova (which may or may not be jet powered) to a collapse with a weak electromagnetic signature. Gravitational waves (GWs) provide the exciting opportunity to peer through the envelope of a dying massive star and directly probe what is occurring inside. We explore whether fallback onto young NSs can be detected by ground-based interferometers. When the incoming material has sufficient angular momentum to form a disk, the accretion spins up the NS sufficiently to produce non-axisymmetric instabilities and gravitational radiation at frequencies of ~700-2400 Hz for ~30-3000 s until collapse to a BH occurs. Using a realistic excess cross-power search algorithm, we show that such events are detectable by Advanced LIGO out to ?17 Mpc. From the rate of nearby core-collapse supernovae in the past five years, we estimate that there will be ~1-2 events each year that are worth checking for fallback GWs. The observation of these unique GW signatures coincident with electromagnetic detections would identify the transient events that are associated with this channel of BH formation, while providing information about the protoneutron star progenitor.

  20. GRAVITATIONAL WAVES FROM FALLBACK ACCRETION ONTO NEUTRON STARS

    SciTech Connect

    Piro, Anthony L.

    2012-12-10

    Massive stars generally end their lives as neutron stars (NSs) or black holes (BHs), with NS formation typically occurring at the low-mass end and collapse to a BH more likely at the high-mass end. In an intermediate regime, with a mass range that depends on the uncertain details of rotation and mass loss during the star's life, an NS is initially formed, which then experiences fallback accretion and collapse to a BH. The electromagnetic consequence of such an event is not clear. Depending on the progenitor's structure, possibilities range from a long gamma-ray burst to a Type II supernova (which may or may not be jet powered) to a collapse with a weak electromagnetic signature. Gravitational waves (GWs) provide the exciting opportunity to peer through the envelope of a dying massive star and directly probe what is occurring inside. We explore whether fallback onto young NSs can be detected by ground-based interferometers. When the incoming material has sufficient angular momentum to form a disk, the accretion spins up the NS sufficiently to produce non-axisymmetric instabilities and gravitational radiation at frequencies of {approx}700-2400 Hz for {approx}30-3000 s until collapse to a BH occurs. Using a realistic excess cross-power search algorithm, we show that such events are detectable by Advanced LIGO out to Almost-Equal-To 17 Mpc. From the rate of nearby core-collapse supernovae in the past five years, we estimate that there will be {approx}1-2 events each year that are worth checking for fallback GWs. The observation of these unique GW signatures coincident with electromagnetic detections would identify the transient events that are associated with this channel of BH formation, while providing information about the protoneutron star progenitor.

  1. Ejecting the envelope of red supergiant stars with jets launched by an inspiralling neutron star

    NASA Astrophysics Data System (ADS)

    Papish, Oded; Soker, Noam; Bukay, Inbal

    2015-05-01

    We study the properties of jets launched by a neutron star (NS) spiralling inside the envelope and core of a red supergiant (RSG). We propose that Thorne-?ytkow objects (TZO) are unlikely to be formed via common envelope (CE) evolution if accretion on to the NS can exceed the Eddington rate with much of the accretion energy directed into jets that subsequently dissipate within the giant envelope. We use the jet-feedback mechanism, where energy deposited by the jets drives the ejection of the entire envelope and part of the core, and find a very strong interaction of the jets with the core material at late phases of the CE evolution. Following our results, we speculate on two rare processes that might take place in the evolution of massive stars. (1) Recent studies have claimed that the peculiar abundances of the HV2112 RSG star can be explained if this star is a TZO. We instead speculate that the rich-calcium envelope comes from a supernova (SN) explosion of a stellar companion that was only slightly more massive than HV2112, such that during its explosion HV2112 was already a giant that intercepted a relatively large fraction of the SN ejecta. (2) We raise the possibility that strong r-process nucleosynthesis, where elements with high atomic weight of A ? 130 are formed, occurs inside the jets that are launched by the NS inside the core of the RSG star.

  2. Neutron star structure and collective excitations of finite nuclei

    NASA Astrophysics Data System (ADS)

    Paar, N.; Moustakidis, Ch. C.; Marketin, T.; Vretenar, D.; Lalazissis, G. A.

    2014-07-01

    A method is introduced that establishes relations between properties of collective excitations in finite nuclei and the phase transition density nt and pressure Pt at the inner edge separating the liquid core and the solid crust of a neutron star. A theoretical framework that includes the thermodynamic method, relativistic nuclear energy density functionals, and the quasiparticle random-phase approximation is employed in a self-consistent calculation of (nt,Pt) and collective excitations in nuclei. Covariance analysis shows that properties of charge-exchange dipole transitions, isovector giant dipole and quadrupole resonances, and pygmy dipole transitions are correlated with the core-crust transition density and pressure. A set of relativistic nuclear energy density functionals, characterized by systematic variation of the density dependence of the symmetry energy of nuclear matter, is used to constrain possible values for (nt,Pt). By comparing the calculated excitation energies of giant resonances, energy-weighted pygmy dipole strength, and dipole polarizability with available data, we obtain the weighted average values: nt=0.09550.0007 fm-3 and Pt=0.590.05 MeV fm-3. This approach crucially depends on experimental results for collective excitations in nuclei and, therefore, accurate measurements are necessary to further constrain the structure of the crust of neutron stars.

  3. The neutron star interior composition explorer (NICER): mission definition

    NASA Astrophysics Data System (ADS)

    Arzoumanian, Z.; Gendreau, K. C.; Baker, C. L.; Cazeau, T.; Hestnes, P.; Kellogg, J. W.; Kenyon, S. J.; Kozon, R. P.; Liu, K.-C.; Manthripragada, S. S.; Markwardt, C. B.; Mitchell, A. L.; Mitchell, J. W.; Monroe, C. A.; Okajima, T.; Pollard, S. E.; Powers, D. F.; Savadkin, B. J.; Winternitz, L. B.; Chen, P. T.; Wright, M. R.; Foster, R.; Prigozhin, G.; Remillard, R.; Doty, J.

    2014-07-01

    Over a 10-month period during 2013 and early 2014, development of the Neutron star Interior Composition Explorer (NICER) mission [1] proceeded through Phase B, Mission Definition. An external attached payload on the International Space Station (ISS), NICER is scheduled to launch in 2016 for an 18-month baseline mission. Its prime scientific focus is an in-depth investigation of neutron stars—objects that compress up to two Solar masses into a volume the size of a city—accomplished through observations in 0.2-12 keV X-rays, the electromagnetic band into which the stars radiate significant fractions of their thermal, magnetic, and rotational energy stores. Additionally, NICER enables the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) demonstration of spacecraft navigation using pulsars as beacons. During Phase B, substantive refinements were made to the mission-level requirements, concept of operations, and payload and instrument design. Fabrication and testing of engineering-model components improved the fidelity of the anticipated scientific performance of NICER's X-ray Timing Instrument (XTI), as well as of the payload's pointing system, which enables tracking of science targets from the ISS platform. We briefly summarize advances in the mission's formulation that, together with strong programmatic performance in project management, culminated in NICER's confirmation by NASA into Phase C, Design and Development, in March 2014.

  4. Cosmological Fast Radio Bursts from Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Totani, Tomonori

    2013-10-01

    Fast radio bursts (FRBs) at cosmological distances have recently been discovered, whose duration is about milliseconds. We argue that the observed short duration is difficult to explain by giant flares of soft gamma-ray repeaters, though their event rate and energetics are consistent with FRBs. Here, we discuss binary neutron star (NS-NS) mergers as a possible origin of FRBs. The FRB rate is within the plausible range of the NS-NS merger rate and its cosmological evolution, while a large fraction of the NS-NS mergers must produce observable FRBs. A likely radiation mechanism is coherent radio emission, like radio pulsars, by magnetic braking when magnetic fields of neutron stars are synchronized to binary rotation at the time of coalescence. Magnetic fields of the standard strength ( 1012-13 G) can explain the observed FRB fluxes, if the conversion efficiency from magnetic braking energy loss to radio emission is similar to that of isolated radio pulsars. Corresponding gamma-ray emission is difficult to detect by current or past gamma-ray burst satellites. Since FRBs tell us the exact time of mergers, a correlated search would significantly improve the effective sensitivity of gravitational wave detectors.

  5. Phenomenological QCD equation of state for massive neutron stars

    NASA Astrophysics Data System (ADS)

    Kojo, Toru; Powell, Philip D.; Song, Yifan; Baym, Gordon

    2015-02-01

    We construct an equation of state for massive neutron stars based on quantum chromodynamics phenomenology. Our primary purpose is to delineate the relevant ingredients of equations of state that simultaneously have the required stiffness and satisfy constraints from thermodynamics and causality. These ingredients are (i) a repulsive density-density interaction, universal for all flavors, (ii) the color-magnetic interaction active from low to high densities, (iii) confining effects, which become increasingly important as the baryon density decreases, and (iv) nonperturbative gluons, which are not very sensitive to changes of the quark density. We use the following "3-window" description: At baryon densities below about twice normal nuclear density, 2 n0, we use the Akmal-Pandharipande-Ravenhall (APR) equation of state, and at high densities, ?(4 -7 )n0 , we use the three-flavor Nambu-Jona-Lasinio (NJL) model supplemented by vector and diquark interactions. In the transition density region, we smoothly interpolate the hadronic and quark equations of state in the chemical potential-pressure plane. Requiring that the equation of state approach APR at low densities, we find that the quark pressure in nonconfining models can be larger than the hadronic pressure, unlike in conventional equations of state. We show that consistent equations of state of stiffness sufficient to allow massive neutron stars are reasonably tightly constrained, suggesting that gluon dynamics remains nonperturbative even at baryon densities 10 n0 .

  6. Computing supernova collapse to neutron stars and black holes

    NASA Technical Reports Server (NTRS)

    Baumgarte, Thomas W.; Shapiro, Stuart L.; Teukolsky, Saul A.

    1995-01-01

    We present a new numerical code for spherical hydrodynamics in general relativity. The code can handle gravitational collapse to a neutron star or to a black hole without the appearance of singularities. Moreover, the variables and equations in the code are very similar to those appearing in traditional Lagrangian supernova codes. Any such existing code can thus be easily adapted to treat collapse where the final fate is uncertain and may be either a neutron star or a black hole. The code is based on the formulation of Hernandez & Misner, in which retarded time is used as coordinate. This prevents the computational grid from penetrating inside any black hole that may form. We present the equations and a complete finite difference scheme for the adiabatic evolution of a fluid that obeys a gamma-law equation of state. We summarize the results of several testbed calculations performed to check our code. We also give the transformation of the analytic Oppenheimer-Snyder solution for homogeneous dust collapse to our coordinate system.

  7. Mass ejection from the merger of binary neutron stars

    NASA Astrophysics Data System (ADS)

    Hotokezaka, Kenta; Kiuchi, Kenta; Kyutoku, Koutarou; Okawa, Hirotada; Sekiguchi, Yu-ichiro; Shibata, Masaru; Taniguchi, Keisuke

    2013-01-01

    Numerical-relativity simulations for the merger of binary neutron stars are performed for a variety of equations of state (EOSs) and for a plausible range of the neutron-star mass, focusing primarily on the properties of the material ejected from the system. We find that a fraction of the material is ejected as a mildly relativistic and mildly anisotropic outflow with the typical and maximum velocities 0.15-0.25c and 0.5-0.8c (where c is the speed of light), respectively, and that the total ejected rest mass is in a wide range 10-4-10-2M?, which depends strongly on the EOS, the total mass, and the mass ratio. The total kinetic energy ejected is also in a wide range between 1049 and 1051ergs. The numerical results suggest that for a binary of canonical total mass 2.7M?, the outflow could generate an electromagnetic signal observable by the planned telescopes through the production of heavy-element unstable nuclei via the r-process or through the formation of blast waves during the interaction with the interstellar matter , if the EOS and mass of the binary are favorable ones.

  8. Nuclear fusion and carbon flashes on neutron stars

    NASA Technical Reports Server (NTRS)

    Taam, R. E.; Picklum, R. E.

    1978-01-01

    This paper reports on detailed calculations of the thermal evolution of the carbon-burning shells in the envelopes of accreting neutron stars for mass-accretion rates of 1 hundred-billionth to 2 billionths of a solar mass per yr and neutron-star masses of 0.56 and 1.41 solar masses. The work of Hansen and Van Horn (1975) is extended to higher densities, and a more detailed treatment of nuclear processing in the hydrogen- and helium-burning regions is included. Results of steady-state calculations are presented, and results of time-dependent computations are examined for accretion rates of 3 ten-billionths and 1 billionth of solar mass per yr. It is found that two evolutionary sequences lead to carbon flashes and that the carbon abundance at the base of the helium shell is a strong function of accretion rate. Upper limits are placed on the accretion rates at which carbon flashes will be important.

  9. COMPOSITIONALLY DRIVEN CONVECTION IN THE OCEANS OF ACCRETING NEUTRON STARS

    SciTech Connect

    Medin, Zach; Cumming, Andrew E-mail: cumming@physics.mcgill.ca

    2011-04-01

    We discuss the effect of chemical separation as matter freezes at the base of the ocean of an accreting neutron star, and argue that the retention of light elements in the liquid acts as a source of buoyancy that drives a slow but continual mixing of the ocean, enriching it substantially in light elements, and leading to a relatively uniform composition with depth. We first consider the timescales associated with different processes that can redistribute elements in the ocean, including convection, sedimentation, crystallization, and diffusion. We then calculate the steady-state structure of the ocean of a neutron star for an illustrative model in which the accreted hydrogen and helium burn to produce a mixture of O and Se. Even though the H/He burning produces only 2% oxygen by mass, the steady-state ocean has an oxygen abundance more than 10 times larger, almost 40% by mass. Furthermore, we show that the convective motions transport heat inward, with a flux of {approx}0.2 MeV nucleon{sup -1} for an O-Se ocean, heating the ocean and steepening the outward temperature gradient. The enrichment of light elements and heating of the ocean due to compositionally driven convection likely have important implications for carbon ignition models of superbursts.

  10. On the spin-down of young neutron stars

    NASA Astrophysics Data System (ADS)

    Bernal, Cristian G.; Negreiros, R.

    2015-12-01

    The Rotation Powered-Pulsars (RPPs) are exposed to a long-term changes in the period of rotation, which are measured by the frequency and its derivatives, ?, ??, ?, obtained from timing observations. The parameter that links these observables with pulsar deceleration is the braking index, n, which is exactly 3 for purely dipolar radiation. Few braking indices have been estimated to date, for very young pulsars, and in all cases, n < 3. These observations suggest that there are complex plasma processes in the magnetosphere of the pulsar that are not fully well understood. In the present work we revisit the magnetic torque problem for young pulsars in the approach of magnetic field growth due ohmic diffusion. We show that such approach could explain the low values of n in very young neutron stars and may be relevant to explain why a small group of neutron stars, found in young supernova remnants or CCOs, exhibit little or no evidence for the presence of a magnetic field.

  11. Gravitational waves from color-magnetic "mountains" in neutron stars.

    PubMed

    Glampedakis, K; Jones, D I; Samuelsson, L

    2012-08-24

    Neutron stars may harbor the true ground state of matter in the form of strange quark matter. If present, this type of matter is expected to be a color superconductor, a consequence of quark pairing with respect to the color and flavor degrees of freedom. The stellar magnetic field threading the quark core becomes a color-magnetic admixture and, in the event that superconductivity is of type II, leads to the formation of color-magnetic vortices. In this Letter, we show that the volume-averaged color-magnetic vortex tension force should naturally lead to a significant degree of nonaxisymmetry in systems such as radio pulsars. We show that gravitational radiation from such color-magnetic "mountains" in young pulsars, such as the Crab and Vela, could be observable by the future Einstein Telescope, thus, becoming a probe of paired quark matter in neutron stars. The detectability threshold can be pushed up toward the sensitivity level of Advanced LIGO if we invoke an interior magnetic field about a factor ten stronger than the surface polar field. PMID:23002735

  12. FORMATION OF STABLE MAGNETARS FROM BINARY NEUTRON STAR MERGERS

    SciTech Connect

    Giacomazzo, Bruno; Perna, Rosalba

    2013-07-10

    By performing fully general relativistic magnetohydrodynamic simulations of binary neutron star mergers, we investigate the possibility that the end result of the merger is a stable magnetar. In particular, we show that, for a binary composed of two equal-mass neutron stars (NSs) of gravitational mass M {approx} 1.2 M{sub Sun} and equation of state similar to Shen et al. at high densities, the merger product is a stable NS. Such NS is found to be differentially rotating and ultraspinning with spin parameter J/M{sup 2} {approx} 0.86, where J is its total angular momentum, and it is surrounded by a disk of Almost-Equal-To 0.1 M{sub Sun }. While in our global simulations the magnetic field is amplified by about two orders of magnitude, local simulations have shown that hydrodynamic instabilities and the onset of the magnetorotational instability could further increase the magnetic field strength up to magnetar levels. This leads to the interesting possibility that, for some NS mergers, a stable and magnetized NS surrounded by an accretion disk could be formed. We discuss the impact of these new results for the emission of electromagnetic counterparts of gravitational wave signals and for the central engine of short gamma-ray bursts.

  13. Asteroseismology of rapidly rotating neutron stars: An alternative approach

    NASA Astrophysics Data System (ADS)

    Doneva, Daniela D.; Kokkotas, Kostas D.

    2015-12-01

    We examine gravitational wave asteroseismology relations for f -modes of rapidly rotating neutron stars. A different approach than previous studies is employed. First, the moment of inertia is used instead of the stellar radius and, second, the normalization of the oscillation frequencies and damping times is different. It is shown that in the nonrotating case this can lead to a much stronger equation of state independence, and our goal is to generalize the static relations to the rapidly rotating case and values of the spherical mode number l ?2 . We employ realistic equations of state that cover a very large range of stiffness in order to better check the universality of the relations. We later explore the inverse problem; i.e., we obtain the neutron star parameters from the observed gravitational frequencies and damping times. It turns out that, with this new set of relations, we can solve the inverse problem with very good accuracy using three frequencies. This was not possible in the previous studies, where one also needed damping times. The asteroseismology relations are also quite accurate for the massive rapidly rotating models that are subject to secular instabilities.

  14. Helium-burning flashes on accreting neutron stars - Effects of stellar mass, radius, and magnetic field

    NASA Technical Reports Server (NTRS)

    Joss, P. C.; Li, F. K.

    1980-01-01

    The effects of a neutron-star mass, radius, and surface magnetic field on the character of helium-burning flashes are studied. It is found that the effects of mass and radius can be described by simple scaling relations. A strong magnetic field decreases the radiative and conductive opacities and inhibits convection in the neutron-star surface layers.

  15. Neutrinos from SN 1987A and cooling of the nascent neutron star

    NASA Technical Reports Server (NTRS)

    Lamb, D. Q.; Loredo, Thomas J.; Melia, Fulvio

    1988-01-01

    The implications of the detection of neutrinos from SN 1987A for the cooling of the nascent neutron star are considered. The nu-bar(e) number N, the apparent temperature, the cooling time scale measured by the Kamioka and IMB detectors, and the inferred neutron star apparent radius and binding energy are all found to provide striking verification of current supernova theory.

  16. Prospects for measuring neutron-star masses and radii with X-ray pulse profile modeling

    SciTech Connect

    Psaltis, Dimitrios; Özel, Feryal; Chakrabarty, Deepto E-mail: fozel@email.arizona.edu

    2014-06-01

    Modeling the amplitudes and shapes of the X-ray pulsations observed from hot, rotating neutron stars provides a direct method for measuring neutron-star properties. This technique constitutes an important part of the science case for the forthcoming NICER and proposed LOFT X-ray missions. In this paper, we determine the number of distinct observables that can be derived from pulse profile modeling and show that using only bolometric pulse profiles is insufficient for breaking the degeneracy between inferred neutron-star radius and mass. However, we also show that for moderately spinning (300-800 Hz) neutron stars, analysis of pulse profiles in two different energy bands provides additional constraints that allow a unique determination of the neutron-star properties. Using the fractional amplitudes of the fundamental and the second harmonic of the pulse profile in addition to the amplitude and phase difference of the spectral color oscillations, we quantify the signal-to-noise ratio necessary to achieve a specified measurement precision for neutron star radius. We find that accumulating 10{sup 6} counts in a pulse profile is sufficient to achieve a ≲ 5% uncertainty in the neutron star radius, which is the level of accuracy required to determine the equation of state of neutron-star matter. Finally, we formally derive the background limits that can be tolerated in the measurements of the various pulsation amplitudes as a function of the system parameters.

  17. Gamma ray bursts from comet neutron star magnetosphere interaction, field twisting and E sub parallel formation

    SciTech Connect

    Colgate, S.A.

    1990-01-01

    Consider the problem of a comet in a collision trajectory with a magnetized neutron star. The question addressed in this paper is whether the comet interacts strongly enough with a magnetic field such as to capture at a large radius or whether in general the comet will escape a magnetized neutron star. 6 refs., 4 figs.

  18. Supermagnetic Neutron Star Surprises Scientists, Forces Revision of Theories

    NASA Astrophysics Data System (ADS)

    2006-08-01

    Astronomers using radio telescopes from around the world have discovered a spinning neutron star with a superpowerful magnetic field -- called a magnetar -- doing things no magnetar has been seen to do before. The strange behavior has forced them to scrap previous theories about radio pulsars and promises to give new insights on the physics behind these extreme objects. Magnetar Artist's Conception of Magnetar With Radio Beams ALL IMAGES AND ANIMATIONS CREDIT: Bill Saxton, NRAO/AUI/NSF Image and Animation Files Magnetar Graphic (above image, JPEG, 32K) Animation With Sound From GBT Detection of XTE J1810-197 (8.6M) Animation With Sound From GBT Detection of XTE J1810-197 (Full Size, 29M) The magnetar, approximately 10,000 light-years from Earth in the direction of the constellation Sagittarius, is emitting powerful, regularly-timed pulses of radio waves just like radio pulsars, which are neutron stars with far less intense magnetic fields. Usually, magnetars are visible only in X-rays and sometimes very weakly in optical and infrared light. "No one has ever found radio pulses coming from a magnetar before. We thought that magnetars didn't do this," said Fernando Camilo of Columbia University. "This object is going to teach us new things about magnetar physics that we would never have learned otherwise," Camilo added. Neutron stars are the remnants of massive stars that have exploded as supernovae. Containing more mass than the Sun, they are compressed to a diameter of only about 15 miles, making them as dense as atomic nuclei. Ordinary pulsars are neutron stars that emit "lighthouse beams" of radio waves along the poles of their magnetic fields. As the star spins, the beam of radio waves is flung around, and when it passes the direction of Earth, astronomers can detect it with radio telescopes. Scientists have found about 1700 pulsars since their first discovery in 1967. While pulsars have strong magnetic fields, about a dozen neutron stars have been dubbed magnetars because their magnetic fields are 100-1,000 times stronger than those of typical pulsars. It is the decay of those incredibly strong fields that powers their strange X-ray emission. "The magnetic field from a magnetar would make an aircraft carrier spin around and point north quicker than a compass needle moves on Earth," said David Helfand, of Columbia University. A magnetar's field is 1,000 trillion times stronger than Earth's, Helfand pointed out. The new object -- named XTE J1810-197 -- was first discovered by NASA's Rossi X-ray Timing Explorer when it emitted a strong burst of X-rays in 2003. While the X-rays were fading in 2004, Jules Halpern of Columbia University and collaborators identified the magnetar as a radio-wave emitter using the National Science Foundation's (NSF) Very Large Array (VLA) radio telescope in New Mexico. Any radio emission is highly unusual for a magnetar. Because magnetars had not been seen to regularly emit radio waves, the scientists presumed that the radio emission was caused by a cloud of particles thrown off the neutron star at the time of its X-ray outburst, an idea they soon would realize was wrong. With knowledge that the magnetar emitted some form of radio waves, Camilo and his colleagues observed it with the Parkes radio telescope in Australia in March and immediately detected astonishingly strong radio pulsations every 5.5 seconds, corresponding to the previously-determined rotation rate of the neutron star. As they continued to observe XTE J1810-197, the scientists got more surprises. Whereas most pulsars become weaker at higher radio frequencies, XTE J1810-197 does not, remaining a strong emitter at frequencies up to 140 GHz, the highest frequency ever detected from a radio pulsar. In addition, unlike normal pulsars, the object's radio emission fluctuates in strength from day to day, and the shape of the pulsations changes as well. These variations likely indicate that the magnetic fields around the pulsar are changing as well. What's causing this behavior? At the moment, the scientists believe that the magnetar's intense magnetic field is twisting, causing changes in the locations where huge electric currents flow along the magnetic-field lines. These currents likely generate the radio pulsations. "To solve this mystery, we'll continue monitoring this crazy object with as many telescopes as we can get our hands on and as often as possible. Hopefully, seeing all these changes with time will give us a deeper understanding of what is really going on in this very extreme environment," said team member Scott Ransom of the National Radio Astronomy Observatory. Because they expect that XTE J1810-197 will fade at all wavelengths, including the radio, the scientists also have observed it with the NSF's Robert C. Byrd Green Bank Telescope and Very Long Baseline Array (VLBA), Parkes and the Australia Telescope Compact Array in Australia, the IRAM telescope in Spain, and the Nancay Observatory in France. John Reynolds and John Sakissian of Parkes Observatory, Neil Zimmerman of Columbia University and Juan Penalver and Aris Karastergiou of IRAM also are members of the research team. The scientists reported their initial findings in the August 24 issue of the scientific journal Nature. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

  19. NetQuakes Instrument in Place

    USGS Multimedia Gallery

    NetQuakes strong-motion instruments enable seismologists to collect extensive data in urban areas where installing traditional seismographs is not practical.  This instrument (in blue, to the right of the upended chairs) takes up very little space in a San Francisco Bay Area resident's garage...

  20. Progenitor neutron stars of the lightest and heaviest millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Fortin, M.; Bejger, M.; Haensel, P.; Zdunik, J. L.

    2016-02-01

    Context. The recent mass measurements of two binary millisecond pulsars, PSR J1614-2230 and PSR J0751+1807 with a mass M = 1.97 ± 0.04 M⊙ and M = 1.26 ± 0.14 M⊙, respectively, indicate a wide range of masses for such objects and possibly also a broad spectrum of masses of neutron stars born in core-collapse supernovae. Aims: Starting from the zero-age main sequence binary stage, we aim at inferring the birth masses of PSR J1614-2230 and PSR J0751+1807 by taking the differences in the evolutionary stages preceding their formation into account. Methods: Using simulations for the evolution of binary stars, we reconstruct the evolutionary tracks leading to the formation of PSR J1614-2230 and PSR J0751+1807. We analyse in detail the spin evolution due to the accretion of matter from a disk in the intermediate-mass/low-mass X-ray binary. We consider two equations of state of dense matter, one for purely nucleonic matter and the other one including a high-density softening due to the appearance of hyperons. Stationary and axisymmetric stellar configurations in general relativity are used, together with a recent magnetic torque model and observationally-motivated laws for the decay of magnetic field. Results: The estimated birth mass of the neutron stars PSR J0751+1807 and PSR J1614-2230 could be as low as 1.0 M⊙ and as high as 1.9 M⊙, respectively. These values depend weakly on the equation of state and the assumed model for the magnetic field and its accretion-induced decay. Conclusions: The masses of progenitor neutron stars of recycled pulsars span a broad interval from 1.0 M⊙ to 1.9 M⊙. Including the effect of a slow Roche-lobe detachment phase, which could be relevant for PSR J0751+1807, would make the lower mass limit even lower. A realistic theory for core-collapse supernovæ should account for this wide range of mass.

  1. Electromagnetic and Radiative Properties of Neutron Star Magnetospheres

    NASA Astrophysics Data System (ADS)

    Li, Jason G.

    2014-05-01

    Magnetospheres of neutron stars are commonly modeled as either devoid of plasma in "vacuum'' models or filled with perfectly conducting plasma with negligible inertia in "force-free'' models. While numerically tractable, neither of these idealized limits can simultaneously account for both the plasma currents and the accelerating electric fields that are needed to explain the morphology and spectra of high-energy emission from pulsars. In this work we improve upon these models by considering the structure of magnetospheres filled with resistive plasma. We formulate Ohm's Law in the minimal velocity fluid frame and implement a time-dependent numerical code to construct a family of resistive solutions that smoothly bridges the gap between the vacuum and force-free magnetosphere solutions. We further apply our method to create a self-consistent model for the recently discovered intermittent pulsars that switch between two distinct states: an "on'', radio-loud state, and an "off'', radio-quiet state with lower spin-down luminosity. Essentially, we allow plasma to leak off open field lines in the absence of pair production in the "off'' state, reproducing observed differences in spin-down rates. Next, we examine models in which the high-energy emission from gamma-ray pulsars comes from reconnecting current sheets and layers near and beyond the light cylinder. The reconnected magnetic field provides a reservoir of energy that heats particles and can power high-energy synchrotron radiation. Emitting particles confined to the sheet naturally result in a strong caustic on the skymap and double peaked light curves for a broad range of observer angles. Interpulse bridge emission likely arises from interior to the light cylinder, along last open field lines that traverse the space between the polar caps and the current sheet. Finally, we apply our code to solve for the magnetospheric structure of merging neutron star binaries. We find that the scaling of electromagnetic luminosity with orbital angular velocity varies between the power 4 for nonspinning stars and the power 1.5 for rapidly spinning millisecond pulsars near contact. Our derived scalings and magnetospheres can be used to help understand electromagnetic signatures from merging neutron stars to be observed by Advanced LIGO.

  2. QuakeSim 2.0

    NASA Technical Reports Server (NTRS)

    Donnellan, Andrea; Parker, Jay W.; Lyzenga, Gregory A.; Granat, Robert A.; Norton, Charles D.; Rundle, John B.; Pierce, Marlon E.; Fox, Geoffrey C.; McLeod, Dennis; Ludwig, Lisa Grant

    2012-01-01

    QuakeSim 2.0 improves understanding of earthquake processes by providing modeling tools and integrating model applications and various heterogeneous data sources within a Web services environment. QuakeSim is a multisource, synergistic, data-intensive environment for modeling the behavior of earthquake faults individually, and as part of complex interacting systems. Remotely sensed geodetic data products may be explored, compared with faults and landscape features, mined by pattern analysis applications, and integrated with models and pattern analysis applications in a rich Web-based and visualization environment. Integration of heterogeneous data products with pattern informatics tools enables efficient development of models. Federated database components and visualization tools allow rapid exploration of large datasets, while pattern informatics enables identification of subtle, but important, features in large data sets. QuakeSim is valuable for earthquake investigations and modeling in its current state, and also serves as a prototype and nucleus for broader systems under development. The framework provides access to physics-based simulation tools that model the earthquake cycle and related crustal deformation. Spaceborne GPS and Inter ferometric Synthetic Aperture (InSAR) data provide information on near-term crustal deformation, while paleoseismic geologic data provide longerterm information on earthquake fault processes. These data sources are integrated into QuakeSim's QuakeTables database system, and are accessible by users or various model applications. UAVSAR repeat pass interferometry data products are added to the QuakeTables database, and are available through a browseable map interface or Representational State Transfer (REST) interfaces. Model applications can retrieve data from Quake Tables, or from third-party GPS velocity data services; alternatively, users can manually input parameters into the models. Pattern analysis of GPS and seismicity data has proved useful for mid-term forecasting of earthquakes, and for detecting subtle changes in crustal deformation. The GPS time series analysis has also proved useful as a data-quality tool, enabling the discovery of station anomalies and data processing and distribution errors. Improved visualization tools enable more efficient data exploration and understanding. Tools provide flexibility to science users for exploring data in new ways through download links, but also facilitate standard, intuitive, and routine uses for science users and end users such as emergency responders.

  3. The Breakin Strain of Neutron Star Crust and Continuous Gravitational Wave Radiation

    NASA Astrophysics Data System (ADS)

    Horowitz, C. J.; Kadau, K.; Hughto, J.; Berry, D. K.

    2009-05-01

    Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. We use large scale molecular dynamics simulations of Coulomb solids to determine the breaking strain. We find that the breaking strain of small single crystals is very large and that this strength is only modestly reduced by impurities, defects, and grain boundaries. Therefore, neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large scale interferometers.

  4. Analysing neutron star in HESS J1731-347 from thermal emission and cooling theory

    NASA Astrophysics Data System (ADS)

    Ofengeim, D. D.; Kaminker, A. D.; Klochkov, D.; Suleimanov, V.; Yakovlev, D. G.

    2015-12-01

    The central compact object in the supernova remnant HESS J1731-347 appears to be the hottest observed isolated cooling neutron star. The cooling theory of neutron stars enables one to explain observations of this star by assuming the presence of strong proton superfluidity in the stellar core and the existence of the surface heat blanketing envelope which almost fully consists of carbon. The cooling model of this star is elaborated to take proper account of the neutrino emission due to neutron-neutron collisions which is not suppressed by proton superfluidity. Using the results of spectral fits of observed thermal spectra for the distance of 3.2 kpc and the cooling theory for the neutron star of age 27 kyr, new constraints on the stellar mass and radius are obtained which are more stringent than those derived from the spectral fits alone.

  5. Prospects for neutron star equation of state constraints using "recycled" millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko

    2016-02-01

    "Recycled" millisecond pulsars are a variety of rapidly spinning neutron stars that typically show thermal X-ray radiation due to the heated surface of their magnetic polar caps. Detailed numerical modeling of the rotation-induced thermal X-ray pulsations observed from recycled millisecond pulsars, including all relevant relativistic and stellar atmospheric effects, has been identified as a promising approach towards an astrophysical determination of the true neutron star mass-radius relation, and by extension the state of cold matter at densities exceeding those of atomic nuclei. Herein, I review the basic model and methodology commonly used to extract information regarding neutron star structure from the pulsed X-ray radiation observed from millisecond pulsars. I also summarize the results of past X-ray observations of these objects and the prospects for precision neutron star mass-radius measurements with the upcoming Neutron Star Interior Composition Explorer (NICER) X-ray timing mission.

  6. In what sense a neutron star-black hole binary is the holy grail for testing gravity?

    SciTech Connect

    Bagchi, Manjari; Torres, Diego F. E-mail: dtorres@ieec.uab.es

    2014-08-01

    Pulsars in binary systems have been very successful to test the validity of general relativity in the strong field regime [1-4]. So far, such binaries include neutron star-white dwarf (NS-WD) and neutron star-neutron star (NS-NS) systems. It is commonly believed that a neutron star-black hole (NS-BH) binary will be much superior for this purpose. But in what sense is this true? Does it apply to all possible deviations?.

  7. In what sense a neutron star-black hole binary is the holy grail for testing gravity?

    NASA Astrophysics Data System (ADS)

    Bagchi, Manjari; Torres, Diego F.

    2014-08-01

    Pulsars in binary systems have been very successful to test the validity of general relativity in the strong field regime [1-4]. So far, such binaries include neutron star-white dwarf (NS-WD) and neutron star-neutron star (NS-NS) systems. It is commonly believed that a neutron star-black hole (NS-BH) binary will be much superior for this purpose. But in what sense is this true? Does it apply to all possible deviations?

  8. Polarization of neutron star surface emission: a systematic analysis

    NASA Astrophysics Data System (ADS)

    Taverna, R.; Turolla, R.; Gonzalez Caniulef, D.; Zane, S.; Muleri, F.; Soffitta, P.

    2015-12-01

    New-generation X-ray polarimeters currently under development promise to open a new window in the study of high-energy astrophysical sources. Among them, neutron stars (NSs) appear particularly suited for polarization measurements. Radiation from the (cooling) surface of an NS is expected to exhibit a large intrinsic polarization degree due to the star strong magnetic field (?1012-1015 G), which influences the plasma opacity in the outermost stellar layers. The polarization fraction and polarization angle as measured by an instrument, however, do not necessary coincide with the intrinsic ones derived from models of surface emission. This is due to the effects of quantum electrodynamics in the highly magnetized vacuum around the star (the vacuum polarization) coupled with the rotation of the Stokes parameters in the plane perpendicular to the line of sight induced by the non-uniform magnetic field. Here, we revisit the problem and present an efficient method for computing the observed polarization fraction and polarization angle in the case of radiation coming from the entire surface of an NS, accounting for both vacuum polarization and geometrical effects due to the extended emitting region. Our approach is fairly general and is illustrated in the case of blackbody emission from an NS with either a dipolar or a (globally) twisted magnetic field.

  9. Explosion of a rotating neutron star near the minimum mass

    NASA Astrophysics Data System (ADS)

    Colpi, Monica; Shapiro, Stuart L.; Teukolsky, Saul A.

    1991-03-01

    A Newtonian calculation is presented for the explosion of an unstable neutron star about the minimum mass, and the amount of neutrino, gravitational, and electromagnetic radiation emitted is estimated. The dynamical evolution of the star is followed by solving the Newtonian equations or motion for a homogeneous, uniformly rotating spheroid with internal pressure and gravity. At the outset, the oblate star is in hydrostatic equilibrium at the minimum mass along an equilibrium curve of fixed angular momentum. The explosion is almost instantaneous, with an intense burst of antineutrinos signaling the onset of abrupt acceleration. Antineutrino luminosities of 10 to the 50th to 10 to the 52nd ergs/s and bulk kinetic energies of order 10 to the 49th ergs are obtained. The results indicate that the gravitational radiation (GR) energy release from the explosion is rather small at E(GR)/M(B) less than 10 to the -14th with an amplitude at maximum acceleration of less than about 5 x 10 to the -23rd sine-squared Theta for a source at a distance of 10 kpc.

  10. Neutron Star Structure in the Presence of Conformally Coupled Scalar Fields

    NASA Technical Reports Server (NTRS)

    Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

    2014-01-01

    Neutron star models are studied in the context of scalar-tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

  11. A theoretical and observational study of the X-ray spectroscopy of isolated neutron stars

    NASA Astrophysics Data System (ADS)

    Mori, Kaya

    2003-10-01

    This thesis consists of a theoretical study of neutron star atmospheres and its application to recent X-ray data on the isolated neutron star 1E1207.4-5209, which shows absorption features. Although the study of pulsars has been carried out mostly in the radio band for many years, spectroscopy study by recent X-ray telescopes provides a powerful tool for describing the interior of neutron stars. In particular, a unique determination of mass and radius from a single neutron star severely constrains the equation of state and composition of the core region of neutron stars. In the first part of my thesis, theoretical work on neutron star atmosphere models is presented. Intensive study of atomic structure in strong magnetic fields typical of neutron stars was undertaken. A novel atomic calculation which computes transition energies and oscillator strengths with sufficient accuracy to analyze high energy resolution data on Chandra and XMM-Newton was performed. In the second part of my thesis, a methodology was established to identify spectral features from strongly- magnetized dense plasmas. Based on the application of the atomic code and methodology to the Chandra data from the isolated neutron star 1E1207.4-5209, it was shown that the observed absorption features are due to Helium-like Oxygen or Neon at B 1012 G. This led to a simultaneous determination of the surface composition, the magnetic field strength and, more importantly, the gravitational redshift. Further constraints on the atmosphere, as well as the neutron star equation of state, can be inferred under the assumption that the neutron star mass is near the canonical value of 1.4 M? . In that case Neon is ruled out, and the atmosphere is unambiguously Oxygen. The corresponding gravitational redshift for the Oxygen atmosphere constrains the equation of state of the interior of 1E1207.4-5209 to be quite stiff.

  12. The CoCoNuT code: from neutron star oscillations to supernova explosions

    NASA Astrophysics Data System (ADS)

    Cerdá-Durán, P.; Gabler, M.; Müller, E.; Font, J. A.; Stergioulas, N.; Obergaulinger, M.; Aloy, M. A.; DeBrye, N.; Cordero-Carrión, I.; Ibáñez, J. M.

    2013-05-01

    CoCoNuT is a numerical code, that evolves the General relativistic magneto-hydrodynamics equations coupled to the Einstein equations in the CFC approximation. Its main purpose is to simulate astrophysical scenarios in which strong gravity is important such as the collapse of massive stars and the evolution of neutron stars. I review recent results of the numerical code regarding neutron star oscillations and core collapse supernova and its observational consequences.

  13. Supersoft Symmetry Energy Encountering Non-Newtonian Gravity in Neutron Stars

    SciTech Connect

    Wen Dehua; Li Baoan; Chen Liewen

    2009-11-20

    Considering the non-Newtonian gravity proposed in grand unification theories, we show that the stability and observed global properties of neutron stars cannot rule out the supersoft nuclear symmetry energies at suprasaturation densities. The degree of possible violation of the inverse-square law of gravity in neutron stars is estimated using an equation of state of neutron-rich nuclear matter consistent with the available terrestrial laboratory data.

  14. Entrainment Coefficient and Effective Mass for Conduction Neutrons in Neutron Star Crust:. Macroscopic Treatment

    NASA Astrophysics Data System (ADS)

    Carter, Brandon; Chamel, Nicolas; Haensel, Pawel

    Phenomena such as pulsar frequency glitches are believed to be attributable to differential rotation of a current of "free" superfluid neutrons at densities above the "drip" threshold in the ionic crust of a neutron star. Such relative flow is shown to be locally describable by adaption of a canonical two-fluid treatment that emphasizes the role of the momentum covectors constructed by differentiation of action with respect to the currents, with allowance for stratification whereby the ionic number current may be conserved even when the ionic charge number Z is altered by beta processes. It is demonstrated that the gauge freedom to make different choices of the chemical basis determining which neutrons are counted as "free" does not affect their "superfluid" momentum covector, which must locally have the form of a gradient (though it does affect the "normal" momentum covector characterizing the protons and those neutrons that are considered to be "confined" in the nuclei). It is shown how the effect of "entrainment" (whereby the momentum directions deviate from those of the currents) is controlled by the (gauge-independent) mobility coefficient {K}, estimated in recent microscopical quantum mechanical investigations, which suggest that the corresponding (gauge-dependent) "effective mass" m⋆ of the free neutrons can become very large in some layers. The relation between this treatment of the crust layers and related work (using different definitions of "effective mass") intended for the deeper core layers is discussed.

  15. The influence of core superfluidity on the neutron stars long-term rotation evolution

    NASA Astrophysics Data System (ADS)

    Barsukov, D. P.; Goglichidze, O. A.; Tsygan, A. I.

    2013-08-01

    We investigate the evolution of neutron star rotation taking into account the superfluidity of the neutrons in the neutron star core. The neutron star is treated as a two-component system consisting of a charged component (including the crust and the core protons, electrons and normal neutrons) and a core superfluid neutron component. The components are supposed to interact through the mutual friction force. We assume that the charged component rotates rigidly. The neutron superfluid velocity field is calculated directly from linearized hydrodynamical equations. It is shown that the superfluid core accelerates the evolution of inclination angle and makes all pulsars evolve to orthogonal state. But as it is known from observations the rate of the angle evolution is not very high. Therefore, a small size of superfluid cores is more likely. These facts may allow to examine superfluid models.

  16. Sequential deconfinement of quark flavors in neutron stars

    SciTech Connect

    Blaschke, D.; Sandin, F.; Klaehn, T.; Berdermann, J.

    2009-12-15

    A scenario is suggested in which the three light quark flavors are sequentially deconfined under increasing pressure in cold asymmetric nuclear matter as found, for example, in neutron stars. The basis for this analysis is a chiral quark matter model of Nambu-Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single-flavor, spin-0 two-flavor, and three-flavor channels. Nucleon dissociation sets in at about the saturation density, n{sub 0}, when the down-quark Fermi sea is populated (d-quark drip line) because of the flavor asymmetry induced by {beta} equilibrium and charge neutrality. At about 3n{sub 0}, u-quarks appear and a two-flavor color superconducting (2SC) phase is formed. The s-quark Fermi sea is populated only at still higher baryon density, when the quark chemical potential is of the order of the dynamically generated strange quark mass. Two different hybrid equations of state (EOSs) are constructed using the Dirac-Brueckner Hartree-Fock (DBHF) approach and the EOS of Shen et al.[H. Shen, H. Toki, K. Oyamatsu, and K. Sumiyoshi, Nucl. Phys. A637, 435 (1998)] in the nuclear matter sector. The corresponding hybrid star sequences have maximum masses of 2.1 and 2.0 M{sub {center_dot}}, respectively. Two- and three-flavor quark-matter phases exist only in gravitationally unstable hybrid star solutions in the DBHF case, whereas the Shen-based EOSs produce stable configurations with a 2SC phase component in the core of massive stars. Nucleon dissociation via d-quark drip could act as a deep crustal heating process, which apparently is required to explain superbursts and cooling of x-ray transients.

  17. Differential rotation and r-modes in magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Chugunov, Andrey I.

    2015-08-01

    Rezzolla et al. drew attention to the second-order secular drift associated with r-modes and claimed that it should lead to enhancement of the magnetic field and suppression of r-mode instability in magnetized neutron stars. We critically revise these results. We present a particular second-order r-mode solution with vanishing secular drift, thus refuting a widely believed statement that secular drift is an unavoidable feature of r-modes. This non-drifting solution is not affected by a magnetic field B, if B ? Bcrit ? 1017 (?/600 Hz) G (? is the spin frequency) and does not lead to secular evolution of the magnetic field. For a general second-order r-mode solution, the drift does not necessarily vanish. The solution can be presented as a superposition of two solutions: one describes the evolution of differential rotation of a non-oscillating star (secular drift; for an unmagnetized star it is an arbitrary stationary rotation stratified on cylinders; for a magnetized star differential rotation evolves on the Alfvn timescale and may lead to enhancement of the magnetic energy), and the other is the non-drifting r-mode solution mentioned above. This representation allows us to conclude that enhancement of the magnetic field energy is limited by the initial energy of differential rotation, which is much less than the total energy of the r-mode (by a factor ? ?2, where ? is the mode amplitude). Hence, enhancement of the magnetic field by drift cannot suppress the r-mode instability. The results can be generalized for any oscillation mode in any medium, if this mode has a non-drifting solution for B = 0.

  18. Explosion Quakes: The 2007 Eruption of Pavlof

    NASA Astrophysics Data System (ADS)

    Smith, C.; McNutt, S. R.; Thompson, G.

    2014-12-01

    Pavlof Volcano on the Alaska Peninsula began to erupt on August 14, 2007 after an 11 year repose. Pavlof is the most active volcano in the Aleutians, with over 40 eruptions in historical times. The 2007 eruption began with low-frequency earthquakes and thermal anomalies. Strombolian activity occurred from a newly formed vent on the SE flank of the volcano. The plume reached 20,000 ft during the peak of the eruption on August 29th and 30th. Seismic activity, monitored by a network of 5 local instruments, consisted of low-frequency events, explosion quakes, volcanic tremor, and lahar-generated signals. Here we focus on explosion quakes. The first explosion quake occurred August 14th at 2:54pm UTC and the last on September 13th at 3:14pm UTC. Explosion events were often embedded in continuous tremor, but could be distinguished by the ground-coupled air waves, which appeared as a high-frequency spike superimposed on the lower-frequency ground waves. Rates were as high as 19 explosion quakes per minute. We establish whether systematic changes in explosion rates, signal properties, and ground-coupled air-wave amplitudes correlate with the height and ash content of the plume. First order trends show a positive correlation between increased explosion quake rates, increased amplitudes, and plume height. In addition, we investigate how atmospheric conditions such as wind speed and direction affect the recording of the ground-coupled air-wave. The time differences in the airwaves at different stations are consistent with the acoustic speed of 340 m/s, but show variations of up to 0.6 s depending on wind speed and direction. Eruptions at Pavlof typically have little or no seismic precursors; this combined with the low visibility common to the area results in Pavlof being dangerous to the many aviation routes that transverse this airspace. It is the goal of this study to determine the conditions under which explosion quake data may be reliably used for more effective monitoring.

  19. Unified description of astrophysical properties of neutron stars independent of the equation of state

    NASA Astrophysics Data System (ADS)

    Pappas, George

    2015-12-01

    In recent years, a lot of work was done that has revealed some very interesting properties of neutron stars. One can relate the first few multipole moments of a neutron star, or quantities that can be derived from them, with relations that are independent of the equation of state (EoS). This is a very significant result that has great implications for the description of neutron stars and in particular for the description of the spacetime around them. Additionally, it was recently shown that there is a four-parameter analytic spacetime, known as the two-soliton spacetime, which can accurately capture the properties of the geometry around neutron stars. This allows for the possibility of describing in a unified formalism the astrophysically relevant properties of the spacetime around a neutron star independently of the particulars of the EoS for the matter of the star. More precisely, the description of these astrophysical properties is done using an EoS omniscient spacetime that can describe the exterior of any neutron star. In the present work, we investigate properties such as the location of the innermost stable circular orbit RISCO (or the surface of the star when the latter overcomes the former), the various frequencies of perturbed circular equatorial geodesics, the efficiency of an accretion disc, its temperature distribution, and other properties associated with the emitted radiation from the disc, in a way that holds for all possible choices of a realistic EoS for the neutron star. Furthermore, we provide proof of principle that if one were to measure the right combinations of pairs of these properties, with the additional knowledge of the mass of the neutron star, one could determine the EoS of the star.

  20. Effective field theory for neutron stars with strong ?--hyperon repulsion

    NASA Astrophysics Data System (ADS)

    Razeira, M.; Mesquita, A.; Vasconcellos, C. A. Z.; Ruffini, R.; Rueda, J. A.; Gomes, R. O.

    2014-09-01

    We investigate the role of many-body correlations in the maximum mass of neutron stars using the effective relativistic QHD-model with parameterized couplings which represents an extended compilation of other effective models found in the literature. Our model exhausts the whole fundamental baryon octet (n, p, ?-, ?0, ?+, ?, ?-, ?0) and simulates corrections to the minimal Yukawa couplings by considering many-body nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (?, ?*), vector-isoscalar (?, ?), vector-isovector (?rrho) and scalar-isovector (?). Following recent experimental results, we consider in our calculations the extreme case where the ?- experiences such a strong repulsion that it does not appear at all in nuclear matter.

  1. Maximum mass of neutron stars with quark matter core

    SciTech Connect

    Takatsuka, Tatsuyuki; Hatsuda, Tetsuo; Masuda, Kota

    2012-11-12

    We propose a new strategy to construct the equation of state (EOS) for neutron stars (NSs) with hadron-quark (H-Q) phase transition, by considering three density-regions. We supplement the EOS at H-Q region, very uncertain due to the confinement-deconfinement problems, by sandwitching in between and matching to the relatively 'well known' EOSs, i.e., the EOS at lower densities (H-phase up to several times nuclear density, calculated from a G-matrix approach) and that at ultra high densities (Q-phase, form a view of asymptotic freedom). Here, as a first step, we try a simple case and discuss the maximum mass of NSs.

  2. R-modes in neutron stars: Theory and observations

    NASA Astrophysics Data System (ADS)

    Haskell, B.

    2015-08-01

    In this paper, I will review the theory behind the gravitational wave (GW) driven r-mode instability in rapidly rotating neutron stars (NSs) and discuss which constraints can be derived from observations of spins and temperatures in low mass X-ray binaries (LMXBs). I will discuss how a standard, 'minimal' NS model is not consistent with the data, and discuss some of the additional physical mechanisms that could reconcile theory with observations. In particular, I will focus on additional forms of damping due to exotic cores and on strong mutual friction due to superfluid vortices cutting through superconducting flux tubes, and examine the repercussions these effects could have on the saturation amplitude of the mode. Finally I will also discuss the possibility that oscillations due to r-modes may have been recently observed in the X-ray light curves of two LMXBs.

  3. Pulsar H(alpha) Bowshocks probe Neutron Star Physics

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2014-08-01

    We propose a KOALA/AAOmega study of southern pulsar bow shocks. These rare, Balmer-dominated, non-radiative shocks provide an ideal laboratory to study the interaction of the relativistic pulsar wind with the ISM. We will cover H(alpha) at high spectral resolution to measure the kinematics of the upstream ISM and the post-shock flow, while the blue channel measures the Balmer decrement and probes for a faint cooling component. These data, with MHD models, allow us to extract the 3D flow geometry and the orientation and asymmetry of the pulsar wind. These data can also measure the pulsar spindown power, thus estimating the neutron star moment of inertia and effecting a fundamental test of dense matter physics.

  4. Surface structure of neutron stars with high magnetic fields

    NASA Technical Reports Server (NTRS)

    Fushiki, I.; Gudmundsson, E. H.; Pethick, C. J.

    1989-01-01

    The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates.

  5. [Nucleosynthesis, Rotation and Magnetism in Accreting Neutron Stars

    NASA Technical Reports Server (NTRS)

    Bildsten, Lars

    2004-01-01

    This is my final report on the NASA ATP grant on nucleosynthesis, rotation and magnetism in accreting neutron stars (NAG5-8658). In my last two reports, I summarized the science that I have accomplished, which covered a large range of topics. For this report, I want to point out the graduate students that were partially supported on this grant and where they are now. Andrew Cumming is an Assistant Professor of Physics at McGill University, Greg Ushomirsky is a researcher at MIT s Lincoln Laboratories, Dean Townsley is a postdoctoral researcher at Univ. of Chicago, Chris Deloye is a postdoctoral researcher at Northwestern University. The other two students, Phil Chang and Tony Piro, are still at UCSB and will be completing their PhD s in Summer 05 and Summer 06.

  6. A new population of radio transient neutron stars

    NASA Astrophysics Data System (ADS)

    Lyne, A. G.

    2010-03-01

    The small fields-of-view of radio telescopes and the short observation times of most radio surveys mean that the transient radio sky is relatively unexplored compared to other regions of the electromagnetic spectrum ( Cordes et al., 2004b). In the largest-scale search ever performed for transient radio sources, we have discovered a new class of neutron stars ( McLaughlin et al., 2006). The eleven new sources are characterized by single dispersed radio bursts with durations between 2 and 30 ms, 1400 MHz peak flux densities from 0.1 to 3.6 Jy and average intervals between events ranging from 4 min to 3 h. So far, no periodicities have been detected in their emission using standard search techniques ( Lorimer and Kramer, 2005), and radio emission is only detectable from these objects for a total of typically less than 1 s per day. However, through an arrival-time analysis of the bursts, we have identified periodicities in the range of 0.4-7 s for ten of the eleven sources. Period derivatives have been measured for three sources; one with a spin period of 4.3 s has an inferred surface dipole magnetic field strength of 5 10 13 G, perhaps indicating a close relationship between this source and the high-energy magnetars ( Woods and Thompson, 2006). Because of the unique properties of this new population, we call them Repeating RAdio Transients, or RRATs. Our discoveries pose challenges to standard models of pulsar emission physics, substantially increase the estimated population of active Galactic neutron stars and highlight the rich variety of radio transient sources that will be discovered by future large-scale transient searches with instruments such as the Square Kilometer Array ( Carilli and Rawlings, 2004).

  7. Absorption Features in Spectra of Magnetized Neutron Stars

    SciTech Connect

    Suleimanov, V.; Hambaryan, V.; Neuhaeuser, R.; Potekhin, A. Y.; Pavlov, G. G.; Adelsberg, M. van; Werner, K.

    2011-09-21

    The X-ray spectra of some magnetized isolated neutron stars (NSs) show absorption features with equivalent widths (EWs) of 50-200 eV, whose nature is not yet well known.To explain the prominent absorption features in the soft X-ray spectra of the highly magnetized (B{approx}10{sup 14} G) X-ray dim isolated NSs (XDINSs), we theoretically investigate different NS local surface models, including naked condensed iron surfaces and partially ionized hydrogen model atmospheres, with semi-infinite and thin atmospheres above the condensed surface. We also developed a code for computing light curves and integral emergent spectra of magnetized neutron stars with various temperature and magnetic field distributions over the NS surface. We compare the general properties of the computed and observed light curves and integral spectra for XDINS RBS 1223 and conclude that the observations can be explained by a thin hydrogen atmosphere above the condensed iron surface, while the presence of a strong toroidal magnetic field component on the XDINS surface is unlikely.We suggest that the harmonically spaced absorption features in the soft X-ray spectrum of the central compact object (CCO) 1E 1207.4-5209 (hereafter 1E 1207) correspond to peaks in the energy dependence of the free-free opacity in a quantizing magnetic field, known as quantum oscillations. To explore observable properties of these quantum oscillations, we calculate models of hydrogen NS atmospheres with B{approx}10{sup 10}-10{sup 11} G(i.e., electron cyclotron energy E{sub c,e}{approx}0.1-1 keV) and T{sub eff} = 1-3 MK. Such conditions are thought to be typical for 1E 1207. We show that observable features at the electron cyclotron harmonics with EWs {approx_equal}100-200 eV can arise due to these quantum oscillations.

  8. SPIN-PRECESSION: BREAKING THE BLACK HOLE-NEUTRON STAR DEGENERACY

    SciTech Connect

    Chatziioannou, Katerina; Cornish, Neil; Klein, Antoine; Yunes, Nicolás

    2015-01-01

    Mergers of compact stellar remnants are prime targets for the LIGO/Virgo gravitational wave detectors. The gravitational wave signals from these merger events can be used to study the mass and spin distribution of stellar remnants, and provide information about black hole horizons and the material properties of neutron stars. However, it has been suggested that degeneracies in the way that the star's mass and spin are imprinted in the waveforms may make it impossible to distinguish between black holes and neutron stars. Here we show that the precession of the orbital plane due to spin-orbit coupling breaks the mass-spin degeneracy, and allows us to distinguish between standard neutron stars and alternative possibilities, such as black holes or exotic neutron stars with large masses and spins.

  9. Properties of neutron stars with hyperons in the relativistic mean field theory

    NASA Astrophysics Data System (ADS)

    Ma, Z. X.; Dai, Z. G.; Lu, T.

    2001-02-01

    We study the equation of state (EOS) of the dense matter in the core of neutron stars with hyperons included and the star structure based on the Zimanyi & Moszkowski (ZM) model in the relativistic mean-field theory with a set of recent satisfactory parameters. The relation between hyperon abundances and baryon number densities is calculated and the distribution of baryons in the core of a typical neutron star of 1.4 M_sun is presented. Our results satisfy the requirements from observations of the mass of binary radio pulsars, and the ratio, I_c/I_tot, of the crustal momentum of inertia to the total one. The actual surface thermal radiation detected seems to indicate that baryons in the core of neutron stars should pair to form a superfluid phase, if hyperons appear in the core of neutron stars.

  10. Bubbles, Bow Shocks and B Fields: The Interplay Between Neutron Stars and Their Environments

    NASA Astrophysics Data System (ADS)

    Gaensler, Bryan M.

    2006-12-01

    Young neutron stars embody Nature's extremes: they spin incredibly rapidly, move through space at enormous velocities, and are imbued with unimaginably strong magnetic fields. Since their progenitor stars do not have any of these characteristics, these properties are presumably all imparted to a neutron star during or shortly after the supernova explosion in which it is formed. This raises two fundamental questions: how do neutron stars attain these extreme parameters, and how are their vast reservoirs of energy then dissipated? I will explain how multi-wavelength observations of the environments of neutron stars not only provide vital forensic evidence on the physics of supernova core collapse, but also spectacularly reveal the winds, jets, shocks and outflows through which these remarkable objects couple to their surroundings.

  11. Complete equation of state for neutron stars using the relativistic Hartree-Fock approximation

    SciTech Connect

    Miyatsu, Tsuyoshi; Cheoun, Myung-Ki; Yamamuro, Sachiko; Nakazato, Ken'ichiro

    2014-05-02

    We construct the equation of state in a wide-density range for neutron stars within relativistic Hartree-Fock approximation. The properties of uniform and nonuniform nuclear matter are studied consistently. The tensor couplings of vector mesons to baryons due to exchange contributions (Fock terms) are included, and the change of baryon internal structure in matter is also taken into account using the quark-meson coupling model. The Thomas-Fermi calculation is adopted to describe nonuniform matter, where the lattice of nuclei and the neutron drip out of nuclei are considered. Even if hyperons exist in the core of a neutron star, we obtain the maximum neutron-star mass of 1.95M{sub ?}, which is consistent with the recently observed massive pulsar, PSR J1614-2230. In addition, the strange vector (?) meson also plays a important role in supporting a massive neutron star.

  12. The long-term rotation dynamics of neutron stars with differentially rotating unmagnetized core

    NASA Astrophysics Data System (ADS)

    Barsukov, D. P.; Goglichidze, O. A.; Tsygan, A. I.

    2014-10-01

    We consider the pulsar long-term rotation dynamics taking into account the non-rigidity of neutron star rotation. We restrict our attention to the models with two essential assumptions: (1) crust-core interaction occurs via the viscosity (magnetic coupling is not important); (2) neutron star shape is symmetrical over the magnetic axis. The neutron star core is described by linearized quasi-stationary Newtonian hydrodynamical equations in one-fluid and two-fluid (neutron superfluidity) approximations. It is shown that in this case the pulsar inclination angle evolves to 0° or 90° very quickly. Since such fast evolution seems to contradict the observation data, either neutron stars are triaxial or the magnetic field plays the leading role in crust-core coupling.

  13. Maximum pulsar mass, equation of state and structure of neutron-star cores

    NASA Astrophysics Data System (ADS)

    Haensel, P.; Zdunik, J. L.

    2016-01-01

    The structure of neutron stars is determined by the equation of state of dense matter in their interiors. Brief review of the equation of state from neutron star surface to its center is presented. Recent discovery of two two-solar-mass pulsars puts interesting constraints on the poorly known equation of state of neutron-star cores for densities greater than normal nuclear matter density. Namely, this equation of state has to be stiff enough to yield maximum allowable mass of neutron stars greater than two solar masses. There are many models of neutron stars cores involving exclusively nucleons that satisfy this constraint. However, for neutron-star models based on recent realistic baryon interaction, and allowing for the presence of hyperons, the hyperon softening of the equation of state yields maximum masses significantly lower than two solar masses. Proposed ways out from this ”hyperon puzzle” are presented. They require a very fine tuning of parameters of dense hadronic matter and quark matter models. Consequences for the mass-radius relation for neutron stars are illustrated. A summary of the present situation and possible perspectives/challenges, as well as possible observational tests, are given.

  14. ROTATIONAL CORRECTIONS TO NEUTRON-STAR RADIUS MEASUREMENTS FROM THERMAL SPECTRA

    SciTech Connect

    Bauböck, Michi; Özel, Feryal; Psaltis, Dimitrios; Morsink, Sharon M.

    2015-01-20

    We calculate the rotational broadening in the observed thermal spectra of neutron stars spinning at moderate rates in the Hartle-Thorne approximation. These calculations accurately account for the effects of the second-order Doppler boosts as well as for the oblate shapes and the quadrupole moments of the neutron stars. We find that fitting the spectra and inferring the bolometric fluxes under the assumption that a star is not rotating causes an underestimate of the inferred fluxes and, thus, radii. The correction depends on the stellar spin, mass, radius, and the observer's inclination. For a 10 km, 1.4 M {sub ☉} neutron star spinning at 600 Hz, the rotational correction to the flux is ∼1%-4%, while for a 15 km neutron star with the same spin period, the correction ranges from 2% for pole-on sources to 12% for edge-on sources. We calculate the inclination-averaged corrections to inferred radii as a function of the neutron-star radius and mass and provide an empirical formula for the corrections. For realistic neutron-star parameters (1.4 M {sub ☉}, 12 km, 600 Hz), the stellar radius is on the order of 4% larger than the radius inferred under the assumption that the star is not spinning.

  15. Investigating variability of quiescent neutron stars in the globular clusters NGC 6440 and Terzan 5

    NASA Astrophysics Data System (ADS)

    Walsh, A. R.; Cackett, E. M.; Bernardini, F.

    2015-05-01

    The quiescent spectrum of neutron star low-mass X-ray binaries typically consists of two components - a thermal component associated with emission from the neutron star surface, and a non-thermal power-law component whose origin is not well understood. Spectral fitting of neutron star atmosphere models to the thermal component is one of the leading methods for measuring the neutron star radius. However, it has been known for years that the X-ray spectra of quiescent neutron stars vary between observations. While most quiescent variability is explained through a variable power-law component, the brightest and best-studied object, Cen X-4, requires a change in the thermal component and such thermal variability could be a problem for measuring neutron star radii. In this paper, we significantly increase the number of sources whose quiescent spectra have been studied for variability. We examine nine potential quiescent neutron stars with luminosities ?1034 erg s-1 over the course of multiple Chandra observations of the globular clusters NGC 6440 and Terzan 5 and find no strong evidence for variability in the effective temperature in seven of the nine sources. Two sources show a potential change in temperature, though this depends on the exact model fitted. CX1 in NGC 6440 is equally well fitted by a variable thermal component or a variable power law. Therefore, the results are inconclusive and we cannot exclude or require thermal variability in that source. CX5 in NGC 6440 shows a potential change in temperature, though this depends on whether a power law is included in the spectral fit or not. This suggests that thermal variability may not be widespread among quiescent neutron stars with luminosities ?1034 erg s-1, and hence thermal radiation remains a promising means to constraining neutron star radii.

  16. Simulations of binary neutron stars with reduced eccentricity

    NASA Astrophysics Data System (ADS)

    Tichy, Wolfgang; Moldenhauer, Niclas; Markakis, Charalampos; Johnson-McDaniel, Nathan; Brgmann, Bernd; Dietrich, Tim; Bernuzzi, Sebastiano

    2015-04-01

    In order to construct initial data, binary neutron stars in quasi-circular orbits are usually modeled as helically symmetric, i.e., stationary in a rotating frame. This symmetry gives rise to a first integral of the Euler equation, often employed for constructing equilibrium solutions via iteration. We have extended this approach to the case of eccentric orbits by considering configurations at apoapsis that are instantaneously stationary in a rotating frame. We approximate the orbit of each star at apoapsis as an ellipse and use the ellipse's inscribed circle to construct a helical symmetry vector. In addition, we add a radial piece to the symmetry vector to model the inspiral. These modifications result in two freely specifiable parameters, an eccentricity parameter e and a radial velocity parameter vr. If both are set to zero one recovers standard initial data. However, when such initial data are evolved one finds that the resulting orbits show a non-negligible eccentricity. We present an iterative method that allows us to adjust the parameters e and vr in such a way that the orbits that result from evolution have reduced eccentricities. This work was supported by NSF Grant PHY-1305387.

  17. Production of unstable heavy neutrinos in proto-neutron stars

    NASA Astrophysics Data System (ADS)

    Albertus, C.; Masip, M.; Prez-Garca, M. A.

    2015-12-01

    We discuss the production of a class of heavy sterile neutrinos ?h in proto-neutron stars. The neutrinos, of mass around 50MeV, have a negligible mixing with the active species but relatively large dimension-5 electromagnetic couplings. In particular, a magnetic dipole moment ? ?10-6GeV-1 implies that they are thermally produced through e+e- ??barh?h in the early phase of the core collapse, whereas a heavy-light transition moment ?tr ?10-8GeV-1 allows their decay ?h ??i ? with a lifetime around 10-3s. This type of electromagnetic couplings has been recently proposed to explain the excess of electron-like events in baseline experiments. We show that the production and decay of these heavy neutrinos would transport energy from the central regions of the star to distances d ? 400km, providing a very efficient mechanism to enhance the supernova shock front and heat the material behind it.

  18. Hunting for Neutron Star with the Swift Satellite

    NASA Astrophysics Data System (ADS)

    Shevchuk, Andrew; Rutledge, R. E.; Fox, D. B.

    2007-12-01

    We are currently pursuing a long-term project to identify new isolated neutron stars from the ROSAT All-Sky Survey Bright Source Catalog using short observations with NASA's Swift satellite. We select our targets via catalog cross-correlation as being likely, on general grounds, to possess a high X-ray to optical/IR/radio flux ratio. These sources are then observed with Swift on a time-available basis; each 1000s observation yields an improved X-ray position and simultaneous UV/optical image, enabling ready discrimination of stellar-type sources, active galaxies, and candidate compact objects. With more than 100 targets observed we have identified several candidate INSs, including our first demonstrated compact object, 1RXS J141256.0+792204. We have also identified other interesting sources including two previously unidentified galaxy clusters, several active galaxies and stars with extreme X-ray properties, and a number of candidate quiescent X-ray binaries. I will review the status of our survey and summarize the results to-date.

  19. A crystalline quark-hadron mixed phase in neutron stars

    SciTech Connect

    Glendenning, N.K.

    1994-08-31

    The mixed phase of a substance undergoing a first order phase transition has entirely different behavior according as the substance has more than one conserved charge or only one, as in the text book examples. In the latter case the pressure and nature of the phases are constants throughout the coexistence phase. For systems with more than one conserved charge (or independent component) we prove two theorems: (1) The pressure and the nature of the phases in equilibrium change continuously as the proportion of the phases varies from one pure phase to the other. (2) If one of the conserved charges is the Coulomb force, an intermediate-range order will be created by the competition between Coulomb and surface interface energy. Their sum is minimized when the coexistence phase assumes a Coulomb lattice of one phase immersed in the other. The geometry will vary continuously as the proportion of phases. We illustrate the theorems for a simple description of the hadron to quark phase transition in neutron stars and find a crystalline phase many kilometers thick. However the theorems are general and pertain to chemical mixtures, nuclear systems, either static as in stars or dynamic as in collisions, and have possible application to phase transitions in the early universe.

  20. Neutrino-driven winds from neutron star merger remnants

    NASA Astrophysics Data System (ADS)

    Perego, A.; Rosswog, S.; Cabezn, R. M.; Korobkin, O.; Kppeli, R.; Arcones, A.; Liebendrfer, M.

    2014-10-01

    We present a detailed, three-dimensional hydrodynamic study of the neutrino-driven winds emerging from the remnant of a neutron star merger. Our simulations are performed with the Newtonian, Eulerian code FISH, augmented by a detailed, spectral neutrino leakage scheme that accounts for neutrino absorption. Consistent with earlier two-dimensional studies, a strong baryonic wind is blown out along the original binary rotation axis within ?100 ms. From this model, we compute a lower limit on the expelled mass of 3.5 10-3 M?, relevant for heavy element nucleosynthesis. Because of stronger neutrino irradiation, the polar regions show substantially larger electron fractions than those at lower latitudes. The polar ejecta produce interesting r-process contributions from A ? 80 to about 130, while the more neutron-rich, lower latitude parts produce elements up to the third r-process peak near A ? 195. We calculate the properties of electromagnetic transients powered by the radioactivity in the wind, in addition to the `macronova' transient stemming from the dynamic ejecta. The polar regions produce ultraviolet/optical transients reaching luminosities up to 1041 erg s-1, which peak around 1 d in optical and 0.3 d in bolometric luminosity. The lower latitude regions, due to their contamination with high-opacity heavy elements, produce dimmer and more red signals, peaking after 2 d in optical and infrared.

  1. The collapse of white dwarfs to neutron stars

    NASA Technical Reports Server (NTRS)

    Woosley, S. E.; Baron, E.

    1992-01-01

    The observable consequences of an accreting white dwarf collapsing directly to a neutron star are considered. The outcome depends critically upon the nature of the wind that is driven by neutrino absorption in the surface layers as the dwarf collapses. Unlike previous calculations which either ignored mass loss or employed inadequate zoning to resolve it, a characteristic mass-loss rate of about 0.005 solar mass/s and an energy input of 5 x 10 exp 50 ergs/s is found. Such a large mass-loss rate almost completely obscures any prompt electromagnetic display and certainly rules out the production by this model of gamma-ray bursts situated at cosmological distances. The occurrence of such collapses with the Milky Way Galaxy might, however, be detected and limited by their nucleosynthesis and gamma-ray line emission. To avoid the overproduction of rare neutron-rich isotopes heavier than iron, such events must be very infrequent, probably happening no more than once every thousand years.

  2. Realistic fission model and the r-process in neutron star mergers

    SciTech Connect

    Shibagaki, S.; Kajino, T.; Chiba, S.; Mathews, G. J.

    2014-05-09

    About half of heavy elements are considered to be produced by the rapid neutron-capture process, r-process. The neutron star merger is one of the viable candidates for the astrophysical site of r-process nucleosynthesis. Nuclear fission reactions play an important role in the r-process of neutron star mergers. However theoretical predictions about fission properties of neutron-rich nuclei have some uncertainties. Especially, their fission fragment distributions are totally unknown and the phenomenologically extrapolated distribution was often applied to nucleosynthesis calculations. In this study, we have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions. We discuss the effects on the r-process in neutron star mergers from the nuclear fission of heavy neutron-rich actinide elements. We also discuss how variations in the fission fragment distributions affect the abundance pattern.

  3. Four-hair relations for differentially rotating neutron stars in the weak-field limit

    NASA Astrophysics Data System (ADS)

    Bretz, Joseph; Yagi, Kent; Yunes, Nicols

    2015-10-01

    The opportunity to study physics at supra-nuclear densities through x-ray observations of neutron stars has led to in-depth investigations of certain approximately universal relations that can remove degeneracies in pulse profile models. One such set of relations determines all of the multipole moments of a neutron star just from the first three (the mass monopole, the current dipole and the mass quadrupole moment) approximately independently of the equation of state. These three-hair relations were found to hold in neutron stars that rotate rigidly, as is the case in old pulsars, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We here extend the three-hair relations to differentially rotating stars for the first time with a generic rotation law using two approximations: a weak-field scheme (an expansion in powers of the neutron star compactness) and a perturbative differential rotation scheme (an expansion about rigid rotation). These approximations allow us to analytically derive approximately universal relations that allow us to determine all of the multipole moments of a (perturbative) differentially rotating star in terms of only the first four moments. These new four-hair relations for differentially rotating neutron stars are found to be approximately independent of the equation of state to a higher degree than the three-hair relations for uniformly rotating stars. Our results can be instrumental in the development of four-hair relations for rapidly differentially rotating stars in full general relativity using numerical simulations.

  4. On the observational appearances of a freely precessing neutron star in Hercules X-1

    NASA Technical Reports Server (NTRS)

    Postnov, K. A.; Prokhorov, M. E.; Shakura, N. I.

    1991-01-01

    Evidence for neutron star free precession is discussed, which is often presumed to be responsible for the observed 35-day cycle in Hercules X-1. The precise formula for the period derivative due to free precession is obtained under assumption that the precession period is much longer than that of the neutron star rotation. The optical light curves to be seen from the binary, with freely precessing accretion neutron star are simulated numerically. This simulation takes into account the reflection effect on the surface of the secondary component and on the accretion disk itself for different diagrams of x-ray emission.

  5. Modeling Phase-resolved Observations of the Surfaces of Magnetic Neutron Stars

    SciTech Connect

    Ho, Wynn C. G.; Mori, Kaya

    2008-02-27

    Recent observations by XMM-Newton detected rotational pulsations in the total brightness and spectrum of several neutron stars. To properly interpret the data, accurate modeling of neutron star emission is necessary. Detailed analysis of the shape and strength of the rotational variations allows a measurement of the surface composition and magnetic field, as well as constrains the nuclear equation of state. We discuss our models of the spectra and light curves of two of the most observed neutron stars, RX J1856.5-3754 and 1E 1207.4-5209, and discuss some implications of our results and the direction of future work.

  6. X-RAY EMISSION FROM NEUTRON STARS:. Some personal reflections and recent developments

    NASA Astrophysics Data System (ADS)

    Trmper, Joachim

    2000-09-01

    After a few remarks about the early history of the subject we present a short review of the present observational situation regarding the X-ray emission from isolated neutron stars. In total 32 objects have been detected with ROSAT, the majority of which are radio pulsars showing non -thermal (magnetospheric) emission. For three radio pulsars and three point sources in SNRs thermal emission has been seen which probably comes from the photospheric of the cooling neutron star. A third class comprising the objects represents neutron stars according matter from the interstellar medium.

  7. Kaon condensation in neutron stars in relativistic mean field theory with isovector-scalar channel interaction

    SciTech Connect

    Wang Guohua; Fu Weijie; Liu Yuxin

    2008-08-15

    We study the properties of neutron stars involving antikaon condensation with three different models in the framework of relativistic mean field (RMF) approximation theory: the Glendenning-Moszkowski (GM) model, the Zimanyi-Moszkowski (ZM) model, and the hybrid derivative coupling (HD) model. We take the isovector-scalar ({delta}-meson) channel interaction into account in our calculations and find that large mass neutron stars with kaon condensation can exist if the kaon optical potential is appropriately weak. The {delta}-meson channel interaction has a significant influence on the property of neutron stars and the effects are a little different for the three models.

  8. Kaon condensation in neutron stars in relativistic mean field theory with isovector-scalar channel interaction

    NASA Astrophysics Data System (ADS)

    Wang, Guo-Hua; Fu, Wei-Jie; Liu, Yu-Xin

    2008-08-01

    We study the properties of neutron stars involving antikaon condensation with three different models in the framework of relativistic mean field (RMF) approximation theory: the Glendenning-Moszkowski (GM) model, the Zimanyi-Moszkowski (ZM) model, and the hybrid derivative coupling (HD) model. We take the isovector-scalar (?-meson) channel interaction into account in our calculations and find that large mass neutron stars with kaon condensation can exist if the kaon optical potential is appropriately weak. The ?-meson channel interaction has a significant influence on the property of neutron stars and the effects are a little different for the three models.

  9. Detecting binary neutron star systems with spin in advanced gravitational-wave detectors

    NASA Astrophysics Data System (ADS)

    Brown, Duncan A.; Harry, Ian; Lundgren, Andrew; Nitz, Alexander H.

    2012-10-01

    The detection of gravitational waves from binary neutron stars is a major goal of the gravitational-wave observatories Advanced LIGO and Advanced Virgo. Previous searches for binary neutron stars with LIGO and Virgo neglected the component stars angular momentum (spin). We demonstrate that neglecting spin in matched-filter searches causes advanced detectors to lose more than 3% of the possible signal-to-noise ratio for 59% (6%) of sources, assuming that neutron star dimensionless spins, cJ/GM2, are uniformly distributed with magnitudes between 0 and 0.4 (0.05) and that the neutron stars have isotropically distributed spin orientations. We present a new method for constructing template banks for gravitational-wave searches for systems with spin. We present a new metric in a parameter space in which the template placement metric is globally flat. This new method can create template banks of signals with nonzero spins that are (anti-)aligned with the orbital angular momentum. We show that this search loses more than 3% of the maximum signal-to-noise for only 9% (0.2%) of binary neutron star sources with dimensionless spins between 0 and 0.4 (0.05) and isotropic spin orientations. Use of this template bank will prevent selection bias in gravitational-wave searches and allow a more accurate exploration of the distribution of spins in binary neutron stars.

  10. An all-purpose metric for the exterior of any kind of rotating neutron star

    NASA Astrophysics Data System (ADS)

    Pappas, George; Apostolatos, Theocharis A.

    2013-03-01

    We have tested the appropriateness of two-soliton analytic metric to describe the exterior of all types of neutron stars, no matter what their equation of state or rotation rate is. The particular analytic solution of the vacuum Einstein equations proved quite adjustable to mimic the metric functions of all numerically constructed neutron star models that we used as a testbed. The neutron star models covered a wide range of stiffness, with regard to the equation of state of their interior, and all rotation rates up to the maximum possible rotation rate allowed for each such star. Apart from the metric functions themselves, we have compared the radius of the innermost stable circular orbit RISCO, the orbital frequency ? equiv d? /dt of circular geodesics, and their epicyclic frequencies ??, ?z, as well as the change of the energy of circular orbits per logarithmic change of orbital frequency ? tilde{E}. All these quantities, calculated by means of the two-soliton analytic metric, fitted with good accuracy the corresponding numerical ones as in previous analogous comparisons (although previous attempts were restricted to neutron star models with either high or low rotation rates). We believe that this particular analytic solution could be considered as an analytic faithful representation of the gravitation field of any rotating neutron star with such accuracy, that one could explore the interior structure of a neutron star by using this space-time to interpret observations of astrophysical processes that take place around it.

  11. The stochastic background of gravitational waves due to the f-mode instability in neutron stars

    NASA Astrophysics Data System (ADS)

    Surace, M.; Kokkotas, K. D.; Pnigouras, P.

    2016-02-01

    This paper presents an estimate for the spectral properties of the stochastic background of gravitational waves emitted by a population of hot, young, rapidly rotating neutron stars throughout the Universe undergoing f-mode instabilities, formed through either core-collapse supernova explosions or the merger of binary neutron star systems. Their formation rate, from which the gravitational wave event rate is obtained, is deduced from observation-based determinations of the cosmic star formation rate. The gravitational wave emission occurs during the spin-down phase of the f-mode instability. For low magnetized neutron stars and assuming 10% of supernova events lead to f-mode unstable neutron stars, the background from supernova-derived neutron stars peaks at Ωgw ~ 10-9 for the l = m = 2f-mode, which should be detectable by cross-correlating a pair of second generation interferometers (e.g. Advanced LIGO/Virgo) with an upper estimate for the signal-to-noise ratio of ≈9.8. The background from supramassive neutron stars formed from binary mergers peaks at Ωgw ~ 10-10 and should not be detectable, even with third generation interferometers (e.g. Einstein Telescope).

  12. Equation of state of neutron star matter, limiting, rotational periods of fast pulsars, and the properties of strange stars

    SciTech Connect

    Weber, F. |; Glendenning, N.K.

    1993-10-25

    In this paper the following items will be treated: The present status of dense nuclear matter calculations and constraints on the behavior of the associated equation of state at high densities from data on rapidly rotating pulsars. Recent finding of the likely existence of a mixed phase of baryons and quarks forming a coulomb lattice in the dense cores of neutron stars. Review of important findings of recently performed calculations of rapidly rotating compact stars. These are constructed in the framework of general relativity theory for a representative collection of realistic nuclear equations of state. Establish the minimum-possible rotational periods of gravitationally bound neutron stars and self-bound strange stars. Its knowledge is of fundamental importance for the decision between pulsars that can be understood as rotating neutron stars and those that cannot (signature of hypothetical self-bound matter of which strange stars are the likely stellar candidates. Investigate the properties of sequences of strange stars. Specifically, we answer the question whether such objects can give rise to the observed phenomena of pulsar glitches, which is at the present time the only astrophysical test of the strange-quark-matter hypothesis.

  13. Small radii of neutron stars as an indication of novel in-medium effects

    NASA Astrophysics Data System (ADS)

    Jiang, Wei-Zhou; Li, Bao-An; Fattoyev, F. J.

    2015-09-01

    At present, neutron star radii from both observations and model predictions remain very uncertain. Whereas different models can predict a wide range of neutron star radii, it is not possible for most models to predict radii that are smaller than about 10km, thus if such small radii are established in the future they will be very difficult to reconcile with model estimates. By invoking a new term in the equation of state that enhances the energy density, but leaves the pressure unchanged we simulate the current uncertainty in the neutron star radii. This new term can be possibly due to the exchange of the weakly interacting light U-boson with appropriate in-medium parameters, which does not compromise the success of the conventional nuclear models. The validity of this new scheme will be tested eventually by more precise measurements of neutron star radii.

  14. Astrophysics of Neutron Stars - Facts and Fiction about their Formation and Functioning

    NASA Astrophysics Data System (ADS)

    Kundt, Wolfgang

    An unconventional survey is presented of the observable properties of neutron stars, and of all astrophysical phenomena possibly related to them, such as their pulsing, clock irregularities, bursting, and flickering, the generation of cosmic rays, of gamma-ray bursts, and of jets, their birth, and their occasional transient appearance as 'supersoft' X-ray sources. The msec pulsars are argued to be born fast, the black-hole candidates to be neutron stars inside of massive disks, and the gamma-ray bursts to be sparks from dense 'blades' accreting spasmodically onto the surfaces of (generally) old neutron stars Supernovae - the likely birth events of neutron stars - are thick-walled explosions, not to be described by Sedov-Taylor waves, which illuminate their gaseous environs via collisions of their 'splinters'.

  15. Oscillations During Thermonuclear X-ray Bursts: A New Probe of Neutron Stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    Observations of thermonuclear (also called Type 1) X-ray bursts from neutron stars in low mass X-ray binaries (LMXB) with the Rossi X-ray Timing Explorer (RXTE) have revealed large amplitude, high coherence X-ray brightness oscillations with frequencies in the 300 - 600 Hz range. Substantial spectral and timing evidence point to rotational modulation of the X-ray burst flux as the cause of these oscillations, and it is likely that they reveal the spin frequencies of neutron stars in LMXB from which they are detected. Here we review the status of our knowledge of these oscillations and describe how they can be used to constrain the masses and radii of neutron stars as well as the physics of thermonuclear burning on accreting neutron stars.

  16. Surface emission from neutron stars and implications for the physics of their interiors.

    PubMed

    Ozel, Feryal

    2013-01-01

    Neutron stars are associated with diverse physical phenomena that take place in conditions characterized by ultrahigh densities as well as intense gravitational, magnetic and radiation fields. Understanding the properties and interactions of matter in these regimes remains one of the challenges in compact object astrophysics. Photons emitted from the surfaces of neutron stars provide direct probes of their structure, composition and magnetic fields. In this review, I discuss in detail the physics that governs the properties of emission from the surfaces of neutron stars and their various observational manifestations. I present the constraints on neutron star radii, core and crust composition, and magnetic field strength and topology obtained from studies of their broadband spectra, evolution of thermal luminosity, and the profiles of pulsations that originate on their surfaces. PMID:23234858

  17. EQUATION OF STATE AND NEUTRON STAR PROPERTIES CONSTRAINED BY NUCLEAR PHYSICS AND OBSERVATION

    SciTech Connect

    Hebeler, K.; Lattimer, J. M.; Pethick, C. J.; Schwenk, A.

    2013-08-10

    Microscopic calculations of neutron matter based on nuclear interactions derived from chiral effective field theory, combined with the recent observation of a 1.97 {+-} 0.04 M{sub Sun} neutron star, constrain the equation of state of neutron-rich matter at sub- and supranuclear densities. We discuss in detail the allowed equations of state and the impact of our results on the structure of neutron stars, the crust-core transition density, and the nuclear symmetry energy. In particular, we show that the predicted range for neutron star radii is robust. For use in astrophysical simulations, we provide detailed numerical tables for a representative set of equations of state consistent with these constraints.

  18. Spin polarized asymmetric nuclear matter and neutron star matter within the lowest order constrained variational method

    SciTech Connect

    Bordbar, G. H.; Bigdeli, M.

    2008-01-15

    In this paper, we calculate properties of the spin polarized asymmetrical nuclear matter and neutron star matter, using the lowest order constrained variational (LOCV) method with the AV{sub 18}, Reid93, UV{sub 14}, and AV{sub 14} potentials. According to our results, the spontaneous phase transition to a ferromagnetic state in the asymmetrical nuclear matter as well as neutron star matter do not occur.

  19. Hans A. Bethe Prize: Neutron Stars and Core-Collapse Supernovae

    NASA Astrophysics Data System (ADS)

    Lattimer, James

    2015-04-01

    Core-collapse supernovae lead to the formation of neutron stars, and both are sensitive to the dense matter equation of state. Hans Bethe first recognized that the matter in the collapsing core of a massive star has a relatively low entropy which prevents nuclear dissociation until nuclei merge near the nuclear saturation density. This recognition means that collapse continues until the core exceeds the saturation density. This prediction forms the foundation for modern simulations of supernovae. These supernovae sample matter up to about twice nuclear saturation density, but neutron stars are sensitive to the equation of state both near the saturation density and at several times higher densities. Two important recent developments are the discovery of two-solar mass neutron stars and refined experimental determinations of the behavior of the symmetry energy of nuclear matter near the saturation density. Combined with the assumption of causality, they imply that the radii of observed neutron stars are largely independent of their mass, and that this radius is in the range of 11 to 13 km. These theoretical results are not only consistent with expectations from theoretical studies of pure neutron matter, but also accumulated observations of both bursting and cooling neutron stars. In the near future, new pulsar timing data, which could lead to larger measured masses as well as measurements of moments of inertia, X-ray observations, such as from NICER, of bursting and other sources, and gravitational wave observations of neutron stars in merging compact binaries, will provide important new constraints on neutron stars and the dense matter equation of state. DOE DE-FG02-87ER-40317.

  20. Does kaon condensation occur in neutron stars in the relativistic mean-field theory?

    NASA Astrophysics Data System (ADS)

    Dai, Z. G.; Cheng, K. S.

    1997-02-01

    We discuss whether kaon condensation occurs in neutron star matter by using the Zimanyi-Moszkowski model in the relativistic mean-field theory. As a comparison, we also discuss the results from the Boguta-Bodmer model. We show that even though hyperons which may increase the critical condensation density are not included, kaon condensation might not occur in stable neutron stars for the Zimanyi-Moszkowski model.

  1. Inertial modes of rigidly rotating neutron stars in Cowling approximation

    SciTech Connect

    Kastaun, Wolfgang

    2008-06-15

    In this article, we investigate inertial modes of rigidly rotating neutron stars, i.e. modes for which the Coriolis force is dominant. This is done using the assumption of a fixed spacetime (Cowling approximation). We present frequencies and eigenfunctions for a sequence of stars with a polytropic equation of state, covering a broad range of rotation rates. The modes were obtained with a nonlinear general relativistic hydrodynamic evolution code. We further show that the eigenequations for the oscillation modes can be written in a particularly simple form for the case of arbitrary fast but rigid rotation. Using these equations, we investigate some general characteristics of inertial modes, which are then compared to the numerically obtained eigenfunctions. In particular, we derive a rough analytical estimate for the frequency as a function of the number of nodes of the eigenfunction, and find that a similar empirical relation matches the numerical results with unexpected accuracy. We investigate the slow rotation limit of the eigenequations, obtaining two different sets of equations describing pressure and inertial modes. For the numerical computations we only considered axisymmetric modes, while the analytic part also covers nonaxisymmetric modes. The eigenfunctions suggest that the classification of inertial modes by the quantum numbers of the leading term of a spherical harmonic decomposition is artificial in the sense that the largest term is not strongly dominant, even in the slow rotation limit. The reason for the different structure of pressure and inertial modes is that the Coriolis force remains important in the slow rotation limit only for inertial modes. Accordingly, the scalar eigenequation we obtain in that limit is spherically symmetric for pressure modes, but not for inertial modes.

  2. Electron exchange and polarization effects on electron captures and neutron emissions by nuclei in white dwarfs and neutron stars

    NASA Astrophysics Data System (ADS)

    Chamel, N.; Fantina, A. F.

    2016-03-01

    In dense stellar environments, nuclei may become unstable against electron captures and/or neutron emissions. These processes are of particular importance for determining the internal constitution of white-dwarf cores and neutron-star crusts. In this paper, the role of electron exchange and polarization effects is studied. In particular, the instability condition for the onset of electron captures and neutron emissions is extended so as to account for electron exchange and polarization. Moreover, general analytical expressions for the corresponding density and pressure are derived. The corrections to the electron-capture threshold in white-dwarf cores are found to be very small. Likewise, the neutron-drip density and pressure in the crusts of accreting and nonaccreting neutron stars are only slightly shifted. Depending on the nuclear mass model employed, electron polarization may change the composition of the crust of nonaccreting neutron stars. On the other hand, the current uncertainties in the masses of neutron-rich Kr and Sr isotopes are found to be more important than electron exchange and polarization effects.

  3. Role of the symmetry energy on the neutron-drip transition in accreting and nonaccreting neutron stars

    NASA Astrophysics Data System (ADS)

    Fantina, A. F.; Chamel, N.; Mutafchieva, Y. D.; Stoyanov, Zh. K.; Mihailov, L. M.; Pavlov, R. L.

    2016-01-01

    In this paper, we study the role of the symmetry energy on the neutron-drip transition in both nonaccreting and accreting neutron stars, allowing for the presence of a strong magnetic field as in magnetars. The density, pressure, and composition at the neutron-drip threshold are determined using the recent set of the Brussels-Montreal microscopic nuclear mass models, which mainly differ in their predictions for the value of the symmetry energy J and its slope L in infinite homogeneous nuclear matter at saturation. Although some correlations between on the one hand the neutron-drip density, the pressure, the proton fraction, and on the other hand J (or equivalently L ) are found, these correlations are radically different in nonaccreting and accreting neutron stars. In particular, the neutron-drip density is found to increase with L in the former case, but decreases in the latter case depending on the composition of ashes from x-ray bursts and superbursts. We have qualitatively explained these different behaviors using a simple mass formula. We have also shown that the details of the nuclear structure may play a more important role than the symmetry energy in accreting neutron-star crusts.

  4. WHEN CAN GRAVITATIONAL-WAVE OBSERVATIONS DISTINGUISH BETWEEN BLACK HOLES AND NEUTRON STARS?

    SciTech Connect

    Hannam, Mark; Fairhurst, Stephen; Brown, Duncan A.; Fryer, Chris L.; Harry, Ian W.

    2013-03-20

    Gravitational-wave observations of compact binaries have the potential to uncover the distribution of masses and spins of black holes and neutron stars in the universe. The binary components' physical parameters can be inferred from their effect on the phasing of the gravitational-wave signal, but a partial degeneracy between the components' mass ratio and their spins limits our ability to measure the individual component masses. At the typical signal amplitudes expected by the Advanced Laser Interferometer Gravitational-wave Observatory (signal-to-noise ratios between 10 and 20), we show that it will in many cases be difficult to distinguish whether the components are neutron stars or black holes. We identify when the masses of the binary components could be unambiguously measured outside the range of current observations: a system with a chirp mass M {<=} 0.871 M{sub Sun} would unambiguously contain the smallest-mass neutron star observed, and a system with M {>=} 2.786 M{sub Sun} must contain a black hole. However, additional information would be needed to distinguish between a binary containing two 1.35 M{sub Sun} neutron stars and an exotic neutron-star-black-hole binary. We also identify those configurations that could be unambiguously identified as black hole binaries, and show how the observation of an electromagnetic counterpart to a neutron-star-black-hole binary could be used to constrain the black hole spin.

  5. ELECTROMAGNETIC EXTRACTION OF ENERGY FROM BLACK-HOLE-NEUTRON-STAR BINARIES

    SciTech Connect

    McWilliams, Sean T.; Levin, Janna

    2011-12-01

    The coalescence of black-hole-neutron-star binaries is expected to be a principal source of gravitational waves for the next generation of detectors, Advanced LIGO and Advanced Virgo. For black hole masses not much larger than the neutron star mass, the tidal disruption of the neutron star by the black hole provides one avenue for generating an electromagnetic counterpart. However, in this work, we demonstrate that, for all black-hole-neutron-star binaries observable by Advanced LIGO/Virgo, the interaction of the black hole with the magnetic field of the neutron star will generate copious luminosity, comparable to supernovae and active galactic nuclei. This novel effect may have already been observed as a new class of very short gamma-ray bursts by the Swift Gamma-Ray Burst Telescope. These events may be observable to cosmological distances, so that any black-hole-neutron-star coalescence detectable with gravitational waves by Advanced LIGO/Virgo could also be detectable electromagnetically.

  6. When can Gravitational-wave Observations Distinguish between Black Holes and Neutron Stars?

    NASA Astrophysics Data System (ADS)

    Hannam, Mark; Brown, Duncan A.; Fairhurst, Stephen; Fryer, Chris L.; Harry, Ian W.

    2013-03-01

    Gravitational-wave observations of compact binaries have the potential to uncover the distribution of masses and spins of black holes and neutron stars in the universe. The binary components' physical parameters can be inferred from their effect on the phasing of the gravitational-wave signal, but a partial degeneracy between the components' mass ratio and their spins limits our ability to measure the individual component masses. At the typical signal amplitudes expected by the Advanced Laser Interferometer Gravitational-wave Observatory (signal-to-noise ratios between 10 and 20), we show that it will in many cases be difficult to distinguish whether the components are neutron stars or black holes. We identify when the masses of the binary components could be unambiguously measured outside the range of current observations: a system with a chirp mass {M} ≤ 0.871 M ? would unambiguously contain the smallest-mass neutron star observed, and a system with {M} ≥ 2.786 {M_? } must contain a black hole. However, additional information would be needed to distinguish between a binary containing two 1.35 M ? neutron stars and an exotic neutron-star-black-hole binary. We also identify those configurations that could be unambiguously identified as black hole binaries, and show how the observation of an electromagnetic counterpart to a neutron-star-black-hole binary could be used to constrain the black hole spin.

  7. Proto-neutron Star Convection in the Post-bounce Epoch of Stellar Core Collapse

    NASA Astrophysics Data System (ADS)

    Swesty, F. D.; Myra, E. S.

    2005-12-01

    We present results of 2-D simulations of convective instabilities in proto-neutron stars in the immediate aftermath of stellar core collapse. The capture of electrons by protons during collapse and the subsequent post-bounce deleptonization sets up a strong gradient in the electron fraction near the proto-neutron star surface. The formation of a strong shock at the outer edge of the homologous core gives rise to a strong entropy gradient. Depending on the precise nature of these gradients, and the equation of state, there are several possible instabilities that can arise in the outer layers of the proto-neutron star. In this poster, we describe the results of our 2-D radiation-hydrodynamic simulations of the proto-neutron star. These simulations have revealed previously unseen beahvior, including stratified convection in the proto-neutron star and a rapid one-time deloptonization burst. We find that, in our models, vigorous proto-neutron star convection does not persist after destabilizing gradients have been eradicated. This work was performed at the State University of New York at Stony Brook as part of the TeraScale Supernova Initiative, and is funded by SciDAC grant DE-FC02-01ER41185 from the U.S. Dept. of Energy, Office of Science High-Energy, Nuclear, and Advanced Scientific Computing Research Programs. We gratefully acknowledge support of the National Energy Research Scientific Computing Center (NERSC) for computational and consulting support.

  8. Electrically charged: An effective mechanism for soft EOS supporting massive neutron star

    NASA Astrophysics Data System (ADS)

    Jing, ZhenZhen; Wen, DeHua; Zhang, XiangDong

    2015-10-01

    The massive neutron star discoverer announced that strange particles, such as hyperons should be ruled out in the neutron star core as the soft Equation of State (EOS) can-not support a massive neutron star. However, many of the nuclear theories and laboratory experiments support that at high density the strange particles will appear and the corresponding EOS of super-dense matters will become soft. This situation promotes a challenge between the astro-observation and nuclear physics. In this work, we introduce an effective mechanism to answer this challenge, that is, if a neutron star is electrically charged, a soft EOS will be equivalently stiffened and thus can support a massive neutron star. By employing a representative soft EOS, it is found that in order to obtain an evident effect on the EOS and thus increasing the maximum stellar mass by the electrostatic field, the total net charge should be in an order of 1020 C. Moreover, by comparing the results of two kind of charge distributions, it is found that even for different distributions, a similar total charge: ~ 2.3 1020 C is needed to support a ~ 2.0 M ? neutron star.

  9. Radio-silent isolated neutron stars as a new astronomical reality

    NASA Astrophysics Data System (ADS)

    Caraveo, Patrizia A.; Bignami, Giovanni F.; Trümper, Joachim E.

    As of today, seven X-ray sources have been tentatively identified as radio-quiet, isolated neutron stars. The family appears to be a rapidly growing one, although not all the objects have been identified with the same degree of certainty. The most convincing example of radio quiet pulsar is certainly Geminga, the neutron star nature of which, proposed in 1983 on the basis of its similarity with the Vela pulsar, has been firmly established with the discovery of its X and γ pulsation. Four more neutron star candidates, originally found in the Einstein data, have been confirmed by ROSAT, which has added to the list two more entries. All this is not the result of an unbiased search. The seven sources were not selected at random: four are inside supernova remnants, an obvious place to search for isolated neutron stars, while the remaining three were singled out because of some peculiarity. Intense γ-ray emission in the case of Geminga, very high X-ray counting rate for RXJ185635-3754, or being the brightest unidentified source in the Einstein medium sensitivity survey, MS 0317-6647. In spite of the limited number of objects and of the observational biases, these seven radio quiet neutron star candidates add valuable pieces of information to the observational panorama of known pulsars. Their properties, inferred from the X-ray emission, offer a coherent picture, pointing towards thermally emitting, cooling neutron stars.

  10. Spin Evolution of Neutron Stars in OB/X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Li, Xiang-Dong; Wang, Zhen-Ru

    2004-08-01

    We have investigated the relation between the orbital period Porb and the spin period Ps of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M? donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B0 stronger than about 3 1012 G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B0<3 1012 G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the Ps-Porb diagram.

  11. The role of neutron star mergers in the chemical evolution of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Cescutti, G.; Romano, D.; Matteucci, F.; Chiappini, C.; Hirschi, R.

    2015-05-01

    Context. The dominant astrophysical production site of the r-process elements has not yet been unambiguously identified. The suggested main r-process sites are core-collapse supernovae and merging neutron stars. Aims: We explore the problem of the production site of Eu. We also use the information present in the observed spread in the Eu abundances in the early Galaxy, and not only its average trend. Moreover, we extend our investigations to other heavy elements (Ba, Sr, Rb, Zr) to provide additional constraints on our results. Methods: We adopt a stochastic chemical evolution model that takes inhomogeneous mixing into account. The adopted yields of Eu from merging neutron stars and from core-collapse supernovae are those that are able to explain the average [Eu/Fe]-[Fe/H] trend observed for solar neighbourhood stars, the solar abundance of Eu, and the present-day abundance gradient of Eu along the Galactic disc in the framework of a well-tested homogeneous model for the chemical evolution of the Milky Way. Rb, Sr, Zr, and Ba are produced by both the s- and r-processes. The r-process yields were obtained by scaling the Eu yields described above according to the abundance ratios observed in r-process rich stars. The s-process contribution by spinstars is the same as in our previous papers. Results: Neutron star binaries that merge in less than 10 Myr or neutron star mergers combined with a source of r-process generated by massive stars can explain the spread of [Eu/Fe] in the Galactic halo. The combination of r-process production by neutron star mergers and s-process production by spinstars is able to reproduce the available observational data for Sr, Zr, and Ba. We also show the first predictions for Rb in the Galactic halo. Conclusions: We confirm previous results that either neutron star mergers on a very short timescale or both neutron star mergers and at least a fraction of Type II supernovae have contributed to the synthesis of Eu in the Galaxy. The r-process production of Sr, Zr, and Ba by neutron star mergers - complemented by an s-process production by spinstars - provide results that are compatible with our previous findings based on other r-process sites. We critically discuss the weak and strong points of both neutron star merging and supernova scenarios for producing Eu and eventually suggest that the best solution is probably a mixed one in which both sources produce Eu. In fact, this scenario reproduces the scatter observed in all the studied elements better. Warning, no authors found for 2015A&A...577A.131.

  12. Three-dimensional hydrodynamic simulations of the combustion of a neutron star into a quark star

    SciTech Connect

    Herzog, Matthias; Roepke, Friedrich K.

    2011-10-15

    We present three-dimensional numerical simulations of turbulent combustion converting a neutron star into a quark star. Hadronic matter, described by a microphysical finite-temperature equation of state, is converted into strange quark matter. We assume this phase, represented by a bag-model equation of state, to be absolutely stable. Following the example of thermonuclear burning in white dwarfs leading to type Ia supernovae, we treat the conversion process as a potentially turbulent deflagration. Solving the nonrelativistic Euler equations using established numerical methods we conduct large eddy simulations including an elaborate subgrid scale model, while the propagation of the conversion front is modeled with a level-set method. Our results show that for large parts of the parameter space the conversion becomes turbulent and therefore significantly faster than in the laminar case. Despite assuming absolutely stable strange quark matter, in our hydrodynamic approximation an outer layer remains in the hadronic phase, because the conversion front stops when it reaches conditions under which the combustion is no longer exothermic.

  13. Constraining scalar-tensor theories of gravity from the most massive neutron stars

    NASA Astrophysics Data System (ADS)

    Palenzuela, Carlos; Liebling, Steven L.

    2016-02-01

    Scalar-tensor (ST) theories of gravity are natural phenomenological extensions to general relativity. Although these theories are severely constrained both by solar system experiments and by binary pulsar observations, a large set of ST families remain consistent with these observations. Recent work has suggested probing the unconstrained region of the parameter space of ST theories based on the stability properties of highly compact neutron stars. Here, the dynamical evolution of very compact stars in a fully nonlinear code demonstrates that the stars do become unstable and that the instability, in some cases, drives the stars to collapse. We discuss the implications of these results in light of recent observations of the most massive neutron star yet observed. In particular, such observations suggest that such a star would be subject to the instability for a certain regime; its existence therefore supports a bound on the ST parameter space.

  14. Possible ambiguities in the equation of state for neutron stars

    SciTech Connect

    Cheoun, Myung-Ki; Miyatsu, Tsuyoshi; Ryu, C. Y.; Deliduman, Cemsinan; Güngör, Can; Keleş, Vildan; Kajino, Toshitaka; Mathews, Grant J.

    2014-05-02

    We addressed possible ambiguities on the properties of neutron stars (NSs) estimated in theoretical sides. First, roles of hyperons inside the NS are discussed through various relativistic mean field (RMF) theories. In particular, the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry is shown to give rise to the increase of hyperon threshold density, similarly to the Fock term effects in RMF theories. As a result, about 2.0 solar mass is obtained with the hyperons. Second, the effect by the modified f(R) gravity, which leaves a room for the dark energy in the Einstein equation to be taken into account, is discussed for the NS in a strong magnetic field (MF). Our results show that the modified gravity with the Kaluza-Klein electro-magnetism theory expanded in terms of a length scale parameter may reasonably describe the NS in strong MF, so called magnetar. Even the super-soft equation of state is shown to be revived by the modified f(R) gravity.

  15. Stability of Hall equilibria in neutron star crusts

    SciTech Connect

    Marchant, Pablo; Reisenegger, Andreas; Valdivia, Juan Alejandro; Hoyos, Jaime H.

    2014-12-01

    In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are 'Hall equilibria', i.e., field configurations that are unaffected by Hall drift. Here we address the crucial question of the stability of these equilibria through axially symmetric (two-dimensional (2D)) numerical simulations of Hall drift and ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D stability of a purely poloidal equilibrium, for which ohmic dissipation makes the field evolve toward an attractor state through adjacent stable configurations, around which damped oscillations occur. For this field, the decay scales with the ohmic timescale. We also study the case of an unstable equilibrium consisting of both poloidal and toroidal field components that are confined within the crust. This field evolves into a stable configuration, which undergoes damped oscillations superimposed on a slow evolution toward an attractor, just as the purely poloidal one.

  16. Radioactively powered emission from black hole-neutron star mergers

    SciTech Connect

    Tanaka, Masaomi; Wanajo, Shinya; Hotokezaka, Kenta; Kyutoku, Koutarou; Kiuchi, Kenta; Sekiguchi, Yuichiro; Shibata, Masaru

    2014-01-01

    Detection of the electromagnetic counterparts of gravitational wave (GW) sources is important to unveil the nature of compact binary coalescences. We perform three-dimensional, time-dependent, multi-frequency radiative transfer simulations for radioactively powered emission from the ejecta of black hole (BH)-neutron star (NS) mergers. Depending on the BH to NS mass ratio, spin of the BH, and equations of state of dense matter, BH-NS mergers can eject more material than NS-NS mergers. In such cases, radioactively powered emission from the BH-NS merger ejecta can be more luminous than that from NS-NS mergers. We show that, in spite of the expected larger distances to BH-NS merger events, the observed brightness of BH-NS mergers can be comparable to or even higher than that of NS-NS mergers. We find that, when the tidally disrupted BH-NS merger ejecta are confined to a small solid angle, the emission from BH-NS merger ejecta tends to be bluer than that from NS-NS merger ejecta for a given total luminosity. Thanks to this property, we might be able to distinguish BH-NS merger events from NS-NS merger events by multi-band observations of the radioactively powered emission. In addition to the GW observations, such electromagnetic observations can potentially provide independent information on the progenitors of GW sources and the nature of compact binary coalescences.

  17. Stability of Hall Equilibria in Neutron Star Crusts

    NASA Astrophysics Data System (ADS)

    Marchant, Pablo; Reisenegger, Andreas; Alejandro Valdivia, Juan; Hoyos, Jaime H.

    2014-12-01

    In the solid crusts of neutron stars, the advection of the magnetic field by the current-carrying electrons, an effect known as Hall drift, should play a very important role as the ions remain essentially fixed (as long as the solid does not break). Although Hall drift preserves the magnetic field energy, it has been argued that it may drive a turbulent cascade to scales at which ohmic dissipation becomes effective, allowing a much faster decay in objects with very strong fields. On the other hand, it has been found that there are "Hall equilibria," i.e., field configurations that are unaffected by Hall drift. Here we address the crucial question of the stability of these equilibria through axially symmetric (two-dimensional (2D)) numerical simulations of Hall drift and ohmic diffusion, with the simplifying assumption of uniform electron density and conductivity. We demonstrate the 2D stability of a purely poloidal equilibrium, for which ohmic dissipation makes the field evolve toward an attractor state through adjacent stable configurations, around which damped oscillations occur. For this field, the decay scales with the ohmic timescale. We also study the case of an unstable equilibrium consisting of both poloidal and toroidal field components that are confined within the crust. This field evolves into a stable configuration, which undergoes damped oscillations superimposed on a slow evolution toward an attractor, just as the purely poloidal one.

  18. Relativistic g-modes in rapidly rotating neutron stars

    SciTech Connect

    Gaertig, Erich; Kokkotas, Kostas D.

    2009-09-15

    We study the g-modes of fast rotating stratified neutron stars in the general relativistic Cowling approximation, where we neglect metric perturbations and where the background models take into account the buoyant force due to composition gradients. This is the first paper studying this problem in a general relativistic framework. In a recent paper [A. Passamonti, B. Haskell, N. Andersson, D. I. Jones, and I. Hawke, Mon. Not. R. Astron. Soc. 394, 730 (2009)], a similar study was performed within the Newtonian framework, where the authors presented results about the onset of CFS-unstable g-modes and the close connection between inertial and gravity modes for sufficiently high rotation rates and small composition gradients. This correlation arises from the interplay between the buoyant force which is the restoring force for g-modes and the Coriolis force which is responsible for the existence of inertial modes. In our relativistic treatment of the problem, we find an excellent qualitative agreement with respect to the Newtonian results.

  19. Hyperon puzzle of neutron stars with Skyrme force models

    NASA Astrophysics Data System (ADS)

    Lim, Yeunhwan; Hyun, Chang Ho; Kwak, Kyujin; Lee, Chang-Hwan

    2015-12-01

    We consider the so-called hyperon puzzle of neutron star (NS). We employ Skyrme force models for the description of in-medium nucleon-nucleon (NN), nucleon-Lambda hyperon (N?) and Lambda-Lambda (??) interactions. A phenomenological finite-range force (FRF) for the ?? interaction is considered as well. Equation of state (EoS) of NS matter is obtained in the framework of density functional theory, and Tolman-Oppenheimer-Volkoff (TOV) equations are solved to obtain the mass-radius relations of NSs. It has been generally known that the existence of hyperons in the NS matter is not well supported by the recent discovery of large-mass NSs (M ? 2M?) since hyperons make the EoS softer than the one without them. For the selected interaction models, N? interactions reduce the maximum mass of NS by about 30%, while ?? interactions can give about 10% enhancement. Consequently, we find that some Skyrme force models predict the maximum mass of NS consistent with the observation of 2M? NSs, and at the same time satisfy observationally constrained mass-radius relations.

  20. Superburst Ignition and Implications for Neutron Star Interiors

    NASA Astrophysics Data System (ADS)

    Brown, Edward F.

    2004-10-01

    Superbursts are thought to be powered by the unstable ignition of a carbon-enriched layer formed from the burning of accreted hydrogen and helium. As shown by Cumming & Bildsten, the short recurrence time hinges on the crust being sufficiently hot at densities ρ>109 g cm-3. In this Letter, we self-consistently solve for the flux coming from the deep crust and core. The temperature at which the carbon unstably ignites is only weakly sensitive to the composition of the ashes of H/He burning, but does depend on the thermal conductivity of the inner crust and the neutrino emissivity of the core. The observed superburst recurrence times and energetics suggest that the crust thermal conductivity is low, as if the crust were amorphous instead of crystalline. If the conductivity is higher, such as from a lattice with impurities, then matching the superburst properties requires that the neutrino emissivity not be stronger than modified Urca. Observations of superbursts-energetics, recurrence times, and cooling times-therefore complement observations of isolated cooling neutron stars and soft X-ray transients in constraining properties of dense matter. Perhaps the most interesting object in this regard is KS 1731-260, which produced a superburst during its protracted accretion outburst, but had a rapidly declining quiescent luminosity.