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Sample records for quaking neutron star

  1. Quantum crystals in neutron stars

    NASA Technical Reports Server (NTRS)

    Canuto, V.; Chitre, S. M.

    1974-01-01

    Using the many-body techniques appropriate for quantum crystals it is shown that the deep interior of a neutron star is most likely an orderly arrangement of neutrons, protons and hyperons forming a solid. It is shown that a liquid or gas arrangement would produce higher energy. If so, a neutron star can be viewed as two solids (crust and core) permeated by a layer of ordinary or (perhaps) superfluid liquid. Astronomical evidence is in favor of such a structure: the sudden jumps in the periods of the Crab and Vela pulsars that differ by a factor of about 100 can be easily explained by the star-quake model. If the Crab is less massive than Vela (i.e., if it is not dense enough to have a solid core), the star-quakes take place in the crust whereas for Vela they occur in the core.

  2. 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.

  3. Magnetized Neutron Stars

    NASA Astrophysics Data System (ADS)

    Liebling, Steven; Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Tohline, Joel

    2008-04-01

    Magnetized neutron stars, whether considered individually or within compact binary systems, demonstrate a number of interesting dynamical effects. Using a distributed adaptive mesh refinement (AMR) code, we evolve such stars and study their dynamics.

  4. 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.

  5. 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.

  6. Neutron stars - General review

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.; Canuto, V.

    1974-01-01

    A review is presented of those properties of neutron stars upon which there is general agreement and of those areas which currently remain in doubt. Developments in theoretical physics of neutron star interiors are summarized with particular attention devoted to hyperon interactions and the structure of interior layers. Determination of energy states and the composition of matter is described for successive layers, beginning with the surface and proceeding through the central region into the core. Problems encountered in determining the behavior of matter in the ultra-high density regime are discussed, and the effects of the magnetic field of a neutron star are evaluated along with the behavior of atomic structures in the field. The evolution of a neutron star is outlined with discussion centering on carbon detonation, cooling, vibrational damping, rotation, and pulsar glitches. The role of neutron stars in cosmic-ray propagation is considered.

  7. 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.

  8. 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.

  9. Neutron Star Compared to Manhattan

    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...

  10. 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.

  11. Matter accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

    Some of the fundamental neutron star parameters, such as the mass and the magnetic field strength, were experimentally determined in accreting neutron star systems. Some of the relevant data and the models used to derive useful information from them, are reviewed concentrating mainly on X-ray pulsars. The latest advances in our understanding of the radiation mechanisms and the transfer in the strongly magnetized polar cap regions are discussed.

  12. High-affinity consensus binding of target RNAs by the STAR/GSG proteins GLD-1, STAR-2 and Quaking

    PubMed Central

    2010-01-01

    Background STAR/GSG proteins regulate gene expression in metazoans by binding consensus sites in the 5' or 3' UTRs of target mRNA transcripts. Owing to the high degree of homology across the STAR domain, most STAR proteins recognize similar RNA consensus sequences. Previously, the consensus for a number of well-characterized STAR proteins was defined as a hexameric sequence, referred to as the SBE, for STAR protein binding element. C. elegans GLD-1 and mouse Quaking (Qk-1) are two representative STAR proteins that bind similar consensus hexamers, which differ only in the preferred nucleotide identities at certain positions. Earlier reports also identified partial consensus elements located upstream or downstream of a canonical consensus hexamer in target RNAs, although the relative contribution of these sequences to the overall binding energy remains less well understood. Additionally, a recently identified STAR protein called STAR-2 from C. elegans is thought to bind target RNA consensus sites similar to that of GLD-1 and Qk-1. Results Here, a combination of fluorescence-polarization and gel mobility shift assays was used to demonstrate that STAR-2 binds to a similar RNA consensus as GLD-1 and Qk-1. These assays were also used to further delineate the contributions of each hexamer consensus nucleotide to high-affinity binding by GLD-1, Qk-1 and STAR-2 in a variety of RNA contexts. In addition, the effects of inserting additional full or partial consensus elements upstream or downstream of a canonical hexamer in target RNAs were also measured to better define the sequence elements and RNA architecture recognized by different STAR proteins. Conclusions The results presented here indicate that a single hexameric consensus is sufficient for high-affinity RNA binding by STAR proteins, and that upstream or downstream partial consensus elements may alter binding affinities depending on the sequence and spacing. The general requirements determined for high-affinity RNA

  13. Origin of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Brecher, K.

    1999-12-01

    The origin of the concept of neutron stars can be traced to two brief, incredibly insightful publications. Work on the earlier paper by Lev Landau (Phys. Z. Sowjetunion, 1, 285, 1932) actually predated the discovery of neutrons. Nonetheless, Landau arrived at the notion of a collapsed star with the density of a nucleus (really a "nucleus star") and demonstrated (at about the same time as, and independent of, Chandrasekhar) that there is an upper mass limit for dense stellar objects of about 1.5 solar masses. Perhaps even more remarkable is the abstract of a talk presented at the December 1933 meeting of the American Physical Society published by Walter Baade and Fritz Zwicky in 1934 (Phys. Rev. 45, 138). It followed the discovery of the neutron by just over a year. Their report, which was about the same length as the present abstract: (1) invented the concept and word supernova; (2) suggested that cosmic rays are produced by supernovae; and (3) in the authors own words, proposed "with all reserve ... the view that supernovae represent the transitions from ordinary stars to neutron stars (italics), which in their final stages consist of extremely closely packed neutrons." The abstract by Baade and Zwicky probably contains the highest density of new, important (and correct) ideas in high energy astrophysics ever published in a single paper. In this talk, we will discuss some of the facts and myths surrounding these two publications.

  14. 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.

  15. The neutron star zoo

    NASA Astrophysics Data System (ADS)

    Harding, Alice K.

    2013-12-01

    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.

  16. 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.

  17. 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.

  18. 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.

  19. Rotating neutron stars with exotic cores: masses, radii, stability

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency (716Hz) and the maximum measured mass (2 M ⊙ . The present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a first-order phase transition, both between pure phases, and into a mixed-phase state, are reviewed. The case of two disjoint families (branches) of rotating neutron stars is discussed and generic features of neutron-star families and of core-quakes triggered by the instabilities are considered.

  20. 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

  1. Gravitoastronomy with neutron stars

    NASA Astrophysics Data System (ADS)

    Woan, Graham

    2004-09-01

    Recent advances in gravitational wave detectors mean that we can start to make astrophysically important statements about the physics of neutron stars based on observed upper limits to their gravitational luminosity. Here we consider statements we can already make about a selection of known radio pulsars, based on data from the LIGO and GEO600 detectors, and look forward to what could be learned from the first detections.

  2. 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

  3. 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.

  4. Modeling Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Park, Conner; Read, Jocelyn; Flynn, Eric; Lockett-Ruiz, Veronica

    2016-03-01

    Gravitational waves, predicted by Einstein's Theory of Relativity, are a new frontier in astronomical observation we can use to observe phenomena in the universe. Laser Interferometer Gravitational wave Observatory (LIGO) is currently searching for gravitational wave signals, and requires accurate predictions in order to best extract astronomical signals from all other sources of fluctuations. The focus of my research is in increasing the accuracy of Post-Newtonian models of binary neutron star coalescence to match the computationally expensive Numerical models. Numerical simulations can take months to compute a couple of milliseconds of signal whereas the Post-Newtonian can generate similar signals in seconds. However the Post-Newtonian model is an approximation, e.g. the Taylor T4 Post-Newtonian model assumes that the two bodies in the binary neutron star system are point charges. To increase the effectiveness of the approximation, I added in tidal effects, resonance frequencies, and a windowing function. Using these observed effects from simulations significantly increases the Post-Newtonian model's similarity to the Numerical signal.

  5. 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.

  6. 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 Chandra’s next decade in this field. PMID:20404205

  7. Neutron Star Mass Distribution in Binaries

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hwan; Kim, Young-Min

    2016-05-01

    Massive neutron stars with ∼ 2Mʘ have been observed in neutron star-white dwarf binaries. On the other hand, well-measured neutron star masses in double-neutron-star binaries are still consistent with the limit of 1.5Mʘ. These observations raised questions on the neutron star equations of state and the neutron star binary evolution processes. In this presentation, a hypothesis of super-Eddington accretion and its implications are discussed. We argue that a 2Mʘ neutron star is an outcome of the super-Eddington accretion during the evolution of neutron star-white dwarf binary progenitors. We also suggest the possibility of the existence of new type of neutron star binary which consists of a typical neutron star and a massive compact companion (high-mass neutron star or black hole) with M ≥ 2Mʘ.

  8. Gravitational Waves from Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kokkotas, Konstantinos

    2016-03-01

    Neutron stars are the densest objects in the present Universe, attaining physical conditions of matter that cannot be replicated on Earth. These unique and irreproducible laboratories allow us to study physics in some of its most extreme regimes. More importantly, however, neutron stars allow us to formulate a number of fundamental questions that explore, in an intricate manner, the boundaries of our understanding of physics and of the Universe. The multifaceted nature of neutron stars involves a delicate interplay among astrophysics, gravitational physics, and nuclear physics. The research in the physics and astrophysics of neutron stars is expected to flourish and thrive in the next decade. The imminent direct detection of gravitational waves will turn gravitational physics into an observational science, and will provide us with a unique opportunity to make major breakthroughs in gravitational physics, in particle and high-energy astrophysics. These waves, which represent a basic prediction of Einstein's theory of general relativity but have yet to be detected directly, are produced in copious amounts, for instance, by tight binary neutron star and black hole systems, supernovae explosions, non-axisymmetric or unstable spinning neutron stars. The focus of the talk will be on the neutron star instabilities induced by rotation and the magnetic field. The conditions for the onset of these instabilities and their efficiency in gravitational waves will be presented. Finally, the dependence of the results and their impact on astrophysics and especially nuclear physics will be discussed.

  9. Neutron star structure from QCD

    NASA Astrophysics Data System (ADS)

    Fraga, Eduardo S.; Kurkela, Aleksi; Vuorinen, Aleksi

    2016-03-01

    In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.

  10. Structure-function studies of STAR family Quaking proteins bound to their in vivo RNA target sites

    SciTech Connect

    Teplova, Marianna; Hafner, Markus; Teplov, Dmitri; Essig, Katharina; Tuschl, Thomas; Patel, Dinshaw J.

    2013-09-27

    Mammalian Quaking (QKI) and its Caenorhabditis elegans homolog, GLD-1 (defective in germ line development), are evolutionarily conserved RNA-binding proteins, which post-transcriptionally regulate target genes essential for developmental processes and myelination. We present X-ray structures of the STAR (signal transduction and activation of RNA) domain, composed of Qua1, K homology (KH), and Qua2 motifs of QKI and GLD-1 bound to high-affinity in vivo RNA targets containing YUAAY RNA recognition elements (RREs). The KH and Qua2 motifs of the STAR domain synergize to specifically interact with bases and sugar-phosphate backbones of the bound RRE. Qua1-mediated homodimerization generates a scaffold that enables concurrent recognition of two RREs, thereby plausibly targeting tandem RREs present in many QKI-targeted transcripts. Structure-guided mutations reduced QKI RNA-binding affinity in vitro and in vivo, and expression of QKI mutants in human embryonic kidney cells (HEK293) significantly decreased the abundance of QKI target mRNAs. Overall, our studies define principles underlying RNA target selection by STAR homodimers and provide insights into the post-transcriptional regulatory function of mammalian QKI proteins.

  11. Chandra Captures Neutron Star Action

    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...

  12. 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.

  13. 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

  14. Kicked Neutron Stars and Microlensing

    NASA Astrophysics Data System (ADS)

    Mollerach, Silvia; Roulet, Esteban

    1997-04-01

    Because of the large kick velocities with which neutron stars are born in supernova explosions, their spatial distribution is more extended than that of their progenitor stars. The large scale height of the neutron stars above the disk plane makes them potential candidates for microlensing of stars in the Large Magellanic Cloud. Adopting for the distribution of kicks the measured velocities of young pulsars, we obtain a microlensing optical depth of τ ~ 2N10 × 10-8 (where N10 is the total number of neutron stars born in the disk in units of 1010). The event duration distribution has the interesting property of being peaked at T ~ 60-80 days, but for the rates to be relevant for the present microlensing searches, it would require N10 >~ 1, a value larger than the usually adopted ones (N10 ~ 0.1-0.2).

  15. Neutron stars and strange matter

    SciTech Connect

    Cooperstein, J.

    1986-01-01

    The likelihood is investigated that quark matter with strangeness of order unity resides in neutron stars. In the strong coupling regime near rho/sub 0/ this is found to be unlikely. Considering higher densities where perturbative expansions are used, we find a lower bound to be at 7rho/sub 0/ for the transition density. This is higher than the inferred density of observed neutron stars, and thus the transition to quark matter is precluded. 15 refs., 3 figs.

  16. 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.

  17. Rapidly rotating neutron star progenitors

    NASA Astrophysics Data System (ADS)

    Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.

    2016-08-01

    Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In the present paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 years. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1 - 1% of the total core collapses, depending on the common envelope efficiency.

  18. 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.

  19. 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.

  20. Anomalous hydrodynamics kicks neutron stars

    NASA Astrophysics Data System (ADS)

    Kaminski, Matthias; Uhlemann, Christoph F.; Bleicher, Marcus; Schaffner-Bielich, Jürgen

    2016-09-01

    Observations show that, at the beginning of their existence, neutron stars are accelerated briskly to velocities of up to a thousand kilometers per second. We argue that this remarkable effect can be explained as a manifestation of quantum anomalies on astrophysical scales. To theoretically describe the early stage in the life of neutron stars we use hydrodynamics as a systematic effective-field-theory framework. Within this framework, anomalies of the Standard Model of particle physics as underlying microscopic theory imply the presence of a particular set of transport terms, whose form is completely fixed by theoretical consistency. The resulting chiral transport effects in proto-neutron stars enhance neutrino emission along the internal magnetic field, and the recoil can explain the order of magnitude of the observed kick velocities.

  1. Modelling magnetically deformed neutron stars

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

    Rotating deformed neutron stars are important potential sources for ground-based gravitational wave interferometers such as LIGO, GEO600 and VIRGO. One mechanism that may lead to significant non-asymmetries is the internal magnetic field. It is well known that a magnetic star will not be spherical and, if the magnetic axis is not aligned with the spin axis, the deformation will lead to the emission of gravitational waves. The aim of this paper is to develop a formalism that would allow us to model magnetically deformed stars, using both realistic equations of state and field configurations. As a first step, we consider a set of simplified model problems. Focusing on dipolar fields, we determine the internal magnetic field which is consistent with a given neutron star model and calculate the associated deformation. We discuss the relevance of our results for current gravitational wave detectors and future prospects.

  2. 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.

  3. Theory of cooling neutron stars versus observations

    SciTech Connect

    Yakovlev, D. G.; Gnedin, O. Y.; Kaminker, A. D.; Potekhin, A. Y.

    2008-02-27

    We review current state of neutron star cooling theory and discuss the prospects to constrain the equation of state, neutrino emission and superfluid properties of neutron star cores by comparing the cooling theory with observations of thermal radiation from isolated neutron stars.

  4. Evolutions of Magnetized Neutron Stars

    NASA Astrophysics Data System (ADS)

    Liebling, Steven; Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Tohline, Joel

    2009-05-01

    Magnetized neutron stars, whether considered individually or within compact binary systems, demonstrate a number of interesting dynamical effects and may represent an important source of observable gravitational waves. In addition, isolated, rotating, magnetized stars serve as a good testbed for a necessarily complex, distributed adaptive mesh refinement (AMR) code. As initial data, we use fully consistent, magnetized, rotating stellar configurations generated with the Lorene toolkit. Here results are presented which (i) demonstrate convergence and stability of the code, (ii) show the evolution of stable and unstable magnetized stars, and (iii) study the effects of a scheme to track the leakage of neutrinos.

  5. Jets from Merging Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-06-01

    With the recent discovery of gravitational waves from the merger of two black holes, its especially important to understand the electromagnetic signals resulting from mergers of compact objects. New simulations successfully follow a merger of two neutron stars that produces a short burst of energy via a jet consistent with short gamma-ray burst (sGRB) detections.Still from the authors simulation showing the two neutron stars, and their magnetic fields, before merger. [Adapted from Ruiz et al. 2016]Challenging SystemWe have long suspected that sGRBs are produced by the mergers of compact objects, but this model has been difficult to prove. One major hitch is that modeling the process of merger and sGRB launch is very difficult, due to the fact that these extreme systems involve magnetic fields, fluids and full general relativity.Traditionally, simulations are only able to track such mergers over short periods of time. But in a recent study, Milton Ruiz (University of Illinois at Urbana-Champaign and Industrial University of Santander, Colombia) and coauthors Ryan Lang, Vasileios Paschalidis and Stuart Shapiro have modeled a binary neutron star system all the way through the process of inspiral, merger, and the launch of a jet.A Merger TimelineHow does this happen? Lets walk through one of the teams simulations, in which dipole magnetic field lines thread through the interior of each neutron star and extend beyond its surface(like magnetic fields found in pulsars). In this example, the two neutron stars each have a mass of 1.625 solar masses.Simulation start (0 ms)Loss of energy via gravitational waves cause the neutron stars to inspiral.Merger (3.5 ms)The neutron stars are stretched by tidal effects and make contact. Their merger produces a hypermassive neutron star that is supported against collapse by its differential (nonuniform) rotation.Delayed collapse into a black hole (21.5 ms)Once the differential rotation is redistributed by magnetic fields and partially

  6. Jets from Merging Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-06-01

    With the recent discovery of gravitational waves from the merger of two black holes, its especially important to understand the electromagnetic signals resulting from mergers of compact objects. New simulations successfully follow a merger of two neutron stars that produces a short burst of energy via a jet consistent with short gamma-ray burst (sGRB) detections.Still from the authors simulation showing the two neutron stars, and their magnetic fields, before merger. [Adapted from Ruiz et al. 2016]Challenging SystemWe have long suspected that sGRBs are produced by the mergers of compact objects, but this model has been difficult to prove. One major hitch is that modeling the process of merger and sGRB launch is very difficult, due to the fact that these extreme systems involve magnetic fields, fluids and full general relativity.Traditionally, simulations are only able to track such mergers over short periods of time. But in a recent study, Milton Ruiz (University of Illinois at Urbana-Champaign and Industrial University of Santander, Colombia) and coauthors Ryan Lang, Vasileios Paschalidis and Stuart Shapiro have modeled a binary neutron star system all the way through the process of inspiral, merger, and the launch of a jet.A Merger TimelineHow does this happen? Lets walk through one of the teams simulations, in which dipole magnetic field lines thread through the interior of each neutron star and extend beyond its surface(like magnetic fields found in pulsars). In this example, the two neutron stars each have a mass of 1.625 solar masses.Simulation start (0 ms)Loss of energy via gravitational waves cause the neutron stars to inspiral.Merger (3.5 ms)The neutron stars are stretched by tidal effects and make contact. Their merger produces a hypermassive neutron star that is supported against collapse by its differential (nonuniform) rotation.Delayed collapse into a black hole (21.5 ms)Once the differential rotation is redistributed by magnetic fields and partially

  7. Slowly braked, rotating neutron stars

    NASA Technical Reports Server (NTRS)

    Sato, H.

    1975-01-01

    A slowly braked, rotating neutron star is believed to be a star which rapidly rotates, has no nebula, is nonpulsing, and has a long initial braking time of ten thousand to a million years because of a low magnetic field. Such an object might be observable as an extended weak source of infrared or radio wave radiation due to the scattering of low-frequency strong-wave photons by accelerated electrons. If these objects exist abundantly in the Galaxy, they would act as sources of relatively low-energy cosmic rays. Pulsars (rapidly braked neutron stars) are shown to have difficulties in providing an adequate amount of cosmic-ray matter, making these new sources seem necessary. The possibility that the acceleration mechanism around a slowly braked star may be not a direct acceleration by the strong wave but an acceleration due to plasma turbulence excited by the strong wave is briefly explored. It is shown that white dwarfs may also be slowly braked stars with braking times longer than 3.15 million years.

  8. Heating and Cooling in Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Cumming, Andrew

    2015-10-01

    Neutron stars in low mass X-ray binaries accrete enough mass over their lifetimes to replace their entire crust. The accreted matter undergoes a series of nuclear reactions in the crust as it is compressed by continued accretion to higher density. These reactions, which include electron captures, neutron emissions, and pycnonuclear reactions, heat the crust and core of the neutron star. In this talk I will discuss what we can learn from observations of transiently accreting neutron stars in quiescence, when accretion has turned off and we can see emission from the neutron star directly. The quiescent luminosity of these neutron stars constrains the neutrino emissivity in the neutron star core. In systems with long accretion outbursts, observations of thermal relaxation of the crust in quiescence enable, for the first time, constraints on the thermal conductivity and heat capacity of the crust. In this way, low mass X-ray binary neutron stars offer a remarkable chance to constrain the properties of dense neutron-rich matter, such as neutron superfluidity and pasta phases in the inner crust of neutron stars.

  9. 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.

  10. Neutron stars as cosmic hadron physics laboratories

    NASA Technical Reports Server (NTRS)

    Pines, D.

    1985-01-01

    Extensive observations of Her-1 with the Exosat satellite have led to a new understanding of both the dynamics of neutron-star superfluids and the free precession of neutron stars. Detailed microscopic calculations on neutron matter and the properties of the pinned crustal superfluid are provided to serve as a basis for comparing theory with observation on neutron stars. Topics discussed include the Hadron matter equation of state, neutron star structure, Hadron superfluids, the vortex creep theory, Vela pulsar glitches, astrophysical constraints on neutron matter energy gaps, the 35 day periodicity of Her-1, and the neutron matter equation of state. It is concluded that since the post-glitch fits and the identification of the 35th periodicity in Her X-1 as stellar wobble require a rigid neutron matter equation of state, the astrophysical evidence for such an equation seems strong, as well as that for an intermediate Delta(rho) curve.

  11. 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)

  12. Accreting Neutron Stars as Astrophysical Laboratories

    NASA Technical Reports Server (NTRS)

    Chakrabarty, Deepto

    2004-01-01

    In the last year, we have made an extremely important breakthrough in establishing the relationship between thermonuclear burst oscillations in accreting neutron stars and the stellar spin. More broadly, we have continued t o make significant scientific progress in all four of the key focus areas identified in our original proposal: (1) the disk-magnetosphere interaction in neutron stars, (2) rapid variability in accreting neutron stars, (3) physics of accretion flows, and (4) fundamental properties of neutron stars. A list of all publications that have arising from this work since the start of our program is given.

  13. 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.

  14. 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.

  15. Planetary Systems Around Neutron Stars

    NASA Astrophysics Data System (ADS)

    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.

  16. 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.

  17. 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,

  18. Thermonuclear runaways on neutron stars

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    Thermonuclear runaways which develop when neutron stars of 0.476 solar masses accrete hydrogen-rich material at 10 to the -10th and 2 x 10 to the -9th solar masses/year have been followed using a numerical model. It is found that a thermal instability occurs at densities in excess of 10 to the 5th g/cu cm and that the maximum accumulated mass required to initiate the runaway is 0.7 x 10 to the -12th and 2.1 x 10 to the -12th solar masses for the mass accretion rates of 10 to the -10th and 2 x 10 to the -9th solar masses/year, respectively. Heating the of the neutron star envelope by hydrogen burning leads to the ignition of helium. The nonequilibrium burning of helium by a combination of (alpha, p), (p, gamma), and (alpha, gamma) reactions involving O-14, O-15, and other heavy nuclei provides the energy for an X-ray burst. The gross properties of these models bear suggestive resemblance to those observed for some X-ray burst sources.

  19. Thermal Emission from Neutron Stars

    NASA Astrophysics Data System (ADS)

    Rajagopal, Mohan

    In the second chapter, we examine the possibility of inspiral of massive black hole binaries produced in galactic mergers, induced by interaction with field stars. We model the evolution of such binaries for a range of galaxy core and binary parameters, using numerical results from the literature to compute the binary's energy and angular momentum loss rates due to stellar encounters and including the effect of back-action on the field stars. Averaging over a population of central black holes and galaxy mergers, we compute the expected background of gravitational radiation with periods Pw~1-10y. Comparison with sensitivities from millisecond pulsar timing suggests that the strongest sources may be detectable with modest improvements to present experiments. In the third chapter, we compute model atmospheres and emergent spectra for low field (B<=1010G) neutron stars, using new opacity and equation of state data from the OPAL project. These computations, incorporating improved treatments of flux transport and convective stability, provide spectra for hydrogen, solar abundance and iron atmospheres. We compare our results to high field magnetic atmospheres, available only for hydrogen. We comment on extension to high fields and the implication of these results for neutron star luminosities and radii. In chapter four we are more ambitious, assembling iron opacities from atomic states in order to treat the case of high magnetic field. Using a Hartree-Fock formalism, we estimate energy levels and photon cross sections for atomic iron in magnetic fields B~1013G. Computing ionization equilibrium and normal mode opacities with these data, we construct LTE neutron star model atmospheres at 5.5 < Log(T eff)<6.5 and compute emergent spectra. We examine the dependence of the emergent spectra on T eff and B. We also show the spectral variation with the angle between the magnetic field and the atmosphere normal and describe the significant limb darkening in the X-ray band. These

  20. Neutron stars as dark matter probes

    SciTech Connect

    Lavallaz, Arnaud de; Fairbairn, Malcolm

    2010-06-15

    We examine whether the accretion of dark matter onto neutron stars could ever have any visible external effects. Captured dark matter which subsequently annihilates will heat the neutron stars, although it seems the effect will be too small to heat close neutron stars at an observable rate while those at the galactic center are obscured by dust. Nonannihilating dark matter would accumulate at the center of the neutron star. In a very dense region of dark matter such as that which may be found at the center of the galaxy, a neutron star might accrete enough to cause it to collapse within a period of time less than the age of the Universe. We calculate what value of the stable dark matter-nucleon cross section would cause this to occur for a large range of masses.

  1. 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

  2. Axion cooling of neutron stars

    NASA Astrophysics Data System (ADS)

    Sedrakian, Armen

    2016-03-01

    Cooling simulations of neutron stars and their comparison with the data from thermally emitting x-ray sources put constraints on the properties of axions, and by extension, of any light pseudoscalar dark matter particles, whose existence has been postulated to solve the strong-C P problem of QCD. We incorporate the axion emission by pair-breaking and formation processes by S - and P -wave nucleonic condensates in a benchmark code for cooling simulations, as well as provide fit formulas for the rates of these processes. Axion cooling of neutron stars has been simulated for 24 models covering the mass range 1 to 1.8 solar masses, featuring nonaccreted iron and accreted light-element envelopes, and a range of nucleon-axion couplings. The models are based on an equation state predicting conservative physics of superdense nuclear matter that does not allow for the onset of fast cooling processes induced by phase transitions to non-nucleonic forms of matter or high proton concentration. The cooling tracks in the temperature vs age plane were confronted with the (time-averaged) measured surface temperature of the central compact object in the Cas A supernova remnant as well as surface temperatures of three nearby middle-aged thermally emitting pulsars. We find that the axion coupling is limited to fa/107 GeV ≥(5 - 10 ) , which translates into an upper bound on axion mass ma≤(0.06 - 0.12 ) eV for Peccei-Quinn charges of the neutron |Cn|˜0.04 and proton |Cp|˜0.4 characteristic for hadronic models of axions.

  3. 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.

  4. 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.

  5. Validating Neutron Star Radius Measurements

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Deepto

    2010-09-01

    Spectral analysis of transient neutron star X-ray emission during bursts and quiescence were both used to estimate the NS radii for different sources. The validities of these methods need to be verified by performing them on the same source respectively. Transient type-I (thermonuclear) X-ray bursters are excellent candidates for testing the consistency between these methods, since they were detected in both bursts and quiescence. Out of 3 candidates: Cen X-4, Aql X-1 and 4U 1608-52, 4U 1608-52 turns out to be the best one due to the lack of archival RXTE burst data for Cen X-4 and the previous reported significant luminosity and temperature variability for Aql X-1 in quiescence. Therefore, we propose a 25 ks Chandra/ACIS-S observation of 4U 1608-52.

  6. 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.

  7. 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.

  8. Observations of Neutron Stars with NICER

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko

    2016-07-01

    The Neutron Star Interior Composition Explorer (NICER) is an approved NASA Explorer Mission of Opportunity that will be deployed as an attached payload on the International Space Station in August of 2016. By virtue of its unprecedented combination of throughput and fast timing capabilities, NICER will enable an empirical determination of the neutron star equation of state via realistic modeling of the pulsed X-ray radiation from millisecond pulsars. In this talk, I will describe the NICER instrument and measurement techniques it will employ, as well as the expected constraints on neutron star structure, and by extension the behavior of matter at supra-nuclear densities.

  9. Radio Detection of Neutron Star Binary Mergers

    NASA Astrophysics Data System (ADS)

    Bear, Brandon; Cardena, Brett; Dispoto, Dana; Papadopoulos, Joanna; Kavic, Michael; Simonetti, John

    2011-10-01

    Neutron star binary systems lose energy through gravitational radiation, and eventually merge. The gravitational radiation from the merger can be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). It is expected that a transient radio pulse will also be produced during the merger event. Detection of such radio transients would allow for LIGO to search for signals within constrained time periods. We calculate the LWA-1 detection rate of transient events from neutron star binary mergers. We calculate the detection rate of transient events from neutron star binary mergers for the Long Wavelength Array and the Eight-meter-wavelength Transient Array.

  10. Position annihilation radiation from neutron stars

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Borner, G. A.; Cohen, J. M.

    1972-01-01

    Matter accreted on the surfaces of neutron stars consists of energetic particles of a few tens to a couple hundred MeV/nucleon, depending on the neutron star mass. In addition to heat, such particles produce nuclear reactions with the surface material. It is proposed that the recently observed 473 + or - 30 keV spectral feature from the galactic center is gravitationally red-shifted positron annihilation radiation produced at the surfaces of old neutron stars. The principal observational tests of the model would be the detection of nuclear gamma ray lines from the galactic center and red-shifted positron annihilation radiation from the galactic disk.

  11. 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.

  12. 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.

  13. 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.

  14. Rotation and cooling of neutron stars

    NASA Astrophysics Data System (ADS)

    Negreiros, R.; Schramm, S.; Weber, F.

    2014-09-01

    Driven by the loss of energy, isolated rotating neutron stars (pulsars) are gradually slowing down to lower frequencies, which increases the tremendous compression of the matter inside of them. This increase in compression changes both the global properties of rotating neutron stars as well as their hadronic core compositions. Both effects may register themselves observationally in the thermal evolution of such stars, as demonstrated in this work. The rotation-driven particle process which we consider here is the direct Urca (DU) process, which is known to become operative in neutron stars if the number of protons in the stellar core exceeds a critical limit of around 11 % to 15 %. We find that neutron stars spinning down from moderately high rotation rates of a few hundred Hertz may be creating just the right conditions where the DU process becomes operative, leading to an observable effect (enhanced cooling) in the temperature evolution of such neutron stars. We will also study the thermal evolution of neutron stars whose spherical symmetry has been broken due to non-zero rotation. For this we will derive the energy balance and transport equations, taking into account the metric of a rotating fluid distribution and solve these equations numerically.

  15. 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.

  16. 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.

  17. Transport coefficients in superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Tolos, Laura; Manuel, Cristina; Sarkar, Sreemoyee; Tarrus, Jaume

    2016-01-01

    We study the shear and bulk viscosity coefficients as well as the thermal conductivity 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 and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.

  18. Magnetic Fields in Superconducting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Lander, S. K.

    2013-02-01

    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.

  19. Neutron stars in Einstein-aether theory

    SciTech Connect

    Eling, Christopher; Jacobson, Ted; Miller, M. Coleman

    2007-08-15

    As current and future experiments probe strong gravitational regimes around neutron stars and black holes, it is desirable to have theoretically sound alternatives to general relativity against which to test observations. Here we study the consequences of one such generalization, Einstein-aether theory, for the properties of nonrotating neutron stars. This theory has a parameter range that satisfies all current weak-field tests. We find that within this range it leads to lower maximum neutron star masses, as well as larger surface redshifts at a particular mass, for a given nuclear equation of state. For nonrotating black holes and neutron stars, the innermost stable circular orbit is only slightly modified in this theory.

  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. Plasma magnetosphere of deformed magnetized neutron star

    NASA Astrophysics Data System (ADS)

    Rayimbaev, J. R.; Ahmedov, B. J.; Juraeva, N. B.; Rakhmatov, A. S.

    2015-04-01

    The plasma magnetosphere surrounding a rotating magnetized neutron star described by non-Kerr spacetime metric in slow rotation approximation has been studied. First we have studied the vacuum solutions of the Maxwell equations in spacetime of slowly rotating magnetized non-Kerr star with dipolar magnetic configuration. Then for the magnetospheric model we have derived second-order differential equation for electrostatic potential from the system of Maxwell equations in spacetime of slowly rotating magnetized non-Kerr star. Analytical solutions of Goldreich-Julian (GJ) charge density along open field lines of slowly rotating magnetized non-Kerr neutron star have been obtained which indicate the modification of an accelerating electric field, charge density along the open field lines and radiating losses of energy of the neutron star by the deformation parameter.

  2. 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.

  3. Thermonuclear flashes on accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Joss, P. C.

    1979-01-01

    Observations of X-ray bursts from binary pulsars and globular clusters are reviewed. The previously proposed hypothesis is considered that such X-ray bursts result from thermonuclear flashes on accreting neutron stars. A general scenario for this mechanism is outlined, and numerical computations of the evolution of the surface layers of an accreting neutron star are discussed. The relation of these calculations to X-ray bursts and other phenomena is examined. Possible improvements in the numerical calculations are suggested.

  4. Population Synthesis of isolated Neutron Stars

    NASA Astrophysics Data System (ADS)

    Gullón Juanes, Miguel

    2015-12-01

    Neutron Stars present a wide variety from the observational point of view. The advent of new and powerful detectors and instruments has opened a new era where the classical picture of neutrons stars seen as radio-pulsars has been modified with new classes such as magnetars, X-ray Isolated Neutron Stars (XINSs) or Central Compact Objects (CCOs) in Supernova Remnants . In addition to the more than 2500 sources detected in the radio band, more than two hundred have also been detected as X-ray and gamma-ray sources. This number is expected to increase in the near future. Despite this apparent diversity, some studies demand a theory able to explain the different classes in terms of the same physical scenario (Kaspi, 2010), in which the evolution of the magnetic field appears to play an important role (Viganò et al., 2013). The Population Synthesis of Neutron Stars, which is the central subject of this thesis, is an interesting approach to understand the problem, as both intrinsic properties and observational biases are taken into account. These technique is based on Monte Carlo methods, applied to simulate the whole population of neutron stars. The main objective of the thesis has been to perform a multi-wavelength study of the different populations of Neutron Stars focusing in the effects of magneto-thermal evolution. This report consists of a global summary of the objectives, methods and main results of the thesis. It is structured as follows. The first chapter gives an introduction to Neutron Stars. Chapter two is a description of the method of Population Synthesis of Neutron Stars. In chapter three a global discussion of the main results is presented. Chapter four closes the report with the conclusions. An appendix is also included which constitutes a description of a method based on the pulsar current analysis.

  5. Hydrodynamical evolution of coalescing binary neutron stars

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.; Shapiro, Stuart L.

    1992-01-01

    The hydrodynamics of the final merging of two neutron stars and the corresponding gravitational wave emission is studied in detail. Various test calculations are presented, including the compressible Roche and Darwin problems and the head-on collision of two polytropes. A complete coalescence calculation is presented for the simplest case of two identical neutron stars, represented by Gamma = 2 polytropes, in a circular orbit, with their spins aligned and synchronized with the orbital rotation.

  6. 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.

  7. Superfluidity of {Lambda} hyperons in neutron stars

    SciTech Connect

    Wang, Y. N.; Shen, H.

    2010-02-15

    We study the {sup 1}S{sub 0} superfluidity of {Lambda} hyperons in neutron star matter and neutron stars. We use the relativistic mean field (RMF) theory to calculate the properties of neutron star matter. In the RMF approach, the meson-hyperon couplings are constrained by reasonable hyperon potentials that include the updated information from recent developments in hypernuclear physics. To examine the {sup 1}S{sub 0} pairing gap of {Lambda} hyperons, we employ several {Lambda}{Lambda} interactions based on the Nijmegen models and used in double-{Lambda} hypernuclei studies. It is found that the maximal pairing gap obtained is a few tenths of a MeV. The magnitude and the density region of the pairing gap are dependent on the {Lambda}{Lambda} interaction and the treatment of neutron star matter. We calculate neutron star properties and find that whether the {sup 1}S{sub 0} superfluidity of {Lambda} hyperons exists in the core of neutron stars mainly depends on the {Lambda}{Lambda} interaction used.

  8. ULXs: Neutron stars versus black holes

    NASA Astrophysics Data System (ADS)

    King, Andrew; Lasota, Jean-Pierre

    2016-05-01

    We consider ultraluminous X-ray systems (ULXs) where the accretor is a neutron star rather than a black hole. We show that the recently discovered example (M82 X-2) fits naturally into the simple picture of ULXs as beamed X-ray sources fed at super-Eddington rates, provided that its magnetic field is weaker (≃1011G) than a new-born X-ray pulsar, as expected if there has been mass gain. Continuing accretion is likely to weaken the field to the point that pulsing stops, and make the system indistinguishable from a ULX containing a black hole. Accordingly we suggest that a significant fraction of all ULXs may actually contain neutron star accretors rather than black holes, reflecting the neutron-star fraction among their X-ray binary progenitors. We emphasize that neutron-star ULXs are likely to have higher apparent luminosities than black hole ULXs for a given mass transfer rate, as their tighter beaming outweighs their lower Eddington luminosities. This further increases the likely proportion of neutron-star accretors among all ULXs. Cygnus X-2 is probably a typical descendant of neutron-star ULXs, which may therefore ultimately end as millisecond pulsar binaries with massive white dwarf companions.

  9. 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

  10. Accreting neutron stars by QFT

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Guang

    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

  11. Dynamical stability of nascent neutron stars

    NASA Astrophysics Data System (ADS)

    Liu, Yuk Tung

    This thesis presents a study of the dynamical stability of nascent neutron stars resulting from the accretion induced collapse of rapidly rotating white dwarfs. Chapter 2 and part of Chapter 3 study the equilibrium models for these neutron stars. They are constructed by assuming that the neutron stars have the same masses, angular momenta, and specific angular momentum distributions as the pre-collapse white dwarfs. If the pre-collapse white dwarf is rapidly rotating, the collapsed object will contain a high density central core of size about 20 km, surrounded by a massive accretion torus extending to hundreds of kilometers from the rotation axis. The ratio of the rotational kinetic energy to gravitational binding energy, β, of these neutron stars is all found to be less than 0.27. Chapter 3 studies the dynamical stability of these neutron stars by numerically evolving the linearized hydrodynamical equations. A dynamical bar-mode instability is observed when the β of the star is greater than the critical value β d ≈ 0.25. It is expected that the unstable mode will persist until a substantial amount of angular momentum is carried away by gravitational radiation. The detectability of these sources is studied and it is estimated that LIGO II is unlikely to detect them unless the event rate is greater than 10-6/year/galaxy. All the calculations on the structure and stability of the neutron stars in Chapters 2 and 3 are carried out using Newtonian hydrodynamics and gravity. Chapter 4 studies the relativistic effects on the structure of these neutron stars. New techniques are developed and used to construct neutron star models to the first post- Newtonian (1PN) order. The structures of the ON models are qualitatively similar to the corresponding Newtonian models, but the values of β are somewhat smaller. The maximum β for these ON neutron stars is found to be 0.24, which is 8% smaller than the Newtonian result (0.26). However, relativistic effects will also change

  12. 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.

  13. Magnetic field decay in isolated neutron stars

    NASA Technical Reports Server (NTRS)

    Goldreich, Peter; Reisenegger, Andreas

    1992-01-01

    Three mechanisms that promote the loss of magnetic flux from an isolated neutron star - Ohmic decay, ambipolar diffusion, and Hall drift - are investigated. Equations of motions are solved for charged particles in the presence of a magnetic field and a fixed background of neutrons, while allowing for the creation and destruction of particles by weak interactions. Although these equations apply to normal neutrons and protons, the present interpretations of their solutions are extended to cover cases of neutron superfluidity and proton superconductivity. The equations are manipulated to prove that, in the presence of a magnetic force, the charged particles cannot be simultaneously in magnetostatic equilibrium and chemical equilibrium with the neutrons. The application of the results to real neutron stars is discussed.

  14. 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)

  15. Thermonuclear processes on accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Joss, P. C.

    1981-01-01

    Theoretical models for X-ray burst sources that invoke thermonuclear flashes on the surface layers of an accreting neutron star are discussed. The historical development of X-ray burst observation is summarized, and a physical picture of a neutron star undergoing accretion is drawn. Detailed numerical computations of the evolution of the surface layers of such a star are reviewed. The need for general relativistic corrections to the model is pointed out. Finally, comparisons are made with observations of X-ray bursts, the rapid burster, fast X-ray transients, X-ray pulsars, and gamma-ray burst sources.

  16. Local distribution of old neutron stars

    NASA Technical Reports Server (NTRS)

    Frei, Szolt; Huang, Xiaolan; Paczynski, Bohdan

    1992-01-01

    The local distribution of old disk neutron stars is approximated with a 1D model, in which the steady state distribution in the direction perpendicular to the Galactic plane is calculated, assuming a variety of the initial radio pulsar positions and velocities, and various Galactic potentials. It is found that the local distribution of old neutron stars is dominated by those that were born with very low velocities. The high-velocity neutron stars spend most of their lifetime far in the Galactic halo and do not contribute much to the local density. Therefore, the rms velocity at birth is not a good indicator of the scale height of the old population. The most likely half-density scale height for the old disk neutron stars is approximately 350 pc, the same as for the old disk G, K, and M stars. If gamma-ray bursts originate on old disk neutron stars, then 350 pc should also be the scale height for the bursters.

  17. Population Synthesis of Double Neutron Stars

    NASA Astrophysics Data System (ADS)

    Tenney, Craig; Lorimer, D.; Bagchi, M.

    2014-01-01

    Globular clusters in our galaxy provide a fertile ground for stars to undergo supernova which leads to the creation of neutron stars. A population synthesis was created to study the population of double neutron stars (DNS) in our Galaxy that originated in globular clusters. The rate of DNS formation is proportional to the cluster's luminosity and the resulting kick from the supernova at birth ejects the DNS from the cluster. Initial conditions are given to the DNS after being ejected and allowed to evolve throughout the galaxy to the present time. With a simulated population of DNS we test to see how many of them are detectable from Earth with radio telescopes. DNS are being used as a way to detect gravitation waves when the two neutron stars spiral into each other. A better constraint on their formation and existence will lead to more accurate predictions for gravitational wave detectors.

  18. 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.; Szilágyi, Béla

    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.

  19. The neutron star mass distribution

    SciTech Connect

    Kiziltan, Bülent; 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 (Δm ≈ 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.

  20. Outer crust of nonaccreting cold neutron stars

    NASA Astrophysics Data System (ADS)

    Rüster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jürgen

    2006-03-01

    The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

  1. Outer crust of nonaccreting cold neutron stars

    SciTech Connect

    Ruester, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Juergen

    2006-03-15

    The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wambach, J.; Anisworth, T. L.; Pines, D.

    1993-01-01

    A microscopic model for the quaisiparticle interaction in neutron matter is presented. Both particle-particle (pp) and particle-hole (ph) correlation are are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for the particle hole interaction and the scattering amplitude on the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the S-1 gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

  7. Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wambach, J; Ainsworth, T. L.; Pines, D.

    1993-01-01

    A microscopic model for the quasiparticle interaction in neutron matter is presented. Both-particle (pp) and particle-hole (ph) correlations are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for particle-hole interaction and the scattering amplitude of the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules for the scattering amplitude are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the (1)S(sub 0) gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

  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. 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

  10. Dark-matter admixed neutron stars

    NASA Astrophysics Data System (ADS)

    Leung, S.-C.; Chu, M.-C.; Lin, L.-M.

    2011-11-01

    We study the hydrostatic equilibrium configuration of an admixture of degenerate dark matter and normal nuclear matter by using a general relativistic two-fluid formalism. We consider non-self-annihilating dark matter particles of mass ˜1GeV. The mass-radius relations and moments of inertia of these dark-matter admixed neutron stars are investigated and the stability of these stars is demonstrated by performing a radial perturbation analysis. We find a new class of compact stars which consists of a small normal matter core with radius of a few kilometers embedded in a ten-kilometer-sized dark matter halo. These stellar objects may be observed as extraordinarily small neutron stars that are incompatible with realistic nuclear matter models.

  11. Asteroseismology of neutron stars and black holes

    NASA Astrophysics Data System (ADS)

    Schutz, B. F.

    2008-10-01

    One of the goals of the large gravitational wave detectors is eventually to observe radiation from oscillations of neutron stars and black holes. These objects have characteristic frequencies of what are called 'quasi-normal' mode oscillations, and these frequencies reveal important information about the source. The frequency spectrum of black holes is very different from that of any stars, so if one or more modes are observed then one can conclusively identify the source as a black hole. For neutron stars the spectrum is similar to that of main-sequence stars, but observing a single mode is enough to put strong constraints on the nuclear-matter equation of state, something which is still highly uncertain. Current detectors could make these observations only if the source were exceptionally close. But planned upgrades could make the first relativistic asteroseismological observations; in particular the GEO600 detector will be optimised for these observations by 2010.

  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. 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.

  14. Holographic Quark Matter and Neutron Stars

    NASA Astrophysics Data System (ADS)

    Hoyos, Carlos; Jokela, Niko; Rodríguez Fernández, David; Vuorinen, Aleksi

    2016-07-01

    We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding equation of state (EOS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first-order phase transition at densities between 2 and 7 times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EOSs, we find maximal stellar masses in excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EOSs. Our calculation predicts that no quark matter exists inside neutron stars.

  15. ASTROPHYSICS: Neutron Stars Imply Relativity's a Drag.

    PubMed

    Schilling, G

    2000-09-01

    A new finding, based on x-rays from distant neutron stars, could be the first clear evidence of a weird relativistic effect called frame dragging, in which a heavy chunk of spinning matter wrenches the space-time around it like an eggbeater. Using data from NASA's Rossi X-ray Timing Explorer, three astronomers in Amsterdam found circumstantial evidence for frame dragging in the flickering of three neutron stars in binary systems. They announced their results in the 1 September issue of The Astrophysical Journal. PMID:17839511

  16. 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.

  17. Holographic Quark Matter and Neutron Stars.

    PubMed

    Hoyos, Carlos; Jokela, Niko; Rodríguez Fernández, David; Vuorinen, Aleksi

    2016-07-15

    We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding equation of state (EOS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first-order phase transition at densities between 2 and 7 times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EOSs, we find maximal stellar masses in excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EOSs. Our calculation predicts that no quark matter exists inside neutron stars. PMID:27472110

  18. 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.

  19. 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.

  20. Oscillations of general relativistic superfluid neutron stars

    NASA Astrophysics Data System (ADS)

    Andersson, N.; Comer, G. L.; Langlois, D.

    2002-11-01

    We develop a general formalism to treat, in general relativity, the nonradial oscillations of a superfluid neutron star about static (non-rotating) configurations. The matter content of these stars can, as a first approximation, be described by a two-fluid model: one fluid is the neutron superfluid, which is believed to exist in the core and inner crust of mature neutron stars; the other fluid is a conglomerate of all charged constituents (crust nuclei, protons, electrons, etc.). We use a system of equations that governs the perturbations both of the metric and of the matter variables, whatever the equation of state for the two fluids. The entrainment effect is explicitly included. We also take the first step towards allowing for the superfluid to be confined to a part of the star by allowing for an outer envelope composed of ordinary fluid. We derive and implement the junction conditions for the metric and matter variables at the core-envelope interface, and briefly discuss the nature of the involved phase transition. We then determine the frequencies and gravitational-wave damping times for a simple model equation of state, incorporating entrainment through an approximation scheme which extends present Newtonian results to the general relativistic regime. We investigate how the quasinormal modes of a superfluid star are affected by changes in the entrainment parameter, and unveil a series of avoided crossings between the various modes. We provide a proof that, unless the equation of state is very special, all modes of a two-fluid star must radiate gravitationally. We also discuss the future detectability of pulsations in a superfluid star and argue that it may be possible (given advances in the relevant technology) to use gravitational-wave data to constrain the parameters of superfluid neutron stars.

  1. 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.

  2. Neutron stars: A cosmic hadron physics laboratory

    NASA Technical Reports Server (NTRS)

    Pines, David

    1989-01-01

    A progress report is given on neutron stars as a cosmic hadron physics laboratory. Particular attention is paid to the crustal neutron superfluid, and to the information concerning its properties which may be deduced from observations of pulsar glitches and postglitch behavior. Current observational evidence concerning the softness or stiffness of the high density neutron matter equation of state is reviewed briefly, and the (revolutionary) implications of a confirmation of the existence of a 0.5 ms pulsar at the core of (Supernova) SN1987A are discussed.

  3. Neutron stars - A cosmic hadron physics laboratory

    NASA Technical Reports Server (NTRS)

    Pines, David

    1989-01-01

    A progress report is given on neutron stars as a cosmic hadron physics laboratory. Particular attention is paid to the crustal neutron superfluid, and to the information concerning its properties which may be deduced from observations of pulsar glitches and postglitch behavior. Current observational evidence concerning the softness or stiffness of the high density neutron matter equation of state is reviewed briefly, and the (revolutionary) implications of a confirmation of the existence of a 0.5 ms pulsar at the core of (Supernova) SN1987A are discussed.

  4. 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

  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. Measurement of the Radius of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Guillot, Sebastien

    2012-07-01

    A physical understanding of the behavior of cold ultra-dense matter -- at and above nuclear density -- can only be achieved by the study of neutron stars. The recent 1.97+/-0.04 Msun measurement for PSR 1614-2230 suggests that strange quark matter and hyperons/kaons condensate equations of state (EoSs) are disfavored, in favor of hadronic EoSs. Over much of the neutron star mass-radius parameter space, the latter EoSs produce lines of nearly constant radii (within about 10%). We present a simultaneous spectral analysis of several globular cluster quiescent low-mass x-ray binaries where we require the radius to be the same among all neutron stars analyzed. Our (preliminary) results suggest a neutron star radius much smaller than previously reported, in the range 7.5-10 km (90% confidence). The Markov-Chain Monte-Carlo method and the Bayesian approach developed in this analysis permits including uncertainties in the distance, in the hydrogen column density, and possible contributions to the spectra due to unmodelled spectrally hard components.

  7. Measurement of the Radius of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Guillot, Sebastien; Rutledge, R. E.; Servillat, M.; Webb, N.

    2013-01-01

    A physical understanding of the behavior of cold ultra dense matter - at and above nuclear density - can only be achieved by the study of neutron stars. The recent 1.97 ± 0.04 M⊙ measurement for PSR 1614-2230 suggests that strange quark matter and hyperons/kaons condensate equations of state (EoSs) are disfavored, in favor of hadronic EoSs. Over much of the neutron star mass-radius parameter space, the latter EoSs produce lines of nearly constant radii (within about 10%). We present a simultaneous spectral analysis of several globular cluster quiescent low-mass X-ray binaries where we require the radius to be the same among all neutron stars analyzed. Our (preliminary) results suggest a neutron star radius much smaller than previously reported, in the range 7.5-10 km (90% confidence). The Markov-Chain Monte-Carlo method and the Bayesian approach developed in this analysis permits including uncertainties in the distance, in the hydrogen column density, and possible contributions to the spectra due to unmodeled spectrally hard components.

  8. Neutron star solutions in perturbative quadratic gravity

    SciTech Connect

    Deliduman, Cemsinan; Ekşi, K.Y.; Keleş, Vildan E-mail: eksi@itu.edu.tr

    2012-05-01

    We study the structure of neutron stars in R+βR{sup μν}R{sub μν} gravity model with perturbative method. We obtain mass-radius relations for six representative equations of state (EoSs). We find that, for |β| ∼ 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 β of this order with the 2 solar mass neutron star recently observed. For values of β 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 mass–radius relation we try to constrain the value of β for each EoS. The associated length scale (β){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 β is most likely much smaller than 10{sup 11} cm{sup 2}.

  9. 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.

  10. Induced Pairing Interaction in Neutron Star Matter

    NASA Astrophysics Data System (ADS)

    Lombardo, U.; Schulze, H.-J.; Zuo, W.

    2013-01-01

    The three superfluid phases supposed to occur in neutron stars are reviewed in the framework of the generalized BCS theory with the induced interaction. The structure of neutron stars characterized by beta-stable asymmetric nuclear matter in equilibrium with the gravitational force discloses new aspects of the pairing mechanism. Some of them are discussed in this report, in particular the formation in dense matter of Cooper pairs in the presence of three-body forces and the interplay between repulsive and attractive polarization effects on isospin T = 1 Cooper pairs embedded into the neutron and proton environment. Quantitative estimates of the energy gaps are reported and their sensitivity to the medium effects, i.e., interaction and polarization, is explored.

  11. Numerical relativistic hydrodynamic simulations of neutron stars

    NASA Astrophysics Data System (ADS)

    Haywood, Joe R.

    Developments in numerical relativistic hydrodynamics over the past thirty years, along with the advent of high speed computers, have made problems needing general relativity and relativistic hydrodynamics tractable. One such problem is the relativistic evolution of neutron stars, either in a head on collision or in binary orbit. Also of current interest is the detection of gravitational radiation from binary neutron stars, black-hole neutron star binaries, binary black holes, etc. Such systems expected to emit gravitational radiation with amplitude large enough to be detected on Earth by such groups as LIGO and VIRGO. Unfortunately, the expected signal strength is below the current noise level. However, signal processing techniques have been developed which should eventually find a signal, if a good theoretical template can be found. In the cases above it is not possible to obtain an analytic solution to the Einstein equations and a numerical approximation is therefore most necessary. In this thesis the Einstein equations are written using the formalism of Arnowitt, Desser and Misner and a conformally flat metric is assumed. Numerical simulations of colliding neutron stars, having either a realistic or Gamma = 2 polytropic equation of state (EOS), are presented which confirm the rise in central density seen by [51, 89] for the softer EOS. For the binary calculation, the results of Wilson et al. [89] are confirmed, which show that the neutron stars can collapse to black holes before colliding when the EOS is realistic and we also confirm results of Miller [56] and others that there is essentially no compression, the central density does not increase, when the stiffer equation of state is used. Finally, a template for the gravitational radiation emitted from the binary is calculated and we show that the frequency of the emitted gravitational waves changes more slowly for the [89] EOS, which may result in a stronger signal in the 50-100 Hz band of LIGO.

  12. Non-identical neutron star twins

    SciTech Connect

    Glendenning, Norman K.; Kettner, Christiane

    1998-07-01

    The work of J. A. Wheeler in the mid 1960's showed that forsmooth equations of state no stable stellar configurations with centraldensities above that corresponding to the limiting mass of 'neutronstars' (in the generic sense) were stable against acoustical vibrationalmodes. A perturbation would cause any such star to collapse to a blackhole or explode. Accordingly, there has been no reason to expect that astable degenerate family of stars with higher density than the knownwhite dwarfs and neutron stars might exist. We have found a class ofexceptions corresponding to certain equations of state that describe afirst order phase transition. We discuss how such a higher density familyof stars could be formed in nature, and how the promising new explorationof oscillations in the X-ray brightness of accreting neutron stars mightprovide a means of identifying them. Our proof of the possible existenceof a third family of degenerate stars is one of principle and rests ongeneral principles like causality, microstability of matter and GeneralRelativity.

  13. Neutron star recoils from anisotropic supernovae.

    NASA Astrophysics Data System (ADS)

    Janka, H.-T.; Mueller, E.

    1994-10-01

    Refering to recent hydrodynamical computations (Herant et al. 1992; Janka & Mueller 1993a) it is argued that neutron star kicks up to a few hundred km/s might be caused by a turbulent overturn of the matter between proto-neutron star and supernova shock during the early phase of the supernova explosion. These recoil speeds ("kick velocities") may be of the right size to explain the measured proper motions of most pulsars and do not require the presence of magnetic fields in the star. It is also possible that anisotropic neutrino emission associated with convective processes in the surface layers of the nascent neutron star (Burrows & Fryxell 1992; Janka & Mueller 1993b; Mueller 1993) provides an acceleration mechanism (Woosley 1987), although our estimates indicate that the maximum attainable velocities are around 200km/s. Yet, it turns out to be very unlikely that the considered stochastic asymmetries of supernova explosions are able to produce large enough recoils to account for pulsar velocities in excess of about 500km/s, which can be found in the samples of Harrison et al. (1993) and Taylor et al. (1993). It is concluded that other acceleration mechanisms have to be devised to explain the fast motion of PSR 2224+65 (transverse speed >=800km/s Cordes et al. 1993) and the high-velocities deduced from associations between supernova remnants and nearby young pulsars (e.g., Frail & Kulkarni 1991; Stewart et al. 1993; Caraveo 1993).

  14. Cooling of neutron stars with diffusive envelopes

    NASA Astrophysics Data System (ADS)

    Beznogov, M. V.; Fortin, M.; Haensel, P.; Yakovlev, D. G.; Zdunik, J. L.

    2016-08-01

    We study the effects of heat blanketing envelopes of neutron stars on their cooling. To this aim, we perform cooling simulations using newly constructed models of the envelopes composed of binary ion mixtures (H-He, He-C, C-Fe) varying the mass of lighter ions (H, He or C) in the envelope. The results are compared with those calculated using the standard models of the envelopes which contain the layers of lighter (accreted) elements (H, He and C) on top of the Fe layer, varying the mass of accreted elements. The main effect is that the chemical composition of the envelopes influences their thermal conductivity and, hence, thermal insulation of the star. For illustration, we apply these results to estimate the internal temperature of the Vela pulsar and to study the cooling of neutron stars of ages of 105 - 106 yr at the photon cooling stage. The uncertainties of the cooling models associated with our poor knowledge of chemical composition of the heat insulating envelopes strongly complicate theoretical reconstruction of the internal structure of cooling neutron stars from observations of their thermal surface emission.

  15. Neutron stars in Horndeski gravity

    NASA Astrophysics Data System (ADS)

    Maselli, Andrea; Silva, Hector O.; Minamitsuji, Masato; Berti, Emanuele

    2016-06-01

    Horndeski's theory of gravity is the most general scalar-tensor theory with a single scalar whose equations of motion contain at most second-order derivatives. A subsector of Horndeski's theory known as "Fab Four" gravity allows for dynamical self-tuning of the quantum vacuum energy, and therefore it has received particular attention in cosmology as a possible alternative to the Λ CDM model. Here we study compact stars in Fab Four gravity, which includes as special cases general relativity ("George"), Einstein-dilaton-Gauss-Bonnet gravity ("Ringo"), theories with a nonminimal coupling with the Einstein tensor ("John"), and theories involving the double-dual of the Riemann tensor ("Paul"). We generalize and extend previous results in theories of the John class and were not able to find realistic compact stars in theories involving the Paul class.

  16. 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.

  17. 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.

  18. Equation of state for neutron star matter

    SciTech Connect

    Shang-Hui, G.; Yun-Zao, G.; Leung, Y.C.; Zong-Wei, L.; Shao-Rong, L.

    1981-05-01

    We modify the relativistic mean field model proposed by Walecka to handle differently the short-range interaction induced by the vector meson. There are three parameters in the modified model, which are then fixed by fitting them to the properties of nuclear matter at saturation. The equation of state for pure neutron matter is computed. Our results differ substantially from those obtained by Walecka, but are in line with those obtained from the potential approach. The maximum neutron star mass is found tobe 1.7 M/sub sun/.

  19. 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.

  20. 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.

  1. Fast Fossil Rotation of Neutron Star Cores

    NASA Astrophysics Data System (ADS)

    Melatos, A.

    2012-12-01

    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 ~103 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.

  2. '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.

  3. Mergers of Binary Neutron Star Systems

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    We present results from fully relativistic simulations of binary neutron star mergers varying the tabular equation of state used to approximate the degenerate material and the mass ratio. The simulations incorporate both magnetic fields and the effects of neutrino cooling. In particular, we examine the amount and properties of material ejected from the merger. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  4. Electromagnetic field dynamics in Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    Neutron star mergers represent one of the most promising sources of gravitational waves (GW) within the bandwidth of advLIGO. In addition to GW, strong magnetic fields may offer the possibility of a characteristic electromagnetic signature allowing for concurrent detection. In this talk we present results from numerical evolutions of such mergers, studying the dynamics of both the gravitational and electromagnetic degrees of freedom.

  5. 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.

  6. HEAD II: Exotic Neutron Stars Introduction

    NASA Astrophysics Data System (ADS)

    Harding, A. K.

    1998-12-01

    There has recently been growing evidence for a new class of astronomical object: isolated neutron stars with extremely high magnetic fields. Such objects were predicted to exist and would be the first known source to be powered by magnetic energy. The talks in this sessions will review evidence from observations of two types of sources: Soft Gamma-ray Repeaters, a class of galactic gamma-ray burst source, and Anomalous X-ray Pulsars, as well as current models.

  7. 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.

  8. Neutron stars interiors: Theory and reality

    NASA Astrophysics Data System (ADS)

    Stone, J. R.

    2016-03-01

    There are many fascinating processes in the universe which we observe in more detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in a core-collapse supernova explosion, one of the most violent events in the universe. As a result, the densest objects in the universe, neutron stars and/or black holes, are created. The physical basis of these events should be understood in line with observation. Unfortunately, available data do not provide adequate constraints for many theoretical models of dense matter. One of the most open areas of research is the composition of matter in the cores of neutron stars. Unambiguous fingerprints for the appearance and evolution of particular components, such as strange baryons and mesons, with increasing density, have not been identified. In particular, the hadron-quark phase transition remains a subject of intensive research. In this contribution we briefly survey the most promising observational and theoretical directions leading to progress in understanding high density matter in neutron stars. A possible way forward in modeling high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC). This model makes connection between hadronic structure and the underlying quark make-up. It offers a natural explanation for the saturation of nuclear force and treats high-density matter, containing the full baryon octet, in terms of four uniquely defined parameters adjusted to properties of symmetric nuclear matter at saturation.

  9. 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.

  10. Neutron stars and strange stars in the chiral SU(3) quark mean field model

    SciTech Connect

    P. Wang; S. Lawley; D. B. Leinweber; A. W. Thomas; A. G. Williams

    2005-06-01

    We investigate the equations of state for pure neutron matter and strange hadronic matter in {beta}-equilibrium, including {Lambda}, {Sigma} and {Xi} hyperons. The masses and radii of pure neutron stars and strange hadronic stars are obtained. For a pure neutron star, the maximum mass is about 1.8 M{sub sun}, while for a strange hadronic star, the maximum mass is around 1.45M{sub sun}. The typical radii of pure neutron stars and strange hadronic stars are about 11.0-12.3 km and 10.7-11.7 km, respectively.

  11. 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.

  12. 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 Ωcr, 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.

  13. 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.

  14. Disk accretion by magnetic neutron stars

    NASA Technical Reports Server (NTRS)

    Ghosh, P.; Lamb, F. K.

    1978-01-01

    A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed description of matter flow in the transition region between the disk and the magnetosphere. It is shown that the disk plasma cannot be completely screened from the stellar magnetic field and that the resulting magnetic coupling between the star and the disk exerts a significant torque on the star. On the assumption that the distortion of the residual stellar field lines threading the disk is limited by reconnection, the total accretion torque on the star is calculated. The calculated torque gives period changes in agreement with those observed in the pulsating X-ray sources and provides a natural explanation of why a fast rotator like Her X-1 has a spin-up rate much below the conventional estimate for slow rotators. It is shown that for such fast rotators, fluctuations in the mass-accretion rate can produce fluctuations in the accretion torque about 100 times larger. For sufficiently fast rotators or, equivalently, for sufficiently low accretion rates, the star experiences a braking torque even while accretion continues and without any mass ejection from its vicinity.

  15. 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.

  16. Nonlinear Tides in Coalescing Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Weinberg, Nevin

    2016-03-01

    Coalescing binary neutron stars are among the most promising sources for ground-based gravitational wave detectors such as Advanced LIGO. Tidal interactions in such systems extract energy from the orbit and, at some level, modify the gravitational wave signal. Previous studies found that tidal effects are probably too small to be detected from individual systems with LIGO. However, these studies typically assumed that the tide can be treated as a linear perturbation to the star. I will show that the linear approximation is invalid even during the early stages of inspiral and that nonlinear fluid effects in the form of tide-internal wave interactions become important around the time the binary first enters LIGO's bandpass (at gravitational wave frequencies around 30 Hz). Although the precise influence of nonlinear fluid effects is not yet well constrained, I will show that they may significantly modify the gravitational wave signal and electromagnetic emission from coalescing binary neutron stars. This research was supported by NASA Grant NNX14AB40G.

  17. 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).

  18. Coalescence of Magnetized Binary Neutron Star Systems

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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. Our simulation tools have recently been improved to incorporate the effects of neutrino cooling and have been generalized to allow for tabular equations of state to describe the degenerate matter. Of particular interest are possible electromagnetic counterparts to the gravitational radiation that emerges from these systems. We focus on magnetospheric interactions that ultimately tap into the gravitational potential energy of the binary to power a Poynting flux and deposition of energy through Joule heating and magnetic reconnection. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  19. 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.

  20. Holographic cold nuclear matter and neutron star

    NASA Astrophysics Data System (ADS)

    Ghoroku, Kazuo; Kubo, Kouki; Tachibana, Motoi; Toyoda, Fumihiko

    2014-04-01

    We have previously found a new phase of cold nuclear matter based on a holographic gauge theory, where baryons are introduced as instanton gas in the probe D8//lineD8 branes. In our model, we could obtain the equation of state (EOS) of our nuclear matter by introducing Fermi momentum. Then, here we apply this model to the neutron star and study its mass and radius by solving the Tolman-Oppenheimer-Volkoff (TOV) equations in terms of the EOS given here. We give some comments for our holographic model from a viewpoint of the other field theoretical approaches.

  1. 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.

  2. 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.

  3. Sound Velocity Bound and Neutron Stars

    SciTech Connect

    Bedaque, Paulo; Steiner, Andrew W

    2015-01-01

    It has been conjectured that the velocity of sound in any medium is smaller than the velocity of light in vacuum divided by sqrt(3). Simple arguments support this bound in nonrelativistic and/or weakly coupled theories. The bound has been demonstrated in several classes of strongly coupled theories with gravity duals and is saturated only in conformal theories. We point out that the existence of neutron stars with masses around two solar masses combined with the knowledge of the equation of state of hadronic matter at low densities is in strong tension with this bound.

  4. Neutron star binaries, pulsars and burst sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1981-01-01

    Unresolved issues involving neutron star binaries, pulsars, and burst sources are described. Attention is drawn to the types of observations most likely to resolve them. Many of these observations are likely to be carried out during the next decade by one or more missions that have been approved or proposed. Flux measurements with an imaging detector and broad-band spectroscopic studies in the energy range 30-150 keV are discussed. The need for soft X-ray and X-ray observations with an instrument which has arcminute angular resolution and an effective area substantially greater than of ROSAT or EXOSAT is also discussed.

  5. 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.

  6. Frontiers the Physics of Dense Matter for Neutron Stars

    NASA Astrophysics Data System (ADS)

    Steiner, Andrew W.

    2016-04-01

    Neutron stars are an excellent laboratory for nuclear physics. They probe the nucleon-nucleon interaction, the structure of nuclei, and the nature of dense QCD in ways which complement current experimental efforts. This article very briefly summarizes some of the current frontiers in neutron stars and dense matter with an emphasis on how our understanding might be improved in the near future.

  7. The Thermodynamic Functions in Curved Space of Neutron Star

    NASA Astrophysics Data System (ADS)

    Hussein, N. A.; Eisa, D. A.; Sayed, E. G.

    2016-04-01

    The aim of this article is to calculate the thermodynamic functions of a neutron star in curved space. We obtained equation of state (EOS) and the excess free energy for a neutron star in curved space up to order n4, where n is the density of particles.

  8. 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.

  9. BINARY NEUTRON STARS IN QUASI-EQUILIBRIUM

    SciTech Connect

    Taniguchi, Keisuke; Shibata, Masaru

    2010-05-15

    Quasi-equilibrium sequences of binary neutron stars are constructed for a variety of equations of state in general relativity. Einstein's constraint equations in the Isenberg-Wilson-Mathews approximation are solved together with the relativistic equations of hydrostationary equilibrium under the assumption of irrotational flow. We focus on unequal-mass sequences as well as equal-mass sequences, and compare those results. We investigate the behavior of the binding energy and total angular momentum along a quasi-equilibrium sequence, the endpoint of sequences, and the orbital angular velocity as a function of time, changing the mass ratio, the total mass of the binary system, and the equation of state of a neutron star. It is found that the orbital angular velocity at the mass-shedding limit can be determined by an empirical formula derived from an analytic estimation. We also provide tables for 160 sequences, which will be useful as a guideline of numerical simulations for the inspiral and merger performed in the near future.

  10. Neutron star accretion and the neutrino fireball

    SciTech Connect

    Colgate, S.A.; Herant, M.E.; Benz, W.

    1991-11-26

    The mixing necessary to explain the ``Fe`` line widths and possibly the observed red shifts of 1987A is explained in terms of large scale, entropy conserving, up and down flows (calculated with a smooth particle 2-D code) taking place between the neutron star and the explosion shock wave due to the gravity and neutrino deposition. Depending upon conditions of entropy and mass flux further accretion takes place in single events, similar to relaxation oscillator, fed by the downward flows of low entropy matter. The shock, in turn, is driven by the upflow of the buoyant high entropy bubbles. Some accretion events will reach a temperature high enough to create a neutrino ``fireball,`` a region hot enough, 11 Mev, so as to be partially opaque to its own (neutrino) radiation. The continuing neutrino deposition drives the explosion shock until the entropy of matter flowing downwards onto the neutron star is high enough to prevent further accretion. This process should result in a robust supernova explosion.

  11. Transient radio bursts from rotating neutron stars.

    PubMed

    McLaughlin, M A; Lyne, A G; Lorimer, D R; Kramer, M; Faulkner, A J; Manchester, R N; Cordes, J M; Camilo, F; Possenti, A; Stairs, I H; Hobbs, G; D'Amico, N; Burgay, M; O'Brien, J T

    2006-02-16

    The radio sky is relatively unexplored for transient signals, although the potential of radio-transient searches is high. This was demonstrated recently by the discovery of a previously unknown type of source, varying on timescales of minutes to hours. Here we report a search for radio sources that vary on much shorter timescales. We found eleven objects characterized by single, dispersed bursts having durations between 2 and 30 ms. The average time intervals between bursts range from 4 min to 3 h with radio emission typically detectable for <1 s per day. From an analysis of the burst arrival times, we have identified periodicities in the range 0.4-7 s for ten of the eleven sources, suggesting origins in rotating neutron stars. Despite the small number of sources detected at present, their ephemeral nature implies a total Galactic population significantly exceeding that of the regularly pulsing radio pulsars. Five of the ten sources have periods >4 s, and the rate of change of the pulse period has been measured for three of them; for one source, we have inferred a high magnetic field strength of 5 x 10(13) G. This suggests that the new population is related to other classes of isolated neutron stars observed at X-ray and gamma-ray wavelengths. PMID:16482150

  12. How loud are neutron star mergers?

    NASA Astrophysics Data System (ADS)

    Bernuzzi, Sebastiano; Radice, David; Ott, Christian D.; Roberts, Luke F.; Mösta, Philipp; Galeazzi, Filippo

    2016-07-01

    We present results from the first large parameter study of neutron star mergers using fully general relativistic simulations with finite-temperature microphysical equations of state and neutrino cooling. We consider equal and unequal-mass binaries drawn from the galactic population and simulate each binary with three different equations of state. Our focus is on the emission of energy and angular momentum in gravitational waves in the postmerger phase. We find that the emitted gravitational-wave energy in the first ˜10 ms of the life of the resulting hypermassive neutron star (HMNS) is about twice the energy emitted over the entire inspiral history of the binary. The total radiated energy per binary mass is comparable to or larger than that of nonspinning black hole inspiral-mergers. About 0.8-2.5% of the binary mass-energy is emitted at kHz frequencies in the early HMNS evolution. We find a clear dependence of the postmerger gravitational wave emission on binary configuration and equation of state and show that it can be encoded as a broad function of the binary tidal coupling constant κ2T. Our results also demonstrate that the dimensionless spin of black holes resulting from subsequent HMNS collapse are limited to ≲0.7 - 0.8 . This may significantly impact the neutrino pair annihilation mechanism for powering short gamma-ray bursts (sGRB).

  13. Diffusive heat blanketing envelopes of neutron stars

    NASA Astrophysics Data System (ADS)

    Beznogov, M. V.; Potekhin, A. Y.; Yakovlev, D. G.

    2016-06-01

    We construct new models of outer heat blanketing envelopes of neutron stars composed of binary ion mixtures (H-He, He-C, C-Fe) in and out of diffusive equilibrium. To this aim, we generalize our previous work on diffusion of ions in isothermal gaseous or Coulomb liquid plasmas to handle non-isothermal systems. We calculate the relations between the effective surface temperature Ts and the temperature Tb at the bottom of heat blanketing envelopes (at a density ρb ˜ 108 - 1010 g cm-3) for diffusively equilibrated and non-equilibrated distributions of ion species at different masses ΔM of lighter ions in the envelope. Our principal result is that the Ts-Tb relations are fairly insensitive to detailed distribution of ion fractions over the envelope (diffusively equilibrated or not) and depend almost solely on ΔM. The obtained relations are approximated by analytic expressions which are convenient for modelling the evolution of neutron stars.

  14. 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.

  15. 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

  16. 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.

  17. Microscopic vortex velocity and implications for neutron star dynamics

    NASA Astrophysics Data System (ADS)

    Gügercinoǧlu, Erbil; Alpar, Mehmet Ali

    2016-07-01

    Rotational dynamics of a neutron star is governed by the distribution and motion of vortex lines within the neutron superfluid. Interaction of the vortex lines with the ambient matter plays an important role in the glitches, thermal evolution and magnetic field evolution of pulsars. Thus, correctly treating the vortex motion both in the inner crust and in the outer core of neutron stars is a key ingredient in modeling a great variety of observational phenomena of pulsars. In this work we outline the first principles to calculate the microscopic vortex velocity in the inner crust as well as in the outer core. Then we discuss some implications for neutron star's dynamics.

  18. The Ps - e relation of double neutron stars

    NASA Astrophysics Data System (ADS)

    Dewi, J. D. M.; Podsiadlowski, Ph.; Pols, O. R.

    2007-08-01

    The seven Galactic double neutron stars (DNS)s exhibit a relation between the pulsar spin period and the orbital eccentricity. We show that this relation can only be produced if the second neutron star received a kick that is substantially smaller (with a velocity dispersion of less than 50 km s-1) than the standard kick received by a single radio pulsar. This demonstrates that the kick mechanism depends on the evolutionary history of the NS progenitor and that the orbital parameters of DNSs are completely determined by the evolution in the preceding helium star - neutron star phase.

  19. Nuclear Matter Equations of State and the Neutron Stars

    SciTech Connect

    Urbanec, M.; Stuchlik, Z.; Betak, E.

    2008-05-12

    The equations of state (EoS) of relativistic asymmetric nuclear matter are obtainable from assumed form of the interaction Lagrangian. They are one of important inputs to describe the neutron stars. The structure of the neutron stars, i.e. the density of matter and the pressure as functions of radial distance starting from their values at the center of a star, is straightforwardly dependent on EoS. Similarly, a limitation on the total mass of the neutron star can be obtained therefrom. Thus, EoS and the underlying nucleon interactions can be tested also by the means of astronomical observations.

  20. Observational constraints on neutron star masses and radii

    NASA Astrophysics Data System (ADS)

    Miller, M. Coleman; Lamb, Frederick K.

    2016-03-01

    Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star - black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method.

  1. Quasistatic Evolution of Binary Neutron Star Systems Before Merging

    NASA Astrophysics Data System (ADS)

    Eriguchi, Y.; Usui, F.

    Binary neutron star systems evolve due to the back reaction of gravitational wave emission. Although this evolution is essentially a time dependent phenomenon, most stages of the evolution can be regarded as if the system were in a stationary state. Consequently we can follow the evolution of binary neutron star systems quasistatically by connecting quasiequilibrium states of binary neutron stars. On the equilibrium sequences of congruent binary neutron star systems there are two important states of equilibrium configurations: 1) the minimum angular momentum state where some unstable phenomenon sets in and 2) the contact state from which a single body sequence will continue. Recent numerical results of quasiequilibrium approaches for the binary neutron star evolution are briefly reviewed and some problems in general relativistic treatments are discussed.

  2. 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.

  3. Computation of Neutron Star Structure Using Modern Equation of State

    NASA Astrophysics Data System (ADS)

    Bordbar, G. H.; Hayati, M.

    Using the modern equations of state derived from microscopic calculations, we have calculated the neutron star structure. For the neutron star, we have obtained a minimum mass about 0.1 M⊙ which is nearly independent of the equation of state, and a maximum mass between 1.47 M⊙ and 1.98 M⊙ which is strongly dependent on the equation of state. It is shown that among the equations of state of neutron star matter which we have used, the stiffest one leads to higher maximum mass and radius and lower central density. It is seen that the given maximum mass for the Reid-93 equation of state shows a good consistency with the accurate observations of radio pulsars. We have indicated that the thickness of neutron star crust is very small compared to the predicted neutron star radius.

  4. 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.

  5. Modeling the Electromagnetic and Gravitational Radiation from Neutron Stars

    NASA Astrophysics Data System (ADS)

    Liebling, Steven; Anderson, Matthew; Hirschmann, Eric; Neilsen, David; Hanna, Chad; Lehner, Luis; Palenzuela, Carlos; Thompson, Christopher; Motl, Patrick

    2012-03-01

    The dynamics of magnetized neutron stars both in binaries and in isolation are modeled with a novel numerical approach able to capture the dynamics of the star(s) and of the surrounding plasma. The stellar dynamics incorporate ideal MHD which appropriately models the regime in which the fluid pressure dominates that of the magnetic field, while the stellar exterior is modeled within the force free approach (magnetic pressure largely dominates that of the fluid). The approach is shown to approach certain known solutions. An intense electromagnetic outburst is observed for the collapsing, rotating star. The approach is also applied to the coalescence of a neutron star binary.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. Equilibrium spin pulsars unite neutron star populations

    NASA Astrophysics Data System (ADS)

    Ho, Wynn; Klus, Helen; Coe, Malcolm; Andersson, Nils

    2015-08-01

    We compare the large number of recent torque measurements of accreting pulsars with a high-mass companion to the standard model for how accretion affects the pulsar spin period. We find that many long spin period (P > 100 s) pulsars must possess either extremely weak (B < 10^10 G) or extremely strong (B > 10^14 G) magnetic fields. We argue that the strong-field solution is more compelling, in which case these pulsars are near spin equilibrium. Our results provide evidence for a fundamental link between pulsars with the slowest spin periods and strong magnetic fields around high-mass companions and pulsars with the fastest spin periods and weak fields around low-mass companions. The strong magnetic fields also connect our pulsars to magnetars and strong-field isolated radio/X-ray pulsars. The strong field and old age of our sources suggests their magnetic field penetrates into the superconducting core of the neutron star.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Surface composition of magnetic neutron stars.

    NASA Technical Reports Server (NTRS)

    Rosen, L. C.; Cameron, A. G. W.

    1972-01-01

    The relative abundances of seven constituent nuclei, He4, C12, O16, Ne20, Mg24, Si28, and Fe56, are calculated as a function of time for neutron star atmospheres within which exist magnetic fields of the order of 10 to the 13th G. The opacity, equation of state of the electrons, and cooling rate of the magnetic star are discussed, and it is shown to be a reasonable approximation to assume an atmosphere to be isothermal. The effects of particle diffusion are included in the nuclear reaction network. Computations are performed both for a constant mass atmosphere and for an atmosphere in which mass is being ejected. It is found that the final abundances are model-independent, as long as the initial model contains predominantly He4. The relative abundances are compared to the cosmic ray spectrum. For both the constant-mass and mass-loss atmospheres, nucleosynthesis proceeds virtually completely to Fe56. However the outermost layers of the envelope, in which no mass is being ejected, are composed almost entirely of He4 with trace amounts of Fe56. After the loss of about 10 to the 21st g, only Fe56 is ejected from atmospheres expelling mass.

  19. 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.

  20. 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.

  1. 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.).

  2. 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.).

  3. 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.

  4. 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

  5. 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%.

  6. The UV Brightness of Quiescent Black Holes and Neutron Stars

    NASA Astrophysics Data System (ADS)

    Hynes, Robert I.; Robinson, E. L.; McClintock, J. E.; Haswell, C. A.

    2006-06-01

    HST/STIS observations of quiescent black hole and neutron star soft X-ray transients have suggested that the two may exhibit dramatically different ultraviolet spectra, with neutron stars being more UV bright. We describe new HST/ACS observations providing near-UV detections of another neutron star system, Aql X-1, and three more black hole systems, X-ray Nova Mus 1991, GRO J0422+32, and X-ray Nova Vel 1993, together with upper limits for the neutron star system XTE J2123-058. These more than double the sample available. We will discuss models for the spectral energy distributions of quiescent soft X-ray transients, and the evidence that they are systematically different in the light of this larger and more significant sample.This work was supported by a grant from the Space Telescope Science Institute.

  7. Measuring the neutron star tidal Love number with inspiral waveforms

    NASA Astrophysics Data System (ADS)

    Favata, Marc

    2014-03-01

    The tidal Love number parameterizes how easily a binary companion deforms a neutron star. This deformation modifies the gravitational field near the neutron star and imprints itself on the binary orbit and gravitational waveform. Measuring the Love number with LIGO or other detectors will help constrain the neutron star equation of state (which is uncertain at high densities). I will discuss an improved parameterization of the waveform's Love-number dependence. I will also discuss how systematic errors will make this number difficult to measure. These systematic errors could arise from unknown post-Newtonian terms that enter at lower orders than tidal effects, or from neglecting small neutron star spins or binary eccentricity.

  8. Neutrino-pair bremsstrahlung in a neutron star crust

    NASA Astrophysics Data System (ADS)

    Ofengeim, D. D.; Kaminker, A. D.; Yakovlev, D. G.

    2014-11-01

    Based on the formalism by Kaminker et al. (Astron. Astrophys., 343 (1999) 1009) we derive an analytic approximation for neutrino-pair bremsstrahlung emissivity due to scattering of electrons by atomic nuclei in a neutron star crust of any realistic composition. The emissivity is expressed through the generalized Coulomb logarithm which we fit by introducing an effective potential of electron-nucleus scattering. In addition, we study the conditions at which the neutrino bremsstrahlung in the crust is affected by strong magnetic fields. The results can be applied for modelling of many phenomena in neutron stars, such as thermal relaxation in young isolated neutron stars and in accreting neutron stars with overheated crust in soft X-ray transients.

  9. Gravitational and Electromagnetic Emission from Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Palenzuela, C.; Lehner, L.; Ponce, M.; Liebling, S. L.; Anderson, M.; Neilsen, D.

    2013-06-01

    The inspiral of a neutron star - neutron star binary is a leading candidate for strong emission of gravitational waves. The interaction between the stellar magnetospheres may also give rise to electromagnetic emissions accompanying the gravity waves as the neutron stars inspiral and merge. We present results from a set of resistive magnetohydrodynamic simulations of mergers computed with full general relativity. We vary the initial magnetic field of the neutron stars including cases where the fields are initially aligned, anit-aligned and where one star’s field dominates over its companion. This presentation is based upon work supported by the National Aeronautics and Space Administration under grant No. NNX13AH01G through the astrophysics theory program.

  10. Calculation of Thermal Conductivity Coefficients for Magnetized Neutron Star

    NASA Astrophysics Data System (ADS)

    Glushikhina, M. V.; Bisnovatyi-Kogan, G. S.

    2015-01-01

    The coefficients that determine the electron heat transfer and diffusion in the crust of neutron stars are calculated on the basis of a solution of the Boltzmann equation with allowance for degeneracy.

  11. X-ray radiation from accreting, magnetized neutron stars

    SciTech Connect

    Pavlov, G.G.

    1984-01-01

    A review is given of recent developments in the theory of emission from a magnetized plasma for accreting neutron star conditions. Some observational data on X-ray pulsars are discussed, and present problems are indicated. 26 references.

  12. Measuring Neutron-Star Spins via Burst Oscillations (core Program)

    NASA Astrophysics Data System (ADS)

    Measuring the spin of neutron stars in low-mass X-ray binaries is one of the great strengths and highest priorities for RXTE. We propose targeted observations of known thermonuclear burst sources which do not have confirmed burst oscillations, as well as previously unknown sources, in order to detect new examples of burst oscillations and thus add to the sample of neutron star spins. We will target sources in states of frequent, bright bursts by triggering on the detection of bursts by INTEGRAL and/or Swift. Detection of neutron stars spinning beyond the present maximum will allow us to significantly constrain the neutron-star equation of state, presently an area of major uncertainty.

  13. Searching for substellar companions of young isolated neutron stars

    NASA Astrophysics Data System (ADS)

    Posselt, B.; Neuhäuser, 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.

  14. 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.

  15. 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.

  16. Crust-core coupling in rotating neutron stars

    SciTech Connect

    Glampedakis, Kostas; Andersson, Nils

    2006-08-15

    Motivated by their gravitational wave driven instability, we investigate the influence of the crust on r-mode oscillations in a neutron star. Using a simplistic model of an elastic neutron star crust with constant shear modulus, we carry out an analytic calculation with the main objective of deriving an expression for the slippage between the core and the crust. Our analytic estimates support previous numerical results and provide useful insights into the details of the problem.

  17. New results in black hole-neutron star merger models

    NASA Astrophysics Data System (ADS)

    Duez, Matthew

    2010-10-01

    I report on the SXS group's recent progress in using numerical general relativity to model one of the most violent and fascinating events in nature: the devouring of a neutron star by a black hole. I will discuss our efforts to simulate more representative and generic binary configurations and also our efforts to incorporate more realistic neutron star microphysics. Our numerical simulations allow us to predict post-merger states and gravitational wave signals.

  18. 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

  19. On the Maximum Mass of Differentially Rotating Neutron Stars.

    PubMed

    Baumgarte; Shapiro; Shibata

    2000-01-01

    We construct relativistic equilibrium models of differentially rotating neutron stars and show that they can support significantly more mass than their nonrotating or uniformly rotating counterparts. We dynamically evolve such "hypermassive" models in full general relativity and show that there do exist configurations that are dynamically stable against radial collapse and bar formation. Our results suggest that the remnant of binary neutron star coalescence may be temporarily stabilized by differential rotation, leading to delayed collapse and a delayed gravitational wave burst. PMID:10587488

  20. The neutrino ground state in a neutron star

    NASA Astrophysics Data System (ADS)

    Kiers, Ken; Tytgat, Michel H. G.

    1999-05-01

    We address a recent claim that the stability of neutron stars implies a lower bound on the mass of the neutrino. We argue that the result obtained by some previous authors is due to an improper summation of an infrared-sensitive series and that a non-perturbative ``resummation'' of the series yields a finite and well-behaved result. The stability of neutron stars thus gives no lower bound on the mass of the neutrino.

  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. 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

  3. Drilling into a neutron star with X-ray transients

    NASA Astrophysics Data System (ADS)

    Brown, Edward

    2010-11-01

    Over the last decade, advances in X-ray astronomy have greatly improved our knowledge of nuclear-powered phenomena on accreting neutron stars, such as type I X-ray bursts, superbursts, and cooling from quiescent neutron star transients. Spurred by these observations, theorists are beginning to reconstruct the nuclear evolution of accreted matter as it journeys from the low-density, proton-rich photosphere to the high-density, neutron-rich core. Knowledge of the interior thermal and compositional structure of the crust is important for understanding the detectability of gravitational wave emission from crust ``mountains,'' the strength of neutrino cooling in the core, the magnetic field evolution of the star, and the ignition of bursts at low mass accretion rates. These phenomena are potentially useful for constraining the dense matter equation of state. In this talk, I shall review our current understanding of the reactions in the neutron star crust. I shall then highlight new observations of cooling neutron star transients and what they reveal about the distribution of nuclei in the crust and the neutrino emissivity of the core. The rapidly cooling lightcurves of neutron star transients imply a highly conductive, cool crust, but the inferred ignition depths of superbursts, if powered by ^12C + ^12C fusion, require a hot crust. I will discuss the tension between these phenomena and possible resolutions.

  4. 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

  5. The birth of neutron stars and black holes

    NASA Astrophysics Data System (ADS)

    Burrows, Adam

    1987-09-01

    The events in the cores of massive stars that lead to supernova explosions and the formation of neutron stars and black holes are discussed. Stellar evolution systematics are reviewed, and complications within those basic systematics are examined. The theory is tested in the light of supernova 1987a.

  6. 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.

  7. 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

  8. Gravitational wave damping of neutron star wobble

    NASA Astrophysics Data System (ADS)

    Cutler, Curt; Jones, David Ian

    2001-01-01

    We calculate the effect of gravitational wave (GW) back reaction on realistic neutron stars (NS's) undergoing torque-free precession. By ``realistic'' we mean that the NS is treated as a mostly fluid body with an elastic crust, as opposed to a rigid body. We find that GW's damp NS wobble on a time scale τθ~2×105 yr [10- 7/(ΔId/I0)]2(kHz/ νs)4, where νs is the spin frequency and ΔId is the piece of the NS's inertia tensor that ``follows'' the crust's principal axis (as opposed to its spin axis). We give two different derivations of this result: one based solely on energy and angular momentum balance, and another obtained by adding the Burke-Thorne radiation reaction force to the Newtonian equations of motion. This problem was treated long ago by Bertotti and Anile, but their claimed result is wrong. When we convert from their notation to ours, we find that their τθ is too short by a factor of ~105 for the typical cases of interest and even has the wrong sign for ΔId negative. We show where their calculation went astray.

  9. Equilibrium spin pulsars unite neutron star populations

    NASA Astrophysics Data System (ADS)

    Ho, Wynn C. G.; Klus, H.; Coe, M. J.; Andersson, Nils

    2014-02-01

    Many pulsars are formed with a binary companion from which they can accrete matter. Torque exerted by accreting matter can cause the pulsar spin to increase or decrease, and over long times, an equilibrium spin rate is achieved. Application of accretion theory to these systems provides a probe of the pulsar magnetic field. We compare the large number of recent torque measurements of accreting pulsars with a high-mass companion to the standard model for how accretion affects the pulsar spin period. We find that many long spin period (P ≳ 100 s) pulsars must possess either extremely weak (B < 1010 G) or extremely strong (B > 1014 G) magnetic fields. We argue that the strong-field solution is more compelling, in which case these pulsars are near spin equilibrium. Our results provide evidence for a fundamental link between pulsars with the slowest spin periods and strong magnetic fields around high-mass companions and pulsars with the fastest spin periods and weak fields around low-mass companions. The strong magnetic fields also connect our pulsars to magnetars and strong-field isolated radio/X-ray pulsars. The strong field and old age of our sources suggest their magnetic field penetrates into the superconducting core of the neutron star.

  10. 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

  11. Quark-hadron composition of rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Mellinger, Richard D., Jr.

    It is well known that isolated neutron stars spin down over time through magnetic braking. To maintain hydrostatic equilibrium as they do so, the density profile of the star changes. At densities as high as those expected to exist in the interiors of neutron stars, this can lead to changes in the state of matter found there. Given several models for the nuclear equations of state, we use numerical techniques to determine, for each, the quark-hadron composition for varying frequencies and the results are presented in both tabular and graphical forms. The CD-ROM, an appendix to this thesis, is available for viewing at the Media Center of the Library.

  12. 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

  13. 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 1.97±0.04 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.

  14. 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

  15. 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.

  16. 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.

  17. Searching for gravitational waves from neutron stars

    NASA Astrophysics Data System (ADS)

    Idrisy, Ashikuzzaman

    In this dissertation we discuss gravitational waves (GWs) and their neutron star (NS) sources. We begin with a general discussion of the motivation for searching for GWs and the indirect experimental evidence of their existence. Then we discuss the various mechanisms through which NS can emit GWs, paying special attention the r-mode oscillations. Finally we end with discussion of GW detection. In Chapter 2 we describe research into the frequencies of r-mode oscillations. Knowing these frequencies can be useful for guiding and interpreting gravitational wave and electromagnetic observations. The frequencies of slowly rotating, barotropic, and non-magnetic Newtonian stars are well known, but subject to various corrections. After making simple estimates of the relative strengths of these corrections we conclude that relativistic corrections are the most important. For this reason we extend the formalism of K. H. Lockitch, J. L. Friedman, and N. Andersson [Phys. Rev. D 68, 124010 (2003)], who consider relativistic polytropes, to the case of realistic equations of state. This formulation results in perturbation equations which are solved using a spectral method. We find that for realistic equations of state the r-mode frequency ranges from 1.39--1.57 times the spin frequency of the star when the relativistic compactness parameter (M/R) is varied over the astrophysically motivated interval 0.110--0.310. Following a successful r-mode detection our results can help constrain the high density equation of state. In Chapter 3 we present a technical introduction to the data analysis tools used in GW searches. Starting from the plane-wave solutions derived in Chapter 1 we develop the F-statistic used in the matched filtering technique. This technique relies on coherently integrating the GW detector's data stream with a theoretically modeled wave signal. The statistic is used to test the null hypothesis that the data contains no signal. In this chapter we also discuss how to

  18. Neutron-capture Nucleosynthesis in the First Stars

    NASA Astrophysics Data System (ADS)

    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. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, and The McDonald Observatory of The University of Texas at Austin.

  19. The formation of double neutron stars and double black holes

    NASA Astrophysics Data System (ADS)

    Nelemans, Gijs

    2016-07-01

    The evolution from two massive stars in a binary to a compact binary with neutron stars or black holes passes through many stages in which the two stars interact. The outcome of many of these is highly uncertain. I will present a study into some of the most important uncertainties and some initial suggestions on how use of Gaia data for the early phases and LIGO/Virgo data on the final systems may constrain the outcome of these uncertain phases. In turn, this knowledge will guide further studies into the detailed physics of the interaction between stars in a massive binary.

  20. Spin-down of neutron stars by neutrino emission

    SciTech Connect

    Dvornikov, Maxim; Dib, Claudio

    2010-08-15

    We study the spin-down of a neutron star during its early stages due to the neutrino emission. The mechanism we consider is the subsequent collisions of the produced neutrinos with the outer shells of the star. We find that this mechanism can indeed slow down the star rotation but only in the first tens of seconds of the core formation, which is when the appropriate conditions of flux and collision rate are met. We find that this mechanism can extract less than 1% of the star angular momentum, a result which is much less than previously estimated by other authors.

  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

  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

    SciTech Connect

    Fryer, Chris L; Belczynski, Krzysztoff; Ramirez-Ruiz, Enrico; Rosswog, Stephan; Shen, Gang

    2015-01-01

    Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO 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 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 gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.

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

    SciTech Connect

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

    2015-10-06

    Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO 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 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 gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.

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

    DOE PAGESBeta

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

    2015-10-06

    Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO 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 merger calculations and equation of state studies to determine the fate of the coresmore » 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 gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.« less

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    A Lagrangian, fully implicit, one-dimensional hydrodynamic computer code is used to evolve thermonuclear runaways in the accreted hydrogen-rich envelopes of 1.0-solar-mass neutron stars with radii of 10 km and 20 km. The simulations produce outbursts lasting from approximately 750 seconds to approximately one week. The peak effective temperatures and luminosities are 2.6 x 10 to the 7th K and 8 x 10 to the 4th solar luminosities for the 10 km study and 5.3 x 10 to the 6th K and 600 solar luminosities for the 20 km study. It is found that hydrodynamic expansion on the 10 km neutron star produced a precursor lasting approximately 0.0001 second. The study assumes that the bursters and transient X-ray sources occur as a result of mass transfer from a secondary onto a neutron star in a fashion analogous to the nova phenomena. The peak temperatures and luminosities are found to be inversely proportional to the radius of the neutron stars and the calculations here, together with those in the literature, indicate that the actual radii of most neutron stars must be closer to 10 km than 20 km.

  7. Observations of Millisecond Variability from Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    1997-04-01

    Observations carried out over the past year by the Rossi X-ray Timing Explorer (RXTE) have revealed both quasiperiodic and nearly coherent oscillations with frequencies from 300 - 1200 Hz in at least 10 low mass X-ray binary (LMXB) systems. The X-ray luminosity from these systems is the result of accretion of matter into the deep gravitational potential well of a neutron star. Four of these sources show nearly coherent oscillations during some thermonuclear X-ray bursts which very likely reveal the long sought millisecond spin periods of neutron stars in at least some LMXB. The millisecond timescales of the quasiperiodic oscillations (QPO) are characteristic of processes occuring in the immediate vicinity of the neutron star and provide a new means to investigate the physics of neutron stars and their environs. I will review the discovery and current understanding of these kHz QPO, as they have come to be known, and briefly discuss what their study can teach us about neutron stars.

  8. Atmosphere composition of quiescent accreting neutron stars in globular clusters

    NASA Astrophysics Data System (ADS)

    Servillat, M.

    2012-12-01

    Through the study of the quiescent X-ray emission of neutron stars in low-mass X-ray binaries it is possible to constrain the equation of state of dense matter. However, the chemical composition of the neutron star atmosphere is still uncertain. Using deep Chandra observations, we report the detailed spectral analysis of a neutron star in the globular cluster M28. For the first time for this kind of object, different atmosphere models composed of hydrogen, helium or carbon are used. The carbon model can be ruled out, and the derived mass and radius are clearly distinct depending on the composition of the atmosphere, leading to different constraints on the equation of state. We compare those results with the other similar neutron stars studied with a hydrogen atmosphere model only and show that a helium model could be relevant in many cases. Measurements of neutron star masses/radii by spectral fitting should consider the possibility of heavier element atmospheres, which produce larger masses/radii for the same data, unless the composition of the accretor is known independently.

  9. 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.

  10. 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

  11. Neutron star natal kicks and the long-term survival of star clusters

    NASA Astrophysics Data System (ADS)

    Contenta, Filippo; Varri, Anna Lisa; Heggie, Douglas C.

    2015-04-01

    We investigate the dynamical evolution of a star cluster in an external tidal field by using N-body simulations, with focus on the effects of the presence or absence of neutron star natal velocity kicks. We show that, even if neutron stars typically represent less than 2 per cent of the total bound mass of a star cluster, their primordial kinematic properties may affect the lifetime of the system by up to almost a factor of 4. We interpret this result in the light of two known modes of star cluster dissolution, dominated by either early stellar evolution mass-loss or two-body relaxation. The competition between these effects shapes the mass-loss profile of star clusters, which may either dissolve abruptly (`jumping'), in the pre-core-collapse phase, or gradually (`skiing'), after having reached core collapse.

  12. Sensitivity of neutron star properties to the equation of state

    NASA Astrophysics Data System (ADS)

    Fattoyev, Farrooh

    2011-01-01

    The subject of this doctoral dissertation is to study the equations of state of nuclear and neutron-star matter. We tackle this problem by employing several models of the relativistic effective interactions. The relativistic effective interactions and their applications to the ground-state properties of medium to heavy nuclei have enjoyed enormous success for the past three decades. With just a few model parameters calibrated to the ground state properties of the closed-shell nuclei, these models exhibit and encode a great amount of physics. However, theses models are untested far away from their narrow window of applicability. In particular, while these models tend to agree on the saturation properties of symmetric nuclear matter, they largely disagree on its density and isospin dependence, especially in the region of high densities and large proton-neutron asymmetries. In order to better understand the properties of nuclear matter at these extreme regions of isospin asymmetry and high-densities, we will apply these models to predict several neutron star properties. Since the matter in the neutron stars are very neutron-rich, while the density of matter in neutron stars spans over a wide range of magnitudes, these compact objects remain unique laboratories for probing the equation of state of neutron-rich matter under conditions unattainable by terrestrial experiments. Thus it is expected that at least the following neutron star properties must be sensitive to the underlying equation of state: maximum mass, typical radii, moments of inertia (both total and crustal), redshifts, and cooling mechanism. We present numerical solutions and in some cases also analytical solutions to each of the properties above. In particular, the sensitivity of the stellar moment of inertia to the neutron-star matter equation of state is examined using accurately-calibrated relativistic mean-field models. We probe this sensitivity by tuning both the density dependence of the symmetry

  13. 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.

  14. Effects of Gravitational Correction on Neutron Stars with Antikaon Condensation

    NASA Astrophysics Data System (ADS)

    Ding, Wen-Bo; Hou, Jia-Wei; Qi, Zhan-Qiang; E, Shan-Shan; Bao, Tmurbagan; Liu, Guang-Zhou; Yu, Zi; Zhao, En-Guang

    2016-06-01

    Effects of gravitational correction through the introduction of U bosons on neutron stars with antikaon condensation are studied in the relativistic mean held theory. How the global properties of neutron stars, redshift and the momentum of inertia are modified by gravitational correction and antikaon condensation are discussed here. Results show that antikaon condensation can occur at the core of pulsar PSR J1614-2230. Gravitational correction and antikaon condensation influence each other, and when coupling constant of U bosons and baryons becomes very high, effects of antikaon condensation almost vanish. Moreover, both the redshift and the momentum of inertia of neutron stars are sensitive to the constant of U bosons. Combining with observation data, we can provide a further constraint on coupling constant of U bosons. Supported by National Natural Science Foundation of China under Grant Nos. 11265009, 11271055, and 11175077, and General Project of Liaoning Provincial Department of Education under Grant No. L2015005

  15. Merger of binary neutron stars in numerical relativity

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru

    2014-09-01

    The merger of binary neutron stars is one of most promising sources of gravitational waves. It is also a promising candidate for the central engine of short-hard gamma-ray bursts and a source of the strong transient electromagnetic signal that could be the counterpart of gravitational-wave signals. Numerical relativity is probably the unique tool for theoretically exploring the merger process, and now, it is powerful enough to provide us a wide variety of aspects of the binary-neutron-star merger. In this talk, I will summarize our current understanding of the entire merger event that is obtained by a large-scale numerical-relativity simulations. In particular, I focus on the relation between the neutron-star equation of state and gravitational waves emitted during the late inspiral and merger phase, and observable electromagnetic signal that is likely to be emitted by the dynamical ejecta through r-process nucleosynthesis.

  16. Magnetic field effects on gravitational waves from binary neutron stars

    NASA Astrophysics Data System (ADS)

    Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Liebling, Steven; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Tohline, Joel

    2008-04-01

    Observational evidence indicates that a fair number of neutron star binaries and neutron star-black hole binaries have a sizable magnetic field which can be responsible for powering pulsars and colimating jets. Magnetic field effects additionally can have a strong influence on the dynamics of the fluid by redistributing angular momentum through different mechanisms (magnetic winding and braking, magneto-rotational instabilities) depending on the strength of the magnetic field and the typical time scales involved in the process. These processes can affect the multipolar structure of the source and consequently the produced gravitational wave. We present results of neutron star binary mergers both with and without magnetic field and discuss the magnetic effects on the gravitational waves, fluid structure, and merger timescale.

  17. 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.

  18. 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.

  19. Gamma-ray bursts and neutron star field decay

    NASA Technical Reports Server (NTRS)

    Hartmann, Dieter; Blumenthal, George; Chuang, Kuan-Wen; Hurley, Kevin; Kargatis, Vincent; Liang, Edison; Linder, Eric

    1992-01-01

    Assuming a Galactic origin of gamma-ray bursts, we use pulsar data to calculate the spatial distribution of neutron stars and determine the sampling depths of current detectors. Based on these distance limits, we calculate the corresponding age distribution of Galactic neutron stars and apply an exponential field decay model to test whether the observed high incidence rate of cyclotron lines is consistent with suggested field decay time scales of order 10 exp 7 years. We find that the properties of the observed population of gamma-ray bursts are inconsistent with the idea that bursts originate at arbitrary times on neutron stars whose fields decay on time scales shorter than about 10 exp 9 years. Possible interpretations of this inconsistency are discussed.

  20. 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.

  1. Magnetic Energy Production by Turbulence in Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    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 (gsim 1016 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 10-4 of the ~1053 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 10-7 erg cm-2, potentially rendering most merging neutron stars in the advanced LIGO and Virgo detection volumes detectable by Swift BAT.

  2. Merging ``real'' neutron stars for gravitational waves and electromagnetic counterparts

    NASA Astrophysics Data System (ADS)

    Duez, Matthew

    2014-03-01

    Having more-or-less succeeded in learning to stably evolve Einstein's equations, numerical relativity is taking the leap to including the physics of neutron stars, which will enable us to construct truly realistic pictures of neutron star-neutron star and black hole-neutron star binary mergers. The neutron star profile affects late inspirals and mergers, leaving its imprint on gravitational waveforms and electromagnetic counterpart signals. Furthermore, we expect neutrino radiation, magnetic field, and nuclear recombination effects to drive the post-merger evolution. In this talk, I will describe some recent neutron star merger simulations combining nuclear physics and general relativity. The goal is to connect assumptions about the nuclear equation of state and the premerger binary to resulting binary trajectories, matter outflows, accretion disk dynamics, and neutrino energy output. These can then hopefully be connected to observable signals in the form of gravitational waves, kilonovae, and gamma ray bursts. It is found that an interesting variety of disks, outflows, and neutrino bursts are possible. Connections to observables are being attempted by tracking nuclear reactions in tidal ejecta and estimating energy injection to gamma ray bursts from neutrino annihilation and other sources. Meanwhile, non-vacuum inspiral simulations are finally approaching the length and accuracy needed for interesting comparisons with binary black hole waveforms and post-Newtonian predictions, these being steps toward a reliable characterization of the imprint of the nuclear equation of state on the gravitational waves. The speaker acknowledges support from NASA Grant No. NNX11AC37G and NSF Grant PHY-1068243.

  3. 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.

  4. 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.

  5. Magnetized neutron stars with superconducting cores: effect of entrainment

    NASA Astrophysics Data System (ADS)

    Palapanidis, K.; Stergioulas, N.; Lander, S. K.

    2015-09-01

    We construct equilibrium configurations of magnetized, two-fluid neutron stars using an iterative numerical method. Working in Newtonian framework we assume that the neutron star has two regions: the core, which is modelled as a two-component fluid consisting of type-II superconducting protons and superfluid neutrons, and the crust, a region composed of normal matter. Taking a new step towards more complete equilibrium models, we include the effect of entrainment, which implies that a magnetic force acts on neutrons, too. We consider purely poloidal field cases and present improvements to an earlier numerical scheme for solving equilibrium equations, by introducing new convergence criteria. We find that entrainment results in qualitative differences in the structure of field lines along the magnetic axis.

  6. X-ray bursts and neutron-star thermonuclear flashes

    NASA Technical Reports Server (NTRS)

    Joss, P. C.

    1977-01-01

    A description is presented of a model concerning the production of X-ray bursts by thermonuclear flashes in the freshly accreted matter near the surface of an accreting neutron star. An investigation is conducted regarding the physical processes relevant to such thermonuclear flashes. It is concluded that thermonuclear flashes may account for some, but not all, of the observed X-ray burst sources. Attention is given to a neutron star undergoing accretion of mass from a binary stellar companion, aspects of energetics, nuclear reactions, and heat transport mechanisms.

  7. 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.

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

    PubMed

    Dupays, Arnaud; Robilliard, Cécile; 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

  9. Neutron stars and the distance to gamma-ray bursters

    NASA Technical Reports Server (NTRS)

    Dermer, Charles D.; Hurley, Kevin C.

    1991-01-01

    Assuming that gamma-ray bursts originate from galactic neutron stars, an analytic method for studying their statistical properties is outlined. If a significant fraction of all neutron stars are born with space velocities of less than approximately 100 km/s, as suggested by studies of pulsar statistics, then the sampling distance to gamma-ray burst sources should be less than about several hundred pc. These results have important implications on theories of radio-pulsar evolution and magnetic-field decay.

  10. 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.

  11. Black Hole - Neutron Star Binary Simulations at Georgia Tech

    NASA Astrophysics Data System (ADS)

    Haas, Roland

    2009-05-01

    Mixed compact object binaries consisting of a black hole and a neutron star are expected to be not only one of the primary sources of gravitational radiation to be observed by interferometric detectors but also the central engine of short gamma-ray bursts. We report on the status of our effort at Georgia Tech to model these mixed binary systems using the moving puncture method. The results are obtained with an enhanced version our vacuum MayaKranc code coupled to the hydrodynamics Whisky code. We present preliminary results of gravitational waveforms and the disruption of the neutron star for simple polytropic equations of state.

  12. 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.

  13. Binary Neutron Star Mergers: Prospects for Multimessenger Observations

    NASA Astrophysics Data System (ADS)

    Neilsen, David; Anderson, Matthew; Lehner, Luis; Liebling, Steven; Palenzuela, Carlos

    2016-03-01

    Binary neutron star mergers are possible progenitors for short gamma-ray bursts. We evolve a binary system of two neutron stars using the fully relativistic Einstein equations from an initial quasi-circular orbit, through and past merger. We consider different finite-temperature, nuclear equations of state, which vary from soft to quite stiff, and allow for magnetization of the system and neutrino cooling via a leakage scheme. We focus on potential observables, other than gravitational waves, produced mainly by the hot, strongly magnetized matter resulting from the merger.

  14. Tables of model atmospheres of bursting neutron stars

    NASA Technical Reports Server (NTRS)

    Madej, Jerzy

    1991-01-01

    This paper presents tables of plane-parallel neutron star model atmospheres in radiative and hydrostatic equilibrium, with effective temperatures of 8 x 10 exp 6, 1.257 x 10 exp 7, 2 x 10 exp 7, and 3 x 10 exp 7 K, and surface gravities of 15.0 and less (cgs units). The equations of model atmospheres on which the tables are based fully account for nonisotropies of the radiation field and effects of noncoherent Compton scattering of thermal X-rays by free electrons. Both the effective temperatures and gravities listed above are measured on the neutron star surface.

  15. 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.

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    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 Schrödinger 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

  19. 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.

  20. Dynamical model of the magnetic field of neutron stars

    NASA Astrophysics Data System (ADS)

    Cummings, F. W.; Dixon, D. D.; Kaus, P. E.

    1992-02-01

    Attention is given to a dynamical model of the magnetization of a neutron star. The model exhibits three distinct behaviors, as characterized in the 2D parameter space of the two relevant parameters. In one region of the parameter space, the magnetization, and correspondingly the magnetic field, behaves erratically and nonperiodically, occasionally producing large pulses of the directional electric and magnetic field. It is suggested that this field is associated with 'bursters', very energetic gamma-rich pulses of the order of 1-s duration, and believed to emanate from solo neutron stars. A second region of parameter space shows the magnetization precessing at a constant period around the spin or conserved angular momentum direction. The third region is a 'dead' region, where the magnetization is aligned with the spin axis, and the star is nonradiating. The model suggests a life history of a neutron star in which the star typically evolves initially from a burster, later becoming a pulsar, and ending as a dead star.

  1. Neutron sources and neutron-capture paths in asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    Maria, Lugaro

    2016-04-01

    Roughly half of the abundances of the elements heavier than iron in the cosmos are produced by slow neutron captures (the s process) in hydrostatic conditions when the neutron density is below roughly 1013 n/cm-3. While it is observationally well confirmed that asymptotic giant branch (AGB) stars are the main site of the s process, we are still facing many problems in the theoretical models and nuclear inputs. Major current issues are the effect of stellar rotation and magnetic fields and the determination of the rate of the neutron source reactions. I will present these problems and discuss the observational constraints that can help us to solve them, including spectroscopically derived abundances, meteoritic stardust, and stellar seismology. Further, I will present evidence that the s process is not the only neutron-capture process to occur in AGB stars: an intermediate process is also required to explain recent observations of post-AGB stars.

  2. Solar flare leaves sun quaking

    NASA Astrophysics Data System (ADS)

    1998-05-01

    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

  3. Erratum: Binary neutron stars with arbitrary spins in numerical relativity [Phys. Rev. D 92, 124012 (2015)

    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.; Szilágyi, Béla

    2016-08-01

    The code used in [Phys. Rev. D 92, 124012 (2015)] erroneously computed the enthalpy at the center of the neutron stars. Upon correcting this error, density oscillations in evolutions of rotating neutron stars are significantly reduced (from ˜20 % to ˜0.5 % ). Furthermore, it is possible to construct neutron stars with faster rotation rates.

  4. Neutron and quark stars in f(R) gravity

    NASA Astrophysics Data System (ADS)

    Astashenok, Artyom V.

    2016-03-01

    The realistic compact star models are considered in f(R) gravity. The main result is that simple modified gravity can be consistent with current observational mass limit of neutron stars, with current data on their masses and radii; also, it simplifies solution of the hyperon problem. The effect of strong magnetic field in R2-gravity is also investigated. The existence of more compact (in comparison with General Relativity) stars with large magnetic fields in central regions is possible. In fact the second branch of stability appears.

  5. 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)

  6. 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.

  7. 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.

  8. Thermonuclear bursts from slowly and rapidly accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Linares, Manuel

    2012-07-01

    Models of thermonuclear burning on accreting neutron stars predict different ignition regimes, depending mainly on the mass accretion rate per unit area. For more than three decades, testing these regimes observationally has met with only partial success. I will present recent results from the Fermi-GBM all-sky X-ray burst monitor, which is yielding robust measurements of recurrence time of rare and highly energetic thermonuclear bursts at the lowest mass accretion rates. I will also present RXTE observations of thermonuclear bursts at high mass accretion rates, including the discovery of millihertz quasi-periodic oscillations and several bursting regimes in a neutron star transient and 11 Hz X-ray pulsar. This unusual neutron star, with higher magnetic field and slower rotation than any other known burster, showed copious bursting activity when the mass accretion rate varied between 10% and 50% of the Eddington rate. I will discuss the role of fuel composition and neutron star spin in setting the burst properties of this system, and the possible implications for the rest of thermonuclear bursters.

  9. 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.

  10. Thermonuclear processes on accreting neutron stars - A systematic study

    NASA Technical Reports Server (NTRS)

    Ayasli, S.; Joss, P. C.

    1982-01-01

    A series of model calculations for the evolution of the surface layers of an accreting neutron star is carried out. The neutron star mass, radius, core temperature, and surface magnetic field strength are systematically varied, as are the accretion rate onto the neutron star surface and the metallicity of the accreting matter, in order to determine the effects of these parameters on the properties of thermonuclear flashes in the surface layers and the emitted X-ray bursts that result from such flashes. The core temperatures required for thermal equilibrium are found to be approximately a factor of 2 lower than estimated in earlier work. Owing to the effects of the gravitational redshift, the emitted X-ray bursts have lower peak luminosities and longer durations than those calculated in the Newtonian approximation. The entrainment of hydrogen into helium flashes can cause the flashes to exhibit a rather wide range of observable effects and can decrease by a factor of more than 2 the ratio of persistent accretion-driven luminosity to time-averaged burst luminosity emitted by the neutron star.

  11. Eccentric Mergers of Black Holes with Spinning Neutron Stars

    NASA Astrophysics Data System (ADS)

    East, William E.; Paschalidis, Vasileios; Pretorius, Frans

    2015-07-01

    We study dynamical capture binary black hole-neutron star (BH-NS) mergers focusing on the effects of the neutron star spin. These events may arise in dense stellar regions, such as globular clusters, where the majority of neutron stars are expected to be rapidly rotating. We initialize the BH-NS systems with positions and velocities corresponding to marginally unbound Newtonian orbits, and evolve them using general-relativistic hydrodynamical simulations. We find that even moderate spins can significantly increase the amount of mass in unbound material. In some of the more extreme cases, there can be up to a third of a solar mass in unbound matter. Similarly, large amounts of tidally stripped material can remain bound and eventually accrete onto the BH—as much as a tenth of a solar mass in some cases. These simulations demonstrate that it is important to treat neutron star spin in order to make reliable predictions of the gravitational wave and electromagnetic transient signals accompanying these sources.

  12. The LIGO Scientific Collaboration search for inspiralling binary neutron stars

    NASA Astrophysics Data System (ADS)

    Brown, Duncan

    2006-04-01

    The three LIGO interferometers and the GEO600 interferometer operate as a network of detectors under the LIGO Scientific Collaboration (LSC). This network has now reached unprecedented levels of sensitivity. In this talk we will present the status and current results from the binary neutron star search in LIGO/GEO data.

  13. 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.

  14. 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.

  15. Probing the Internal Composition of Neutron Stars with Gravitational Waves

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Gravitational waves from neutron star binaries carry information about the equation of state of supranuclear matter through a parameter called tidal deformability. This parameter measures the quadrupole deformation of a neutron star in the presence of an external field. Its measurability has been assessed in a number of studies, concluding it could provide important information about the equation of state of neutron star matter. In this talk, I will describe a complimentary approach to the problem of equation of state determination, one which focuses on how information from gravitational waves can be translated in ways that could be of direct benefit to nuclear physicists. Specifically, I will talk about what gravitational waves can tell us about the internal composition of neutron stars, information that is directly applicable to equation of state modeling. I will also briefly discuss the importance of spin-induced precession in the quality of information extracted. We acknowledge support from the Onassis Foundation, NSF CAREER Grant PHY-1250636, NSF Award PHY-1306702, and NSF CAREER Grant PHY-1055103.

  16. 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

  17. Measuring surface temperature of isolated neutron stars and related problems

    NASA Astrophysics Data System (ADS)

    Teter, Marcus Alton

    New and exciting results for measuring neutron star surface temperatures began with the successful launch of the Chandra X-ray observatory. Among these results are new detections of neutron star surface temperatures which have made it possible to seriously test neutron star thermal evolution theories. The important new temperature determination of the Vela pulsar (Pavlov, et al., 2001a) requires a non-standard cooling scenario to explain it. Apart from this result, we have measured PSR B1055-52's surface temperature in this thesis, determining that it can be explained by standard cooling with heating. Our spectral fit of the combined data from ROSAT and Chandra have shown that a three component model, two thermal blackbodies and an non-thermal power-law, is required to explain the data. Furthermore, our phase resolved spectroscopy has begun to shed light on the geometry of the hot spot on PSR B1055-52's surface as well as the structure of the magnetospheric radiation. Also, there is strong evidence for a thermal distribution over its surface. Most importantly, the fact that PSR B1055-52 does not have a hydrogen atmosphere has been firmly established. To reconcile these two key observations, on the Vela pulsar and PSR B1055-52, we tested neutron star cooling with neutrino processes including the Cooper pair neutrino emission process. Overall, it has been found that a phase change associated with pions being present in the cores of more massive neutron stars explains all current of the data. A transition from neutron matter to pion condensates in the central stellar core explains the difference between standard and non-standard cooling scenarios, because the superfluid suppression of pion cooling will reduce the emissivity of the pion direct URCA process substantially. A neutron star with a mass of [Special characters omitted.] with a medium stiffness equation of state and a T72 type neutron superfluid models the standard cooling case well. A neutron star of [Special

  18. Entrainment parameters in a cold superfluid neutron star core

    SciTech Connect

    Chamel, Nicolas; Haensel, Pawel

    2006-04-15

    Hydrodynamic simulations of neutron star cores that are based on a two-fluid description in terms of a neutron-proton superfluid mixture require the knowledge of the Andreev-Bashkin entrainment matrix which relates the momentum of one constituent to the currents of both constituents. This matrix is derived for arbitrary nuclear asymmetry at zero temperature and in the limits of small relative currents in the framework of the energy density functional theory. The Skyrme energy density functional is considered as a particular case. General analytic formulas for the entrainment parameters and various corresponding effective masses are obtained. These formulas are applied to the liquid core of a neutron star composed of homogeneous plasma of nucleons, electrons, and possibly muons in {beta} equilibrium.

  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. Simulating binary neutron stars: Dynamics and gravitational waves

    NASA Astrophysics Data System (ADS)

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

    2008-01-01

    We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first-order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the had computational infrastructure for distributed adaptive mesh refinement.

  1. Spin evolution of a proto-neutron star

    NASA Astrophysics Data System (ADS)

    Camelio, Giovanni; Gualtieri, Leonardo; Pons, José A.; Ferrari, Valeria

    2016-07-01

    We study the evolution of the rotation rate of a proto-neutron star, born in a core-collapse supernova, in the first seconds of its life. During this phase, the star evolution can be described as a sequence of stationary configurations, which we determine by solving the neutrino transport and the stellar structure equations in general relativity. We include in our model the angular momentum loss due to neutrino emission. We find that the requirement of a rotation rate not exceeding the mass-shedding limit at the beginning of the evolution implies a strict bound on the rotation rate at later times. Moreover, assuming that the proto-neutron star is born with a finite ellipticity, we determine the emitted gravitational wave signal and estimate its detectability by present and future ground-based interferometric detectors.

  2. 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.

  3. Neutron star equation of state and QPO observations

    NASA Astrophysics Data System (ADS)

    Urbanec, Martin; Stuchlík, Zdeněk; Török, Gabriel; Bakala, Pavel; Čermák, 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 Ω 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}, Ω, EOS and can be compared to the observationally determined pairs of eigenfrequencies in order to eliminate the unsatisfactory sets (KR, rho_{c}, Ω, 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}, Ω, EOS) into the chromosome we use the Gray code. As a fitness function we use correspondence between the observed and calculated pairs of eigenfrequencies.

  4. QPO observations related to neutron star equations of state

    NASA Astrophysics Data System (ADS)

    Stuchlik, Zdenek; Urbanec, Martin; Török, 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 Ω and central energy density ρc . 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,ρc , Ω, EOS and can be compared to the observationally determined pairs of eigenfrequencies in order to eliminate the unsatisfactory sets (KR,ρc , Ω, 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,ρ, Ω, EOS) into chromosome we used Gray code. As a fitness function we use correspondence between the observed and calculated pairs of eigenfrequencies.

  5. Quark matter nucleation in neutron stars and astrophysical implications

    NASA Astrophysics Data System (ADS)

    Bombaci, Ignazio; Logoteta, Domenico; Vidaña, Isaac; Providência, Constança

    2016-03-01

    A phase of strong interacting matter with deconfined quarks is expected in the core of massive neutron stars. We investigate the quark deconfinement phase transition in cold (T=0 and hot β -stable hadronic matter. Assuming a first order phase transition, we calculate and compare the nucleation rate and the nucleation time due to quantum and thermal nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) (i.e. a compact star with no fraction of deconfined quark matter) is metastable to the conversion to a quark star (QS) (i.e. a hybrid star or a strange star). This process liberates an enormous amount of energy, of the order of 1053erg, which causes a powerful neutrino burst, likely accompanied by intense gravitational waves emission, and possibly by a second delayed (with respect to the supernova explosion forming the HS) explosion which could be the energy source of a powerful gamma-ray burst (GRB). This stellar conversion process populates the QS branch of compact stars, thus one has in the Universe two coexisting families of compact stars: pure hadronic stars and quark stars. We introduce the concept of critical mass M_{cr} for cold HSs and proto-hadronic stars (PHSs), and the concept of limiting conversion temperature for PHSs. We show that PHSs with a mass M < M_{cr} could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.

  6. Neutron Stars Accreting Matter and A Wave Model

    NASA Astrophysics Data System (ADS)

    Wagner, Orvin E.

    2000-04-01

    In 1990 I proposed that oscillating stars and planets radiate quantum like standing waves providing for the spacings of planets and satellites. Waves also provide stability for star systems and the universe (see Physics Essays 12(1): 3-10 for a wave equation and solutions). Radii of orbits are given by r=R(exp(kN)) where R is the radius of the star and N is the orbit integer. k is 0.625 for matter free regions apparently becoming less depending on the density of matter present. This equation or similar may provide an incredibly simple explanation of the most often observed QPO's of matter accreting neutron stars if one assumes that the highest amplitude, highest frequency QPO is due to the N=2 orbit. Since incredibly large gravitational fields are involved the equation may be different. In the usual model a second weaker observed lower frequency QPO is explained as the beat frequency of the star spin frequency with the large amplitude QPO. High density neutron stars likely provide particularly strong orbital forces constraining the accreting matter. See the Wagner web site.

  7. Stochastic Background from Coalescences of Neutron Star-Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Regimbau, T.; de Freitas Pacheco, J. A.

    2006-05-01

    In this work, numerical simulations were used to investigate the gravitational stochastic background produced by coalescences of double neutron star systems occurring up to z~5. The cosmic coalescence rate was derived from Monte Carlo methods using the probability distributions for massive binaries to form and for a coalescence to occur in a given redshift. A truly continuous background is produced by events located only beyond the critical redshift z*=0.23. Events occurring in the redshift interval 0.027

  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. Binding Energies of Hyperonic Matter and Applications to Neutron Stars

    SciTech Connect

    Uechi, Hiroshi; Uechi, Schun T.

    2011-10-21

    The conserving nonlinear, nonchiral {sigma}-{omega}-{rho} hadronic mean-field approximation is applied to saturation properties of nuclear and hyperonic matter, properties of hadron and hadron-quark neutron stars. Nonlinear interactions are renormalized self-consistently as effective coupling constants, effective masses, and sources of equations of motion by maintaining thermodynamic consistency to the mean-field approximation. The effective masses and coupling constants become density-dependent, and they simultaneously determine binding energies and saturation properties of nuclear matter and hyperonic matter. The conserving nonlinear {sigma}-{omega}-{rho} mean-field approximation with vacuum fluctuation corrections and strange quark matter defined by the MIT-bag model were employed to examine properties of hadron-(strange) quark stars. We found that hadron-quark stars become more stable at high densities compared to pure hadronic and strange quark stars.

  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

  11. 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.

  12. 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.

  13. A New Code for Proto-neutron Star Evolution

    NASA Astrophysics Data System (ADS)

    Roberts, L. F.

    2012-08-01

    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.

  14. 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.

  15. Instability of superfluid flow in the neutron star core

    NASA Astrophysics Data System (ADS)

    Link, B.

    2012-04-01

    Pinning of superfluid vortices to magnetic flux tubes in the outer core of a neutron star supports a velocity difference of ˜105 cm s-1 between the neutron superfluid and the proton-electron fluid as the star spins down. Under the Magnus force that arises on the vortex array, vortices undergo vortex creep through thermal activation or quantum tunnelling. We examine the hydrodynamic stability of this situation. Vortex creep introduces two low-frequency modes, one of which is unstable above a critical wavenumber for any non-zero flow velocity of the neutron superfluid with respect to the charged fluid. For typical pinning parameters of the outer core, the superfluid flow is unstable over wavelengths λ≲ 10 m and over time-scales of ˜(λ/1 m)1/2 yr down to ˜1 d. The vortex lattice could degenerate into a tangle, and the superfluid flow would become turbulent. We suggest that superfluid turbulence could be responsible for the red timing noise seen in many neutron stars, and find a predicted spectrum that is generally consistent with observations.

  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. 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.

  18. 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.

  19. 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.

  20. 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.

  1. X-ray Polarisation in highly-magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Turolla, Roberto

    2016-07-01

    Radiation emitted in the vicinity of an isolated neutron star is expected to be intrinsically polarized because the high magnetic field (B˜10^{12}-10^{15} G) strongly affects the plasma opacity. The polarization fraction and polarization angle measured by an instrument, however, do not necessary coincide with the intrinsic ones, due to the effects of both quantum electrodynamics in the highly magnetized vacuum around the star (the vacuum polarization) and rotation of the Stokes parameters in the plane perpendicular to the line of sight induced by the non-uniform magnetic field. I'll review theoretical estimates for the polarization observables in the case of thermal surface emission from neutron stars and of the (soft) X-ray emission from magnetars, where magnetospheric reprocessing of radiation by resonant cyclotron scattering is important. The potentials of X-ray polarimetry to probe the physical conditions in neutron star sources and to test, for the first time, vacuum polarization are discussed in connection with the recently proposed polarimetric missions, like XIPE.

  2. Signatures of field induced spin polarization of neutron star matter in seismic vibrations of paramagnetic neutron star

    NASA Astrophysics Data System (ADS)

    Bastrukov, S. I.; Yang, J.; Podgainy, D. V.; Weber, F.

    2003-04-01

    A macroscopic model of the dissipative magneto-elastic dynamics of viscous spin polarized nuclear matter is discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of non-radial torsional magneto-elastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameters taken from early and current works on transport coefficients of dense matter. It is found that the effect of viscosity is crucial for the lifetime of magneto-torsion vibrations but it does not appreciably affect the periods of this seismic mode which fall in the realm of periods of pulsed emission of soft gamma-ray repeaters and anomalous x-ray pulsars - young super-magnetized neutron stars, radiating, according to the magnetar model, at the expense of the magnetic energy release. Finally, we present arguments that the long periodic pulsed emission of these stars in a quiescent regime of radiation can be interpreted as a manifestation of weakly damped seismic magneto-torsion vibrations exhibiting the field induced spin polarization of baryon matter.

  3. Axisymmetric toroidal modes of general relativistic magnetized neutron star models

    SciTech Connect

    Asai, Hidetaka; Lee, Umin E-mail: lee@astr.tohoku.ac.jp

    2014-07-20

    We calculate axisymmetric toroidal modes of magnetized neutron stars with a solid crust in the general relativistic Cowling approximation. We assume that the interior of the star is threaded by a poloidal magnetic field, which is continuous at the surface with an outside dipole field. We examine the cases of the field strength B{sub S} ∼ 10{sup 16} G at the surface. Since separation of variables is not possible for the oscillations of magnetized stars, we employ finite series expansions for the perturbations using spherical harmonic functions. We find discrete normal toroidal modes of odd parity, but no toroidal modes of even parity are found. The frequencies of the toroidal modes form distinct mode sequences and the frequency in a given mode sequence gradually decreases as the number of radial nodes of the eigenfunction increases. From the frequency spectra computed for neutron stars of different masses, we find that the frequency is almost exactly proportional to B{sub S} and is well represented by a linear function of R/M for a given B{sub S}, where M and R are the mass and radius of the star. The toroidal mode frequencies for B{sub S} ∼ 10{sup 15} G are in the frequency range of the quasi-periodic oscillations (QPOs) detected in the soft-gamma-ray repeaters, but we find that the toroidal normal modes cannot explain all the detected QPO frequencies.

  4. Stellar encounters involving neutron stars in globular cluster cores

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Encounters between a 1.4 solar mass neutron star and a 0.8 solar mass red giant (RG) and between a 1.4 solar mass neutron star (NS) and an 0.8 solar mass main-sequence (MS) star have been successfully simulated. In the case of encounters involving an RG, bound systems are produced when the separation at periastron passage R(MIN) is less than about 2.5 R(RG). At least 70 percent of these bound systems are composed of the RG core and NS forming a binary engulfed in a common envelope of what remains of the former RG envelope. Once the envelope is ejected, a tight white dwarf-NS binary remains. For MS stars, encounters with NSs will produce bound systems when R(MIN) is less than about 3.5 R(MS). Some 50 percent of these systems will be single objects with the NS engulfed in a thick disk of gas almost as massive as the original MS star. The ultimate fate of such systems is unclear.

  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. Vacuum fluctuation inside a star and their consequences for neutron stars, a simple model

    NASA Astrophysics Data System (ADS)

    Caspar, G.; Rodríguez, I.; Hess, P. O.; Greiner, W.

    2016-04-01

    Applying semi-classical quantum mechanics, the vacuum fluctuations within a star are determined, assuming a constant mass density and applying a monopole approximation. It is found that the density for the vacuum fluctuations does not only depend linearly on the mass density, as assumed in a former publication, where neutron stars up to 6 solar masses were obtained. This is used to propose a simple model on the dependence of the dark energy to the mass density, as a function of the radial distance r. It is shown that stars with up to 200 solar masses can, in principle, be obtained. Though, we use a phenomenological model, it shows that in the presence of vacuum fluctuations stars with large masses can be stabilized and probably stars up to any mass can exist, which usually are identified as black holes.

  7. 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 Λ 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 Λ 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 Λ 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

  8. Neutron stars: Cosmic laboratories for matter under extreme conditions

    NASA Astrophysics Data System (ADS)

    Bombaci, Ignazio; Logoteta, Domenico

    2016-05-01

    The true nature and the internal constitution of the compact stars known as neutron stars (NSs) is one of the most fascinating enigma in modern astrophysics. We discuss some of the present models for the internal structure of NSs and the connection with the properties of ultra dense hadronic matter. In particular, we discuss the role of strangeness on the equation of state and the implications of the measurement of 2 solar mass NSs in PSR J1614-2230 and PSR J0348+0432.

  9. 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.

  10. 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

  11. The freedom to choose neutron star magnetic field equilibria

    NASA Astrophysics Data System (ADS)

    Glampedakis, Kostas; Lasky, Paul D.

    2016-08-01

    Our ability to interpret and glean useful information from the large body of observations of strongly magnetised neutron stars rests largely on our theoretical understanding of magnetic field equilibria. We answer the following question: is one free to arbitrarily prescribe magnetic equilibria such that fluid degrees of freedom can balance the equilibrium equations? We examine this question for various models for neutron star matter; from the simplest single-fluid barotrope to more realistic non-barotropic multifluid models with superfluid/superconducting components, muons and entropy. We do this for both axi- and non-axisymmetric equilibria, and in Newtonian gravity and general relativity. We show that, in axisymmetry, the most realistic model allows complete freedom in choosing a magnetic field equilibrium whereas non-axisymmetric equilibria are never completely arbitrary.

  12. 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

  13. The energetics and environments of young neutron stars

    NASA Astrophysics Data System (ADS)

    Gelfand, Joseph David

    In this thesis, information concerning the energetics and environments of isolated young neutron star is used to study the formation and physical properties of these objects. I first present evidence that compact X-ray source, 1E 1547.0-5408, is a magnetar--a neutron star with an extremely strong magnetic field. I then present the results of radio observations of SGR 1806-20 after the 2004 December 27 giant flare which detected a new, variable radio source at the position of this magnetar. Measurements of the flux, position, size, and orientation of this source suggest that the observed radio emission is being powered by the interaction between material ablated off the surface of this neutron star during the giant flare and the surrounding ambient medium, and that this emission is now dominated by hotspots in the layer of shocked ambient material which surrounds the neutron star ejecta. Lastly, I present a hydrodynamic model for the evolution of a pulsar wind nebula (PWN) inside a supernova remnant (SNR), and use this model to infer the properties of the progenitor supernova and central neutron star for three objects--SNR G292.0+1.8, PWN 3C 58, and non-thermal Galactic radio source G328.4+0.2. I find that, if G292.0+1.8 is a SNR where the PWN has not yet collided with the reverse shock, as suggested by the weakness of S, Si, and Fe lines in the thermal X-ray spectrum of this source, G292.0+1.8 was most likely created in a low kinetic energy ([Special characters omitted.] 10 51 ergs), high ejecta mass ([Special characters omitted.] 10 [Special characters omitted.] ) explosion. For 3C 58, I am unable to find a combination of supernova explosion energy and ejecta mass, ambient density, and neutron star initial period and braking index which can reproduced the observed size, expansion velocity, and mass of thermal X-ray emitting material of this PWN if it was created during SN 1181. If I relax this restriction on the age of 3C 58, we find that the observed properties

  14. Neutron star evolutions using the discontinuous Galerkin method

    NASA Astrophysics Data System (ADS)

    Hebert, Francois; SXS Collaboration Collaboration

    2016-03-01

    Relativistic hydrodynamic simulations enable us, for instance, to generate templates used for gravitational-wave detections of black hole-neutron star mergers, or to understand supernova explosion mechanisms. But the limited accuracy of the simulation algorithms used, often based on the finite volume method, constrains the insight we can obtain into these problems. We aim to improve the accuracy of our simulations by using a discontinuous Galerkin method. This method's attractiveness arises from its combination of spectral convergence properties for smooth solutions with robust stability properties for shocks. We present our work implementing a testbed discontinuous Galerkin GR-hydro code, and show our results for test evolutions of an isolated neutron star.

  15. Electromagnetic and Gravitational Outputs from Binary-Neutron-Star Coalescence

    NASA Astrophysics Data System (ADS)

    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.

  16. Collapse of magnetized hypermassive neutron stars in general relativity.

    PubMed

    Duez, Matthew D; Liu, Yuk Tung; Shapiro, Stuart L; Shibata, Masaru; Stephens, Branson C

    2006-01-27

    Hypermassive neutron stars (HMNSs)--equilibrium configurations supported against collapse by rapid differential rotation--are possible transient remnants of binary neutron-star mergers. Using newly developed codes for magnetohydrodynamic simulations in dynamical spacetimes, we are able to track the evolution of a magnetized HMNS in full general relativity for the first time. We find that secular angular momentum transport due to magnetic braking and the magnetorotational instability results in the collapse of an HMNS to a rotating black hole, accompanied by a gravitational wave burst. The nascent black hole is surrounded by a hot, massive torus undergoing quasistationary accretion and a collimated magnetic field. This scenario suggests that HMNS collapse is a possible candidate for the central engine of short gamma-ray bursts. PMID:16486677

  17. Systematic Parameter Errors in Inspiraling Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Favata, Marc

    2014-03-01

    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.

  18. 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.

  19. Polarized X-rays from accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Dipankar

    2016-07-01

    Accreting neutron stars span a wide range in X-ray luminosity and magnetic field strength. Accretion may be wind-fed or disk-fed, and the dominant X-ray flux may originate in the disk or a magnetically confined accretion column. In all such systems X-ray polarization may arise due to Compton or Magneto-Compton scattering, and on some occasions polarization of non-thermal emission from jet-like ejection may also be detectable. Spectral and temporal behaviour of the polarized X-rays would carry information regarding the radiation process, as well as of the matter dynamics - and can assist the detection of effects such as the Lense-Thirring precession. This talk will review our current knowledge of the expected X-ray polarization from accreting neutron stars and explore the prospects of detection with upcoming polarimetry missions.

  20. Conditions for jet formation in accreting neutron stars: the magnetic field decay

    NASA Astrophysics Data System (ADS)

    García, Federico; Aguilera, Deborah N.; Romero, Gustavo E.

    2011-02-01

    Accreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the magnetic field has decayed due to accretion. We solve the induction equation for the magnetic field diffusion in a realistic neutron star crust and discuss the possibility of jet launching in systems like the recently detected Supergiant Fast X-ray Transients.

  1. 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.

  2. 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.

  3. The Signature of Black Hole-Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    Black hole-neutron star (BHNS) binaries are key gravitational wave sources, merging in the frequency band to which Earth-based GW detectors are most sensitive. Furthermore, as possible candidates for short-hard gamma ray bursts, combined observations in both gravitational and electromagnetic bands of BHNS mergers is thus an exciting possibility. This talk will discuss results from simulations that account for gravitational and magnetic effects as well as connections with processes capable of explaining key features of gamma ray bursts.

  4. 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.

  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. Neutron Star Kicks and their Relationship to Supernovae Ejecta Mass

    NASA Astrophysics Data System (ADS)

    Bray, J. C.; Eldridge, J. J.

    2016-05-01

    We propose a simple model to explain the velocity of young neutron stars. We attempt to confirm a relationship between the amount of mass ejected in the formation of the neutron star and the `kick' velocity imparted to the compact remnant resulting from the process. We assume the velocity is given by vkick = α (Mejecta/Mremnant) + β . To test this simple relationship we use the BPASS (Binary Population and Spectral Synthesis) code to create stellar population models from both single and binary star evolutionary pathways. We then use our Remnant Ejecta and Progenitor Explosion Relationship (REAPER) code to apply different α and β values and three different `kick' orientations then record the resulting velocity probability distributions. We find that while a single star population provides a poor fit to the observational data, the binary population provides an excellent fit. Values of α = 70 km s-1 and β = 110 km s-1 reproduce the Hobbs et al. (2005) observed 2-dimensional velocities and α = 70 km s-1 and β = 120 km s-1 reproduce their inferred 3-dimensional velocity distribution for nearby single neutron stars with ages less than 3 Myrs. After testing isotropic, spin-axis aligned and orthogonal to spin-axis `kick' orientations, we find no statistical preference for a `kick' orientation. While ejecta mass cannot be the only factor that determines the velocity of supernovae compact remnants, we suggest it is a significant contributor and that the ejecta based `kick' should replace the Maxwell-Boltzmann velocity distribution currently used in many population synthesis codes.

  7. 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.

  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. Dense baryonic matter: Constraints from recent neutron star observations

    NASA Astrophysics Data System (ADS)

    Hell, Thomas; Weise, Wolfram

    2014-10-01

    Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of 2M⊙ neutron stars rules out many soft equations of state with prominent "exotic" compositions. The present work reviews the conditions required for the pressure as a function of baryon density to satisfy these constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov-Nambu-Jona-Lasinio model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless additional strongly repulsive correlations, e.g., through vector current interactions between quarks, are introduced. The extent to which strangeness can accumulate in the equation of state is also discussed.

  10. Linking electromagnetic and gravitational radiation in coalescing binary neutron stars

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    We expand on our study of the gravitational and electromagnetic emissions from the late stage of an inspiraling neutron star binary as presented in Palenzuela et al. [Phys. Rev. Lett. 111, 061105 (2013)]. Interactions between the stellar magnetospheres, driven by the extreme dynamics of the merger, can yield considerable outflows. We study the gravitational and electromagnetic waves produced during the inspiral and merger of a binary neutron star system using a full relativistic, resistive magnetohydrodynamics evolution code. We show that the interaction between the stellar magnetospheres extracts kinetic energy from the system and powers radiative Poynting flux and heat dissipation. These features depend strongly on the configuration of the initial stellar magnetic moments. Our results indicate that this power can strongly outshine pulsars in binaries and have a distinctive angular and time-dependent pattern. Our discussion provides more detail than Palenzuela et al., showing clear evidence of the different effects taking place during the inspiral. Our simulations include a few milliseconds after the actual merger and study the dynamics of the magnetic fields during the formation of the hypermassive neutron star. We also briefly discuss the possibility of observing such emissions.

  11. Thermonuclear reactions in cool accreting neutron stars and burst phenomena

    NASA Technical Reports Server (NTRS)

    Miyaji, S.; Nomoto, K.

    1985-01-01

    The ignition of accreting materials on neutron stars is explored using strongly coupled plasma analytical techniques. The calculations cover the ignition temperature and density at the bottom of the accreted envelope of a neutron star. Emphasis is placed on low-temperature ignitions which take place at high densities. The investigation is extended to the accretion of material from a white dwarf in the form of pure He, C + O, or O + Ne + Mg. It is shown that electrons are strongly degenerate in low-temperature flashes, where the ignition is more dependent on density than on temperature. Precursor flashes 0.4-0.7 the intensity of the main burst will appear before the main bursts. The intensity relationship indicates that the appropriate model for an X-ray burst from a neutron star accreting from a white dwarf is a He shell flash in the presence of a hydrogen-rich atmosphere. The flash will have a maximum energy of 2 x 10 to the 43 ergs and could last as long as 40,000 sec.

  12. 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.

  13. Gamma-ray bursts from neutron star detonation

    SciTech Connect

    Michel, F.C.

    1988-09-25

    A phenomenological gamma-ray burst model postulating the injection of 10/sup 51/--10/sup 53/ ergs into a neutron star by Paczyn-acute-accentski and by Goodman is closely reminiscent of what a relativistic version of a type I supernova might look like. Burning to tightly bound quark complexes (i.e., particles) could go explosively, just as the final burning of helium to iron disrupts a white darf in some models of type I supernovae. Particle theorists have for some years entertained the possibility that compressing nuclear matter may lead irreversibly to an exothermic formation of ''quark'' matter. From stellar evolution, we know that nuclear burning does not proceed directly to the known endpoint (iron) but is halted at various intermediate stages (e.g., at helium). Thus when the central densities of a neutron star begin to rise to that at which a transition to quark matter would be expected (10--20 times nuclear) owing to accretion or fusion with a companion neutron star, explosive burning may take place. Active galactic nuclei could be powered by such events and are therefore possible source regions. The particles themselves would be massive tightly bound bosons having zero spin, zero charge, and zero magnetic moment, hence could possible evidence themselves in the form of ''dark'' ( = nonluminous) matter or ''WIMPs'' (weakly interacting massive particles). The relativistic shocks from such events should accelerate cosmic rays more efficiently than the usual supernova shocks.

  14. 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.

  15. 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.

  16. General relativistic models of binary neutron stars in quasiequilibrium

    NASA Astrophysics Data System (ADS)

    Baumgarte, T. W.; Cook, G. B.; Scheel, M. A.; Shapiro, S. L.; Teukolsky, S. A.

    1998-06-01

    We perform fully relativistic calculations of binary neutron stars in corotating, circular orbit. While Newtonian gravity allows for a strict equilibrium, a relativistic binary system emits gravitational radiation, causing the system to lose energy and slowly spiral inwards. However, since inspiral occurs on a time scale much longer than the orbital period, we can treat the binary to be in quasiequilibrium. In this approximation, we integrate a subset of the Einstein equations coupled to the relativistic equation of hydrostatic equilibrium to solve the initial value problem for binaries of arbitrary separation. We adopt a polytropic equation of state to determine the structure and maximum mass of neutron stars in close binaries for polytropic indices n=1, 1.5 and 2. We construct sequences of constant rest-mass and locate turning points along energy equilibrium curves to identify the onset of orbital instability. In particular, we locate the innermost stable circular orbit and its angular velocity. We construct the first contact binary systems in full general relativity. These arise whenever the equation of state is sufficiently soft (n>~1.5). A radial stability analysis reveals no tendency for neutron stars in close binaries to collapse to black holes prior to merger.

  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. 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 Δ 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 Δ 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⊙.

  19. Magnetized Neutron-Star Mergers and Gravitational-Wave Signals

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

    We investigate the influence of magnetic fields upon the dynamics of, and resulting gravitational waves from, a binary neutron-star merger in full general relativity coupled to ideal magnetohydrodynamics. We consider two merger scenarios: one where the stars have aligned poloidal magnetic fields and one without. Both mergers result in a strongly differentially rotating object. In comparison to the nonmagnetized scenario, the aligned magnetic fields delay the full merger of the stars. During and after merger we observe phenomena driven by the magnetic field, including Kelvin-Helmholtz instabilities in shear layers, winding of the field lines, and transition from poloidal to toroidal magnetic fields. These effects not only mediate the production of electromagnetic radiation, but also can have a strong influence on the gravitational waves. Thus, there are promising prospects for studying such systems with both types of waves.

  20. Levitating atmospheres of Eddington-luminosity neutron stars

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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 general relativity-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.

  1. 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.

  2. 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.

  3. Improved Universal No-Hair Relations for Neutron Stars

    NASA Astrophysics Data System (ADS)

    Majumder, Barun; Yagi, Kent; Yunes, Nicolas

    2016-03-01

    The exterior gravitational field of an astrophysical body can be characterized by its multipole moments. No-hair theorems for black holes state that the exterior gravitational field can be completely described in terms of their mass and spin angular momentum. Similar no-hair like relations have been recently found for neutron stars which are approximately independent of the internal structure of the star. Missions like NICER and LOFT will observe the pulse profiles of millisecond pulsars and thermonuclear bursters. The equation-of-state (EoS) independent relations may break degeneracies among the relevant observables in the modeling of X-ray pulse and atomic line profiles. The amount of EoS independence of these approximately universal relations depends on how one adimensionalizes the multipole moments of the star with stellar mass, spin and radius. We show that for slowly-rotating neutron stars in both non-relativistic limit and full General Relativity, the optimal normalization of the multipole moments exist that minimizes the EoS dependence in the universal relations. The relations among the moment of inertia and higher order moments can be improved from the original ones approximately by a factor of two. Nicolas Yunes acknowledges support from NSF CAREER Award PHY-1250636. Barun Majumder is supported by the Fulbright-Nehru Postdoctoral Research Fellowship.

  4. Lense-Thirring precession around neutron stars with known spin

    NASA Astrophysics Data System (ADS)

    Van Doesburgh, Marieke; van der Klis, Michiel

    2016-07-01

    Quasi periodic oscillations (QPOs) between 300 and 1200 Hz in the X-ray emission from low mass X-ray binaries have been linked to Keplerian orbital motion at the inner edge of accretion disks. Lense-Thirring precession is precession of the line of nodes of inclined orbits with respect to the equatorial plane of a rotating object due to the general relativistic effect of frame dragging. The Lense-Thirring model of Stella and Vietri (1998) explains QPOs observed in neutron star low mass X-ray binaries at frequencies of a few tens of Hz by the nodal precession of the orbits at the inner disk edge at a precession frequency, ν_{LT} , identical to the Lense-Thirring precession of a test particle orbit. A quadratic relation between ν_{LT} and the Keplerian orbital frequency, and a linear dependence on spin frequency are predicted. In early work (van Straaten et al., 2003) this quadratic relation was confirmed to remarkable precision in three objects of uncertain spin. Since the initial work, many neutron star spin frequencies have been measured in X-ray sources that show QPOs at both low and high frequency. Using archival data from the Rossi X-ray Timing Explorer, we compare the Lense-Thirring prediction to the properties of quasi periodic oscillations measured in a sample of 14 low mass X-ray binaries of which the neutron star spin frequencies can be inferred from their bursting behaviour. We find that in the range predicted for the precession frequency, we can distinguish two different oscillations that often occur simultaneously. In previous works, these two oscillations have often been confused. For both frequencies, we find correlations with inferred Keplerian frequency characterized by power laws with indices that differ significantly from the prediction of 2.0 and therefore inconsistent with the Lense-Thirring model. Also, the specific moment of inertia of the neutron star required by the observed frequencies exceeds values predicted for realistic equations of

  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. Herschel and Spitzer Observations of Slowly Rotating, Nearby Isolated Neutron Stars

    NASA Astrophysics Data System (ADS)

    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 μm) 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.

  7. Influence of the σ-ω meson interaction on neutron star matter

    NASA Astrophysics Data System (ADS)

    Shao, Guo-Yun; Liu, Yu-Xin

    2009-02-01

    Relativistic mean field theory with nonlinear scalar self-interaction and isoscalar scalar-vector cross-interaction is used to study the properties of neutron star matter in β equilibrium with and without hyperons. The influence of σ-ω meson cross-interaction on the properties of neutron star matter and the mass-radius relation of neutron stars is examined with attractive and repulsive Σ potential, respectively. The calculated result indicates that the cross-interaction softens the equation of state (EOS) of nuclear (hadronic) matter and reduces the maximum mass of neutron stars. It also decreases the densities for hyperonization to occur and lowers the center density of neutron stars. The increase of the cross-interaction strength enhances the softening effect of hyperons on the EOS. Meanwhile the repulsive Σ potential stiffens slightly the EOS and influences obviously the composition of neutron star matter.

  8. A neutron star with a carbon atmosphere in the Cassiopeia A supernova remnant.

    PubMed

    Ho, Wynn C G; Heinke, Craig O

    2009-11-01

    The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron-star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) are expected. Despite detailed searches, observations have been unable to confirm the atmospheric composition of isolated neutron stars. Here we report an analysis of archival observations of the compact X-ray source in the centre of the Cassiopeia A supernova remnant. We show that a carbon atmosphere neutron star (with low magnetic field) produces a good fit to the spectrum. Our emission model, in contrast with others, implies an emission size consistent with theoretical predictions for the radius of neutron stars. This result suggests that there is nuclear burning in the surface layers and also identifies the compact source as a very young ( approximately 330-year-old) neutron star. PMID:19890325

  9. Scientific goals of SCHOOLS & QUAKES

    NASA Astrophysics Data System (ADS)

    Brückl, Ewald; Köberl, 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 Mürz 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 für 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

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

    SciTech Connect

    Manuel, Cristina; Tolos, Laura; Tarrús, 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 ω ∼ 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.

  11. Compression of matter in the center of accreting neutron stars

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Aims: To estimate the feasibility of dense-matter phase transition, we studied the evolution of the central density as well as the baryon chemical potential of accreting neutron stars. We compared the thin-disk accretion with and without the magnetic field torque with the spin-down scenario for a selection of recent equations of state. Methods: We compared the prevalent (in the recycled-pulsar context) Keplerian thin-disk model, in which the matter is accreted from the marginally-stable circular orbit, with the recent magnetic-torque model that takes into account the influence of stellar magnetic field on the effective inner boundary of the disk. Calculations were performed using a multi-domain spectral methods code in the framework of General Relativity. We considered three equations of state consistent with the recently measured mass of PSR J1614-2230, 1.97 ± 0.04 M⊙ (one of them softened by the appearance of hyperons). Results: If there is no magnetic torque and efficient angular momentum transfer from the disk to the star, substantial central compression is limited to the region of initial stellar masses close to the maximum mass. Outside the maximum mass vicinity, accretion-induced central compression is significant only if the angular momentum transfer is inefficient. Accounting for the magnetic field effectively decreases the efficiency of angular momentum transfer and implies a significant central compression. Conclusions: An efficient angular momentum transfer from a thin disk onto a non-magnetized neutron star does not provide a good mechanism for the central compression and possible phase transition. Substantial central compression is possible for a broad range of masses of slowly-rotating initial configurations for magnetized neutron stars. Accretion-induced central compression is particularly strong for stiff equation of state with a high-density softening.

  12. 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.

  13. Constraints on neutron star models of gamma-burst sources from the Einstein Observatory

    NASA Technical Reports Server (NTRS)

    Pizzichini, G.; Gottardi, M.; Atteia, J.-L.; Barat, C.; Hurley, K.; Niel, M.; Vedrenne, G.; Laros, J. G.; Cline, T. L.; Desai, U. D.

    1986-01-01

    Six Einstein observations of five gamma-ray burst sources are presented and discussed. With one possible exception, no point source was detected in any of the observations. The data are interpreted in the framework of neutron star models for gamma bursters. Upper limits are derived for the surface temperatures of the neutron stars assumed to be responsible for the bursts. It is shown that the lack of soft X-ray emission may impose stringent constraints on accretion rates onto neutron stars.

  14. 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.

  15. Radiative Corrections to the Neutron Star Mass Inferred from QPO Frequencies

    NASA Astrophysics Data System (ADS)

    Abramowicz, M. A.; Kluźniak, W.; Yu, W.

    2011-12-01

    The frequencies of kHz QPOs are widely interpreted as being indicative of the values of characteristic frequencies related to orbital motion around neutron stars, e.g., the radial epicyclic frequency. In regions directly exposed to the radiation from the luminous neutron star these frequencies change with the luminosity. Including radiative corrections will change the neutron star mass value inferred from the QPO frequencies. Radiative forces may also be behind the puzzling phenomenon of parallel tracks.

  16. Gravitational radiation from neutron stars deformed by crustal Hall drift

    NASA Astrophysics Data System (ADS)

    Suvorov, A. G.; Mastrano, A.; Geppert, U.

    2016-07-01

    A precondition for the radio emission of pulsars is the existence of strong, small-scale magnetic field structures (`magnetic spots') in the polar cap region. Their creation can proceed via crustal Hall drift out of two qualitatively and quantitatively different initial magnetic field configurations: a field confined completely to the crust and another which penetrates the whole star. The aim of this study is to explore whether these magnetic structures in the crust can deform the star sufficiently to make it an observable source of gravitational waves. We model the evolution of these field configurations, which can develop, within ˜104-105 yr, magnetic spots with local surface field strengths ˜1014 G maintained over ≳106 yr. Deformations caused by the magnetic forces are calculated. We show that, under favourable initial conditions, a star undergoing crustal Hall drift can have ellipticity ɛ ˜ 10-6, even with sub-magnetar polar field strengths, after ˜105 yr. A pulsar rotating at ˜102 Hz with such ɛ is a promising gravitational wave source candidate. Since such large deformations can be caused only by a particular magnetic field configuration that penetrates the whole star and whose maximum magnetic energy is concentrated in the outer core region, gravitational wave emission observed from radio pulsars can thus inform us about the internal field structures of young neutron stars.

  17. Neutron Reactions in Accreting Neutron Stars: A New Pathway to Efficient Crust Heating

    SciTech Connect

    Gupta, Sanjib S.; Kawano, Toshihiko; Moeller, Peter

    2008-12-05

    In our calculation of neutron star crust heating we include several key new model features. In earlier work electron capture (EC) only allowed neutron emission from the daughter ground state; here we calculate, in a deformed quasi-random-phase approximation (QRPA) model, EC decay rates to all states in the daughter that are allowed by Gamow-Teller selection rules and energetics. The subsequent branching ratios between the 1n,...,xn channels and the competing {gamma} decay are calculated in a Hauser-Feshbach model. In our multicomponent plasma model a single (EC, xn) reaction step can produce several neutron-deficient nuclei, each of which can further decay by (EC, xn). Hence, the neutron emission occurs more continuously with increasing depth as compared to that in a one-component plasma model.

  18. 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.

  19. Rapidly rotating neutron stars in dilatonic Einstein-Gauss-Bonnet theory

    NASA Astrophysics Data System (ADS)

    Kleihaus, Burkhard; Kunz, Jutta; Mojica, Sindy; Zagermann, Marco

    2016-03-01

    We construct sequences of rapidly rotating neutron stars in dilatonic Einstein-Gauss-Bonnet theory, employing two equations of state for the nuclear matter. We analyze the dependence of the physical properties of these neutron stars on the Gauss-Bonnet coupling strength. For a given equation of state we determine the physically relevant domain of rapidly rotating neutron stars, which is delimited by the set of neutron stars rotating at the Kepler limit, the set of neutron stars along the secular instability line, and the set of static neutron stars. As compared to Einstein gravity, the presence of the Gauss-Bonnet term decreases this domain, leading to lower values for the maximum mass as well as to smaller central densities. The quadrupole moment is decreased by the Gauss-Bonnet term for rapidly rotating neutron stars, while it is increased for slowly rotating neutron stars. The universal relation between the quadrupole moment and the moment of inertia found in general relativity appears to extend to dilatonic Einstein-Gauss-Bonnet theory with very little dependence on the coupling strength of the Gauss-Bonnet term. The neutron stars carry a small dilaton charge.

  20. Theoretical study of diffusion processes around a non-rotating neutron star

    NASA Astrophysics Data System (ADS)

    Andra, D.; Rosyid, M. F.

    2014-10-01

    The general relativistic diffusion process on curved space-time manifold around a non-rotating neutron star has been analyzed. The general relativistic diffusion equation of diffusive particles around non-rotating neutron star is derived by constructing phase space in the parametrization of observer time in the hyperbolic coordinate system. This diffusion equation describes the stochastic dynamic of particles around non-rotating neutron stars. In this work we also have studied the diffusion processes around a non-rotating neutron star for asymptotic case.

  1. 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.

  2. Simulation of the Magnetic Field Evolution in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Hoyos, J.; Reisenegger, A.; Valdivia, J. A.

    Using a numerical simulation, we study the effects of ambipolar diffusion and ohmic diffusion on the magnetic field evolution in the interior of an isolated neutron star (Goldreich & Reisenegger 1992; Reisenegger et al. 2005; Hoyos et al. 2007). We are interested in the behavior of the magnetic field on a long time scale, over which all Alfven and sound waves have been damped. We model the stellar interior as an electrically neutral plasma composed of neutrons, protons and electrons, which can interact with each other through collisions and electromagnetic forces. Weak interactions convert neutrons and charged particles into each other, erasing chemical imbalances. As a first step, we assume that the magnetic field points in one fixed Cartesian direction but can vary along an orthogonal direction. We start with a uniform-density background threaded by a homogeneous magnetic field and study the evolution of a magnetic perturbation as well as the density fluctuations it induces in the particles. We show that the system evolves through different quasi-equilibrium states and estimate the characteristic time scales on which these quasi-equilibria occur as a function of the magnetic field intensity, the collisional strength between the particles, the weak interaction rate, and the ohmic resistivity. We intend in a near future to extend this simulation to two dimensions in order to study an axially symmetric star geometry.

  3. GB 790305 as a very strongly magnetized neutron star

    NASA Technical Reports Server (NTRS)

    Paczynski, Bohdan

    1992-01-01

    The March 5 1979 event was the strongest gamma-ray burst ever observed. Its location in the sky is known with an accuracy of about 10 arcsec, and it coincides with the N49 supernova remnant in the Large Magellanic Cloud. The main burst was followed by a soft tail with the periodic 8 s modulation, and 16 soft gamma events over the following few years. If the source is a magnetic neutron star with the 8 s rotation period and the age of about 10 exp 4 years as indicated by N49 then the field strength of about 5 x 10 exp 14 gauss is implied. The corresponding critical luminosity is about 10 exp 4 L(Edd), as the electron scattering opacity is suppressed by the strong magnetic field. This luminosity is consistent with the observed peak flux of the soft tail and the soft repeaters. The soft spectrum may be approximated with the photospheric emission at kT(eff) = 17 keV. The corresponding photospheric radius is about 14 km, compatible with a neutron star hypothesis. The total magnetic energy of the star is about 4 x 10 exp 46 erg, more than enough to power the March 5 event and all its repeaters.

  4. 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=nv¯i 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 given—subject 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.

  5. High-Frequency QPOs as a Product of Inner Disk Dynamics around Neutron Stars

    SciTech Connect

    Hakan Erkut, M.

    2011-09-21

    The kHz QPOs observed in a neutron star low mass X-ray binary are likely to be produced in the innermost regions of accretion disk around the neutron star. The rotational dynamics of the inner disk can be characterized by the presence of either sub-Keplerian or super-Keplerian accretion flow depending on the relative fastness of the neutron spin as compared to the Keplerian frequency at the inner disk radius. Within the magnetosphere-disk interaction model, the frequency difference between the two kHz QPOs observed in a given source can be estimated to be slightly higher than or nearly around the neutron star spin frequency if the neutron star is a slow rotator and less than the stellar spin frequency if the neutron star is a fast rotator.

  6. Internal composition of proto-neutron stars under strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Franzon, B.; Dexheimer, V.; Schramm, S.

    2016-08-01

    In this work, we study the effects of magnetic fields and rotation on the structure and composition of proto-neutron stars. A hadronic chiral SU(3) model is applied to cold neutron stars and proto-neutron stars with trapped neutrinos and at fixed entropy per baryon. We obtain general relativistic solutions for neutron and proto-neutron stars endowed with a poloidal magnetic field by solving Einstein-Maxwell field equations in a self-consistent way. As the neutrino chemical potential decreases in value over time, this alters the chemical equilibrium and the composition inside the star, leading to a change in the structure and in the particle population of these objects. We find that the magnetic field deforms the star and significantly alters the number of trapped neutrinos in the stellar interior, together with strangeness content and temperature in each evolution stage.

  7. Axial Symmetric Solutions to Einstein's Field Equations for Deformed Neutron Stars

    NASA Astrophysics Data System (ADS)

    Zubairi, Omair; Weber, Fridolin

    2016-03-01

    Traditional models of neutron stars are constructed under of assumption that they are perfect spheres. This is not correct, however, if the matter inside of neutron stars is described by an non-isotropic model for the equation of state. Examples of such stars are magnetars and neutron stars that would contain color-superconducting quark matter. In this work, we derive the stellar structure equations which describe the properties of non-isotropic neutron stars. The equations are solved numerically in two dimensions. We calculate stellar properties such as masses and radii along with pressure and density profiles and investigate any changes from conventional spherically symmetric neutron stars. This work was supported through the National Science Foundation under Grants PHYS-1411708 and DUE-1259951. Additional computing resources were provided by the CSRC at SDSU and the Department of Sciences at Wentworth Institute of Technology.

  8. 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.

  9. Giant pulsar glitches and the inertia of neutron star crusts

    NASA Astrophysics Data System (ADS)

    Delsate, T.; Chamel, N.; Gürlebeck, N.; Fantina, A. F.; Pearson, J. M.; Ducoin, C.

    2016-07-01

    Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.

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

    NASA Astrophysics Data System (ADS)

    Taverna, Roberto

    2016-07-01

    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 (≈ 10 ^{12}-10 ^{15} G). We 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.

  11. 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.

  12. Hybridizing Gravitationl Waveforms of Inspiralling Binary Neutron Star Systems

    NASA Astrophysics Data System (ADS)

    Cullen, Torrey; LIGO Collaboration

    2016-03-01

    Gravitational waves are ripples in space and time and were predicted to be produced by astrophysical systems such as binary neutron stars by Albert Einstein. These are key targets for Laser Interferometer and Gravitational Wave Observatory (LIGO), which uses template waveforms to find weak signals. The simplified template models are known to break down at high frequency, so I wrote code that constructs hybrid waveforms from numerical simulations to accurately cover a large range of frequencies. These hybrid waveforms use Post Newtonian template models at low frequencies and numerical data from simulations at high frequencies. They are constructed by reading in existing Post Newtonian models with the same masses as simulated stars, reading in the numerical data from simulations, and finding the ideal frequency and alignment to ``stitch'' these waveforms together.

  13. 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.

  14. Quasiequilibrium sequences of binary neutron stars undergoing dynamical scalarization

    NASA Astrophysics Data System (ADS)

    Taniguchi, Keisuke; Shibata, Masaru; Buonanno, Alessandra

    2015-01-01

    We calculate quasiequilibrium sequences of equal-mass, irrotational binary neutron stars in a scalar-tensor theory of gravity that admits dynamical scalarization. We model neutron stars with realistic equations of state (notably through piecewise polytropic equations of state). Using these quasiequilibrium sequences we compute the binary's scalar charge and binding energy versus orbital angular frequency. We find that the absolute value of the binding energy is smaller than in general relativity, differing at most by ˜14 % at high frequencies for the cases considered. We use the newly computed binding energy and the balance equation to estimate the number of gravitational-wave (GW) cycles during the adiabatic, quasicircular inspiral stage up to the end of the sequence, which is the last stable orbit or the mass-shedding point, depending on which comes first. We find that, depending on the scalar-tensor parameters, the number of GW cycles can be substantially smaller than in general relativity. In particular, we obtain that when dynamical scalarization sets in around a GW frequency of ˜130 Hz , the sole inclusion of the scalar-tensor binding energy causes a reduction of GW cycles from ˜120 Hz up to the end of the sequence (˜1200 Hz ) of ˜11 % with respect to the general-relativity case. (The number of GW cycles from ˜120 Hz to the end of the sequence in general relativity is ˜270 .) We estimate that when the scalar-tensor energy flux is also included the reduction in GW cycles becomes of ˜24 %. Quite interestingly, dynamical scalarization can produce a difference in the number of GW cycles with respect to the general-relativity point-particle case that is much larger than the effect due to tidal interactions, which is on the order of only a few GW cycles. These results further clarify and confirm recent studies that have evolved binary neutron stars either in full numerical relativity or in post-Newtonian theory, and point out the importance of developing

  15. Binary Neutron Star Mergers: Prospects for Multimessenger Observations

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We evolve a binary system of two, equal-mass neutron stars in a quasi-circular orbit through and past merger. We consider different nuclear equations of state, which vary from soft to quite stiff, and allow for magnetization of the system and neutrino cooling via a leakage scheme. Here, I focus on potential observables, other than gravitational waves, produced mainly by the hot, strongly magnetized matter resulting from the merger and study their dependence on both the equation of state and the initial magnetic field strength.

  16. 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 α-capture on 12C with the much faster 12C(p,γ)13N(α,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.

  17. Cyclotron line resonant transfer through neutron star atmospheres

    NASA Technical Reports Server (NTRS)

    Wang, John C. L.; Wasserman, Ira M.; Salpeter, Edwin E.

    1988-01-01

    Monte Carlo methods are used to study in detail the resonant radiative transfer of cyclotron line photons with recoil through a purely scattering neutron star atmosphere for both the polarized and unpolarized cases. For each case, the number of scatters, the path length traveled, the escape frequency shift, the escape direction cosine, the emergent frequency spectra, and the angular distribution of escaping photons are investigated. In the polarized case, transfer is calculated using both the cold plasma e- and o-modes and the magnetic vacuum perpendicular and parallel modes.

  18. 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.

  19. 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.

  20. 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.

  1. Hypernuclei and the Hyperon Problem in Neutron Stars

    SciTech Connect

    Bedaque, Paulo

    2015-01-01

    The likely presence of $\\Lambda$ baryons in dense hadronic matter tends to soften the equation of state to an extend 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 $\\Lambda$ particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on non-strange dense matter, including its uncertainties, to conclude that the interaction between $\\Lambda$s and dense matter has to become repulsive at densities below three times the nuclear saturation density.

  2. 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.

  3. Topics in the physics and astrophysics of neutron stars

    NASA Astrophysics Data System (ADS)

    Postnikov, Sergey

    In this dissertation, four topics related to the physics and astrophysics of neutron stars are studied. Two first topics deal with microscopical physics processes in the star outer crust and the last two with macroscopical properties of a star, such as mass and radius. In the first topic, the thermodynamical and transport properties of a dilute gas in which particles interact through a delta-shell potential are investigated. Through variations of a single parameter related to the strength and size of the delta-shell potential, the scattering length and effective range that determine the low-energy elastic scattering cross sections can be varied over wide ranges including the case of the unitary limit (infinite scattering length). It is found that the coefficients of shear viscosity, thermal conductivity and diffusion all decrease when the scattering length becomes very large and also when resonances occur as the temperature is increased. The calculated ratios of the shear viscosity to entropy density as a function of temperature for various interaction strengths (and therefore scattering lengths) were found to lie well above the recently suggested minimal value of (4pi)-1h/kB. A new result is the value of (4/5) for the dimensionless ratio of the energy density times the diffusion coefficient to viscosity for a dilute gas in the unitary limit. Whether or not this ratio changes upon the inclusion of more than two-body interactions is an interesting avenue for future investigations. These investigations shed pedagogical light on the issue of the thermal and transport properties of an interacting system in the unitary limit, of much current interest in both atomic physics and nuclear physics in which very long scattering lengths feature prominently at very low energies. In the second topic, the shear viscosity of a Yukawa liquid, a model for the outer crust of a neutron star, is calculated in both the classical and quantum regimes. Results of semi-analytic calculations

  4. Intense electromagnetic outbursts from collapsing hypermassive neutron stars

    NASA Astrophysics Data System (ADS)

    Lehner, Luis; Palenzuela, Carlos; Liebling, Steven L.; Thompson, Christopher; Hanna, Chad

    2012-11-01

    We study the gravitational collapse of a magnetized neutron star using a novel numerical approach able to capture both the dynamics of the star and the behavior of the surrounding plasma. In this approach, a fully general relativistic magnetohydrodynamics implementation models the collapse of the star and provides appropriate boundary conditions to a force-free model which describes the stellar exterior. We validate this strategy by comparing with known results for the rotating monopole and aligned rotator solutions and then apply it to study both rotating and nonrotating stellar collapse scenarios and contrast the behavior with what is obtained when employing the electrovacuum approximation outside the star. The nonrotating electrovacuum collapse is shown to agree qualitatively with a Newtonian model of the electromagnetic field outside a collapsing star. We illustrate and discuss a fundamental difference between the force-free and electrovacuum solutions, involving the appearance of large zones of electric-dominated field in the vacuum case. This provides a clear demonstration of how dissipative singularities appear generically in the nonlinear time evolution of force-free fluids. In both the rotating and nonrotating cases, our simulations indicate that the collapse induces a strong electromagnetic transient, which leaves behind an uncharged, unmagnetized Kerr black hole. In the case of submillisecond rotation, the magnetic field experiences strong winding, and the transient carries much more energy. This result has important implications for models of gamma-ray bursts. Even when the neutron star is surrounded by an accretion torus (as in binary merger and collapsar scenarios), a magnetosphere may emerge through a dynamo process operating in a surface shear layer. When this rapidly rotating magnetar collapses to a black hole, the electromagnetic energy released can compete with the later output in a Blandford-Znajek jet. Much less electromagnetic energy is

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Universal three-body repulsion suggested by neutron stars

    SciTech Connect

    Takatsuka, T.; Nishizaki, S.; Tamagaki, R.

    2008-04-29

    Because of a serious inconsistency between theory and observation for the mass of hyperon-mixed neutron stars, it is suggested that some 'extra repulsion' is needed in hypernuclear systems. A 3-body force repulsion is tested for two cases, a 2{pi}-exchange via {delta}-excitation type (2{pi}{delta}) and a string-junction model (SJM) for the quark structure of baryons. It is found that the 2{pi}{delta} model generates an increasing repulsion with increasing density but cannot produce the 'extra repulsion' in hyperon-mixed neutron stars because it does not work on a {lambda} due to the lack of {lambda}{lambda}{pi} direct coupling. It is pointed out that the 'extra repulsion' should act universally, i.e., independent of baryon species. The SJM 3-body repulsion can satisfy the condition of universality because of the flavor-independence and the {l_brace}2{pi}{delta}+SJM{r_brace} scheme is shown to be a promising candidate for the 'extra repulsion', maintaining consistency with the empirical saturation property of nuclear matter.

  10. 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.

  11. Simulations of the Inspiral and Merger of Magnetized Neutron Stars

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Anderson, M.; Hirschman, E. W.; Lehner, L.; Liebling, S. L.; Neilsen, D.; Palenzuela, C.; Tohline, J. E.

    2008-05-01

    We present simulations of the inspiral, merger and eventual collapse of neutron star binaries calculated in full general relativity. The Einstein equations are solved in a first order reduction of the general harmonic formulation while the matter is evolved in the MHD approximation. Each binary component initially has a dipole magnetic field perpendicular to the orbital plane. We use the adaptive mesh refinement package HAD to resolve the disparate length scales in the problem ranging from the radiation zone down to the internal dynamics of the neutron stars. For aligned fields and our chosen field strength, we find that magnetic effects delay the merger somewhat - thus boosting the gravitational wave signal from the binary. As we will discuss, the magnetic field significantly impacts the distribution of matter and angular momentum in the super-massive, merged object after merger. This work has been supported in part by NSF grants AST 04-07070 and PHY 03-26311, and in part through NASA's ATP program grants NAG5-8497, NAG5-13430 and NNX07AG84G. The computations were performed on computer facilities provided through the Teragrid, LONI, LSU and BYU.

  12. Probing double neutron star evolution with pulsar observations

    NASA Astrophysics Data System (ADS)

    Ferdman, Robert

    2016-07-01

    Pulsars in double neutron star (DNS) binary systems represent a distinct population among pulsar binaries. Within this class of system, the formation channel through which the second neutron star (NS) is formed can differ in ways that can leave distinct observable signatures. In particular, measured DNS properties provide clues about prior interactions and the progenitor supernova event that has left behind the second-formed NS. In this talk I will present results from long-term timing analysis and profile studies of several pulsars in DNS systems, including highly relativistic binaries such as PSR J0737-3039A from the double pulsar system and the recently discovered PSR J1913+1102. I will place them in the larger context of the DNS population, and demonstrate our attempt to distinguishing the different evolutionary channels that are possible for these systems. Doing so will also provide crucial complimentary information to current and future observations by ground-based gravitational-wave detectors such as Advanced LIGO and VIRGO, which are particularly sensitive to merging DNS systems.

  13. Unexpected Windy Weather Around a Highly Magnetized Neutron Star

    NASA Astrophysics Data System (ADS)

    Younes, George A.; Kouveliotou, Chryssa; Kargaltsev, Oleg; Gill, Ramandeep; Granot, Jonathan; Watts, Anna; Gelfand, Joseph; Baring, Matthew G.; Kust Harding, Alice; Pavlov, George G.; van der Horst, Alexander; Huppenkothen, Daniela; Gögüs, Ersin; Lin, Lin; Roberts, Oliver

    2016-04-01

    Magnetars and rotation-powered pulsars (RPPs) historically represented two distinct subclasses of neutron stars. Magnetars are slowly-rotating (~2-12 s), isolated neutron stars (NSs) with super-strong magnetic fields, B~10^13-10^15 G. RPPs, on the other hand, are rapidly-rotating (~0.01-0.3~s), isolated NSs with surface dipole magnetic field in the range ~10^11-10^13 G. Most pulsars possess a large rotational energy loss rate that powers a relativistic magnetized particle wind, often seen as a pulsar wind nebula (PWN; the Crab PWN being the most famous). There has not yet been convincing evidence for a wind nebula around magnetars, most likely due to their low rotational energy loss rate. Here, we report the study of new deep X-ray observations of the peculiar extended emission around the magnetar Swift J1834.9-0846. Our new results strongly support a wind nebula as the nature of the extended emission, thus, establishing Swift J1834.9-0846 as the first magnetar to possess a surrounding nebula. This implies that wind nebulae are no longer exclusive to RPPs and, along with recent discoveries in the field, further narrow the gaps between these two sub-populations of isolated NSs. The physical properties of this wind nebula, however, show peculiarities, especially its high radiative efficiency of about 10%, only shared with two other known very young RPPs, the Crab and its twin.

  14. 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.

  15. 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, Ω, Ω˙, Ω¨, 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.

  16. 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.

  17. 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

  18. 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.

  19. 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

  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

  2. 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.

  3. 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.

  4. Constraining the State of Ultra-dense Matter with the Neutron Star Interior Composition Explorer

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko

    2016-04-01

    [This presentation is submitted on behalf of the entire NICER Science Team] The state of cold matter at densities exceeding those of atomic nuclei remains one of the principal outstanding problems in modern physics. Neutron stars provide the only known setting in the universe where these physical conditions can be explored. Thermal X-ray radiation from the physical surface of a neutron star can serve as a powerful tool for probing the poorly understood behavior of the matter in the dense stellar interior. For instance, realistic modeling of the thermal X-ray modulations observed from rotation-powered millisecond pulsars can produce stringent constraints on the neutron star mass-radius relation, and by extension the state of supra-nuclear matter. I will describe the prospects for precision neutron star equation of state constraints with millisecond pulsars using the forthcoming Neutron Star Interior Composition Explorer (NICER) X-ray timing mission.

  5. 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?.

  6. 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?

  7. A Survey of Chemical Separation in Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Mckinven, Ryan; Cumming, Andrew; Medin, Zach; Schatz, Hendrik

    2016-06-01

    The heavy element ashes of rp-process hydrogen and helium burning in accreting neutron stars are compressed to high density where they freeze, forming the outer crust of the star. We calculate the chemical separation on freezing for a number of different nuclear mixtures resulting from a range of burning conditions for the rp-process. We confirm the generic result that light nuclei are preferentially retained in the liquid and heavy nuclei in the solid. This is in agreement with the previous study of a 17-component mixture of rp-process ashes by Horowitz et al., but extends that result to a much larger range of compositions. We also find an alternative phase separation regime for the lightest ash mixtures which does not demonstrate this generic behavior. With a few exceptions, we find that chemical separation reduces the expected {Q}{{imp}} in the outer crust compared to the initial rp-process ash, where {Q}{{imp}} measures the mean-square dispersion in atomic number Z of the nuclei in the mixture. We find that the fractional spread of Z plays a role in setting the amount of chemical separation and is strongly correlated to the divergence between the two/three-component approximations and the full component model. The contrast in Y e between the initial rp-process ashes and the equilibrium liquid composition is similar to that assumed in earlier two-component models of compositionally driven convection, except for very light compositions which produce nearly negligible convective driving. We discuss the implications of these results for observations of accreting neutron stars.

  8. Neutron star structure in the presence of conformally coupled scalar fields

    NASA Astrophysics Data System (ADS)

    Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

    2014-10-01

    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.

  9. 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.

  10. Saturation of the f -mode instability in neutron stars. II. Applications and results

    NASA Astrophysics Data System (ADS)

    Pnigouras, Pantelis; Kokkotas, Kostas D.

    2016-07-01

    We present the first results on the saturation of the f -mode instability in neutron stars due to nonlinear mode coupling. Emission of gravitational waves drives the f -mode (fundamental mode) unstable in fast-rotating, newborn neutron stars. The initial growth phase of the mode is followed by its saturation, because of energy leaking to other modes of the star. The saturation point determines the strain of the generated gravitational-wave signal, which can then be used to extract information about the neutron star's equation of state. The parent (unstable) mode couples via parametric resonances with pairs of daughter modes, with the triplets' evolution exhibiting a rich variety of behaviors. We study both supernova- and merger-derived neutron stars, simply modeled as polytropes in a Newtonian context, and show that the parent may couple to many different daughter pairs during the star's evolution through the instability window, with the saturation amplitude changing by orders of magnitude.

  11. A Hot Water Bottle for Aging Neutron Stars?

    NASA Astrophysics Data System (ADS)

    Rajagopal, Krishna

    We understand many of the properties of the densest phase of quark matter rigorously from first principles QCD. However, the nature of the second-most-dense phase of quark matter remains unclear. A recently proposed candidate for this phase features both neutrino emissivity and specific heat that are parametrically enhanced relative to those of all other proposed phases of dense matter -- quark or nuclear. If present within a layer of a neutron star, it would control the cooling of the star. The neutrino-dominated cooling would look like standard Direct-URCA as the two enhancements cancel, but old stars, say tens of millions of years and older, would stay orders of magnitude warmer than in any other scenario. Most of my talk will consist of explaining this abstract. At the end, I will explain why it currently remains unclear whether this hot water bottle phase really is the second-densest form of quark matter, and will discuss an alternative possibility.

  12. 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.

  13. 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.

  14. Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

    NASA Astrophysics Data System (ADS)

    Silva, Hector O.; Sotani, Hajime; Berti, Emanuele

    2016-04-01

    The lowest neutron star masses currently measured are in the range 1.0 - 1.1~M⊙, but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass M/M⊙ = 1.174 ± 0.004 (Martinez et al. 2015) in a double neutron star system suggests that low-mass neutron stars may be an interesting target for gravitational-wave detectors. Furthermore, Sotani et al. (2014) recently found empirical formulas relating the mass and surface redshift of nonrotating neutron stars to the star's central density and to the parameter η ≡ (K0L2)1/3, where K0 is the incompressibility of symmetric nuclear matter and L is the slope of the symmetry energy at saturation density. Motivated by these considerations, we extend the work by Sotani et al. (2014) to slowly rotating and tidally deformed neutron stars. We compute the moment of inertia, quadrupole moment, quadrupole ellipticity, tidal and rotational Love number and apsidal constant of slowly rotating neutron stars by integrating the Hartle-Thorne equations at second order in rotation, and we fit all of these quantities as functions of η and of the central density. These fits may be used to constrain η, either via observations of binary pulsars in the electromagnetic spectrum, or via near-future observations of inspiralling compact binaries in the gravitational-wave spectrum.

  15. Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

    NASA Astrophysics Data System (ADS)

    Silva, Hector O.; Sotani, Hajime; Berti, Emanuele

    2016-07-01

    The lowest neutron star masses currently measured are in the range 1.0-1.1 M⊙, but these measurement have either large uncertainties or refer to isolated neutron stars. The recent claim of a precisely measured mass M/M⊙ = 1.174 ± 0.004 (Martinez et al. 2015) in a double neutron star system suggests that low-mass neutron stars may be an interesting target for gravitational-wave detectors. Furthermore, Sotani et al. recently found empirical formulas relating the mass and surface redshift of non-rotating neutron stars to the star's central density and to the parameter η ≡ (K0L2)1/3, where K0 is the incompressibility of symmetric nuclear matter and L is the slope of the symmetry energy at saturation density. Motivated by these considerations, we extend the work by Sotani et al. to slowly rotating and tidally deformed neutron stars. We compute the moment of inertia, quadrupole moment, quadrupole ellipticity, tidal and rotational Love number and apsidal constant of slowly rotating neutron stars by integrating the Hartle-Thorne equations at second order in rotation, and we fit all of these quantities as functions of η and of the central density. These fits may be used to constrain η, either via observations of binary pulsars in the electromagnetic spectrum, or via near-future observations of inspiralling compact binaries in the gravitational-wave spectrum.

  16. Four-hair relations for differentially rotating neutron stars in the weak-field limit

    NASA Astrophysics Data System (ADS)

    Bretz, Joseph; Yagi, Kent; Yunes, Nicolas

    2016-03-01

    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, the three-hair relations, were found to hold in neutron stars that rotate rigidly, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We 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). The resulting relations include the fourth moment, hence deemed the four-hair relations for differentially rotating neutron stars, and 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.

  17. [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.

  18. Electromagnetic Counterparts from Tilted Magnetized Binary Neutron-Stars Mergers

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    Recent studies have demonstrated that the interaction of magnetospheres in binary neutron star systems can radiate strongly electromagnetically. We study here a broader set of configurations accounting for tilted/misaligned dipoles in coalescing binaries and analyze the resulting Poynting flux and its correlation to the dynamics. In particular, the misalignment of the dipoles results in a very dynamic system with magnetic reconnections, sheer layers, and current sheets. The electromagnetic radiation displays a distinctive pulsating behaviour tied to the orbital dynamics and stellar dipole orientations and the overall power of this radiation. This work was supported by the NSF grants PHY-0969827 (LIU), PHY-0969811 (BYU), NASA's ATP grant NNX13AH01G, and NSERC through a Discovery Grant.

  19. 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.

  20. On the HBO Mechanism of X-Ray Neutron Star

    NASA Astrophysics Data System (ADS)

    Zhang, C. M.; Dolgov, A.

    We ascribe the 15-60 Hz Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the orbiting accreted matter at the boundary of magnetosphere-disk of X-ray neutron star (NS). Considering the relativistic motion mechanism for the kHz QPO, that the radii of the inner disk and magnetosphere-disk of NS are correlated with each other by a factor is assumed. The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The theoretical relations between 15-60 Hz QPO (HBO) frequency and the twin kHz QPOs are similar to the measured empirical formula. Further, the better fitted NS mass by the proposed model is about 1.9 solar masses for the detected LMXBs.

  1. Gravitational lensing of gravitational waves from merging neutron star binaries

    SciTech Connect

    Wang, Yun; Stebbins, Albert; Turner, Edwin L.

    1996-05-01

    We discuss the gravitational lensing of gravitational waves from merging neutron star binaries, in the context of advanced LIGO type gravitational wave detectors. We consider properties of the expected observational data with cut on the signal-to-noise ratio \\rho, i.e., \\rho>\\rho_0. An advanced LIGO should see unlensed inspiral events with a redshift distribution with cut-off at a redshift z_{\\rm max} < 1 for h \\leq 0.8. Any inspiral events detected at z>z_{\\rm max} should be lensed. We compute the expected total number of events which are present due to gravitational lensing and their redshift distribution for an advanced LIGO in a flat Universe. If the matter fraction in compact lenses is close to 10\\%, an advanced LIGO should see a few strongly lensed events per year with \\rho >5.

  2. Multidimensional Simulations of Convection on the Surface of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Malone, Christopher M.; Zingale, M.; Nonaka, A.; Almgren, A. S.; Bell, J. B.

    2008-09-01

    We present preliminary results of plane-parallel multidimensional simulations of helium burning in the accreted layer of a neutron star, under conditions amenable to Type I X-Ray Bursts. Using a low Mach number hydrodynamics code, MAESTRO, we are able to follow the heating from nuclear reactions and watch it drive convection throughout the layer. We report on the dynamics and energetics leading up to thermonuclear runaway as well as the state of the system in which the burning front will propagate. This work is supported under DOE/Office of Nuclear Physics grant No. DE-FG02-06ER41448 to SUNY Stony Brook, and by the SciDAC Program of the DOE Office of Mathematics, Information, and Computational Sciences under the U.S. Department of Energy under contract No. DE-AC02-05CH11231.

  3. Fast Radio Bursts from the Inspiral of Double Neutron Stars

    NASA Astrophysics Data System (ADS)

    Wang, Jie-Shuang; Yang, Yuan-Pei; Wu, Xue-Feng; Dai, Zi-Gao; Wang, Fa-Yin

    2016-05-01

    In this Letter, we propose that a fast radio burst (FRB) could originate from the magnetic interaction between double neutron stars (NSs) during their final inspiral within the framework of a unipolar inductor model. In this model, an electromotive force is induced on one NS to accelerate electrons to an ultra-relativistic speed instantaneously. We show that coherent curvature radiation from these electrons moving along magnetic field lines in the magnetosphere of the other NS is responsible for the observed FRB signal, that is, the characteristic emission frequency, luminosity, duration, and event rate of FRBs can be well understood. In addition, we discuss several implications of this model, including double-peaked FRBs and possible associations of FRBs with short-duration gamma-ray bursts and gravitational-wave events.

  4. Long-term evolution of crustal neutron star magnetic fields

    NASA Technical Reports Server (NTRS)

    Urpin, V. A.; Chanmugam, G.; Sang, Yeming

    1994-01-01

    We have derived an analytic solution to the asymptotic behavior of dipolar magnetic fields that are generated in the crusts of neutron stars. We show that if the conductivity is due to impurity scattering, as expected for late stages of evolution, the surface field strength at the magnetic pole declines with the power law B(sub p) approximately = (t/t(sub 0))(exp -2/3). The results are shown to be qualitatively consistent with detailed numerical calculations. These latter results are consistent with some recent analyses of pulsar statistics and the magnetic fields of several binary pulsars with white dwarf companions whose ages have been determined. The dependence of the surface magnetic field on spin period of the pulsar is derived.

  5. Hypernuclei and the Hyperon Problem in Neutron Stars

    DOE PAGESBeta

    Bedaque, Paulo

    2015-01-01

    The likely presence ofmore » $$\\Lambda$$ baryons in dense hadronic matter tends to soften the equation of state to an extend 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 $$\\Lambda$$ particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on non-strange dense matter, including its uncertainties, to conclude that the interaction between $$\\Lambda$$s and dense matter has to become repulsive at densities below three times the nuclear saturation density.« less

  6. 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.

  7. 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).

  8. 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.

  9. 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 (φ) meson also plays a important role in supporting a massive neutron star.

  10. 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.

  11. Observational results from cooling neutron stars in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Degenaar, Nathalie

    2016-07-01

    The composition and structure of the ~1 km thick, solid crust of neutron stars is responsible for many of their observable properties, and plays a fundamental role in the emission of gravitational waves and the evolution of their magnetic field. When residing in an X-ray binary, a neutron star accretes gas from a companion star. As matter accumulates on the neutron star surface, the underlying crust is compressed and heated due to nuclear reactions induced by this compression. Once accretion switches off, sensitive X-ray satellites can be employed to observe how the heated crust cools. Comparing these observations with theoretical simulations provides very valuable insight into the structure and composition of the crusts of neutron stars. I will present the latest observational results and challenges in this research field.

  12. 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.

  13. Bright transients from strongly-magnetized neutron star-black hole mergers

    NASA Astrophysics Data System (ADS)

    D'Orazio, Daniel J.; Levin, Janna; Murray, Norman W.; Price, Larry

    2016-07-01

    Direct detection of black hole-neutron star pairs is anticipated with the advent of aLIGO. Electromagnetic counterparts may be crucial for a confident gravitational-wave detection as well as for extraction of astronomical information. Yet black hole-neutron star pairs are notoriously dark and so inaccessible to telescopes. Contrary to this expectation, a bright electromagnetic transient can occur in the final moments before merger as long as the neutron star is highly magnetized. The orbital motion of the neutron star magnet creates a Faraday flux and corresponding power available for luminosity. A spectrum of curvature radiation ramps up until the rapid injection of energy ignites a fireball, which would appear as an energetic blackbody peaking in the x ray to γ rays for neutron star field strengths ranging from 1012 to 1016 G respectively and a 10 M⊙ black hole. The fireball event may last from a few milliseconds to a few seconds depending on the neutron star magnetic-field strength, and may be observable with the Fermi Gamma-Ray Burst Monitor with a rate up to a few per year for neutron star field strengths ≳1014 G . We also discuss a possible decaying post-merger event which could accompany this signal. As an electromagnetic counterpart to these otherwise dark pairs, the black-hole battery should be of great value to the development of multi-messenger astronomy in the era of aLIGO.

  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. Rotational Corrections to Neutron-star Radius Measurements from Thermal Spectra

    NASA Astrophysics Data System (ADS)

    Bauböck, Michi; Özel, Feryal; Psaltis, Dimitrios; Morsink, Sharon M.

    2015-01-01

    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 ⊙ 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 ⊙, 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.

  16. 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.

  17. 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.

  18. Observational constraints on neutron star Masses and Radii

    NASA Astrophysics Data System (ADS)

    Heinke, Craig

    2016-07-01

    There are major uncertainties in the composition and structure of neutron star (NS) interiors, making measurements of the compactness and thermal properties of NSs quite valuable. Dozens of NSs have precisely measured masses (generally through radio timing of pulsars). However, current methods for precise measurement of radius, and thus compactness, generally suffer from conflicting interpretations of observable quantities. I will summarize the questions at issue, and the current state of the data. For instance, for quiescent low-mass X-ray binaries in globular clusters, these include issues of atmospheric composition, distance determination methods, and the possible presence of hot spots on the surface. The thermal properties of NSs, mostly set by neutrino emission from the core, divulge information about the core composition, and its superfluid properties. Young NSs appear to be well-described by "minimal cooling" (see Page's talk), while some old NSs in low-mass X-ray binaries show evidence for strongly enhanced neutrino core cooling. The young NS in Cassiopeia A has been reported to show rapid cooling, that has been interpreted as indicating that the neutrons in the core are transitioning to a superfluid state. The initial cooling measurement was too rapid; it is currently unclear whether the Cas A NS is cooling rapidly or not. I will conclude with some discussion of paths forward toward constraints in these directions, besides the NICER instrument.

  19. Production of unstable heavy neutrinos in proto-neutron stars

    NASA Astrophysics Data System (ADS)

    Albertus, C.; Masip, M.; Pérez-García, M. A.

    2015-12-01

    We discuss the production of a class of heavy sterile neutrinos νh in proto-neutron stars. The neutrinos, of mass around 50 MeV, have a negligible mixing with the active species but relatively large dimension-5 electromagnetic couplings. In particular, a magnetic dipole moment μ ≈10-6 GeV-1 implies that they are thermally produced through e+e- →νbarhνh in the early phase of the core collapse, whereas a heavy-light transition moment μtr ≈10-8 GeV-1 allows their decay νh →νi γ with a lifetime around 10-3 s. 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 ≈ 400 km, providing a very efficient mechanism to enhance the supernova shock front and heat the material behind it.

  20. 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.

  1. Gravitational wave constraints on the shape of neutron stars

    NASA Astrophysics Data System (ADS)

    Johnson-McDaniel, Nathan K.

    2013-08-01

    We show that there is a direct relation between upper limits on (or potential future measurements of) the m=2 quadrupole moments of slowly rotating neutron stars and the l=m=2 deformation of the star’s surface, in full general relativity, to first order in the perturbation. This relation only depends on the star’s structure through its mass and radius. All one has to assume about the star’s constituents is that the stress-energy tensor at its surface is that of a perfect fluid, which will be true with good accuracy in almost all the situations of interest, and that the magnetic field configuration there is force free, which is likely to be a good approximation. We then apply this relation to the stars which have direct LIGO/Virgo bounds on their m=2 quadrupole moment, below the spin-down limit, and compare with the expected surface deformations due to rotation. In particular, we find that LIGO observations have constrained the Crab pulsar’s l=m=2 surface deformation to be smaller than its l=2, m=0 deformation due to rotation, for all the causal equations of state we consider, a statement that could not have been made just using the upper bounds on the l=m=2 deformation from electromagnetic observations.

  2. A crystalline quark-hadron mixed phase in neutron stars

    NASA Astrophysics Data System (ADS)

    Glendenning, N. K.

    1994-08-01

    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.

  3. 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.

  4. Maximum mass of neutron stars and strange neutron-star cores

    NASA Astrophysics Data System (ADS)

    Zdunik, J. L.; Haensel, P.

    2013-03-01

    Context. The recent measurement of mass of PSR J1614-2230 rules out most existing models of the equation of state (EOS) of dense matter with high-density softening due to hyperonization that were based on the recent hyperon-nucleon and hyperon-hyperon interactions, which leads to a "hyperon puzzle". Aims: We study a specific solution of this hyperon puzzle that consists of replacing a too soft hyperon core by a sufficiently stiff quark core. In terms of the quark structure of the matter, one replaces a strangeness-carrying baryon phase of confined quark triplets, some of them involving s quarks, by a quark plasma of deconfined u, d, and s quarks. Methods: We constructed an analytic approximation that fits modern EOSs of the two flavor (2SC) and the color-flavor-locked (CFL) color-superconducting phases of quark matter very well. Then, we used it to generate a continuum of EOSs of quark matter. This allowed us to simulate continua of sequences of first-order phase transitions at prescribed pressures, from hadronic matter to the 2SC and then to the CFL state of color-superconducting quark matter. Results: We obtain constraints in the parameter space of the EOS of superconducting quark cores, EOS.Q, resulting from Mmax > 2 M⊙. These constraints depend on the assumed EOS of baryon phase, EOS.B. We also derive constraints that would result from significantly higher measured masses. For 2.4 M⊙ the required stiffness of the CFL quark core is close to the causality limit while the density jump at the phase transition is very small. Conclusions: The condition Mmax > 2 M⊙ puts strong constraints on the EOSs of the 2SC and CFL phases of quark matter. Density jumps at the phase transitions have to be sufficiently small and sound speeds in quark matter sufficiently large. The condition of thermodynamic stability of the quark phase results in a maximum mass of hybrid stars similar to that of purely baryon stars. This is due to the phase transition of quark matter back to

  5. Four-hair relations for differentially rotating neutron stars in the weak-field limit

    NASA Astrophysics Data System (ADS)

    Bretz, Joseph; Yagi, Kent; Yunes, Nicolás

    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.

  6. 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.

  7. Order-of-magnitude physics of neutron stars. Estimating their properties from first principles

    NASA Astrophysics Data System (ADS)

    Reisenegger, Andreas; Zepeda, Felipe S.

    2016-03-01

    We use basic physics and simple mathematics accessible to advanced undergraduate students to estimate the main properties of neutron stars. We set the stage and introduce relevant concepts by discussing the properties of "everyday" matter on Earth, degenerate Fermi gases, white dwarfs, and scaling relations of stellar properties with polytropic equations of state. Then, we discuss various physical ingredients relevant for neutron stars and how they can be combined in order to obtain a couple of different simple estimates of their maximum mass, beyond which they would collapse, turning into black holes. Finally, we use the basic structural parameters of neutron stars to briefly discuss their rotational and electromagnetic properties.

  8. Effects of Rapid Spin on the Spectra and Pulse Profiles of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Ozel, Feryal; Psaltis, Dimitrios; Baubock, Michi; Chakrabarty, Deepto; Morsink, Sharon

    2014-08-01

    A large number of sources that are prime targets for determining neutron star masses and radii spin at 300-700 Hz. At these high spin frequencies, neutron stars become oblate and their spacetime acquires a significant quadrupole moment. In this talk, I will present the rotational broadening and distortion of thermal and line spectra due to these effects. I will also discuss the asymmetry and the energy dependence introduced by the stellar spin to X-ray pulse profiles. I will conclude by describing ways to mitigate and/or exploit these rapid spin effects when measuring neutron star radii.

  9. 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.

  10. Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity

    SciTech Connect

    Charbonneau, James; Zhitnitsky, Ariel E-mail: arz@phas.ubc.ca

    2010-08-01

    The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation.

  11. 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.

  12. 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.

  13. Possibility of an s-wave pion condensate in neutron stars reexamined

    SciTech Connect

    Ohnishi, A.; Jido, D.; Sekihara, T.; Tsubakihara, K.

    2009-09-15

    We examine possibilities of pion condensation with zero momentum (s-wave condensation) in neutron stars by using the pion-nucleus optical potential U and the relativistic mean field (RMF) models. We use low-density phenomenological optical potentials parametrized to fit deeply bound pionic atoms or pion-nucleus elastic scatterings. The proton fraction (Y{sub p}) and electron chemical potential ({mu}{sub e}) in neutron star matter are evaluated in RMF models. We find that the s-wave pion condensation hardly takes place in neutron stars and especially has no chance if hyperons appear in neutron star matter and/or the b{sub 1} parameter in U has density dependence.

  14. Low-frequency quasi-periodic oscillations in black hole and neutron star LMXBs

    NASA Astrophysics Data System (ADS)

    Ingram, Adam

    2016-07-01

    Low-frequency quasi-periodic oscillations (QPOs) are routinely seen in the X-ray flux of accreting black holes and neutron stars. Since the QPO frequency correlates with the low frequency power spectral break in the same manner for both object classes, it is reasonable to believe that these oscillations have the same physical origin in neutron stars as they do in black holes. However, recent successes in modelling black hole low frequency QPOs as Lense-Thirring precession contrast sharply with failures of the same model in neutron stars. This could be attributable to the significant extra complexity, both in the physics and in the observed power spectra, of accreting neutron stars when compared with black holes. Alternatively, the QPO mechanism really is the same for the two object classes, but in that case, why does the Lense-Thirring model work so well for black holes? I will review the current state of this field.

  15. PSR J1400--1438: A Potential Laboratory for Fundamental Neutron Star Physics

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko

    2013-10-01

    The pulsed thermal X-ray radiation from radio millisecond pulsars (MSPs) can provide valuable insight into the fundamental physics of neutron stars. Realistic pulse shape modeling, including relativistic and atmospheric effects, has begun to offer important constraints on the magnetic field geometry, properties of the surface, and most importantly, the neutron star equation of state. For binary MSPs, combining this method with an independent precision mass measurement can yield definitive constraints on neutron star structure. We propose an exploratory XMM-Newton energy-resolved timing observation of PSR J1400-1438, a recently discovered nearby binary MSP, to establish if it is suitable as a laboratory for fundamental neutron star physics.

  16. The long and the short of it: modelling double neutron star and collapsar Galactic dynamics

    NASA Astrophysics Data System (ADS)

    Kiel, Paul D.; Hurley, Jarrod R.; Bailes, Matthew

    2010-07-01

    Understanding the nature of galactic populations of double compact binaries (where both stars are a neutron star or black hole) has been a topic of interest for many years, particularly the coalescence rate of these binaries. The only observed systems thus far are double neutron star systems containing one or more radio pulsars. However, theorists have postulated that short-duration gamma-ray bursts may be evidence of coalescing double neutron star or neutron star-black hole binaries, while long-duration gamma-ray bursts are possibly formed by tidally enhanced rapidly rotating massive stars that collapse to form black holes (collapsars). The work presented here examines populations of double compact binary systems and tidally enhanced collapsars. We make use of BINPOP and BINKIN, two components of a recently developed population synthesis package. Results focus on correlations of both binary and spatial evolutionary population characteristics. Pulsar and long-duration gamma-ray burst observations are used in concert with our models to draw the conclusions that (i) double neutron star binaries can merge rapidly on time-scales of a few million years (much less than that found for the observed double neutron star population), (ii) common-envelope evolution within these models is a very important phase in double neutron star formation and (iii) observations of long gamma-ray burst projected distances are more centrally concentrated than our simulated coalescing double neutron star and collapsar Galactic populations. Better agreement is found with dwarf galaxy models although the outcome is strongly linked to the assumed birth radial distribution. The birth rate of the double neutron star population in our models ranges from 4 to 160 Myr-1 and the merger rate ranges from 3 to 150 Myr-1. The upper and lower limits of the rates result from including electron-capture supernova kicks to neutron stars and decreasing the common-envelope efficiency, respectively. Our double

  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. 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.

  19. Loud and Bright: Gravitational and possible electromagnetic signals induced by binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Palenzuela, Carlos; Lehner, Luis; Ponce, Marcelo; Thompson, Chris; Liebling, Steve; Neilsen, Dave; Hirschmann, Eric; Anderson, Matt; Motl, Patrick

    2013-04-01

    Our main goal is to investigate how the strongly gravitating and highly dynamical behavior of magnetized binary neutron stars can affect the plasma in the magnetosphere in such a way that powerful electromagnetic emissions can be induced, as well as stressing its connection with gravitational waves produced by the system. Such phenomena is a natural candidate for bright (EM) and loud (GW) emissions, as pulsars are strong electromagnetic emitters on one hand, and merging binary neutron stars are powerful sources of gravitational radiation.

  20. 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.

  1. 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.

  2. Pair cascades in the magnetospheres of strongly magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Medin, Zach; Lai, Dong

    2010-08-01

    We present numerical simulations of electron-positron pair cascades in the magnetospheres of magnetic neutron stars for a wide range of surface fields (Bp = 1012-1015 G), rotation periods (0.1-10 s) and field geometries. This has been motivated by the discovery in recent years of a number of radio pulsars with inferred magnetic fields comparable to those of magnetars. Evolving the cascade generated by a primary electron or positron after it has been accelerated in the inner gap of the magnetosphere, we follow the spatial development of the cascade until the secondary photons and electron-positron pairs leave the magnetosphere, and we obtain the pair multiplicity and the energy spectra of the cascade pairs and photons under various conditions. Going beyond previous works, which were restricted to weaker fields (B <~ afew × 1012 G), we have incorporated in our simulations detailed treatments of physical processes that are potentially important (especially in the high-field regime) but were either neglected or crudely treated before, including photon splitting with the correct selection rules for photon polarization modes, one-photon pair production into low Landau levels for the e+/-, and resonant inverse Compton scattering from polar cap hotspots. We find that even for B >> BQ = 4 × 1013 G, photon splitting has a small effect on the multiplicity of the cascade since a majority of the photons in the cascade cannot split. One-photon decay into e+ e- pairs at low Landau levels, however, becomes the dominant pair production channel when B >~ 3 × 1012 G; this tends to suppress synchrotron radiation so that the cascade can develop only at a larger distance from the stellar surface. Nevertheless, we find that the total number of pairs and their energy spectrum produced in the cascade depend mainly on the polar cap voltage BpP-2, and are weakly dependent on Bp (and P) alone. We discuss the implications of our results for the radio pulsar death line and for the hard X

  3. Dynamical mass ejection from binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-08-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad $\\sim 60^\\circ$ angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer timescales after the mergers, or from core-collapse supernovae.

  4. Dynamical mass ejection from binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-08-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad ˜60° angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer time-scales after the mergers, or from core-collapse supernovae.

  5. Dynamical Mass Ejection from Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-05-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad ˜60° angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer timescales after the mergers, or from core-collapse supernovae.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  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

  12. 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.

  13. Neutron star glitches have a substantial minimum size

    NASA Astrophysics Data System (ADS)

    Espinoza, C. M.; Antonopoulou, D.; Stappers, B. W.; Watts, A.; Lyne, A. G.

    2014-05-01

    Glitches are sudden spin-up events that punctuate the steady spin-down of pulsars and are thought to be due to the presence of a superfluid component within neutron stars. The precise glitch mechanism and its trigger, however, remain unknown. The size of glitches is a key diagnostic for models of the underlying physics. While the largest glitches have long been taken into account by theoretical models, it has always been assumed that the minimum size lay below the detectability limit of the measurements. In this paper we define general glitch detectability limits and use them on 29 yr of daily observations of the Crab pulsar, carried out at Jodrell Bank Observatory. We find that all glitches lie well above the detectability limits and by using an automated method to search for small events we are able to uncover the full glitch size distribution, with no biases. Contrary to the prediction of most models, the distribution presents a rapid decrease of the number of glitches below ˜0.05 μHz. This substantial minimum size indicates that a glitch must involve the motion of at least several billion superfluid vortices and provides an extra observable which can greatly help the identification of the trigger mechanism. Our study also shows that glitches are clearly separated from all the other rotation irregularities. This supports the idea that the origin of glitches is different to that of timing noise, which comprises the unmodelled random fluctuations in the rotation rates of pulsars.

  14. 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.

  15. Pinned vortex hopping in a neutron star crust

    NASA Astrophysics Data System (ADS)

    Haskell, B.; Melatos, A.

    2016-09-01

    The motion of superfluid vortices in a neutron star crust is at the heart of most theories of pulsar glitches. Pinning of vortices to ions can decouple the superfluid from the crust and create a reservoir of angular momentum. Sudden large-scale unpinning can lead to an observable glitch. In this paper, we investigate the scattering of a free vortex off a pinning potential and calculate its mean free path, in order to assess whether unpinned vortices can skip multiple pinning sites and come close enough to their neighbours to trigger avalanches, or whether they simply hop from one pinning site to its neighbour, giving rise to a more gradual creep. We find that there is a significant range of parameter space in which avalanches can be triggered, thus supporting the hypothesis that they may lie at the origin of pulsar glitches. For realistic values of the pinning force and superfluid drag parameters, we find that avalanches are more likely in the higher density regions of the crust where pinning is stronger. Physical differences in stellar parameters, such as mass and temperature, may lead to a switch between creep-like motion and avalanches, explaining the different characteristics of glitching pulsars.

  16. Helium burning and neutron sources in the stars

    NASA Astrophysics Data System (ADS)

    Aliotta, M.; Junker, M.; Prati, P.; Straniero, O.; Strieder, F.

    2016-04-01

    Helium burning represents an important stage of stellar evolution as it contributes to the synthesis of key elements such as carbon, through the triple- α process, and oxygen, through the 12C( α, γ)16O reaction. It is the ratio of carbon to oxygen at the end of the helium burning stage that governs the following phases of stellar evolution leading to different scenarios depending on the initial stellar mass. In addition, helium burning in Asymptotic Giant Branch stars, provides the two main sources of neutrons, namely the 13C( α, n)16O and the 22Ne( α, n)25Mg, for the synthesis of about half of all elements heavier than iron through the s-process. Given the importance of these reactions, much experimental work has been devoted to the study of their reaction rates over the last few decades. However, large uncertainties still remain at the energies of astrophysical interest which greatly limit the accuracy of stellar models predictions. Here, we review the current status on the latest experimental efforts and show how measurements of these important reaction cross sections can be significantly improved at next-generation deep underground laboratories.

  17. Neutron Star Magnetic Field Evolution, Crust Movement, and Glitches: Erratum

    NASA Astrophysics Data System (ADS)

    Ruderman, Malvin; Zhu, Tianhua; Chen, Kaiyou

    1998-08-01

    In the paper "Neutron Star Magnetic Field Evolution, Crust Movement, and Glitches" by Malvin Ruderman, Tianhua Zhu, and Kaiyou Chen (ApJ, 492, 267 [1998]), the following corrections should be made: Four lines below equation (24), "with v_phi still the same as that of the Vela" should be replaced by "with each vortex line-flux-tube intersection force still the same as that in Vela." Just after equation (25), "as long as 3 - n is less than 1, but 3 - n = 1 otherwise" should be inserted. There is no change in Table 1. The authors also note that a new analysis of observations of the period history of PSR 0540-69 gives a most probable spin-down index n = 2.5 (S. Eikenberg, G. Fazio, and S. Ransom, ApJ, 492, 754 [1998]), which removes the major discrepancy between the observed and model spin-down indices and makes the remarks about it below equation (25) no longer relevant.

  18. Simulated magnetic field expulsion in neutron star cores

    NASA Astrophysics Data System (ADS)

    Elfritz, J. G.; Pons, J. A.; Rea, N.; Glampedakis, K.; Viganò, D.

    2016-03-01

    The study of long-term evolution of neutron star (NS) magnetic fields is key to understanding the rich diversity of NS observations, and to unifying their nature despite the different emission mechanisms and observed properties. Such studies in principle permit a deeper understanding of the most important parameters driving their apparent variety, e.g. radio pulsars, magnetars, X-ray dim isolated NSs, gamma-ray pulsars. We describe, for the first time, the results from self-consistent magnetothermal simulations considering not only the effects of the Hall-driven field dissipation in the crust, but also adding a complete set of proposed driving forces in a superconducting core. We emphasize how each of these core-field processes drive magnetic evolution and affect observables, and show that when all forces are considered together in vectorial form, the net expulsion of core magnetic flux is negligible, and will have no observable effect in the crust (consequently in the observed surface emission) on megayear time-scales. Our new simulations suggest that strong magnetic fields in NS cores (and the signatures on the NS surface) will persist long after the crustal magnetic field has evolved and decayed, due to the weak combined effects of dissipation and expulsion in the stellar core.

  19. Formation of double neutron star systems as implied by observations

    NASA Astrophysics Data System (ADS)

    Beniamini, Paz; Piran, Tsvi

    2016-03-01

    Double Neutron Stars (DNS) have to survive two supernovae (SNe) and still remain bound. This sets strong limits on the nature of the second collapse in these systems. We consider the masses and orbital parameters of the DNS population and constrain the two distributions of mass ejection and kick velocities directly from observations with no a priori assumptions regarding evolutionary models and/or the types of the SNe involved. We show that there is strong evidence for two distinct types of SNe in these systems, where the second collapse in the majority of the observed systems involved small mass ejection (ΔM ≲ 0.5 M⊙) and a corresponding low-kick velocity (vk ≲ 30 km s-1). This formation scenario is compatible, for example, with an electron-capture SN. Only a minority of the systems have formed via the standard SN scenario involving larger mass ejection of ˜2.2 M⊙ and kick velocities of up to 400 km s-1. Due to the typically small kicks in most DNS (which are reflected by rather low proper motion), we predict that most of these systems reside close to the Galactic disc. In particular, this implies that more NS-NS mergers occur close to the Galactic plane. This may have non-trivial implications to the estimated merger rates of DNS and to the rate of LIGO/VIRGO detections.

  20. 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.