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1

Alfvén seismic vibrations of crustal solid-state plasma in quaking paramagnetic neutron star  

Microsoft Academic Search

Magneto-solid-mechanical model of two-component, core-crust, paramagnetic neutron star responding to quake-induced perturbation by differentially rotational, torsional, oscillations of crustal electron-nuclear solid-state plasma about axis of magnetic field frozen in the immobile paramagnetic core is developed. Particular attention is given to the node-free torsional crust-against-core vibrations under combined action of Lorentz magnetic and Hooke's elastic forces; the damping is attributed to

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

2010-01-01

2

Eigenfrequencies of Nodeless Elastic Vibrations Locked in the Crust of Quaking Neutron Star  

Microsoft Academic Search

The Newtonian solid-mechanical theory of non-compressional spheroidal and torsional nodeless elastic vibrations in the homogenous crust model of a quaking neutron star is developed and applied to the modal classification of the quasi-periodic oscillations (QPOs) of X-ray luminosity in the aftermath of giant flares in SGR 1806-20 and SGR 1900+14. Particular attention is given to the low-frequency QPOs in the

S. I. Bastrukov; H.-K. Chang; G.-T. Chen; I. V. Molodtsova

2008-01-01

3

Pulsating magneto-dipole radiation of quaking neutron star powered by energy of Alfven seismic vibrations  

Microsoft Academic Search

The impact of magnetic field decay on radiative activity of quaking neutron\\u000astar undergoing Lorentz-force-driven torsional seismic vibrations about axis of\\u000aits dipole magnetic moment is studied. We found that monotonic depletion of\\u000ainternal magnetic field pressure is accompanied by the loss of vibration energy\\u000aof the star that causes its vibration period to lengthen at a rate proportional\\u000ato

S. I. Bastrukov; I. V. Molodtsova; J. W. Yu; R. X. Xu

2010-01-01

4

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

SciTech Connect

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

Bastrukov, S.; Xu, R.-X. [State Key Laboratory of Nuclear Physics, Peking University, 100871 Beijing (China); Molodtsova, I. [Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation); Takata, J. [Hong Kong University (Hong Kong); Chang, H.-K. [National Tsing Hua University, 30013 Hsinchu, Taiwan (China)

2010-11-15

5

Quaking neutron star deriving radiative power of oscillating magneto-dipole emission from energy of Alfv\\\\'en seismic vibrations  

Microsoft Academic Search

It is shown that depletion of the magnetic field pressure in a quaking neutron star undergoing Lorentz-force-driven torsional seismic vibrations about axis of its dipole magnetic moment is accompanied by the loss of vibration energy of the star that causes its vibration period to lengthen at a rate proportional to the rate of magnetic field decay. Highlighted is the magnetic-field-decay

S. I. Bastrukov; I. V. Molodtsova; J. W. Yu; R. X. Xu

2010-01-01

6

Eigenmodes of elastic vibrations of quaking neutron star encoded in QPOs on light curves of SGR flares  

Microsoft Academic Search

The Newtonian solid-mechanical theory of nodeless spheroidal and torsional of elastic seismic vibrations trapped in the crust of a quaking neutron star is outlined and applied to the modal classification of the quasi-periodic oscillations (QPOs) of X-ray luminosity in the aftermath of giant flares in SGR 1806-20 and SGR 1900+14. The presented analysis relies heavily on the Samuelsson-Andersson identification of

Sergey Bastrukov; Hsiang-Kuang Chang; Irina Molodtsova; Gwan-Ting Chen

2007-01-01

7

Nodeless differentially rotational Alfv\\\\'en oscillations of crustal solid-state plasma in quaking neutron star  

Microsoft Academic Search

The two-component, core-crust, model of a neutron star with homogenous internal and dipolar external magnetic field is studied responding to quake-induced perturbation by substantially nodeless differentially rotational Alfv\\\\'en oscillations of the perfectly conducting crustal matter about axis of fossil magnetic field frozen in the immobile core. The energy variational method of the magneto-solid-mechanical theory of a viscoelastic perfectly conducting medium

S. I. Bastrukov; H.-K. Chang; I. V. Molodtsova; J. Takata

2008-01-01

8

EIGENFREQUENCIES OF NODELESS ELASTIC VIBRATIONS LOCKED IN THE CRUST OF QUAKING NEUTRON STAR  

Microsoft Academic Search

The Newtonian solid-mechanical theory of non-compressional spheroidal and\\u000atorsional nodeless elastic vibrations in the homogenous crust model of a\\u000aquaking neutron star is developed and applied to the modal classification of\\u000athe quasi-periodic oscillations (QPOs) of X-ray luminosity in the aftermath of\\u000agiant flares in SGR 1806-20 and SGR 1900+14. Particular attention is given to\\u000athe low-frequency QPOs in the

S. I. BASTRUKOV; H.-K. CHANG; G.-T. CHEN; I. V. MOLODTSOVA

2008-01-01

9

Pulsating magneto-dipole radiation of a quaking neutron star powered by energy of Alfvén seismic vibrations  

Microsoft Academic Search

We compute the characteristic parameters of the magneto-dipole radiation of a neutron star undergoing torsional seismic vibrations under the action of Lorentz restoring force about an axis of a dipolar magnetic field experiencing decay. After a brief outline of the general theoretical background of the model of a vibration-powered neutron star, we present numerical estimates of basic vibration and radiation

Sergey Bastrukov; Jun-Wei Yu; Ren-Xin Xu; Irina Molodtsova

2011-01-01

10

Torsional Nodeless Vibrations of a Quaking Neutron Star Restored by the Combined Forces of Shear Elastic and Magnetic Field Stresses  

Microsoft Academic Search

Within the framework of Newtonian magneto-solid mechanics, relying on equations appropriate for a perfectly conducting elastic continuous medium threaded by a uniform magnetic field, the asteroseismic model of a neutron star undergoing axisymmetric global torsional nodeless vibrations under the combined action of Hooke's elastic and Lorentz magnetic forces is considered with emphasis on a toroidal Alfvén mode of differentially rotational

S. I. Bastrukov; G.-T. Chen; H.-K. Chang; I. V. Molodtsova; D. V. Podgainy

2009-01-01

11

Neutron skins and neutron stars  

NASA Astrophysics Data System (ADS)

Background: The neutron skin of a heavy nucleus as well as many neutron-star properties are highly sensitive to the poorly constrained density dependence of the symmetry energy.Purpose: To provide for the first time meaningful theoretical errors and to assess the degree of correlation between the neutron-skin thickness of 208Pb and several neutron-star properties.Methods: A proper covariance analysis based on the predictions of an accurately calibrated relativistic functional “FSUGold” is used to quantify theoretical errors and correlation coefficients.Results: We find correlation coefficients of nearly 1 (or -1) between the neutron-skin thickness of 208Pb and a host of observables of relevance to the structure, dynamics, and composition of neutron stars.Conclusions: We suggest that a follow-up Lead Radius Experiment (PREX) measurement, ideally with a 0.5% accuracy, could significantly constrain the equation of state of neutron-star matter.

Fattoyev, F. J.; Piekarewicz, J.

2012-07-01

12

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

PubMed

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

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

2012-07-01

13

The Neutron Star Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

2000-01-01

14

Neutron Stars and Quark Stars  

NASA Astrophysics Data System (ADS)

The tremendous densities reached in the centers of neutron stars provide a high pressure environment in which exciting particles processes are likely compete with each other and novel phases of matter may exist. The particle processes range from the generation of hyperons, to quark deconfinement, to the formation of kaon condensates and H-matter. Another striking possibility concerns the formation of absolutely stable strange quark matter. In the latter event all neutron stars could in fact be strange (quark matter) stars, which would be largely composed of pure quark matter possibly enveloped in a thin nuclear crust made up ordinary hadronic matter. This paper gives an overview of the properties of both classes of stars.

Weber, Fridolin

2004-08-01

15

Hyperons in neutron stars  

SciTech Connect

Generalized beta equilibrium involving nucleons, hyperons, and isobars is examined for neutron star matter. The hyperons produce a considerable softening of the equation of state. It is shown that the observed masses of neutron stars can be used to settle a recent controversy concerning the nuclear compressibility. Compressibilities less than 200 MeV are incompatible with observed masses. 7 refs., 9 figs.

Glendenning, N.K.

1986-04-01

16

The Neutron Stars Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is\\u000aused to derive a lower limit on the mean velocity of neutron stars at birth.\\u000aThe secular evolution of the population is simulated following the paths of a\\u000astatistical sample of stars for different values of the initial kick velocity,\\u000adrawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

1999-01-01

17

Neutron stars as cosmic neutron matter laboratories  

SciTech Connect

Recent developments which have radically changed our understanding of the dynamics of neutron star superfluids and the free precession of neutron stars are summarized, and the extent to which neutron stars are cosmic neutron matter laboratories is discussed. 17 refs., 1 tab.

Pines, D.

1986-01-01

18

Structure of Neutron Stars.  

National Technical Information Service (NTIS)

Structure of neutron stars consisting of a cold and catalyzed superdense matter were investigated by integrating the equations for hydrostatic equilibrium based on the General Relativity theory. The equations of state were obtained with the help of semiem...

C. K. Cheong

1974-01-01

19

The Violent Neutron Star  

NASA Astrophysics Data System (ADS)

Neutron stars enable us to study both the highest densities and the highest magnetic fields in the known Universe. In this article I review what can be learned about such fundamental physics using magnetar bursts. Both the instability mechanisms that trigger the bursts, and the subsequent dynamical and radiative response of the star, can be used to explore stellar and magnetospheric structure and composition.

Watts, A. L.

2012-12-01

20

Double Neutron Star Systems and Natal Neutron Star Kicks  

Microsoft Academic Search

We study the four double neutron star systems found in the Galactic disk in terms of the orbital characteristics of their immediate progenitors and the natal kicks imparted to neutron stars. Analysis of the effect of the second supernova explosion on the orbital dynamics, combined with recent results from simulations of rapid accretion onto neutron stars, lead us to conclude

Chris Fryer; Vassiliki Kalogera

1997-01-01

21

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

PubMed Central

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.

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

2013-01-01

22

Hyperons and neutron stars  

NASA Astrophysics Data System (ADS)

In this work we briefly review some of the effects of hyperons on neutron and proto-neutron star properties. We revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, due to the presence of hyperons, a puzzle which has become more intriguing due the recent measurements of the unusually high masses of the millisecond pulsars PSR J1614-2230 (1.97±0.04M?) and PSR J1903+0327 (1.667±0.021M?). We examine also the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

Vidaña, Isaac

2013-09-01

23

Black Holes and Neutron Stars  

NASA Astrophysics Data System (ADS)

Black holes and neutron stars are the compact remnants of massive stars. They represent one of the key intersections between astronomy and fundamental physics - both are classes of objects which are sufficiently compact that Newtonian gravity cannot be used to describe the forces near their surfaces. The structure of neutron stars furthermore presents one of the few key tests of the equation of state of nuclear matter. This chapter will review some of the key theoretical results underpinning the current understanding of neutron stars and black holes. It will also describe the observations of neutron stars and black holes both in isolation (as thermal emitters and as radio pulsars for the case of neutron stars) and in close binaries, where accretion processes can make these objects bright X-ray sources. Additionally, this chapter will detail the formation processes of both neutron stars and black holes in general, and also the formation of close binaries containing such objects.

Maccarone, Thomas J.

24

QCD in Neutron Stars and Strange Stars  

SciTech Connect

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.

Weber, Fridolin [Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1233 (United States); Negreiros, Rodrigo [FIAS, Goethe University, Ruth Moufang Str 1, 60438 Frankfurt (Germany)

2011-05-24

25

KAON CONDENSATION IN NEUTRON STARS.  

SciTech Connect

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

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

2001-04-24

26

On observing neutron star oscillations  

Microsoft Academic Search

To investigate detecting and identifying neutron star oscillations in x ray sources, a technique for computing the light curves produced from polar cap hotspots on rotating, oscillating neutron stars is developed. The calculations include the effects of general relativity on the photon trajectories and allow for anisotropic beaming of radiation from the polar caps. A simple model, based on stellar

Tod E. Strohmayer

1992-01-01

27

Grand unification of neutron stars  

PubMed Central

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.

Kaspi, Victoria M.

2010-01-01

28

?-condensation and neutron star cooling  

NASA Astrophysics Data System (ADS)

We show, within the context of an independent particle model, that ?- condensation should occur in neutron stars having baryon densities exceeding~0.4 - 0.5 fm-3. This high concentration of ?- implies a very fast cooling rate for `hot' neutron stars. Work supported by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under AFOSR Grant 70-1866A.

Kogut, J.; Manassah, J. T.

1972-09-01

29

Complexity and neutron star structure  

NASA Astrophysics Data System (ADS)

We apply the statistical measure of complexity introduced by López-Ruiz, Mancini and Calbet (1995) [1] to neutron star structure. We continue the recent application of Sañudo and Pacheco (2009) [2] to white dwarfs. The interplay of gravity, the short-range nuclear force and the very short-range weak interaction shows that neutron stars, under the current theoretical framework, are ordered (low complexity) systems.

Chatzisavvas, K. Ch.; Psonis, V. P.; Panos, C. P.; Moustakidis, Ch. C.

2009-10-01

30

Old and new neutron stars  

SciTech Connect

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.

Ruderman, M.

1984-09-01

31

Pulsars and Isolated Neutron Stars  

Microsoft Academic Search

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\\u000a core with a mass more than 1.4 times the solar mass, M{in?}, to hold itself up against gravity once its nuclear fuel is exhausted.\\u000a This implies that a star left with M > 1.4

W. Becker; F. Haberl; J. Trümper

2002-01-01

32

Maximum mass of neutron stars  

NASA Astrophysics Data System (ADS)

We determine the structure of neutron stars within a Brueckner-Hartree-Fock approach based on realistic nucleon-nucleon, nucleon-hyperon, and hyperon-hyperon interactions. Our results indicate rather low maximum masses below 1.4 solar masses. This feature is insensitive to the nucleonic part of the EOS due to a strong compensation mechanism caused by the appearance of hyperons and represents thus strong evidence for the presence of nonbaryonic “quark” matter in the interior of heavy stars.

Schulze, H.-J.; Polls, A.; Ramos, A.; Vidaña, I.

2006-05-01

33

Neutron Star in Cassiopeia A  

NASA Video Gallery

This brief animation shows Cassiopeia A, the remains of a massive star 11,000 light years away from Earth, along with an illustrated inset of a neutron star within the supernova. X-rays from NASA's Chandra X-ray Observatory are shown in red, green and blue along with optical data from the Hubble Space Telescope in gold. Credit: X-ray: NASA/CXC/xx; Optical: NASA/STScI; Illustration: NASA/CXC/ M.Weiss

Sydney B

2011-02-23

34

Magnetoelastic pulsations of neutron stars  

Microsoft Academic Search

We discuss non-radial pulsations of a non-rotating neutron star brought to equilibrium in the state of superparamagnetic magnetization of stellar material. High-lighted are equations of magneto-elastodynamics underlying macroscopic description of large-scale motions of magnetically anisotropic neutron matter possessing properties of elastic Fermi-solid. It is shown that incompressible permanently magnetized nuclear matter can transmit perturbations by transverse magnetoelastic waves. The unique

Sergey Bastrukov; Jongmann Yang; Dmitry Podgainy; Fridolin Weber

2001-01-01

35

Binary neutron star GRB model  

SciTech Connect

In this paper we present the preliminary results of a model for the production of gamma-ray bursts (GRBs) through the compressional heating of binary neutron stars near their last stable orbit prior to merger. Recent numerical studies of the general relativistic (GR) hydrodynamics in three spatial dimensions of close neutron star binaries (NSBs) have uncovered evidence for the compression and heating of the individual neutron stars (NSs) prior to merger. This effect will have significant effect on the production of gravitational waves, neutrinos and, ultimately, energetic photons. The study of the production of these photons in close NSBs and, in particular, its correspondence to observed GRBs is the subject of this paper. The gamma-rays arise as follows. Compressional heating causes the neutron stars to emit neutrino pairs which, in turn, annihilate to produce a hot electron-positron pair plasma. This pair- photon plasma expands rapidly until it becomes optically thin, at which point the photons are released. We show that this process can indeed satisfy three basic requirements of a model for cosmological gamma-ray bursts: 1) sufficient gamma-ray energy release (> 10{sup 51} ergs) to produce observed fluxes, 2) a time-scale of the primary burst duration consistent with that of a ``classical`` GRB ({approximately} 10 seconds), 3) peak of photon number spectrum matches that of ``classical`` GRB ({approximately} 300 keV).

Wilson, J.R. [Lawrence Livermore National Lab., CA (United States)][Notre Dame Univ., IN (United States); Salmonson, J.D.; Mathews, G.J. [Notre Dame Univ., IN (United States)

1997-11-11

36

Planetary Systems Around Neutron Stars.  

National Technical Information Service (NTIS)

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 precisio...

A. Wolszczan

1997-01-01

37

Magnetic fields in neutron stars  

NASA Astrophysics Data System (ADS)

This work aims at studying how magnetic fields affect the observational properties and the long-term evolution of isolated neutron stars, which are the strongest magnets in the universe. The extreme physical conditions met inside these astronomical sources complicate their theoretical study, but, thanks to the increasing wealth of radio and X-ray data, great advances have been made over the last years. A neutron star is surrounded by magnetized plasma, the so-called magnetosphere. Modeling its global configuration is important to understand the observational properties of the most magnetized neutron stars, magnetars. On the other hand, magnetic fields in the interior are thought to evolve on long time-scales, from thousands to millions of years. The magnetic evolution is coupled to the thermal one, which has been the subject of study in the last decades. An important part of this thesis presents the state-of-the-art of the magneto-thermal evolution models of neutron stars during the first million of years, studied by means of detailed simulations. The numerical code here described is the first one to consistently consider the coupling of magnetic field and temperature, with the inclusion of both the Ohmic dissipation and the Hall drift in the crust.

Viganò, Daniele

2013-09-01

38

Constraining the Birth Events of Neutron Stars  

NASA Astrophysics Data System (ADS)

The prescient remark by Baade and Zwicky that supernovae beget neutron stars did little to prepare us for the remarkable variety of observational manifestations such objects display. Indeed, during the first thirty years of the empirical study of neutron stars, only a handful were found to be associated with the remnants of exploded stars. But recent X-ray and radio observations have gone a long way toward justifying the theoretical link between supernovae and neutron stars, and have revealed the wide range of properties with which newborn compact remnants are endowed. We review here our current state of knowledge regarding neutron star-supernova remnant associations, pointing out the pitfalls and the promise which such links hold. We discuss work on the ranges of neutron star velocities, initial spin periods, and magnetic field strengths, as well as on the prevalence of pulsar wind nebulae. The slots in neutron star demography held by AXPs, SGRs, radio-quiet neutron stars, and other denizens of the zoo are considered. We also present an attempt at a comprehensive census of neutron star-remnant associations and discuss the selection effects militating against finding more such relationships. We conclude that there is no pressing need to invoke large black hole or silent neutron star populations, and that the years ahead hold great promise for producing a more complete understanding of neutron star birth parameters and their subsequent evolution.

Kaspi, V. M.; Helfand, D. J.

39

Properties of Neutron Star Critical Collapses  

NASA Astrophysics Data System (ADS)

Critical phenomena in gravitational collapse opened a new mathematical vista into the theory of general relativity and may ultimately entail fundamental physical implication in observations. However, at present, the dynamics of critical phenomena in gravitational collapse scenarios are still largely unknown. My thesis seeks to understand the properties of the threshold in the solution space of the Einstein field equations between the black hole and neutron star phases, understand the properties of the neutron star critical solution and clarify the implication of these results on realistic astrophysical scenarios. We develop a new set of neutron star-like initial data to establish the universality of the neutron star critical solution and analyze the structure of neutron star and neutron star-like critical collapses via the study of the phase spaces. We also study the different time scales involved in the neutron star critical solution and analyze the properties of the critical index via comparisons between neutron star and neutron star-like initial data. Finally, we explore the boundary of the attraction basin of the neutron star critical solution and its transition to a known set of non-critical fixed points.

Wan, Mew-Bing

2010-01-01

40

From Nuclei to Neutron Stars  

NASA Astrophysics Data System (ADS)

I will describe recent theoretical advances in nuclear structure and nuclear astrophysics that have been instrumental in unraveling the connections between nuclear physics and astrophysics. The role of nuclei, neutrino processes, and the states of matter at extreme density, in nucleosynthesis, supernova explosions and neutron star phenomena are not only known to be important, but we now understand specific correlations between the underlying nuclear physics and astrophysical observations. These developments are impacting and benefiting from both terrestrial nuclear experiments and astrophysical observations. I will discuss this interplay and explore how this synergy will help forge the path forward to develop a quantitative theory for dense systems, from nuclei to neutron stars. I highlight advances in describing strongly coupled many-body systems and discuss the emerging connections between nuclear structure, dense matter and cold-atom physics.

Reddy, Sanjay

2007-10-01

41

Band structure effects for dripped neutrons in neutron star crust  

Microsoft Academic Search

The outer layers of a neutron star are supposed to be formed of a solid Coulomb lattice of neutron rich nuclei. At densities above neutron drip density (about one thousandth of nuclear saturation density), this lattice is immersed in a neutron fluid. Bragg scattering of those dripped neutrons by the nuclei which has been usually neglected is investigated, within a

Nicolas Chamel

2005-01-01

42

Evolution of Neutron Stars and Observational Constraints  

NASA Astrophysics Data System (ADS)

The structure and evolution of neutron stars is discussed with a view towards constraining the properties of high density matter through observations. The structure of neutron stars is illuminated through the use of several analytical solutions of Einstein’s equations which, together with the maximally compact equation of state, establish extreme limits for neutron stars and approximations for binding energies, moments of inertia and crustal properties as a function of compactness. The role of the nuclear symmetry energy is highlighted and constraints from laboratory experiments such as nuclear masses and heavy ion collisions are presented. Observed neutron star masses and radius limits from several techniques, such as thermal emissions, X-ray bursts, gammaray flares, pulsar spins and glitches, spin-orbit coupling in binary pulsars, and neutron star cooling, are discussed. The lectures conclude with a discusson of proto-neutron stars and their neutrino signatures.

Lattimer, J.

2010-10-01

43

White Dwarfs, Neutron Stars and Black Holes  

ERIC Educational Resources Information Center

|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)|

Szekeres, P.

1977-01-01

44

Neutron Stars and Pulsars (IAU S291)  

NASA Astrophysics Data System (ADS)

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

van Leeuwen, Joeri

2013-04-01

45

Post-Newtonian diagnosis of quasiequilibrium configurations of neutron star-neutron star and neutron star-black hole binaries  

SciTech Connect

We use a post-Newtonian diagnostic tool to examine numerically generated quasiequilibrium initial data sets for nonspinning double neutron star and neutron star-black hole binary systems. The post-Newtonian equations include the effects of tidal interactions, parametrized by the compactness of the neutron stars and by suitable values of 'apsidal' constants, which measure the degree of distortion of stars subjected to tidal forces. We find that the post-Newtonian diagnostic agrees well with the double neutron star initial data, typically to better than half a percent except where tidal distortions are becoming extreme. We show that the differences could be interpreted as representing small residual eccentricity in the initial orbits. In comparing the diagnostic with preliminary numerical data on neutron star-black hole binaries, we find less agreement.

Berti, Emanuele; Iyer, Sai; Will, Clifford M. [McDonnell Center for the Space Sciences, Department of Physics, Washington University, St. Louis, Missouri 63130 (United States)

2008-01-15

46

Superfluidity in the Core of Neutron Stars  

NASA Astrophysics Data System (ADS)

The year (1958) after the publication of the BCS theory, Bohr, Mottelson & Pines showed that nuclei should also contain superfluid neutrons and superconducting protons. In 1959, A. Migdal proposed that neutron superfluidity should also occur in the interior of neutron stars. Pairing in nuclei forms Cooper pairs with zero spin, but the relevant component of the nuclear interaction becomes repulsive at densities larger than the nuclear matter density. It has been proposed that neutron-neutron interaction in the spin-triplet state, and L=1 orbital angular momentum, that is known to be attractive from laboratory experiments, may result in a new form of neutron superfluidity in the neutron star interior. I will review our present understanding of the structure of neutron stars and describe how superfluidity strongly affects their thermal evolution. I will show how a ``Minimal Model'' that excludes the presence of ``exotic'' matter (Bose condensates, quarks, etc.) is compatible with most observations of the surface temperatures of young isolated neutron stars in the case this neutron superfluid exists. Compared to the case of isotropic spin-zero Cooper pairs, the formation of anisotropic spin-one Cooper pairs results in a strong neutrino emission that leads to an enhanced cooling of neutron stars after the onset of the pairing phase transition and allows the Minimal Cooling scenario to be compatible with most observations. In the case the pairing critical temperature Tc is less than about 6 x10^8 K, the resulting rapid cooling of the neutron star may be observable. It was recently reported that 10 years of Chandra observations of the 333 year young neutron star in the Cassiopeia A supernova remnant revealed that its temperature has dropped by about 5%. This result indicates that neutrons in this star are presently becoming superfluid and, if confirmed, provides us with the first direct observational evidence for neutron superfluidity at supra-nuclear densities.

Page, Dany

2013-04-01

47

Make a Quake  

NSDL National Science Digital Library

When quakes strike urban areas, the toll in life and property can be great. Luckily, scientists have been working to uncover safer methods of construction and new structural techniques that "mitigate" the effects of earthquakes. In this simple simulation, you choose the ground on which to erect your building and which quake-proofing technological prevention to employ. You can then subject your building to three levels of intensity and see how it stands up.

2010-01-01

48

Planetary Systems Around Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

Wolszczan, Alexander

1997-01-01

49

Gravitational Waves from Low Mass Neutron Stars  

NASA Astrophysics Data System (ADS)

Recently, using large scale molecular dynamics simulations, we determined that neutron star crust is very strong, some 10 billion times stronger than steel [1]. This makes star crust the strongest material known and it can support relatively large ``mountains''. These bumps on rapidly rotating neutron stars can radiate strong gravitational waves (GW). Therefore, we strongly encourage ongoing and future searches for continuous GW. In the present paper, we speculate that low mass neutron stars, although they may be difficult to produce, could be even stronger GW sources. We find that the crust can support very large ellipticities (fractional differences in moments of inertia) of 0.001 or even larger in low mass neutron stars. This is because a larger fraction of a low mass neutron star is solid crust compared to a 1.4 solar mass star and because the weaker gravity allows the crust to support even larger mountains. Therefore, if low mass neutron stars can be produced, for example via fragmentation during a neutron star merger, then they could produce very strong continuous gravitational waves. [4pt] [1] C. J. Horowitz and K. Kadau, Phys. Rev. Lett. 102:191102,2009. )

Horowitz, C. J.

2010-02-01

50

The Stratified Model of Neutron Star  

Microsoft Academic Search

It is well known that distribution of density of hadron matter in neutron star interior is stratified. In proposal model, the structure of neutron star is treat like the stiff core surrounded by dynamical layer. The underlying physical assumption is that stellar matter of outer layers has elastic properties and its dynamical behavior is described by nuclear elastodynamics equations. It

V. Papoyan; S. Bastrukov; D. Podgayni

1998-01-01

51

Neutron Star Kicks: Mechanisms and Observational Constraints  

Microsoft Academic Search

Observations over the last decade have shown that neutron stars (NSs) receive a kick velocity (of order a hundred to a thousand km s-1) at birth. The physical origin of the kicks and the related supernova asymmetry is an unsolved problem. We study observational constraints on kicks for isolated pulsars and for neutron stars in binary systems. For several young

Dong Lai; Chen Wang; Jinlin Han

2006-01-01

52

On the Maximum Mass of Neutron Stars  

NASA Astrophysics Data System (ADS)

One of the most intriguing questions about neutron stars concerns their maximum mass. The answer is intimately related to the properties of matter at densities far beyond that found in heavy atomic nuclei. The current view on the internal constitution of neutron stars and on their maximum mass, both from theoretical and observational studies, are briefly reviewed.

Chamel, N.; Haensel, P.; Zdunik, J. L.; Fantina, A. F.

2013-07-01

53

Close binary neutron star systems  

NASA Astrophysics Data System (ADS)

We present a method to calculate solutions to the initial value problem in (3 + 1) general relativity corresponding to binary neutron-star systems (BNS) in irrotational quasi-equilibrium orbits. The initial value equations are solved using a conformally flat spatial metric tensor. The stellar fluid dynamics corresponds to that of systems with zero vorticity in the inertial reference frame. Irrotational systems like the ones analyzed in the present work are likely to resemble the final stages of the evolution of neutron-star binaries, thus providing insights on the inspiral process. The fluid velocity is derived from the gradient of a scalar potential. A numerical program was developed to solve the elliptic equations for the metric fields and the fluid velocity potential. We discuss the different numerical techniques employed to achieve high resolution across the stellar volume, as well as the methods used to find solutions to the Poisson-like equations with their corresponding boundary conditions. We present sequences of quasi-stable circular orbits which conserve baryonic mass. These sequences mimic the time evolution of the inspiral and are obtained without solving the complex evolution equations. They also provide sets of initial value data for future time evolution codes, which should be valid very close to the final merger. We evaluate the emission of gravitational radiation during the evolution through multipole expansions methods.

Marronetti, Pedro

1999-12-01

54

Asteroseismic model of paramagnetic neutron star  

Microsoft Academic Search

We investigate an asteroseismic model of non-rotating paramagnetic neutron star with core-crust stratification of interior pervaded by homogeneous internal and dipolar external magnetic field, presuming that neutron degenerate Fermi-matter of the star core is in the state of Pauli's paramagnetic permanent magnetization caused by polarization of spin magnetic moments of neutrons along the axis of magnetic field of collapsed massive

S. I. Bastrukov; I. V. Molodtsova; H.-K. Chang; J. Takata

2009-01-01

55

Symmetry Energy, Neutron Star Crust and Neutron Skin Thickness  

NASA Astrophysics Data System (ADS)

We analyze the correlations of the slope and curvature parameters of the symmetry energy with the neutron skin thickness of neutron-rich isotopes, and the crust-core transition density in neutron stars. The results are obtained within the microscopic Brueckner-Hartree-Fock approach, and are compared with those obtained with several Skyrme and relativistic mean field models.

Vidaña, Isaac; Providência, Constança; Polls, Artur; Rios, Arnau

2011-05-01

56

Probing the interiors of accreting neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars in low mass X-ray binaries accrete hydrogen and helium from a low mass companion. The neutron star can be observed directly in X-rays during periods of quiescence, when accretion switches off, or during thermonuclear X-ray bursts which result from unstable thermonuclear burning of the accreted matter. Recent long term monitoring observations of these systems have revealed new types of long duration X-ray bursts resulting from unstable burning of thick helium or carbon layers. The properties of these long bursts are sensitive to the heat flux emerging from deep in the star, and therefore give a new way to probe neutron star cooling. I discuss the current constraints on the neutrino emissivity of the stellar core, and the dense matter interior, including the possibility that these stars are in fact strange stars.

Cumming, Andrew

2006-10-01

57

Appearance of hyperons in neutron stars  

SciTech Connect

By employing a recently constructed hyperon-nucleon potential the equation of state of {beta}-equilibrated and charge neutral nucleonic matter is calculated. The hyperon-nucleon potential is a low-momentum potential which is obtained within a renormalization group framework. Based on the Hartree-Fock approximation at zero temperature the densities at which hyperons appear in neutron stars are estimated. For several different bare hyperon-nucleon potentials and a wide range of nuclear matter parameters it is found that hyperons in neutron stars are always present. These findings have profound consequences for the mass and radius of neutron stars.

Dapo, H. [Institut fuer Kernphysik, TU Darmstadt, Schlossgartenstr. 9, D-64289 Darmstadt (Germany); Schaefer, B.-J. [Institut fuer Physik, Karl-Franzens-Universitaet Graz, Universitaetsplatz 5, A-8010 Graz (Austria); Wambach, J. [Institut fuer Kernphysik, TU Darmstadt, Schlossgartenstr. 9, D-64289 Darmstadt (Germany); Gesellschaft fuer Schwerionenforschung mbH, Planckstr. 1, D-64291 Darmstadt (Germany)

2010-03-15

58

Stellar Wind Disruption by an Orbiting Neutron Star: Neutron Star Close-up  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. The large scale structure seen in the accretion wake is powered by the release of gravitational potential energy near the surface of the neutron star. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

59

Neutron star cooling: effects of envelope physics  

SciTech Connect

Neutron star cooling calculations are reported which employ improved physics in the calculation of the temperature drop through the atmosphere. The atmosphere microphysics is discussed briefly. The predicted neutron star surface temperatures, in the interesting interval 200 less than or equal to t (yr) less than or equal to 10/sup 5/, do not differ appreciably from the earlier results of Van Riper and Lamb (1981) for a non-magnetic star; for a magnetic star, the surface temperature is lower than in the previous work. Comparison with observational limits show that an exotic cooling mechanism, such as neutrino emission from a pion condensate or in the presence of percolating quarks, is not required unless the existence of a neutron star in the Tycho or SN1006 SNRs is established.

Van Riper, K.A.

1982-01-01

60

Neutron rich matter, neutron stars, and their crusts  

NASA Astrophysics Data System (ADS)

Neutron rich matter is at the heart of many fundamental questions in Nuclear Physics and Astrophysics. What are the high density phases of QCD? Where did the chemical elements come from? What is the structure of many compact and energetic objects in the heavens, and what determines their electromagnetic, neutrino, and gravitational-wave radiations? Moreover, neutron rich matter is being studied with an extraordinary variety of new tools such as Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that is using parity violation to measure the neutron radius in 208Pb. This has important implications for neutron stars and their crusts. Using large scale molecular dynamics, we model the formation of solids in both white dwarfs and neutron stars. We find neutron star crust to be the strongest material known, some 10 billion times stronger than steel. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, we describe a new equation of state for supernova and neutron star merger simulations based on the Virial expansion at low densities, and large scale relativistic mean field calculations.

Horowitz, C. J.

2011-09-01

61

pi-condensation and neutron star cooling  

Microsoft Academic Search

We show, within the context of an independent particle model, that pi- condensation should occur in neutron stars having baryon densities exceeding~0.4 - 0.5 fm-3. This high concentration of pi- implies a very fast cooling rate for `hot' neutron stars. Work supported by the Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under AFOSR

J. Kogut; J. T. Manassah

1972-01-01

62

Statified model of a neutron star  

Microsoft Academic Search

Evolutionary calculations based on realistic equations of state indicate the stratified nature of the distribution of hadron\\u000a matter in the interiors of neutron stars. In the proposed model, the stratified structure of a neutron star is treated as\\u000a a rigid inert core surrounded by a dynamical layer. The physical basis for the model is the concept of the stellar matter

S. I. Bastrukov; V. V. Papoyan; D. V. Podgainyi

1999-01-01

63

Radiative falloff in neutron star spacetimes  

NASA Astrophysics Data System (ADS)

We systematically study the late-time tails of scalar waves propagating in neutron star spacetimes. We consider uniform density neutron stars, for which the background spacetime is analytic and the compaction of the star can be varied continuously between the Newtonian limit 2M/R<<1 and the relativistic Buchdahl limit 2M/R=8/9. We study the reflection of a finite wave packet off neutron stars of different compactions 2M/R and find that a Newtonian, an intermediate, and a highly relativistic regime can be clearly distinguished. In the highly relativistic regime, the reflected signal is dominated by quasi-periodic peaks, which originate from the wave packet bouncing back and forth between the center of the star and the maximum of the background curvature potential at R~3M. Between these peaks, the field decays according to a power law. In the Buchdahl limit 2M/R-->8/9 the light travel time between the center and the maximum or the curvature potential grows without bound, so that the first peak arrives only at infinitely late time. The modes of neutron stars can therefore no longer be excited in the ultra-relativistic limit, and it is in this sense that the late-time radiative decay from neutron stars loses all its features and gives rise to power-law tails reminiscent of Schwarzschild black holes.

Pavlidou, Vasiliki; Tassis, Konstantinos; Baumgarte, Thomas W.; Shapiro, Stuart L.

2000-10-01

64

Thermal Evolution of Neutron Stars: Current Status  

NASA Astrophysics Data System (ADS)

Since the first detection of thermal radiation directly from the stellar surface of four pulsars by ROSAT, number of neutron stars with detected thermal radiation has increased significantly. By carefully analyzing the data and comparing the results with thermal evolution theories, we now have realistic hope for exploring the composition of ultrahigh density matter. Currently, the data of Vela pulsar already suggest that the core of high mass neutron stars should include such exotic particles as hyperons and/or pion condensates. However, to confirm such possibilities, more such data for more pulsars are badly needed. Fortunately, it was found recently that soft X-ray transients (SXT) in low-mass X-ray binaries (LMXB) can provide additional such extra data when they are in quiescence. These data helped us better understand the composition of neutron star crusts and atmospheres also. From careful analysis of the very recent data from very long Chandra observations of the neutron star in Cassiopeia A (Cas A) supernova remnant, its temperature, not just the upper limit, was determined. Moreover, further analysis of its archival data from observations over long period of time (˜ 10 years), has led to the striking finding that this neutron star is cooling rapidly. Its implication could help us reach deeper insight to the nature of neutron stars. We will summarize these developments, and emphasize those future observatories such as ASTRO-H will mean breakthroughs in this exciting area.

Tsuruta, S.

2011-12-01

65

Gamma-Ray Bursts from Decompressing Neutron Star Material()  

Microsoft Academic Search

We explore the possibility that decompressing neutron star material may be a source for the isotropic gamma-ray bursts observed by the Compton Gamma Ray Observatory. Such material might be ejected during the collision or tidal disruption of a neutron star in a binary sytem or as a result of neutron star seismic activity. Without gravitational confinement, this extremely neutron-rich material

G. J. Mathews; M. B. Aufderheide; M. T. Ressell; R. D. Rogers; B. S. Meyer; D. N. Schramm

1992-01-01

66

Limiting rotational period of neutron stars  

SciTech Connect

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

Glendenning, N.K. (Nuclear Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 (United States))

1992-11-15

67

Limiting rotational period of neutron stars  

NASA Astrophysics Data System (ADS)

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

Glendenning, Norman K.

1992-11-01

68

Cooling of neutron stars with hyperons  

SciTech Connect

One of the greatest difficulties encountered in the study of neutron stars lies in the connection between the observed properties of the stars and their interior physics. This difficulty is two-fold: on the one hand, measurements associated with the pulsed emission from pulsars and x-ray binaries are sensitive to details of emission and accretion mechanisms and consequently, depend more upon the surface properties of neutron stars than their interior properties. On the other hand, even where a dependence upon interior conditions can be established, this dependence is often masked by other considerations and typically involves just the overall M vs. R relation, which is not particularly sensitive to the detailed composition of the star. In contrast with pulsed emission phenomena, the possibility of detecting unpulsed blackbody x-rays from neutron star surfaces provides a more direct and fairly sensitive probe of interior conditions. Detection of such radiation allows one to establish a surface temperature for the star (assuming a particular value for the radius), which through solutions of the general relativistic heat transport equations in the crust, provides an estimate of the interior temperature. Because young neutron stars cool primarily by means of neutrino emission from the interior, the latter quantity is rather sensitive to the interior equation of state.

Maxwell, O.V.

1984-11-01

69

HYPERACCRETING NEUTRON STAR DISKS AND NEUTRINO ANNIHILATION  

SciTech Connect

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

Zhang Dong; Dai, Z. G., E-mail: dongzhanghz@gmail.co, E-mail: dzg@nju.edu.c [Department of Astronomy, Nanjing University, Nanjing 210093 (China)

2009-09-20

70

Three-body force effect on P3 F2 neutron superfluidity in neutron matter, neutron star matter, and neutron stars  

NASA Astrophysics Data System (ADS)

We investigate the effect of microscopic three-body forces on the P3 F2 neutron superfluidity in neutron matter, ?-stable neutron star matter, and neutron stars by using the BCS theory and the Brueckner-Hartree-Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon-nucleon interaction. We have concentrated on studying the three-body force effect on the P3 F2 neutron pairing gap. It is found that the three-body force effect considerably enhances the P3 F2 neutron superfluidity in neutron star matter and neutron stars.

Zuo, W.; Cui, C. X.; Lombardo, U.; Schulze, H.-J.

2008-07-01

71

Outer crust of nonaccreting cold neutron stars  

NASA Astrophysics Data System (ADS)

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.

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

2006-03-01

72

Formation and evolution of neutron star binaries.  

NASA Astrophysics Data System (ADS)

The high mass X-ray binaries (HMXB) represent a normal stage in the evolution of high mass binary systems, since due to the effects of mass transfer high mass binaries in general are not expected to be disrupted by the supernova explosion of the initially most massive component. The formation rate of neutron stars in high mass binaries in the Galaxy is estimated to be (3 - 4.5)×10-3yr-1. Roughly half of these systems will later on evolve into "standard" HMXB, the other half into Be/X-ray binaries. The number of Be/X-binaries in the Galaxy is estimated to be about 2×104. During their later evolution all standard HMXB and about half of the Be/X-ray binaries are expected to merge and form Thorne-Zytkow stars. In the other half of the Be/X-ray binaries (systems with P ? 100d) the neutron star will not completely spiral into its companion and a very close binary consisting of the neutron star and the heavy-element core of its companion will remain. Since the latter core is in most cases less massive than 4 Msun, its collapse to a neutron star, in the second supernova explosion, will in most cases not unbind the systems, and a close eccentric-orbit neutron star binary with an orbital period 1.5 - 12 hr will remain. These systems will later on merge due to the emission of gravitational radiation. The birthrate of these double neutron star binaries (which will all merge within a few billion years after their birth) in the Galaxy is conservatively estimated to be (4 - 8)×10-5yr-1.

van den Heuvel, E. P. J.

73

Dissipative processes in superfluid neutron stars  

SciTech Connect

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.

Mannarelli, Massimo [Departament d'Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos (ICCUB), Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); Colucci, Giuseppe [Universita di Bari, I-70126 Bari, Italia and .N.F.N., Sezione di Bari, I-70126 Bari (Italy); Manuel, Cristina [Instituto de Ciencias del Espacio (IEEC/CSIC), Campus Universitat Autonoma de Barcelona, Facultat de Ciencies, Torre C5 E-08193 Bellaterra (Barcelona) (Spain)

2011-05-23

74

The Mystery of the Lonely Neutron Star  

NASA Astrophysics Data System (ADS)

The VLT Reveals Bowshock Nebula around RX J1856.5-3754 Deep inside the Milky Way, an old and lonely neutron star plows its way through interstellar space. Known as RX J1856.5-3754 , it measures only ~ 20 km across. Although it is unusually hot for its age, about 700,000 °C, earlier observations did not reveal any activity at all, contrary to all other neutron stars known so far. In order to better understand this extreme type of object, a detailed study of RX J1856.5-3754 was undertaken by Marten van Kerkwijk (Institute of Astronomy of the University of Utrecht, The Netherlands) and Shri Kulkarni (California Institute of Technology, Pasadena, California, USA). To the astronomers' delight and surprise, images and spectra obtained with the ESO Very Large Telescope (VLT) now show a small nearby cone-shaped ("bowshock") nebula. It shines in the light from hydrogen atoms and is obviously a product of some kind of interaction with this strange star. Neutron stars - remnants of supernova explosions Neutron stars are among the most extreme objects in the Universe. They are formed when a massive star dies in a "supernova explosion" . During this dramatic event, the core of the star suddenly collapses under its own weight and the outer parts are violently ejected into surrounding space. One of the best known examples is the Crab Nebula in the constellation Taurus (The Bull). It is the gaseous remnant of a star that exploded in the year 1054 and also left behind a pulsar , i.e., a rotating neutron star [1]. A supernova explosion is a very complex event that is still not well understood. Nor is the structure of a neutron star known in any detail. It depends on the extreme properties of matter that has been compressed to incredibly high densities, far beyond the reach of physics experiments on Earth [2]. The ultimate fate of a neutron star is also unclear. From the observed rates of supernova explosions in other galaxies, it appears that several hundred million neutron stars must have formed in our own galaxy, the Milky Way. However, most of these are now invisible, having since long cooled down and become completely inactive while fading out of sight. An unsual neutron star - RX J1856.5-3754 Some years ago, the X-ray source RX J1856.5-3754 was found by the German ROSAT X-ray satellite observatory. Later observations with the Hubble Space Telescope (cf. STScI-PR97-32 ) detected extremely faint optical emission from this source and conclusively proved that it is an isolated neutron star [3]. There is no sign of the associated supernova remnant and it must therefore be at least 100,000 years "old". Most interestingly, and unlike younger isolated neutron stars or neutron stars in binary stellar systems, RX J1856.5-3754 does not show any sign of activity whatsoever, such as variability or pulsations. As a unique member of its class, RX J1856.5-3754 quickly became the centre of great interest among astronomers. It apparently presented the first, very welcome opportunity to perform detailed studies of the structure of a neutron star, without the disturbing influence of ill-understood activity. One particular question arose immediately. The emission of X-rays indicates a very high temperature of RX J1856.5-3754 . However, from the moment of their violent birth, neutron stars are thought to lose energy and to cool down continuously. But then, how can an old neutron star like this one be so hot? One possible explanation is that some interstellar material, gas and/or dust grains, is being captured by its strong gravitational field. Such particles would fall freely towards the surface of the neutron star and arrive there with about half the speed of light. Since the kinetic energy of these particles is proportionate to the second power of the velocity, even small amounts of matter would deposit much energy upon impact, thereby heating the neutron star. The spectrum of RX J1856.5-3754 The new VLT study by van Kerkwijk and Kulkarni of RX J1856.5-3754 was first aimed at taking optical spectra, in order to study its s

2000-09-01

75

Magnetic field evolution of accreting neutron stars  

NASA Astrophysics Data System (ADS)

We discuss the effect of accretion on the evolution of the magnetic field of a neutron star and highlight the main unresolved issues. Charged, accreted matter is funneled towards the magnetic poles where it heats the stellar surface and alters its magnetic structure resulting in an overall reduction of the magnetic dipole moment. Mechanisms for accretion-induced field reduction include accelerated Ohmic decay, vortex-fluxoid interactions, and magnetic burial or screening. We discuss how these can be integrated into a global model and detail recent self-consistent, three-dimensional, magneto-hydrodynamic, calculations (using analytic Grad-Shafranov methods and the numerical solver ZEUS-MP) which incorporate global resistive instabilities. These models can explain why neutron stars in binaries have systematically lower magnetic dipole moments than isolated neutron stars. Finally we discuss applications including the evolution of accreting millisecond pulsars and type-I X-ray bursts, magnetars, and gravitational waves.

Payne, D. J. B.; Vigelius, M.; Melatos, A.

2008-10-01

76

Remarks concerning kaon condensation in neutron stars  

SciTech Connect

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

Wang Guohua; Fu Weijie [Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Liu Yuxin [Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (China)

2007-12-15

77

Physics in Strong Magnetic Fields Near Neutron Stars.  

ERIC Educational Resources Information Center

|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)|

Harding, Alice K.

1991-01-01

78

Pulse Profiles from Thermally Emitting Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

Turolla, R.; Nobili, L.

2013-05-01

79

Neutrino oscillations in neutron star matter  

NASA Astrophysics Data System (ADS)

Mazurek's (1979) hypothesis, that neutrino oscillations may be able to transfer leptonic, zero-point energy to baryons during the gravitational collapse of a massive star which ends in a stellar explosion, is discussed. Upon derivation of the characteristic lengths for neutrino oscillation propagation in vacuum and in extremely dense matter, it becomes evident that vacuum oscillations can be suppressed in dense matter and that they should therefore have no influence on the neutrino emission of neutron stars.

Haubold, H. J.

1982-03-01

80

Neutron stars observations as astrophysical probes  

NASA Astrophysics Data System (ADS)

Several aspects of observations of neutron stars and compact extragalactic radio sources are considered, with particular regard to their use in constraining certain astrophysical phenomena. A theoretical treatment of the pulse arrivel time analysis can be used to quantitatively probe noise processes affecting the pulsar period and the propagation of the radiation. Important constraints on the background of cosmological gravitational radiation can be derived from timing such pulsars. The thermal X-rays emitted from a warm neutron star, either cooling from its initial formation or heated by internal dissipation are considered. Constructing model atmospheres appropriate to such stars with various effective temperatures and elemental abundances, their emergent spectra and bolometric correction were calculated for observation bands of various X-ray satellites. It was concluded that the present limits on neutron star surface flux are even more constraining that those derived assuming that the spectra are blackbody. How this effects models of neutron star interiors, formation, and cooling are examined. The refraction of radio waves from pulsars and other compact sources by interstellar plasma is also studied.

Romani, Roger William

81

Gravitational wave background from rotating neutron stars  

NASA Astrophysics Data System (ADS)

The background of gravitational waves produced by the ensemble of rotating neutron stars (which includes pulsars, magnetars, and gravitars) is investigated. A formula for ?(f) (a function that is commonly used to quantify the background, and is directly related to its energy density) is derived, without making the usual assumption that each radiating system evolves on a short time scale compared to the Hubble time; the time evolution of the systems since their formation until the present day is properly taken into account. Moreover, the formula allows one to distinguish the different parts of the background: the unresolvable (which forms a stochastic background or confusion noise, since the waveforms composing it cannot be either individually observed or subtracted out of the data of a detector) and the resolvable. Several estimations of the background are obtained, for different assumptions on the parameters that characterize neutron stars and their population. In particular, different initial spin period distributions lead to very different results. For one of the models, with slow initial spins, the detection of the background by present or planned detectors can be rejected. However, other models do predict the detection of the background, that would be unresolvable, by the future ground-based gravitational wave detector ET. A robust upper limit for the background of rotating neutron stars is obtained; it does not exceed the detection threshold of two cross-correlated Advanced LIGO interferometers. If gravitars exist and constitute more than a few percent of the neutron star population, then they produce an unresolvable background that could be detected by ET. Under the most reasonable assumptions on the parameters characterizing a neutron star, the background is too faint to be detected. Previous papers have suggested neutron star models in which large magnetic fields (like the ones that characterize magnetars) induce big deformations in the star, which produce a stronger emission of gravitational radiation. Considering the most optimistic (in terms of the detection of gravitational waves) of these models, an upper limit for the background produced by magnetars is obtained; it could be detected by ET, but not by BBO or DECIGO. Simple approximate formulas to characterize both the total and the unresolvable backgrounds are given for the ensemble of rotating neutron stars, and, for completion, also for the ensemble of binary star systems.

Rosado, Pablo A.

2012-11-01

82

Baryon Superfluidity in Neutron Star Cores  

NASA Astrophysics Data System (ADS)

Whether hyperons admixed in neutron star cores could be superfluid or not is investigated by a realistic approach to take account of the information on YY and YN interactions from hypernuclear data. It is found that the ?-superfluid is surely realized, though in a restricted density region, and also the ?-- and ?--superfluids have a strong possibility to be realized. A comment is given to the influences of hyperon components on neutron superfluidity.

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

2003-04-01

83

The Influence of the ?-FIELD on Neutron Stars  

NASA Astrophysics Data System (ADS)

The effects of scalar-isovector meson ? field on the neutron star matter is investigated in the framework of relativistic mean field (RMF) theory. We find that the ?-field reduces the binding energy per baryon and enhances the strangeness contents of the neutron star. The moment of inertia of neutron stars is enhanced by including the ?-field.

Mi, A. J.; Zuo, W.; Li, A.

2008-02-01

84

Generalized equation of state for cold superfluid neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

85

Electromagnetic torques and alignment of neutron stars  

NASA Astrophysics Data System (ADS)

Certain consequences of the high magnetic field associated with a rotating neutron star were studied. A general equation for the electromagnetic torque on the star is formulated. This consists of two distinct contributions, i.e. a retardation torque and a magnetospheric torque acting on the star. The retardation torque results naturally from a mathematical treatment of the retardation correction to the magnetic field of the star. A torque obtained from a Taylor series expansion was identified as a third-order term and its component along the rotation axis is consistent with the classical decelerating torque known in the past. The magnetospheric torque which results from the currents in the magnetosphere, is identified and included in the calculation. There is, however, no anomalous effeect on the alignment and spindown rate of the star. The calculation is extended to the quadrupole moment of the star. It is found that there is no effective aligning torque or anomalous spindown effect from the rotating quadrupole field of the star. The alignment of the star and a possible twisting motion about the dipole moment of the star are discussed.

Ng, K. K.

86

Keplerian frequency of uniformly rotating neutron stars and strange stars  

NASA Astrophysics Data System (ADS)

Aims: We calculate Keplerian (mass shedding) configurations of rigidly rotating neutron stars and strange stars with crusts. We check the validity of the empirical formula for Keplerian frequency, f_K, proposed by Lattimer & Prakash, f_K(M)=C (M/M_?)1/2(R/10~km)-3/2, where M is the (gravitational) mass of the Keplerian configuration, R is the (circumferential) radius of the non-rotating configuration of the same gravitational mass, and C=1.04~kHz. Methods: Numerical calculations are performed using precise 2D codes based on the multi-domain spectral methods. We use a representative set of equations of state (EOSs) of neutron stars and quark stars. Results: We show that the empirical formula for f_K(M) holds within a few percent for neutron stars with realistic EOSs, provided 0.5~M_?neutron stars for an EOS, and C=C_NS=1.08~kHz. Similar precision is obtained for strange stars with 0.5~M_?star of the same mass, R_K(M)=a R(M), with a_NS? a_SS ? 1.44. The value of a_SS is very weakly dependent on the mass of the crust of the strange star. Both a values are smaller than the analytic value a_Roche=1.5 from the relativistic Roche model.

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

2009-08-01

87

A binary neutron star GRB model  

SciTech Connect

In this paper we present the preliminary results of a model for the production of gamma-ray bursts (GRBs) through the compressional heating of binary neutron stars near their last stable orbit prior to merger. Recent numerical studies of the general relativistic (GR) hydrodynamics in three spatial dimensions of close neutron star binaries (NSBs) have uncovered evidence for the compression and heating of the individual neutron stars (NSs) prior to merger 12. This effect will have significant effect on the production of gravitational waves, neutrinos and, ultimately, energetic photons. The study of the production of these photons in close NSBs and, in particular, its correspondence to observed GRBs is the subject of this paper. The gamma-rays arise as follows. Compressional heating causes the neutron stars to emit neutrino pairs which, in turn, annihilate to produce a hot electron-positron pair plasma. This pair-photon plasma expands rapidly until it becomes optically thin, at which point the photons are released. We show that this process can indeed satisfy three basic requirements of a model for cosmological gamma-ray bursts: (1) sufficient gamma-ray energy release ({gt}10{sup 51} ergs) to produce observed fluxes, (2) a time-scale of the primary burst duration consistent with that of a {open_quotes}classical{close_quotes} GRB ({approximately}10 seconds), and (3) the peak of the photon number spectrum matches that of {open_quotes}classical{close_quotes} GRB ({approximately}300 keV). {copyright} {ital 1998 American Institute of Physics.}

Wilson, J.R.; Salmonson, J.D. [University of California, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Wilson, J.R.; Mathews, G.J. [University of Notre Dame, Department of Physics, Notre Dame, Indiana 46556 (United States)

1998-05-01

88

High energy radiation from neutron stars  

SciTech Connect

Topics covered include young rapidly spinning pulsars; static gaps in outer magnetospheres; dynamic gaps in pulsar outer magnetospheres; pulse structure of energetic radiation sustained by outer gap pair production; outer gap radiation, Crab pulsar; outer gap radiation, the Vela pulsar; radioemission; and high energy radiation during the accretion spin-up of older neutron stars. 26 refs., 10 figs. (GHT)

Ruderman, M.

1985-04-01

89

Diffusive Nuclear Burning in Neutron Star Envelopes  

Microsoft Academic Search

We calculate the rate of hydrogen burning for neutron stars (NSs) with hydrogen atmospheres and an underlying reservoir of nuclei capable of proton capture. This burning occurs in the exponentially suppressed diffusive tail of H that extends to the hotter depths of the envelope where protons are rapidly captured. This process, which we call diffusive nuclear burning (DNB), can change

Philip Chang; Lars Bildsten

2003-01-01

90

Tidal Love Numbers of Neutron Stars  

SciTech Connect

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.

Hinderer, Tanja [Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States)], E-mail: tph25@cornell.edu

2008-04-20

91

Stellar Wind Disruption by an Orbiting Neutron Star  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

92

Oscillations of dissipative superfluid neutron stars  

SciTech Connect

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

Andersson, N.; Haskell, B. [School of Mathematics, University of Southampton, Southampton SO17 1BJ (United Kingdom); Glampedakis, K. [SISSA, via Beirut 2-4, 34014 Trieste (Italy); Theoretical Astrophysics, Auf der Morgenstelle 10, University of Tuebingen, Tuebingen D-72076 (Germany)

2009-05-15

93

The late stages of evolution of helium star-neutron star binaries and the formation of double neutron star systems  

Microsoft Academic Search

With a view to understanding the formation of double neutron-stars (DNS), we\\u000ainvestigate the late stages of evolution of helium stars with masses of 2.8 -\\u000a6.4 Msun in binary systems with a 1.4 Msun neutron-star companion. We found\\u000athat mass transfer from 2.8 - 3.3 Msun helium stars and from 3.3 - 3.8 Msun in\\u000avery close orbits (P_orb

J. D. M. Dewi; O. R. Pols

2003-01-01

94

Observational constrains on the EoS of neutron stars.  

NASA Astrophysics Data System (ADS)

In observations of neutron star Soft X-ray Transients (SXTs) in quiescence which allow for a spectral study, the spectrum was found to be well-fit by a neutron star atmosphere model (NSA) sometimes supplemented with a power-law component. Theories about the time averaged mass accretion rates in neutron star SXTs, the pycnonuclear reactions taking place in the neutron star crust combined with neutron star cooling theory predictions, yield a neutron star core temperature. This hot neutron star core, moderated by the neutron star atmosphere, is thought to be observed during the quiescent phase of neutron star SXTs. In theory, a NSA-fit provides means to measure the mass and radius of the neutron star and hence constrain the equation of state (EoS) of matter at supranuclear densities. In addition several neutron star SXTs so far remain undetected, constraining their cooling rate. I'll discuss the current state of the observations and indicate possible future observations that could help contrain the equation of state further.

Jonker, Peter

95

Probing thermonuclear burning on accreting neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one second the entire surface is burned, which is observable as a sharp rise in the emitted X-ray flux: a type I X-ray burst. Afterwards the neutron star surface cools down on a timescale of ten to one hundred seconds. During these bursts the surface of an accreting neutron star can be observed directly, which makes them instrumental for studying this type of stars. We have studied rare kinds of X-ray bursts. One such rare burst is the superburst, which lasts a thousand times longer than an ordinary burst. Superbursts are thought to result from the explosive burning of a thick carbon layer, which lies deeper inside the neutron star, close to a layer known as the crust. A prerequisite for the occurrence of a superburst is a high enough temperature, which is set by the temperature of the crust and the heat conductivity of the envelope. The latter is lowered by the presence of heavy elements that are produced during normal X-ray bursts. Using a large set of observations from the Wide Field Camera's onboard the BeppoSAX satellite, we find that, at high accretion rate, sources which do not exhibit normal bursts likely have a longer superburst recurrence time, than the observed superburst recurrence time of one burster. We analyze in detail the first superburst from a transient source, which went into outburst only 55 days before the superburst. Recent models of the neutron star crust predict that this is too small a time to heat the crust sufficiently for superburst ignition, indicating that the models need to be extended with a new heat source. Another rare phenomenon is the occurrence of bursts with recurrence times of less than 30 minutes. In a long set of observations of the source EXO 0748-676 we find for the first time triple bursts, where three bursts occur within 30 minutes. This time is too short to accrete new fuel for the next burst, which suggests that not all hydrogen and helium is burned during the first burst. Finally, using a hydrodynamic stellar evolution code we create a multi-zone numerical model of the neutron star envelope. For the first time we include mixing due to rotation and a rotationally induced magnetic field. We find that thermonuclear burning proceeds in a stable manner at a lower heat flux of the crust for models including mixing. This may explain the observed transition of stable to unstable burning at a lower mass accretion rate than models previously predicted.

Keek, L.

2008-12-01

96

Instabilities in Very Young Neutron Stars: Temperature  

NSDL National Science Digital Library

This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the temperature structure for 20 milliseconds after the shock stalls. The minimum temperature is approximately 1.35 MeV. The maximum temperature varies from 6 MeV at the beginning of the calculation to 10 MeV at the later times.

Oneil, Pamela; Fryxell, Bruce; Burrows, Adam

1994-02-12

97

Instabilities in Very Young Neutron Stars: Density  

NSDL National Science Digital Library

This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the density evolution for 20 milliseconds after the shock stalls. The density is plotted on a log scale. Values range from 10^9 gm-cm^3 at the outer boundary to 1.4 x 10^12 gm-cm^3 at the inner boundary.

Oneil, Pamela; Fryxell, Bruce; Burrows, Adam

1994-02-12

98

Frictional instabilities in neutron star interiors  

NASA Astrophysics Data System (ADS)

The neutron superfluid in an inner crust of neutron stars is thought to be weakly coupled to the crust (charged components) and responsible for the slow postglitch relaxation of the pulse frequency. The linear stability analysis predicts that the system of superfluid and crust coupled through a temperature-sensitive frictional interaction is unstable for the thermal and rotational disturbances when the internal temperature falls down below a critical value. We have calculated the thermal and rotational evolution of neutron stars directly including the superfluid-crust coupling in the fully nonlinear equations. The frictional instability sets in at the critical temperature as predicted from the linear analysis. The subsequent thermal and rotational is quite different from the evolution predicted by the previous models which assume the stable coupling between superfluid and crust. The neutron star exhibits a limit cycle-like behavior in which the temperature and the angular velocity difference between superfluid and crust oscillate. The temperature increase in a fraction of a cycle largely enhances friction between superfluid and crust, which causes so high a rate of the angular momentum transfer from the superfluid to the crust that the crust rotation is spun up. We suggest that the rotational behavior following the frictional instability may be responsible for an unusually large second derivative of the rotation rate observed in PSR 1620-26. We also discuss the other implications of our study on the pulsar observations.

Shibazaki, Noriaki; Mochizuki, Yuko

1995-01-01

99

QuakeTables: The Fault Database for QuakeSim  

NASA Astrophysics Data System (ADS)

The QuakeSim project will provide the first web-services based, interoperable environment for doing large-scale forward models for earthquake processes. Through a web-services based portal, QuakeSim provides global access to geologic reference models of faults and fault data, simple analysis tools, new parallel forward models, and visualization support. The database system for this project must manage a variety of types of earthquake science data and information, including real and simulated data, and pre-existing structured collections containing "validated" data from official sources such as U.S. and California Geological Surveys, and "non-validated" data sets such as Virtual California. The fault database component of QuakeSim is called QuakeTables. QuakeTables was developed using a basic public domain database management system (DBMS), MySQL, to be ported to a more fully functional relational DBMS. These systems support the definition, storage, access, and control of collections of structured data. To provide for the access and manipulation of heterogeneous data sources, the integration of information from such sources, and the structural organization and data mining of this data, QuakeTables employs techniques for wrapper-based information fusion to support data source access and integration. QuakeTables is searchable with annotated fault records from original sources. The QuakeSim team designed the fields that constitute the database records and provided a web-based interface that enables the submitting and accessing of those records. The fields include primary geologic and paleoseismic fault parameters (fault location/geometry, slip rate at measured location, measurements of co-seismic displacement, dates and locations of previous ruptures) as well as non-primary fault parameters such as names, segments and characteristic recurrence interval.

Grant, L. B.; Donnellan, A.; McLeod, D.; Pierce, M.; Chen, A. Y.; Gould, M.; Noriega-Carlos, G.; Paul, R.; Sung, S.; Ta, M. V.

2004-12-01

100

Neutron degeneracy and plasma physics effects on radiative neutron captures in neutron star crust  

NASA Astrophysics Data System (ADS)

We consider the astrophysical reaction rates for radiative neutron capture reactions (n,?) in the crust of a neutron star. The presence of degenerate neutrons at high densities (mainly in the inner crust) can drastically affect the reaction rates. Standard rates assuming a Maxwell-Boltzmann distribution for neutrons can underestimate the rates by several orders of magnitude. We derive simple analytical expressions for reaction rates at a variety of conditions with account for neutron degeneracy. We also discuss the plasma effects on the outgoing radiative transition channel in neutron radiative capture reactions and show that these effects can also increase the reaction rates by a few orders of magnitude. In addition, using detailed balance, we analyze the effects of neutron degeneracy and plasma physics on reverse (?,n) photodisintegration. We discuss the dependence of the reaction rates on temperature and neutron chemical potential and outline the efficiency of these reactions in the neutron star crust.

Shternin, P. S.; Beard, M.; Wiescher, M.; Yakovlev, D. G.

2012-07-01

101

Stochastic background from inspiralling double neutron stars  

SciTech Connect

We review the contribution of extra galactic inspiralling double neutron stars, to the LISA astrophysical gravitational wave foreground. Using recent fits of the star formation rate, we show that sources beyond z{sub *}=0.005 contribute to a truly continuous background, which may dominate the LISA instrumental noise in the range 3{approx_equal}10{sup -4}-1x10{sup -2} Hz and overwhelm the galactic WD-WD confusion noise at frequencies larger than {nu}{sub o}{approx_equal}2x10{sup -3}.

Regimbau, Tania [Dpt. ARTEMIS, Observatoire de la Cote d'Azur, BP 429 06304 Nice (France)

2007-02-15

102

Equation of state of neutron star crust and fusion reactions of neutron rich nuclei in accreting neutron stars  

NASA Astrophysics Data System (ADS)

The crust of a neutron star accounts for less than 1% of its mass, however any information of the core gets filtered by the crust. Additionally, a good understanding of the crust is important in order to understand the phenomenon of glitches, to construct models of neutron stars, and to predict order of magnitude of gravitational waves emitted by neutron stars. The crust is a Coulomb crystal formed by neutron rich ions arranged in a lattice of embedded in a relativistic background of electrons. Using the Wigner-Seitz approximation to model the structure of the crystal, I apply relativistic mean field formalism to calculate the composition and the equation of state of the crust of a cold, isolated neutron star. I find the average composition in the crust as a function of density and use the obtained Equation of State to model neutron stars. We also study fusion reactions in the crust of accreting neutron stars. These reactions are an important source of heat, and the depth at which these reactions occur is important to determine the temperature profile of the star. Fusion reactions depend strongly on the atomic number Z; nuclei with Z < 6 can fuse at low densities in the liquid ocean, however, nuclei with Z = 8 or higher may not burn until higher densities where the crust is solid and electron capture reactions result in neutron-rich nuclei. We calculate the astrophysical S factor for fusion reactions of neutron rich nuclei, including 24O+ 24O and 28Ne+28Ne, using a simple barrier penetration model. We calculate the rate of thermonuclear fusion for 24O+24O and find that 24O should burn at densities near 1011g/cm3. The energy released from this and similar reactions may be important for the temperature profile of the star.

Dussan, Helber

103

Nucleon Superfluidity in Asymmetric Nuclear Matter and Neutron Star Matter  

SciTech Connect

We have investigate the nucleon superfluidity in asymmetric nuclear matter and neutron star matter by using the Brueckner-Hartree-Fock approach and the BCS theory. We have predicted the isospin-asymmetry dependence of the nucleon superfluidity in asymmetric nuclear matter and discussed particularly the effect of microscopic three-body forces. It has been shown that the three-body force leads to a strong suppression of the proton {sup 1}S{sub 0} superfluidity in beta-stable neutron star matter. Whereas the microscopic three-body force is found to enhance remarkably the {sup 3}PF{sub 2} neutron superfluidity in neutron star matter and neutron stars.

Zuo Wei [Institute of Modern Physics, Chinese Academy of Science, Lanzhou 730000 (China); Lombardo, U. [Department of Physics and Astrophysics, Catania University, Via Santa Sofia 64, I-95123 (Italy)

2010-05-12

104

The Gravitational Constant, the Chandrasekhar Limit, and Neutron Star Masses  

Microsoft Academic Search

The Chandrasekhar mass limit sets the scale for the late evolutionary stages of massive stars, including the formation of neutron stars in core collapse supernovae. Because its value depends on the gravitational constant G, the masses of these neutron stars retain a record of past values of G. Using Bayesian statistical techniques, I show that measurements of the masses of

S. E. Thorsett

1996-01-01

105

Population synthesis of old neutron stars in the galaxy  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

2000-01-01

106

Population Synthesis of Old Neutron Stars in the Galaxy  

Microsoft Academic Search

The paucity of old, isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic, Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov

2000-01-01

107

The neutron star and black hole initial mass function  

Microsoft Academic Search

Using recently calculated models for massive stellar evolution and supernovae coupled to a model for Galactic chemical evolution, neutron star and black hole birth functions (number of neutron stars and black holes as a function of their mass) are determined for the Milky Way galaxy. For these stars that explode as Type II supernovae, the models give birth functions that

F. X. Timmes; S. E. Woosley; Thomas A. Weaver

1996-01-01

108

The Neutron Star and Black Hole Initial Mass Function  

Microsoft Academic Search

Using recently calculated models for massive stellar evolution and supernovae coupled to a model for Galactic chemical evolution, neutron star and black hole birth functions (number of neutron stars and black holes as a function of their mass) are determined for the Milky Way galaxy. For those stars that explode as Type II supernovae, the models give birth functions that

F. X. Timmes; S. E. Woosley; Thomas A. Weaver

1996-01-01

109

Tertiary nuclear burning - neutron star deflagration  

SciTech Connect

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. 26 references.

Michel, F.C.

1988-04-01

110

A dynamical description of neutron star crusts  

NASA Astrophysics Data System (ADS)

Neutron Stars are natural laboratories where fundamental properties of matter under extreme conditions can be explored. Modern nuclear physics input as well as many-body theories are valuable tools which may allow us to improve our understanding of the physics of those compact objects. In this work the occurrence of exotic structures in the outermost layers of neutron stars is investigated within the framework of a microscopic model. In this approach the nucleonic dynamics is described by a time-dependent mean field approach at around zero temperature. Starting from an initial crystalline lattice of nuclei at subnuclear densities the system evolves toward a manifold of self-organized structures with different shapes and similar energies. These structures are studied in terms of a phase diagram in density and the corresponding sensitivity to the isospin-dependent part of the equation of state and to the isotopic composition is investigated.

de la Mota, V.; Sébille, F.; Eudes, Ph

2013-03-01

111

Afterglow of a Binary Neutron Star Merger  

NASA Astrophysics Data System (ADS)

The merger of two neutron stars often results in a rapidly and differentially rotating hypermassive neutron star (HMNS). We show by numerical-relativity simulation that the magnetic-field profile around such HMNS is dynamically varied during its subsequent evolution, and as a result, electromagnetic radiation with a large luminosity ~0.1B 2 R 3? is emitted with baryons (B, R, and ? are poloidal magnetic-field strength at stellar surface, stellar radius, and angular velocity of an HMNS). The predicted luminosity of electromagnetic radiation, which is primarily emitted along the magnetic-dipole direction, is ~1047(B/1013 G)2(R/10 km)3(?/104 rad s-1) erg s-1, which is comparable to the luminosity of quasars.

Shibata, Masaru; Suwa, Yudai; Kiuchi, Kenta; Ioka, Kunihito

2011-06-01

112

FAST FOSSIL ROTATION OF NEUTRON STAR CORES  

SciTech Connect

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.

Melatos, A., E-mail: amelatos@unimelb.edu.au [School of Physics, University of Melbourne, Parkville, VIC 3010 (Australia)

2012-12-10

113

Magnetized Binary Neutron Star Merger Simulations  

NASA Astrophysics Data System (ADS)

We perform general relativistic magnetized binary neutron star (BNS) merger simulations. Our aim of this study is to explore a magnetic field amplification mechanism in BNS mergers and a final configuration of amplified magnetic field. Our main findings are that the magnetic field is amplified by the Kelvin Helmholtz instability at the merger and magneto rotational instability inside an accretion torus, which is formed after a remnant massive neutron star collapses to a black hole. The saturation energy of magnetic field is several percents of a kinetic energy of the accretion torus. Our result suggests that a long-term simulation with a high resolution is mandatory to explore the final state of magnetized BNS merger.

Kiuchi, K.; Kyutoku, K.; Hotokezaka, K.; Sekiguchi, Y.; Shibata, M.

2013-04-01

114

Steady spherical hypercritical accretion onto neutron stars  

SciTech Connect

The present study of hypercritical accretion flows onto neutron stars considers steady-state, spherically symmetric flows whose accretion rate range is characterized by the carrying away of gravitational-accretion energy by neutrinos. The models used encompass pair production, radiation diffusion, and general relativistic effects. While pair pressure dominates throughout the accretion envelope when accretion rates above about 100 solar masses/yr, radiation diffusion becomes important when the accretion rate falls below about 0.001 solar masses/yr. At the lower accretion rates, free fall toward the neutron-star surface stops and an extended, quasi-static, radiation pressure-supported envelope emerges which is probably dynamically unstable. 35 refs.

Houck, J.C.; Chevalier, R.A. (Virginia, University, Charlottesville (United States))

1991-07-01

115

Analysis of nonradial pulsations of a homogeneous neutron star  

Microsoft Academic Search

Nonradial pulsations of an isolated neutron star were studied in two continuum models — a self-gravitating spherical mass of an inviscid, incompressible fluid and an elastic Fermi continuum. A detailed analytical derivation of natural spheroidal and torsional oscillation frequencies of a neutron star of mass 1.4M? based on notions about neutron matter as an elastic Fermi continuum is given. A

S. I. Bastrukov; I. V. Molodtsova; A. A. Bukatina

1995-01-01

116

Internal Constitution of Neutron and Strange Stars  

Microsoft Academic Search

In the first of these two lectures I will discuss the rich constitution of neutron stars as a consequence of the Pauli principle which is engaged by the dominance of gravity over the nuclear force. Three especially interesting phenomena are discussed in this contect--(1) a mechanism for the formation of low-mass black holes distinct in their mass-range from the black

Norman K. Glendenning

1997-01-01

117

Natural MHD oscillations of a neutron star  

Microsoft Academic Search

Natural, low-frequency, hydromagnetic oscillations of an isolated, nonrotating neutron star, which are localized in the peripheral\\u000a crust, the structure of which is determined by the electron-nuclear plasma (the Ae phase), are studied. The plasma medium\\u000a of the outer crust is treated as a homogeneous, infinitely conducting, incompressible continuum, the motions of which are\\u000a determined by the equations of magnetohydrodynamics. In

S. I. Bastrukov; I. V. Molodtsova; V. V. Papoyan; D. V. Podgainyi

1997-01-01

118

Relativistic Superfluid Models for Rotating Neutron Stars  

Microsoft Academic Search

This article starts by providing an introductory overview of the theoretical mechanics of rotating neutron stars as developed\\u000a to account for the frequency variations, and particularly the discontinuous glitches, observed in pulsars. The theory suggests,\\u000a and the observations seem to confirm, that an essential role is played by the interaction between the solid crust and inner\\u000a layers whose superfluid nature

Brandon Carter

2001-01-01

119

Neutron star inner crust and symmetry energy  

NASA Astrophysics Data System (ADS)

The cell structure of clusters in the inner crust of a cold ?-equilibrium neutron star is studied within a Thomas-Fermi approach and compared with other approaches that include shell effects. Relativistic nuclear models are considered. We conclude that the symmetry energy slope L may have quite dramatic effefcts on the cell structure if it is very large or small. Rodlike and slablike pasta clusters have been obtained in all models except one with a large slope L.

Grill, Fabrizio; Providência, Constança; Avancini, Sidney S.

2012-05-01

120

Numerical relativity simulations of binary neutron stars  

NASA Astrophysics Data System (ADS)

We present a new numerical relativity code designed for simulations of compact binaries involving matter. The code is an upgrade of the BAM code to include general relativistic hydrodynamics and implements state-of-the-art high-resolution-shock-capturing schemes on a hierarchy of mesh refined Cartesian grids with moving boxes. We test and validate the code in a series of standard experiments involving single neutron star spacetimes. We present test evolutions of quasiequilibrium equal-mass irrotational binary neutron star configurations in quasicircular orbits which describe the late inspiral to merger phases. Neutron star matter is modeled as a zero-temperature fluid; thermal effects can be included by means of a simple ideal gas prescription. We analyze the impact that the use of different values of damping parameter in the Gamma-driver shift condition has on the dynamics of the system. The use of different reconstruction schemes and their impact in the post-merger dynamics is investigated. We compute and characterize the gravitational radiation emitted by the system. Self-convergence of the waves is tested, and we consistently estimate error bars on the numerically generated waveforms in the inspiral phase.

Thierfelder, Marcus; Bernuzzi, Sebastiano; Brügmann, Bernd

2011-08-01

121

Differential Rotation in Neutron Stars: Magnetic Braking and Viscous Damping  

Microsoft Academic Search

Differentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars, according to general relativity. The remnant of a binary neutron star merger may give rise to such a ``hypermassive'' object. While such a star may be dynamically stable against gravitational collapse and bar formation, the radial stabilization due to differential rotation is likely to

Stuart L. Shapiro

2000-01-01

122

Many faces of young neutron stars  

NASA Astrophysics Data System (ADS)

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

Vasisht, Gautam

123

Dynamics of dissipative multifluid neutron star cores  

NASA Astrophysics Data System (ADS)

We present a Newtonian multifluid formalism for superfluid neutron star cores, focusing on the additional dissipative terms which arise when one takes into account the individual dynamical degrees of freedom associated with the coupled “fluids.” The problem is of direct astrophysical interest as the nature of the dissipative terms can have significant impact on the damping of the various oscillation modes of the star and the associated gravitational-wave signatures. A particularly interesting application concerns the gravitational-wave driven instability of f- and r-modes. We apply the developed formalism to two specific three-fluid systems: (i) a hyperon core in which both ? and ?- hyperons are present and (ii) a core of deconfined quarks in the color-flavor-locked phase in which a population of neutral K0 kaons is present. The formalism is, however, general and can be applied to other problems in neutron-star dynamics (such as the effect of thermal excitations close to the superfluid transition temperature) as well as laboratory multifluid systems.

Haskell, B.; Andersson, N.; Comer, G. L.

2012-09-01

124

Neutron star spin-kick velocity correlation effect on binary neutron star coalescence rates and spin-orbit misalignment of the components  

Microsoft Academic Search

We study the effect of the neutron star spin-kick velocity alignment observed in young radio pulsars on the coalescence rate of binary neutron stars. Two scenarios are considered for neutron star formation: when the kick is always present, and when it is small or absent if a neutron star is formed in a binary system as a result of electron-capture

K. A. Postnov; A. G. Kuranov

2008-01-01

125

Neutron Star Astronomy with the HST  

NASA Astrophysics Data System (ADS)

Since its launch in 1990, HST has played a leading role in optical studies of isolated neutron stars, both radio-loud pulsars and radio-silent ones, paving the way to follow-up observations performed with 8 m-class telescopes, like the VLT, the Gemini, and Subaru. Here, I present the last results obtained mostly by the WFPC2, before its de-commissioning after the last refurbishment mission in May 2009, from the observations of the rotation-powered pulsars PSR B0540-69, PSR B1055-52 and of the central compact object 1E 1207.4-5209 in the PKS 1209-52 SNR.

Mignani, Roberto P.

2011-08-01

126

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

SciTech Connect

We investigate the equations of state for pure neutron matter and for nonstrange and strange hadronic matter in {beta} equilibrium, including {lambda},{sigma}, and {xi} hyperons. The masses and radii of these kinds of stars are obtained. For a pure neutron star, the maximum mass is about 1.8M{sub sun}, while for a strange (nonstrange) hadronic star in {beta} equilibrium, the maximum mass is around 1.45M{sub sun} (1.7M{sub sun}). The typical radii of pure neutron stars and strange hadronic stars are about 11.5-13.0 km and 11.5-12.5 km, respectively.

Wang, P.; Lawley, S. [Special Research Center for the Subatomic Structure of Matter (CSSM) and Department of Physics, University of Adelaide 5005 (Australia); Jefferson Laboratory, 12000 Jefferson Ave., Newport News, Virginia 23606 (United States); Leinweber, D.B.; Williams, A.G. [Special Research Center for the Subatomic Structure of Matter (CSSM) and Department of Physics, University of Adelaide 5005 (Australia); Thomas, A.W. [Jefferson Laboratory, 12000 Jefferson Ave., Newport News, Virginia 23606 (United States)

2005-10-01

127

On the Mass Distribution and Birth Masses of Neutron Stars  

NASA Astrophysics Data System (ADS)

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 ? and a dispersion of 0.24 M ?. 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 ?, but with a dispersion of only 0.05 M ?. 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 ? and a dispersion of 0.2 M ?, 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 ~2 M ? suggests that only a few of these neutron stars cross the mass threshold to form low-mass black holes.

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

2012-09-01

128

On the properties of matter in neutron stars  

Microsoft Academic Search

A review of recent developments in the description of neutron star matter is presented, and its relevance to pulsar observations is discussed. Some aspects of the accretion of matter on neutron stars are reviewed, and some of the relevant properties of binary X-ray sources are presented. This review is aimed at the astrophysicist. For a detailed review of the nuclear

Gerhard Börner

1973-01-01

129

Constraints on neutron star masses and radii from kilohertz QPOs  

SciTech Connect

The frequencies of the highest-frequency kilohertz QPOs recently discovered in some sixteen neutron stars in low-mass X-ray binary systems are most likely orbital frequencies. If so, these QPOs provide tight upper bounds on the masses and radii of these neutron stars and interesting new constraints on the equation of state of neutron star matter. If the frequency of a kilohertz QPO can be established as the orbital frequency of the innermost stable circular orbit, this would confirm one of the key predictions of general relativity in the strong-field regime. If the spin frequency of the neutron star can also be determined, the frequency of the QPO would fix the mass of the neutron star for each assumed equation of state. Here we describe how bounds on the stellar mass and radius can be derived and how these bounds are affected by the stellar spin. We also discuss detection of the innermost stable circular orbit.

Lamb, Frederick K. [University of Illinois at Urbana-Champaign, Department of Physics and Department of Astronomy, 1110 W. Green St., Urbana, Illinois 61801 (United States); Coleman Miller, M. [University of Chicago, Department of Astronomy and Astrophysics, 5640 S. Ellis Avenue, Chicago, Illinois 60637 (United States); Psaltis, Dimitrios [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts 20218 (United States)

1998-04-27

130

Shear modulus of neutron star crust  

NASA Astrophysics Data System (ADS)

The shear modulus of solid neutron star crust is calculated by the thermodynamic perturbation theory, taking into account ion motion. At a given density, the crust is modelled as a body-centred cubic Coulomb crystal of fully ionized atomic nuclei of one type with a uniform charge-compensating electron background. Classic and quantum regimes of ion motion are considered. The calculations in the classic temperature range agree well with previous Monte Carlo simulations. At these temperatures, the shear modulus is given by the sum of a positive contribution due to the static lattice and a negative ? T contribution due to the ion motion. The quantum calculations are performed for the first time. The main result is that at low temperatures the contribution to the shear modulus due to the ion motion saturates at a constant value, associated with zero-point ion vibrations. Such behaviour is qualitatively similar to the zero-point ion motion contribution to the crystal energy. The quantum effects may be important for lighter elements at higher densities, where the ion plasma temperature is not entirely negligible compared to the typical Coulomb ion interaction energy. The results of numerical calculations are approximated by convenient fitting formulae. They should be used for precise neutron star oscillation modelling, a rapidly developing branch of stellar seismology.

Baiko, D. A.

2011-09-01

131

A Neutron Star in F-sharp  

NASA Astrophysics Data System (ADS)

In ths commentary on the Hessels et al paper reporting the discovery of the shortest spin period millisecond pulsar (MSP) Ter5-ad in the globular cluster Terzan 5, I also point out a new explanation for possible minimum spin periods, P, of MSPs without requiring gravitational radiation (or other) slow-down torques. If the accretion of matter required to spinup a MSP also reduces (buries) the neutron star (NS) magnetic field, B, as commonly believed, an inverse correlation between neutron star mass, M, and B is expected together with a positive correlation between P and B. Both are suggested for the 4 MSPs with NS mass measures reported (Latimer and Prakash 2004, Science, 304, 536) to have <~10% uncertainties. The correlations imply the Ter5-ad NS has ~2.5 Msun, B ~5 x 10^7 G and thus Pdot ~3 x 10^-21 s/s which can be tested when a timing solution is found. If confirmed, the highest spin frequency NSs do not pulse simply because their B fields are too low.

Grindlay, Jonathan E.

2006-03-01

132

BINARY NEUTRON STARS IN QUASI-EQUILIBRIUM  

SciTech Connect

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.

Taniguchi, Keisuke [Department of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201 (United States); Shibata, Masaru [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan)

2010-05-15

133

Neutron star accretion and the neutrino fireball  

SciTech Connect

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.

Colgate, S.A. (Los Alamos National Lab., NM (United States)); Herant, M.E. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)); Benz, W. (Steward Observatory, Tucson, AZ (United States))

1991-11-26

134

Neutron star accretion and the neutrino fireball  

SciTech Connect

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.

Colgate, S.A. [Los Alamos National Lab., NM (United States); Herant, M.E. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Benz, W. [Steward Observatory, Tucson, AZ (United States)

1991-11-26

135

The Gravitational Constant, the Chandrasekhar Limit, and Neutron Star Masses  

Microsoft Academic Search

The Chandrasekhar mass limit sets the scale for the late evolutionary stages\\u000aof massive stars, including the formation of neutron stars in core collapse\\u000asupernovae. Because its value depends on the gravitational constant G, the\\u000amasses of these neutron stars retain a record of past values of G. Using\\u000aBayesian statistical techniques, I show that measurements of the masses of

S. E. Thorsett

1996-01-01

136

Advection of magnetic flux by accretion disks around neutron stars  

Microsoft Academic Search

The aim of our research is to address why millisecond pulsars have relatively weak surface magnetic fields, of about 10^8 G, with a narrow spread. We propose that the accretion of plasma from the companion star fully screens the original neutron star field, but the accretion disk carries additional magnetic flux from the companion star, or itself can generate field

S. Flores-Tulian; A. Reisenegger

2007-01-01

137

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

Microsoft Academic Search

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

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

2003-01-01

138

Relativistic tidal properties of neutron stars  

SciTech Connect

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.

Damour, Thibault; Nagar, Alessandro [Institut des Hautes Etudes Scientifiques, 91440 Bures-sur-Yvette (France); ICRANet, 65122 Pescara (Italy)

2009-10-15

139

Differential Rotation in Neutron Stars: Magnetic Braking and Viscous Damping  

Microsoft Academic Search

Diffferentially rotating stars can support significantly more mass in\\u000aequilibrium than nonrotating or uniformly rotating stars, according to general\\u000arelativity. The remnant of a binary neutron star merger may give rise to such a\\u000a``hypermassive'' object. While such a star may be dynamically stable against\\u000agravitational collapse and bar formation, the radial stabilization due to\\u000adifferential rotation is likely to

Stuart L. Shapiro

2000-01-01

140

Black hole-neutron star mergers at realistic mass ratios  

NASA Astrophysics Data System (ADS)

Black hole-neutron star mergers resulting in the disruption of the neutron star and the formation of an accretion disk and/or the ejection of unbound material are prime candidates for the joint detection of gravitational-wave and electromagnetic signals. Whether the disruption of the neutron star occurs or not depends on the parameters of the binary, and particularly on the mass ratio, the black hole spin, and the neutron star equation of state. The characteristics of the merger remnant, and thus of any post-merger electromagnetic signal, also vary widely with the parameters of the binary. Numerical simulations of black hole-neutron star mergers have generally considered fairly low mass black holes (M<7Msun), even though higher masses are favored by both population synthesis models and observations of X-ray binaries. In this talk, we will discuss numerical results for higher mass black holes (M˜10Msun), and in particular the conditions under which the neutron star disrupts, the ejection of unbound material, and the effects of both the neutron star radius and the black hole spin on the gravitational wave signal and the characteristics of the post-merger remnant.

Foucart, Francois; Deaton, Brett; Duez, Matthew; Kidder, Lawrence; MacDonald, Ilana; Ott, Christian; Pfeiffer, Harald; Scheel, Mark; Szilagyi, Bela; Teukolsky, Saul

2013-04-01

141

Compositional freeze-out of neutron star crusts  

NASA Astrophysics Data System (ADS)

We have investigated the crustal properties of neutron stars without fallback accretion. We have calculated the chemical evolution of the neutron star crust in three different cases (a modified Urca process without the thermal influence of a crust, a thick crust and a direct Urca process with a thin crust) in order to determine the detailed composition of the envelope and atmosphere as the nuclear reactions freeze out. Using a nuclear reaction network up to technetium, we calculate the distribution of nuclei at various depths of the neutron star. The nuclear reactions quench when the cooling time-scale is shorter than the inverse of the reaction rate. Trace light elements among the calculated isotopes may have enough time to float to the surface before the layer crystallizes and form the atmosphere or envelope of the neutron star. The composition of the neutron star envelope determines the total photon flux from the surface, and the composition of the atmosphere determines the emergent spectrum. Our calculations using each of the three cooling models indicate that without accretion of fallback the neutron star atmospheres are dependent on the assumed cooling process of the neutron star. Each of the cooling methods has different elements composing the atmosphere: for the modified Urca process, the atmosphere is 28Si, the thick crust has an atmosphere of 50Cr and the thin crust has an atmosphere of 40Ca. In all the three cases, the atmospheres are composed of elements which are lighter than iron.

Hoffman, Kelsey; Heyl, Jeremy

2009-12-01

142

Superfluid heat conduction and the cooling of magnetized neutron stars  

SciTech Connect

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

Cirigliano, Vincenzo [Los Alamos National Laboratory; Reddy, Sanjay [Los Alamos National Laboratory; Sharma, Rishi [Los Alamos National Laboratory; Aguilera, Deborah N [BUENOS AIRES

2008-01-01

143

Attributes of a rotating neutron star with a hyperon core  

SciTech Connect

We study the effect of rotation on the global properties of a neutron star with a hyperon core in an effective chiral model with varying nucleon effective masses within a mean-field approach. The resulting gross properties of the rotating compact star sequences are then compared and analyzed with other theoretical predictions and observations from neutron stars. The maximum mass of the compact star predicted by the model lies in the range of (1.4-2.4)M{sub {center_dot}} at Kepler frequency {omega}{sub K}, which is consistent with recent observations of high mass stars, thereby reflecting the sensitivity of the underlying nucleon effective mass in the dense matter equation of state. We also discuss the implications of the experimental constraints from the flow data from heavy-ion collisions on the global properties of rotating neutron stars.

Jha, T. K.; Mishra, H.; Sreekanth, V. [Theoretical Physics Division, Physical Research Laboratory, Navrangpura, Ahmedabad, India-380 009 (India)

2008-04-15

144

Attributes of a rotating neutron star with a hyperon core  

NASA Astrophysics Data System (ADS)

We study the effect of rotation on the global properties of a neutron star with a hyperon core in an effective chiral model with varying nucleon effective masses within a mean-field approach. The resulting gross properties of the rotating compact star sequences are then compared and analyzed with other theoretical predictions and observations from neutron stars. The maximum mass of the compact star predicted by the model lies in the range of (1.4-2.4)M? at Kepler frequency ?K, which is consistent with recent observations of high mass stars, thereby reflecting the sensitivity of the underlying nucleon effective mass in the dense matter equation of state. We also discuss the implications of the experimental constraints from the flow data from heavy-ion collisions on the global properties of rotating neutron stars.

Jha, T. K.; Mishra, H.; Sreekanth, V.

2008-04-01

145

The neutron star born in the Antlia supernova remnant  

NASA Astrophysics Data System (ADS)

Among all known young nearby neutron stars, we search for the neutron star that was born in the same supernova event that formed the Antlia supernova remnant (SNR). We also look for a runaway star that could have been the former companion to the neutron star (if it exists) and then got ejected due to the same supernova. We find the pulsar PSR J0630-2834 to be the best candidate for a common origin with the Antlia SNR. In that scenario, the SNR is ?1.2 Myr old and is presently located at a distance of ?138 pc. We consider the runaway star HIP 47155 a former companion candidate to PSR J0630-2834. The encounter time and place is consistent with both stars being ejected from the Antlia SNR. We measured the radial velocity of HIP 47155 as 32.42 ± 0.70 km s-1.

Tetzlaff, N.; Torres, G.; Neuhäuser, R.; Hohle, M. M.

2013-10-01

146

Testing Formulations with Binary Neutron Star Simulations  

NASA Astrophysics Data System (ADS)

New formulations for the evolution of gravitational fields in numerical relativity are continuously presented to the scientific community. Their main goal is to achieve stable and reliable evolutions of compact-object binaries. However, due to the complexity of the required numerical work, few of the many formulations found in the literature have been tested on binary evolutions. We introduce in this paper a new testing ground for numerical methods based on the simulation of binary neutron stars (BNS). Our objective is to benchmark new formalisms against the currently most stable simulations. BNS simulations usually require extensive computational resources and the length of the runs could, in principle, render these tests impractical. Here we show how small, low resolution grids can be used to gain insight into the stability of different numerical schemes, with runs that only take a few hours on single-processor workstations.

Marronetti, Pedro

2005-04-01

147

Resonant Shattering of Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

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 ˜1046-1047erg 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.

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

2012-01-01

148

Black-hole-neutron-star mergers: Disk mass predictions  

NASA Astrophysics Data System (ADS)

Determining the final result of black-hole-neutron-star mergers, and, in particular, the amount of matter remaining outside the black hole at late times and its properties, has been one of the main motivations behind the numerical simulation of these systems. Black-hole-neutron-star binaries are among the most likely progenitors of short gamma-ray bursts—as long as massive (probably a few percents of a solar mass), hot accretion disks are formed around the black hole. Whether this actually happens strongly depends on the physical characteristics of the system, and, in particular, on the mass ratio, the spin of the black hole, and the radius of the neutron star. We present here a simple two-parameter model, fitted to existing numerical results, for the determination of the mass remaining outside the black hole a few milliseconds after a black-hole-neutron-star merger (i.e., the combined mass of the accretion disk, the tidal tail, and the potential ejecta). This model predicts the remnant mass within a few percents of the mass of the neutron star, at least for remnant masses up to 20% of the neutron star mass. Results across the range of parameters deemed to be the most likely astrophysically are presented here. We find that, for 10M? black holes, massive disks are only possible for large neutron stars (RNS?12km), or quasiextremal black hole spins (aBH/MBH?0.9). We also use our model to discuss how the equation of state of the neutron star affects the final remnant, and the strong influence that this can have on the rate of short gamma-ray bursts produced by black-hole-neutron-star mergers.

Foucart, Francois

2012-12-01

149

Nuclei in Strongly Magnetised Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

We discuss the ground state properties of matter in outer and inner crusts of neutron stars under the influence of strong magnetic fields. In particular, we demonstrate the effects of Landau quantization of electrons on compositions of neutron star crusts. First we revisit the sequence of nuclei and the equation of state of the outer crust adopting the Baym, Pethick and Sutherland (BPS) model in the presence of strong magnetic fields and most recent versions of the theoretical and experimental nuclear mass tables. Next we deal with nuclei in the inner crust. Nuclei which are arranged in a lattice, are immersed in a nucleonic gas as well as a uniform background of electrons in the inner crust. The Wigner-Seitz approximation is adopted in this calculation and each lattice volume is replaced by a spherical cell. The coexistence of two phases of nuclear matter—liquid and gas, is considered in this case. We obtain the equilibrium nucleus corresponding to each baryon density by minimizing the free energy of the cell. We perform this calculation using Skyrme nucleon-nucleon interaction with different parameter sets. We find nuclei with larger mass and charge numbers in the inner crust in the presence of strong magnetic fields than those of the zero field case for all nucleon-nucleon interactions considered here. However, SLy4 interaction has dramatic effects on the proton fraction as well as masses and charges of nuclei. This may be attributed to the behaviour of symmetry energy with density in the sub-saturation density regime. Further we discuss the implications of our results to shear mode oscillations of magnetars.

Nandi, Rana; Bandyopadhyay, Debades

150

Neutron star formation in theoretical supernovae. Low mass stars and white dwarfs  

SciTech Connect

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. The conditions for which neutron stars form from accretion-induced collapse of white dwarfs in clsoe binary systems is also examined.

Nomoto, K.

1986-01-01

151

The Role of Helium Stars in the Formation of Double Neutron Stars  

Microsoft Academic Search

We have calculated the evolution of 60 model binary systems consisting of helium stars in the mass range of MHe=2.5-6Msolar with a 1.4 Msolar neutron star companion to investigate the formation of double neutron star systems. Orbital periods ranging from 0.09 to 2 days are considered, corresponding to Roche lobe overflow starting from the helium main sequence to after the

N. Ivanova; K. Belczynski; V. Kalogera; F. A. Rasio; R. E. Taam

2003-01-01

152

Relativistic effective interaction for nuclei, giant resonances, and neutron stars  

NASA Astrophysics Data System (ADS)

Nuclear effective interactions are useful tools in astrophysical applications especially if one can guide the extrapolations to the extremes regions of isospin and density that are required to simulate dense, neutron-rich systems. Isospin extrapolations may be constrained in the laboratory by measuring the neutron skin thickness of a heavy nucleus, such as Pb208. Similarly, future observations of massive neutron stars will constrain the extrapolations to the high-density domain. In this contribution we introduce a new relativistic effective interaction that is simultaneously constrained by the properties of finite nuclei, their collective excitations, and neutron-star properties. By adjusting two of the empirical parameters of the theory, one can efficiently tune the neutron skin thickness of Pb208 and the maximum neutron-star mass. We illustrate this procedure in response to the recent interpretation of x-ray observations by Steiner, Lattimer, and Brown that suggests that the FSUGold effective interaction predicts neutron-star radii that are too large and a maximum stellar mass that is too small. The new effective interaction is fitted to a neutron skin thickness in Pb208 of only Rn-Rp=0.16 fm and yields a moderately large maximum neutron-star mass of 1.94 M?.

Fattoyev, F. J.; Horowitz, C. J.; Piekarewicz, J.; Shen, G.

2010-11-01

153

Lev Landau and the concept of neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

154

Equation of State of Hypernuclear Matter and Neutron Stars  

NASA Astrophysics Data System (ADS)

These lectures contain a pedagogical introduction to the equation of state of nuclear matter and to the structure of neutron stars. Particular attention is devoted to the ?-equilibrium conditions and to the composition of neutron stars. The possible appearance of hyperons to reach the ?-equilibrium when the density increases is carefully analyzed. In general, the introduction of new degrees of freedom, such as for instance the hyperons, produces a softening of the equation of state and as a consequence the maximum mass of the neutron star decreases. Finally, relevant observational data are compared with microscopic predictions.

Rios, A.; Polls, A.; Ramos, A.; Vidaña, I.

155

A Second Neutron Star in M4?  

NASA Astrophysics Data System (ADS)

We show that the optical counterpart of the X-ray source CX 1 in M4 is a ~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). Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

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

2012-05-01

156

Resonant Shattering of Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

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. We also discuss the application of such shattering flares as electromagnetic counterparts to gravitational wave bursts from elliptic and parabolic encounters in dense star clusters.

Tsang, David; Read, J.; Hinderer, T.; Piro, A.

2013-01-01

157

The spin evolution of neutron stars with the superfluid core  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

158

Magnetic Interactions in Coalescing Neutron Star Binaries  

NASA Astrophysics Data System (ADS)

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

Piro, Anthony L.

2012-08-01

159

Physics of dense matter, neutron stars, and supernova  

SciTech Connect

Nuclear and astrophysical evidence on the equation of state of dense matter is examined. The role of hyperonization of matter in the development of proto-neutron stars is briefly discussed. 7 refs., 4 figs.

Glendenning, N.K.

1989-02-01

160

Solid state physics and cooling of neutron stars  

Microsoft Academic Search

First we show the possible effect of the ‘magnetic’ condensation on cooling of neutron stars. Its observational significance (especially for younger pulsars such as the Crab pulsar) is emphasized. Other effects of solid state physics on cooling are also discussed.

Sachiko Tsuruta

1975-01-01

161

Fundamental frequencies of elastic gravitational vibrations of a neutron star  

Microsoft Academic Search

The long wavelength vibrations of a homogeneous non-rotating neutron star are studied within the framework of the nuclear fluid-dynamics. The stellar continuum is modelled by incompressible hadronic matter with properties of an isotropic elastic solid. The equilibrium and large-scale dynamics of the neutron star is presumed to be dominated by Newtonian self-gravtiy. The eigenfrequencies of spheroidal and torsional elastic-gravitational vibrations

S. I. Bastrukov; E. N. Piliugin

1993-01-01

162

Phase separation in the crust of accreting neutron stars  

SciTech Connect

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.

Horowitz, C. J.; Berry, D. K.; Brown, E. F. [Department of Physics and Nuclear Theory Center, Indiana University, Bloomington, Indiana 47405 (United States); University Information Technology Services, Indiana University, Bloomington, Indiana 47408 (United States); Department of Physics and Astronomy, National Superconducting Cyclotron Laboratory and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824 (United States)

2007-06-15

163

Phase transitions in nucleonic matter and neutron-star cooling.  

PubMed

A new scenario for neutron-star cooling is suggested by the correspondence between pion condensation, induced by critical spin-isospin fluctuations, and the metal-insulator phase transition in a 2D electron gas. Above the threshold density for pion condensation, the neutron single-particle spectrum acquires an insulating gap that quenches neutron contributions to neutrino production. In the liquid phase just below the transition, the fluctuations play dual roles by (i) creating a multisheeted neutron Fermi surface that extends to low momenta and activates the normally forbidden direct Urca cooling mechanism, and (ii) amplifying the nodeless P-wave neutron superfluid gap while suppressing S-wave pairing. Lighter stars without a pion-condensed core undergo slow cooling, whereas enhanced cooling occurs in heavier stars via direct Urca emission from a thin shell of the interior. PMID:15524862

Khodel, V A; Clark, J W; Takano, M; Zverev, M V

2004-10-05

164

Structure of neutron stars in tensor-vector-scalar theory  

SciTech Connect

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

Lasky, Paul D.; Sotani, Hajime; Giannios, Dimitrios [Theoretical Astrophysics, Eberhard Karls University of Tuebingen, Tuebingen 72076 (Germany); Max Planck Institute for Astrophysics, Box 1317, D-85741 Garching (Germany)

2008-11-15

165

Thermal Evolution of Isolated Neutron Stars: Pairing, Pairing, and Pairing  

SciTech Connect

The thermal evolution of young isolated neutron stars is driven by neutrino emission from matter at the highest densities reached in their inner core. As such, these objects are direct probes of the structure of matter at supranuclear density. However, pairing of the neutrino emitting baryons, or quarks, can significantly alter their emission efficiency and the predicted thermal evolution is very sensitive to assumptions about gap size(s). After a brief description of these physical processes, I compare with present observational data models of cooling neutron stars driven by slow or fast neutrino emission. Depending on the assumed size of the neutron {sup 3}P{sub 2}-{sup 3}F{sub 2} gap, a minimal model of neutron stars can accommodate all present data, with the exception of the cold pulsar J0007.0+7303 in the supernova remnant CTA 1. However, in case this gap is vanishingly small or very large, the estimated surface temperatures of more than a half of the observed young cooling neutron stars would imply the intervention of some form of enhanced neutrino emission. Unfortunately, the present uncertainty on the size of the neutron {sup 3}P{sub 2}-{sup 3}F{sub 2} gap precludes us to draw any definitive conclusion about the state of dense matter from the sole study of isolated neutron stars.

Page, Dany [Departamento de Astrofisica Teorica, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico)

2009-05-07

166

Finite temperature neutron matter and rotating neutron stars in the quark meson coupling model  

NASA Astrophysics Data System (ADS)

A mean-field description of nonoverlaping nucleon bags bound by the self-consistent exchange of ?, ?, and ? mesons is used to investigate the properties of neutron matter at finite temperature. We use the equation of state of zero temperature to study the rotating neutron star in the Komatsu-Eriguchi-Hachisu method. The mass, radius, and angular velocity of the neutron star are calculated and compared with the Walecka model.

Panda, P. K.; Sahu, R.; Das, C.

1999-09-01

167

Diffusive Nuclear Burning in Neutron Star Envelopes  

NASA Astrophysics Data System (ADS)

We calculate the rate of hydrogen burning for neutron stars (NSs) with hydrogen atmospheres and an underlying reservoir of nuclei capable of proton capture. This burning occurs in the exponentially suppressed diffusive tail of H that extends to the hotter depths of the envelope where protons are rapidly captured. This process, which we call diffusive nuclear burning (DNB), can change the H abundance at the NS photosphere on timescales as short as 102-104 yr. In the absence of diffusion, the hydrogen at the photosphere (where T~106 K and ?~0.1 g cm-3) would last for far longer than a Hubble time. Our work impacts the understanding of the evolution of surface abundances of isolated NSs, which is important to their thermal spectrum and their effective temperature-core temperature relation. In this paper we calculate the rate of H burning when the overall consumption rate is controlled by the nuclear timescales, rather than diffusion timescales. The immediate application is for H burning on millisecond radio pulsars and in quiescence for the accreting NS Cen X-4. We will apply this work to young radio pulsars and magnetars once we have incorporated the effects of strong B>1012 G magnetic fields.

Chang, Philip; Bildsten, Lars

2003-03-01

168

Neutron Star Crust in Strong Magnetic Fields  

NASA Astrophysics Data System (ADS)

We discuss the effects of strong magnetic fields through Landau quantization of electrons on the structure and stability of nuclei in neutron star crust. In strong magnetic fields, this leads to the enhancement of the electron number density with respect to the zero field case. We obtain the sequence of equilibrium nuclei of the outer crust in the presence of strong magnetic fields adopting most recent versions of the experimental and theoretical nuclear mass tables. For B ~ 1016G, it is found that some new nuclei appear in the sequence and some nuclei disappear from the sequence compared with the zero field case. Further we investigate the stability of nuclei in the inner crust in the presence of strong magnetic fields using the Thomas-Fermi model. The coexistence of two phases of nuclear matter - liquid and gas, is considered in this case. The proton number density is significantly enhanced in strong magnetic fields B ~ 1017G through the charge neutrality. We find nuclei with larger mass number in the presence of strong magnetic fields than those of the zero field. These results might have important implications for the transport properties of the crust in magnetars.

Nandi, Rana; Bandyopadhyay, Debades

2011-09-01

169

Hydrodynamical Neutron Star Kicks in Three Dimensions  

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

170

Resonant shattering of neutron star crusts.  

PubMed

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

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

2012-01-05

171

Physics of systems containing neutron stars  

NASA Astrophysics Data System (ADS)

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.

Shaham, Jacob

1995-01-01

172

Resonant Shattering of Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

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.

Tsang, David; Read, Jocelyn; Hinderer, Tanja; Piro, Anthony

2012-03-01

173

Resonant Shattering of Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

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[Unsupported Character] - [Unsupported Character -]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.

Tsang, David; Read, J. S.; Hinderer, T.; Piro, A.

2012-05-01

174

HYDRODYNAMICAL NEUTRON STAR KICKS IN THREE DIMENSIONS  

SciTech Connect

Using three-dimensional (3D) simulations of neutrino-powered supernova explosions, we show that the hydrodynamical kick scenario proposed by Scheck et al. on the basis of two-dimensional (2D) models can yield large neutron star (NS) recoil velocities also in 3D. Although the shock stays relatively spherical, standing accretion-shock and convective instabilities lead to a globally asymmetric mass and energy distribution in the post-shock layer. An anisotropic momentum distribution of the ejecta is built up only after the explosion sets in. Total momentum conservation implies the acceleration of the NS on a timescale of 1-3 s, mediated mainly by long-lasting, asymmetric accretion downdrafts and the anisotropic gravitational pull of large inhomogeneities in the ejecta. In a limited set of 15 M{sub sun} models with an explosion energy of about 10{sup 51} erg, this stochastic mechanism is found to produce kicks from <100 km s{sup -1} to {approx}>500 km s{sup -1}, and kicks {approx}>1000 km s{sup -1} seem possible. Strong rotational flows around the accreting NS do not develop in our collapsing, non-rotating progenitors. The NS spins therefore remain low with estimated periods of {approx}500-1000 ms and no alignment with the kicks.

Wongwathanarat, Annop; Janka, Hans-Thomas; Mueller, Ewald, E-mail: annop@mpa-garching.mpg.d [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany)

2010-12-10

175

Gravitational radiation during coalescence of neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

176

Neutron Star Structure and the Equation of State  

NASA Astrophysics Data System (ADS)

The structure of neutron stars is considered from theoretical and observational perspectives. We demonstrate an important aspect of neutron star structure: the neutron star radius is primarily determined by the behavior of the pressure of matter in the vicinity of nuclear matter equilibrium density. In the event that extreme softening does not occur at these densities, the radius is virtually independent of the mass and is determined by the magnitude of the pressure. For equations of state with extreme softening or those that are self-bound, the radius is more sensitive to the mass. Our results show that in the absence of extreme softening, a measurement of the radius of a neutron star more accurate than about 1 km will usefully constrain the equation of state. We also show that the pressure near nuclear matter density is primarily a function of the density dependence of the nuclear symmetry energy, while the nuclear incompressibility and skewness parameters play secondary roles. In addition, we show that the moment of inertia and the binding energy of neutron stars, for a large class of equations of state, are nearly universal functions of the star's compactness. These features can be understood by considering two analytic, yet realistic, solutions of Einstein's equations, by, respectively, Buchdahl and Tolman. We deduce useful approximations for the fraction of the moment of inertia residing in the crust, which is a function of the stellar compactness and, in addition, the pressure at the core-crust interface.

Lattimer, J. M.; Prakash, M.

2001-03-01

177

PSR J1840-1419: A Very Cool Neutron Star  

NASA Astrophysics Data System (ADS)

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 ? bb < 24+17 -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 × 1013 and 9.4 × 1013 G, respectively. Our temperature upper limits for these stars are kT ? bb < 123+20 -33 eV and kT ? bb < 115+16 -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.

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

2013-02-01

178

Energy density functional for nuclei and neutron stars  

NASA Astrophysics Data System (ADS)

Background: Recent observational data on neutron star masses and radii provide stringent constraints on the equation of state of neutron rich matter [Annu. Rev. Nucl. Part. Sci.ARPSDF0163-899810.1146/annurev-nucl-102711-095018 62, 485 (2012)].Purpose: We aim to develop a nuclear energy density functional that can be simultaneously applied to finite nuclei and neutron stars.Methods: We use the self-consistent nuclear density functional theory (DFT) with Skyrme energy density functionals and covariance analysis to assess correlations between observables for finite nuclei and neutron stars. In a first step two energy functionals—a high density energy functional giving reasonable neutron properties, and a low density functional fitted to nuclear properties—are matched. In a second step, we optimize a new functional using exactly the same protocol as in earlier studies pertaining to nuclei but now including neutron star data. This allows direct comparisons of performance of the new functional relative to the standard one.Results: The new functional TOV-min yields results for nuclear bulk properties (energy, rms radius, diffraction radius, and surface thickness) that are of the same quality as those obtained with the established Skyrme functionals, including SV-min. When comparing SV-min and TOV-min, isoscalar nuclear matter indicators vary slightly while isovector properties are changed considerably. We discuss neutron skins, dipole polarizability, separation energies of the heaviest elements, and proton and neutron drip lines. We confirm a correlation between the neutron skin of 208Pb and the neutron star radius.Conclusions: We demonstrate that standard energy density functionals optimized to nuclear data do not carry information on the expected maximum neutron star mass, and that predictions can only be made within an extremely broad uncertainty band. For atomic nuclei, the new functional TOV-min performs at least as well as the standard nuclear functionals, but it also reproduces expected neutron star data within assumed error bands. This functional is expected to yield more reliable predictions in the region of very neutron rich heavy nuclei.

Erler, J.; Horowitz, C. J.; Nazarewicz, W.; Rafalski, M.; Reinhard, P.-G.

2013-04-01

179

Cooling of the neutron star in Cassiopeia A  

NASA Astrophysics Data System (ADS)

We demonstrate that the high-quality cooling data observed for the young neutron star in the supernova remnant Cassiopeia A over the past 10 years—as well as all other reliably known temperature data of neutron stars—can be comfortably explained within the “nuclear medium cooling” scenario. The cooling rates of this scenario account for medium-modified one-pion exchange in dense matter and polarization effects in the pair-breaking formations of superfluid neutrons and protons. Crucial for the successful description of the observed data is a substantial reduction of the thermal conductivity, resulting from a suppression of both the electron and nucleon contributions to it by medium effects. In a few more decades of continued monitoring of Cassiopeia A, the observed data may allow one to put additional constraints on the efficiency of different cooling processes in neutron stars.

Blaschke, D.; Grigorian, H.; Voskresensky, D. N.; Weber, F.

2012-02-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

181

Quark Matter Nucleation in Neutron Stars  

NASA Astrophysics Data System (ADS)

We study the quark deconfinement phase transition in cold (T = 0) and hot ?-stable hadronic matter. Assuming a first-order phase transition, we calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We show that above a threshold value of the central pressure a pure hadronic star (HS) is metastable to the conversion to a quark star (QS) (i.e. hybrid star or strange star). We introduce the concept of critical mass Mcr for cold HSs and proto-hadronic stars, and the concept of limiting conversion temperature for proto-hadronic stars. We show that proto-hadronic stars with a mass M < Mcr could survive the early stages of their evolution without decaying to QSs. Finally, we discuss the possible evolutionary paths of proto-hadronic stars.

Bombaci, I.

182

Spin-down of neutron stars by neutrino emission  

SciTech Connect

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.

Dvornikov, Maxim [Centro Cientifico-Tecnologico de Valparaiso and Departamento de Fisica, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile); IZMIRAN, 142190, Troitsk, Moscow Region (Russian Federation); Dib, Claudio [Centro Cientifico-Tecnologico de Valparaiso and Departamento de Fisica, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile)

2010-08-15

183

Cooling of young neutron stars in GRB associated to supernovae  

NASA Astrophysics Data System (ADS)

Context. The traditional study of neutron star cooling has been generally applied to quite old objects such as the Crab Pulsar (957 years) or the central compact object in Cassiopeia A (330 years) with an observed surface temperature ~106 K. However, recent observations of the late (t = 108-109 s) emission of the supernovae (SNe) associated to GRBs (GRB-SN) show a distinctive emission in the X-ray regime consistent with temperatures ~107-108 K. Similar features have been also observed in two Type Ic SNe SN 2002ap and SN 1994I that are not associated to GRBs. Aims: We advance the possibility that the late X-ray emission observed in GRB-SN and in isolated SN is associated to a hot neutron star just formed in the SN event, here defined as a neo-neutron star. Methods: We discuss the thermal evolution of neo-neutron stars in the age regime that spans from ~1 min (just after the proto-neutron star phase) all the way up to ages <10-100 yr. We examine critically the key factor governing the neo-neutron star cooling with special emphasis on the neutrino emission. We introduce a phenomenological heating source, as well as new boundary conditions, in order to mimic the high temperature of the atmosphere for young neutron stars. In this way we match the neo-neutron star luminosity to the observed late X-ray emission of the GRB-SN events: URCA-1 in GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in GRB031203-SN2003lw. Results: We identify the major role played by the neutrino emissivity in the thermal evolution of neo-neutron stars. By calibrating our additional heating source at early times to ~1012-1015 erg/g/s, we find a striking agreement of the luminosity obtained from the cooling of a neo-neutron stars with the prolonged (t = 108-109 s) X-ray emission observed in GRB associated with SN. It is therefore appropriate a revision of the boundary conditions usually used in the thermal cooling theory of neutron stars, to match the proper conditions of the atmosphere at young ages. The traditional thermal processes taking place in the crust might be enhanced by the extreme high-temperature conditions of a neo-neutron star. Additional heating processes that are still not studied within this context, such as e+e- pair creation by overcritical fields, nuclear fusion, and fission energy release, might also take place under such conditions and deserve further analysis. Conclusions: Observation of GRB-SN has shown the possibility of witnessing the thermal evolution of neo-neutron stars. A new campaign of dedicated observations is recommended both of GRB-SN and of isolated Type Ic SN.

Negreiros, R.; Ruffini, R.; Bianco, C. L.; Rueda, J. A.

2012-04-01

184

Thermal conductivity of ions in a neutron star envelope  

NASA Astrophysics Data System (ADS)

We analyse the thermal conductivity of ions (equivalent to the conductivity of phonons in crystalline matter) in a neutron star envelope. We calculate the ion/phonon thermal conductivity in a crystal of atomic nuclei using variational formalism and performing momentum space integration by Monte Carlo method. We take into account phonon-phonon and phonon-electron scattering mechanisms and show that phonon-electron scattering dominates at not too low densities. We extract the ion thermal conductivity in ion liquid or gas from literature. Numerical values of the ion/phonon conductivity are approximated by analytical expressions, valid for T >~ 105K and 105gcm-3 <~ ? <~ 1014gcm-3. Typical magnetic fields B ~ 1012 G in neutron star envelopes do not affect this conductivity although they strongly reduce the electron thermal conductivity across the magnetic field. The ion thermal conductivity remains much smaller than the electron conductivity along the magnetic field. However, in the outer neutron star envelope it can be larger than the electron conductivity across the field, which is important for heat transport across magnetic field lines in cooling neutron stars. The ion conductivity can greatly reduce the anisotropy of heat conduction in outer envelopes of magnetized neutron stars.

Chugunov, A. I.; Haensel, P.

2007-11-01

185

Atmosphere composition of quiescent accreting neutron stars in globular clusters  

NASA Astrophysics Data System (ADS)

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.

Servillat, M.

2012-12-01

186

Conditions for Steady Detectable Gravitational Radiation from Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

The gravitational-wave and accretion driven evolution of the angular velocity, core temperature, and (small) amplitude of an r-mode of neutron stars in low-mass X-ray binaries and similar systems is investigated. The conditions required for evolution to a stable equilibrium state (with gravitational wave flux proportional to average X-ray flux) are determined. In keeping with conclusions derived by Kaminker, Yakovlev and Gnedin (2002) from observations of neutron star cooling, the core neutrons are taken to be normal while the core protons and hyperons and the crust neutrons are taken to be singlet superfluids. The dominant sources of damping are then hyperon bulk viscosity (if much of the core has a density at least 2--3 times nuclear density) and (e-e and n-n scattering and possibly magnetic) shear viscosity within the core--crust boundary layer. It is found that a stable equilibrium state can be reached if the superfluid transition temperature of the hyperons is sufficiently small (<= 2x 109 K), allowing steady gravitational radiation (at a frequency f? 4/3P, with P the neutron star spin period) from Sco X-1 and several other neutron stars in low-mass X-ray binaries to be potentially detectable by the Advanced LIGO (and VIRGO) arrays. This work was supported by NSF grant PHY-0070935.

Wagoner, R. V.

2003-03-01

187

Neutron star spin-kick velocity correlation effect on binary neutron star coalescence rates and spin-orbit misalignment of the components  

Microsoft Academic Search

We study the effect of the neutron star spin -- kick velocity alignment\\u000aobserved in young radio pulsars on the coalescence rate of binary neutron\\u000astars. Two scenarios of the neutron star formation are considered: when the\\u000akick is always present and when it is small or absent if a neutron star is\\u000aformed in a binary system due to

K. A. Postnov; A. G. Kuranov

2007-01-01

188

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

SciTech Connect

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.

Weber, F.; Glendenning, N.K.

1992-11-02

189

Close-limit approximation to neutron star collisions.  

NASA Astrophysics Data System (ADS)

The authors develop a close-limit approximation to the head-on collision of two neutron stars similar to that used to treat the merger of black hole binaries. This approximation can serve as a useful benchmark test for future fully non-linear studies. For neutron star binaries, the close-limit approximation involves assuming that the merged object can be approximated as a perturbed, stable neutron star during the ring-down phase of the coalescence. The authoras introduce a prescription for the construction of initial data sets, discuss the physical plausibility of the various assumptions involved, and briefly investigate the character of the gravitational radiation produced during the merger. The numerical results show that several of the merged object's fluid pulsation modes are excited to a significant level.

Gabrielle, D.; Andersson, N.; Kokkotas, K. D.; Laguna, P.; Pullin, J. A.; Ruoff, J.

1999-11-01

190

Searching for Debris Disks Around Isolated Neutron Stars  

NASA Astrophysics Data System (ADS)

I will review the current status of searches for debris disks around isolated neutron stars. Such disks could have formed from supernova fallback and their existence have been proposed to explain a few observed properties of neutron stars. Mid-infrared counterparts to two magnetars, 4U 0142+61 and 1E 2259+586, have been detected, and the broad-band spectrum of the first source, which is relatively well determined, can be described by emission from an X-ray heated dust disk. Deep infrared searches, including Spitzer observations, for similar emission around a few neutron stars of different types have been conducted, while with no detections thus far. Using recently released WISE all-sky survey data, we are working on searches for mid-infrared counterparts to all known pulsars. The results will also be presented.

Wang, Zhongxiang

2013-01-01

191

Magnetic Energy Production by Turbulence in Binary Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

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.

Zrake, Jonathan; MacFadyen, Andrew I.

2013-06-01

192

Relativistic URCA Processes in Neutron Stars with AN Antikaon Condesate  

NASA Astrophysics Data System (ADS)

A recently developed effective relativistic theory for nuclear matter is applied to the description of the cooling process of baryon degenerate neutron star matter through neutrino emission considering direct URCA processes. In our approach nucleons and antikaon condensates interact with ?, ?, ?, ? and ? meson fields. Our results indicate a substantial decrease of the critical threshold density for the URCA process. This is because the presence of these interacting degrees of freedom increase the proportion of protons, producing simultaneously the reduction of the isospin asymmetry in nuclear matter. Our results also indicate that neutron stars with larger masses than MNE ~ 0.9M?, which represents the stellar critical threshold (the mass of the neutron star whose baryon central density reached the critical density) would be cooled efficiently and be outside the possibility of observation by heat radiation in a few years.

Razeira, Moisés; Mesquita, Alexandre; Vasconcellos, César A. Z.; Gomes, Rosana O.; Pérez Martínez, Aurora; Pérez Rojas, Hugo; Manreza Paret, Daryel

193

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

SciTech Connect

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.

Weber, F.; Glendenning, N.K.

1992-11-02

194

Neutron-capture elements in extremely metal-poor stars  

NASA Astrophysics Data System (ADS)

Extremely metal-poor stars exhibit large scatter in the abundance ratios (e.g. [Sr/Fe] and [Ba/Fe], as well as [Sr/Ba]), and sometimes show very large enhancements of neutron-capture elements with respect to iron. However, recent abundance measurements for large samples of metal-poor stars suggest that neutron-capture elements are deficient in general in the lowest metallicity range and the scatter in their abundance ratios is rather small. The metallicity at which the abundance ratios show the largest scatter is dependent on elements: Ba shows largest scatter at [Fe/H] = -3, while Sr shows larger scatter at lower metallicity. Such trends suggest metallicity dependence of the contributions of nucleosynthesis processes that produce light and heavy neutron-capture elements. A clear cut-off is found in the Sr/Ba distribution at [Fe/H] = -3.5. This suggests a metallicity dependence of the process that provides light neutron-capture elements. Recent abundance studies for a large sample of very metal-poor stars found by the Sloan Digital Sky Survey (SDSS) discovered a carbon-enhanced metal-poor star that has [Fe/H] = -3.7 and a large excess of Sr with no detectable Ba. This is a similar feature to that found in the hyper metal-poor star HE 1327-2326 ([Fe/H] = -5.6) and indicates that the progenitors of such carbon-enhanced stars with no excess of heavy neutron-capture elements could be a source of light neutron-capture elements.

Aoki, Wako

2012-11-01

195

X-Ray Emission from Pulsars and Neutron Stars  

Microsoft Academic Search

\\u000a 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\\u000a 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\\u000a exhausted. This implies that a star left with M › 1.4

Werner Becker

2009-01-01

196

Supernova Kicks, Magnetic Braking, and Neutron Star Binaries  

Microsoft Academic Search

We consider the formation of low-mass X-ray binaries (LMXBs) containing accreting neutron stars via the helium star supernova channel. The predicted relative number of short-period transients provides a sensitive test of the input physics in this process. We investigate the effect of varying mean kick velocities, orbital angular momentum loss efficiencies, and common-envelope ejection efficiencies on the subpopulation of short-period

Vassiliki Kalogera; Ulrich Kolb; A. R. King

1998-01-01

197

X-ray spectra from convective photospheres of neutron stars  

SciTech Connect

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.

Zavlin, V.E. [Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Germany); Pavlov, G.G. [Pennsylvania State Univ., PA (United States)]|[Ioffe Institute of Physics and Technology, St. Petersburg, RU (United States); Shibanov, Yu.A. [Ioffe Institute of Physics and Technology, St. Petersburg (Russian Federation); Rogers, F.J.; Iglesias, C.A. [Lawrence Livermore National Lab., CA (United States)

1996-01-17

198

Gravitational Waves and the Maximum Spin Frequency of Neutron Stars  

NASA Astrophysics Data System (ADS)

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 LX when considering an enlarged sample size of millisecond X-ray pulsars.

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

2012-02-01

199

On the spreading layer emission in luminous accreting neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

200

Neutron stars and the distance to gamma-ray bursters  

SciTech Connect

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. 19 refs.

Dermer, C.D.; Hurley, K.C. (Rice University, Houston, TX (United States) California, University, Berkeley (United States))

1991-08-01

201

The Dynamics and Outcomes of Rapid Infall onto Neutron Stars  

NASA Astrophysics Data System (ADS)

We present an extensive study of accretion onto neutron stars in which the velocity of the neutron star and structure of the surrounding medium is such that the Bondi-Royle accretion exceeds 10-4 Msun yr-1. Two types of initial conditions are considered for a range of entropies and chemical compositions: an atmosphere in pressure equilibrium above the neutron star, and a freely falling inflow of matter from infinity (also parameterized by the infall rate). We then evolve the system with one- and two-dimensional hydrodynamic codes to determine the outcome. For most cases, hypercritical (also termed "super Eddington") accretion caused by rapid neutrino cooling allows the neutron star to accrete above the Bondi-Hoyle rate as previously pointed out by Chevalier. However, for a subset of simulations which corresponds to evolutionarily common events, convection driven by neutrino heating can lead to explosions by a mechanism similar to that found in core-collapse supernovae. Armed with the results from our calculations, we are in a position to predict the fate of a range of rapid-infall neutron star accretors present in certain low-mass X-ray binaries, common envelope systems, supernova fallbacks, and Thorne-Zytkow objects (TZOs). A majority of the common envelope systems that we considered led to explosions expelling the envelope, halting the neutron star's inward spiral, and allowing the formation of close binary systems. As a result, the smothered neutron stars produced in the collisions studied by Davies & Benz may also explode, probably preventing them from forming millisecond pulsars. For the most massive supernovae, in which the fallback of material toward the neutron star after a successful explosion is large, we find that a black hole is formed in a few seconds. Finally, we argue that the current set of TZO formation scenarios is inadequate and leads instead to hypercritical accretion and black hole formation. Moreover, it appears that many of the current TZ models have structures ill suited for modeling by mixing-length convection. This has prompted us to develop a simple test to determine the viability of this approximation for a variety of convective systems.

Fryer, Chris L.; Benz, Willy; Herant, Marc

1996-04-01

202

The neutron star and black hole initial mass function  

SciTech Connect

Using recently calculated models for massive stellar evolution and supernovae coupled to a model for Galactic chemical evolution, neutron star and black hole birth functions (number of neutron stars and black holes as a function of their mass) are determined for the Milky Way galaxy. For these stars that explode as Type II supernovae, the models give birth functions that are bimodal with peaks at 1.27 and 1.76 {ital M}{sub {circle_dot}} and average masses within those peaks of 1.28 and 1.73 {ital M}{sub {circle_dot}}. For these stars that explode as Type Ib there is a narrower spread of remnant masses, the average being 1.32 {ital M}{sub {circle_dot}}, and less evidence for bimodality. These values will be increased, especially in the more massive Type II supernovae, if significant accretion continues during the initial launching of the shock, and the number of heavier neutron stars could be depleted by black hole formation. The principal reason for the dichotomy in remnant masses for Type II is the difference in the presupernova structure of stars above and below 19 {ital M}{sub {circle_dot}}, the mass separating stars that burn carbon convectively from those that produce less carbon and burn radiatively. The Type Ib{close_quote}s and the lower mass group of the Type II{close_quote}s compare favorably with measured neutron star masses, and in particular to the Thorsett {ital et} {ital al}. (1993) determination of the average neutron star mass in 17 systems; 1.35{plus_minus}0.27 {ital M}{sub {circle_dot}}. Variations in the exponent of a Salpeter initial mass function are shown not to affect the locations of the two peaks in the distribution function, but do affect their relative amplitudes. Sources of uncertainty, in particular placement of the mass cut and sensitivity to the explosion energy, are discussed, and estimates of the total number of neutron stars and black holes in the Galaxy are given. (Abstract Truncated)

Timmes, F.X. [Laboratory for Astrophysics and Space Research, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60667 (United States)]|[, Board of Studies in Astronomy and Astrophysics, UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, California 95064 (United States)]|[, General Studies Division, Lawrence Livermore National Laboratory, Livermore, California 94550. (United States); Woosley, S.E. [Board of Studies in Astronomy and Astrophysics, UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, California 95064 (United States)]|[General Studies Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Weaver, T.A. [General Studies Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

1996-02-01

203

Unified description of dense matter in neutron stars and magnetars  

NASA Astrophysics Data System (ADS)

We have recently developed a set of equations of state based on the nuclear energy density functional theory providing a unified description of the different regions constituting the interior of neutron stars and magnetars. The nuclear functionals, which were constructed from generalized Skyrme effective nucleon-nucleon interactions, yield not only an excellent fit to essentially all experimental atomic mass data but were also constrained to reproduce the neutron-matter equation of state as obtained from realistic many-body calculations.

Chamel, N.; Pavlov, R. L.; Mihailov, L. M.; Velchev, Ch. J.; Stoyanov, Zh. K.; Mutafchieva, Y. D.; Ivanovich, M. D.; Fantina, A. F.; Pearson, J. M.; Goriely, S.

2013-03-01

204

Observational prospects for massive stars with degenerate neutron cores  

NASA Astrophysics Data System (ADS)

In this paper we present observable characteristics of massive stars with degenerate neutron cores, or Thorne-Zytkow objects, which would distinguish them from other stars. Spectroscopically these stars are red supergiants, but they have peculiar surface abundances compared with 'normal' red supergiants. This is due to the convection of rp-process products from the nuclear burning region to the surface. We present predictions of surface abundances of elelments heavier than iron. In particular, Mo should have an abundance greater than 1000 times solar. We estimate that several of the about 100 red supergiants within 5 kpc of the Sun are Thorne-Zytkow objects.

Biehle, Garrett T.

1994-01-01

205

Dark Matter, Neutron Stars, and Strange Quark Matter  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

206

Differentiating Neutron Star Models by X-Ray Polarimetry  

NASA Astrophysics Data System (ADS)

The nature of pulsars is still unknown because of the non-perturbative effects of the fundamental strong interaction, so various models of pulsar inner structures are suggested, either for conventional neutron stars or quark stars. Additionally, a quark-cluster matter state is conjectured for cold matter at supranuclear density, and as a result pulsars can be quark-cluster stars. Besides understanding the different manifestations, the most important issue is to find an effective way to observationally differentiate these models. X-ray polarimetry plays an important role here. The thermal x-ray polarization of quark/quark-cluster stars is focused on, and while the thermal x-ray linear polarization percentage is typically higher than ~ 10% in normal neutron star models, the percentage of quark/quark-cluster stars is almost zero. This could then be an effective method to identify quark/quark-cluster stars by soft x-ray polarimetry. We are therefore expecting to detect thermal x-ray polarization in the coming decades.

Lu, Ji-Guang; Xu, Ren-Xin; Feng, Hua

2013-05-01

207

Crustal Heating and Quiescent Emission from Transiently Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

Nuclear reactions occurring at densities ~1012 g cm-3 in the crust of a transiently accreting neutron star efficiently maintain the core at a temperature ~ (5-10)x107 K. When accretion halts, the envelope relaxes to a thermal equilibrium set by the flux from the hot core, as if the neutron star were newly born. For the time-averaged accretion rates (<~10-10 Msolar yr-1) typical of low-mass X-ray transients, standard neutrino cooling is unimportant and the core thermally reradiates the deposited heat. The resulting luminosity is ~ 5x1032-5x1033 ergs s-1 and agrees with many observations of transient neutron stars in quiescence. Confirmation of this mechanism would strongly constrain rapid neutrino cooling mechanisms for neutron stars (e.g., a pion condensate). Thermal emission had previously been dismissed as a predominant source of quiescent emission since blackbody spectral fits implied an emitting area much smaller than a neutron star's surface. However, as with thermal emission from radio pulsars, fits with realistic emergent spectra will imply a substantially larger emitting area. Other emission mechanisms, such as accretion or a pulsar shock, can also operate in quiescence and generate intensity and spectral variations over short timescales. Indeed, quiescent accretion may produce gravitationally redshifted metal photoionization edges in the quiescent spectra (detectable with AXAF and XMM). We discuss past observations of Aql X-1 and note that the low-luminosity (less than 1034 ergs s-1) X-ray sources in globular clusters and the Be star/X-ray transients are excellent candidates for future study.

Brown, Edward F.; Bildsten, Lars; Rutledge, Robert E.

1998-09-01

208

Deformation and crustal rigidity of rotating neutron stars  

NASA Astrophysics Data System (ADS)

Aims: We calculate parameters A and B of the Baym-Pines model of the hydro-elastic equilibrium of rotating neutron stars. Parameter A determines the energy increase of a non-rotating star due to a quadrupolar deformation of its shape. Parameter B determines residual quadrupolar deformation due to the crustal shear strain in a neutron star that spun down to a non-rotating state. Methods: The calculations of {A} are based on precise numerical 2D calculations for rotating neutron stars with the realistic equations of state (EOSs) of dense matter. An approximate, but quite precise, formula for B is used, which allows us to separate the contribution of the crust from the dependence on the stellar mass M and radius R. The elastic shear strain distribution within the crust is modeled following Cutler et al. (2003). Realistic EOSs of neutron star cores are used, some of them with high-density softening due to the appearance of hyperons or a phase transition to an exotic state. Results: The values A(M) and B(M) were calculated for 0.2 M _?neutron star core, combined with several crust models. A standard formula based on the incompressible fluid model is shown to severely underestimate the value of A. For M<0.7 M_? the values of A(M) are nearly EOS-independent and are given (within a few percent) by a universal formula A=3.87 (M/M_?)7/3 × 1053 erg. We derive the scaling of B with respect to R and M, also valid for a thick crust. We show that B for accreted crust strongly depends on pycnonuclear fusions at ?>1012 g cm-3.

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

2008-11-01

209

Proton localization in the neutron star matter.  

NASA Astrophysics Data System (ADS)

Single proton localization in the neutron matter is studied by means of the self-consistent Hartree-Fock calculations. Ranges of the total density in which the localization is possible are derived and the corresponding proton and neutron density profiles are presented. Perspectives of the full inclusion of spin degrees of freedom are discussed.

Burzynski, K.; Dobaczewski, J.

1996-02-01

210

From Crust to Core:. a Brief Review of Quark Matter in Neutron Stars  

NASA Astrophysics Data System (ADS)

This paper provides a short overview of the multifaceted, possible role of quark matter for compact stars (neutron stars and strange quark matter stars). We began with a variational investigation of the maximum possible energy densities in the cores of neutron stars. This is followed by a brief discussion of the possible existence of quark matter in the cores of neutron stars and how such matter could manifest itself in neutron star observables. The possible presence of color superconducting strange quark matter nuggets in the crusts of neutron stars is reviewed next, and their impact on the pycnonuclear reaction rates in the crusts of neutron stars is discussed. The second part of the paper discusses the impact of ultra-strong electric fields on the bulk properties of strange quark matter stars and presents results of a preliminary study that models the thermal evolution of radio-quiet, X-ray bright, central compact objects (CCOs).

Weber, F.; Hamil, O.; Mimura, K.; Negreiros, R.

211

Combustion of a neutron star into a strange quark star: The neutrino signal  

NASA Astrophysics Data System (ADS)

There are strong indications that the process of conversion of a neutron star into a strange quark star proceeds as a strong deflagration implying that in a few milliseconds almost the whole star is converted. Starting from the three-dimensional hydrodynamic simulations of the combustion process which provide the temperature profiles inside the newly born strange star, we calculate for the first time the neutrino signal that is to be expected if such a conversion process takes place. The neutrino emission is characterized by a luminosity and a duration that is typical for the signal expected from protoneutron stars and represents therefore a powerful source of neutrinos which could be possibly directly detected in case of events occurring close to our Galaxy. We discuss moreover possible connections between the birth of strange stars and explosive phenomena such as supernovae and gamma-ray bursts.

Pagliara, Giuseppe; Herzog, Matthias; Röpke, Friedrich K.

2013-05-01

212

Neutron Star Population Dynamics. I. Millisecond Pulsars  

NASA Astrophysics Data System (ADS)

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

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

1997-06-01

213

Neutron star dynamics, braking indices and energy dissipation  

NASA Astrophysics Data System (ADS)

Models of pulsar glitches and postglich relaxation are reviewed. Implications for braking indices due to internal torques in the neutron star, and energy dissipation by internal torques are discussed. All recent observations of pulsars with large (Vela pulsar like) glitches and second derivatives are seen to fit with the same glitch dynamics that the Vela pulsar exhibits.

Alpar, M. A.

214

Testing general metric theories of gravity with bursting neutron stars  

SciTech Connect

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.

Psaltis, Dimitrios [Departments of Physics and Astronomy, University of Arizona, Tucson, Arizona 85721 (United States)

2008-03-15

215

The Einstein@Home search for new neutron stars  

NASA Astrophysics Data System (ADS)

Einstein@Home is a volunteer distributed computing project with more than a quarter-million participants. I will describe the current status of its search for new neutron stars, using data from radio telescopes and gravitational wave observatories. I will also talk about the first Einstein@Home discoveries, of new radio pulsars found in data from the Arecibo Observatory.

Allen, Bruce

2011-04-01

216

Elastodynamic treatment of non-radial pulsations of neutron stars  

Microsoft Academic Search

The elastodynamic approach is outlined which has been developed to investigate stability of neutron star to small-amplitude deformations accompanying non-radial pulsations. Numerical estimates for the frequency and relaxation time of non-radial spheroidal and torsional gravitational-elastic modes are presented

S. Bastrukov; V. Papoyan; D. Podgainy; F. Weber

1998-01-01

217

X-ray spectra from convective photospheres of neutron stars.  

National Technical Information Service (NTIS)

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 ir...

V. E. Zavlin G. G. Pavlov Y. Shibanov F. J. Rogers C. A. Iglesias

1996-01-01

218

Thermonuclear Stability of Material Accreting onto a Neutron Star  

NASA Astrophysics Data System (ADS)

We present a global linear stability analysis of nuclear fuel accumulating on the surface of an accreting neutron star, and we identify the conditions under which thermonuclear bursts are triggered. The analysis reproduces all the recognized regimes of hydrogen and helium bursts and in addition shows that at high accretion rates, near the limit of stable burning, there is a regime of ``delayed mixed bursts'' that is distinct from the more usual ``prompt mixed bursts.'' In delayed mixed bursts, a large fraction of the fuel is burned stably before the burst is triggered. Bursts thus have longer recurrence times but at the same time have somewhat smaller fluences. Therefore, the parameter ?, which measures the ratio of the energy released via accretion to that generated through nuclear reactions in the burst, is up to an order of magnitude larger than for prompt bursts. This increase in ? near the threshold of stable burning has been seen in observations. We explore a wide range of mass accretion rates, neutron star radii, and core temperatures and calculate a variety of burst properties. From a preliminary comparison with data, we suggest that bursting neutron stars may have hot cores, with Tcore>~107.5 K, consistent with interior cooling via the modified Urca or similar low-efficiency process, rather than Tcore~107 K, as expected for the direct Urca process. There is also an indication that neutron star radii are somewhat small, <~10 km. Both of these conclusions need to be confirmed by comparing more careful calculations with better data.

Narayan, Ramesh; Heyl, Jeremy S.

2003-12-01

219

Nuclear Symmetry Energy Effects on Neutron Stars Properties  

NASA Astrophysics Data System (ADS)

We construct a class of nuclear equations of state based on a schematic potential model, that originates from the work of Prakash et al.,1 which reproduce the results of most microscopic calculations. The equations of state are used as input for solving the Tolman-Oppenheimer-Volkov equations for the corresponding neutron stars. The potential part contribution of the symmetry energy to the total energy is parametrized in a generalized form both for low and high values of the baryon density. Special attention is devoted to the construction of the symmetry energy in order to reproduce the results of most microscopic calculations of dense nuclear matter. The obtained nuclear equations of state are applied for the systematic study of the global properties of a neutron star (masses, radii and composition). The calculated masses and radii of the neutron stars are plotted as a function of the potential part parameters of the symmetry energy. A linear relation between these parameters, the radius and the maximum mass of the neutron star is obtained. In addition, a linear relation between the radius and the derivative of the symmetry energy near the saturation density is found. We also address the problem of the existence of correlation between the pressure near the saturation density and the radius.

Psonis, V. P.; Moustakidis, Ch. C.; Massen, S. E.

220

The Soft Gamma Repeaters : A New Class of Neutron Stars  

NASA Astrophysics Data System (ADS)

The soft gamma repeaters are a peculliar group of transient sources, distinguished from the more common `classical' gamma ray bursters by their multiple repititions, and by their relatively soft spectral energy distributions. One SGR in the Large Magellanic Cloud (a satellite system of our Galaxy) emitted the brightest gamma-ray burst ever detected, on March 5, 1979. At its peak, this burst outshone a more typical X-ray flash (powered by thermonuclear burning) by almost ten million. A preponderance of evidence suggests that Soft Gamma Repeaters are young neutron stars possessing magnetic fields 10-100 times the QED strength. The associated stresses are sufficient to fracture the outer rigid crust of the neutron star, and to induce a steady X-ray glow from its surface. In distinction with ordinary radio pulsars, the magnetic field itself -- rather than the rotation -- is the dominant source of free energy. Recent observations have confirmed a prediction of this model, that the SGR sources are slowly rotating (by the standards of young neutron stars) and that their spin periods are increasing rapidly. I will outline how quantum electrodynamic effects modify the emergent X-ray spectrum, how measurements of the spin evolution of an SGR can be used to probe its superfluid interior, and how measurements of post-burst afterglow from the heated neutron star provide a direct diagnostic of the magnetic field.

Thompson, Christopher

1998-11-01

221

r-Mode Runaway and Rapidly Rotating Neutron Stars.  

PubMed

We present a simple spin-evolution model that predicts that rapidly rotating accreting neutron stars will be confined mainly to a narrow range of spin frequencies: P=1.5-5 ms. This is in agreement with current observations of neutron stars in both the low-mass X-ray binaries and the millisecond radio pulsars. The main ingredients in the model are (1) the instability of r-modes above a critical spin rate, (2) the thermal runaway that is due to the heat released as viscous damping mechanisms counteract the r-mode growth, and (3) a revised estimate of the strength of the dissipation that is due to the presence of a viscous boundary layer at the base of the crust in an old and relatively cold neutron star. We discuss the gravitational waves that are radiated during the brief r-mode-driven spin-down phase. We also briefly touch on how the new estimates affect the predicted initial spin periods of hot young neutron stars. PMID:10790075

Andersson; Jones; Kokkotas; Stergioulas

2000-05-01

222

Neutron star structure with modern nucleonic three-body forces  

SciTech Connect

We provide convenient parametrizations of the high-density nuclear equation of state obtained within the Brueckner-Hartree-Fock approach using different modern nucleon-nucleon potentials together with compatible microscopic nuclear three-body forces. The corresponding neutron star mass-radius relations are also presented.

Li, Z. H. [INFN-LNS, Via Santa Sofia 62, I-95123 Catania (Italy); Schulze, H.-J. [INFN Sezione di Catania, Via Santa Sofia 64, I-95123 Catania (Italy)

2008-08-15

223

Gamma-ray Bursts from Neutron Star Mergers.  

National Technical Information Service (NTIS)

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

T. Piran

1993-01-01

224

Prompt Merger Collapse and the Maximum Mass of Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

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

2013-09-01

225

Prompt merger collapse and the maximum mass of neutron stars.  

PubMed

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

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

2013-09-25

226

3P2 superfluidity in neutron star matter  

NASA Astrophysics Data System (ADS)

3P2 superfluidity of neutrons in neutron star matter is investigated using several potential models and the separation method. As a first step, the dependence of the pure 3P2 energy gap on the projection M of total momentum J is analyzed. The energy gap functions for pure 3P2 pairing are treated as vectors indexed by M, and it is shown that the magnitudes of these vectors at Fermi surface are close to each other, whereas their components are different. On the basis of these works, the influence of hyperons on the energy gap for 3P2 neutron pairing, with and without coupling to the 3F2 state, at Fermi surface in neutron star matter is studied. The results show that in the OPEG case hyperons increase the energy gap when the baryon number density is in the range of 0.2 fm-30.33 fm-3, and in the Argonne ?18 case hyperons increase the energy gap in the whole range where the 3P2 superfluidity exists. The energy gaps are zero in two types of neutron star matter for the Bonn potential.

Chen, Wei; Li, Bao-Jiang; Wen, De-Hua; Liu, Liang-Gang

2008-06-01

227

Thermalization time and specific heat of the neutron stars crust  

SciTech Connect

We discuss the thermalization process of the neutron star's crust described by solving the heat-transport equation with a microscopic input for the specific heat of baryonic matter. The heat equation is solved with initial conditions specific to a rapid cooling of the core. To calculate the specific heat of inner-crust baryonic matter, that is, nuclear clusters and unbound neutrons, we use the quasiparticle spectrum provided by the Hartree-Fock-Bogoliubov approach at finite temperature. In this framework, we analyze the dependence of the crust thermalization on pairing properties and on cluster structure of inner-crust matter. It is shown that the pairing correlations reduce the crust thermalization time by a large fraction. The calculations show also that the nuclear clusters have a non-negligible influence on the time evolution of the surface temperature of the neutron star.

Fortin, M. [Institut de Physique Nucleaire, IN2P3-CNRS, and Universite Paris-Sud, F-91406 Orsay Cedex (France); Ecole Normale Superieure, Departement de Physique, 24 rue Lhomond, F-75005 Paris (France); Grill, F. [Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133 Milan (Italy); Margueron, J. [Institut de Physique Nucleaire, IN2P3-CNRS, and Universite Paris-Sud, F-91406 Orsay Cedex (France); Page, Dany [Departamento de Astrofisica Teorica, Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, 04360 Mexico City Distrito Federal (Mexico); Sandulescu, N. [National Institute of Physics and Nuclear Engineering, RO-76900 Bucharest (Romania)

2010-12-15

228

Neutron stars and nuclei in the modified relativistic Hartree approximation  

NASA Astrophysics Data System (ADS)

We have examined the properties of neutron-rich matter and finite nuclei in the modified relativistic Hartree approximation for several values of the renormalization parameter, ?, around the standard choice of ? equal to the nucleon mass M. Observed neutron-star masses do not effectively constrain the value of ?. However, for finite nuclei the value ?/M = 0.79, suggested by nuclear matter data, provides a good account of the bulk properties with a sigma mass of about 600 MeV. This value of ?/M renders the effective three- and four-body scalar self-couplings to be zero at 60% of equilibrium nuclear matter density. We have also found that the matter part of the exchange diagram has little impact on the bulk properties of neutron stars.

Prakash, M.; Ellis, P. J.; Heide, E. K.; Rudaz, S.

1994-08-01

229

Neutron star equation of state and QPO observations  

NASA Astrophysics Data System (ADS)

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

Urbanec, Martin; Stuchlík, Zden?k; Török, Gabriel; Bakala, Pavel; ?ermák, Petr

2007-12-01

230

QPO observations related to neutron star equations of state  

NASA Astrophysics Data System (ADS)

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

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

231

Differential Rotation in Neutron Stars: Magnetic Braking and Viscous Damping  

NASA Astrophysics Data System (ADS)

Differentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars, according to general relativity. The remnant of a binary neutron star merger may give rise to such a ``hypermassive'' object. While such a star may be dynamically stable against gravitational collapse and bar formation, the radial stabilization due to differential rotation is likely to be temporary. Magnetic braking and viscosity combine to drive the star to uniform rotation, even if the seed magnetic field and the viscosity are small. This process inevitably leads to delayed collapse, which will be accompanied by a delayed gravitational wave burst and, possibly, a gamma-ray burst. We provide a simple, Newtonian MHD calculation of the braking of differential rotation by magnetic fields and viscosity. The star is idealized as a differentially rotating, infinite cylinder consisting of a homogeneous, incompressible conducting gas. We solve analytically the simplest case in which the gas has no viscosity and the star resides in an exterior vacuum. We treat numerically cases in which the gas has internal viscosity and the star is embedded in an exterior, low-density, conducting medium. Our evolution calculations are presented to stimulate more realistic MHD simulations in full 3+1 general relativity. They serve to identify some of the key physical and numerical parameters, scaling behavior, and competing timescales that characterize this important process.

Shapiro, Stuart L.

2000-11-01

232

Stochastic Background from Coalescences of Neutron Star-Neutron Star Binaries  

NASA Astrophysics Data System (ADS)

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

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

2006-05-01

233

Instabilities in Very Young Neutron Stars: Electron Fraction  

NSDL National Science Digital Library

This simulation shows the first 20 milliseconds in the life of a neutron star which is formed in a Type II supernova. After an initial collapse phase, the neutron star becomes unstable to convection. The resulting convective motions destroy the spherical symmetry of the star and rapidly mix the inner regions. In addition, the neutrino flux from the neutron star will be non-spherical and will be significantly enhanced by the convective motions. This may have major implications for the Type II supernova mechanism. The calculation was performed using the Piecewise-Parabolic Method for hydrodynamics. The computational grid contained 300 zones in radius and 200 zones in angle. The inner 200 zones in radius were uniformly spaced, ranging from the inner boundary at 25 km to 175 km. The outer 100 zones were non-uniformly spaced and stretched to 2000 km. Only the inner 200 zones are plotted. The inner boundary was treated as a hard sphere. At the outer boundary, zero gradients for all the variables were assumed. Periodic boundary conditions were used along the sides of the grid. The following sequence shows the mixing of composition which results from the convective motions. The variable plotted is the electron fraction Ye, which ranges from 0.2 to 0.5.

Oneil, Pamela; Fryxell, Bruce; Burrows, Adam

1994-02-12

234

The needle in the haystack: where to look for more isolated cooling neutron stars  

NASA Astrophysics Data System (ADS)

Context: Isolated, cooling neutron stars with thermal X-ray emission remain rarely-detected objects despite many searches investigating the ROSAT data. Aims: We simulate the population of close-by young cooling neutron stars to explain the current observational results. Given the inhomogenity of the neutron star distribution on the sky, it is particularly interesting to identify promising sky regions with respect to ongoing and future searches. Methods: Applying a population synthesis model, the inhomogenity of the progenitor distribution and the inhomogenity of the X-ray absorbing interstellar medium are considered for the first time. The total number of observable neutron stars is derived with respect to ROSAT count rates. In addition, we present sky maps of neutron star locations, and discuss age and distance distributions of the simulated neutron stars. Implications for future searches are discussed. Results: With our advanced model, we can succesfully explain the observed log N-log S distribution of close-by neutron stars. Cooling neutron stars will be most abundant in the directions of rich OB associations. We expect new candidates to be identified behind the Gould Belt, in particular in the Cygnus-Cepheus region. We expect them to be on average younger and hotter than the known population of isolated, cooling neutron stars. In addition, we propose to use data on runaway stars to search for more radio-quiet, cooling neutron stars.

Posselt, B.; Popov, S. B.; Haberl, F.; Trümper, J.; Turolla, R.; Neuhäuser, R.

2008-05-01

235

Neutron star accretion and the neutrino fireball.  

National Technical Information Service (NTIS)

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 ...

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

1991-01-01

236

Neutron star in the presence of a torsion-dilaton field  

NASA Astrophysics Data System (ADS)

We develop the general theory of stars in Saa's model of gravity with propagating torsion and study the basic stationary state of a neutron star. Our numerical results show that the torsion force decreases the role of the gravity in the star configuration, leading to significant changes in the neutron star masses depending on the equation of state of star matter. The inconsistency of Saa's model with Roll - Krotkov - Dicke and Braginsky - Panov experiments is discussed.

Boyadjiev, T.; Fiziev, P.; Yazadjiev, S.

1999-07-01

237

X-Ray Bursts from Accreting Magnetic Neutron Stars  

NASA Astrophysics Data System (ADS)

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

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

1996-05-01

238

NUCLEAR CONSTRAINTS ON PROPERTIES OF NEUTRON STAR CRUSTS  

SciTech Connect

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

Xu Jun; Chen Liewen; Ma Hongru [Institute of Theoretical Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Li Baoan [Department of Physics, Texas A and M University-Commerce, Commerce, TX 75429-3011 (United States)], E-mail: xujun@comp.tamu.edu, E-mail: hrma@sjtu.edu.cn, E-mail: lwchen@sjtu.edu.cn, E-mail: Bao-An_Li@tamu-commerce.edu

2009-06-01

239

Internal Constitution of Neutron and Strange Stars  

Microsoft Academic Search

In the first of these two lectures I will discuss the rich constitution of\\u000aneutron stars as a consequence of the Pauli principle which is engaged by the\\u000adominance of gravity over the nuclear force. Three especially interesting\\u000aphenomena are discussed in this contect--(1) a mechanism for the formation of\\u000alow-mass black holes distinct in their mass-range from the black

Norman K. Glendenning

1997-01-01

240

Magnetic Lensing near Ultramagnetized Neutron Stars  

Microsoft Academic Search

Extremely strong magnetic fields change the vacuum index of refraction. This\\u000ainduces a lensing effect that is not unlike the lensing phenomenon in strong\\u000agravitational fields. The main difference between the two is the polarization\\u000adependency of the magnetic lensing, a behaviour that induces a handful of\\u000ainteresting effects. The main prediction is that the thermal emission of\\u000aneutron stars

Nir J. Shaviv; Jeremy S. Heyl; Yoram Lithwick

1999-01-01

241

Probing properties of neutron stars with terrestrial nuclear reactions  

SciTech Connect

Heavy-ion reactions induced by neutron-rich nuclei provide the unique opportunity in terrestrial laboratories to constrain the nuclear symmetry energy Esym in a broad density range. A conservative constraint, 32({rho}/{rho}0)0.7 < Esym({rho}) < 32({rho}/{rho}0)1.1, around the nuclear matter saturation density {rho}0 has recently been obtained from analyzing the isospin diffusion data within a transport model for intermediate energy heavy-ion reactions. This subsequently puts a stringent constraint on properties of neutron stars, especially their radii and cooling mechanisms.

Li Baoan [Department of Physics, Texas A and M University-Commerce, Commerce, TX 75429 (United States); Department of Chemistry and Physics, P.O. Box 419, Arkansas State University, State University, AR 72467-0419 (United States); Chen Liewen [Institute of Theoretical Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Center of Theoretical Nuclear Physics, National Laboratory of Heavy-Ion Accelerator, Lanzhou, 730000 (China); Ko, C.M. [Cyclotron Institute, Texas A and M University, College Station, Texas 77843 (United States); Physics Department, Texas A and M University, College Station, Texas 77843 (United States); Steiner, Andrew W. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Yong Gaochan [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

2006-11-02

242

Ferromagnetic neutron stars: Axial anomaly, dense neutron matter, and pionic wall  

NASA Astrophysics Data System (ADS)

We show that a chiral nonlinear sigma model coupled to degenerate neutrons exhibits a ferromagnetic phase at high density. The magnetization is due to the axial anomaly acting on the parallel layers of neutral pion domain walls spontaneously formed at high density. The emergent magnetic field would reach the QCD scale ˜1019[G], which suggests that the quantum anomaly can be a microscopic origin of the magnetars (highly magnetized neutron stars).

Eto, Minoru; Hashimoto, Koji; Hatsuda, Tetsuo

2013-10-01

243

Accretion by a Neutron Star Moving at a High Kick Velocity in the Supernova Ejecta  

Microsoft Academic Search

We suggest a two-dimensional time dependent analytic model to describe the accretion of matter onto a neutron star moving at a high speed across the ejecta left in the aftermath of a supernova explosion. The formation of a strange star resulting from the accretion is also addressed. The newborn neutron star is assumed to move outward at a kick velocity

Xu Zhang; Ye Lu; Yong-Heng Zhao

2007-01-01

244

Neutron-capture nucleosynthesis in AGB stars  

NASA Astrophysics Data System (ADS)

Recent AGB models including diffusive overshoot or rotational effects suggest the partial mixing (PM) of protons from the H-rich envelope into the C-rich layers during the third dredge-up. In order to study the impact of such a mixing on the surface abundances, nucleosynthesis calculations based on stellar AGB models are performed for different assumptions of protons (ranging from X_pmix=10-6 to 0.7) in the PM zone. For high proton-to-12C abundance ratios, light nuclei such as fluorine and sodium are efficiently produced, while heavier s-process nuclei are synthesized for lower proton-to-12C ratios. In the framework of the PM model, assuming a smooth exponentially decreasing proton profile, the surface 19F abundance evolution is correlated with that of s-process nuclei in agreement with observations. However, as a function of the surface C/O abundance ratio, the surface 19F enrichment remains difficult to reconcile with observations in AGB stars. Sodium is predicted to be efficiently produced in a small region of the PM zone with proton-to-12C abundance ratio of about 10, but with large overproduction factors (up to fifty times higher than the sodium left over by the hydrogen burning shell). The primary 13C pocket formed in the PM zone at low proton-to-12C ratios is responsible for an efficient production of s-process nuclei. A table of elemental overabundances predicted at the surface of AGB stars at four different metallicities is presented. All the nucleosynthesis calculations are shown to suffer from major nuclear reaction rate uncertainties, in particular, 13C (p,?) 14N, 14N (n,p) 14C and 22Ne (?,n) 25Mg. The major uncertainties associated with the amount of protons mixed into the C-rich zone are found in the extent of the PM zone rather than in the adopted H profile. Finally, the PM scenario predicts that low-metallicity AGB stars enriched in s-process elements should exhibit a large overproduction of Pb and Bi compared to other s-isotopes. The search of such Pb-stars is highly encouraged.

Goriely, S.; Mowlavi, N.

2000-10-01

245

Stellar neutron sources and s-Process in Massive Stars  

NASA Astrophysics Data System (ADS)

Potential stellar neutron sources for the s-process in massive stars are associated with ?-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the buildup of the neutron sources ^22Ne, and ^26Mg during the helium-burning phase in stars. A critical influence on these reactions is expected to come from low-energy resonances at stellar energies between 300 keV and 1500 keV. It is possible that these resonances are characterized by a pronounced cluster structure near the ?-threshold. Direct measurements of capture reactions to study the cluster structure are handicapped by the Coulomb barrier and limited detector resolutions. Hence, inelastic ?-scattering on these nuclei has been used as an alternative tool to probe into the level structure. In reference to this, the experiment performed using the Grand Raiden Spectrometer at RCNP, Osaka will be discussed and preliminary results will be presented.

Talwar, R.; Berg, G. P. A.; Bin, L.; Couder, M.; Deboer, R.; Fang, X.; Fujita, H.; Fujita, Y.; Goerres, J.; Hatanaka, K.; Itoh, T.; Kadoya, T.; Long, A.; Masaru, Y.; Matsuda, Y.; Miki, K.; Tamii, A.; Wiescher, M.

2012-10-01

246

Binary Neutron Stars: Equilibrium Models beyond Spatial Conformal Flatness  

NASA Astrophysics Data System (ADS)

Equilibria of binary neutron stars in close circular orbits are computed numerically in a waveless formulation: the full Einstein-relativistic-Euler system is solved on an initial hypersurface to obtain an asymptotically flat form of the 4-metric and an extrinsic curvature whose time derivative vanishes in a comoving frame. Two independent numerical codes are developed, and solution sequences that model inspiraling binary neutron stars during the final several orbits are successfully computed. The binding energy of the system near its final orbit deviates from earlier results of third post-Newtonian and of spatially conformally flat calculations. The new solutions may serve as initial data for merger simulations and as members of quasiequilibrium sequences to generate gravitational-wave templates, and may improve estimates of the gravitational-wave cutoff frequency set by the last inspiral orbit.

Ury?, K?ji; Limousin, François; Friedman, John L.; Gourgoulhon, Eric; Shibata, Masaru

2006-10-01

247

Phase-Resolved Optical Emission from Isolated Neutron Stars  

NASA Astrophysics Data System (ADS)

In the last two years the number of pulsars with confirmed optical pulsations has increased from 3 to 5, with new `middle aged' candidate data coming to light, and several other `upper limit' objects. Based upon this growing dataset, the implications for current theoretical models for both emission theory and neutron star structure is assessed. In particular, through considerations of the resolved unpulsed predominately thermal optical flux we are able to constrain (R/d) for two nearby middle aged neutron stars, yielding upper limits for the radius of Geminga (<= 9.5 km) and the distance of PSR B0656+14 (~210 pc). From the pulsed emission we are able to show that modifications to existing phenomenological models are required to take account of emission primarily near the light cylinder.

Shearer, A.; Golden, A.; O'Conner, P.; Beskin, G.; Redfern, M.

1999-07-01

248

1S0 Nucleon Superfluidity in Neutron Star Matter  

NASA Astrophysics Data System (ADS)

We investigate the nucleon superfluidity in the 1S0 channel in neutron star matter using the relativistic mean field theory and the BCS theory. We discuss particularly the influence of the isovector scalar interaction which is considered by exchanging ? meson on the nucleon superfluidity. It is found that the ? meson leads to a growth of the nucleon 1S0 pairing energy gaps in a middle density range of the existing nucleon superfluidity. In addition, when the density ?B > 0.36 fm-3, the proton 1S0 pairing energy gap obviously decreases. The density range of the proton 1S0 superfluidity is narrowed due to the presence of ? mesons. In our results, the ? meson not only changes the EOS and bulk properties but also changes the cooling properties of neutron stars.

Xu, Yan; Liu, Guang-Zhou; Liu, Cheng-Zhi; Fan, Cun-Bo; Han, Xing-Wei; Zhu, Ming-Feng; Wang, Hong-Yan; Zhang, Xiao-Jun

2013-06-01

249

Quark matter in neutron stars within the field correlator method  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

250

Neutron star models with Douchin-Haensel equation of state  

NASA Astrophysics Data System (ADS)

In order to compute the internal structure of a neutron star and its space-time geometry, the unified equation of state obtained by Douchin and Haensel is used. The results are given in graphical form, in which the variations of mass and of radius are given as functions of central density and of dimensionless central pressure. The last one is a measure of the strength of gravitational field. The numerical results are in good agreement with those obtained by Douchin and Haensel. The maximum mass, reached at the central density 2.8 . 1018 kg . m-3, is 2.09 MSun, the corresponding radius is 9.85 km and the dimensionless central pressure is 0.53. The space-time geometry inside the neutron star and in its neighborhood is studied. The coefficients, which give the proper time and the radial distance, are determined.

Ureche, Vasile; Roman, Rodica; Oproiu, Tiberiu

2007-03-01

251

Possible implications of asymmetric fermionic dark matter for neutron stars  

NASA Astrophysics Data System (ADS)

We consider the implications of fermionic asymmetric dark matter (ADM) for a "mixed neutron star" composed of ordinary baryons and dark fermions. We find examples, where for a certain range of dark fermion mass – when it is less than that of ordinary baryons – such systems can reach higher masses than the maximal values allowed for ordinary ("pure") neutron stars. This is shown both within a simplified, heuristic Newtonian analytic framework with non-interacting particles and via a general relativistic numerical calculation, under certain assumptions for the dark matter equation of state. Our work applies to various dark fermion models such as mirror matter models and to other models where the dark fermions have self-interactions.

Goldman, I.; Mohapatra, R. N.; Nussinov, S.; Rosenbaum, D.; Teplitz, V.

2013-10-01

252

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

SciTech Connect

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.

Ghezzi, Cristian R. [Instituto de Matematica, Estatistica e Computacao Cientifica, Universidade Estadual de Campinas, Campinas, Sao Paulo (Brazil)

2005-11-15

253

Surface Vibrations of Stratified Neutron Star in the Newtonian Limit of Gravity  

Microsoft Academic Search

From theoretical analysis of the radial distribution of bulk density in the neutron star interior it follows that a neutron star is a strongly stratified compact stellar object with a rather complicated layering structure: the density of outer layers (crust, neutron-rich nuclei, electrons) is much less than the density of the inner region of the stiff core (dense matter of

S. I. Bastrukov

1996-01-01

254

White dwarfs and neutron stars with neutrino retention  

SciTech Connect

The mass and radius of white dwarfs and neutron stars as functions of the central density are calculated with allowance for the effect of neutrino retention. A model in which all the fermions are degenerate and a neutrino flux is absent is analyzed. It is shown that neutrino retention leads to a considerable increase in the mass limit and a shift of the point of stability loss toward lower densities.

Vartanyan, Y.L.; Ovakimova, N.K.

1978-09-01

255

Atomic Spectral Features during Thermonuclear Flashes on Neutron Stars  

Microsoft Academic Search

The gravitational redshift measured by Cottam, Paerels, and Mendez for the neutron star (NS) in the low-mass X-ray binary EXO 0748 -676 depends on the identification of an absorption line during a type I burst as the Halpha line from hydrogenic Fe. We show that Fe is present above the photosphere as long as M>4×10-13 Msolar yr-1 during the burst.

Lars Bildsten; Philip Chang; Frits Paerels

2003-01-01

256

Predicting neutron star spins from twin kHz QPOs  

NASA Astrophysics Data System (ADS)

We briefly review the proposed relations between the frequencies of twin kilohertz quasi-periodic oscillations (kHz QPOs) and the spin frequencies in neutron star low-mass X-ray binaries (NSLMXBs). To test the validity of the proposed models, we estimate the spin frequencies under these theoretical relations and compare them with the measured ones. It seems that magnetohydrodynamic (MHD) oscillations are more promising to account for the kHz QPOs.

Shi, Changsheng

2010-01-01

257

Smashing the Guitar: An Evolving Neutron Star Bow Shock  

Microsoft Academic Search

The Guitar Nebula is a spectacular example of an Halpha bow shock nebula produced by the interaction of a neutron star with its environment. The radio pulsar B2224+65 is traveling at ~800-1600 km s-1 (for a distance of 1-2 kpc), placing it on the high-velocity tail of the pulsar velocity distribution. Here we report time evolution in the shape of

S. Chatterjee; J. M. Cordes

2004-01-01

258

The Cosmic Coalescence Rates for Double Neutron Star Binaries  

Microsoft Academic Search

We report on the newly increased event rates due to the recent discovery of the highly relativistic binary pulsar J0737-3039. Using a rigorous statistical method, we present the calculations reported by Burgay et al., which produce a coalescence rate for Galactic double neutron star (DNS) systems that is higher by a factor of 6-7 compared to estimates made prior to

V. Kalogera; C. Kim; D. R. Lorimer; M. Burgay; N. D'Amico; A. Possenti; R. N. Manchester; A. G. Lyne; B. C. Joshi; M. A. McLaughlin; M. Kramer; J. M. Sarkissian; F. Camilo

2004-01-01

259

Electromagnetic activity of a pulsating paramagnetic neutron star  

Microsoft Academic Search

The fact that neutron star matter possesses the capability of maintaining a highly intense magnetic field has been and still\\u000a is among the most debatable issues in pulsar astrophysics. Over the years, there were several independent suggestions that\\u000a the dominant source of pulsar magnetism is either the field-induced or the spontaneous magnetic polarization of the baryon\\u000a material. The Pauli paramagnetism

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

2002-01-01

260

Black Hole and Neutron Star Transients in Quiescence  

Microsoft Academic Search

We consider the X-ray luminosity difference between neutron star and black hole soft X-ray transients (NS and BH SXTs) in quiescence. The current observational data suggest that BH SXTs are significantly fainter than NS SXTs. The luminosities of quiescent BH SXTs are consistent with the predictions of binary-evolution models for the mass transfer rate if (1) accretion occurs via an

Kristen Menou; Ann A. Esin; Ramesh Narayan; Michael R. Garcia; Jean-Pierre Lasota; Jeffrey E. McClintock

1999-01-01

261

Photon-electron-positron interactions in neutron star magnetospheres  

SciTech Connect

The particle-energy dependence of the radiative braking force exerted on relativistic electrons and positrons is studied for several different elementary interaction processes: Thomson, Compton, and cyclotron scattering and electron-positron-pair creation. If certain criteria are met these processes can significantly retard particle acceleration by the electric field in the magnetosphere of an active neutron star. Moreover, hard gamma rays may be generated. Some astrophysical implications are discussed. 18 references.

Kardashev, N.S.; Mitrofanov, I.G.; Novikov, I.D.

1984-12-01

262

Shattering Flares during Close Encounters of Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

Tsang, David

2013-11-01

263

Lattice defects in the crust of a neutron star  

NASA Astrophysics Data System (ADS)

We investigate the problem of defects in the crust of a neutron star and their possible astrophysical consequences. We consider point defects (impurities, lattice vacancies) and microcrystalline structures resulting from non-equilibrium processes (nuclear condensation, ionic migration, crystallization, etc.) as well as from equilibrium configurations at finite temperature. Our findings suggest that the presence of impurities is likely while vacancies, microcrystals or a glassy state are probably absent.

de Blasio, F. V.; Lazzari, G.

1998-04-01

264

Structure of Neutron Stars with Unified Equations of State  

NASA Astrophysics Data System (ADS)

We present a set of three unified equations of states (EoSs) based on the nuclear energy-density functional (EDF) theory. These EoSs are based on generalized Skyrme forces fitted to essentially all experimental atomic mass data and constrained to reproduce various properties of infinite nuclear matter as obtained from many-body calculations using realistic two- and three-body interactions. The structure of cold isolated neutron stars is discussed in connection with some astrophysical observations.

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

2012-12-01

265

Thermal origin of neutron star magnetic fields  

NASA Astrophysics Data System (ADS)

The authors summarize and extend the analysis of thermoelectric phenomena in degenerate stars due to Urpin and Yakovlev (1980) and calculate necessary conditions for field generation. A linearized calculation of the growth of the field in the solid crust is given, which demonstrates that small seed fields can grow exponentially for sufficiently large heat fluxes. Non-linear growth of the field in the liquid is described. If the field strength can grow to ?1011 G, the electron gyrofrequency will exceed the collision frequency and the field growth in the solid will enter the non-linear phase. The Hall effect will lead to rapid convection of magnetic flux and the creation of progressively larger scale structure, perhaps resulting in the establishment of an axisymmetric field geometry. In the absence of external heat sources, the interior of the star will cool and the field will decay. The authors outline some of the observational consequences of this theory for pulsars, binary X-ray sources, X- and ?-ray bursters and white dwarfs.

Blandford, R. D.; Applegate, J. H.; Hernquist, L.

1983-09-01

266

Magnetic Compton scattering near a hot neutron star polar CAP  

NASA Astrophysics Data System (ADS)

We presents results of a model for the energetics of electrons accelerated away from a neutron star polar cap by the large electric fields generated by the rotating highly magnetized neutron star. The energy loss mechanisms we consider in our calculations include magnetic Compton scattering of thermal X-ray photons, triplet pair production, and curvature radiation emission. The electron acceleration mechanism is assumed to operate only to a height above the polar cap approximately equal to the polar cap radius. We find several interesting results. First, magnetic Compton scattering is the dominant energy loss process when the electron Lorentz factors are below 107 for typical gamma-ray pulsar magnetic fields and surface temperatures. The amount of energy converted to photons by accelerated electrons ranges from approximately 10-100% of gammao mc2 for pulsar parameters similar to those observed where gammao is the maximum Lorentz factor an electron can attain with no radiative losses. We also find that if B is greater than 1013 G and T is greater than 3 x 10(exp6)K, the Lorentz factors of the electrons can be limited to values of 102-103 assuming values for the size of the neutron star thermal polar cap comparable to the polar cap size determined by the open field lines. Such small Lorentz factors may be capable of explaining the gamma-ray emission from PSR 1509-58 which is observed only to about 1 MeV.

Sturner, S. J.; Dermer, C. D.

1995-05-01

267

Neutron star deformation due to multipolar magnetic fields  

NASA Astrophysics Data System (ADS)

Certain multiwavelength observations of neutron stars, such as intermittent radio emissions from rotation-powered pulsars beyond the pair-cascade death line, the pulse profile of the magnetar SGR 1900+14 after its 1998 August 27 giant flare and X-ray spectral features of PSR J0821-4300 and SGR 0418+5729, suggest that the magnetic fields of non-accreting neutron stars are not purely dipolar and may contain higher order multipoles. Here, we calculate the ellipticity of a non-barotropic neutron star with (i) a quadrupole poloidal-toroidal field, and (ii) a purely poloidal field containing arbitrary multipoles, deriving the relation between the ellipticity and the multipole amplitudes. We present, as a worked example, a purely poloidal field comprising dipole, quadrupole and octupole components. We show the correlation between field energy and ellipticity for each multipole, that the l = 4 multipole has the lowest energy, and that l = 5 has the lowest ellipticity. We show how a mixed multipolar field creates an observationally testable mismatch between the principal axes of inertia (to be inferred from gravitational wave data) and the magnetic inclination angle. Strong quadrupole and octupole components (with amplitudes ˜102 times higher than the dipole) in SGR 0418+5729 still yield ellipticity ˜10-8, consistent with current gravitational wave upper limits. The existence of higher multipoles in fast-rotating objects (e.g. newborn magnetars) has interesting implications for the braking law and hence phase tracking during coherent gravitational wave searches.

Mastrano, A.; Lasky, P. D.; Melatos, A.

2013-09-01

268

Linking electromagnetic and gravitational radiation in coalescing binary neutron stars  

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

269

Neutron star cooling in various sets of nucleon coupling constants  

NASA Astrophysics Data System (ADS)

The influences of nucleon coupling constants on the neutrino scatting and cooling properties of neutron stars are investigated. The results in the GM1, GPS250 and NL-SH parameter sets show that the magnitude of the neutrino emissivity and density ranges where the dUrca process of nucleons is allowed differ obviously between the three parameter sets in nucleon-only and hyperonic matter. Furthermore, the neutron stars in the GPS250 set cool very quickly, whereas those in the NL-SH set cool slowly. The cooling rate of the former can be almost three times more that of the latter. It can be concluded that the stiffer the equation of state, the slower the corresponding neutron stars cool. The hyperon ? makes neutrino emissivity due to the direct Urca process of nucleons lower compared with nucleon-only matter, and postpones the dUrca process with muons. However, these ? effects are relatively weaker in the GPS250 set than in the GM1 set.

Ding, Wen-Bo; Yu, Zi; Mi, Geng; Wang, Chun-Yan

2013-05-01

270

Topics in the physics and astrophysics of neutron stars  

NASA Astrophysics Data System (ADS)

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 in both regimes are presented for various temperatures and densities, and compared with those of classical molecular dynamical simulations performed for the same system by collaborators from Indiana University. For heavy-ion plasmas, as energetically favored in the outer crust of a neutron star, excellent agreement was found between the results of semi-analytic calculations and those of molecular dynamical simulations. However, in the case of light-ion plasmas, substantial differences were found between the results of quantum and classical cases, which underscores the importance of incorporating quantum effects in molecular dynamical simulations, even in the dilute limit. In the third topic, first steps are taken to reconstruct the uncertain high-density nuclear equation of state from the measured masses and radii of several individual stars. Inherent errors of the measurements are incorporated into the analysis. A new inversion procedure of the Tolman-Oppenheimer-Volkov stellar structure equation is developed so that a model independent dense matter of equation can be derived from observations. Successful tests of the inversion procedure emphasize the need to determine the masses and especially the radii of several individual stars. The aim here is to provide a benchmark equation of state for theoretical advances to be made. The fourth topic is concerned with the emerging field of gravitational-wave detections and its ability to shed light on the dense matter equation of state. In an external tidal gravitational field, as for example in binary star configurations, each star deforms and acquires a quadrupole moment. The quadrupole polarizability given by the coefficient of proportionality between the induced moment and the field called the tidal Love number after the English mathematician Love. By calculating Love numbers for several model equations of state, connections between the underlying equation of state, star structure and the tidal Love numbers of normal neutron stars and self-bound strange quark matter stars are established. It is shown that the meas

Postnikov, Sergey

271

Conditions for phase equilibrium in supernovae, protoneutron, and neutron stars  

NASA Astrophysics Data System (ADS)

We investigate 1st order phase transitions in a general way, if not the single particle numbers of the system but only some particular charges like e.g. baryon number are conserved. In addition to globally conserved charges, we analyze the implications of locally conserved charge fractions, like e.g. local electric charge neutrality or locally fixed proton or lepton fractions. The conditions for phase equilibrium are derived and it is shown, that the properties of a phase transformation do not depend on the locally conserved fractions but only on the number of globally conserved charges. Finally, the general formalism is applied to the liquid-gas phase transition of nuclear matter and the hadron-quark phase transition for typical astrophysical environments like in supernovae, protoneutron, or neutron stars. We demonstrate that the Maxwell construction known from cold-deleptonized neutron star matter with two locally charge neutral phases requires modifications and further assumptions concerning the applicability for hot lepton-rich matter. All relevant combinations of local and global conservation laws are analyzed, and the physical meaningful cases are identified. Several new kinds of mixed phases are presented, as e.g. a locally charge neutral mixed phase in protoneutron stars which will disappear during the cooling and deleptonization of the protoneutron star.

Hempel, M.; Pagliara, G.; Schaffner-Bielich, J.

2009-12-01

272

Quark-Gluon Plasma in Neutron Stars  

NASA Astrophysics Data System (ADS)

This work is a study of nuclear matter at high densities considering the hadronic and quark phases at zero temperature. We describe the hadron-meson phase using a phenomenological Lagrangian which exhibits a parametrization, through mathematical constants, of the intensity of the meson-nucleon coupling. We have included into the formalism the chemical equilibrium equations, lepton degrees of freedom, the fundamental octet of baryons and the charge neutrality condition. In the quark matter study, we have considered the classic MIT bag model with a constant bag pressure. Phase transition is determined by the Gibbs criteria. The influence of the model couplings in the determination of the phase transition density is discussed. We have also calculated maximum mass and radius for hybrid stars.

Jacobsen, R. B.; Vasconcellos, C. A. Z.; Bodmann, B. E. J.; Fernández, F.

2010-04-01

273

Stellar Wind Disruption by an Orbiting Neutron Star: Low X-Ray Luminosity  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. This simulation, in the reference frame of the neutron star, shows conditions of low X-ray luminosity. in which there is a small accretion radius, a slight asymmetry, and short timescales for variability. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

274

Stellar Wind Disruption by an Orbiting Neutron Star: Moderate X-Ray Luminosity  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. This simulation, in the reference frame of the neutron star, shows conditions of low X-ray luminosity. in which there is a large accretion radius, significant asymmetry, and long timescales for variability. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

275

Stellar Wind Disruption by an Orbiting Neutron Star: High X-Ray Luminosity  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. This simulation, in the reference frame of the neutron star, shows conditions of high X-ray luminosity. in which there is a weak bowshock, no oscillation, and a large photoionization wake. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

276

Detectability of equation of state parameters from black hole-neutron star inspiral  

NASA Astrophysics Data System (ADS)

Gravitational waves from compact binaries containing neutron stars may provide an important source of information regarding the neutron star equation of state. In contrast to binary neutron star inspirals where finite size effects are observed from tidal interactions and post-merger oscillations, the main finite size effect in black hole-neutron star systems is tidal disruption of the neutron star and its effect on the black hole ringdown. Recently Shibata et al. performed a set of black hole-neutron star simulations where two equation of state parameters were systematically varied. Using these simulations, we discuss the accuracy to which equation of state parameters can be measured with Advanced LIGO and the proposed Einstein Telescope.

Lackey, Benjamin; Kyutoku, Koutarou; Shibata, Masaru; Brady, Patrick; Friedman, John

2011-04-01

277

Complex Orbital Dynamics of a Double Neutron Star System Revolving around a Massive Black Hole  

NASA Astrophysics Data System (ADS)

We investigate the orbital dynamics of hierarchical three-body systems containing a double neutron star system orbiting around a massive black hole. These systems show complex dynamical behavior because of relativistic coupling between orbits of the neutron stars in the double neutron star system and the orbit of the double neutron star system around the black hole. The orbital motion of the neutron stars around each other drives a loop mass current, which gives rise to gravito-magnetism. Generally, gravito-magnetism involves a rotating black hole. The hierarchical three-body system that we consider is an unusual situation in which black hole rotation is not required. Using a gravito-electromagnetic formulation, we calculate the orbital precession and nutation of the double neutron star system. These precession and nutation effects are observable, thus providing probes to the spacetime around black holes as well as tests of gravito-electromagnetism in the framework of general relativity.

Remmen, Grant; Wu, Kinwah

2013-04-01

278

Complex orbital dynamics of a double neutron star system revolving around a massive black hole  

NASA Astrophysics Data System (ADS)

We investigate the orbital dynamics of hierarchical three-body systems containing a double neutron star system orbiting around a massive black hole. These systems show complex dynamical behaviour because of relativistic coupling between orbits of the neutron stars in the double neutron star system and the orbit of the double neutron star system around the black hole. The orbital motion of the neutron stars around each other drives a loop mass current, which gives rise to gravitomagnetism. Generally, gravitomagnetism involves a rotating black hole. The hierarchical three-body system that we consider is an unusual situation in which black hole rotation is not required. Using a gravitoelectromagnetic formulation, we calculate the orbital precession and nutation of the double neutron star system. These precession and nutation effects are observable, thus providing probes to the space-time around black holes as well as tests of gravitoelectromagnetism in the framework of general relativity.

Remmen, Grant N.; Wu, Kinwah

2013-04-01

279

Coalescing neutron stars - gravitational waves from polytropic models.  

NASA Astrophysics Data System (ADS)

The dynamics, time evolution of the mass distribution, and gravitational wave signature of coalescing neutron stars described by polytropes are compared with three simulations published previously: (a) "Run 2" of Zhuge et al. (1994PhRvD..50.6247Z), (b) "Model III" of Shibata et al. (1992, Prog, Theor. Phys. 88, 1079), and (c) "Model A64" of Ruffert et al. (1996A&A...311..532R). We aim at studying the differences due to the use of different numerical methods, different implementations of the gravitational wave backreaction, and different equations of state. We integrate the three-dimensional Newtonian equations of hydrodynamics by the Riemann-solver based "Piecewise Parabolic Method" on an equidistant Cartesian grid. Comparison (a) confronts the results of our grid-based PPM scheme with those from an SPH code. We find that due to the lower numerical viscosity of the PPM code, the post-merging oscillations and pulsations can be followed for a longer time and lead to larger secondary and tertiary maxima of the gravitational wave luminosity and to a stronger peak of the gravitational wave spectrum at a frequency of about f=~1.8KHz when compared to the results of Zhuge et al. (1994PhRvD..50.6247Z). In case (b) two grid based codes with the same backreaction formalism but differing hydrodynamic integrators and slightly different initial conditions are compared. Instead of rotationally deformed initial neutron stars we use spherically shaped stars. Satisfactory agreement of the amplitude of the gravitational wave luminosity is established, although due to the different initial conditions a small time delay develops in the onset of the dynamical instability setting in when the two stars come very close. In (c) we find that using a polytropic equation of state instead of the high-density equation of state of Lattimer & Swesty (1991, Nucl. Phys. A535, 331) employed by Ruffert et al. (1996A&A...311..532R) does not change the overall dynamical evolution of the merger and yields agreement of the gravitational wave signature to within 20% accuracy. Whereas the polytropic law describes the dynamical behaviour of the bulk of the matter at and above nuclear density sufficiently well, we, however, find clear differences of the structure and evolution of the outer layers of the neutron stars where the stiffness of the equation of state is largely overestimated. This has important implications for questions like mass loss and disk formation during the merging of binary neutron stars.

Ruffert, M.; Rampp, M.; Janka, H.-T.

1997-05-01

280

Advection of magnetic flux by accretion disks around neutron stars  

NASA Astrophysics Data System (ADS)

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

Flores-Tulian, S.; Reisenegger, A.

281

Neutron Rich Matter at Subnuclear Densities in Neutron Stars and Supernovae  

NASA Astrophysics Data System (ADS)

The virial expansion is used to make model independent determinations of the composition, equation of state, and neutrino response of nuclear matter at densities near 1011 to 1013 g cm-3. Experimental nucleon-nucleon, alpha-nucleon, and alpha-alpha scattering phase shifts are used as input. We compare to existing model dependent equations of state such as Lattimer-Swesty and Shen. Our virial expansion corrects nuclear statistical equilibrium (NSE) models for the strong interactions between nuclei and or nucleons. Next, properties of the complex "nuclear pasta" phases in the inner crust of neutron stars are determined with large scale molecular dynamics simulations. Finally, we present an update of the Parity Radius Experiment (PREX) to measure the neutron skin in 208Pb. This has many implications for neutron stars.

Horowitz, Charles J.

282

General relativistic simulations of magnetized binary neutron star mergers  

SciTech Connect

Binary neutron stars (NSNS) are expected to be among the leading sources of gravitational waves observable by ground-based laser interferometers and may be the progenitors of short-hard gamma-ray bursts. We present a series of general relativistic NSNS coalescence simulations both for unmagnetized and magnetized stars. We adopt quasiequilibrium initial data for circular, irrotational binaries constructed in the conformal thin-sandwich (CTS) framework. We adopt the BSSN formulation for evolving the metric and a high-resolution shock-capturing scheme to handle the magnetohydrodynamics. Our simulations of unmagnetized binaries agree with the results of Shibata, Taniguchi and Uryu [M. Shibata, K. Taniguchi, and K. Uryu, Phys. Rev. D 68, 084020 (2003).]. In cases in which the mergers result in a prompt collapse to a black hole, we are able to use puncture gauge conditions to extend the evolution and determine the mass of the material that forms a disk. We find that the disk mass is less than 2% of the total mass in all cases studied. We then add a small poloidal magnetic field to the initial configurations and study the subsequent evolution. For cases in which the remnant is a hypermassive neutron star, we see measurable differences in both the amplitude and phase of the gravitational waveforms following the merger. For cases in which the remnant is a black hole surrounded by a disk, the disk mass and the gravitational waveforms are about the same as the unmagnetized cases. Magnetic fields substantially affect the long-term, secular evolution of a hypermassive neutron star (driving 'delayed collapse') and an accretion disk around a nascent black hole.

Liu, Y.T.; Shapiro, Stuart L.; Etienne, Zachariah B.; Taniguchi, Keisuke [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2008-07-15

283

Gamma-ray bursts via pair plasma fireballs from heated neutron stars  

SciTech Connect

In this paper the authors model the emission from a relativistically expanding e{sup +}e{sup {minus}} pair plasma fireball originating near the surface of a heated neutron star. This pair fireball is deposited via the annihilation of neutrino pairs emanating from the surface of the hot neutron star. The heating of neutron stars may occur in close neutron star binary systems near their last stable orbit. The authors model the relativistic expansion and subsequent emission of the plasma and find {approximately} 10{sup 51}--10{sup 52} ergs in {gamma}-rays are produced with spectral and temporal properties consistent with observed gamma-ray bursts.

Salmonson, J D; Wilson, J R; Matthews, G J

2000-01-11

284

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

SciTech Connect

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.

Romani, R.W.; Rajagopal, M. [Stanford Univ., CA (United States). Dept. of Physics; Rogers, F.J.; Iglesias, C.A. [Lawrence Livermore National Lab., CA (United States)

1995-05-23

285

Instanton effects in the equation of state for dense neutron star matter  

Microsoft Academic Search

Vacuum fluctuation effects in quantum chromodynamics due to instantons were studied in dense neutron state matter. In the density region of interest to neutron star cores, a density dependence of approximately (n syb B)(-1\\/3) was found.

C. G. Kaellman

1979-01-01

286

Instanton Effects in the Equation of State for Dense Neutron Star Matter.  

National Technical Information Service (NTIS)

Vacuum fluctuation effects in quantum chromodynamics due to instantons were studied in dense neutron state matter. In the density region of interest to neutron star cores, a density dependence of approximately (n syb B)(-1/3) was found.

C. G. Kaellman

1979-01-01

287

Studies of neutron star X-ray binaries  

NASA Astrophysics Data System (ADS)

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

Thompson, Thomas W. J.

288

Critical phenomena in neutron stars: I. Linearly unstable nonrotating models  

NASA Astrophysics Data System (ADS)

We consider the evolution in full general relativity of a family of linearly unstable isolated spherical neutron stars under the effects of very small perturbations as induced by the truncation error. Using a simple ideal-fluid equation of state, we find that this system exhibits a type I critical behaviour, thus confirming the conclusions reached by Liebling et al (2010 arXiv:1001.0575v1) for rotating magnetized stars. Exploiting the relative simplicity of our system, we are able to carry out a more in-depth study providing solid evidence of the criticality of this phenomenon and also to give a simple interpretation of the putative critical solution as a spherical solution with the unstable mode being the fundamental F-mode. Hence for any choice of the polytropic constant, the critical solution will distinguish the set of subcritical models migrating to the stable branch of the models of equilibrium from the set of subcritical models collapsing to a black hole. Finally, we study how the dynamics changes when the numerical perturbation is replaced by a finite-size, resolution-independent velocity perturbation and show that in such cases a nearly critical solution can be changed into either a sub- or supercritical one. The work reported here also lays the basis for the analysis carried in a companion paper, where the critical behaviour in the head-on collision of two neutron stars is instead considered (Kellerman et al 2010 Class. Quantum Grav. 27 235016).

Radice, David; Rezzolla, Luciano; Kellerman, Thorsten

2010-12-01

289

Plasmon excitations in homogeneous neutron-star matter  

SciTech Connect

We study the possible collective plasma modes which can affect neutron-star thermodynamics and different elementary processes in the baryonic density range between nuclear saturation {rho}{sub 0} and 3{rho}{sub 0}. In this region, the expected constituents of neutron-star matter are mainly neutrons, protons, electrons, and muons (npe{mu} matter), under the constraint of beta equilibrium. The elementary plasma excitations of the pe{mu} three-fluid medium are studied in the RPA framework. We emphasize the relevance of the Coulomb interaction among the three species, in particular, the interplay of the electron and muon screening in suppressing the possible proton plasma mode, which is converted into a sound-like mode. The Coulomb interaction alone is able to produce a variety of excitation branches and the full spectral function shows a rich structure at different energy. The genuine plasmon mode is pushed at high energy and it contains mainly an electron component with a substantial muon component, which increases with density. The plasmon is undamped for not too large momentum and is expected to be hardly affected by the nuclear interaction. All the other branches, which fall below the plasmon, are damped or over-damped.

Baldo, M.; Ducoin, C. [Universita di Catania, Dipartimento di Fisica (Italy)

2009-07-15

290

Tidal Streams in Massive X-ray Binary Systems: Neutron Star Close-up  

NSDL National Science Digital Library

A tiny neutron star orbits incessantly around a massive star with a diameter a million times larger than its own. The high luminosity of the massive star drives a strong wind from its surface. The neutron star crashes through this wind at over 300 kilometers per second. The gravity and X-ray luminosity of the neutron star act to disrupt the wind, producing an extended wake of dense gas trailing behind the neutron star. In this simulation, the tidal distortion of the primary star and the resultant tidal stream is shown. The numerical simulations depicted here were computed using the Cray X-MP 48 at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign.

Mcconnell, Alan; Blondin, John; Stevens, Ian; Kallman, Tim; Fryxell, Bruce; Taam, Ron

1990-07-10

291

Three-dimensional evolution of differentially rotating magnetized neutron stars  

NASA Astrophysics Data System (ADS)

We construct a new three-dimensional general relativistic magnetohydrodynamics code, in which a fixed mesh refinement technique is implemented. To ensure the divergence-free condition as well as the magnetic flux conservation, we employ the method by Balsara [J. Comp. Physiol.JRCPA30373-0859 174, 614 (2001); J. Comp. Phys. 228, 5040 (2009)JCTPAH0021-999110.1016/j.jcp.2009.03.038]. Using this new code, we evolve differentially rotating magnetized neutron stars, and find that a magnetically driven outflow is launched from the star exhibiting a kink instability. The matter ejection rate and Poynting flux are still consistent with our previous finding [M. Shibata, Y. Suwa, K. Kiuchi, and K. Ioka, Astrophys. J. 734, L36 (2011)] obtained in axisymmetric simulations.

Kiuchi, Kenta; Kyutoku, Koutarou; Shibata, Masaru

2012-09-01

292

Axion cyclotron emissivity of magnetized white dwarfs and neutron stars  

NASA Astrophysics Data System (ADS)

The energy loss rate of a magnetized electron gas emitting axions a due to the process e--->e-+a is derived for arbitrary magnetic field strength B. Requiring that for a strongly magnetized neutron star the axion luminosity is smaller than the neutrino luminosity we obtain the bound gae<~10-10 for the axion electron coupling constant. This limit is considerably weaker than the bound derived earlier by Borisov and Grishina using the same method. Applying a similar argument to magnetic white dwarf stars results in the more stringent bound gae<~9×10-13(T/107K)5/4(B/1010G)-2, where T is the internal temperature of the white dwarf.

Kachelriess, M.; Wilke, C.; Wunner, G.

1997-07-01

293

Temperature profiles of accretion discs around rapidly rotating strange stars in general relativity: A comparison with neutron stars  

NASA Astrophysics Data System (ADS)

We compute the temperature profiles of accretion discs around rapidly rotating strange stars, using constant gravitational mass equilibrium sequences of these objects, considering the full effect of general relativity. Beyond a certain critical value of stellar angular momentum (J), we observe the radius (r_orb) of the innermost stable circular orbit (ISCO) to increase with J (a property seen neither in rotating black holes nor in rotating neutron stars). The reason for this is traced to the crucial dependence of dr_orb/dJ on the rate of change of the radial gradient of the Keplerian angular velocity at r_orb with respect to J. The structure parameters and temperature profiles obtained are compared with those of neutron stars, as an attempt to provide signatures for distinguishing between the two. We show that when the full gamut of strange star equation of state models, with varying degrees of stiffness are considered, there exists a substantial overlap in properties of both neutron stars and strange stars. However, applying accretion disc model constraints to rule out stiff strange star equation of state models, we notice that neutron stars and strange stars exclusively occupy certain parameter spaces. This result implies the possibility of distinguishing these objects from each other by sensitive observations through future X-ray detectors.

Bhattacharyya, S.; Thampan, A. V.; Bombaci, I.

2001-06-01

294

CONSTRAINTS ON NATAL KICKS IN GALACTIC DOUBLE NEUTRON STAR SYSTEMS  

SciTech Connect

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.

Wong, Tsing-Wai; Willems, Bart; Kalogera, Vassiliki, E-mail: TsingWong2012@u.northwestern.ed, E-mail: b-willems@northwestern.ed, E-mail: vicky@northwestern.ed [Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)

2010-10-01

295

The Coalescence Rate of Double Neutron Star Systems  

Microsoft Academic Search

We estimate the coalescence rate of close binaries with two neutron stars\\u000a(NS) and discuss the prospects for the detection of NS-NS inspiral events by\\u000aground-based gravitational-wave observatories, such as LIGO. We derive the\\u000aGalactic coalescence rate using the observed sample of close NS-NS binaries\\u000a(PSR B1913+16 and PSR B1534+12) and examine in detail each of the sources of\\u000auncertainty

V. Kalogera; R. Narayan; D. N. Spergel; J. H. Taylor

2000-01-01

296

Optical, ultraviolet, and infrared observations of isolated neutron stars  

NASA Astrophysics Data System (ADS)

Forty years passed since the optical identification of the first isolated neutron star (INS), the Crab pulsar. 25 INSs have been now identified in the optical (O), near-ultraviolet (nUV), or near-infrared (nIR), hereafter UVOIR, including rotation-powered pulsars (RPPs), magnetars, and X-ray-dim INSs (XDINSs), while deep investigations have been carried out for compact central objects (CCOs), Rotating RAdio transients (RRATs), and high-magnetic field radio pulsars (HBRPs). In this review I describe the status of UVOIR observations of INSs, their emission properties, and I present the results from recent observations.

Mignani, Roberto P.

2011-04-01

297

Virtual Trips to Black Holes and Neutron Stars  

NSDL National Science Digital Library

Ever wonder what it would look like to travel to a black hole? A neutron star? If so, you might find this page interesting. Here you will find descriptions and MPEG movies that take you on such exciting trips. These movies are scientifically accurate computer animations made with strict adherence to Einstein's General Theory of Relativity. The descriptions are written to be understandable on a variety of levels - from the casually curious to the professionally inquisitive. It is hoped that students from grade school to graduate school will find these virtual trips educational.

Nemiroff, Robert

2009-03-31

298

Vortex pinning by quenched randomness in neutron stars  

NASA Astrophysics Data System (ADS)

Pulsar glitches are commonly attributed to the transfer of angular momentum from the superfluid to the solid crust. The change in angular momentum of the neutron superfluid is determined by the motion of its vortex lines. In the star's inner crust, we assume vortices are pinned by density fluctuations of defects (vacancies in the nuclear lattice or impurities) and move by the process of vortex creep. The vortex line, subjected to a random potential, has many metastable states for which a barrier energy and a pinning force are estimated. Scaling properties of vortex creep including both quantum and classical unpinning processes are obtained, namely the vortex creep velocity and the crossover temperature.

Chevalier, Eric

1993-09-01

299

Maximum mass and radius of neutron stars, and the nuclear symmetry energy  

NASA Astrophysics Data System (ADS)

We calculate the equation of state of neutron matter with realistic two- and three-nucleon interactions using quantum Monte Carlo techniques and illustrate that the short-range three-neutron interaction determines the correlation between neutron matter energy at nuclear saturation density and higher densities relevant to neutron stars. Our model also makes an experimentally testable prediction for the correlation between the nuclear symmetry energy and its density dependence—determined solely by the strength of the short-range terms in the three-neutron force. The same force provides a significant constraint on the maximum mass and radius of neutron stars.

Gandolfi, S.; Carlson, J.; Reddy, Sanjay

2012-03-01

300

Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity  

Microsoft Academic Search

White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in

Vasileios Paschalidis; Morgan MacLeod; Thomas W. Baumgarte; Stuart L. Shapiro

2009-01-01

301

Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity  

Microsoft Academic Search

White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in

Vasileios Paschalidis; Morgan MacLeod; Thomas W. Baumgarte; Stuart L. Shapiro

2010-01-01

302

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

SciTech Connect

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.

Colgate, S.A.

1990-01-01

303

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

Microsoft Academic Search

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

G. Pizzichini; M. Gottardi; J.-L. Atteia; C. Barat; K. Hurley; M. Niel; G. Vedrenne; J. G. Laros; W. D. Evans; E. E. Fenimore; R. W. Klebesadel; T. L. Cline; U. D. Desai; V. G. Kurt; A. V. Kuznetsov; V. M. Zenchenko

1986-01-01

304

Gamma-ray pulsars: the Compton Observatory contribution to the study of isolated neutron stars  

Microsoft Academic Search

The four instruments on the Compton Gamma Ray Observatory have identified at least seven isolated neutron stars by their pulsed gamma-ray emission. For all of these, the gamma radiation represents the largest observable fraction of the spin-down luminosity, making the gamma rays important diagnostics of particle acceleration and interaction in the neutron star magnetospheres. Several other ``candidate'' pulsars have tentative

D. J. Thompson; A. K. Harding; W. Hermsen; M. P. Ulmer

1997-01-01

305

Gamma-ray pulsars: the Compton Observatory contribution to the study of isolated neutron stars  

Microsoft Academic Search

The four instruments on the Compton Gamma Ray Observatory have identified at least seven isolated neutron stars by their pulsed gamma-ray emission. For all of these, the gamma radiation represents the largest observable fraction of the spin-down luminosity, making the gamma rays important diagnostics of particle acceleration and interaction in the neutron star magnetospheres. Several other “candidate” pulsars have tentative

D. J. Thompson; A. K. Harding; W. Hermsen; M. P. Ulmer

1997-01-01

306

Impact of strange quark matter nuggets on pycnonuclear reaction rates in the crusts of neutron stars  

Microsoft Academic Search

This article presents an investigation into the pycnonuclear reaction rates in dense crustal matter of neutron stars contaminated with strange quark matter nuggets. The presence of such nuggets in the crustal matter of neutron stars would be a natural consequence if Witten's strange quark matter hypothesis is correct. The methodology presented in this article is a recreation of a recent

B. Golf; J. Hellmers; F. Weber

2009-01-01

307

Impact of strange quark matter nuggets on pycnonuclear reaction rates in the crusts of neutron stars  

Microsoft Academic Search

This paper presents an investigation into the pycnonuclear reaction rates in dense crustal matter of neutron stars contaminated with strange quark matter nuggets. The presence of such nuggets in the crustal matter of neutron stars would be a natural consequence if Witten's strange quark matter hypothesis is correct. The methodology presented in this paper is a recreation of a recent

Fridolin Weber; Barbara Golf; Joe Hellmers

2009-01-01

308

Pulsating Neutron Star as a Source of Quasistatic Waves of Gravity in Interstellar Medium  

Microsoft Academic Search

The hydrodynamic waves of gravity in the galactic interstellar medium generated by a pulsating neutron star are discussed in this paper. It is shown that the frequency of oscillations of interstellar gas-dust matter in this wave is proportional to that for the g-mode in the neutron star bulk. The corresponding periods are of the millisecond duration. The collective oscillations of

S. Bastrukov; I. Molodtsova; J. Yang; V. Papoyan

2005-01-01

309

The Structure of Neutron Star by Using the Quark-Meson Coupling Model  

NASA Astrophysics Data System (ADS)

We investigate the structure of neutron star within the framework of the quark-meson coupling model, considering hyperons and kaon condensation. In order to compare the EoS with that from quark matter, the MIT bag model is used. We calculate the mass and radius of a neutron star by using Tolman-Oppenheimer-Volkov equations.

Ryu, C. Y.; Cheoun, Myung-Ki

310

Equation of state of dense matter and maximum rotation frequency of neutron stars  

Microsoft Academic Search

Maximum rotation frequency of uniformly rotating neutron star models, determined by the mass shedding condition, {OMEGA}_max_, has been calculated using a high precision numerical method, for a large set of equations of state of dense matter. The values of {OMEGA}_max_ for the subset of equations of state, which are causal within neutron star models, are fitted, within a few percent,

P. Haensel; M. Salgado; S. Bonazzola

1995-01-01

311

Equation of state of dense matter and the minimum mass of cold neutron stars  

Microsoft Academic Search

Equilibrium configurations of cold neutron stars near the minimum mass are studied, using the recent equation of state SLy, which describes in a unified, physically consistent manner, both the solid crust and the liquid core of neutron stars. Results are compared with those obtained using an older FPS equation of state of cold catalyzed matter. The value of Mmin =~

P. Haensel; J. L. Zdunik; F. Douchin

2002-01-01

312

GRAVITATIONAL WAVES FROM FALLBACK ACCRETION ONTO NEUTRON STARS  

SciTech Connect

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

Piro, Anthony L. [Theoretical Astrophysics, California Institute of Technology, 1200 E. California Blvd., M/C 350-17, Pasadena, CA 91125 (United States); Thrane, Eric, E-mail: piro@caltech.edu, E-mail: eric.thrane@ligo.org [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)

2012-12-10

313

Gravitational Waves from Fallback Accretion onto Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

Piro, Anthony L.; Thrane, Eric

2012-12-01

314

Prospects for Gravitational-Wave Observations of Neutron-Star Tidal Disruption in Neutron-Star-Black-Hole Binaries  

NASA Astrophysics Data System (ADS)

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

Vallisneri, Michele

2000-04-01

315

Pulsar Wind Nebulae: On their growing diversity and association with highly magnetized neutron stars  

NASA Astrophysics Data System (ADS)

The 1968 discovery of the Crab and Vela pulsars in their respective supernova remnants (SNRs) confirmed Baade and Zwicky's 1934 prediction that supernovae form neutron stars. Observations of Pulsar Wind Nebulae (PWNe), particularly with the Chandra X-ray Observatory, have in the past decade opened a new window to focus on the neutron stars' relativistic winds, study their interaction with their hosting SNRs, and find previously missed pulsars. While the Crab has been thought for decades to represent the prototype of PWNe, we now know of different classes of neutron stars and PWNe whose properties differ from the Crab. In this talk, I review the current status of neutron stars/PWNe-SNRs associations, and highlight the growing diversity of PWNe with an X-ray eye on their association with highly magnetized neutron stars. I conclude with an outlook to future high-energy studies.

Safi-Harb, Samar

2013-03-01

316

Binary neutron stars: Equilibrium models beyond spatial conformal flatness  

NASA Astrophysics Data System (ADS)

Equilibria of binary neutron stars in close circular orbits are computed numerically in a waveless approximation to general relativity. The new formulation exactly solves the Einstein-Euler system written in 3+1 form on a spacelike hypersurface. All components of the field equation are written elliptic equations, and hence all metric components, including the spatial metric, have Coulomb-type fall off. We choose the time-derivative of conformal three-metric to vanish on a spacelike hypersurface for a waveless condition, and impose helical symmetry for the other quantities. Two independent numerical codes, one based on a finite difference method, the other on a spectral method, are developed, and solution sequences that model inspiraling binary neutron stars during the final several orbits are successfully computed. The binding energy of the system near its final orbit deviates from earlier results of third post-Newtonian and of spatially conformally flat calculations. The new solutions may serve as initial data for merger simulations and as members of quasiequilibrium sequences to generate gravitational wave templates, and may improve estimates of the gravitational-wave cutoff frequency set by the last inspiral orbit.

Uryu, Koji; Limousin, Francois; Friedman, John; Gourgoulhon, Eric; Shibata, Masaru

2006-04-01

317

Smashing the Guitar: An Evolving Neutron Star Bow Shock  

NASA Astrophysics Data System (ADS)

The Guitar Nebula is a spectacular example of an H? bow shock nebula produced by the interaction of a neutron star with its environment. The radio pulsar B2224+65 is traveling at ~800-1600 km s-1 (for a distance of 1-2 kpc), placing it on the high-velocity tail of the pulsar velocity distribution. Here we report time evolution in the shape of the Guitar Nebula, the first such observations for a bow shock nebula, as seen in H? imaging with the Hubble Space Telescope. The morphology of the nebula provides no evidence for anisotropy in the pulsar wind nor for fluctuations in the pulsar wind luminosity. The nebula shows morphological changes over two epochs spaced by 7 years that imply the existence of significant gradients and inhomogeneities in the ambient interstellar medium. These observations offer astrophysically unique, in situ probes of length scales between 5×10-4 and 0.012 pc. Model fitting suggests that the nebula axis-and thus the three-dimensional velocity vector-lies within 20° of the plane of the sky and also jointly constrains the distance to the neutron star and the ambient density.

Chatterjee, S.; Cordes, J. M.

2004-01-01

318

COMPOSITIONALLY DRIVEN CONVECTION IN THE OCEANS OF ACCRETING NEUTRON STARS  

SciTech Connect

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.

Medin, Zach; Cumming, Andrew, E-mail: zmedin@physics.mcgill.ca, E-mail: cumming@physics.mcgill.ca [Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A 2T8 (Canada)

2011-04-01

319

Modeling the spatial distribution of neutron stars in the Galaxy  

NASA Astrophysics Data System (ADS)

In this paper we investigate the space and velocity distributions of old neutron stars (aged 109 to 1010 yr) in our Galaxy. Galactic old Neutron Stars (NSs) population fills a torus-like area extending to a few tens kiloparsecs above the galactic plane. The initial velocity distribution of NSs is not well known, in this work we adopt a three component initial distribution, as given by the contribution of kick velocities, circular velocities and Maxwellian velocities. For the spatial initial distribution we use a ? function. We then use Monte Carlo simulations to follow the evolution of the NSs under the influence of the Paczy?ski Galactic gravitational potential. Our calculations show that NS orbits have a very large Galactic radial expansion and that their radial distribution peak is quite close to their progenitors' one. We also study the NS vertical distribution and find that it can well be described by a double exponential low. Finally, we investigate the correlation of the vertical and radial distribution and study the radial dependence of scale-heights.

Taani, Ali; Naso, Luca; Wei, Yingchun; Zhang, Chengmin; Zhao, Yongheng

2012-10-01

320

Atmospheres and Spectra of Strongly Magnetized Neutron Stars  

NASA Astrophysics Data System (ADS)

We construct atmosphere models for strongly magnetized neutron stars with surface fields B ˜1012 -1015 G and effective temperatures Teff ˜106 - 107 K. The atmospheres directly determine the characteristics of thermal emission from isolated neutron stars, including radio pulsars, soft gamma-ray repeaters, and anomalous X-ray pulsars. In our models, the atmosphere is composed of pure hydrogen or helium and is assumed to be fully ionized. The radiative opacities include free-free absorption and scattering by both electrons and ions computed for the two photon polarization modes in the magnetized electron-ion plasma. We describe a modified (due to the two photon modes) Unsöld-Lucy temperature correction method to establish radiative equilibrium and the resulting temperature profile. We discuss the effect of vacuum polarization, which modifies the dielectric property of the medium and gives rise to a resonance feature in the opacity; this feature is narrow and occurs at a photon energy that depends on the plasma density. Vacuum polarization can also induce resonant conversion of photon modes via a mechanism analogous to the MSW mechanism for neutrino oscillation. We discuss the subtleties in treating the vacuum polarization effects. We show that vacuum polarization produces a broad depression in the X-ray flux at high energies, which arises from the density dependence of the vacuum resonance feature and the large density gradient present in the atmosphere, and the depression of continuum flux strongly suppresses the equivalent width of the ion cyclotron line.

Ho, W. C. G.; Lai, D.

2003-01-01

321

Simulations of the Inspiral and Merger of Magnetized Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

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

2008-05-01

322

Gravitational Waves from Color-Magnetic ``Mountains'' in Neutron Stars  

NASA Astrophysics Data System (ADS)

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.

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

2012-08-01

323

Vibration Powered Radiation of Quaking Magnetar  

Microsoft Academic Search

In juxtaposition with the standard model of rotation powered pulsar, the model of vibration powered magnetar undergoing quake-induced torsional Alfven vibrations in its own ultra strong magnetic field experiencing decay is considered. The presented line of argument shows that gradual decrease of frequencies (lengthening of periods) of long-periodic pulsed radiation detected from set of X-ray sources can be attributed to

S. Bastrukov; J. W. Yu; R. X. Xu; I. Molodtsova

2011-01-01

324

An all-sky search algorithm for continuous gravitational waves from spinning neutron stars in binary systems  

Microsoft Academic Search

Rapidly spinning neutron stars with non-axisymmetric mass distributions are expected to generate quasi-monochromatic continuous gravitational waves. While many searches for unknown, isolated spinning neutron stars have been carried out, there have been no previous searches for unknown sources in binary systems. Since current search methods for unknown, isolated neutron stars are already computationally limited, expanding the parameter space searched to

E. Goetz; K. Riles

2011-01-01

325

REVIEWS OF TOPICAL PROBLEMS: Cooling of neutron stars and superfluidity in their cores  

NASA Astrophysics Data System (ADS)

We study the heat capacity and neutrino emission reactions (direct and modified Urca processes, nucleon-nucleon bremsstrahlung, Cooper pairing of nucleons) in the supranuclear density matter of neutron star cores with superfluid neutrons and protons. Various superfluidity types are analysed (singlet-state pairing and two types of triplet-state pairing, without and with gap nodes at the nucleon Fermi surface). The results are used for cooling simulations of isolated neutron stars. Both the standard cooling and the cooling enhanced by the direct Urca process are strongly affected by nucleon superfluidity. Comparison of the cooling theory of isolated neutron stars with observations of their thermal radiation may give stringent constraints on the critical temperatures of the neutron and proton superfluidities in the neutron star cores.

Yakovlev, Dmitrii G.; Levenfish, Kseniya P.; Shibanov, Yurii A.

1999-08-01

326

Stellar evolution on the borderline of white dwarf and neutron star formation  

Microsoft Academic Search

This thesis is about the evolution of stars, specifically about the final fate of stars at the borderline between the formation of white dwarfs and neutron stars. It is well known that the mass and the metallicity are the two determining factors in stellar evolution, and for a given initial chemical composition, the mass essentially defines the final fate: Lower

A. J. T. Poelarends

2007-01-01

327

Mergers of irrotational neutron star binaries in conformally flat gravity  

NASA Astrophysics Data System (ADS)

We present the first results from our new general relativistic, Lagrangian hydrodynamics code, which treats gravity in the conformally flat (CF) limit. The evolution of fluid configurations is described using smoothed particle hydrodynamics (SPH), and the elliptic field equations of the CF formalism are solved using spectral methods in spherical coordinates. The code was tested on models for which the CF limit is exact, finding good agreement with the classical Oppenheimer-Volkov solution for a relativistic static spherical star as well as the exact semianalytic solution for a collapsing spherical dust cloud. By computing the evolution of quasiequilibrium neutron star binary configurations in the absence of gravitational radiation back reaction, we have confirmed that these configurations can remain dynamically stable all the way to the development of a cusp. With an approximate treatment of radiation reaction, we have calculated the complete merger of an irrotational binary configuration from the innermost point on an equilibrium sequence through merger and remnant formation and ringdown, finding good agreement with previous relativistic calculations. In particular, we find that mass loss is highly suppressed by relativistic effects, but that, for a reasonably stiff neutron star equation of state, the remnant is initially stable against gravitational collapse because of its strong differential rotation. The gravity wave signal derived from our numerical calculation has an energy spectrum which matches extremely well with estimates based solely on quasiequilibrium results, deviating from the Newtonian power-law form at frequencies below 1 kHz, i.e., within the reach of advanced interferometric detectors.

Faber, Joshua A.; Grandclément, Philippe; Rasio, Frederic A.

2004-06-01

328

Supersoft Symmetry Energy Encountering Non-Newtonian Gravity in Neutron Stars  

SciTech Connect

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

Wen Dehua [Department of Physics, South China University of Technology, Guangzhou 510641 (China); Department of Physics and Astronomy, Texas A and M University-Commerce, Commerce, Texas 75429-3011 (United States); Li Baoan [Department of Physics and Astronomy, Texas A and M University-Commerce, Commerce, Texas 75429-3011 (United States); Chen Liewen [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China)

2009-11-20

329

Inner Crusts of Neutron Stars in Strongly Quantizing Magnetic Fields  

NASA Astrophysics Data System (ADS)

We study the ground-state properties of inner crusts of neutron stars in the presence of strong magnetic fields of ~1017 G. Nuclei coexist with a neutron gas and reside in a uniform gas of electrons in the inner crust. This problem is investigated within the Thomas-Fermi model. We extract the properties of nuclei based on the subtraction procedure of Bonche, Levit, and Vautherin. The phase space modification of electrons due to Landau quantization in the presence of strong magnetic fields leads to the enhancement of electron as well as proton fractions at lower densities of ~0.001 fm-3. We find the equilibrium nucleus at each average baryon density by minimizing the free energy and show that, in the presence of strong magnetic fields, it is lower than that in the field-free case. The size of the spherical cell that encloses a nucleus along with the neutron and electron gases becomes smaller in strong magnetic fields compared to the zero-field case. Nuclei with larger mass and atomic numbers are obtained in the presence of strong magnetic fields compared with cases of zero field.

Nandi, Rana; Bandyopadhyay, Debades; Mishustin, Igor N.; Greiner, Walter

2011-08-01

330

Sequential deconfinement of quark flavors in neutron stars  

SciTech Connect

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

Blaschke, D. [Institute for Theoretical Physics, University of Wroclaw, PL-50204 Wroclaw (Poland); Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Sandin, F. [Fundamental Interactions in Physics and Astrophysics, University of Liege, B-4000 Liege (Belgium); EISLAB, Luleaa University of Technology, S-97187 Luleaa (Sweden); Klaehn, T. [Institute for Theoretical Physics, University of Wroclaw, PL-50204 Wroclaw (Poland); Physics Division, Argonne National Laboratory, Argonne, Illinois 60439-4843 (United States); Berdermann, J. [Deutsches Elektronen Synchrotron, Platanenallee 6, D-15738 Zeuthen (Germany)

2009-12-15

331

The effect of quantized magnetic flux lines on the dynamics of superfluid neutron star cores  

Microsoft Academic Search

We investigate dynamical coupling time-scales of a neutron star's superfluid core, taking into account the interactions of quantized neutron vortices with quantized flux lines of the proton superconductor in addition to the previously considered scattering of the charged components against the spontaneous magnetization of the neutron vortex line. We compare the cases where vortex motion is constrained in different ways

T. Sidery; M. A. Alpar

2009-01-01

332

A Massive Neutron Star in the Globular Cluster M5  

NASA Astrophysics Data System (ADS)

We report the results of 19 years of Arecibo timing for two pulsars in the globular cluster NGC 5904 (M5), PSR B1516+02A (M5A) and PSR B1516+02B (M5B). This has resulted in the measurement of the proper motions of these pulsars and, by extension, that of the cluster itself. M5B is a 7.95 ms pulsar in a binary system with a >0.13 Msolar companion and an orbital period of 6.86 days. In deep HST images, no optical counterpart is detected within ~2.5 ? of the position of the pulsar, implying that the companion is either a white dwarf or a low-mass main-sequence star. The eccentricity of the orbit (e=0.14) has allowed a measurement of the rate of advance of periastron: ??=0.0142deg+/-0.0007deg yr-1. We argue that it is very likely that this periastron advance is due to the effects of general relativity, the total mass of the binary system then being 2.29+/-0.17 Msolar. The small measured mass function implies, in a statistical sense, that a very large fraction of this total mass is contained in the pulsar: Mp=2.08+/-0.19 Msolar (1 ?) there is a 5% probability that the mass of this object is <1.72 Msolar and a 0.77% probability that 1.2 Msolar<=Mp<=1.44 Msolar. Confirmation of the median mass for this neutron star would exclude most ``soft'' equations of state for dense neutron matter. Millisecond pulsars (MSPs) appear to have a much wider mass distribution than is found in double neutron star systems; about half of these objects are significantly more massive than 1.44 Msolar. A possible cause is the much longer episode of mass accretion necessary to recycle a MSP, which in some cases corresponds to a much larger mass transfer.

Freire, Paulo C. C.; Wolszczan, Alex; van den Berg, Maureen; Hessels, Jason W. T.

2008-06-01

333

Initial data for neutron star binaries with arbitrary spins  

NASA Astrophysics Data System (ADS)

The starting point of any general relativistic numerical simulation is a solution of the Hamiltonian and momentum constraints that (ideally) represents an astrophysically realistic scenario. We present a new method to produce initial data sets for binary neutron stars with arbitrary spins and orbital eccentricities. The method only provides approximate solutions to the constraints. However, we show that the corresponding constraint violations subside after a few orbits, becoming comparable to those found in evolutions of standard conformally flat, helically symmetric binary initial data. We evolve in time data sets corresponding to binaries with spins aligned, zero, and antialigned with the orbital angular momentum. These simulations show the orbital “hang-up” effect previously seen in binary black holes. Additionally, they show orbital eccentricities that can be up to 1 order of magnitude smaller than those found in helically symmetric initial sets evolutions.

Tsatsin, Petr; Marronetti, Pedro

2013-09-01

334

Cosmic background of gravitational waves from rotating neutron stars  

NASA Astrophysics Data System (ADS)

The extragalactic background of gravitational waves produced by tri-axial rotating neutron stars was calculated, under the assumption that the properties of the underlying pulsar population are the same of those of the galactic population, recently derived by Regimbau & de Freitas Pacheco (\\cite{Regimbau00}). For an equatorial ellipticity of varepsilon = 10-6, the equivalent density parameter due to gravitational waves has a maximum amplitude in the range 2x10-11-3x10-9, around 0.9-1.5 kHz. The main factors affecting the theoretical predictions are discussed. This background is comparable to that produced by the ``ring-down'' emission from distorted black holes. The detection possibility of this background by a future generation of gravitational antennas is also examined.

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

2001-09-01

335

Maximum mass of neutron stars with quark matter core  

NASA Astrophysics Data System (ADS)

We propose a new strategy to construct the equation of state (EOS) for neutron stars (NSs) with hadron-quark (H-Q) phase transition, by considering three density-regions. We supplement the EOS at H-Q region, very uncertain due to the confinement-deconfinement problems, by sandwitching in between and matching to the relatively ``well known'' EOSs, i.e., the EOS at lower densities (H-phase up to several times nuclear density, calculated from a G-matrix approach) and that at ultra high densities (Q-phase, form a view of asymptotic freedom). Here, as a first step, we try a simple case and discuss the maximum mass of NSs.

Takatsuka, Tatsuyuki; Hatsuda, Tetsuo; Masuda, Kota

2012-11-01

336

Internal Heating of Old Neutron Stars: Contrasting Different Mechanisms  

SciTech Connect

The thermal emission detected from the millisecond pulsar J0437-4715 is not explained by standard cooling models of neutron stars without a heating mechanism. We investigated three heating mechanisms controlled by the rotational braking of the pulsar: breaking of the solid crust, superfluid vortex creep, and non-equilibrium reactions ('rotochemical heating'). We find that the crust cracking mechanism does not produce detectable heating. Given the dependence of the heating mechanisms on spin-down parameters, which leads to different temperatures for different pulsars, we study the thermal evolution for two types of pulsars: young, slowly rotating 'classical' pulsars and old, fast rotating millisecond pulsars (MSPs). We find that the rotochemical heating and vortex creep mechanism can be important both for classical pulsars and MSPs.

Gonzalez, Denis; Reisenegger, Andreas [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Fernandez, Rodrigo [Institute for Advanced Study, Princeton, NJ 08540 (United States)

2010-08-04

337

Measuring neutron-star radii with gravitational-wave detectors.  

PubMed

Coalescing binary neutron stars (NS) are expected to be an important source of gravitational waves (GW) detectable by laser interferometers. We present here a simple method for determining the compactness ratio M/R of NS based on the observed deviation of the GW energy spectrum from point-mass behavior at the end of inspiral. Our method is based on the properties of quasiequilibrium binary NS sequences and does not require the computation of the full GW signal h(t). Combined with the measurement of the NS masses during inspiral, the determination of M/R will allow very strong constraints to be placed on the equation of state of dense nuclear matter. PMID:12484994

Faber, Joshua A; Grandclément, Philippe; Rasio, Frederic A; Taniguchi, Keisuke

2002-11-18

338

Surface structure of neutron stars with high magnetic fields  

NASA Astrophysics Data System (ADS)

The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates.

Fushiki, I.; Gudmundsson, E. H.; Pethick, C. J.

1989-07-01

339

Surface structure of neutron stars with high magnetic fields  

SciTech Connect

The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates. 38 refs.

Fushiki, I.; Gudmundsson, E.H.; Pethick, C.J. (Illinois Univ., Urbana (USA); Univ. of Iceland, Reykjavik; Nordisk Institut for Teoretisk Atomfysik, Copenhagen (Denmark))

1989-07-01

340

Impact of accretion on the statistics of neutron star masses  

NASA Astrophysics Data System (ADS)

We have collected the parameter of 38 neutron stars (NSs) in binary systems with spin periods and measured masses. By adopting the Boot-strap method, we reproduced the procedure of mass calculated for each system separately, to determine the truly mass distribution of the NS that obtained from observation. We also applied the Monte-Carlo simulation and introduce the characteristic spin period 20 ms, in order to distinguish between millisecond pulsars (MSPs) and less recycled pulsars. The mass distributions of MSPs and the less recycled pulsars could be fitted by a Gaussian function as 1.45+/-0.42 M? and 1.31+/-0.17 M? (with 1?) respectively. As such, the MSP masses are heavier than those in less recycled systems by factor of ~ 0.13M?, since the accretion effect during the recycling process.

Cheng, Z.; Taani, A.; Zhao, Y. H.

2013-02-01

341

Atmospheres and spectra of strongly magnetized neutron stars  

NASA Astrophysics Data System (ADS)

We construct atmosphere models for strongly magnetized neutron stars with surface fields [formmu10]B~1012-1015G and effective temperatures [formmu11]Teff~106-107K. The atmospheres directly determine the characteristics of thermal emission from isolated neutron stars, including radio pulsars, soft gamma-ray repeaters, and anomalous X-ray pulsars. In our models, the atmosphere is composed of pure hydrogen or helium and is assumed to be fully ionized. The radiative opacities include free-free absorption and scattering by both electrons and ions computed for the two photon polarization modes in the magnetized electron-ion plasma. Since the radiation emerges from deep layers in the atmosphere with [formmu12]?>~102gcm-3, plasma effects can significantly modify the photon opacities by changing the properties of the polarization modes. In the case where the magnetic field and the surface normal are parallel, we solve the full, angle-dependent, coupled radiative transfer equations for both polarization modes. We also construct atmosphere models for general field orientations based on the diffusion approximation of the transport equations and compare the results with models based on full radiative transport. In general, the emergent thermal radiation exhibits significant deviation from blackbody, with harder spectra at high energies. The spectra also show a broad feature [formmu13](?E/EBi~1) around the ion cyclotron resonance [formmu14]EBi=0.63(Z/A)(B/1014G)keV, where Z and A are the atomic charge and atomic mass of the ion, respectively; this feature is particularly pronounced when [formmu15]EBi>~3kTeff. Detection of the resonance feature would provide a direct measurement of the surface magnetic fields on magnetars.

Ho, Wynn C. G.; Lai, Dong

2001-11-01

342

Reassessing the fundamentals: On the evolution, ages and masses of neutron stars  

NASA Astrophysics Data System (ADS)

The evolution, ages and masses of neutron stars are the fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these indirectly probed features play an important role in understanding a very broad range of astrophysical processes that are, in many cases, not empirically accessible otherwise. For the majority of pulsars, the only observables are the rotational period (P), and its derivative (P?) which gives the rate of change in the spin. I start with calculating the joint P-P? distributions of millisecond pulsars for the standard evolutionary model in order to assess whether millisecond pulsars are the unequivocal descendants of low mass X-ray binaries. We show that the P-P? density implied by the standard evolutionary model is inconsistent with observations, which suggests that it is unlikely that millisecond pulsars have evolved from a single coherent progenitor population. In the absence of constraints from the binary companion or supernova remnant, the standard method for estimating pulsar ages is to infer an age from the rate of spin-down. I parametrically incorporate constraints that arise from binary evolution and limiting physics to derive a "modified spin-down age" for millisecond pulsars. We show that the standard method can be improved by this approach to achieve age estimates closer to the true age. Then, I critically review radio pulsar mass measurements and present a detailed examination through which we are able to put stringent constraints on the underlying neutron star mass distribution. For the first time, we are able to analyze a sizable population of neutron star-white dwarf systems in addition to double neutron star systems with a technique that accounts for systematically different measurement errors. We find that neutron stars that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. Neutron stars in double neutron star and neutron star-white dwarf systems show consistent respective peaks at 1.35 M? and 1.50 M? , which suggest significant mass accretion (Deltam ? 0.15 M? ) has occurred during the spin up phase. We find a mass cutoff at 2 M? for neutron stars with white dwarf companions which establishes a firm lower bound for the maximum neutron star mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for neutron star matter. The lack of truncation close to the maximum mass cutoff suggests that the 2 M? limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare super-massive neutron stars is possible.

Kiziltan, Bulent

343

MD simulations of electron and WIMP scattering from neutron star crust  

NASA Astrophysics Data System (ADS)

Neutron star crust is composed of a crystal lattice of atomic nuclei embedded in a relativistic degenerate electron gas. We use molecular dynamics simulations to determine the crystal structure of neutron star crust material. From these simulations, we calculated the static structure factor S(q) that describes the scattering of electrons, neutrinos, or weakly interacting dark matter particles (WIMPs) from ions in the crust. The scattering of electrons determines the crust thermal conductivity, while WIMP scattering from the crust may allow dark matter particles to be trapped in neutron stars.

Fish, Jake; Horowitz, Charles

2012-10-01

344

Analytical representations of unified equations of state of neutron-star matter  

NASA Astrophysics Data System (ADS)

Analytical representations are derived for two equations of state (EOSs) of neutron-star matter: FPS and SLy. Each of these EOSs is unified, that is, it describes the crust and the core of a neutron star using the same physical model. Two versions of the EOS parametrization are considered. In the first one, pressure and mass density are given as functions of the baryon density. In the second version, pressure, mass density, and baryon density are given as functions of the pseudo-enthalpy, which makes this representation particularly useful for 2-D calculations of stationary rotating configurations of neutron stars.

Haensel, P.; Potekhin, A. Y.

2004-12-01

345

A crystalline quark-hadron mixed phase in neutron stars  

NASA Astrophysics Data System (ADS)

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.

Glendenning, N. K.

1994-08-01

346

Nonlinear decay of r modes in rapidly rotating neutron stars  

NASA Astrophysics Data System (ADS)

We investigate the dynamics of r modes at amplitudes in the nonlinear regime for rapidly but uniformly rotating neutron stars with a polytropic equation of state. For this, we perform three-dimensional relativistic hydrodynamical simulations, making the simplifying assumption of a fixed spacetime. To excite r modes, we linearly scale exact eigenfunctions to large amplitudes. We find that for initial dimensionless amplitudes around three, r modes decay on time scales around ten oscillation periods, while at amplitudes of order unity, they are stable over the evolution time scale. Together with the decay, a strong differential rotation develops, conserving the total angular momentum, with angular velocities in the range 0.5…1.2 of the initial one. We evolved two models with different rotation rates and found slower decay for the more rapidly rotating one. We present r-mode eigenfunctions and frequencies, and compare them to known analytic results for slowly rotating Newtonian stars. As a diagnostic tool, we discuss conserved energy and angular momentum for the case of a fixed axisymmetric background metric and introduce a measure for the energy of nonaxisymmetric fluid oscillation modes.

Kastaun, Wolfgang

2011-12-01

347

Statistics of magnetic fields and fluxes of massive OB stars and the origin of neutron star magnetic fields  

NASA Astrophysics Data System (ADS)

Based on the newest measurements, statistical properties of rms mean magnetic fields of OB and neutron stars (NSs) were investigated. The magnetic field distribution function f(B) for OB stars was determined and a sharp decrease of f(B) for weak magnetic fields was found. The mean magnetic fluxes F for all massive stars and NSs with measured magnetic fields was estimated, and it was found that log F = 27.7 for OB stars and log F = 24.5 for NSs. To explain the large differences of the fluxes from normal and neutron stars we studied the birth and evolution of isolated neutron stars in the whole volume of our Galaxy with our new code of population synthesis. We started modeling %with our code from the birth of massive OB stars and followed their motion within the spiral arms to the point of supernova explosion. Next we considered the evolution of NS up to the death line with considering the magnetic field decay. We found that a significant magnetic field decay occurs during the first million years of a NS's life. We have estimated the mean time of the Ohmic decay for NS. We modeled the distributions of pulsar periods P, of period derivatives \\dot P, and of pulsar magnetic fields B, and found that they are in a good agreement with those taken from \\cite{ATNF}.

Igoshev, A. P.; Kholtygin, A. F.

2011-12-01

348

Gravitational waves from spinning black hole-neutron star binaries: dependence on black hole spins and on neutron star equations of state  

NASA Astrophysics Data System (ADS)

We study the merger of black hole-neutron star binaries with a variety of black hole spins aligned or antialigned with the orbital angular momentum, and with the mass ratio in the range MBH/MNS=2-5, where MBH and MNS are the mass of the black hole and neutron star, respectively. We model neutron-star matter by systematically parametrized piecewise polytropic equations of state. The initial condition is computed in the puncture framework adopting an isolated horizon framework to estimate the black hole spin and assuming an irrotational velocity field for the fluid inside the neutron star. Dynamical simulations are performed in full general relativity by an adaptive-mesh refinement code, SACRA. The treatment of hydrodynamic equations and estimation of the disk mass are improved. We find that the neutron star is tidally disrupted irrespective of the mass ratio when the black hole has a moderately large prograde spin, whereas only binaries with low mass ratios, MBH/MNS?3, or small compactnesses of the neutron stars bring the tidal disruption when the black hole spin is zero or retrograde. The mass of the remnant disk is accordingly large as ?0.1M?, which is required by central engines of short gamma-ray bursts, if the black hole spin is prograde. Information of the tidal disruption is reflected in a clear relation between the compactness of the neutron star and an appropriately defined “cutoff frequency” in the gravitational-wave spectrum, above which the spectrum damps exponentially. We find that the tidal disruption of the neutron star and excitation of the quasinormal mode of the remnant black hole occur in a compatible manner in high mass-ratio binaries with the prograde black hole spin. The correlation between the compactness and the cutoff frequency still holds for such cases. It is also suggested by extrapolation that the merger of an extremely spinning black hole and an irrotational neutron star binary does not lead to the formation of an overspinning black hole.

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

2011-09-01

349

Deep Imaging Of A Candidate Isolated Neutron Star  

NASA Astrophysics Data System (ADS)

Only seven isolated radio-quiet neutron stars (XINS) emitting thermal X-rays are known, too few to address fundamental issues such as the equation of state of degenerate neutron matter. To expand this sample, we used the Sloan Digital Sky Survey (SDSS) to examine 10,000 ROSAT error circles and identified a dozen X-ray sources lacking plausible optical counterparts. Short Chandra observations of these XINS candidates pinpointed the sources, and the very small Chandra error circle of one observed candidate remained completely optically blank in SDSS, making this source a prime new XINS candidate. A follow-up observation with XMM-Newton provided us with the first measurements of the source's spectral energy distribution, but did not eliminate the possibility that it is a highly obscured AGN or a radio-quiet BL Lac. The deep optical imaging proposed here, which will require only an hour of Gemini North time to reach V~26 mag, will elucidate the nature of this intriguing blank-field X-ray source.

Agueros, Marcel; Anderson, Scott; Margon, Bruce; Posselt, Bettina; Voges, Wolfgang

2008-02-01

350

New Type of Deeper, Longer Quake Discovered  

NSDL National Science Digital Library

This radio broadcast reports on the discovery of a new kind of earthquake that is much deeper and longer lasting than other kinds of quakes. These long, super-deep tremors originate at a depth of 15-20 miles, below the crust in the upper mantle of Earth, and last 10-20 minutes. The broadcast reports on their occurrence in California and how research is being conducted to determine their relationship to other seismic activity along the San Andreas Fault. The clip is 4 minutes and 48 seconds in length.

351

Maximum mass of neutron stars and strange neutron-star cores  

NASA Astrophysics Data System (ADS)

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 the baryon phase (reconfinement) that we find for both EOS.B. Therefore, to obtain Mmax > 2 M? for hybrid stars, both sufficiently strong additional hyperon repulsion at high-density baryon matter and a sufficiently stiff EOS of quark matter would be needed. However, we think that the high-density instability, which results in the reconfinement of quark matter, indicates actually the inadequacy of the point-particle model of baryons in dense matter at ? ? 5 ÷ 8?0. We expect that reconfinement can be removed by a sufficient stiffening of the baryon phase, resulting from the repulsive finite size contribution for baryons to the EOS.

Zdunik, J. L.; Haensel, P.

2013-03-01

352

The effects of mass on the radiation of a relativistically rotating neutron star  

NASA Astrophysics Data System (ADS)

We investigate the effect of mass on the radiation of a relativistically rotating neutron star. The method of Haxton and Ruffini is used to find the radiation flux from a relativistically rotating neutron star. By extending the idea of a point charge orbiting a black hole, a pulsar is modeled by simulating a relativistically rotating magnetic dipole embedded within a neutron star. The resulting equations retain the mass of the neutron star, thereby introducing effects of general relativity on the radiation from the dipole. We present exact solutions to the modeling equation as well as plots of energy spectra at different rotational velocities and inclination angles. We also present plots of total energy versus mass and two tables containing a comparison of energy ratios. These demonstrate that, for realistic neutron star masses, the high speed enhancement of the radiation is always more than compensated by the frame dragging effect, leading to a net reduction of radiation from the star. It is found that the inclusion of mass not only reduced the special relativistic enhancement, but negates it entirely as the mass of the neutron star approaches the mass limit.

Herbst, R. S.; Qadir, A.; Momoniat, E.

2013-12-01

353

A unified equation of state of dense matter and neutron star structure  

NASA Astrophysics Data System (ADS)

An equation of state (EOS) of neutron star matter, describing both the neutron star crust and the liquid core, is calculated. It is based on the effective nuclear interaction SLy of the Skyrme type, which is particularly suitable for the application to the calculation of the properties of very neutron rich matter (Chabanat et al. 1997, 1998). The structure of the crust, and its EOS, is calculated in the T=0 approximation, and under the assumption of the ground state composition. The crust-core transition is a very weakly first-order phase transition, with relative density jump of about one percent. The EOS of the liquid core is calculated assuming (minimal) npemu composition. Parameters of static neutron stars are calculated and compared with existing observational data on neutron stars. The minimum and maximum masses of static neutron stars are 0.094 Msun and 2.05 Msun, respectively. Effects of rotation on the minimum and the maximum mass of neutron stars are briefly discussed.

Douchin, F.; Haensel, P.

2001-12-01

354

Evolution of neutron star + He star binaries: an alternative evolutionary channel to intermediate-mass binary pulsars  

NASA Astrophysics Data System (ADS)

It is difficult for intermediate-mass X-ray binaries to form compact intermediate-mass binary pulsars (IMBPs) with a short orbital-period ( ? 3 d), which have heavy ( ? 0.4 M?) CO or ONeMg white dwarf (WD) companions. Since neutron star + He star binaries may experience common-envelope evolution, they have some advantage to account for the formation of short orbital-period IMBPs. In this work, we explore the probability of IMBPs formed by this evolutionary channel. Using Eggleton's stellar evolution code, considering that the dead pulsars were spun up by the accreting material and angular momentum from the He star companions, we have calculated the evolution of a large number of neutron star + He star binaries. Our simulated results indicate that the NS + He star evolutionary channel can produce IMBPs with a WD of ˜ 0.5-1.1 M? and an orbital period of 0.03-20 d, in which pulsars have a spin period of 1.4-200 ms. Comparing the calculated results with the observational parameters (spin period and orbital period) of nine compact IMBPs, the NS + He star evolutionary channel can account for the formation of four sources. Therefore, NS + He star binaries offer an alternative evolutionary channel to compact IMBPs.

Chen, Wen-Cong; Liu, Wei-Min

2013-05-01

355

X-Ray Polarimetery of Neutron Stars from a CubeSat  

NASA Astrophysics Data System (ADS)

The propagation of radiation in the intense magnetic fields surrounding neutron stars is strongly affected by the fundamental quantum mechanical properties of photons and electrons as described by the theory of quantum electrodynamics (QED). Measurement of the polarization of X-rays emitted from the surface of a highly magnetized neutron star will unambiguously verify (or reject) a unique signature of strong-field QED and probe the neutron star magnetic field and X-ray emission geometry. We describe an instrument capable of measuring the polarization of soft X-rays from thermally-emitting isolated neutron stars that can be accomplished at modest cost by exploiting CubeSats as novel vehicles for high energy astrophysics.

Kaaret, Philip

2013-04-01

356

Circinus X-1: A Neutron Star Doing Its Best Impression Of A Black Hole?  

NASA Astrophysics Data System (ADS)

The X-ray binary Circinus X-1 is a trailblazer in many ways: (a) It is one of only two neutron star X-ray binaries with a resolved radio jet, making it a prototype and defining member of the class of neutron star microquasars. (b) It is one of only two microquasars with well established large scale, diffuse radio lobes. (c) Its jet has been clocked at a Lorentz factor of Gamma=16, potentially making it the fastest microquasar to date. (d) Finally, Circinus X-1 has become the first and only neutron star XRB with a resolved X-ray jet: Recent Chandra and radio observations show the source in glorious detail, revealing parsec scale shocks and arcsecon scale extended X-ray emission. I will discuss the constraints we can put on the jet power from this neutron star and their implications for our understanding of relativistic jets from compact objects as a whole.

Heinz, Sebastian; Sell, P.; Schulz, N.; Brandt, N.; Calvelo, D.; Jonker, P.

2011-09-01

357

Crystalline structure in the confined-deconfined mixed phase: Neutron stars as an example.  

National Technical Information Service (NTIS)

We review the differences in first order phase transition of single and multi-component systems, and then discuss the crystalline structure expected to exist in the mixed confined deconfined phase of hadronic matter. The particular context of neutron star...

N. K. Glendenning

1996-01-01

358

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

SciTech Connect

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.

Ohnishi, A.; Jido, D. [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Sekihara, T. [Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Tsubakihara, K. [Department of Physics, Faculty of Science, Hokkaido University, Sapporo 060-0810 (Japan)

2009-09-15

359

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

NASA Astrophysics Data System (ADS)

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.

Charbonneau, James; Zhitnitsky, Ariel

2010-08-01

360

Statistical ages and the cooling rate of X-ray dim isolated neutron stars  

NASA Astrophysics Data System (ADS)

The cooling theory of neutron stars is corroborated by its comparison with observations of thermally emitting isolated neutron stars and accreting neutron stars in binary systems. An important ingredient for such an analysis is the age of the object, which, typically, is obtained from the spin-down history. This age is highly uncertain if the object's magnetic field varies appreciably over time. Other age estimators, such as supernova remnant ages and kinematic ages, only apply to a handful of neutron stars. We conduct a population synthesis study of the nearby isolated thermal emitters and obtain their ages statistically from the observed luminosity function of these objects. We argue that a more sensitive blind scan of the Galactic disc with the upcoming space telescopes can help to constrain the ages to higher accuracy.

Gill, Ramandeep; Heyl, Jeremy S.

2013-11-01

361

Hyperon Density Dependence of Hyperon-Nucleon Interactions in Neutron Stars  

NASA Astrophysics Data System (ADS)

The hyperon density dependence (YDD) of hyperon-nucleon interactions are studied in the relativistic mean field (RMF) model and their influences on the properties of neutron stars are studied. The extended RMF considered the interior quarks coordinates of hyperon and bring a hyperon density dependent factor, f(?Y), to the meson-hyperon coupling vertexes. The hyperon density dependence of YN interaction affect the properties of neutron stars only after the corresponding hyperon appears. Then, the influences of the density dependence factors are almost ignored at low densities, which are clear at high densities. The compositions and properties of neutron stars are studied with and without the YDD of YN interactions for the different ?--nucleus effective potentials, (30, 0, -30)MeV. The calculated results indicated that the YDD of YN interaction soften the equation of state of neutron stars at high densities.

Dang, L.; Yue, P.; Li, L.; Ning, P. Z.

362

Gravitational scattering of asteroids onto neutron stars as a cause of gamma-ray bursts  

NASA Astrophysics Data System (ADS)

A mechanism is proposed by which asteroids may be scattered onto neutron stars causing impulsive and perhaps all gamma-ray bursts. Asteroids which remain bound to the neutron star after it is formed can, through close encounters with planets, enter a region of magnetic drag near the star. This region is larger than the star's collisional cross section; it is approximately 10 to the 10th cm in radius and hence produces an interesting rate if even only a small fraction of all neutron stars are responsible for these bursts. The 1979 March 5 burst is interpreted in this context, and all of the observational constraints except for its suggested association with N49 in the LMC can be satisfied. The model predicts that gamma-ray bursts have a low luminosity (10 to the 35th ergs/s) X-ray precursor of fairly long duration (10,000 s).

van Buren, D.

1981-10-01

363

Merger of white dwarf-neutron star binaries: Prelude to hydrodynamic simulations in general relativity  

Microsoft Academic Search

White dwarf-neutron star binaries generate detectable gravitational\\u000aradiation. We construct Newtonian equilibrium models of corotational white\\u000adwarf-neutron star (WDNS) binaries in circular orbit and find that these models\\u000aterminate at the Roche limit. At this point the binary will undergo either\\u000astable mass transfer (SMT) and evolve on a secular time scale, or unstable mass\\u000atransfer (UMT), which results in

Vasileios Paschalidis; Morgan MacLeod; Thomas W. Baumgarte; Stuart L. Shapiro

2009-01-01

364

Absorption features in the spectra of X-ray bursting neutron stars  

Microsoft Academic Search

Context: The discovery of photospheric absorption lines in XMM-Newton spectra of the X-ray bursting neutron star in EXO 0748-676 by Cottam and collaborators allows us to constrain the neutron star mass-radius ratio from the measured gravitational redshift. A radius of R=9{-}12 km for a plausible mass range of M=1.4{-}1.8 M_&sun; was derived by these authors. Aims: It has been claimed

Thomas Rauch; Valery Suleimanov; Klaus Werner

2008-01-01

365

The spin period - eccentricity relation of double neutron stars: evidence for weak supernova kicks?  

Microsoft Academic Search

Double neutron stars (DNSs), binary systems consisting of a radio pulsar and\\u000aa generally undetected second neutron star (NS), have proven to be excellent\\u000alaboratories for testing the theory of general relativity. The seven systems\\u000adiscovered in our Galaxy exhibit a remarkably well-defined relation between the\\u000apulsar spin period and the orbital eccentricity. Here we show, using a simple\\u000amodel

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

2005-01-01

366

Superfluid Friction and Late-Time Thermal Evolution of Neutron Stars  

Microsoft Academic Search

The recent temperature measurements of the two older isolated neutron stars PSR 1929+10 and PSR 0950+08 (ages of 3x10^6 and 2x10^7 yr, respectively) indicate that these objects are heated. A promising candidate heat source is friction between the neutron star crust and the superfluid it is thought to contain. We study the effects of superfluid friction on the long-term thermal

Michelle B. Larson; Bennett Link

1999-01-01

367

Elastodynamical properties of nuclear matter from the observed activity of neutron stars  

Microsoft Academic Search

The review is devoted to the elastodynamic approach to continuum mechanics of self-gravitating nuclear matter constituting inerior of neutron stars. Making use of energy variational pronciple periods of gravitational-elastic spheroidal (s-mode) and torsional (t-mode) pulsations of neutron stars as well as Alfvenic MHD oscillations are computed. The manifestation of the above pulsations in the spectrum of radio pulsars is discussed.

S. I. Bastrukov; I. V. Molodtsova; D. V. Podgainyi; F. Weber; V. V. Papoyan

1999-01-01

368

LETTER TO THE EDITOR: Non-radial vibrations of neutron stars  

Microsoft Academic Search

Non-radial oscillations of a non-rotating neutron star are studied. A neutron star is modelled by a spherically symmetric distribution of nuclear matter possessing the properties of an elastic solid bounded by Newtonian gravity. The analytic formalism describing the spheroidal gravitation-elastic vibrations is developed. Emphasis is placed on calculation of the eigenfrequencies of non-radial vibrations. First numerical estimates are presented and

S. I. Bastrukov; I. V. Molodtsova; V. V. Papoyan; F. Weber

1996-01-01

369

Restrictions to neutron star models based on twin-peak quasi-periodic oscillations  

NASA Astrophysics Data System (ADS)

In a series of works - Török et al. (2010, 2012a) and Urbanec et al. (2010a) - we explored restrictions to neutron star properties that are implied by various models of twin-peak quasi-periodic oscillations. Here we sketch an attempt to confront the obtained mass-angular-momentum relations and limits on neutron star compactness with the parameters estimated by assuming various equations of state and the spin frequency of the atoll source 4U 1636-53.

Török, Gabriel; Urbanec, Martin; Goluchová, Kate?ina; Bakala, Pavel; Šrámková, Eva; Stuchlík, Zden?k

2013-03-01

370

Long Type I X-Ray Bursts and Neutron Star Interior Physics  

Microsoft Academic Search

Two types of long-duration type I X-ray bursts have been discovered by long-term monitoring observations of accreting neutron stars: superbursts and ``intermediate duration'' bursts. We investigate the sensitivity of their ignition conditions to the interior thermal properties of the neutron star. First, we compare the observed superburst light curves to cooling models. Our fits require ignition column depths in the

Andrew Cumming; Jared Macbeth; Dany Page

2006-01-01

371

Dynamical evolution of black hole-neutron star binaries in general relativity: Simulations of tidal disruption  

SciTech Connect

We calculate the first dynamical evolutions of merging black hole-neutron star binaries that construct the combined black hole-neutron star spacetime in a general relativistic framework. We treat the metric in the conformal flatness approximation, and assume that the black hole mass is sufficiently large compared to that of the neutron star so that the black hole remains fixed in space. Using a spheroidal spectral methods solver, we solve the resulting field equations for a neutron star orbiting a Schwarzschild black hole. The matter is evolved using a relativistic, Lagrangian, smoothed particle hydrodynamics (SPH) treatment. We take as our initial data recent quasiequilibrium models for synchronized neutron star polytropes generated as solutions of the conformal thin-sandwich (CTS) decomposition of the Einstein field equations. We are able to construct from these models relaxed SPH configurations whose profiles show good agreement with CTS solutions. Our adiabatic evolution calculations for neutron stars with low-compactness show that mass transfer, when it begins while the neutron star orbit is still outside the innermost stable circular orbit, is more unstable than is typically predicted by analytical formalisms. This dynamical mass loss is found to be the driving force in determining the subsequent evolution of the binary orbit and the neutron star, which typically disrupts completely within a few orbital periods. The majority of the mass transferred onto the black hole is accreted promptly; a significant fraction ({approx}30%) of the mass is shed outward as well, some of which will become gravitationally unbound and ejected completely from the system. The remaining portion forms an accretion disk around the black hole, and could provide the energy source for short-duration gamma-ray bursts.

Faber, Joshua A.; Shapiro, Stuart L.; Taniguchi, Keisuke [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Baumgarte, Thomas W. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Department of Physics and Astronomy, Bowdoin College, Brunswick, Maine 04011 (United States); Rasio, Frederic A. [Department of Physics and Astronomy, Northwestern University, Evanston, Illinois, 60208 (United States)

2006-01-15

372

Equation of State of Dense Matter and Maximum Mass of Neutron Stars  

Microsoft Academic Search

Theoretical models of the equation of state (EOS) of neutron-star matter (starting with the crust and ending at the densest region of the stellar core) are reviewed. Apart from a broad set of baryonic EOSs, strange quark matter, and even more exotic (abnormal and Q-matter) EOSs are considered. Results of calculations of M_max for non-rotating neutron stars and exotic compact

P. Haensel

2003-01-01

373

The slow-neutron capture process in low-metallicity asymptotic giant branch stars  

NASA Astrophysics Data System (ADS)

Elements heavier than iron are produced in asymptotic giant branch (AGB) stars via the slow neutron capture process (s process). Recent observations of s-process-enriched Carbon Enhanced Metal-Poor (CEMP) stars have provided an unprecedented wealth of observational constraints on the operation of the s-process in low-metallicity AGB stars. We present new preliminary full network calculations of low-metallicity AGB stars, including a comparison to the composition of a few s-process rich CEMP stars. We also discuss the possibility of using halo planetary nebulae as further probes of low-metallicity AGB nucleosynthesis.

Karakas, Amanda I.; Lugaro, Maria; Campbell, Simon W.

2010-03-01

374

Luminosity Differences between Black Holes and Neutron Stars  

NASA Astrophysics Data System (ADS)

We compare the X-ray (1-20 keV) and hard X-ray (20-200 keV) luminosities of black hole binaries (BHBs; i.e., binaries for which the mass of the compact object is known to exceed 3 Msun) and X-ray bursters (neutron star binaries, NSBs). We discuss two ways of distinguishing a BHB from a NSB: (1) If the X-ray luminosity exceeds 1O37 ergs s-1, the hard X-ray luminosity of BHBs is relatively unaffected, whereas the hard X-ray luminosity of NSBs decreases drastically; and (2) the hard X-ray luminosity of BHBs is commonly in the range 1037-6 x 1O37 ergs s-1, whereas for NSBs it is ? 1O37 ergs s-1. We show that late in their decays transient BHBs (e.g., GRS 1124-68) have X-ray and hard X-ray luminosities comparable to those observed for NSBs. Thus BHBs can be distinguished from NSBs only at relatively high luminosities. We also compare NSBs with the so-called black hole candidates (BHCs; i.e., systems with similar spectral/temporal properties to BHBs). The X-ray and hard X-ray luminosities of LMC X-1, GRO J0422+32, GRS 1915+105, 4U 1543-47, and 4U 1630-47 are much larger than the maximum luminosities observed from NSBs, which supports the idea that they contain black holes. Three other BHCs, namely GRS 1716-249, 1E 174O.7-2942, and GRS 1758-258 (which all lack an ultrasoft spectral component), have hard X-ray luminosities at least a factor of ˜2-3 above the maximum observed from NSBs, which suggests that these objects also contain black hole primaries. The case of GX 339-4 remains very uncertain because of the large uncertainty in its distance estimates (from 1.3 to 4 kpc). Assuming the larger distance, the X-ray and hard X-ray luminosities of the source, and its luminosity related spectral changes which are similar to transient BHBs (e.g., GRS 1124-68), support the idea that it contains a black hole. Finally, the X-ray and hard X-ray luminosities of the puzzling X-ray source 4U 1957+11 are in the range of those observed for NSBs, consistent with the idea that it might contain a neutron star. If 4U t957 + t t is, in fact, a neutron star system, this would establish that the combination of a power-law tail and an ultrasoft component (which is present in the spectrum of 4U 1957+11) is not a unique spectral signature of an accreting black hole.

Barret, Didier; McClintock, Jeffrey E.; Grindlay, Jonathan E.

1996-12-01

375

When can Gravitational-wave Observations Distinguish between Black Holes and Neutron Stars?  

NASA Astrophysics Data System (ADS)

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.

Hannam, Mark; Brown, Duncan A.; Fairhurst, Stephen; Fryer, Chris L.; Harry, Ian W.

2013-03-01

376

ELECTROMAGNETIC EXTRACTION OF ENERGY FROM BLACK-HOLE-NEUTRON-STAR BINARIES  

SciTech Connect

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.

McWilliams, Sean T.; Levin, Janna, E-mail: stmcwill@princeton.edu [Institute for Strings, Cosmology and Astroparticle Physics (ISCAP), Columbia University, New York, NY 10027 (United States)

2011-12-01

377

Inertial modes of rigidly rotating neutron stars in Cowling approximation  

SciTech Connect

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.

Kastaun, Wolfgang [Department of Theoretical Astrophysics, Universitaet Tuebingen, 72076 Tuebingen (Germany)

2008-06-15

378

Pair cascades in the magnetospheres of strongly magnetized neutron stars  

NASA Astrophysics Data System (ADS)

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-ray emission from magnetized neutron stars.

Medin, Zach; Lai, Dong

2010-08-01

379

Non-Radial Oscillations of Neutron Stars and the Detection of Gravitational Waves  

NASA Astrophysics Data System (ADS)

We study the non-radial oscillations of relativistic neutron stars, in particular the (fundamental) f-modes, which are believed to be the most relevant for the gravitational wave emission of perturbed isolated stars. The expected frequencies of the f-modes are compared to the sensitivity range of Mario Schenberg, the Brazilian gravitational wave spherical detector.

Chirenti, Cecilia; Silveira, Patrick R.; Aguiar, Odylio D.

380

Neutron star interiors and the equation of state of ultra-dense matter  

SciTech Connect

There has been much recent progress in our understanding of quark matter, culminating in the discovery that if such matter exists in the cores of neutron stars it ought to be in a color superconducting state. This paper explores the impact of superconducting quark matter on the properties (e.g., masses, radii, surface gravity, photon emission) of compact stars.

Weber, F.; Negreiros, R.; Rosenfield, P. [Dept. of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182 (United States); Torres i Cuadrat, Andreu [Physics Department, Universitat Autonoma de Barcelona (Spain)

2007-02-27

381

A New Formation Channel for Double Neutron Stars Without Recycling: Implications for Gravitational Wave Detection  

Microsoft Academic Search

We report on a new evolutionary path leading to the formation of close double neutron stars (NSs), with the unique characteristic that none of the two NSs ever had the chance to be recycled by accretion. The existence of this channel stems from the evolution of helium-rich stars (cores of massive NS progenitors), which has been neglected in most previous

Krzysztof Belczynski; Vassiliki Kalogera

2001-01-01

382

Black holes, white dwarfs and neutron stars: The physics of compact objects  

Microsoft Academic Search

The contents include: Star deaths and the formation of compact objects; White dwarfs; Rotation and magnetic fields; Cold equation of state above neutron drip; Pulsars; Accretion onto black holes; Supermassive stars and black holes; Appendices; and Indexes. This book discusses one aspect, compact objects, of astronomy and provides information of astrophysics or general relativity.

S. L. Shapiro; S. A. Teukolsky; Alan P. Lightman

1983-01-01

383

The accreting neutron stars are quasars, and the universe does not expand  

Microsoft Academic Search

The reliable theory of the evolution of heavy stars predicts the existence of a type of neutron stars which accrete a cloud of dirty hydrogen (accretors). Although they are very small (some hundreds of kilometres), the accretors should be easily observable because the accretion raises the surface temperature over 1 000 000 K, but they are never detected. The reason

Jacques Moret-Bailly

2004-01-01

384

Three-dimensional hydrodynamic simulations of the combustion of a neutron star into a quark star  

NASA Astrophysics Data System (ADS)

We present three-dimensional numerical simulations of turbulent combustion converting a neutron star into a quark star. Hadronic matter, described by a microphysical finite-temperature equation of state, is converted into strange quark matter. We assume this phase, represented by a bag-model equation of state, to be absolutely stable. Following the example of thermonuclear burning in white dwarfs leading to type Ia supernovae, we treat the conversion process as a potentially turbulent deflagration. Solving the nonrelativistic Euler equations using established numerical methods we conduct large eddy simulations including an elaborate subgrid scale model, while the propagation of the conversion front is modeled with a level-set method. Our results show that for large parts of the parameter space the conversion becomes turbulent and therefore significantly faster than in the laminar case. Despite assuming absolutely stable strange quark matter, in our hydrodynamic approximation an outer layer remains in the hadronic phase, because the conversion front stops when it reaches conditions under which the combustion is no longer exothermic.

Herzog, Matthias; Röpke, Friedrich K.

2011-10-01

385

How Neutron Star Radius Measurements Can Constrain the Nuclear Equation of State  

NASA Astrophysics Data System (ADS)

Precision measurements of neutron star structure may soon become possible from isolated neutron stars like RX J185635-3754 or from transient X-ray sources in globular clusters. Analyses of thermal emission, coupled with atmosphere models, yield estimates of the `radiation radius' R? , which is related to the mass M and R by R? =R/? 1-2GM/Rc2. Further information, such as from redshifts or observations of binary companions, may make possible simultaneous measurements of mass and radius. It is demonstrated that knowledge of the neutron star radius to an accuracy of 1 km or better permits a useful determination of the pressure of neutron star matter in the range 1-2ns, where ns=0.16 fm-3 (2.7 1014 g cm-3) is the nuclear saturation density. This pressure primarily depends upon dSv(n)/dn, where Sv(n) is the density-dependent nuclear symmetry energy. In principle, Sv(n) can be inferred from nuclear systematics (masses, neutron skins, fission barrier heights). A new precision measurement of the neutron skin thickness of 208Pb being carried out at Jefferson Lab will significantly reduce experimental uncertainties. An interesting collaboration to fix Sv(n), developed from objects differing in size by 1020, is thus at hand. Better knowledge of Sv(n) is needed to predict properties of neutron-rich nuclei found in supernovae, r-process simulations, and neutron star crusts. It is shown that a neutron star's moment of inertia, the fraction of the moment of inertia residing in the star's crust, and the stellar binding energy are nearly universal functions of the star's mass and radius, irrespective of the underlying equation of state. These features can be understood by considering analytic solutions of Einstein's equations, due to Buchdahl and Tolman. Further constraints from neutrino observations of proto-neutron stars and from observations of pulsar glitches are thus possible. The neutron star maximum mass, however, depends upon the pressure at several times ns and cannot be gleaned from radius measurements alone.

Lattimer, J. M.

2001-12-01

386

Cooling of hybrid neutron stars and hypothetical self-bound objects with superconducting quark cores  

Microsoft Academic Search

We study the consequences of superconducting quark cores (with color-flavor-locked phase as representative example) for the evolution of temperature profiles and cooling curves in quark-hadron hybrid stars and in hypothetical self-bound objects having no hadron shell (quark core neutron stars). The quark gaps are varied from 0 to Deltaq =50 MeV. For hybrid stars we find time scales of 1\\/5,

D. Blaschke; H. Grigorian; D. N. Voskresensky

2001-01-01

387

Neutron Capture Elements in s-Process-Rich, Very Metal-Poor Stars  

Microsoft Academic Search

We report abundance estimates for neutron capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP 625-44 and LP 706-7. These stars are subgiants whose surface abundances are likely to have been strongly affected by mass transfer from companion asymptotic giant branch (AGB) stars that have since evolved to white dwarfs. The

Wako Aoki; Sean G. Ryan; John E. Norris; Timothy C. Beers; Hiroyasu Ando; Nobuyuki Iwamoto; Toshitaka Kajino; Grant J. Mathews; Masayuki Y. Fujimoto

2001-01-01

388

Coupled Spin, Mass, Magnetic field, and Orbital Evolution of Accreting Neutron stars  

Microsoft Academic Search

The present study is mainly addressed to the coupled spin, mass, magnetic field, orbital separation, and orbital period evolution of a neutron star entering a close binary system with a low mass main sequence companion, which loses mass in form of homogenous stellar wind. We apply flux expulsion of the magnetic field from the superfluid superconductive core of a neutron

M. Mirtorabi; A. Javadi Khasraghi; S. Abdolrahimi

2006-01-01

389

On the stability of global non-radial pulsations of neutron stars  

Microsoft Academic Search

A neutron star is the cosmic nuclear object in which the energy of gravitational pull is brought to equilibrium by elastic energy stored in the neutron Fermi-continuum. Evidence for the viscoelastic behaviour of a stellar nuclear matter provides a seismological model of pulsar glitches interpreted as a sudden release of the elastic energy. In laboratory nuclear physics, the signatures of

S. I. Bastrukov; F. Weber; D. V. Podgainy

1999-01-01

390

Effects of Strong Magnetic Fields on Neutron Star Structure  

NASA Astrophysics Data System (ADS)

We study static neutron stars with poloidal magnetic fields and a simple class of electric current distributions consistent with the requirement of stationarity. For this class of electric current distributions, we find that magnetic fields are too large for static configurations to exist when the magnetic force pushes a sufficient amount of mass off-center that the gravitational force points outward near the origin in the equatorial plane. (In our coordinates an outward gravitational force corresponds to ?lngtt/?r>0, where t and r are respectively time and radial coordinates and gtt is coefficient of dt2 in the line element.) For the equations of state (EOSs) employed in previous work, we obtain configurations of higher mass than had been reported; we also present results with more recent EOSs. For all EOSs studied, we find that the maximum mass among these static configurations with magnetic fields is noticeably larger than the maximum mass attainable by uniform rotation, and that for fixed values of baryon number the maximum mass configurations are all characterized by an off-center density maximum.

Cardall, Christian Y.; Prakash, Madappa; Lattimer, James M.

2001-06-01

391

Merger of black hole and neutron star in general relativity  

NASA Astrophysics Data System (ADS)

Some of the latest results of the simulation for the merger of black hole (BH)-neutron star (NS) binaries in full general relativity is presented. As the initial condition, we prepare a quasicircular state in which the BH is modeled by a moving puncture with no spin. The ?-law equation of state with ? = 2 and irrotational velocity field are used for modeling the NS. The BH mass is chosen to be ~4 Msolar, whereas the rest-mass of the NS is ~1.4 Msolar and the radius is ~13 km. The NS is tidally disrupted near the innermost stable orbit but more than ~90% of the material is quickly swallowed into the BH and the resultant disk mass is ~0.1 Msolar. The thermal energy of the material in the disk increases by the shock heating occurred in the collision between the spiral arms. Our results indicate that the merger between a low-mass BH and its companion NS may form a central engine of short-gamma-ray bursts. Gravitational waveforms are also presented. We find that the amplitude of gravitational waves quickly decreases after the tidal disruption and the amplitude of the quasinormal mode ringing is small.

Shibata, Masaru; Taniguchi, Keisuke; Uryu, Koji

2008-01-01

392

Photospheric Radius Expansion in Superburst Precursors from Neutron Stars  

NASA Astrophysics Data System (ADS)

Thermonuclear runaway burning of carbon is in rare cases observed from accreting neutron stars as day-long X-ray flares called superbursts. In the few cases where the onset is observed, superbursts exhibit a short precursor burst at the start. In each instance, however, the data are of insufficient quality for spectral analysis of the precursor. Using data from the propane anti-coincidence detector of the Proportional Counter Array instrument on the Rossi X-ray Timing Explorer, we perform the first detailed time-resolved spectroscopy of precursors. For a superburst from 4U 1820-30 we demonstrate the presence of photospheric radius expansion. We find the precursor to be 1.4-2 times more energetic than other short bursts from this source, indicating that the burning of accreted helium is insufficient to explain the full precursor. Shock heating would be able to account for the shortfall in energy. We argue that this precursor is a strong indication that the superburst starts as a detonation, and that a shock induces the precursor. Furthermore, we employ our technique to study the superexpansion phase of the same superburst in greater detail.

Keek, L.

2012-09-01

393

Constraining the neutron star equation of state using quiescent low-mass X-ray binaries  

SciTech Connect

Chandra or XMM-Newton observations of quiescent low-mass X-ray binaries can provide important constraints on the equation of state of neutron stars. The mass and radius of the neutron star can potentially be determined from fitting a neutron star atmosphere model to the observed X-ray spectrum. For a radius measurement it is of critical importance that the distance to the source is well constrained since the fractional uncertainty in the radius is at least as large as the fractional uncertainty in the distance. Uncertainties in modelling the neutron star atmosphere remain. At this stage it is not yet clear if the soft thermal component in the spectra of many quiescent X-ray binaries is variable on timescales too short to be accommodated by the cooling neutron star scenario. This can be tested with a long XMM-Newton observation of the neutron star X-ray transient Cen X-4 in quiescence. With such an observation one can use the Reflection Grating Spectrometer spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X-ray spectral fitting of the EPIC pn and MOS spectra and allows one to investigate whether the variability observed in the quiescent X-ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in N{sub H}. This will test whether the soft thermal component can indeed be due to the hot thermal glow of the neutron star. Irrespective of the outcome of such a study, the observed cooling in quiescence in sources for which the crust is significantly out of thermal equilibrium with the core due to a prolonged outburst, such as KS 1731-260, seem excellent candidates for mass and radius determinations through modelling the observed X-rays with a neutron star atmosphere model (the caveats about the source distance and atmosphere modelling do also apply here obviously and presently prevent one from obtaining such constraints). Finally, the fact that the soft thermal glow in sources such as SAX J1808.4-3658 and 1H 1905+000 has not been detected in quiescence means that the neutron star cores of these sources must be cold. The most plausible explanation seems to be that the neutron stars are more massive than 1.4 M{sub {center_dot}} and cool via the direct URCA process.

Jonker, P. G. [SRON, Netherlands Institute for Space Research, 3584 CA, Utrecht (Netherlands); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, Massachusetts (United States); Astronomical Institute, Utrecht University, 3508 TA, Utrecht (Netherlands)

2008-02-27

394

Constraining the neutron star equation of state using quiescent low-mass X-ray binaries  

NASA Astrophysics Data System (ADS)

Chandra or XMM-Newton observations of quiescent low-mass X-ray binaries can provide important constraints on the equation of state of neutron stars. The mass and radius of the neutron star can potentially be determined from fitting a neutron star atmosphere model to the observed X-ray spectrum. For a radius measurement it is of critical importance that the distance to the source is well constrained since the fractional uncertainty in the radius is at least as large as the fractional uncertainty in the distance. Uncertainties in modelling the neutron star atmosphere remain. At this stage it is not yet clear if the soft thermal component in the spectra of many quiescent X-ray binaries is variable on timescales too short to be accommodated by the cooling neutron star scenario. This can be tested with a long XMM-Newton observation of the neutron star X-ray transient Cen X-4 in quiescence. With such an observation one can use the Reflection Grating Spectrometer spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X-ray spectral fitting of the EPIC pn and MOS spectra and allows one to investigate whether the variability observed in the quiescent X-ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in NH. This will test whether the soft thermal component can indeed be due to the hot thermal glow of the neutron star. Irrespective of the outcome of such a study, the observed cooling in quiescence in sources for which the crust is significantly out of thermal equilibrium with the core due to a prolonged outburst, such as KS 1731-260, seem excellent candidates for mass and radius determinations through modelling the observed X-rays with a neutron star atmosphere model (the caveats about the source distance and atmosphere modelling do also apply here obviously and presently prevent one from obtaining such constraints). Finally, the fact that the soft thermal glow in sources such as SAX J1808.4-3658 and 1H 1905+000 has not been detected in quiescence means that the neutron star cores of these sources must be cold. The most plausible explanation seems to be that the neutron stars are more massive than 1.4 Msolar and cool via the direct URCA process.

Jonker, P. G.

2008-02-01

395

Quantizing Magnetic Field and Quark-Hadron Phase Transition in a Neutron Star  

SciTech Connect

We investigate the influence of a strong magnetic field on various properties of neutron stars with quark-hadron phase transition. The one-gluon exchange contribution in a magnetic field is calculated in a relativistic Dirac-Hartree-Fock approach. In a magnetic field of 5{times}10{sup 18} G in the center of the star, the overall equation of state is softer in comparison to the field-free case resulting in the reduction of maximum mass of the neutron star. {copyright} {ital 1997} {ital The American Physical Society}

Bandyopadhyay, D.; Pal, S. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700 064 (India); Chakrabarty, S. [IUCAA, P.B. 4, Ganeshkhind, Pune 411007, India] [Divakaran, P.P. (SPIC Mathematical Institute, 92, G.N. Chetty Road, T.Nagar, Chennai-600 017, India)

1997-09-01

396

Deformations of accreting neutron star crusts and gravitational wave emission  

NASA Astrophysics Data System (ADS)

Motivated by the remarkably narrow range of measured spin frequencies of ~20 accreting (and weakly magnetic) neutron stars in the Galaxy, Bildsten conjectured that their spin-up had been halted by the emission of gravitational waves. If so, then the brightest persistent X-ray source on the sky, Scorpius X-1, should be detected by gravitational wave interferometers within 10 years. Bildsten pointed out that small non-axisymmetric temperature variations in the accreted crust will lead to `wavy' electron capture layers, and the resulting horizontal density variations near e- capture layers create a mass quadrupole moment. Neglecting the elastic response of the crust, Bildsten estimated that even e- capture layers in the thin outer crust can develop the quadrupole necessary to balance accretion torque with gravitational waves, M? ~ 10-10 - 2 x 10-8 Msolar yr-1, Q22~1037- 1038gcm-2 for accretion rates M? <~ 5 x 10-9 Msolar yr-1. We present a full calculation of the crust's elastic adjustment to the density perturbations induced by the temperature-sensitive e- capture reactions. We find that, due to the tendency of the denser material to sink rather than spread sideways, neglecting the elastic response of the crust overestimates, by a factor of 20-50, the Q22 that results from a wavy capture layer in the thin outer crust. However, we find that this basic picture, when applied to capture layers in the deep inner crust, can still generate Q22 in the necessary range, as long as there are <~5per cent lateral temperature variations at densities in excess of 1012gcm-3, and as long as the crustal breaking strain is high enough. By calculating the thermal flow throughout the core and the crust, we find that temperature gradients this large are easily maintained by asymmetric heat sources or lateral composition gradients in the crust. If the composition or heating asymmetries are independent of the accretion rate, then for (M?>rsim10-11 Msolar yr-1), the induced quadrupole moments have approximately the same scaling, ~M?1/2, as that necessary to balance the accretion torque at the same spin frequency for all M?. Temperature gradients in the deep crust lead to a modulation in the thermal emission from the surface of the star that is correlated with Q22. In addition, a ~0.5per cent lateral variation in the nuclear charge-to-mass ratio in the crust will also result in a Q22 sufficient to halt spin-up from accretion even in the absence of a lateral temperature gradient. We also derive a general relation between the stresses and strains in the crust and the maximum quadrupole moment they can generate. We show, under quite general conditions, that maintaining a Q22 of the magnitude necessary to balance the accretion torque requires a dimensionless strain ?5?, ?~10-2 at near-Eddington accretion rates, of order the breaking strain of conventional materials. This leads us to speculate that accreting neutron stars reach the same equilibrium spin because they all are driven to the maximum Q22 that the crust can sustain.

Ushomirsky, Greg; Cutler, Curt; Bildsten, Lars

2000-12-01

397

The Effect of Quantized Magnetic Flux Lines on the Dynamics of Superfluid Neutron Star Cores  

Microsoft Academic Search

We investigate dynamical coupling timescales of a neutron star's superfluid\\u000acore, taking into account the interactions of quantized neutron vortices with\\u000aquantized flux lines of the proton superconductor in addition to the previously\\u000aconsidered scattering of the charged components against the spontaneous\\u000amagnetization of the neutron vortex line. We compare the cases where vortex\\u000amotion is constrained in different ways

T. Sidery; M. A. Alpar

2009-01-01

398

Mn, Cu, and Zn abundances in barium stars and their correlations with neutron capture elements  

Microsoft Academic Search

Barium stars are optimal sites for studying the correlations between the neutron-capture elements and other species that may be depleted or enhanced, because they act as neutron seeds or poisons during the operation of the s-process. These data are necessary to help constrain the modeling of the neutron-capture paths and explain the s-process abundance curve of the solar system. Chemical

D. M. Allen; G. F. Porto de Mello

2011-01-01

399

Spin-down of Neutron Stars and Compositional Transitions in the Cold Crustal Matter  

Microsoft Academic Search

Transitions of nuclear compositions in the crust of a neutron star induced by stellar spin-down are evaluated at zero temperature. We construct a compressible liquid-drop model for the energy of nuclei immersed in a neutron gas, including pairing and shell correction terms, in reference to the known properties of the ground state of matter above neutron drip density, 4.3 x

Kei Iida; Katsuhiko Sato

1997-01-01

400

Spin-Down of Neutron Stars and Compositional Transitions in the Cold Crustal Matter  

Microsoft Academic Search

Transitions of nuclear compositions in the crust of a neutron star induced by stellar spin-down are evaluated at zero temperature. We construct a compressible liquid-drop model for the energy of nuclei immersed in a neutron gas, including pairing and shell correction terms, in reference to the known properties of the ground state of matter above neutron drip density, 4.3 times

K. Iida; K. Sato

1998-01-01

401

Rapid scientific response to Landers quake  

NASA Astrophysics Data System (ADS)

Early on the morning of June 28, 1992, millions of people in southern California were awakened by the largest earthquake (Ms 7.5, Mw 7.4) in the western U.S. in the past 40 years. The quake initiated near the town of Landers, Calif., at 11:57 (GMT) and ruptured to the north and then the northwest along a 70-km stretch of the Mojave Shear Zone. Fortunately, the strongest shaking occurred in uninhabited regions of the Mojave desert, but one child was killed in Yucca Valley and 400 people were injured in the surrounding area. The communities of Landers, Yucca Valley, and Joshua Tree in San Bernardino County sustained significant ($100 million) damage to buildings and roads. Damage to water and power lines also caused problems in many of the desert areas.

Mori, J.; Hudnut, K.; Jones, L.; Hauksson, E.; Hutton, K.

402

Collapsing Neutron Stars Driven by Critical Magnetic Fields and Exploding Bose-Einstein Condensates  

NASA Astrophysics Data System (ADS)

A Bose-Einstein condensate of a neutral vector boson bearing an anomalous magnetic moment is suggested as a model for ferromagnetic origin of magnetic fields in neutron stars. The vector particles are assumed to arise from parallel spin-paired neutrons. A negative pressure perpendicular to the external field B is acting on this condensate, which for large densities, compress the system, and may produce a collapse. An upper bound of the magnetic fields observable in neutron stars is given. In the the non-relativistic limit, the analogy with the behavior of exploding Bose-Einstein condensates (BECs) for critical values of the magnetic field is briefly discussed.

Pérez Rojas, H.; Pérez Martínez, A.; Mosquera Cuesta, Herman J.

403

Transport parameters in neutron stars from in-medium NN cross sections  

SciTech Connect

We present a numerical study of shear viscosity and thermal conductivity of symmetric nuclear matter, pure neutron matter, and beta-stable nuclear matter, in the framework of the Brueckner theory. The calculation of in-medium cross sections and nucleon effective masses is performed with a consistent two- and three-body interaction. The investigation covers a wide baryon density range as needed in the applications to neutron stars. The results for the transport coefficients in beta-stable nuclear matter are used to make preliminary predictions on the damping time scales of nonradial modes in neutron stars.

Zhang, H. F. [School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000 (China); Lombardo, U. [Dipartimento di Fisica and INFN-LNS, Via S. Sofia 64, I-95123 Catania (Italy); Zuo, W. [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

2010-07-15

404

Interaction between vortices and nuclei in the inner crust of neutron stars  

SciTech Connect

The inner crust of a neutron star is expected to contain a Coulomb lattice of nuclei immersed in a superfluid sea of free neutrons. The rotation of the star induces the formation of vortices in the neutron sea, whose dynamics is influenced by the interaction with the nuclei. In particular, this interaction is important to determine whether it is energetically advantageous for vortices to pin on nuclei or not. We find that the pinning energy is sensitive to quantal size effects. In fact, the nuclear shell structure tends to hinder the formation of vortices inside the nuclear volume.

Avogadro, P. [RIKEN, 2-1 Hirosawa, Wako-shi. Saitama 351-0198 (Japan); Barranco, F. [Departamento de Fisica Aplicada III, Universidad de Sevilla, Escuela Superior de Ingenieros, Sevilla, 41092, Camino de los Descubrimientos s/n (Spain); Broglia, R. A. [Dipartimento di Fisica, Universita degli Studi di Milano, Milano, 20133, Via Celoria 16 (Italy) and Niels Bohr Institute, University of Copenhagen, Copenhagen Oe, Blegdamsvej 17 2100 (Denmark); INFN, Sezione di Milano, Milano, 20133, Via Celoria 16 (Italy); Vigezzi, E. [INFN, Sezione di Milano, Milano, 20133, Via Celoria 16 (Italy)

2009-05-04

405

Constraining neutron-star tidal Love numbers with gravitational-wave detectors  

SciTech Connect

Ground-based gravitational wave detectors may be able to constrain the nuclear equation of state using the early, low frequency portion of the signal of detected neutron star-neutron star inspirals. In this early adiabatic regime, the influence of a neutron star's internal structure on the phase of the waveform depends only on a single parameter {lambda} of the star related to its tidal Love number, namely, the ratio of the induced quadrupole moment to the perturbing tidal gravitational field. We analyze the information obtainable from gravitational wave frequencies smaller than a cutoff frequency of 400 Hz, where corrections to the internal-structure signal are less than 10%. For an inspiral of two nonspinning 1.4M{sub {center_dot}} neutron stars at a distance of 50 Megaparsecs, LIGO II detectors will be able to constrain {lambda} to {lambda}{<=}2.0x10{sup 37} g cm{sup 2} s{sup 2} with 90% confidence. Fully relativistic stellar models show that the corresponding constraint on radius R for 1.4M{sub {center_dot}} neutron stars would be R{<=}13.6 km (15.3 km) for a n=0.5 (n=1.0) polytrope with equation of state p{proportional_to}{rho}{sup 1+1/n}.

Flanagan, Eanna E.; Hinderer, Tanja [Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853 (United States)

2008-01-15

406

Neutron star mass-radius relation with gravitational field shielding by a scalar field  

NASA Astrophysics Data System (ADS)

The currently well-developed models for equations of state (EoSs) have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass. To explain these measurements, the theory of gravitational field shielding by a scalar field is applied. This theory was recently developed in accordance with the five-dimensional (5D) fully covariant Kaluza-Klein (KK) theory that has successfully unified Einstein's general relativity and Maxwell's electromagnetic theory. It is shown that a massive, compact neutron star can generate a strong scalar field, which can significantly shield or reduce its gravitational field, thus making it more massive and more compact. The mass-radius relation developed under this type of modified gravity can be consistent with these recent measurements of neutron stars. In addition, the effect of gravitational field shielding helps explain why the supernova explosions of some very massive stars (e.g., 40 Msolar as measured recently) actually formed neutron stars rather than black holes as expected. The EoS models, ruled out by measurements of small radius and/or large mass neutron stars according to the theory of general relativity, can still work well in terms of the 5D fully covariant KK theory with a scalar field.

Zhang, Bo-Jun; Zhang, Tian-Xi; Guggilla, Padmaja; Dokhanian, Mostafa

2013-05-01

407

Evolution of neutron stars with toroidal magnetic fields: Axisymmetric simulation in full general relativity  

SciTech Connect

We study the stability of neutron stars with toroidal magnetic fields by magnetohydrodynamic simulation in full general relativity under the assumption of axial symmetry. Nonrotating and rigidly rotating neutron stars are prepared for a variety of magnetic field configuration. For modeling the neutron stars, the polytropic equation of state with the adiabatic index {gamma}=2 is used for simplicity. It is found that nonrotating neutron stars are dynamically unstable for the case where toroidal magnetic field strength varies {proportional_to} {omega}-bar{sup 2k-1} with k{>=}2 (here {omega}-bar is the cylindrical radius), whereas for k=1 the neutron stars are stable. After the onset of the instability, unstable modes grow approximately in the Alfven time scale and, as a result, a convective motion is excited to change the magnetic field profile until a new state, which is stable against axisymmetric perturbation, is reached. We also find that rotation plays a role in stabilization, although the instability still occurs in the Alfven time scale when the ratio of magnetic energy to rotational kinetic energy is larger than a critical value {approx}0.2. Implication for the evolution of magnetized protoneutron stars is discussed.

Kiuchi, Kenta [Department of Physics, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555 (Japan); Shibata, Masaru [Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro, Tokyo 153-8902 (Japan); Yoshida, Shijun [Astronomical Institute, Tohoku University, Sendai 980-8578 (Japan)

2008-07-15

408

Moment of inertia, radii, surface emission from a new theoretical understanding of Neutron Stars  

NASA Astrophysics Data System (ADS)

We formulate the equations of neutron stars taking into account the strong, weak, electromagnetic and gravitational interactions within a new fully general relativistic Thomas-Fermi approach. The nuclear interactions are described by the exchange of the sigma, omega, and rho virtual mesons. The constancy of the generalized chemical potential, for short Klein potentials, of the particle species is required as a condition of equilibrium throughout the star. The continuity of the Klein potentials in the transition from the core to the crust imposes the presence of a strong electric field larger than the critical one for vacuum polarization. Correspondingly, the electron density decreases in the core-crust transition region. Such a phenomenon leads to neutron stars with crusts with masses and thickness smaller with respect to the ones of traditional neutron star configurations that satisfy local charge neutrality from the center all the way up to the surface. We present new estimates of the mass-radius relation, moment of inertia, quadrupole moment, and period of rotation of neutron stars. The consequences on the emission process and timing properties of neutron stars, as well as the possible consequences on QPO emission, are considered.

Belvedere, Riccardo; Ruffini, Remo; Xue, She-Sheng; Rueda Hernandez, Jorge Armando

2012-07-01

409

Determination of the internal structure of neutron stars from gravitational wave spectra  

NASA Astrophysics Data System (ADS)

In this paper the internal structure of a neutron star is shown to be inferrable from its gravitational-wave spectrum. Iteratively applying the inverse scheme of the scaled coordinate logarithmic perturbation method for neutron stars proposed by Tsui and Leung [Astrophys. J. 631, 495 (2005)ASJOAB0004-637X10.1086/432525], we are able to determine the mass, the radius and the mass distribution of a star from its quasinormal mode frequencies of stellar pulsation. In addition, accurate equation of state of nuclear matter can be obtained from such inversion scheme. Explicit formulas for the case of axial w-mode oscillation are derived here and numerical results for neutron stars characterized by different equations of state are shown.

Tsui, L. K.; Leung, P. T.; Wu, J.

2006-12-01

410

Neutron Star Kicks Affected by Standing Accretion Shock Instability for Core-Collapse Supernovae  

NASA Astrophysics Data System (ADS)

We investigate a proto-neutron star kick velocity estimated from kinetic momentum of a flow around the proto-neutron star after the standing accretion shock instability grows. In this study, ten different types of random perturbations are imposed on the initial flow for each neutrino luminosity. We found that the kick velocities of proto-neutron star are widely distributed from 40 km s-1 to 180 km s-1 when the shock wave reaches 2000 km away from the center of the star. The average value of kick velocity is 115 km s-1, whose value is smaller than the observational ones. The kick velocities do not depend on the neutrino luminosity.

Nakano, Wakana Iwakami; Kotake, Kei; Ohnishi, Naofumi; Yamada, Shoichi; Sawada, Keisuke

2012-09-01

411

A link between measured neutron star masses and lattice QCD data  

NASA Astrophysics Data System (ADS)

We study the hadron-quark phase transition in neutron star matter and the structural properties of hybrid stars using an equation of state (EOS) for the quark phase derived with the field correlator method (FCM). We make use of the measured neutron star masses, and particularly the mass of PSR J1614-2230, to constrain the values of the gluon condensate G2 which is one of the EOS parameter within the FCM. We find that the values of G2 extracted from the mass measurement of PSR J1614-2230 are fully consistent with the values of the same quantity derived, within the FCM, from recent lattice quantum chromodynamics (QCD) calculations of the deconfinement transition temperature at zero baryon chemical potential. The FCM thus provides a powerful tool to link numerical calculations of QCD on a space-time lattice with neutron stars physics.

Bombaci, Ignazio; Logoteta, Domenico

2013-06-01

412

Gravitational waves from nonspinning black hole-neutron star binaries: Dependence on equations of state  

NASA Astrophysics Data System (ADS)

We report results of a numerical-relativity simulation for the merger of a black hole-neutron star binary with a variety of equations of state (EOSs) modeled by piecewise polytropes. We focus, in particular, on the dependence of the gravitational waveform at the merger stage on the EOSs. The initial conditions are computed in the moving-puncture framework, assuming that the black hole is nonspinning and the neutron star has an irrotational velocity field. For a small mass ratio of the binaries (e.g., MBH/MNS=2, where MBH and MNS are the masses of the black hole and neutron star, respectively), the neutron star is tidally disrupted before it is swallowed by the black hole irrespective of the EOS. Especially for less-compact neutron stars, the tidal disruption occurs at a more distant orbit. The tidal disruption is reflected in a cutoff frequency of the gravitational-wave spectrum, above which the spectrum amplitude exponentially decreases. A clear relation is found between the cutoff frequency of the gravitational-wave spectrum and the compactness of the neutron star. This relation also depends weakly on the stiffness of the EOS in the core region of the neutron star, suggesting that not only the compactness but also the EOS at high density is reflected in gravitational waveforms. The mass of the disk formed after the merger shows a similar correlation with the EOS, whereas the spin of the remnant black hole depends primarily on the mass ratio of the binary, and only weakly on the EOS. Properties of the remnant disks are also analyzed.

Kyutoku, Koutarou; Shibata, Masaru; Taniguchi, Keisuke

2010-08-01

413

Gravitational waves from nonspinning black hole-neutron star binaries: Dependence on equations of state  

SciTech Connect

We report results of a numerical-relativity simulation for the merger of a black hole-neutron star binary with a variety of equations of state (EOSs) modeled by piecewise polytropes. We focus, in particular, on the dependence of the gravitational waveform at the merger stage on the EOSs. The initial conditions are computed in the moving-puncture framework, assuming that the black hole is nonspinning and the neutron star has an irrotational velocity field. For a small mass ratio of the binaries (e.g., M{sub BH}/M{sub NS}=2, where M{sub BH} and M{sub NS} are the masses of the black hole and neutron star, respectively), the neutron star is tidally disrupted before it is swallowed by the black hole irrespective of the EOS. Especially for less-compact neutron stars, the tidal disruption occurs at a more distant orbit. The tidal disruption is reflected in a cutoff frequency of the gravitational-wave spectrum, above which the spectrum amplitude exponentially decreases. A clear relation is found between the cutoff frequency of the gravitational-wave spectrum and the compactness of the neutron star. This relation also depends weakly on the stiffness of the EOS in the core region of the neutron star, suggesting that not only the compactness but also the EOS at high density is reflected in gravitational waveforms. The mass of the disk formed after the merger shows a similar correlation with the EOS, whereas the spin of the remnant black hole depends primarily on the mass ratio of the binary, and only weakly on the EOS. Properties of the remnant disks are also analyzed.

Kyutoku, Koutarou; Shibata, Masaru; Taniguchi, Keisuke [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro, Tokyo 153-8902 (Japan)

2010-08-15

414

Big black hole, little neutron star: Magnetic dipole fields in the Rindler spacetime  

NASA Astrophysics Data System (ADS)

As a black hole and neutron star approach during inspiral, the field lines of a magnetized neutron star eventually thread the black hole event horizon and a short-lived electromagnetic circuit is established. The black hole acts as a battery that provides power to the circuit, thereby lighting up the pair just before merger. Although originally suggested as an electromagnetic counterpart to gravitational-wave detection, a black hole battery is of more general interest as a novel luminous astrophysical source. To aid in the theoretical understanding, we present analytic solutions for the electromagnetic fields of a magnetic dipole in the presence of an event horizon. In the limit that the neutron star is very close to a Schwarzschild horizon, the Rindler limit, we can solve Maxwell’s equations exactly for a magnetic dipole on an arbitrary worldline. We present these solutions here and investigate a proxy for a small segment of the neutron star orbit around a big black hole. We find that the voltage the black hole battery can provide is in the range ˜1016 statvolts with a projected luminosity of 1042ergs/s for an M=10M? black hole, a neutron star with a B-field of 1012G, and an orbital velocity ˜0.5c at a distance of 3M from the horizon. Larger black holes provide less power for binary separations at a fixed number of gravitational radii. The black hole/neutron star system therefore has a significant power supply to light up various elements in the circuit possibly powering bursts, jets, beamed radiation, or even a hot spot on the neutron star crust.

D'Orazio, Daniel J.; Levin, Janna

2013-09-01

415

Possible dark energy imprints in the gravitational wave spectrum of mixed neutron-dark-energy stars  

NASA Astrophysics Data System (ADS)

In the present paper we study the oscillation spectrum of neutron stars containing both ordinary matter and dark energy in different proportions. Within the model we consider, the equilibrium configurations are numerically constructed and the results show that the properties of the mixed neuron-dark-energy star can differ significantly when the amount of dark energy in the stars is varied. The oscillations of the mixed neuron-dark-energy stars are studied in the Cowling approximation. As a result we find that the frequencies of the fundamental mode and the higher overtones are strongly affected by the dark energy content. This can be used in the future to detect the presence of dark energy in the neutron stars and to constrain the dark-energy models.

Yazadjiev, Stoytcho S.; Doneva, Daniela D.

2012-03-01

416

Double core evolution. 7: The infall of a neutron star through the envelope of its massive star companion  

NASA Astrophysics Data System (ADS)

Binary systems with properties similar to those of high-mass X-ray binaries are evolved through the common envelope phase. Three-dimensional simulations show that the timescale of the infall phase of the neutron star depends upon the evolutionary state of its massive companion. We find that tidal torques more effectively accelerate common envelope evolution for companions in their late core helium-burning stage and that the infall phase is rapid (approximately several initial orbital periods). For less evolved companions the decay of the orbit is longer; however, once the neutron star is deeply embedded within the companion's envelope the timescale for orbital decay decreases rapidly. As the neutron star encounters the high-density region surrounding the helium core of its massive companion, the rate of energy loss from the orbit increases dramatically leading to either partial or nearly total envelope ejection. The outcome of the common envelope phase depends upon the structure of the evolved companion. In particular, it is found that the entire common envelope can be ejected by the interaction of the neutron star with a red supergiant companion in binaries with orbital periods similar to those of long-period Be X-ray binaries. For orbital periods greater than or approximately equal to 0.8-2 yr (for companions of mass 12-24 solar mass) it is likely that a binary will survive the common envelope phase. For these systems, the structure of the progenitor star is characterized by a steep density gradient above the helium core, and the common envelope phase ends with a spin up of the envelope to within 50%-60% of corotation and with a slow mass outflow. The efficiency of mass ejection is found to be approximately 30%-40%. For less evolved companions, there is insufficient energy in the orbit to unbind the common envelope and only a fraction of it is ejected. Since the timescale for orbital decay is always shorter than the mass-loss timescale from the common envelope, the two cores will likely merge to form a Thorne-Zytkow object. Implications for the origin of Cyg X-3, an X-ray source consisting of a Wolf-Rayet star and a compact companion, and for the fate of the remnant binary consisting of a helium star and a neutron star are briefly discussed.

Terman, James L.; Taam, Ronald E.; Hernquist, Lars

1995-05-01

417

RESTORATION OF QUAKING ASPEN WOODLANDS INVADED BY WESTERN JUNIPER  

Technology Transfer Automated Retrieval System (TEKTRAN)

Western juniper (Juniperus occidentalis spp. occidentalis Hook.) woodlands are rapidly replacing lower elevation (< 2100 m) quaking aspen (Populus tremuloides Michx.) stands throughout the northern Great Basin. Aspen restoration is important because these communities provide important habitat for w...

418

Radiative Transfer Simulations of Neutron Star Merger Ejecta  

NASA Astrophysics Data System (ADS)

Mergers of binary neutron stars (NSs) are among the most promising gravitational wave (GW) sources. Next generation GW detectors are expected to detect signals from NS mergers within about 200 Mpc. The detection of electromagnetic wave (EM) counterparts is crucial to understanding the nature of GW sources. Among the possible EM emission from the NS merger, emission powered by radioactive r-process nuclei is one of the best targets for follow-up observations. However, predictions so far have not taken into account detailed r-process element abundances in the ejecta. We perform for the first time radiative transfer simulations of the NS merger ejecta including all the r-process elements from Ga to U. We show that the opacity of the NS merger ejecta is about ? = 10 cm2 g-1, which is higher than that of Fe-rich Type Ia supernova ejecta by a factor of ~100. As a result, the emission is fainter and lasts longer than previously expected. The spectra are almost featureless due to the high expansion velocity and bound-bound transitions of many different r-process elements. We demonstrate that the emission is brighter for a higher mass ratio of the two NSs and a softer equation of state adopted in the merger simulations. Because of the red color of the emission, follow-up observations in red optical and near-infrared (NIR) wavelengths will be the most efficient. At 200 Mpc, the expected brightness of the emission is i = 22-25 AB mag, z = 21-23 AB mag, and 21-24 AB mag in the NIR JHK bands. Thus, observations with wide-field 4 m- and 8 m-class optical telescopes and wide-field NIR space telescopes are necessary. We also argue that the emission powered by radioactive energy can be detected in the afterglow of nearby short gamma-ray bursts.

Tanaka, Masaomi; Hotokezaka, Kenta

2013-10-01

419

Relativistic SPH Simulations of Black Hole -- Neutron Star Binary Mergers  

NASA Astrophysics Data System (ADS)

We investigate numerically the mergers of Black Hole -- Neutron Star (BH--NS) binaries with small mass ratios (q?MNS/MBH˜0.1). We are interested in how the binary characteristics (such as the BH spin, the orbital inclination, and the NS equation of state) affect the evolution and outcome of such mergers, and under which conditions they can be viable progenitors of short gamma-ray bursts (GRBs). We use a 3-D relativistic SPH (Smoothed Particle Hydrodynamics) code to perform a series of simulations, varying the BH spin a, from a/M=0 to a/M=0.99, and changing the NS orbital inclination with respect to the BH spin, in the full range 0-180^o. Furthermore we experiment with different polytropic equations of state for the NS. We find that the formation of a disk or torus of significant mass around the BH (massive enough that its subsequent accretion onto the BH can power a short GRB event) can take place only for highly spinning BHs (a/M > 0.9) and small to moderate orbital inclinations (<40^o). Smaller BH spins will lead to accretion of the entire NS prior to or shortly after the NS disruption. Similar outcomes are seen for higher orbital inclinations. We also extract the gravitational-wave (GW) signal emitted during the final inspiral and merger phases. The waveforms are calculated using a post-Newtonian approximation at PN3.5 order. We show the distinct imprint of the orbital inclination on the waveforms, and the effect of both the BH spin and the NS equation of state on the GW energy spectra from these mergers. Supported by NSF Grant PHY-0855592.

Rasio, F.; Rantsiou, Emmanouela; Laguna, P.

2011-04-01

420

Magnetized Neutron Star Atmospheres: Beyond the Cold Plasma Approximation  

NASA Astrophysics Data System (ADS)

All the neutron star (NS) atmosphere models published so far have been calculated in the "cold plasma approximation," which neglects the relativistic effects in the radiative processes, such as cyclotron emission/absorption at harmonics of cyclotron frequency. Here, we present new NS atmosphere models which include such effects. We calculate a set of models for effective temperatures T eff = 1-3 MK and magnetic fields B ~ 1010-1011 G, typical for the so-called central compact objects (CCOs