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1

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

2

Quake  

Microsoft Academic Search

Quake, developed and published in 1996 by id Software, represented a critical turning point in the world of firstperson shooters,\\u000a leaving behind the likes of Doom (id Software 1993), Marathon (Bungie Software 1994) and Duke Nukem 3D (3D Realms 1996), and paving the way for Half-Life (Valve Software 1998), Unreal (Epic Games & Digital Extremes 1998) and Halo (Bungie Studios

Patrick Curry

3

Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Cottam, J.

2007-01-01

4

Neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars are laboratories for dense matter and gravitational physics. Observations of neutron stars from sources such as radio pulsars, low-mass X-ray binaries, X-ray bursts and thermally-emitting neutron stars are setting bounds to neutron star masses, radii, rotation rates, temperatures and ages. Mass measurements constrain the equation of state at the highest densities and set firm bounds to the highest possible density of cold matter. Radii constrain the equation of state in the vicinity of the nuclear saturation density and yield information about the density dependence of the nuclear symmetry energy. Laboratory measurements and theoretical studies of pure neutron matter are in remarkable agreement with observational bounds.

Lattimer, James M.

2014-05-01

5

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

6

Neutron star cooling  

Microsoft Academic Search

The impact of nuclear physics theories on cooling of isolated neutron stars\\u000ais analyzed. Physical properties of neutron star matter important for cooling\\u000aare reviewed such as composition, the equation of state, superfluidity of\\u000avarious baryon species, neutrino emission mechanisms. Theoretical results are\\u000acompared with observations of thermal radiation from neutron stars. Current\\u000aconstraints on theoretical models of dense matter,

D. G. Yakovlev; O. Y. Gnedin; M. E. Gusakov; A. D. Kaminker; K. P. Levenfish; A. Y. Potekhin

2005-01-01

7

Neutron Star Collision  

NSDL National Science Digital Library

Systems of orbiting neutron stars are born when the cores of two old stars collapse in supernova explosions. Neutron stars have the mass of our Sun but are the size of a city, so dense that boundaries between atoms disappear. Einsteins theory of general relativity predicts that the orbit shrinks from ripples of space-time called gravitational waves. After about 1 billion simulation years, the two neutron stars closely circle each other at 60,000 revolutions per minute. The stars finally merge in a few milliseconds, sending out a burst of gravitational waves.

Bock, Dave; Shalf, John; Swesty, Doug; Calder, Alan; Wang, Ed

1999-01-21

8

Neutron star models  

NASA Technical Reports Server (NTRS)

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

Canuto, V.; Bowers, R. L.

1981-01-01

9

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

10

Converting neutron stars into strange stars  

NASA Technical Reports Server (NTRS)

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

Olinto, A. V.

1991-01-01

11

Superfluidity in Neutron Stars  

Microsoft Academic Search

MATTER in the interior of a typical neutron star is a mixture of three degenerate interacting quantum liquids-neutrons, protons and electrons, the latter two having a density at most a few per cent that of the neutrons1. The mixture, bounded on the inside by a superdense core of hadrons, muons and so on, and most likely by a solid mantle

Gordon Baym; Christopher Pethick; David Pines

1969-01-01

12

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

13

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

14

Planets Around Neutron Stars  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

15

Atmospheres around Neutron Stars  

NASA Astrophysics Data System (ADS)

Interest in the behavior of atmospheres around neutron stars has grown astronomically in the past few years. Some of this interest arrived in the wake of the explosion of Supernova 1987A and its elusive remnant; spawning renewed interest in a method to insure material ``fall-back'' onto the adolescent neutron star in an effort to transform it into a silent black hole. However, the bulk of the activity with atmospheres around neutron stars is concentrated in stellar models with neutron star, rather than white dwarf, cores; otherwise known as Thorne-Zytkow objects. First a mere seed in the imagination of theorists, Thorne-Zytkow objects have grown into an observational reality with an ever-increasing list of formation scenarios and observational prospects. Unfortunately, the analytic work of Chevalier on supernova fall-back implies that, except for a few cases, the stellar simulations of Thorne-Zytkow objects are missing an important aspect of physics: neutrinos. Neutrino cooling removes the pressure support of these atmospheres, allowing accretion beyond the canonical Eddington rate for these objects. We present here the results of detailed hydrodynamical simulations in one and two dimensions with the additional physical effects of neutrinos, advanced equations of state, and relativity over a range of parameters for our atmosphere including entropy and chemical composition as well as a range in the neutron star size. In agreement with Chevalier, we find, under the current list of formation scenarios, that the creature envisioned by Thorne and Zytkow will not survive the enormous appetite of a neutron star. However, neutrino heating (a physical effect not considered in Chevalier's analysis) can play an important role in creating instabilities in some formation schemes, leading to an expulsion of matter rather than rapid accretion. By placing scrutiny upon the formation methods, we can determine the observational prospects for each.

Fryer, Chris L.; Benz, Willy

1994-12-01

16

Neutron Rich Nuclei and Neutron Stars  

NASA Astrophysics Data System (ADS)

The PREX experiment at Jefferson Laboratory measures the neutron radius of 208Pb with parity violating electron scattering in a way that is free from most strong interaction uncertainties. The 208Pb radius has important implications for neutron rich matter and the structure of neutron stars. We present first PREX results, describe future plans, and discuss a follow on measurement of the neutron radius of 48Ca. We review radio and X-ray observations of neutron star masses and radii. These constrain the equation of state (pressure versus density) of neutron rich matter. We present a new energy functional that is simultaneously fit to both nuclear and neutron star properties. In this approach, neutron star masses and radii constrain the energy of neutron matter. This avoids having to rely on model dependent microscopic calculations of neutron matter. The functional is then used to predict the location of the drip lines and the properties of very neutron rich heavy nuclei.

Horowitz, C. J.

2014-09-01

17

Neutrinos from neutron stars  

NASA Technical Reports Server (NTRS)

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

Helfand, D. J.

1979-01-01

18

The Neutron Star Census  

NASA Astrophysics Data System (ADS)

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 velocity 0<=<=550 km s-1. The spin-down, induced by dipole losses and by the interaction with the ambient medium, is tracked together with the dynamical evolution in the Galactic potential, allowing for the determination of the fraction of stars which are, at present, in each of the four possible stages: ejector, propeller, accretor, and georotator. Taking from the ROSAT All Sky Survey an upper limit of ~10 accreting neutron stars within ~140 pc from the Sun, we infer a lower bound for the mean kick velocity, >~200-300 km s-1, corresponding to a velocity dispersion ?V>~125-190 km s-1. The same conclusion is reached for both a constant magnetic field (B~1012 G) and a magnetic field decaying exponentially with a timescale ~109 yr. Such high velocities are consistent with those derived from radio pulsar observations. Present results, moreover, constrain the fraction of low-velocity stars, which could have escaped pulsar statistics, to less than 1%.

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

2000-02-01

19

Superfluidity in Neutron Star Matter  

Microsoft Academic Search

The research on the superfluidity of neutron matter can be traced back to Migdal’s observation that neutron stars are good\\u000a candidates for being macroscopic superfluid systems [1]. And, in fact, during more than two decades of neutron-star physics the presence of neutron and proton superfluid phases\\u000a has been invoked to explain the dynamical and thermal evolution of a neutron star.

Umberto Lombardo; Hans-Josef Schulze

2001-01-01

20

Neutron Star Mysteries  

NASA Astrophysics Data System (ADS)

Neutron stars provide a unique laboratory in which to explore the nuclear equation of state at high densities. Nevertheless, their interior structure and equation of state have remained a mystery. Recently, a number of advances have been made toward unraveling this mystery. The first direct optical images of a nearby neutron star have been obtained from HST. High quality data for X-ray emission from low-mass X-ray binaries, including observations of nearly coherent oscillations (NCO's) and quasi-periodic oscillations (QPOs) now exist. The existence of a possible absorption feature as well as pulsar light curves and glitches, and studies of soft-gamma repeaters, have all led to significant new constraints on the mass-radius relation and maximum mass of neutron stars. We also discuss how models of supernova explosion dynamics and the associated r-process nucleosynthesis also constrain the nuclear equation of state, along with heavy-ion and monopole resonance data. Recent work on the search for the Friedman-Chandrasekhar-Schutz instability and the effects of internal magnetic fields are also discussed. The overall constraints on the neutron star equation of state are summarized.

Mathews, G. J.; Fragile, P. C.; Suh, I.; Wilson, J. R.

2003-04-01

21

Seattle Quake  

NSDL National Science Digital Library

By watching this National Geographic video, you will learn about the seismic activity of Seattle, Washington. Seattle sits on the type of ground that would amplify the effects of an earthquake. Watch how scientists are preparing for the inevitable next quake.

2010-01-01

22

Got Quakes?  

NSDL National Science Digital Library

This resource contains instructions for building a seismometer to record movements of the Earth's crust using a cereal box, string, a paper cup, strips of paper, and weights, such as marbles or washers. The resource is part of the teacher's guide accompanying the video, NASA SCI Files: The Case of the Shaky Quake. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

23

Neutron Star Cooling  

Microsoft Academic Search

Observation of cooling neutron stars can potentially provide information\\u000aabout the states of matter at supernuclear densities. We review physical\\u000aproperties important for cooling such as neutrino emission processes and\\u000asuperfluidity in the stellar interior, surface envelopes of light elements due\\u000ato accretion of matter and strong surface magnetic fields. The neutrino\\u000aprocesses include the modified Urca process, and the

D. G. Yakovlev; O. Y. Gnedin

2004-01-01

24

Neutron Stars as Physics Laboratories  

Microsoft Academic Search

X-ray timing and spectrophotometry of accretion-powered neutron stars have been used to determine or constrain many of the intrinsic properties of these stars, including their masses, radii, magnetic fields, spin frequencies, and internal structure. These measurements have important implications for the evolution of ordinary and neutron stars in binary systems, the supernova process in massive stars, accretion-induced collapse of white

F. K. Lamb

1994-01-01

25

Electrodynamics of neutron stars  

NASA Astrophysics Data System (ADS)

Although the standard model for radio pulsars is a rotating magnetized neutron star and the vast majority (if not all) of pulsars are thought to have appreciable inclination angles between the spin and magnetization axes, most theoretical papers use simplified field models (e.g., aligned spin axis and magnetic dipole axis). Deutsch long ago gave exact (in vacuo) closed expressions for these inclined fields (modulo some typos and oversights), but these expressions were rather clumsy and required extensive hand processing to convert into ordinary functions of radius and angle for the electromagnetic fields. Moreover, these expressions were effectively written down by inspection (no details of the derivations given), which leaves the reader with little physical understanding of where the various electric and magnetic field components come from, particularly near the neutron star surface where many models assume the radio emission is generated. Finally, rather little analysis of what these fields implied was given beyond speculation that they could accelerate cosmic rays. As pulsar models become more sophisticated, it seems important that all researchers use a consistent set of underlying fields, which we hope to present here, as well as understand why these fields are present. It is also interesting to know what happens to charged particles from the star that move in these fields. Close to the star, ambient particles tend to simply /ExB drift around the star with the same rotational velocity as the star itself. But far from the star, charged particles are accelerated away in the wave zone, as was first pointed out by Ostriker and Gunn. We expand their calculations using more general fields and elucidate the particle's dynamics accordingly. Very efficient acceleration is observed even for particles starting at 103 light-cylinder distances. We also stress the effects of a non-zero radial magnetic field. Electrons are accelerated to much higher energies than, say, protons (not to the same energy as when the two cross a fixed potential drop). We pay particular attention to particles accelerated along the spin axis (particles that might be involved in jet formation). An important limitation to the present work is the neglect of collective radiation reaction. Single particle radiation reaction (e.g., Compton scattering of the wave flux) is not an accurate estimate of the forces on a plasma. We are working on remedying this limitation.

Michel, F. C.; Li, H.

1999-09-01

26

Axion emission from neutron stars  

NASA Technical Reports Server (NTRS)

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

Iwamoto, N.

1984-01-01

27

Nonradial oscillations of neutron stars  

Microsoft Academic Search

Linear, adiabatic, Newtonian, nonradial pulsation analyses have been performed for finite-temperature neutron star models with a fluid core, solid crust, and thin surface fluid ocean, including the effects of the neutron star crust. The pulsation equations are considered, including the spheroidal and toroidal modes. A local analysis is performed to provide information about the pulsation modes in the short-wavelength limit.

P. N. Mcdermott; H. M. Van Horn; C. J. Hansen

1988-01-01

28

Theory of neutron star magnetospheres  

Microsoft Academic Search

The theory of neutron star magnetospheres is presented with reference to the most important observational data on neutron stars available to date. In particular, attention is given to the nature of pulsars and pulsar properties and statistics; phenomenological models; the aligned rotator and oblique rotator models; the disk models; alternative models; and radio emission models. The discussion also covers winds

F. C. Michel

1991-01-01

29

The Physics of Neutron Stars  

Microsoft Academic Search

Neutron stars are some of the densest manifestations of massive objects in the universe. They are ideal astrophysical laboratories for testing theories of dense matter physics and provide connections among nuclear physics, particle physics, and astrophysics. Neutron stars may exhibit conditions and phenomena not observed elsewhere, such as hyperon-dominated matter, deconfined quark matter, superfluidity and superconductivity with critical temperatures near

J. M. Lattimer; M. Prakash

2004-01-01

30

QPO Constraints on Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Miller, M. Coleman

2005-01-01

31

Grand unification of neutron stars.  

PubMed

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

Kaspi, Victoria M

2010-04-20

32

The Diversity of Neutron Stars  

NASA Astrophysics Data System (ADS)

Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the >1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby, isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population---distances, ages, and magnetic fields---the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 1e6 year-old cooling neutron stars with magnetic fields above 1e13 Gauss. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication of central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

Kaplan, David L.

2004-12-01

33

Neutron Star Crustal Mass Fractions  

SciTech Connect

We are investigating mass fractions on the crust of a neutron star which would remain after one year of cooling. We use cooling curves corresponding with various densities, or depths, of the neutron star just after its formation. We assume the modified Urca process dominates the energy budget of the outer layers of the star in order to calculate the temperature of the neutron star as a function of time. Using a nuclear reaction network up to technetium, we calculate how the distribution of nuclei quenches at various depths of the neutron star crust. The initial results indicate that {sup 28}Si is the lightest isotope to be optically thick on the surface after one year of cooling.

Hoffman, Kelsey L.; Heyl, Jeremy S. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia V6T 1Z1 (Canada)

2008-02-27

34

Astrometric Observations of Neutron Stars  

NASA Astrophysics Data System (ADS)

Precision astrometry on neutron stars can yield model-independent distances and velocities to neutron stars. I will review how such measurements are being exploited, for example, to locate neutron star birth sites, establish reference frame ties, model the Galactic electron density distribution, and constrain the astrophysics of supernova explosions. In the short term, systematic surveys and high sensitivity on very long baselines will produce ongoing science dividends from precision astrometry. In the longer term, new technology such as focal plane arrays, new telescopes such as the Square Kilometre Array, and synergy with new instruments such as Gaia, LSST, and GLAST, all hold great promise in an upcoming era of microarcsecond astrometry

Chatterjee, Shami

2009-07-01

35

Children's Literature on Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Struck, James

36

Unified EOS for neutron stars  

NASA Astrophysics Data System (ADS)

The equation of state (EOS) of dense matter is a crucial input for the neutron-star structure calculations. This Fortran code can obtain a "unified EOS" in the many-body calculations based on a single effective nuclear Hamiltonian, and is valid in all regions of the neutron star interior. For unified EOSs, the transitions between the outer crust and the inner crust and between the inner crust and the core are obtained as a result of many-body calculations.

Chamel, Nicolas; Potekhin, Alexander

2014-03-01

37

Limits to Neutron Star Spin  

NASA Astrophysics Data System (ADS)

Over the past decade our understanding of accreting neutron stars has been revolutionized. Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast, coherent X-ray intensity oscillations (hereafter, ``burst oscillations'') during thermonuclear X-ray bursts from 13 low mass X-ray binaries (LMXBs). Although many of their detailed properties remain to be fully understood, it is now beyond doubt that these oscillations result from spin modulation of the thermonuclear burst flux from the neutron star surface. In addition, RXTE observations led to the discovery of the first accreting millisecond pulsars, the sample of which now includes six systems, several of which are in extremely compact binary systems with essentially massive planet companions. These millisecond timing phenomena are providing powerful new probes of the formation, evolution and structure of neutron stars. I will describe recent efforts to constrain neutron star structure using detailed modelling of their properties. I will also discuss what the observed distribution of neutron star spin frequencies is telling us about the torques which may act to limit the ultimate spin up of accreting neutron stars.

Strohmayer, Tod

2005-04-01

38

The birth of neutron stars  

Microsoft Academic Search

Results from the first detailed numerical simulations of the Kelvin-Helmholtz phase of the birth of a neutron star are presented. The transformation of a hot, bloated electron-rich residue into a cold, compact, neutronized object is studied. Its behavior during the first 20 sec of its life is investigated. The physics relevant to the problem and its exploration are discussed, and

A. Burrows; J. M. Lattimer

1986-01-01

39

Neutron Stars in Supernova Remnants  

Microsoft Academic Search

I briefly summarize some facts and ideas concerning the presence of neutron\\u000astars in Supernova remnants. While sources similar to the Crab Nebula require\\u000athe presence of a central energetic object, shell-type remnants such as Cas A\\u000aare compatible with the presence of neutron stars releasing a weak relativistic\\u000awind.

Franco Pacini

1999-01-01

40

Neutron star moments of inertia  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

41

The nuclear physics of neutron stars  

NASA Astrophysics Data System (ADS)

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

Piekarewicz, J.

2014-05-01

42

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

43

Neutron Stars as Physics Laboratories  

NASA Astrophysics Data System (ADS)

X-ray timing and spectrophotometry of accretion-powered neutron stars have been used to determine or constrain many of the intrinsic properties of these stars, including their masses, radii, magnetic fields, spin frequencies, and internal structure. These measurements have important implications for the evolution of ordinary and neutron stars in binary systems, the supernova process in massive stars, accretion-induced collapse of white dwarfs and neutron stars, and the properties of extremely dense matter. High-speed X-ray spectrophotometry has also revealed a variety of phenomena, such as pulse-frequency variations, QPOs, aperiodic X-ray variability, and systematic X-ray brightness and spectral changes that provide valuable information about the structure and dynamics of accretion flows, the interaction of such flows with the magnetic fields and surfaces of neutron stars, and hydrodynamics in the presence of intense radiation and very strong magnetic fields. The X-ray Timing Explorer will have a unique combination of large-area detectors, 2--200 keV energy response, all-sky monitors, microsecond time resolution, sophisticated onboard data processing, high telemetry rates, and unprecedented maneuverability and is expected to produce major advances in these areas of physics and astrophysics. Some of the possible advances will be described.

Lamb, F. K.

1994-12-01

44

Astrometric observations of neutron stars  

NASA Astrophysics Data System (ADS)

Precision astrometry can yield model-independent distances and velocities for neutron stars. Such measurements can be exploited, for example, to locate neutron star birth sites, establish reference frame ties, model the Galactic electron density distribution, and constrain the astrophysics of supernova explosions. As a case study, I discuss recent some parallax and proper motion measurements, and their scientific implications for supernova core collapse and the velocities of ordinary pulsars versus magnetars. I also outline the calibration techniques that are enabling sub-milliarcsecond astrometry of neutron stars with VLBI. In the short term, systematic surveys and high sensitivity on very long baselines will produce ongoing science dividends from precision astrometry at radio wavelengths. In the longer term, new technology such as focal plane arrays, new telescopes such as the Square Kilometre Array, and synergy with new instruments such as Gaia, LSST, and GLAST, all hold great promise in an upcoming era of microarcsecond astrometry.

Chatterjee, S.

2008-07-01

45

Coalescing binary neutron star systems  

NASA Astrophysics Data System (ADS)

We present numerical studies of coalescing neutron star pairs with Newtonian hydrodynamics coupled to the 2.5 Post-Newtonian radiation reaction of Blanchet, Damour, and Schäfer [1]. Our simulations evolve the Euler equations using a modification of the ZEUS 2-D algorithm [2] and use a Fast Fourier Transformation method for solving the Poisson equation for the gravitational and radiation reaction potentials. We find that the radiation reaction produces a significant effect on a neutron star pair when compared to a purely Newtonian simulation. .

Calder, Alan C.; Swesty, F. Douglas; Wang, Edward Y. M.

2001-10-01

46

Nonradial oscillations of neutron stars  

NASA Technical Reports Server (NTRS)

Linear, adiabatic, Newtonian, nonradial pulsation analyses have been performed for finite-temperature neutron star models with a fluid core, solid crust, and thin surface fluid 'ocean', including the effects of the neutron star crust. The pulsation equations are considered, including the spheroidal and toroidal modes. A local analysis is performed to provide information about the pulsation modes in the short-wavelength limit. Numerical calculations are made on the mode spectrum and systematic properties. Damping mechanisms are investigated, including gravitational radiation damping, neutrino emission damping, electromagnetic radiation from an oscillating stellar magnetic field, nonadiabatic effects, and internal friction and viscosity.

Mcdermott, P. N.; Van Horn, H. M.; Hansen, C. J.

1988-01-01

47

Chandra Observations of Neutron Stars: An Overview  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

48

Isolated Neutron Stars: Accretors and Coolers  

Microsoft Academic Search

As many as 109 neutron stars populate the Galaxy, but only ~103 are directly observed as pulsars or as accreting sources in X-ray binaries. In principle, also the accretion of the interstellar medium may make isolated neutron stars shine, and their weak luminosity could be detected in soft X-rays. Recent ROSAT observations have convincingly shown that neutron stars accreting from

Aldo Treves; Roberto Turolla; Silvia Zane; Monica Colpi

2000-01-01

49

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

50

Relativistic binary neutron star coalescence.  

National Technical Information Service (NTIS)

The authors report on the first results from a (3+1) dimensional general relativistic hydrodynamics code to describe the evolution of a neutron-star binary system. The relativistic field equations are exactly solved at each time slice with a constrain tha...

J. R. Wilson G. J. Mathews

1994-01-01

51

Eccentric binary neutron star mergers  

NASA Astrophysics Data System (ADS)

Neutron star binaries offer a rich phenomenology in terms of gravitational waves and merger remnants. However, most general relativistic studies have been performed for nearly circular binaries, with the exception of head-on collisions. We present the first numerical relativity investigation of mergers of eccentric equal-mass neutron star binaries that probes the regime between head-on and circular. In addition to gravitational waves generated by the orbital motion, we find that the signal also contains a strong component due to stellar oscillations (f modes) induced by tidal forces, extending a classical result for Newtonian binaries. The merger can lead to rather massive disks on the order of 10% of the total initial mass.

Gold, Roman; Bernuzzi, Sebastiano; Thierfelder, Marcus; Brügmann, Bernd; Pretorius, Frans

2012-12-01

52

Neutron Stars in Supernova Remnants  

NASA Technical Reports Server (NTRS)

The grant provided funds for a conference entitled 'Neutron Stars in Supernova Remnants' held in Boston on 14-17 August 2001, in part to support invited speakers and students attending the meeting. The conference was completed on the specified dates and was a considerable success, attracting over 100 scientists from around the world. The conference included talks and papers on the most recent work in this field, including results from the Chandra X-ray Observatory, XMM-Newton, the Parkes Multibeam Pulsar Survey, the Very Large Array, and many other facilities. Theoretical work based on the latest results was also highlighted. The Proceedings of the conference have now been published as 'Neutron Stars in Supernova Remnants'. In addition, a large fraction of the papers from the conference have been submitted to astro-ph, and the volume in indexed through the Astronomical Data System.

Slane, Patrick; Kaluzienski, Lou (Technical Monitor)

2002-01-01

53

Neutron Stars in the News  

NSDL National Science Digital Library

In this science literacy extension students read and analyze two different articles about XMM-Newton discoveries involving neutron stars and their magnetic fields. This is Activity 4 of the Supernova Guide developed by the XMM-Newton and GLAST E/PO programs. The guide features extensive background information, assessment rubrics, student worksheets, extension and transfer activities, and detailed information about physical science and mathematics content standards. Note: In 2008, GLAST was renamed Fermi, for the physicist Enrico Fermi.

54

Neutrino emission from neutron stars  

Microsoft Academic Search

We review the main neutrino emission mechanisms in neutron star crusts and cores. Among them are the well-known reactions such as the electron–positron annihilation, plasmon decay, neutrino bremsstrahlung of electrons colliding with atomic nuclei in the crust, as well as the Urca processes and neutrino bremsstrahlung in nucleon–nucleon collisions in the core. We emphasize recent theoretical achievements, for instance, band

D. G. Yakovlev; A. D. Kaminker; O. Y. Gnedin; P. Haensel

2001-01-01

55

Birth accelerations of neutron stars  

NASA Astrophysics Data System (ADS)

We suggest that neutron stars experienced at birth three related physical changes, which may originate in magneto-rotational instabilities: (i) an increase in period from the initial value P 0 to the current value Ps , implying a change of rotational energy ? E rot; (ii) an exponential decay of its magnetic field from the initial value B 0 to the current surface value Bs , implying a change of radiative energy ? E rad; and (iii) an increase of space velocity from the initial value v 0 to the current value v, implying a change of kinetic energy ? E kin. These changes are assumed to be connected by ? E rad + ? E kin = ? E rot. This means that the radiation loss and increase of kinetic energy are both at the expense of a rotational energy loss. It is shown that this energy conversion occurs during times of order of 10-4 s if the neutron stars are born with magnetic fields in the range of 1015-1016 G and initial periods in range 1-20 ms. It is shown that the birth accelerations of neutron stars are of the order of 108g.

Heras, Ricardo

2013-03-01

56

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

57

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

58

Burst Oscillations: Watching Neutron Stars Spin  

NASA Technical Reports Server (NTRS)

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

Strohmayer, Tod

2010-01-01

59

Accreting Neutron Stars as Astrophysical Laboratories  

NASA Technical Reports Server (NTRS)

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

Chakrabarty, Deepto

2004-01-01

60

On the conversion of neutron stars into quark stars  

NASA Astrophysics Data System (ADS)

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

Pagliara, Giuseppe

2014-03-01

61

Planetary Systems Around Neutron Stars  

NASA Technical Reports Server (NTRS)

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

62

Initial Parameters of Neutron Stars  

NASA Astrophysics Data System (ADS)

A subpopulation of neutron stars (NSs), known as central compact objects (CCOs) in supernova remnants, are suspected to be low-field objects basing on P - ? measurements for three of them. The birth rate of low-field NSs is probably comparable with the birth rate of normal radio pulsars. However, among compact objects in High-Mass X-ray Binaries (HMXBs) we do not see robust candidates for low-field NSs. We propose that this contradiction can be solved if magnetic fields of CCOs was buried due to strong fall-back, and then the field emerges on the time scale 104 -105 yrs.

Popov, S. B.; Turolla, R.

2012-12-01

63

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

64

Neutron Star Interior Composition Explorer (NICE)  

NASA Technical Reports Server (NTRS)

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

Gendreau, Keith C.; Arzoumanian, Zaven

2008-01-01

65

Neutron stars in Einstein-aether theory  

Microsoft Academic Search

As current and future experiments probe strong gravitational regimes around neutron stars and black holes, it is desirable to have theoretically sound alternatives to general relativity against which to test observations. Here we study the consequences of one such generalization, Einstein-aether theory, for the properties of nonrotating neutron stars. This theory has a parameter range that satisfies all current weak-field

Christopher Eling; Ted Jacobson; M. Coleman Miller

2007-01-01

66

Nonstandard thermal evolution of neutron stars  

NASA Technical Reports Server (NTRS)

A neutron star may cool much faster than through the 'standard' scenario. Here we calculate thermal evolution of neutron stars through various 'nonstandard' fast cooling scenarios, and the results are compared with the currently up-dated observational data. We discuss the possibility of distinguishing between the standard and various, different nonstandard scenarios, through the current and future X-ray satellite observations.

Umeda, Hideyuki; Tsuruta, Sachiko; Nomoto, Ken'ichi

1994-01-01

67

Incompressibility of nuclear matter and neutron stars  

SciTech Connect

A lower limit on the nuclear-matter incompressibility is determined from the constraint on the maximum calculated neutron-star mass, which cannot be smaller than the observed masses of the majority of neutron stars. The value obtained in this way is 370 MeV, which exceeds substantially the commonly accepted value of 234 MeV.

Birbrair, B. L.; Kryshen, E. L., E-mail: evgeny.kryshen@cern.c [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation)

2010-09-15

68

Rotating Neutron Stars, Pulsars and Supernova Remnants  

Microsoft Academic Search

I SHALL discuss here some problems connected with theories linking the pulsars to the rotation of neutron stars (ref. 1 and a preprint by L. Woltjer). Because neutron stars can be formed during a supernova explosion, their rotation could be coupled with the surrounding gaseous remnant2,3: the following considerations will therefore also refer to the problem of the activity observed

F. Pacini

1968-01-01

69

Thermal and magnetic properties of neutron stars  

SciTech Connect

The interaction of the magnetic field with the heat flux in neutron stars is investigated. It is proposed that the magnetic field develops as a result of thermal processes in the liquid and solid phases of neutron star envelopes. Necessary conditions for the growth to occur are derived and it is shown that surface fields comparable to those observed would result. The magnetization of neutron stars in binary systems (which have magnetic properties differing substantially from those of isolated pulsars) can be explained by thermal processes associated with accretion flows. In order to study magnetic effects on neutron star cooling a number of subsidiary issues are considered. The thermal structure of unmagnetized neutron star envelopes is examined using approximate analytical models. From the results it is possible to justify a number of simplifying assumptions and extend them to the magnetized case. The effect of the field on the magnetic properties of the electron gas in neutron star crusts is considered. It is shown that the gas is unstable to the formation of domains of alternating magnetization. The influence of the field on the electron transport properties of neutron star envelopes is examined in detail. Accurate expressions are derived for all components of the relevant transport tensors, taking into account quantum mechanical and relativistic effects. Finally, these results are used to study the thermal structure of magnetized neutron star envelopes.

Hernquist, L.E.

1985-01-01

70

Remnant massive neutron stars of binary neutron star mergers: Evolution process and gravitational waveform  

NASA Astrophysics Data System (ADS)

Massive (hypermassive and supramassive) neutron stars are likely to be often formed after the merger of binary neutron stars. We explore the evolution process of the remnant massive neutron stars and gravitational waves emitted by them, based on numerical-relativity simulations for binary neutron star mergers employing a variety of equations of state and choosing a plausible range of the neutron star mass of binaries. We show that the lifetime of remnant hypermassive neutron stars depends strongly on the total binary mass and also on the equations of state. Gravitational waves emitted by the remnant massive neutron stars universally have a quasiperiodic nature of an approximately constant frequency although the frequency varies with time. We also show that the frequency and time-variation feature of gravitational waves depend strongly on the equations of state. We derive a fitting formula for the quasiperiodic gravitational waveforms, which may be used for the data analysis of a gravitational-wave signal.

Hotokezaka, Kenta; Kiuchi, Kenta; Kyutoku, Koutarou; Muranushi, Takayuki; Sekiguchi, Yu-ichiro; Shibata, Masaru; Taniguchi, Keisuke

2013-08-01

71

Neutron stars as dark matter probes  

SciTech Connect

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

Lavallaz, Arnaud de; Fairbairn, Malcolm [Physics, King's College London, Strand, London WC2R 2LS (United Kingdom)

2010-06-15

72

Neutron stars in the derivative coupling model  

SciTech Connect

Properties of neutron stars derived from the hybrid derivative coupling model of nuclear field theory are studied. Generalized beta equilibrium with all baryon types to convergence is allowed. Hyperon couplings compatible with the inferred binding energy of the lambda hyperon in saturated nuclear matter predict a large hyperon population, with neutrons having a bare majority population in a 1.5{ital M}{sub {circle dot}} neutron star. Among the properties studied are the limits on rotation imposed by gravitation-radiation-reaction instabilities as moderated by viscosity. These instabilities place a lower limit on rotational periods of neutron and hybrid stars of about 1 ms.

Glendenning, N.K.; Weber, F. (Nuclear Science Division, Lawrence Berkeley Laboratory, University of California, One Cyclotron Road, Berkeley, California 94720 (United States)); Moszkowski, S.A. (University of California at Los Angeles, Department of Physics, Los Angeles , California 90024 (United States))

1992-02-01

73

Can neutron stars constrain dark matter?  

SciTech Connect

Because of their strong gravitational field, neutron stars capture weakly interacting dark matter particles (WIMPs) more efficiently compared to other stars, including the white dwarfs. Once captured, the WIMPs sink to the neutron star center and annihilate, heating the star. We find that this heat could lead to detectable effects on the surface temperature of old neutron stars, especially those in dark-matter-rich regions such as the Galactic center or cores of globular clusters. The capture and annihilation is fully efficient even for WIMP-to-nucleon cross sections (elastic or inelastic) as low as {approx}10{sup -45} cm{sup 2}, and for the annihilation cross sections as small as {approx}10{sup -57} cm{sup 2}. Thus, detection of a sufficiently cold neutron star in a dark-matter-rich environment would exclude a wide range of dark matter candidates, including those with extremely small cross sections.

Kouvaris, Chris; Tinyakov, Peter [Service de Physique Theorique, Universite Libre de Bruxelles, 1050 Brussels (Belgium)

2010-09-15

74

Magnetosphere of Oscillating Neutron Star. Nonvacuum Treatment  

Microsoft Academic Search

We generalize a formula for the Goldreich-Julian charge density (\\\\rho),\\u000aoriginally derived for rotating neutron star, for arbitrary oscillations of a\\u000aneutron star with arbitrary magnetic field configuration under assumption of\\u000alow current density in the inner parts of the magnetosphere. As an application\\u000awe consider toroidal oscillation of a neutron star with dipole magnetic field\\u000aand calculate energy losses.

A. N. Timokhin; G. S. Bisnovatyi-Kogan; H. C. Spruit

1999-01-01

75

On the maximum mass of neutron stars  

Microsoft Academic Search

Upper limits to the maximum mass of neutron stars with locally isotropic pressure are derived within the framework of general relativity and discussed. The equations of stellar structure for stars with locally anisotropic pressure are derived from the field equations of general relativity, and upper limits to the maximum mass for such stars as derived and discussed. The equations of

D. R. Mikkelsen

1975-01-01

76

Isolated Neutron Stars: Accretors and Coolers  

NASA Astrophysics Data System (ADS)

As many as 109 neutron stars populate the Galaxy, but only ~103 are directly observed as pulsars or as accreting sources in X-ray binaries. In principle, also the accretion of the interstellar medium may make isolated neutron stars shine, and their weak luminosity could be detected in soft X-rays. Recent ROSAT observations have convincingly shown that neutron stars accreting from the interstellar medium are extremely rare, if observed at all, in contrast with earlier theoretical predictions. Until now two possible explanations for their elusiveness have been proposed: their velocity distribution may peak at ~200-400 km s-1, as inferred from pulsar statistics, and this would severely choke accretion; the magnetic field may decay on timescales ~108-109 yr, preventing a large fraction of neutron stars from entering the accretor stage. The search for accreting neutron stars has produced up to now a handful of promising candidates. While little doubt is left that these objects are indeed isolated neutron stars, the nature of their emission is still controversial. In particular, accreting objects can be confused with much younger, cooling neutron stars. However, a combination of observations and theoretical modeling may help in discriminating between the two classes.

Treves, Aldo; Turolla, Roberto; Zane, Silvia; Colpi, Monica

2000-03-01

77

Merging neutron stars: asymmetric systems  

NASA Astrophysics Data System (ADS)

We present the results of 3D, Newtonian hydrodynamic calculations of the last stages of the inspiral and the final coalescence of neutron star binary systems. Our focus is on slightly asymmetric systems, where the asymmetry stems from either different masses (1.3 and 1.4 M?) or spins of both components. Almost immediately after contact a fast rotating, very massive central object forms. All calculations exhibit baryonic masses above 2.3 M?, thus based on our calculations it is not possible to decide on the fate of the central core of the merged configuration. It might collapse immediately to a black hole, but also the creation of a supermassive neutron star with ~ 2.8 M? cannot firmly be excluded. Depending on the asymmetry of the system the central object receives a kick of several hundred kilometers per second. Different spins of both components do not jeopardize the formation of (to within numerical resolution) baryon free funnels above the poles of the central objects. In the case of different masses the less massive components get disrupted and engulf the more massive companions that stay rather unaffected by the collision. The amount of ejected material is in a similar range as for symmetric systems and could contribute substantially to the enrichment of the Galaxy with heavy r-process elements. Test calculations indicate that the amount of ejected material is basically determined by the high density behaviour of the nuclear equation of state. Test calculations for the hybrid artificial viscosity scheme that is used for this work are given in the appendix.

Rosswog, S.; Davies, M. B.; Thielemann, F.-K.; Piran, T.

2000-08-01

78

Gravitational waves from low mass neutron stars  

SciTech Connect

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

Horowitz, C. J. [Department of Physics and Nuclear Theory Center, Indiana University, Bloomington, Indiana 47405 (United States)

2010-05-15

79

Neutron Stars and Thermonuclear X-ray Bursts  

NASA Technical Reports Server (NTRS)

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

Bhattacharyya, Supid

2007-01-01

80

Experimental approach to neutron stars  

NASA Astrophysics Data System (ADS)

The equation of state (EOS) of nuclear matter is of fundamental importance in many areas of nuclear physics and astrophysics In the laboratory, there are different means to study the nuclearmatter equation of state and its density dependence in particular: nuclear masses, neutron skins, pygmy resonance, and nuclear structure at the drip line give access to nuclear matter properties at densities lower than and at saturation density ?0. Heavy ion reactions at energies above 0.1 AGeV are the only means to study nuclear matter at densities larger than normal nuclear matter density ?0. In the beamenergy range of 0.1 to 2A GeV nuclear matter is compressed upto three times ?0. Access to nuclear matter properties is achieved by simulating nuclear collisions by means of microscopic transport codes, or statistical or hydrodynamicalmodels. Characteristics of heavy-ion collisions are discussed, and experimental observables which allow to constrain nuclear matter properties by comparing experimental results with those of transport codes are presented. Special emphasis will be given to the density dependence of the symmetry energy which is the most relevant connection between neutron stars and heavy ion collisions.

Leifels, Yvonne

2014-05-01

81

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

82

Position annihilation radiation from neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

83

DYNAMICAL CAPTURE BINARY NEUTRON STAR MERGERS  

SciTech Connect

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

East, William E.; Pretorius, Frans [Department of Physics, Princeton University, Princeton, NJ 08544 (United States)

2012-11-20

84

LARGE-MASS NEUTRON STARS WITH HYPERONIZATION  

SciTech Connect

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

Jiang Weizhou [Department of Physics, Southeast University, Nanjing 211189 (China); Li Baoan [Department of Physics and Astronomy, Texas A and M University-Commerce, Commerce, TX 75429 (United States); Chen Liewen [Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (China)

2012-09-01

85

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

86

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 star binaries, we investigate the late stages of evolution of helium stars with masses of 2.8-6.4Msolar in binary systems with a 1.4-Msolar neutron star companion. We found that mass transfer from 2.8- to 3.3-Msolar helium stars (originating from main-sequence stars with masses of 10-12Msolar that underwent case B evolution, or

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

2003-01-01

87

Plasma physics of accreting neutron stars  

NASA Technical Reports Server (NTRS)

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

Ghosh, Pranab; Lamb, Frederick K.

1991-01-01

88

The Neutron Star Interior Composition Explorer  

NASA Technical Reports Server (NTRS)

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

Gendreau, Keith C.

2008-01-01

89

Neutron stars: A taste of pasta?  

NASA Astrophysics Data System (ADS)

Comparing quantitative calculations of the magnetic field decay of neutron stars and their corresponding spin evolution with observations suggests a high degree of disorder in the inner crust, which might provide evidence for nuclear 'pasta'.

Newton, William G.

2013-07-01

90

Electromagnetic damping of neutron star oscillations  

NASA Technical Reports Server (NTRS)

A simple model of magnetic field perturbations driven by neutron star oscillations is used to estimate the electromagnetic power radiated by g-modes and torsional oscillations. The calculation assumes that the neutron star has a frozen-in magnetic field which is perturbed by the oscillatory motions of the surface. The disturbances propagate into the vacuum as outgoing electromagnetic waves. The relative effectiveness of Joule heating of the neutron star crust by pulsation-induced electric currents is estimated. It is concluded that electromagnetic damping is the dominant energy dissipation mechanism for quadrupole g-mode oscillations of neutron stars. For dipole spheroidal modes, both electromagnetic radiation and Joule heating are important, and there is no gravitational radiation emitted by these modes.

Mcdermott, P. N.; Savedoff, M. P.; Van Horn, H. M.; Zweibel, E. G.; Hansen, C. J.

1984-01-01

91

Theoretical Studies of Accreting Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Taam, Ronald E.

2003-01-01

92

Shaky Quake Cake  

NSDL National Science Digital Library

In this demonstration, sheet cakes are used to show how tectonic forces create convergent, divergent and transform plate boundaries. The resource is part of the teacher's guide accompanying the video, NASA SCI Files: The Case of the Shaky Quake. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

93

Chandra Observations of Isolated Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Weisskopf, Martin

2006-01-01

94

Neutron star constraints on the H dibaryon  

SciTech Connect

We study the influence of a possible H dibaryon condensate on the equation of state and the overall properties of neutron stars whose population otherwise contains nucleons and hyperons. In particular, we are interested in the question of whether neutron stars and their masses can be used to say anything about the existence and properties of the H dibaryon. We find that the equation of state is softened by the appearance of a dibaryon condensate and can result in a mass plateau for neutron stars. If the limiting neutron star mass is about that of the Hulse-Taylor pulsar a condensate of H dibaryons of vacuum mass {approximately}2.2GeV and a moderately attractive potential in the medium could not be ruled out. On the other hand, if the medium potential were even moderately repulsive, the H would not likely exist in neutron stars. If neutron stars of mass {approximately}1.6M{sub {circle_dot}} were known to exist, attractive medium effects for the H could be ruled out. {copyright} {ital 1998} {ital The American Physical Society}

Glendenning, N.K.; Schaffner-Bielich, J. [Nuclear Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)] [Nuclear Science Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)

1998-08-01

95

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

96

Neutron Stars and the Discovery of Pulsars.  

ERIC Educational Resources Information Center

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

Greenstein, George

1985-01-01

97

Disk accretion by magnetic neutron stars  

Microsoft Academic Search

A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed description of matter flow in the transition region between the disk and the magnetosphere. It is shown that the disk plasma cannot be completely screened from the stellar magnetic field and that the resulting magnetic coupling between the star and the disk exerts

P. Ghosh; F. K. Lamb

1978-01-01

98

Effects of vacuum structure on neutron stars  

NASA Astrophysics Data System (ADS)

We study the equation of state for neutron matter using the Walecka model including quantum corrections for baryons and sigma mesons through a realignment of the vacuum. We next use this equation of state to calculate the radius, mass, and other properties of rotating neutron stars.

Panda, P. K.; Sahu, R.; Mishra, S.

2000-11-01

99

Energy Emission from a Neutron Star  

Microsoft Academic Search

ALTHOUGH there are still many problems concerning the supernovae, there is little doubt that a very dense stellar core has to be left behind after the explosion (at least in some cases). During the contraction of this core, inverse beta reactions take place and transform most of the nuclei and electrons into neutrons. If the mass of the neutron star

F. Pacini

1967-01-01

100

Magnetic field decay in isolated neutron stars  

Microsoft Academic Search

Three mechanisms that promote the loss of magnetic flux from an isolated neutron star - Ohmic decay, ambipolar diffusion, and Hall drift - are investigated. Equations of motions are solved for charged particles in the presence of a magnetic field and a fixed background of neutrons, while allowing for the creation and destruction of particles by weak interactions. Although these

Peter Goldreich; Andreas Reisenegger

1992-01-01

101

Forecasting Neutron Star Temperatures: Predictability and Variability  

NASA Astrophysics Data System (ADS)

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

Page, Dany; Reddy, Sanjay

2013-12-01

102

Forecasting neutron star temperatures: predictability and variability.  

PubMed

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

Page, Dany; Reddy, Sanjay

2013-12-13

103

The Neutron Star Mass Distribution  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

104

Evolutions of magnetized and rotating neutron stars  

SciTech Connect

We study the evolution of magnetized and rigidly rotating neutron stars within a fully general relativistic implementation of ideal magnetohydrodynamics with no assumed symmetries in three spatial dimensions. The stars are modeled as rotating, magnetized polytropic stars, and we examine diverse scenarios to study their dynamics and stability properties. In particular, we concentrate on the stability of the stars and possible critical behavior. In addition to their intrinsic physical significance, we use these evolutions as further tests of our implementation, which incorporates new developments to handle magnetized systems.

Liebling, Steven L. [Department of Physics, Long Island University-C.W. Post Campus, Brookville, New York 11548 (United States); Lehner, Luis [Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2L 2Y5 (Canada); Department of Physics, University of Guelph, Guelph, Ontario, N1G 2W1 (Canada); Canadian Institute for Advanced Research, Cosmology and Gravity Program, Toronto, Ontario (Canada); Neilsen, David [Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602 (United States); Palenzuela, Carlos [Canadian Institute for Theoretical Astrophysics (CITA), Toronto, Ontario, M5S 3H8 (Canada); Max Planck Institut for Gravitational Physics, Albert Einstein Institute, Am Muhlenberg 1, D-14476 Golm (Germany)

2010-06-15

105

Strong Quake Strikes Japan  

NASA Astrophysics Data System (ADS)

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

Showstack, Randy

2011-03-01

106

Neutron stars and the cosmological constant problem  

NASA Astrophysics Data System (ADS)

The gravitational aether theory is a modification of general relativity that decouples vacuum energy from gravity, and thus can potentially address the cosmological constant problem. The classical theory is distinguishable from general relativity only in the presence of relativistic pressure (or vorticity). Since the interior of neutron stars has high pressure and as their mass and radius can be measured observationally, they are the perfect laboratory for testing the validity of the aether theory. In this paper, we solve the equations of stellar structure for the gravitational aether theory and find the predicted mass-radius relation of nonrotating neutron stars using two different realistic proposals for the equation of state of nuclear matter. We find that the maximum neutron-star mass predicted by the aether theory is 12%-16% less than the maximum mass predicted by general relativity assuming these two equations of state. We also show that the effect of aether is similar to modifying the equation of state in general relativity. The effective pressure of the neutron star given by the aether theory at a fiducial density differs from the values given by the two nuclear equations of state to an extent that can be constrained using future gravitational wave observations of neutron stars in compact systems. This is a promising way to test the aether theory if further progress is made in constraining the equation of state of nuclear matter in densities above the nuclear saturation density.

Kamiab, Farbod; Afshordi, Niayesh

2011-09-01

107

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

108

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

109

Ultrahigh energy neutrinos from galactic neutron stars  

NASA Technical Reports Server (NTRS)

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

Helfand, D. J.

1979-01-01

110

A Two Solar Mass Neutron Star  

NASA Astrophysics Data System (ADS)

There are over 200 known radio millisecond pulsars in the Galaxy and its globular cluster system. These incredibly stably and rapidly rotating neutron stars can be "timed" over timescales of weeks to decades to provide extremely precise measurements of a variety of interesting physical parameters and/or effects. Improvements in timing precision and a doubling of the number of known millisecond pulsars over the past 5-6 years are allowing us to make significantly better mass measurements of many neutron stars. In this talk I report on recent progress in the field, including a precise measurement of a two Solar mass neutron star, PSR J1614-2230, via relativistic Shapiro delay. This single measurement has many implications for the nature of matter at supra-nuclear densities and on a variety of topics in astrophysics.

Ransom, Scott

2011-04-01

111

Asteroseismology of neutron stars and black holes  

NASA Astrophysics Data System (ADS)

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

Schutz, B. F.

2008-10-01

112

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

113

Constraining Neutron Star Matter with Quantum Chromodynamics  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

114

Symmetry energy: nuclear masses and neutron stars  

NASA Astrophysics Data System (ADS)

We describe the main features of our most recent Hartree-Fock-Bogoliubov nuclear mass models, based on 16-parameter generalized Skyrme forces. They have been fitted to the data of the 2012 Atomic Mass Evaluation, and favour a value of 30MeV for the symmetry coefficient J , the corresponding root-mean square deviation being 0.549MeV. We find that this conclusion is compatible with measurements of neutron-skin thickness. By constraining the underlying interactions to fit various equations of state of neutron matter calculated ab initio our models are well adapted to a realistic and unified treatment of all regions of neutron stars. We use our models to calculate the composition, the equation of state, the mass-radius relation and the maximum mass. Comparison with observations of neutron stars again favours a value of J = 30 MeV.

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

2014-02-01

115

An instability in neutron stars at birth  

NASA Technical Reports Server (NTRS)

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

Burrows, Adam; Fryxell, Bruce A.

1992-01-01

116

Positron annihilation radiation from neutron stars  

NASA Technical Reports Server (NTRS)

Balloon observations of a low energy flux line at 2 x 0.001 photons cm/2 s/1 from the galactic center region around 470 keV are interpreted as the positron annihilation radiation that occurs on the surface of old neutron stars and is redshifted by their gravitational fields. An astrophysical model is formulated to explain the observed flux that provides for about 0.2 neutron stars per 3 x 10 to the 49th power cubic meters assuming that the disk thickness is about 1.5 x 10 to the 19th power meters.

Borner, G. A.

1973-01-01

117

Chandra Observations of Neutron Stars: An Overview  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

118

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

119

Neutron source, neutron density and the origin of barium stars  

Microsoft Academic Search

The authors present new high resolution spectra of the MgH profiles in nine barium stars, and determine, by spectral synthesis techniques, the magnesium isotopic ratios in each star. When compared with recent AGB nucleosynthesis calculations, they can emphatically rule out the operation of the 22Ne(alpha, n)25Mg reaction as the neutron source responsible for the s-process enhancements observed in these barium

Robert A. Malaney; David L. Lambert

1988-01-01

120

Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

121

Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

122

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

123

Generalized equation of state for cold superfluid neutron stars  

SciTech Connect

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.; Goriely, S. [Institut d'Astronomie et d'Astrophysique, Universite Libre de Bruxelles, B-1050 Brussels (Belgium); Pearson, J. M. [Departement de Physique, Universite de Montreal, Montreal (Quebec), H3C 3J7 (Canada)

2011-09-21

124

Neutron Star Structure and the Equation of State  

Microsoft Academic Search

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

J. M. Lattimer; M. Prakash

2001-01-01

125

Chandra Observations of Supernova Remnants and Neutron Stars: An Overview  

NASA Technical Reports Server (NTRS)

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

Weisskopf, Martin C.

2002-01-01

126

Neutron star observations: Prognosis for equation of state constraints  

Microsoft Academic Search

We investigate how current and proposed observations of neutron stars can lead to an understanding of the state of their interiors and the key unknowns: the typical neutron star radius and the neutron star maximum mass. We consider observations made not only with photons, ranging from radio waves to X-rays, but also those involving neutrinos and gravity waves. We detail

James M. Lattimer; Madappa Prakash

2007-01-01

127

Neutron Stars and Pulsar: Three Years of Chandra Operations  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

128

Neutron stars: A cosmic hadron physics laboratory  

NASA Technical Reports Server (NTRS)

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

Pines, David

1989-01-01

129

The Neutron Star Interior Composition Explorer  

NASA Astrophysics Data System (ADS)

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

Angelini, Lorella; NICE Team

2008-03-01

130

Neutron stars and the cosmological constant problem  

Microsoft Academic Search

The gravitational aether theory is a modification of general relativity that decouples vacuum energy from gravity, and thus can potentially address the cosmological constant problem. The classical theory is distinguishable from general relativity only in the presence of relativistic pressure (or vorticity). Since the interior of neutron stars has high pressure and as their mass and radius can be measured

Farbod Kamiab; Niayesh Afshordi

2011-01-01

131

Nuclear Physics Problems for Accreting Neutron Stars.  

National Technical Information Service (NTIS)

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

R. K. Wallace S. E. Woosley

1983-01-01

132

Observational constraints on hyperons in neutron stars  

SciTech Connect

The possibility that neutron stars may contain substantial hyperon populations has important implications for neutron-star cooling and, through bulk viscosity, the viability of the r-modes of accreting neutron stars as sources of persistent gravitational waves. In conjunction with laboratory measurements of hypernuclei, astronomical observations were used by Glendenning and Moszkowski [Phys. Rev. Lett. 67, 2414 (1991)] to constrain the properties of hyperonic equations of state within the framework of relativistic mean-field theory. We revisit the problem, incorporating recent measurements of high neutron-star masses and a gravitational redshift. We find that only the stiffest of the relativistic hyperonic equations of state commonly used in the literature is compatible with the redshift. However, it is possible to construct stiffer equations of state within the same framework which produce the observed redshift while satisfying the experimental constraints on hypernuclei, and we do this. The stiffness parameter that most affects the redshift is not the incompressibility but rather the hyperon coupling. Nonrelativistic potential-based equations of state with hyperons are not constrained by the redshift, primarily due to a smaller stellar radius.

Lackey, Benjamin D.; Nayyar, Mohit; Owen, Benjamin J. [Center for Gravitational Wave Physics, Institute for Gravitational Physics and Geometry, Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802-6300 (United States)

2006-01-15

133

Temperature effects in pulsating superfluid neutron stars  

NASA Astrophysics Data System (ADS)

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

Kantor, Elena M.; Gusakov, Mikhail E.

2011-05-01

134

Physics of Systems Containing Neutron Stars.  

National Technical Information Service (NTIS)

This grant dealt with several topics related to the dynamics of systems containing a compact object. Most of the research dealt with systems containing Neutron Stars (NS's), but a Black Hole (BH) or a White Dwarf (WD) in situations relevant to NS systems ...

M. Ruderman

1996-01-01

135

Physics of Systems Containing Neutron Stars.  

National Technical Information Service (NTIS)

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 Dwa...

J. Shaham

1995-01-01

136

Particle Acceleration in Axisymmetric, Magnetized Neutron Stars.  

National Technical Information Service (NTIS)

The potential drop in the polar cap region of a rotating, magnetized neutron star is found, assuming that the magnetic field is dipolar, with the field aligned (or anti-aligned) with the rotation axis. The curvature of the field lines is of critical impor...

K. B. Baker P. A. Sturrock

1977-01-01

137

Pion(-) Condensation and Neutron Star Cooling.  

National Technical Information Service (NTIS)

The authors, within the context of an independent particle model, that Pion(-) condensation should occur in neutron stars having baryon densities exceeding about 0.4-0.5/fm cubed. This high concentration of pion(-) implies a very fast cooling rate for 'ho...

J. Kogut J. T. Manassah

1972-01-01

138

Neutron Star Mass Measurements. I. Radio Pulsars  

Microsoft Academic Search

There are now about 50 known radio pulsars in binary systems, including at least five in double neutron star binaries. In some cases, the stellar masses can be directly determined from measurements of relativistic orbital effects. In others, only an indirect or statistical estimate of the masses is possible. We review the general problem of mass measurement in radio pulsar

S. E. Thorsett; Deepto Chakrabarty

1999-01-01

139

Physics of strongly magnetized neutron stars  

Microsoft Academic Search

There has recently been growing evidence for the existence of neutron stars possessing magnetic fields with strengths that exceed the quantum critical field strength of 4.4 × 1013 G, at which the cyclotron energy equals the electron rest mass. Such evidence has been provided by new discoveries of radio pulsars having very high spin-down rates and by observations of bursting

Alice K. Harding; Dong Lai

2006-01-01

140

Direct URCA process in neutron stars  

Microsoft Academic Search

We show that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11--15%. The proton concentration, which is determined by the poorly known symmetry energy of matter above nuclear density, exceeds the critical value in many current calculations. If it occurs, the direct URCA process enhances neutrino emission and

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

1991-01-01

141

Magnetic Screening in Accreting Neutron Stars  

Microsoft Academic Search

We investigate whether the magnetic field of an accreting neutron star may be diamagnetically screened by the accreted matter. We assume the freshly accumulated material is unmagnetized and calculate the rate at which the intrinsic stellar magnetic flux is transported into it via Ohmic diffusion from below. For very high accretion rates M (larger than the Eddington rate MEdd), Brown

Andrew Cumming; Ellen G. Zweibel; Lars Bildsten

2001-01-01

142

Nuclear physics problems for accreting neutron stars  

SciTech Connect

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

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

1983-01-01

143

Neutron Star Magnetic Field Evolution, Crust Movement, and Glitches  

Microsoft Academic Search

Spinning superfluid neutrons in the core of a neutron star interact strongly with coexisting superconducting protons. One consequence is that the outward (inward) motion of core superfluid neutron vortices during spin-down (spin-up) of a neutron star may alter the core's magnetic field. Such core field changes are expected to result in movements of the stellar crust and changes in the

Malvin Ruderman; Tianhua Zhu; Kaiyou Chen

1998-01-01

144

Quasiuniversal Properties of Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

Binary neutron star mergers are studied using nonlinear 3+1 numerical relativity simulations and the analytical effective-one-body model. The effective-one-body model predicts quasiuniversal relations between the mass-rescaled gravitational wave frequency and the binding energy at the moment of merger and certain dimensionless binary tidal coupling constants depending on the stars' Love numbers, compactnesses, and the binary mass ratio. These relations are quasiuniversal in the sense that, for a given value of the tidal coupling constant, they depend significantly neither on the equation of state nor on the mass ratio, though they do depend on stars spins. The spin dependence is approximately linear for small spins aligned with the orbital angular momentum. The quasiuniversality is a property of the conservative dynamics; nontrivial relations emerge as the binary interaction becomes tidally dominated. This analytical prediction is qualitatively consistent with new, multiorbit numerical relativity results for the relevant case of equal-mass irrotational binaries. Universal relations are, thus, expected to characterize neutron star mergers dynamics. In the context of gravitational wave astronomy, these universal relations may be used to constrain the neutron star equation of state using waveforms that model the merger accurately.

Bernuzzi, Sebastiano; Nagar, Alessandro; Balmelli, Simone; Dietrich, Tim; Ujevic, Maximiliano

2014-05-01

145

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

146

Fallback Disks, Magnetars and Other Neutron Stars  

NASA Astrophysics Data System (ADS)

The presence of matter with angular momentum, in the form of a fallback disk around a young isolated neutron star will determine its evolution. This leads to an understanding of many properties of different classes of young neutron stars, in particular a natural explanation for the period clustering of AXPs, SGRs and XDINs. The spindown or spinup properties of a neutron star are determined by the dipole component of the magnetic field. The natural possibility that magnetars and other neutron stars may have different strengths of the dipole and higher multipole components of the magnetic field is now actually required by observations on the spindown rates of some magnetars. This talk gives a broad overview and some applications of the fallback disk model to particular neutron stars. Salient points are: (i) A fallback disk has already been observed around the AXP 4U 0142+61 some years ago. (ii) The low observed spindown rate of the SGR 0418+5729 provides direct evidence that the dipole component of the field is in the 1012 G range. All properties of the SGR 0418+5729 at its present age can be explained by spindown under torques from a fallback disk. (iii) The anomalous braking index of PSR J1734-3333 can also be explained by the fallback disk model which gives the luminosity, period, period derivative and the period second derivative at the present age. (iv) These and all applications to a variety of other sources employ the same disk physics and evolution, differing only in the initial conditions of the disk.

Alpar, M. Ali; Çal??kan, ?.; Ertan, Ü.

2013-02-01

147

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

148

Rare Isotopes and Accreting Neutron Stars, X-Ray Bursts, Neutron Star Crust, rp-Process  

SciTech Connect

Rare isotopes from the proton drip line to the neutron drip line are produced on the surface and crust of accreting neutron stars. Understanding their properties is essential to address the open questions raised by a variety of new observations of X-ray binaries, in particular X-ray bursters and transients. This paper provides an introduction to the topic.

Schatz, H. [National Superconductiong Cyclotron Laboratory, Dept. of Physics and Astronomy, Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)

2008-01-24

149

Confirming a substellar companion candidate around a neutron star  

NASA Astrophysics Data System (ADS)

In a search for substellar companions around young neutron stars, we found an indication for a very faint near-infrared source at the position of the isolated neutron star RXJ0806.4-4123. The suspected near-IR source cannot be the neutron star itself because the latter is much too faint to be detected. Recent Herschel 160 microm observations of the field point to an additional dusty belt around the neutron star. The outer location of the dusty belt could be explained by the presence of a substellar companion around the neutron star. We propose deeper near-infrared observations with FLAMINGOS-2 to confirm that the near-infrared source is real. The observation could provide the first direct detection of a substellar companion around a neutron star. However, even a non-detection would be interesting to constrain evolution models of the dusty belt around the neutron star.

Posselt, Bettina; Luhman, Kevin

2014-08-01

150

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

151

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

152

Coalescing Models of Binary Neutron Star Systems  

NASA Astrophysics Data System (ADS)

Coalescing pairs of neutron stars are expected to be among the sources of gravitational waves that will be observed by gravitational wave detectors in the next decade. Accurate theoretical predictions of the gravitational wave signatures of these events will be required to extract the signals from background noise. Post-Newtonian models can be applied to these systems, but full 3-d simulations are required to properly capture tidal effects, particularly in the last several orbits. We present additional results of our numerical studies of coalescing neutron star pairs with Newtonian hydrodynamics coupled to the 2.5 Post-Newtonian radiation reaction of Blanchet, Damour, and Schafer (1990). Our simulations evolve the Euler equations using a modification of the ZEUS 2-d algorithm (Stone and Norman 1992) and use a Fast Fourier Transformation method for solving the Poisson equation for the gravitational field. We find that the radiation reaction produces a dramatic effect on a configuration of neutron stars when compared to a purely Newtonian simulation. Our method of simulation produces results that allow us to examine the structure of the gravitational wave radiation producing regions of the configuration. We find that a majority of the gravitational wave radiation produced during simulations of the coalescence emanates from the tidally distorted regions of the stars rather than the regions of highest density.

Calder, A. C.; Wang, E. Y. M.; Swesty, F. D.

1999-09-01

153

Hiding a neutron star inside a wormhole  

NASA Astrophysics Data System (ADS)

We consider neutron-star-plus-wormhole configurations supported by a massless ghost scalar field. The neutron fluid is modeled by an anisotropic equation of state. When the central energy density of the fluid is of comparable magnitude to the one of the scalar field, configurations with an equator at the center and a double throat arise. These double-throat wormholes can be either partially or completely filled by the neutron fluid. In the latter case, the passage of light—radiated by the neutron matter—through these wormholes is studied. A stability analysis indicates that all considered configurations are unstable with respect to linear perturbations, independent of whether the fluid is isotropic or anisotropic.

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

2014-04-01

154

Relativistic tidal properties of neutron stars  

Microsoft Academic Search

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 Gmul=[length]2l+1 measuring the lth-order mass multipolar moment GMa1...al induced in a star by an external lth-order gravito-electric tidal field Ga1...al; (ii) a gravito-magnetic-type coefficient Gsigmal=[length]2l+1 measuring the lth spin

Thibault Damour; Alessandro Nagar

2009-01-01

155

Relativistic tidal properties of neutron stars  

Microsoft Academic Search

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{sub l}=[length]{sup 2l+1} measuring the lth-order mass multipolar moment GM{sub a}{sub ...a{sub I}} induced in a star by an external lth-order gravito-electric tidal field G{sub a}{sub ...a{sub I}}; (ii)

Alessandro Nagar; Thibault Damour

2009-01-01

156

Ferromagnetism in neutron matter and its implication for the neutron star equation of state  

NASA Astrophysics Data System (ADS)

We investigate the possible contribution of the ferromagnetic phase of neutron matter in the neutron star interior to the star's magnetic field. We introduce a relativistic, self-consistent calculation of the ferromagnetic phase in neutron matter within the context of the relativistic mean-field approximation. The presence of the ferromagnetic phase stiffens the star's equation of state which implies a larger neutron star radius compared to the non-ferromagnetic case.

Diener, J. P. W.; Scholtz, F. G.

2011-09-01

157

Ferromagnetism in neutron matter and its implication for the neutron star equation of state  

SciTech Connect

We investigate the possible contribution of the ferromagnetic phase of neutron matter in the neutron star interior to the star's magnetic field. We introduce a relativistic, self-consistent calculation of the ferromagnetic phase in neutron matter within the context of the relativistic mean-field approximation. The presence of the ferromagnetic phase stiffens the star's equation of state which implies a larger neutron star radius compared to the non-ferromagnetic case.

Diener, J. P. W. [Institute of Theoretical Physics, Stellenbosch University, P.O. Box X1, Matieland, 7602 (South Africa); Scholtz, F. G. [Institute of Theoretical Physics, Stellenbosch University, P.O. Box X1, Matieland, 7602 (South Africa); National Institute for Theoretical Physics, P.O. Box X1, Matieland, 7602 (South Africa)

2011-09-21

158

Quasinormal modes of superfluid neutron stars  

NASA Astrophysics Data System (ADS)

We study nonradial oscillations of neutron stars with superfluid baryons, in a general relativistic framework, including finite temperature effects. Using a perturbative approach, we derive the equations describing stellar oscillations, which we solve by numerical integration, employing different models of nucleon superfluidity, and determining frequencies and gravitational damping times of the quasinormal modes. As expected by previous results, we find two classes of modes, associated to superfluid and non-superfluid degrees of freedom, respectively. We study the temperature dependence of the modes, finding that at specific values of the temperature, the frequencies of the two classes of quasinormal modes show avoided crossings, and their damping times become comparable. We also show that, when the temperature is not close to the avoided crossings, the frequencies of the modes can be accurately computed by neglecting the coupling between normal and superfluid degrees of freedom. Our results have potential implications on the gravitational wave emission from neutron stars.

Gualtieri, L.; Kantor, E. M.; Gusakov, M. E.; Chugunov, A. I.

2014-07-01

159

Fallback Debris Disks Around Young Neutron Stars  

NASA Astrophysics Data System (ADS)

Our Spitzer/IRAC discovery of a dusty debris disk around the young neutron star 4U 0142+61 is likely the first detection of a supernova fallback disk around a neutron star. Here we propose to test three aspects of this hypothesis with targeted Spitzer observations: (1) IRAC imaging of the magnetar 1E 2259+586, to see if debris disks are ubiquitous; (2) deep MIPS 24 micron imaging of 4U 0142+61 to probe the long-wavelength tail of the disk and measure its radial extent; and (3) IRAC subarray observations of 4U 0142+61 designed to detect for 8.7 sec pulsations or set an upper limit on their amplitude. This last measurement will allow us to definitively discriminate whether the mid-IR emission arises from an X-ray heated debris disk or the pulsar magnetosphere.

Chakrabarty, Deepto; Kaplan, David; Wachter, Stefanie; Wang, Zhongxiang

2007-05-01

160

AFTERGLOW OF A BINARY NEUTRON STAR MERGER  

SciTech Connect

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 {approx}0.1B {sup 2} R {sup 3}{Omega} is emitted with baryons (B, R, and {Omega} 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 {approx}10{sup 47}(B/10{sup 13} G){sup 2}(R/10 km){sup 3}({Omega}/10{sup 4} rad s{sup -1}) erg s{sup -1}, which is comparable to the luminosity of quasars.

Shibata, Masaru; Suwa, Yudai; Kiuchi, Kenta [Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Ioka, Kunihito [KEK Theory Center and the Graduate University for Advanced Studies, Oho, Tsukuba 305-0801 (Japan)

2011-06-20

161

Electromagnetic multipole fields of neutron stars  

NASA Technical Reports Server (NTRS)

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

Roberts, W. J.

1979-01-01

162

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

163

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

164

Analytical models of neutron star envelopes  

SciTech Connect

The thermal structure of neutron star envelopes is investigated using approximate analytical formulae. In the degenerate layers the thermal structure equation is solved exactly for electron-dominated heat transport. In the nondegenerate layers it is shown that if the opacity is a power-law function of density and temperature, then the T(rho) profiles lie along curves of constant thermal conductivity. The two solutions are matched at intermediate densities to give an approximate relation between the heat flux and the core temperature of the neutron star. The dependence on various uncertain factors is found explicitly, allowing a detailed understanding of the physical processes that control the heat flux. The possible significance of the results to cooling calculations that take into account strong magnetic fields is discussed.

Hernquist, L.; Applegate, J.H.

1984-12-01

165

Plasma magnetosphere of rotating magnetized neutron star in the braneworld  

Microsoft Academic Search

Plasma magnetosphere surrounding rotating magnetized neutron star in the braneworld has been studied. For the simplicity of calculations Goldreich-Julian charge density is analyzed for the aligned neutron star with zero inclination between magnetic field and rotation axis. From the system of Maxwell equations in spacetime of slowly rotating star in braneworld, second-order differential equation for electrostatic potential is derived. Analytical

V. S. Morozova; B. J. Ahmedov; A. A. Abdujabbarov; A. I. Mamadjanov

2010-01-01

166

Free precession of neutron stars - Role of possible vortex pinning  

Microsoft Academic Search

Vortex pinning affects neutron-star free precession by modifying its frequency and geometry, in a gyroscopic effect. For neutron stars with low oblateness, the free-precession frequency is given by the product of the ratio of moments of inertia of the pinned superfluid to the rigid component of the rest of the star times half the superfluid vorticity. This poses a severe

J. Shaham

1977-01-01

167

Gravitational waves from hot young rapidly rotating neutron stars  

Microsoft Academic Search

Gravitational radiation drives an instability in the r-modes of young rapidly rotating neutron stars. This instability is expected to carry away most of the angular momentum of the star by gravitational radiation emission, leaving a star rotating at about 100 Hz. In this paper we model in a simple way the development of the instability and evolution of the neutron

Benjamin J. Owen; Lee Lindblom; Curt Cutler; Bernard F. Schutz; Alberto Vecchio; Nils Andersson

1998-01-01

168

Maximum Mass of a Neutron Star  

Microsoft Academic Search

On the basis of Einstein's theory of relativity, the principle of causality, and Le Chatelier's principle, it is here established that the maximum mass of the equilibrium configuration of a neutron star cannot be larger than 3.2M[m?]. The extremal principle given here applies as well when the equation of state of matter is unknown in a limited range of densities.

Clifford E. Rhoades; Remo Ruffini

1974-01-01

169

Topological vector currents and neutron star kicks  

NASA Astrophysics Data System (ADS)

We propose that the asymmetry required to create neutron star kicks with large magnitudes, v>800km/s, is carried by non-dissipating currents that travel along the superconducting vortices in the neutron star. These currents, called topological vector currents, appear specifically in systems with non-zero magnetic flux and an asymmetry in the number of left and right-handed fermions. A satisfying explanation for large kicks does not yet exist. Two candidates are hydrodynamic instabilities and asymmetric neutrino flux. With hydrodynamic kicks an asymmetric mass distribution triggers an asymmetric explosion during formation but it is not clear that enough momentum is produced. Neutrino kicks involve neutrino transport caused by the magnetic field and the weak interaction, but the required momentum is generated at temperatures high enough that detailed balance washes out the asymmetry. Kicks from topological currents are powered by the electron chemical potential, not the temperature, so are not washed out and the momentum carried by these currents appears to be capable of generating the large velocities observed in some neutron stars.

Charbonneau, James

2008-05-01

170

Dissipation in relativistic superfluid neutron stars  

NASA Astrophysics Data System (ADS)

We analyse damping of oscillations of general relativistic superfluid neutron stars. To this aim we extend the method of decoupling of superfluid and normal oscillation modes first suggested in Gusakov & Kantor. All calculations are made self-consistently within the finite temperature superfluid hydrodynamics. The general analytic formulas are derived for damping times due to the shear and bulk viscosities. These formulas describe both normal and superfluid neutron stars and are valid for oscillation modes of arbitrary multipolarity. We show that (i) use of the ordinary one-fluid hydrodynamics is a good approximation, for most of the stellar temperatures, if one is interested in calculation of the damping times of normal f modes, (ii) for radial and p modes such an approximation is poor and (iii) the temperature dependence of damping times undergoes a set of rapid changes associated with resonance coupling of neighbouring oscillation modes. The latter effect can substantially accelerate viscous damping of normal modes in certain stages of neutron-star thermal evolution.

Gusakov, M. E.; Kantor, E. M.; Chugunov, A. I.; Gualtieri, L.

2013-01-01

171

Neutron star inner crust: Nuclear physics input  

NASA Astrophysics Data System (ADS)

A fully self-consistent model of the neutron star inner crust based upon models of the nucleonic equation of state at zero temperature is constructed. The results nearly match those of previous calculations of the inner crust given the same input equation of state. The extent to which the uncertainties in the symmetry energy, the compressibility, and the equation of state of low-density neutron matter affect the composition of the crust are examined. The composition and pressure of the crust is sensitive to the description of low-density neutron matter and the nuclear symmetry energy, and the latter dependence is nonmonotonic, giving larger nuclei for moderate symmetry energies and smaller nuclei for more extreme symmetry energies. Future nuclear experiments may help constrain the crust and future astrophysical observations may constrain the nuclear physics input.

Steiner, Andrew W.

2008-03-01

172

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

173

Updates of the nuclear equation of state for core-collapse supernovae and neutron stars: effects of 3-body forces, QCD, and magnetic fields  

NASA Astrophysics Data System (ADS)

We summarize several new developments in the nuclear equation of state for supernova simulations and neutron stars. We discuss an updated and improved Notre-Dame-Livermore Equation of State (NDL EoS) for use in supernovae simulations. This Eos contains many updates. Among them are the effects of 3- body nuclear forces at high densities and the possible transition to a QCD chiral and/or super-conducting color phase at densities. We also consider the neutron star equation of state and neutrino transport in the presence of strong magnetic fields. We study a new quantum hadrodynamic (QHD) equation of state for neutron stars (with and without hyperons) in the presence of strong magnetic fields. The parameters are constrained by deduced masses and radii. The calculated adiabatic index for these magnetized neutron stars exhibit rapid changes with density. This may provide a mechanism for star-quakes and flares in magnetars. We also investigate the strong magnetic field effects on the moments of inertia and spin down of neutron stars. The change of the moment of inertia associated with emitted magnetic flares is shown to match well with observed glitches in some magnetars. We also discuss a perturbative calculation of neutrino scattering and absorption in hot and dense hyperonic neutron-star matter in the presence of a strong magnetic field. The absorption cross-sections show a remarkable angular dependence in that the neutrino absorption strength is reduced in a direction parallel to the magnetic field and enhanced in the opposite direction. The pulsar kick velocities associated with this asymmetry comparable to observed pulsar velocities and may affect the early spin down rate of proto-neutron star magnetars with a toroidal field configuration.

Mathews, G. J.; Meixner, M.; Olson, J. P.; Suh, I.-S.; Kajino, T.; Maruyama, T.; Hidaka, J.; Ryu, C.-Y.; Cheoun, M.-K.; Lan, N. Q.

2013-07-01

174

Population Synthesis for Neutron Star Systems with Intrinsic Kicks  

Microsoft Academic Search

We use a Monte Carlo binary synthesis code to model the formation and\\u000aevolution of neutron star systems including high-mass X-ray binaries, low-mass\\u000aX-ray binaries, double neutron star systems and radio pulsars. Our focus is on\\u000athe signature imprinted on such systems due to natal kicks to neutron stars\\u000aover and above that imparted by orbital motions. The code incorporates

Chris Fryer; Adam Burrows; Willy Benz

1997-01-01

175

Population Syntheses for Neutron Star Systems with Intrinsic Kicks  

Microsoft Academic Search

We use a Monte Carlo binary synthesis code to model the formation and evolution of neutron star systems including high-mass X-ray binaries, low-mass X-ray binaries, double neutron star systems, and radio pulsars. Our focus is on the signature imprinted on such systems due to natal kicks to neutron stars over and above that imparted by orbital motions. The code incorporates

Chris Fryer; Adam Burrows; Willy Benz

1998-01-01

176

Isolated neutron stars in the galaxy: from magnetars to antimagnetars  

SciTech Connect

Using the model with decaying magnetic fields it is possible to describe with one smooth (log-Gaussian) initial magnetic field distribution three types of isolated neutron stars: radiopulsar, magnetars, and cooling close-by compact objects. The same model is used here to make predictions for old accreting isolated neutron stars. It is shown that using the updated field distribution we predict a significant fraction of isolated neutron stars at the stage of accretion despite long subsonic propeller stage.

Boldin, P. A., E-mail: boldin.pavel@gmail.com [Moscow Engineering Physics Institute (State University) (Russian Federation); Popov, S. B., E-mail: polar@sai.msu.ru [Moscow State University, Sternberg Astronomical Institute (Russian Federation)

2012-07-15

177

Relativistic tidal properties of neutron stars  

NASA Astrophysics Data System (ADS)

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??=[length]2?+1 measuring the ?th-order mass multipolar moment GMa1…a? induced in a star by an external ?th-order gravito-electric tidal field Ga1…a?; (ii) a gravito-magnetic-type coefficient G??=[length]2?+1 measuring the ?th spin multipole moment GSa1…a? induced in a star by an external ?th-order gravito-magnetic tidal field Ha1…a?; and (iii) a dimensionless “shape” Love number h? measuring the distortion of the shape of the surface of a star by an external ?th-order gravito-electric tidal field. All the dimensionless tidal coefficients G??/R2?+1, G??/R2?+1, and h? (where R is the radius of the star) are found to have a strong sensitivity to the value of the star’s “compactness” c?GM/(c02R) (where we indicate by c0 the speed of light). In particular, G??/R2?+1˜k? is found to strongly decrease, as c increases, down to a zero value as c is formally extended to the “black hole (BH) limit” cBH=1/2. The shape Love number h? is also found to significantly decrease as c increases, though it does not vanish in the formal limit c?cBH, but is rather found to agree with the recently determined shape Love numbers of black holes. The formal vanishing of ?? and ?? as c?cBH 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

2009-10-01

178

On the properties of matter in neutron stars  

NASA Technical Reports Server (NTRS)

A qualitative description of the interior of a neutron star is presented, giving attention also to the validity of the 'isotropic fluid' approximation. The atmosphere and surface of a neutron star are considered together with aspects concerning nuclear and solid state physics in the crust, the liquid interior, the hyperon core, neutron star models, and pulsar observations. Accretion processes are also investigated, taking into account such topics as the Eddington limit, accretion rates, the death of pulsars, changes of the surface composition of neutron stars by accretion, questions of X-ray emission, and aspects of gamma radiation emission.

Boerner, G.

1973-01-01

179

Burst Oscillations: A New Spin on Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Strohmayer, Tod

2007-01-01

180

Neutron stars in f(R) gravity with perturbative constraints  

SciTech Connect

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

Cooney, Alan; DeDeo, Simon; Psaltis, Dimitrios [Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States); Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501 (United States); Departments of Astronomy and Physics, University of Arizona, Tucson, Arizona 85721 (United States)

2010-09-15

181

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

182

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

NASA Astrophysics Data System (ADS)

With a view to understanding the formation of double neutron star binaries, we investigate the late stages of evolution of helium stars with masses of 2.8-6.4Msolar in binary systems with a 1.4-Msolar neutron star companion. We found that mass transfer from 2.8- to 3.3-Msolar helium stars (originating from main-sequence stars with masses of 10-12Msolar that underwent case B evolution, or 9-10Msolar that experienced case C mass transfer) as well as from 3.3 to 3.8Msolar in very close orbits (Porb<~ 0.25 d) will end up in a common-envelope and spiral-in phase due to the development of a convective helium envelope at the end of the calculation. If the neutron star has sufficient time to complete the spiralling-in process in the envelope of the helium star before the core collapses, the system will produce very tight double neutron star binaries (Porb~ 0.01 d) with a very short merger time-scale, i.e. of the order of 1 Myr or less. These systems would have important consequences for the detection rate of gravitational-wave radiation and for the understanding of ?-ray burst progenitors. On the other hand, if the time left until the explosion is shorter than the orbital-decay time-scale, the system will undergo a supernova (SN) explosion during the common-envelope phase. Helium stars with masses 3.3-3.8Msolar in wider orbits (Porb>~ 0.25 d) and those more massive than 3.8Msolar do not develop a convective envelope and therefore are not expected to go through common-envelope evolution. The remnants of these massive helium stars are double neutron star pulsars with periods in the range of 0.1-1 d. This suggests that this range of mass (originating from main-sequence stars more massive than 12Msolar that underwent case B evolution, or more massive than 10Msolar that experienced case C mass transfer) includes the progenitors of the galactic double neutron star pulsars with close orbits (B1913+16 and B1534+12). A minimum kick velocity of 70 and 0 km s-1 (for B1913+16 and B1534+12, respectively) must have been imparted at the birth of the companion to the pulsar. The double neutron stars with wider orbits (J1518+4904 and probably J1811-1736) are produced from helium star-neutron star binaries that avoid Roche lobe overflow, with the helium star being more massive than 2.5Msolar, i.e. the remnants of main-sequence stars more massive than 10Msolar in relatively wide orbits. For these systems, the minimum kick velocities are 50 and 10 km s-1 (for J1518+4904 and J1811-1736, respectively).

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

2003-09-01

183

I-Love-Q: Unexpected Universal Relations for Neutron Stars and Quark Stars  

NASA Astrophysics Data System (ADS)

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

Yagi, Kent; Yunes, Nicolás

2013-07-01

184

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

SciTech Connect

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

Hernquist, L.

1986-06-01

185

TeV mu neutrinos from young neutron stars.  

PubMed

Neutron stars are efficient accelerators for bringing charges up to relativistic energies. We show that if positive ions are accelerated to approximately 1 PeV near the surface of a young neutron star (t(age) less than or nearly 10(5) yr), protons interacting with the star's radiation field produce beamed mu neutrinos with energies of approximately 50 TeV that could produce the brightest neutrino sources at these energies yet proposed. These neutrinos would be coincident with the radio beam, so that, if the star is detected as a radio pulsar, the neutrino beam will sweep the Earth; the star would be a "neutrino pulsar." Looking for nu(mu) emission from young neutron stars will provide a valuable probe of the energetics of the neutron star magnetosphere. PMID:15904352

Link, Bennett; Burgio, Fiorella

2005-05-13

186

EQUATION OF STATE FOR MASSIVE NEUTRON STARS  

SciTech Connect

Using the relativistic Hartree-Fock approximation, we investigate the properties of neutron-star matter in detail. In the present calculation, we consider not only the tensor coupling of vector mesons to octet baryons and the form factors at interaction vertices but also the change in the internal (quark) structure of baryons in dense matter. The relativistic Hartree-Fock calculations are performed in two ways: one with coupling constants determined by SU(6) (quark model) symmetry and the other with coupling constants based on SU(3) (flavor) symmetry. For the latter case, we use the latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle composition of the core matter in SU(3) symmetry is completely different from that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the density region below {approx}1.2 fm{sup -3}, while in the ESC08 model only the {Xi}{sup -} hyperon is produced. Furthermore, the medium modification of the internal baryon structure hardens the equation of state for the core matter. Taking all these effects into account, we can obtain the maximum neutron-star mass which is consistent with the recently observed mass, 1.97 {+-} 0.04 M{sub Sun} (PSR J1614-2230). We therefore conclude that the extension from SU(6) symmetry to SU(3) symmetry in meson-baryon couplings and the internal baryon structure variation in matter considerably enhance the mass of neutron stars. Furthermore, the effects of the form factor at the vertex and the Fock contribution, including the tensor coupling due to vector mesons, are indispensable for describing the core matter.

Katayama, Tetsuya; Saito, Koichi; Miyatsu, Tsuyoshi, E-mail: koichi.saito@rs.tus.ac.jp [Department of Physics, Faculty of Science and Technology, Tokyo University of Science (TUS), Noda 278-8510 (Japan)

2012-12-15

187

Poloidal magnetic fields in superconducting neutron stars  

NASA Astrophysics Data System (ADS)

We develop the formalism for computing the magnetic field within an axisymmetric neutron star with a strong type II superconductor core surrounded by a normal conductor. The formalism takes full account of the constraints imposed by hydrostatic equilibrium with a barotropic equation of state. A characteristic of this problem is that the currents and fields need to be determined simultaneously and self-consistently. Within the core, the strong type II limit B ? H allows us to compute the shapes of individual field lines. We specialize to purely poloidal magnetic fields that are perpendicular to the equator, and develop the `most dipolar case' in which field lines are vertical at the outer radius of the core, which leads to a magnetic field at the stellar surface that is as close to a dipole as possible. We demonstrate that although field lines from the core may only penetrate a short distance into the normal shell, boundary conditions at the inner radius of the normal shell control the field strength on the surface. Remarkably, we find that for a Newtonian N = 1 polytrope, the surface dipole field strength is Bsurf ? Hb?b/3, where Hb is the magnetic field strength at the outer boundary of the type II core and ?bR is the thickness of the normal shell. For reasonable models, Hb ? 1014 G and ?b ? 0.1 so the surface field strength is Bsurf ? 3 × 1012 G, comparable to the field strengths of many radio pulsars. In general, Hb and ?b are both determined by the equation of state of nuclear matter and by the mass of the neutron star, but Bsurf ˜ 1012 G is probably a robust result for the `most dipolar' case. We speculate on how the wide range of neutron star surface fields might arise in situations with less restrictions on the internal field configuration. We show that quadrupolar distortions are ˜-10-9(Hb/1014 G)2 and arise primarily in the normal shell for B ? Hb.

Henriksson, K. T.; Wasserman, I.

2013-06-01

188

Merging Neutron Star - Black Hole Binaries  

NASA Astrophysics Data System (ADS)

In order to simulate the merging of a binary consisting of a neutron star and a black hole with the aim to compute neutrino emission, the three-dimensional Newtonian equations of hydrodynamics were integrated by the `Piecewise Parabolic Method'. We took into account the effects of the emission of gravitational waves and the corresponding backreaction on the hydrodynamics. The properties of neutron star matter were described by the equation of state of Lattimer and Swesty (1991). Energy loss and changes of the electron abundance due to the emission of neutrinos were taken into account by an elaborate ``neutrino leakage scheme'', which is based on a careful evaluation of the lepton number and energy source terms of all neutrino and antineutrino flavors. The simulations were performed with four nested Cartesian grids which allowed for both a good resolution near the central black hole and a large computational volume (details to be found in Ruffert & Janka, Astron & Astrophys, 344, 573, (1999) and references therein). We model the black hole by a vacuum sphere with a Paczy?ski-Wiita potential. In a post-processing step, we evaluated our models for the energy deposition by ?bar? annihilation around the merging objects. Due to the emission of gravitational waves the orbital separation decreases until the neutron star gets torn apart to form an accretion disk around the black hole. We will discuss the dynamics of the merging, the properties of the torus and neutrino energy emitted to review the viability of the merger scenario as central engines for GRBs.

Ruffert, Maximilian

2000-04-01

189

Theory of Radiation Transfer in Neutron Star Atmospheres  

NASA Technical Reports Server (NTRS)

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

Zavlin, Vyacheslav

2006-01-01

190

Holographic cold nuclear matter and neutron star  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

191

Structure of the Impure Neutron Star Crust  

NASA Astrophysics Data System (ADS)

X-ray observations of LMXBs have shown that in some systems accretion onto a neutron star from a companion can lead to the crust becoming thermally decoupled from the core. After accretion stops, the crust is observed to cool at a rate that implies a high level of crystalline order. We perform Molecular Dynamics (MD) simulations to compute the structure of an impure Coulomb solid and also compute diffusion constants for these systems. We then present the first results of the structure of an impure Coulomb solid and also give the first results for diffusion constants in a multicomponent Coulomb solid.

Hughto, Joseph; Horowitz, Charles; Schneider, Andre; Berry, Don

2013-04-01

192

Neutron star coupling to its environment  

NASA Technical Reports Server (NTRS)

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

Salvati, Marco; Pacini, Franco

1987-01-01

193

Nonthermal accretion disk models around neutron stars  

NASA Technical Reports Server (NTRS)

We consider the structure and emission spectra of nonthermal accretion disks around both strongly and weakly magnetized neutron stars. Such disks may be dissipating their gravitational binding energy and transferring their angular momentum via semicontinuous magnetic reconnections. We consider specifically the structure of the disk-stellar magnetospheric boundary where magnetic pressure balances the disk pressure. We consider energy dissipation via reconnection of the stellar field and small-scale disk turbulent fields of opposite polarity. Constraints on the disk emission spectrum are discussed.

Tavani, M.; Liang, Edison P.

1994-01-01

194

Electron capture rates for neutron star crusts  

NASA Astrophysics Data System (ADS)

In the study of the crust of an accreting neutron star, electron capture rates on nuclei in the mass range A=20-106 from the neutron deficient region to the neutron drip line are needed. At the low temperatures typical of a neutron star crust (T9 ˜ 0.4) the determination of the phase space poses a problem since the integrand is very sharply peaked and an error in finding the peak using numerical differentiation or cruder maximum-locator methods will result in inaccuracies at the energies where the integrand has its highest value. In this work we present a global set of temper- ature and density-dependent continuum electron capture rates and a fast phase space calculator valid for low temperatures. The electron capture rates have been calculated using Gamow-Teller strength distributions from the quasi-particle random-phase approximation (QRPA, [1]) nuclear model. We present a new analytic technique to carry out the evaluation of the phase space for electron capture that is fast enough to be implemented in a reaction network. The integral is split into two separate terms at the chemical potential of the electron gas, thus eliminating the need to find the peak of the integrand. The Coulomb correction, which is essentially constant over the range of energies considered, is taken outside the integral and is evaluated at a suitable effective energy which is a function of the charge of the capturing nucleus, the temperature, the chemical potential and the threshold. We compare our calculated electron capture rates to the compilations by Fuller, Fowler and Newman [2] and by Langanke and Martínez-Pinedo [3].

Becerril Reyes, Ana Delia; Gupta, S.; Schatz, S.; Kratz, K. L.; Möller, P.

195

QuakeSim Project Networking  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

196

Fermionic condensation in ultracold atoms, nuclear matter and neutron stars  

NASA Astrophysics Data System (ADS)

We investigate the Bose-Einstein condensation of fermionic pairs in three different superfluid systems: ultracold and dilute atomic gases, bulk neutron matter, and neutron stars. In the case of dilute gases made of fermionic atoms the average distance between atoms is much larger than the effective radius of the inter-atomic potential. Here the condensation of fermionic pairs is analyzed as a function of the s-wave scattering length, which can be tuned in experiments by using the technique of Feshbach resonances from a small and negative value (corresponding to the Bardeen-Cooper-Schrieffer (BCS) regime of Cooper Fermi pairs) to a small and positive value (corresponding to the regime of the Bose-Einstein condensate (BEC) of molecular dimers), crossing the unitarity regime where the scattering length diverges. In the case of bulk neutron matter the s-wave scattering length of neutron-neutron potential is negative but fixed, and the condensate fraction of neutron-neutron pairs is studied as a function of the total neutron density. Our results clearly show a BCS-quasiunitary-BCS crossover by increasing the neutron density. Finally, in the case of neutron stars, where again the neutron-neutron scattering length is negative and fixed, we determine the condensate fraction as a function of the distance from the center of the neutron star, finding that the maximum condensate fraction appears in the crust of the neutron star.

Salasnich, Luca

2014-04-01

197

Maximum mass of neutron stars - Dependence on the assumptions  

Microsoft Academic Search

A variational approach is used to find the equation of state that maximizes the mass for a neutron star in Brans-Dicke theory. The increase of the maximum mass for neutron stars in general relativity is estimated when slow rotation is allowed. We also calculate the dependence of the maximum mass on the choice of density below which the equation of

R. A. Saenz

1977-01-01

198

Maximum mass of neutron stars: Dependence on the assumptions  

Microsoft Academic Search

A variational approach is used to find the equation of state that maximizes the mass for a neutron star in Brans-Dicke theory. The increase of the maximum mass for neutron stars in general relativity is estimated when slow rotation is allowed. We also calculate the dependence of the maximum mass on the choice of density below which the equation of

R. A. Saenz

1977-01-01

199

Neutron Stars in Massive Binaries - Part Two - Computer Simulation  

Microsoft Academic Search

This paper presents the second part of the work where for the first time the joint evolution of a neutron and a normal star in a close massive binary is computed. Physical characteristics for various types of massive binaries with neutron stars, as well as their occurrence in the Galaxy, are determined by the method of computer simulation. The total

V. G. Kornilov; V. M. Lipunov

1983-01-01

200

Neutron stars in massive binary systems. I - Classification and evolution  

Microsoft Academic Search

A classification of close binary systems is presented and analytic expressions are derived that fully describe the evolution of both the normal and the neutron star of such a system. Inventories of neutron and normal star states are presented and combined into a classification system by a given method. Analytic descriptions of the accretion regime and rate, the equation of

V. G. Kornilov; V. M. Lipunov

1983-01-01

201

Neutron star evolution in eccentric-orbit binaries  

Microsoft Academic Search

For the first time, the evolution of neutron stars in an eccentric orbit is considered. It is shown that a special class of systems exists, in which the steady-state accretion is in principle unattainable, the neutron star passing permanently from the state of accretion to that of the propeller and vice versa. It is possible that the fastest accreting pulsar

V. S. Gnusareva; V. M. Lipunov

1985-01-01

202

Neutron stars in massive binary systems. II. Numerical modeling  

Microsoft Academic Search

The joint evolution of a neutron and a normal star in a close massive binary is calculated in the report for the first time. The physical characteristics of the various classes of massive binary systems containing neutron stars and their abundance in the Galaxy are determined by the method of numerical modeling. The total number of types of systems which

V. G. Kornilov; V. M. Lipunov

1983-01-01

203

Neutron star dynamos and the origins of pulsar magnetism  

Microsoft Academic Search

Neutron star convection is a transient phenomenon and has an extremely high magnetic Reynolds number. In this sense, a neutron star dynamo is the quintessential fast dynamo. The convective motions are only mildly turbulent on scales larger than the approximately 100 cm neutrino mean free path, but the turbulence is well developed on smaller scales. Several fundamental issues in the

Christopher Thompson; Robert C. Duncan

1993-01-01

204

Relativistic Processes and the Internal Structure of Neutron Stars  

SciTech Connect

Models for the internal composition of Dense Compact Stars are reviewed as well as macroscopic properties derived by observations of relativistic processes. Modeling of pure neutron matter Neutron Stars is presented and crust properties are studied by means of a two fluid model.

Alvarez-Castillo, D. E.; Kubis, S. [Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Krakow (Poland)

2011-10-14

205

Transition density and pressure in hot neutron stars  

SciTech Connect

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

Xu Jun [Cyclotron Institute, Texas A and M University, College Station, Texas 77843-3366 (United States); Chen Liewen [Department of Physics, Shanghai Jiao Tong University, Shanghai 200240 (China); Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000 (China); Ko, Che Ming [Cyclotron Institute and Department of Physics and Astronomy, Texas A and M University, College Station, Texas 77843-3366 (United States); Li Baoan [Department of Physics and Astronomy, Texas A and M University-Commerce, Commerce, Texas 75429-3011 (United States)

2010-05-15

206

Neutron Star Structure in the Presence of Scalar Fields  

NASA Technical Reports Server (NTRS)

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

Kazanas, Demosthenes

2004-01-01

207

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

208

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

209

Imaging Black Hole and Neutron Star Binaries  

NASA Astrophysics Data System (ADS)

Tomography offers one of the few approaches to spatial examination of X-ray binaries which enables us to study the geometry of the accretion flow in detail and to examine spectral signatures that differentiate between neutron stars and black holes. We propose to observe two systems (the black hole candidate V1408 Aql and the neutron star system, V801 Ara) which are especially suitable for the study of disk evolution and instabilities. The optical variations of V1408 Aql have been variously attributed to a heated secondary or a thin disk, whereas its X-ray spectrum is attributed to a pure disk. Our tomographic images will allow us to identify unambiguously the presence or absence of a disk. V801 Ara shows superbursts in addition to bursts making it a prime candidate to show disk eccentricity, which provides important clues about the nature of the disk evolution. The data obtained will also allow us to improve the radial velocities, measure K2 from the irradiated emission lines, and refine the mass ratios by fitting the rotational broadening of the secondary for each system.

Dil Vrtilek, Saeqa; Peris, Charith; Cechura, Jan

2013-02-01

210

Physics of systems containing neutron stars  

NASA Technical Reports Server (NTRS)

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

Ruderman, Malvin

1996-01-01

211

Gravitational and Electromagnetic Emission from Binary Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

212

Gravity Wave Oscillations from Rapidly Rotating Neutron Stars  

Microsoft Academic Search

The association of the nearly coherent brightness oscillations during thermonuclear X-ray bursts from neutron star low-mass X-ray binaries with the rotation period of these neutron stars raises the possibility that these stars are spinning fast enough to become unstable to gravity wave radiation. In such cases, the surface deformations caused by the gravity wave instability may be sufficient to create

G. J. Mathews; J. R. Wilson

1999-01-01

213

Relativity and Neutron Stars: I. The Maximum Mass of Neutron Stars. II. Gravitational Waves from Stellar Collapse  

Microsoft Academic Search

The study of neutron stars provides us with an excellent example for the application of relativity to astrophysics. General relativity or any of the other relativistic theories of gravity will have important consequences for the birth, evolution and final state for such compact objects. We first look at the upper mass limit for neutron stars. Einstein's general theory of relativity

Richard Anthony Saenz

1977-01-01

214

Mass and radius formulas for low-mass neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars, produced at the death of massive stars, are often regarded as giant neutron-rich nuclei. This picture is especially relevant for low-mass (below about solar mass, M_?) neutron stars, where non-nucleonic components are not expected to occur. Due to the saturation property of nucleonic matter, leading to the celebrated liquid-drop picture of atomic nuclei, empirical nuclear masses and radii can be approximately expressed as a function of atomic mass number. It is, however, not straightforward to express masses and radii of neutron stars even in the low-mass range where the structure is determined by a balance between the pressure of neutron-rich nucleonic matter and gravity. Such expressions would be of great use given possible simultaneous mass and radius measurements. Here we successfully construct theoretical formulas for the masses and radii of low-mass neutron stars from various models that are consistent with empirical masses and radii of stable nuclei. In this process, we discover a new equation-of-state parameter that characterizes the structure of low-mass neutron stars. This parameter, which plays a key role in connecting the mass-radius relation of the laboratory nuclei to that of the celestial objects, could be constrained from future observations of low-mass neutron stars.

Sotani, Hajime; Iida, Kei; Oyamatsu, Kazuhiro; Ohnishi, Akira

2014-05-01

215

Energy Density Functional for Nuclei and Neutron Stars  

SciTech Connect

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

Erler, J. [UTK/ORNL/German Cancer Research Center-Heidelberg; Horowitz, C. J. [UTK/ORNL/Indiana University; Nazarewicz, Witold [UTK/ORNL/University of Warsaw; Rafalski, M. [UTK/ORNL; Reinhard, P.-G. [Universitat Erlangen, Germany

2013-01-01

216

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

217

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

NASA Technical Reports Server (NTRS)

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

Swank, Jean

2008-01-01

218

Breaking strain of neutron star crust and gravitational waves.  

PubMed

Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of the neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Because of the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large-scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in magnetar giant flares and microflares. PMID:19518937

Horowitz, C J; Kadau, Kai

2009-05-15

219

Neutron star's initial spin period distribution  

NASA Astrophysics Data System (ADS)

We analyse different possibilities to explain the wide initial spin period distribution of radio pulsars presented by Noutsos et al. With a population synthesis modelling, we demonstrate that magnetic field decay can be used to interpret the difference between the recent results by Noutsos et al and those by Popov and Turolla, where a much younger population of neutron stars associated with supernova remnants with known ages has been studied. In particular, an exponential field decay with ?mag = 5 Myr can produce a `tail' in the reconstructed initial spin period distribution up to P0 > 1 s starting with a standard Gaussian with = 0.3 s and ?P = 0.15 s. Another option to explain the difference between initial spin period distributions from Noutsos et al. and Popov and Turolla - the emerging magnetic field - is also briefly discussed.

Igoshev, A. P.; Popov, S. B.

2013-06-01

220

Neutron Star Structure In The Presence of Scalar Fields  

NASA Technical Reports Server (NTRS)

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

Crawford, James P.; Kazanas, Demosthenes

2004-01-01

221

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 timescale 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 have 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 three cases the atmospheres are composed of elements which are lighter then iron.

Hoffman, Kelsey L.; Heyl, J. S.

2010-01-01

222

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

223

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

Aguilera, Deborah N. [Tandar Laboratory, Comision Nacional de Energia Atomica, Avenida Gral. Paz 1499, 1650 San Martin, Buenos Aires (Argentina); Cirigliano, Vincenzo; Reddy, Sanjay; Sharma, Rishi [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Pons, Jose A. [Department of Applied Physics, University of Alicante, Apartado de Correos 99, E-03080 Alicante (Spain)

2009-03-06

224

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

225

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

226

MAGNETIC INTERACTIONS IN COALESCING NEUTRON STAR BINARIES  

SciTech Connect

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

Piro, Anthony L., E-mail: piro@caltech.edu [Theoretical Astrophysics, California Institute of Technology, 1200 E California Blvd., M/C 350-17, Pasadena, CA 91125 (United States)

2012-08-10

227

Composition temperature-dependent g modes in superfluid neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

228

Neutron Stars and Thermonuclear X-ray Bursts  

NASA Technical Reports Server (NTRS)

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

Bhattacharyya, Sudip

2007-01-01

229

Understanding Neutron Stars using Thermonuclear X-ray Bursts  

NASA Technical Reports Server (NTRS)

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

Bhattacharyya, S.

2007-01-01

230

Does mass accretion lead to field decay in neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

231

MUFFINS: Metallurgy Uncovers Forced Fractures Inside Neutron Stars  

NASA Astrophysics Data System (ADS)

As a result of nuclear reactions within the neutron star crust, even neutron stars that have not accreted matter can have impurities in their crust. These impurities would have an effect on the mechanical properties of the crust, possibly creating a more brittle structure. In order to investigate the properties of an impure crust we are performing molecular dynamic simulations using the Large scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). The simulations are run at fixed energy and volume with the isotopes interacting via a repulsive Yukawa potential. Here we present effects of impurities with respect the the breaking strain in a non-accreting neutron star crust.

Hoffman, Kelsey L.; Heyl, J. S.

2011-01-01

232

Evolution of the Magnetic Field in Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

In this thesis we address the question of the evolution of the magnetic field in neutron stars. There has been sufficient observational indication suggesting a causal connection between the binary history of neutron stars and the evolution of their magnetic field. In particular, it is believed that the generation of the low-field millisecond pulsars is a consequence of the processing of normal high-field neutron stars in binary systems. Therefore, in this thesis we try to understand the mechanism of field evolution in neutron stars that are members of binary systems with an aim to understand the problem of millisecond pulsar generation. To this end we have looked at four related problems as described below : 1. the effect of diamagnetic screening on the final field of a neutron star accr eting material from its binary companion; 2. evolution of magnetic flux located in the crust of an accreting neutron star; 3. application of the above-mentioned model to real systems and a comparison with observations; 4. an investigation into the consequences of magnetic flux being initially located in the core of the star and its observational implications.

Konar, Sushan

1997-11-01

233

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

234

Molecular Dynamics Simulations of Non-accreting Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

Neutron stars which do not accrete material can still have impurities in their crust, due to nuclear reactions in the crust. These impurities in the crust could affect the mechanical properties of the neutron star crust. In order to investigate the properties of the crust of a non-accreting neutron star we are performing molecular dynamic simulations of the crust. We are using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), where simulations are run at fixed energy and volume, with the isotopes interacting via a repulsive Yukawa potential. Here we are presenting the preliminary results of the equilibrium structure of the solid neutron star crust using abundances of a non-accreting source.

Hoffman, Kelsey L.; Heyl, J. S.

2010-02-01

235

The inside-out view on neutron-star magnetospheres  

NASA Astrophysics Data System (ADS)

We construct hydromagnetic neutron star equilibria which allow for a non-zero electric current distribution in the exterior. The novelty of our models is that the neutron star's interior field is in equilibrium with its magnetosphere, thus bridging the gap between previous work in this area, which either solves for the interior assuming a vacuum exterior or solves for the magnetosphere without modelling the star itself. We consider only non-rotating stars in this work, so our solutions are most immediately applicable to slowly rotating systems such as magnetars. Nonetheless, we demonstrate that magnetospheres qualitatively resembling those expected for both magnetars and pulsars are possible within our framework. The `inside-out' approach taken in this paper should be more generally applicable to rotating neutron stars, where the interior and exterior regions are again not independent but evolve together.

Glampedakis, K.; Lander, S. K.; Andersson, N.

2014-01-01

236

Structural analysis of the Quaking homodimerization interface  

PubMed Central

Quaking is a prototypical member of the STAR protein family, which plays key roles in posttranscriptional gene regulation by controlling mRNA translation, stability and splicing. QkI-5 has been shown to regulate mRNA expression in the central nervous system, but little is known about its roles in other tissues. STAR proteins function as dimers and bind to bipartite RNA sequences, however, the structural and functional roles of homo- and hetero-dimerization are still unclear. Here, we present the crystal structure of the QkI dimerization domain, which adopts a similar stacked helix-turn-helix arrangement as its homologs GLD-1 and Sam68, but differs by an additional helix inserted in the dimer interface. Variability of the dimer interface residues likely ensures selective homodimerization by preventing association with non-cognate STAR family proteins in the cell. Mutations that inhibit dimerization also significantly impair RNA binding in vitro, alter QkI-5 protein levels, and impair QkI function in a splicing assay in vivo. Together our results indicate that a functional Qua1 homodimerization domain is required for QkI-5 function in mammalian cells.

Beuck, Christine; Qu, Song; Fagg, W. Samuel; Ares, Manuel; Williamson, James R.

2012-01-01

237

MHD Stability of Polar Caps of Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

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

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

2000-12-01

238

On the Maximum Mass of Differentially Rotating Neutron Stars.  

PubMed

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

Baumgarte; Shapiro; Shibata

2000-01-01

239

Thermal neutron flux measurements in the STAR experimental hall  

NASA Astrophysics Data System (ADS)

We report measurements of thermal neutron fluxes at different locations in the STAR experimental hall during RHIC Run 13 with proton-proton collisions at ?{s}=510 GeV. We compare these measurements to calculations based on PYTHIA as a minimum bias event generator, detailed GEANT3 simulation of the STAR detector and experimental hall, and with GCALOR as the neutron transport code. A fairly good agreement was found between simulation and measurements.

Fisyak, Yuri; Tsai, Oleg; Videbæk, Flemming; Xu, Zhangbu

2014-08-01

240

ON THE MASS DISTRIBUTION AND BIRTH MASSES OF NEUTRON STARS  

SciTech Connect

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

Oezel, Feryal; Psaltis, Dimitrios; Santos Villarreal, Antonio [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Narayan, Ramesh [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138,USA (United States)

2012-09-20

241

Nature of Fault Planes in Solid Neutron Star Matter  

NASA Astrophysics Data System (ADS)

The properties of tectonic earthquake sources are compared with those deduced here for fault planes in solid neutron star matter. Neutron star matter, not being absolutely stable and with isotropic pressure several orders of magnitude greater than its shear modulus, cannot exhibit brittle fracture at any temperature or magnetic field strength. This conclusion is significant for current theories of pulsar glitches and of the anomalous X-ray pulsars and soft gamma repeaters.

Jones, P. B.

2003-09-01

242

Do pions condense in neutron-star matter  

SciTech Connect

Pion condensates in neutron-star matter, formed either as new modes, or on states identifiable with those of the free pion are studied. A description of neutron-star matter at finite temperature is formulated upon a suitable basis of realistic interactions in a modified background field description, and leads to the onset of a pion condensate between the density of nuclear matter and the density of free hadrons. This condensate, however, is blocked when strange hadrons are incorporated in the description.

Wheeler, J W; Gleeson, A M

1983-04-01

243

Instability Windows and Evolution of Rapidly Rotating Neutron Stars  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

244

Instability windows and evolution of rapidly rotating neutron stars.  

PubMed

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

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

2014-04-18

245

From ultracold Fermi Gases to Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Salomon, Christophe

2012-02-01

246

Extensive population synthesis of isolated neutron stars with field decay  

NASA Astrophysics Data System (ADS)

We perform population synthesis studies of different types of neutron stars (thermally emitting isolated neutron stars, normal radio pulsars, magnetars) taking into account the magnetic field decay and using results from the most recent advances in neutron star cooling theory. For the first time, we confront our results with observations using simultaneously the Log N--Log S distribution for nearby isolated neutron stars, the Log N--Log L distribution for magnetars, and the distribution of radio pulsars in the P--? diagram. For this purpose, we fix a baseline neutron star model (all microphysics input), and other relevant parameters to standard values (velocity distribution, mass spectrum, etc.), only allowing to vary the initial magnetic field strength. We find that our theoretical model is consistent with all sets of data if the initial magnetic field distribution function follows a log-normal law with < log(B0/[G])>~13.25 and ?log B0~0.6. The typical scenario includes about 10% of neutron stars born as magnetars, significant magnetic field decay during the first million years of a NS life (only about a factor of 2 for low field neutron stars but more than an order of magnitude for magnetars), and a mass distribution function dominated by low mass objects. This model explains satisfactorily all known populations. Evolutionary links between different subclasses may exist, although robust conclusions are not yet possible. We apply the obtained field distribution and the model of decay to study long-term evolution of neuton stars till the stage of accretion from the interstellar medium. It is shown that though the subsonic propeller stage can be relatively long, initially highly magnetized neutron stars (B0>~1013 G) reach the accretion regime within the Galactic lifetime if their kick velocities are not too large. The fact that in previous studies made >10 years ago, such objects were not considered results in a slight increase of the Accretor fraction in comparison with earlier conclusions. Most of the neutron stars similar to the Magnificent seven are expected to become accreting from the interstellar medium after few billion years of their evolution. They are the main predecestors of accreting isolated neutron stars.

Popov, S. B.; Boldin, P. A.; Miralles, J. A.; Pons, J. A.; Posselt, B.

2011-09-01

247

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

PubMed

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

Bauswein, A; Janka, H-T

2012-01-01

248

Physics of systems containing neutron stars  

NASA Technical Reports Server (NTRS)

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

249

The Masses of Two Binary Neutron Star Systems  

Microsoft Academic Search

The measurement or constraint of the masses of neutron stars and their binary\\u000acompanions tests theories of neutron star structure and of pulsar formation and\\u000aevolution. We have measured the rate of the general relativistic advance of the\\u000alongitude of periastron for the pulsar PSR B1802$-$07:\\u000a$\\\\dot\\\\omega=0\\\\fdg060\\\\pm0\\\\fdg009\\\\,\\\\mbox{yr}^{-1}$, which implies a total system\\u000amass, pulsar plus companion star, of $M=1.7\\\\pm0.4\\\\,\\\\Msun$. We

S. E. Thorsett; Z. Arzoumanian; M. M. McKinnon; J. H. Taylor

1993-01-01

250

Neutrino emission from triplet pairing of neutrons in neutron stars  

SciTech Connect

Neutrino emission resulting from the pair breaking and formation processes in the bulk triplet superfluid in neutron stars is investigated taking into account anomalous weak interactions. I consider the problem in the BCS approximation discarding Fermi-liquid effects. By this approach I derive self-consistent equations for anomalous vector and axial-vector vertices of weak interactions taking into account {sup 3}P{sub 2}-{sup 3}F{sub 2} mixing. Further, I simplify the problem and consider pure {sup 3}P{sub 2} pairing with m{sub j}=0, as is adopted in the minimal-cooling paradigm. As was expected because of current conservation, I have obtained a large suppression of neutrino emissivity in the vector channel. More exactly, the neutrino emission through the vector channel vanishes in the nonrelativistic limit V{sub F}=0. The axial channel is also found to be moderately suppressed. Total neutrino emissivity is suppressed by a factor of 1.9x10{sup -1} relative to original estimates using bare weak vertices.

Leinson, L. B. [Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS, RU-142190 Troitsk, Moscow Region (Russian Federation)

2010-02-15

251

HUBBLE SEES A NEUTRON STAR ALONE IN SPACE  

NASA Technical Reports Server (NTRS)

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

2002-01-01

252

How can Newly Born Rapidly Rotating Neutron Stars Become Magnetars?  

NASA Astrophysics Data System (ADS)

In a newly born (high-temperature and Keplerian rotating) neutron star, r-mode instability can lead to stellar differential rotation, which winds the seed poloidal magnetic field (~1011 G) to generate an ultra-high (~1017 G) toroidal field component. Subsequently, by succumbing to the Tayler instability, the toroidal field could be partially transformed into a new poloidal field. Through such dynamo processes, the newly born neutron star with sufficiently rapid rotation could become a magnetar on a timescale of ~102 - 3 s, with a surface dipolar magnetic field of ~1015 G. Accompanying the field amplification, the star could spin down to a period of ~5 ms through gravitational wave radiation due to the r-mode instability and, in particular, the non-axisymmetric stellar deformation caused by the toroidal field. This scenario provides a possible explanation for why the remnant neutron stars formed in gamma-ray bursts and superluminous supernovae could be millisecond magnetars.

Cheng, Quan; Yu, Yun-Wei

2014-05-01

253

Limits on self-interacting dark matter from neutron stars.  

PubMed

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

Kouvaris, Chris

2012-05-11

254

Fast radio bursts: the last sign of supramassive neutron stars  

NASA Astrophysics Data System (ADS)

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

Falcke, Heino; Rezzolla, Luciano

2014-02-01

255

Neutron stars in a varying speed of light theory  

NASA Astrophysics Data System (ADS)

We study neutron stars in a varying speed of light (VSL) theory of gravity in which the local speed of light depends upon the value of a scalar field ?. We find that the masses and radii of the stars are strongly dependent on the strength of the coupling between ? and the matter field and that for certain choices of coupling parameters, the maximum neutron star mass can be arbitrarily small. We also discuss the phenomenon of cosmological evolution of VSL stars (analogous to the gravitational evolution in scalar-tensor theories) and we derive a relation showing how the fractional change in the energy of a star is related to the change in the cosmological value of the scalar field.

Whinnett, A. W.

2003-07-01

256

Electrodynamics of disk-accreting magnetic neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

257

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

NASA Astrophysics Data System (ADS)

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

2011-02-01

258

Neutron-capture Nucleosynthesis in the First Stars  

NASA Astrophysics Data System (ADS)

Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, and The McDonald Observatory of The University of Texas at Austin.

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

2014-04-01

259

The Case of the Neutron Star With a Wayward Wake  

NASA Astrophysics Data System (ADS)

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

2006-06-01

260

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

261

Mergers of binary neutron stars with realistic spin  

NASA Astrophysics Data System (ADS)

Simulations of binary neutron stars have seen great advances in terms of physical detail and numerical quality. However, the spin of the neutron stars, one of the simplest global parameters of binaries, remains mostly unstudied. We present the first fully nonlinear general relativistic dynamical evolutions of the last three orbits for constraint-satisfying initial data of spinning neutron star binaries, with astrophysically realistic spins aligned and antialigned to the orbital angular momentum. The initial data are computed with the constant rotational velocity approach. The dynamics of the systems is analyzed in terms of gauge-invariant binding energy vs orbital angular momentum curves. By comparing to a binary black hole configuration, we can estimate the different tidal and spin contributions to the binding energy for the first time. First results on the gravitational waveforms are presented. The phase evolution during the orbital motion is significantly affected by spin-orbit interactions, leading to delayed or early mergers. Furthermore, a frequency shift in the main emission mode of the hypermassive neutron star is observed. Our results suggest that a detailed modeling of merger waveforms requires the inclusion of spin, even for the moderate magnitudes observed in binary neutron star systems.

Bernuzzi, Sebastiano; Dietrich, Tim; Tichy, Wolfgang; Brügmann, Bernd

2014-05-01

262

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

SciTech Connect

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

Staff, Jan E. [Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Tower Drive, Baton Rouge, LA 70803-4001 (United States); Jaikumar, Prashanth; Chan, Vincent [Department of Physics and Astronomy, California State University Long Beach, 1250 Bellflower Boulevard, Long Beach, CA 90840 (United States); Ouyed, Rachid [Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4 (Canada)

2012-05-20

263

Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

264

Quasiequilibrium black hole-neutron star binaries in general relativity  

SciTech Connect

We construct quasiequilibrium sequences of black hole-neutron star binaries in general relativity. We solve Einstein's constraint equations in the conformal thin-sandwich formalism, subject to black hole boundary conditions imposed on the surface of an excised sphere, together with the relativistic equations of hydrostatic equilibrium. In contrast to our previous calculations we adopt a flat spatial background geometry and do not assume extreme mass ratios. We adopt a {gamma}=2 polytropic equation of state and focus on irrotational neutron star configurations as well as approximately nonspinning black holes. We present numerical results for ratios of the black hole's irreducible mass to the neutron star's ADM mass in isolation of M{sub irr}{sup BH}/M{sub ADM,0}{sup NS}=1, 2, 3, 5, and 10. We consider neutron stars of baryon rest mass M{sub B}{sup NS}/M{sub B}{sup max}=83% and 56%, where M{sub B}{sup max} is the maximum allowed rest mass of a spherical star in isolation for our equation of state. For these sequences, we locate the onset of tidal disruption and, in cases with sufficiently large mass ratios and neutron star compactions, the innermost stable circular orbit. We compare with previous results for black hole-neutron star binaries and find excellent agreement with third-order post-Newtonian results, especially for large binary separations. We also use our results to estimate the energy spectrum of the outgoing gravitational radiation emitted during the inspiral phase for these binaries.

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

2007-04-15

265

Sensitivity of neutron star properties to the equation of state  

NASA Astrophysics Data System (ADS)

The subject of this doctoral dissertation is to study the equations of state of nuclear and neutron-star matter. We tackle this problem by employing several models of the relativistic effective interactions. The relativistic effective interactions and their applications to the ground-state properties of medium to heavy nuclei have enjoyed enormous success for the past three decades. With just a few model parameters calibrated to the ground state properties of the closed-shell nuclei, these models exhibit and encode a great amount of physics. However, theses models are untested far away from their narrow window of applicability. In particular, while these models tend to agree on the saturation properties of symmetric nuclear matter, they largely disagree on its density and isospin dependence, especially in the region of high densities and large proton-neutron asymmetries. In order to better understand the properties of nuclear matter at these extreme regions of isospin asymmetry and high-densities, we will apply these models to predict several neutron star properties. Since the matter in the neutron stars are very neutron-rich, while the density of matter in neutron stars spans over a wide range of magnitudes, these compact objects remain unique laboratories for probing the equation of state of neutron-rich matter under conditions unattainable by terrestrial experiments. Thus it is expected that at least the following neutron star properties must be sensitive to the underlying equation of state: maximum mass, typical radii, moments of inertia (both total and crustal), redshifts, and cooling mechanism. We present numerical solutions and in some cases also analytical solutions to each of the properties above. In particular, the sensitivity of the stellar moment of inertia to the neutron-star matter equation of state is examined using accurately-calibrated relativistic mean-field models. We probe this sensitivity by tuning both the density dependence of the symmetry energy and the high density component of the equation of state, properties that are at present poorly constrained by existing laboratory data. Particularly attractive is the study of the fraction of the moment of inertia contained in the solid crust. Analytic treatments of the crustal moment of inertia reveal a high sensitivity to the transition pressure at the core-crust interface. Motivated by a recent astrophysical measurement of the pressure of cold matter above nuclear-matter saturation density, we compute the equation of state of neutron-star matter using various accurately calibrated relativistic models. We found the predictions of these models to be in fairly good agreement with the measured equation of state. In the effort to explain the observational data 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 208Pb and the maximum neutron star mass. The new effective interaction is moderately soft at intermediate densities and relatively stiff at high densities. It is fitted to a neutron skin thickness in 208Pb of only Rn--Rp = 0.16 fm and a moderately large maximum neutron star mass of 1.94 MSun consistent with the latest observation. Last, theoretical uncertainties in the predictions of relativistic mean-field models are estimated using a chi-square minimization procedure that is implemented by studying the small oscillations around the chi-square minimum. It is shown that such statistical analysis provides access to a wealth of information that would normally remain hidden. The power of covariance analysis is illustrated in two relativistic mean field models. By performing this analysis one obtains meaningful theoretical uncertainties for both model parameters and predicted observables. Moreover, it is shown, how covariance analysis is able to establish robust correlations between physical observables.

Fattoyev, Farrooh

266

The Origin of Magnetars, The Role of Anisotropic neutron superfluid of Neutron Stars  

NASA Astrophysics Data System (ADS)

We estimate the strength of the induced magnetic field due to the Pauli paramagnetic moment of the 3P2 Cooper pairs for the anisotropic (3P2) neutron superfluid under the applied magnetic field (B0) in neutron stars. The induced magnetic field of the anisotropic (3P2) neutron superfluid is as follows. B(in) ? {1.9}/{T_7} ? B_0 (T7 denotes the interior temperature of the neutron star in unit of 107 K), ? = {m(^3P_2)}/{0.1 Msun} RNS, 6-3. The induced magnetic field will gradually increase with the temperature of the neutron star decreasing in their late evolutionary stage. A magnetar may appear in a condition when T7? ? . The upper limit of the magnetic field for the magnetars is Bmax (in)(^3P_2) ? 2.02× 1014?.

Peng, Qiu-He; Luo, Zhi-Quan

2006-12-01

267

Thermal emission from low-field neutron stars (Gänsicke+, 2002)  

NASA Astrophysics Data System (ADS)

We present a new grid of LTE model atmospheres for weakly magnetic (B<~1010G) neutron stars, using X opacity and equation of state data from the OPAL project and employing a fully frequency- and angle-dependent radiation transfer. Model spectra for low-field neutron stars with three different photospheric compositions are presented: (1) pure hydrogen atmospheres, (2) atmospheres with solar abundances, and (3) pure iron atmospheres. Each grid covers 29 effective temperatures log(Teff[K])=5.10-6.50 in steps of 0.05. The model spectra are tabulated as angle-averaged unredshifted (surface) Eddington fluxes. All spectra have been calculated for a canonical neutron star configuration, Mns=1.4M?, Rns=10km, corresponding to a surface gravitational acceleration of log(g)=14.386. The same model grids are also available as XSPEC tables at http://legacy.gsfc.nasa.gov/docs/xanadu/xspec/models/gbr.html (3 data files).

Gänsicke, B. T.; Braje, T. M.; Romani, R. W.

2002-04-01

268

Thermonuclear Burning as a Probe of Neutron Star  

NASA Technical Reports Server (NTRS)

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

Strohmayer, Tod

2008-01-01

269

f-Mode instability in relativistic neutron stars.  

PubMed

We present the first calculation of the basic properties of the f-mode instability in rapidly rotating relativistic neutron stars, adopting the Cowling approximation. By accounting for dissipation in neutron star matter, i.e., shear or bulk viscosity and superfluid mutual friction, we calculate the associated instability window. For our specific stellar model, a relativistic polytrope, we obtain a minimum gravitational growth time scale (for the dominant ?=m=4 mode) of the order of 10(3)-10(4)??s near the Kepler frequency ?(K) while the instability is active above ?0.92???(K) and for temperatures ?(10(9)-2×10(10))??K, characteristic of newborn neutron stars. PMID:21981489

Gaertig, E; Glampedakis, K; Kokkotas, K D; Zink, B

2011-09-01

270

Accreting Millisecond Pulsars: Neutron Star Masses and Radii  

NASA Technical Reports Server (NTRS)

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

Strohmayer, Tod

2004-01-01

271

Can We Observe Accreting, Isolated Neutron Stars?  

NASA Astrophysics Data System (ADS)

We discuss the observability of isolated neutron stars (NSs) accreting interstellar material as sources of quiescent and transient UV and X-ray radiation. We study their spatial and kinematic properties in the solar neighborhood through Monte Carlo simulations of 10(5) orbits in the Galactic potential. We present a much faster semi-analytic technique which is capable of reproducing the full kinematic properties of the local NS population in remarkable agreement with the Monte Carlo results. We derive the accretion rate distributions associated with the various phases of the interstellar medium (ISM). Assuming blackbody emission and 10(9) NSs in the Galaxy, we estimate that, in the case of isotropic (polar cap) accretion, of order 2000 (10000) old NSs should be observed as X-ray sources in the ROSAT-XRT all-sky survey, with up to 600 (100) of them showing up at longer wavelengths in the ROSAT-WFC survey. The number of detectable NSs in the forthcoming EUVE all-sky survey should be close to 200 (20). If old NSs are magnetized, we estimate that an additional 1000 sources located in giant molecular clouds should be observed in the ROSAT-XRT survey. NSs detected by ROSAT-XRT will be strongly concentrated towards the Galactic plane. Isolated NSs in the local cavity can contribute only 0.1% of the SXRB at 100 eV. We argue, however, that the integrated emission from solitary NSs accreting material in the Galactic plane could give rise to the Galactic X-ray ridges observed by Exosat and HEAO A-2. We investigate the emission properties of accreting NSs moving supersonically in dense atomic and molecular clouds, and show that they will produce elongated, \\lq`cometary" HII regions, a possible characteristic observational signature. Material accumulated by slow accretion onto the polar cap of magnetized NSs located in diffuse clouds might be unstable to nuclear burning and lead to X-ray bursts. We estimate a rate of 25 yr(-1) energetic, ~ 5times 10(37) ergs events within 1 kpc, which might be detectable by HETE. Such bursts may also be responsible for some of the fast X-ray transients observed by HEAO A-1.

Blaes, Omer; Madau, Piero

1992-12-01

272

Parameters of rotating neutron stars with and without hyperons  

NASA Astrophysics Data System (ADS)

Context. The discovery of a 2 M? neutron star provided a robust constraint for the theory of exotic dense matter, bringing into question the existence of strange baryons in the interiors of neutron stars. Although many theories fail to reproduce this observational result, several equations of state containing hyperons are consistent with it. Aims: We study global properties of stars using equations of state containing hyperons, and compare them to those without hyperons to find similarities, differences, and limits that can be compared with the astrophysical observations. Methods: Rotating, axisymmetric, and stationary stellar configurations in general relativity are obtained, and their global parameters are studied. Results: Approximate formulæ describing the behavior of the maximum and minimum stellar mass, compactness, surface redshifts, and moments of inertia as functions of spin frequency are provided. We also study the thin disk accretion and compare the spin-up evolution of stars with different moments of inertia.

Bejger, M.

2013-04-01

273

Exploring the origin of neutron star magnetic field: magnetic properties of the progenitor OB stars  

NASA Astrophysics Data System (ADS)

Ferrario & Wickramasinghe (2006) explored the hypothesis that the magnetic fields of neutron stars are of fossil origin. In this context, they predicted the field distribution of the progenitor OB stars, finding that 5 per cent of main sequence massive stars should have fields in excess of 1 kG. We have carried out sensitive ESPaDOnS spectropolarimetric observations to search for direct evidence of such fields in all massive B- and O-type stars in the Orion Nebula Cluster star-forming region. We have detected unambiguous Stokes V Zeeman signatures in spectra of three out of the eight stars observed (38%). Using a new state-of-the-art Bayesian analysis, we infer the presence of strong (kG), organised magnetic fields in their photospheres. For the remaining five stars, we constrain any dipolar fields in the photosphere to be weaker than about 200 G. Statistically, the chance of finding three ~1 kG fields in a sample of eight OB stars is quite low (less than 1%) if the predictions of Ferrario & Wickramasinghe are correct. This implies that either the magnetic fields of neutron stars are not of fossil origin, that the flux-evolution model of Ferrario & Wickramasinghe is incomplete, or that the ONC has unusual magnetic properties. We are undertaking a study of other young star clusters, in order to better explore these possibilities.

Petit, Véronique; Wade, Gregg A.; Drissen, Laurent; Montmerle, Thierry

2008-02-01

274

Many-Particle Theory of Nuclear Systems with Application to Neutron Star Matter.  

National Technical Information Service (NTIS)

The research is reported concerning energy-density relation for the normal state of neutron star matter, and the effects of superfluidity and polarization on neutron star matter. Considering constraints on variation, and the theory of quantum fluids, thre...

D. A. Chakkalakal C. Yang

1973-01-01

275

Gravitational Radiation Instability in Hot Young Neutron Stars  

Microsoft Academic Search

We show that gravitational radiation drives an instability in hot young\\u000arapidly rotating neutron stars. This instability occurs primarily in the l=2\\u000ar-mode and will carry away most of the angular momentum of a rapidly rotating\\u000astar by gravitational radiation. On the timescale needed to cool a young\\u000aneutron star to about T=10^9 K (about one year) this instability can

Lee Lindblom; Benjamin J. Owen; Sharon M. Morsink

1998-01-01

276

Recycling of Neutron Stars in Common Envelopes and Hypernova Explosions  

Microsoft Academic Search

In this paper we propose a new plausable mechanism of supernova explosions\\u000aspecific to close binary systems. The starting point is the common envelope\\u000aphase in the evolution of a binary consisting of a red super giant and a\\u000aneutron star. As the neutron star spirals towards the center of its companion\\u000ait spins up via disk accretion. Depending on

Maxim V. Barkov; Serguei S. Komissarov

2010-01-01

277

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

Microsoft Academic Search

Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge Z. Nuclei with Z{<=}6 can fuse at low densities in a liquid ocean. However, nuclei with Z=8 or

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

2008-01-01

278

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

Microsoft Academic Search

Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge Z. Nuclei with Z<=6 can fuse at low densities in a liquid ocean. However, nuclei with Z=8 or

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

2008-01-01

279

Thermal emission of neutron stars with internal heaters  

NASA Astrophysics Data System (ADS)

Using 1D and 2D cooling codes, we study thermal emission from neutron stars with steady state internal heaters of various intensities and geometries (blobs or spherical layers) located at different depths in the crust. The generated heat tends to propagate radially, from the heater down to the stellar core and up to the surface; it is also emitted by neutrinos. In local regions near the heater, the results are well described with the 1D code. The heater's region projects on to the stellar surface forming a hotspot. There are two heat propagation regimes. In the first, conduction outflow regime (realized at heat rates H0 ? 1020 erg cm-3 s-1 or temperatures Th ? 109 K in the heater), the thermal surface emission of the star depends on the heater's power and neutrino emission in the stellar core. In the second, neutrino outflow regime (H_0 ? 10^{20} erg cm^{-3 s^{-1}} or T_h ? 10^9 K), the surface thermal emission becomes independent of heater's power and the physics of the core. The largest (a few per cent) fraction of heat power is carried to the surface if the heater is in the outer crust and the heat regime is intermediate. The results can be used for modelling young cooling neutron stars (prior to the end of internal thermal relaxation), neutron stars in X-ray transients, magnetars and high-B pulsars, as well as merging neutron stars.

Kaminker, A. D.; Kaurov, A. A.; Potekhin, A. Y.; Yakovlev, D. G.

2014-08-01

280

Role of isospin physics in supernova matter and neutron stars  

SciTech Connect

We investigate the liquid-gas phase transition of hot protoneutron stars shortly after their birth following supernova explosion and the composition and structure of hyperon-rich (proto)neutron stars within a relativistic mean-field model where the nuclear symmetry energy was constrained from the measured neutron skin thickness of finite nuclei. Light clusters are abundantly formed with increasing temperature well inside the neutrino-sphere for a uniform supernova matter. Liquid-gas phase transition is found to suppress the cluster yield within the coexistence phase as well as decrease considerably the neutron-proton asymmetry over a wide density range. We find symmetry energy has a modest effect on the boundaries and the critical temperature for the liquid-gas phase transition, and the composition depends more sensitively on the number of trapped neutrinos and temperature of the protoneutron star. The influence of hyperons in the dense interior of stars makes the overall equation of state soft. However, neutrino trapping distinctly delays the appearance of hyperons because of an abundance of electrons. We also find that a softer symmetry energy further makes the onset of hyperon less favorable. The resulting structures of the (proto)neutron stars with hyperons and with liquid-gas phase transition are discussed.

Sharma, Bharat K.; Pal, Subrata [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

2010-11-15

281

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

282

GRAVITATIONAL WAVES AND THE MAXIMUM SPIN FREQUENCY OF NEUTRON STARS  

SciTech Connect

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

Patruno, Alessandro; Haskell, Brynmor; D'Angelo, Caroline [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam (Netherlands)

2012-02-10

283

I-Q Relation for Rapidly Rotating Neutron Stars  

NASA Astrophysics Data System (ADS)

We consider a universal relation between moment of inertia and quadrupole moment of arbitrarily fast rotating neutron stars. Recent studies suggest that this relation breaks down for fast rotation. We find that it is still universal among various suggested equations of state for constant values of certain dimensionless parameters characterizing the magnitude of rotation. One of these parameters includes the neutron star radius, leading to a new universal relation expressing the radius through the mass, frequency, and spin parameter. This can become a powerful tool for radius measurements.

Chakrabarti, Sayan; Delsate, Térence; Gürlebeck, Norman; Steinhoff, Jan

2014-05-01

284

Decoupling of superfluid and normal modes in pulsating neutron stars  

NASA Astrophysics Data System (ADS)

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

Gusakov, Mikhail E.; Kantor, Elena M.

2011-04-01

285

Decoupling of superfluid and normal modes in pulsating neutron stars  

SciTech Connect

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

Gusakov, Mikhail E. [Ioffe Physical Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation); Kantor, Elena M. [Ioffe Physical Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation); St. Petersburg State Polytechnical University, Polytekhnicheskaya 29, 195251 St. Petersburg (Russian Federation)

2011-04-15

286

Hyperons and nuclear symmetry energy in neutron star matter  

SciTech Connect

In this work, masses and radii of neutron stars are considered to investigate the effect of nuclear symmetry energy on astrophysical observables. A relativistic mean-field model with density-dependent meson-baryon coupling constants is employed in describing the equation of state of dense nuclear matter, and the density dependencies of the symmetry energies are quoted from the recent phenomenological formulas obtained from heavy-ion data at subnuclear saturation densities. Since hyperons can take part in the {beta}-equilibrium of the dense matter inside neutron stars, we include hyperons in our estimation and their roles are discussed in combination with that of the nuclear symmetry energy.

Ryu, Chung-Yeol [Department of Physics, Hanyang University, Seoul 133-791 (Korea, Republic of); Hyun, Chang Ho [Department of Physics Education, Daegu University, Gyeongsan 712-714 (Korea, Republic of); Lee, Chang-Hwan [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of)

2011-09-15

287

Equation of state of nucleon matter and neutron star structure  

Microsoft Academic Search

Properties of dense nucleon matter and the structure of neutron stars are\\u000astudied using variational chain summation methods and the new Argonne v18\\u000atwo-nucleon interaction. The neutron star gravitational mass limit obtained\\u000awith this interaction is 1.67 M_{solar}. Boost corrections to the two-nucleon\\u000ainteraction, which give the leading relativistic effect of order (v\\/c)^2, as\\u000awell as three-nucleon interactions, are also

A. Akmal; V. R. Pandharipande; D. G. Ravenhall

1998-01-01

288

Tables of model atmospheres of bursting neutron stars  

NASA Technical Reports Server (NTRS)

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

Madej, Jerzy

1991-01-01

289

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

290

Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

291

Continuous gravitational waves from isolated Galactic neutron stars in the advanced detector era  

NASA Astrophysics Data System (ADS)

We consider a simulated population of isolated Galactic neutron stars. The rotational frequency of each neutron star evolves through a combination of electromagnetic and gravitational-wave emission. The magnetic field strength dictates the dipolar emission, and the ellipticity (a measure of a neutron star’s deformation) dictates the gravitational-wave emission. Through both analytic and numerical means, we assess the detectability of the Galactic neutron star population and bound the magnetic field strength and ellipticity parameter space of Galactic neutron stars with or without a direct gravitational-wave detection. While our simulated population is primitive, this work establishes a framework by which future efforts can be conducted.

Wade, Leslie; Siemens, Xavier; Kaplan, David L.; Knispel, Benjamin; Allen, Bruce

2012-12-01

292

Population synthesis of old neutron stars in the galaxy  

NASA Astrophysics Data System (ADS)

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 velocity 0 (V) 550 km s-1. The spin-down induced by dipole losses and the interaction with the ambient medium is tracked together with the dynamical evolution in the Galactic potential, allowing for the determination of the fraction of stars which are, at present, in each of the four possible stages: ejector, propeller, accretor, and georotator. Taking from the ROSAT All Sky Survey an upper limit of 10 accreting neutron stars within 140 pc from the Sun, we infer a lower bound for the mean kick velocity, (V) 200-300 km s-1. The same conclusion is reached for both a constant (B 10l2 G) and a magnetic field decaying exponentially with a timescale ˜ 109 yr. Present results, moreover, constrain the fraction of low-velocity stars, which could have escaped pulsar statistics, to ? 1%.

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

293

Population Synthesis of Old Neutron Stars in the Galaxy  

NASA Astrophysics Data System (ADS)

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 velocity 0 LE LE 550 km/s. The spin-down, induced by dipole losses and the interaction with the ambient medium, is tracked together with the dynamical evolution in the Galactic potential, allowing for the determination of the fraction of stars which are, at present, in each of the four possible stages: Ejector, Propeller, Accretor, and Georotator. Taking from the ROSAT All-Sky Survey an upper limit of ~10 accreting neutron stars within ~140 pc from the Sun, we infer a lower bound for the mean kick velocity, GT (or approximately) 200--300 km/s. The same conclusion is reached for both a constant (B ~1012 G) and an exponentially decaying magnetic field with a timescale ~109 yr. Present results, moreover, constrain the fraction of low-velocity stars which could have escaped pulsar statistics to < (or approximately) 1%.

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

2000-05-01

294

Mixed neutron-star-plus-wormhole systems: Linear stability analysis  

NASA Astrophysics Data System (ADS)

We consider configurations consisting of a neutron star with a wormhole at the core. The wormhole is held open by a ghost scalar field with a quartic coupling. The neutron matter is described by a perfect fluid with a polytropic equation of state. We obtain static regular solutions for these systems. A stability analysis, however, shows that they are unstable with respect to linear perturbations.

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

2013-05-01

295

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

Microsoft Academic Search

In the inner crust of a neutron star, at densities above the “drip” threshold, unbound “conduction” neutrons can move freely past through the ionic lattice formed by the nuclei. The relative current density ni=nv¯i of such conduction neutrons will be related to the corresponding mean particle momentum pi by a proportionality relation of the form ni=Kpi in terms of a

Brandon Carter; Nicolas Chamel; Pawel Haensel

2005-01-01

296

The magnetosphere of an oscillating neutron star. Non-vacuum treatment  

Microsoft Academic Search

We generalize a formula for the Goldreich-Julian charge density (rhoGJ), originally derived for a rotating neutron star, for arbitrary oscillations of a neutron star with an arbitrary magnetic field configuration under the assumption of low current density in the inner parts of the magnetosphere. As an application, we consider the toroidal oscillation of a neutron star with a dipole magnetic

A. N. Timokhin; G. S. Bisnovatyi-Kogan; H. C. Spruit

2000-01-01

297

Accretion of Matter onto Highly Magnetized Neutron Stars: Final Report, July 1-September 30, 1985.  

National Technical Information Service (NTIS)

A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns. (ERA citation 12:044375)

L. Hernquist

1986-01-01

298

Perturbative approach to the structure of rapidly rotating neutron stars  

SciTech Connect

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

Benhar, Omar; Ferrari, Valeria; Gualtieri, Leonardo [Dipartimento di Fisica 'G. Marconi', Universita degli Studi di Roma, 'La Sapienza', P.le A. Moro 2, 00185 Rome (Italy); INFN, Sezione Roma 1, P.le A. Moro 2, 00185 Rome (Italy); Marassi, Stefania [Dipartimento di Fisica 'G. Marconi', Universita degli Studi di Roma, 'La Sapienza', P.le A. Moro 2, 00185 Rome (Italy)

2005-08-15

299

Dark matter, neutron stars, and strange quark matter.  

PubMed

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

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

2010-10-01

300

Further stable neutron star models from f(R) gravity  

NASA Astrophysics Data System (ADS)

Neutron star models in perturbative f(R) gravity are considered with realistic equations of state. In particular, we consider the FPS, SLy and other equations of state and a case of piecewise equation of state for stars with quark cores. The mass-radius relations for f(R) = R+R(e-R/R0-1) model and for R2 models with logarithmic and cubic corrections are obtained. In the case of R2 gravity with cubic corrections, we obtain that at high central densities (? > 10?ns, where ?ns = 2.7 × 1014 g/cm3 is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ~ 1.9Msolar (SLy equation). A similar situation takes place for AP4 and BSK20 EoS. Such an effect can give rise to more compact stars than in General Relativity. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level. Another interesting result can be achieved in modified gravity with only a cubic correction. For some EoS, the upper limit of neutron star mass increases and therefore these EoS can describe realistic star configurations (although, in General Relativity, these EoS are excluded by observational constraints).

Astashenok, Artyom V.; Capozziello, Salvatore; Odintsov, Sergei D.

2013-12-01

301

Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity  

Microsoft Academic Search

We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can be formed in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both act on differentially rotating stars to redistribute angular momentum. Simulations of these stars are carried out in axisymmetry using our recently developed codes which

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

2006-01-01

302

High space velocities of single radio pulsars versus low orbital eccentricities and masses of double neutron stars: Evidence for two different neutron star formation mechanisms  

NASA Astrophysics Data System (ADS)

Radio pulsars tend to be high-velocity objects, which implies that the majority of them received a velocity kick of several hundreds of km s -1 at birth. However, six of the eight known double neutron stars in the galactic disk have quite low orbital eccentricities (0.085-0.27), indicating - taking into account the eccentricity induced by the mass-loss effects in the second supernova - that their second-born neutron stars received hardly any velocity kick at birth. The second-born neutron stars in these systems tend to have low masses (1.25 ± 0.07 M ?) and the same is true for the neutron star in the close white dwarf-neutron star system PSRJ 1145-6545, which also is the second-born star in a system of low eccentricity ( e = 0.17). Such a low mass would fit well with the formation of the second-born neutron stars by the electron-capture collapse of a Chandrasekhar-mass degenerate O-Ne-Mg core of stars of initial main-sequence mass between 8 and about 12 M ?. Podsiadlowski et al. (2004) have pointed out that neutron-star formation in this mass range is possible only if the star is in a close binary, following loss of the hydrogen envelope, while single stars can leave neutron stars only if they started out with masses above about 12 M ?; in the latter case a neutron star forms by the final collapse of an iron core. We point out here that the low masses of the second-born neutron stars in the low-eccentricity double neutron stars, together with the high space velocities of the single radio pulsars find a consistent explanation if one postulates, following ( Van den Heuvel, 2004; Podsiadlowski et al., 2004; Dewi et al., 2005) that neutron stars formed by electron-capture collapse of a degenerate O-Ne-Mg core receive hardly any kick velocity at birth, whereas neutron stars formed by iron-core collapse receive a large space velocity at birth. The existence of a population of low-kick neutron stars in binaries has important implications for understanding the formation of the neutron star population of globular clusters and for the origin of low-mass X-ray binaries and their descendants, the wide circular-orbit binary radio pulsars.

van den Heuvel, Edward P. J.

2010-03-01

303

Deformation of a magnetized neutron star  

NASA Astrophysics Data System (ADS)

Magnetars are compact stars, which are observationally determined to have very strong surface magnetic fields of the order of 1014-1015 G. The center of the star can potentially have a magnetic field several orders of magnitude larger. We study the effect of the field on the mass and shape of such a star. In general, we assume a nonuniform magnetic field inside the star, which varies with density. The magnetic energy and pressure as well as the metric are expanded as multipoles in spherical harmonics up to the quadrupole term. Solving the Einstein equations for the gravitational potential, one obtains the correction terms as functions of the magnetic field. Using a nonlinear model for the hadronic EoS the excess mass and change in equatorial radius of the star due to the magnetic field are quite significant if the surface field is 1015 G and the central field is about 1018 G. For a value of the central magnetic field strength of 1.75×1018 G, we find that both the excess mass and the equatorial radius of the star changes by about 3-4% compared to the spherical solution.

Mallick, Ritam; Schramm, Stefan

2014-04-01

304

Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter  

SciTech Connect

We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the {sup 3}P{sub 2} channel. We find that the critical temperature for this superfluid transition is {approx_equal}0.5x10{sup 9} K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star.

Page, Dany [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Mexico D.F. 04510 (Mexico); Prakash, Madappa [Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701-2979 (United States); Lattimer, James M. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States); Steiner, Andrew W. [Joint Institute for Nuclear Astrophysics, National Superconducting Cyclotron Laboratory and, Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States)

2011-02-25

305

Rapid cooling of the neutron star in Cassiopeia A triggered by neutron superfluidity in dense matter.  

PubMed

We propose that the observed cooling of the neutron star in Cassiopeia A is due to enhanced neutrino emission from the recent onset of the breaking and formation of neutron Cooper pairs in the (3)P(2) channel. We find that the critical temperature for this superfluid transition is ?0.5×10(9) K. The observed rapidity of the cooling implies that protons were already in a superconducting state with a larger critical temperature. This is the first direct evidence that superfluidity and superconductivity occur at supranuclear densities within neutron stars. Our prediction that this cooling will continue for several decades at the present rate can be tested by continuous monitoring of this neutron star. PMID:21405561

Page, Dany; Prakash, Madappa; Lattimer, James M; Steiner, Andrew W

2011-02-25

306

Isolated neutron stars and studies of their interiors  

NASA Astrophysics Data System (ADS)

In these lectures presented at Baikal summer school on physics of elementary particles and astrophysics 2011, I present a wide view of neutron star astrophysics with special attention paid to young isolated compact objects and studies of the properties of their interiors using astronomical methods.

Popov, S. B.

2012-12-01

307

Can dark matter explain the braking index of neutron stars?  

NASA Astrophysics Data System (ADS)

We explore a new mechanism of slowing down the rotation of neutron stars via accretion of millicharged dark matter. We find that this mechanism yields pulsar braking indices that can be substantially smaller than the standard n˜3 of the magnetic dipole radiation model for millicharged dark matter particles that are not excluded by existing experimental constraints thus accommodating existing observations.

Kouvaris, Chris; Pérez-García, M. Ángeles

2014-05-01

308

The Neutron star Interior Composition ExploreR  

NASA Astrophysics Data System (ADS)

The Neutron star Interior Composition ExploreR (NICER) will be a NASA Explorer Mission of Opportunity, currently in a Phase A study, dedicated to the study of neutron stars, the only places in the Universe where all four fundamental forces of Nature are simultaneously important. Answering the long-standing astrophysics question "How big is a neutron star?," NICER will confront nuclear physics theory with unique observational constraints, exploring the exotic states of matter within neutron stars and revealing their interior and surface compositions through rotation-resolved X-ray spectroscopy. Absolute time-referenced data will allow NICER to probe the extreme physical environments of the most powerful cosmic particle accelerators known. Finally, NICER will definitively measure the stabilities of pulsars as clocks, with implications for gravitational-wave detection, a pulsar-based timescale, and autonomous spacecraft navigation. NICER will fly on the International Space Station while Fermi is in orbit and post-RXTE, enabling the discovery of new high-energy pulsars and providing continuity in X-ray timing astrophysics.

Arzoumanian, Zaven; Gendreau, K.; NICER Team

2012-01-01

309

Binary Neutron Stars in General Relativity: Quasiequilibrium Models  

Microsoft Academic Search

We perform fully relativistic calculations of binary neutron stars in quasiequilibrium circular orbits. We integrate Einstein's equations together with the relativistic equation of hydrostatic equilibrium to solve the initial-value problem for equal-mass binaries of arbitrary separation. We construct sequences of constant rest mass and identify the innermost stable circular orbit and its angular velocity. We find that the quasiequilibrium maximum

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

1997-01-01

310

The maximum mass of a cold neutron star  

Microsoft Academic Search

The maximum mass of a static cold neutron star is calculated according to the bimetric gravitation theory and according to the general relativity theory for an assumed equation of state containing two parameters. For a certain choice of the parameters, the bimetric maximum mass is found to be 8.1 solar masses, while that of general relativity is 1.46 solar masses,

J. Rosen; N. Rosen

1975-01-01

311

Quasiequilibrium black hole-neutron star binaries in general relativity  

Microsoft Academic Search

We construct quasiequilibrium sequences of black hole-neutron star binaries in general relativity. We solve Einstein's constraint equations in the conformal thin-sandwich formalism, subject to black hole boundary conditions imposed on the surface of an excised sphere, together with the relativistic equations of hydrostatic equilibrium. In contrast to our previous calculations we adopt a flat spatial background geometry and do not

Keisuke Taniguchi; Joshua A. Faber; Stuart L. Shapiro; Thomas W. Baumgarte

2007-01-01

312

On the Maximum Mass of Differentially Rotating Neutron Stars  

Microsoft Academic Search

We construct relativistic equilibrium models of differentially rotating neutron stars and show that they can support significantly more mass than their nonrotating or uniformly rotating counterparts. We dynamically evolve such ``hypermassive'' models in full general relativity and show that there do exist configurations that are dynamically stable against radial collapse and bar formation. Our results suggest that the remnant of

Thomas W. Baumgarte; Stuart L. Shapiro; Masaru Shibata

2000-01-01

313

Quark deconfinement in high-mass neutron stars  

NASA Astrophysics Data System (ADS)

In this paper, we explore whether or not quark deconfinement may occur in high-mass neutron stars such as J1614 - 2230 (1.97±0.04M?) and J0348 + 0432 (2.01±0.04M?). Our study is based on a nonlocal extension of the SU(3) Nambu-Jona-Lasinio (n3NJL) model with repulsive vector interactions among the quarks. This model goes beyond the frequently used local version of the Nambu-Jona-Lasinio (NJL) model by accounting for several key features of QCD which are not part of the local model. Confined hadronic matter is treated in the framework of nonlinear relativistic mean field theory. We find that both the local as well as the nonlocal NJL model predict the existence of extended regions of mixed quark-hadron (quark-hybrid) matter in high-mass neutron stars with masses of 2.1 to 2.4M?. Pure quark matter in the cores of neutron stars is obtained for certain parametrizations of the hadronic lagrangian and choices of the vector repulsion among quarks. The radii of high-mass neutron stars with quark-hybrid matter and/or pure quark matter cores in their centers are found to lie in the canonical range of 12 to 13 km.

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

2014-01-01

314

Generation of neutron star magnetic fields by thermomagnetic effects  

NASA Astrophysics Data System (ADS)

A linear stage of the magnetic field generation in outer (rho of less than about 10 to the 11th g/cu cm) layers of rather hot rotating neutron stars by thermomagnetic phenomena which accompany the heat transport from the stellar core is considered. For a neutron star with surface gravity of 10 to the 14th cm/second-squared whose envelope consists of degenerate electrons and Fe-56 ions in the fluid phase, the thermomagnetic instability is developed at surface temperatures, T(e), of more than about 3 million K and rotation periods of less than about 1 s. Axially-symmetric toroidal modes of magnetic field are unstable. In particular, at T(e) of 5 million K, the maximal instability increment equals 1/70 d and corresponds to the magnetic configuration with wavelength of about 80 m in the meridional direction and maximal field at a depth of about 40 m. At this T(e) the magnetic field modes with wavelengths of between about 30 m to 1 km are generated. If T(e) falls down to 3 million K due to the neutron star cooling, the instability increment decreases to zero, while the spectrum of wavelengths tightens to about 120 m. It is possible that at the nonlinear stage the proposed mechanism leads to the generation of strong magnetic fields of about 10 to the 10th to 10 to the 13th G present in the surface layers of neutron stars.

Urpin, V. A.; Levshakov, S. A.; Iakovlev, D. G.

1986-04-01

315

Constraints on the symmetry energy from neutron star observations  

NASA Astrophysics Data System (ADS)

The modeling of many neutron star observables incorporates the microphysics of both the stellar crust and core, which is tied intimately to the properties of the nuclear matter equation of state (EoS). We explore the predictions of such models over the range of experimentally constrained nuclear matter parameters, focusing on the slope of the symmetry energy at nuclear saturation density L. We use a consistent model of the composition and EoS of neutron star crust and core matter to model the binding energy of pulsar B of the double pulsar system J0737-3039, the frequencies of torsional oscillations of the neutron star crust and the instability region for r-modes in the neutron star core damped by electron-electron viscosity at the crust-core interface. By confronting these models with observations, we illustrate the potential of astrophysical observables to offer constraints on poorly known nuclear matter parameters complementary to terrestrial experiments, and demonstrate that our models consistently predict L < 70 MeV.

Newton, W. G.; Gearheart, M.; Wen, De-Hua; Li, Bao-An

2013-03-01

316

Equation-of-state-independent relations in neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars are extremely relativistic objects which abound in our universe and yet are poorly understood, due to the high uncertainty on how matter behaves in the extreme conditions which prevail in the stellar core. It has recently been pointed out that the moment of inertia I, the Love number ?, and the spin-induced quadrupole moment Q of an isolated neutron star, are related through functions which are practically independent of the equation of state. These surprising universal I-?-Q relations pave the way for a better understanding of neutron stars, most notably via gravitational-wave emission. Gravitational-wave observations will probe highly dynamical binaries and it is important to understand whether the universality of the I-?-Q relations survives strong-field and finite-size effects. We apply a post-Newtonian-affine approach to model tidal deformations in compact binaries and show that the I-? relation depends on the inspiral frequency, but is insensitive to the equation of state. We provide a fit for the universal relation, which is valid up to a gravitational wave frequency of ˜900Hz and accurate to within a few percent. Our results strengthen the universality of I-?-Q relations, and are relevant for gravitational-wave observations with advanced ground-based interferometers. We also discuss the possibility of using the Love-compactness relation to measure the neutron-star radius with an uncertainty ?10% from gravitational-wave observations.

Maselli, Andrea; Cardoso, Vitor; Ferrari, Valeria; Gualtieri, Leonardo; Pani, Paolo

2013-07-01

317

Gravitational Radiation and Rotation of Accreting Neutron Stars  

Microsoft Academic Search

Recent discoveries by the Rossi X-Ray Timing Explorer indicate that most of the rapidly accreting ( M dot >~10^{-11} Msolar {yr}^{-1} ) weakly magnetic ( B<<1011 G) neutron stars in the Galaxy are rotating at spin frequencies nu s>~250 Hz. Remarkably, they all rotate in a narrow range of frequencies (no more than a factor of 2, with many within

Lars Bildsten

1998-01-01

318

The cooling of quasi-persistent neutron star transients  

NASA Astrophysics Data System (ADS)

Neutron star transients with outburst durations of several years allow observations to constrain the cooling rate of the heated neutron star crust. Pycnonuclear reactions in the crust heat the neutron star interior and can elevate the crust temperature considerably with respect to that of the core if the thermal conductivity is sufficiently low. For various scenarios of the physics of the crust and core, we have computed families of quiescent lightcurves for different outburst durations, accretion rates, and quiescent intervals. I will compare these lightcurves with observations, and highlight recent efforts to compute the nuclear reaction chains in the crust for a realistic distribution of rp-process ashes. The unstable ignition of carbon, which powers superbursts, is strongly dependent on the temperature in the neutron star crust and is thus also sensitive to the physics of the crust and core. Interestingly, KS1731-260 had at least one superburst during its protracted accr! etion outburst but also had a rapidly declining quiescent luminosity. I will compare the superburst ignition conditions from our time-dependent calculations with observations.

Brown, Edward

319

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

320

Hydromagnetic equilibrium in non-barotropic multifluid neutron stars  

NASA Astrophysics Data System (ADS)

Traditionally, the subject of hydromagnetic equilibrium in neutron stars has been addressed in the context of standard magnetohydrodynamics, with matter obeying a barotropic equation of state. In this paper we take a step towards a more realistic treatment of the problem by considering neutron stars with interior superfluid components. In this multifluid model, stratification associated with a varying matter composition (the relative proton to neutron density fraction) enters as a natural ingredient, leading to a non-barotropic system. After formulating the hydromagnetic equilibrium of superfluid/superconducting neutron stars as a perturbation problem, we focus on the particular case of a three-fluid system consisting of superfluid neutrons and normal protons and electrons. We determine the equilibrium structure of dipolar magnetic fields with a mixed poloidal-toroidal composition. We find that, with respect to barotropic models, stratification has the generic effect of leading to equilibria with a higher fraction of magnetic energy stored in the toroidal component. However, even in models with strong stratification, the poloidal and toroidal components are comparable, with the former contributing the bulk of the magnetic energy.

Glampedakis, K.; Andersson, N.; Lander, S. K.

2012-02-01

321

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

2013-09-27

322

Correlation energy of nuclear matter and neutron star masses  

SciTech Connect

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

Trojan, Ernst; Vlasov, George V. [Moscow Institute for Physics and Technology, P. O. Box 3, Moscow 125080 (Russian Federation)

2010-04-15

323

A Theoretical Analysis of Thermal Radiation from Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Applegate, James H.

1993-01-01

324

Gravity Wave Oscillations from Rapidly Rotating Neutron Stars  

NASA Astrophysics Data System (ADS)

The association of the nearly coherent brightness oscillations during thermonuclear X-ray bursts from neutron star low-mass X-ray binaries with the rotation period of these neutron stars raises the possibility that these stars are spinning fast enough to become unstable to gravity wave radiation. In such cases, the surface deformations caused by the gravity wave instability may be sufficient to create a secondary brightness oscillation of a few hundred hertz in the X-ray spectrum. So far, no positive identification of such a secondary oscillation frequency has been made, but we review some tantalizing hints from the Rossi X-ray Timing Explorer measurements of Aql X-1.

Fragile, P. C.; Mathews, G. J.; Wilson, J. R.

1999-12-01

325

Deep crustal heating in a multicomponent accreted neutron star crust  

NASA Astrophysics Data System (ADS)

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

Steiner, Andrew W.

2012-05-01

326

The ? Well Depth and the Proto Neutron Star Matter  

NASA Astrophysics Data System (ADS)

The effect of the ? well depth U_{\\varSigma}^{(N)} on a proto neutron star (PNS) is examined within the framework of relativistic mean field theory for the baryon octet system. It is found that the well depth U_{\\varSigma}^{(N)} will affect the structures of the PNS. With the well depth U_{\\varSigma}^{(N)} growing from 0 to 30 MeV, the field strength of meson ?, the chemical potentials of electrons and neutrons, the relative number density of p, e, ?, ?, ? 0, the mass and the pressure of a PNS all increase while the relative number density of n, ? -, ? -, ? 0, ? + decrease. It is also found that the larger changes of the hyperon coupling constants, which is connected to the ? well depth U_{\\varSigma}^{(N)}, will lead to the smaller changes in the neutron star mass and this shows the mass of PNS is not very sensitive to the hyperon coupling constants.

Zhao, Xian-Feng; Zhang, Li

2013-02-01

327

Accreting neutron star spins and the equation of state  

SciTech Connect

X-ray timing of neutron stars in low-mass X-ray binaries (LMXBs) with the Rossi X-ray Timing Explorer has since 1996 revealed several distinct high-frequency phenomena. Among these are oscillations during thermonuclear (type-I) bursts, which (in addition to persistent X-ray pulsations) are thought to trace the neutron star spin. The recent discoveries of 294 Hz burst oscillations in IGR J17191-2821, and 182 Hz pulsations in Swift J1756.9-2508, brings the total number of measured LMXB spin rates to 22. An open question is why the majority of the {approx_equal}100 known neutron stars in LMXBs show neither pulsations nor burst oscillations.Recent observations suggest that persistent pulsations may be more common than previously thought, although detectable intermittently, and in some cases at very low duty cycles. For example, the 377.3 Hz pulsations in HETE J1900.1-2455 were only present in the first few months of it's outburst, and have been absent since (although X-ray activity continues). Intermittent (persistent) pulsations have since been detected in a further two sources. In two of these three systems the pulsations appear to be related to the thermonuclear burst activity, but in the third (Aql X-1) they are not. This phenomenon offers new opportunities for spin measurements in known systems.Such measurements can constrain the poorly-known neutron star equation of state, and neutron stars in LMXBs offer observational advantages over rotation-powered pulsars which make the detection of more rapidly-spinning examples more likely. Even so, spin rates of at least 50% faster than the present maximum appear necessary to give constraints stringent enough to discriminate between the various models. Although the future prospects for such rapidly-spinning objects do not appear optimistic, several additional observational approaches are possible for LMXBs. The recent study of EXO 0748-676 is an example.

Galloway, Duncan [School of Physics and School of Mathematical Sciences, Monash University, VIC 3800 (Australia)

2008-02-27

328

Recycling of neutron stars in common envelopes and hypernova explosions  

NASA Astrophysics Data System (ADS)

In this paper, we propose a new plausible mechanism of supernova explosions specific to close binary systems. The starting point is the common envelope phase in the evolution of a binary consisting of a red supergiant and a neutron star. As the neutron star spirals towards the centre of its companion it spins up via disc accretion. Depending on the specific angular momentum of the gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach millisecond periods either when it is still inside the common envelope or after it has merged with the companion core. The high accretion rate may result in the strong differential rotation of the neutron star and generation of the magnetar-strength magnetic field. The magnetar wind can blow away the common envelope if its magnetic field is as strong as 1015 G and can destroy the entire companion if it is as strong as 1016 G. The total explosion energy can be comparable to the rotational energy of a millisecond pulsar and reach 1052 erg. However, only a small amount of 56Ni is expected to be produced this way. The result is an unusual Type II supernova with very high luminosity during the plateau phase, followed by a sharp drop in brightness and a steep light-curve tail. The remnant is either a solitary magnetar or a close binary involving a Wolf-Rayet star and a magnetar. When this Wolf-Rayet star explodes, it will be a third supernova explosion in the same binary.

Barkov, Maxim V.; Komissarov, Serguei S.

2011-07-01

329

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

NASA Technical Reports Server (NTRS)

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

Thompson, David J.

2010-01-01

330

Dark matter seeding in neutron stars  

NASA Astrophysics Data System (ADS)

We present a mechanism that may seed compact stellar objects with stable lumps of quark matter, or strangelets, through the self-annihilation of gravitationally accreted WIMPs. We show that dark matter particles with masses above a few GeV may provide enough energy in the nuclear medium for quark deconfinement and subsequent strangelet formation. If this happens this effect may then trigger a partial or full conversion of the star into a strange star. We set a new limit on the WIMP mass in the few-GeV range that seems to be consistent with recent indications in dark matter direct detection experiments.

Pérez-García, M. Ángeles; Silk, Joseph; Stone, Jirina R.

2012-04-01

331

Binding Energies of Hyperonic Matter and Applications to Neutron Stars  

SciTech Connect

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

Uechi, Hiroshi [Department of Distributions and Communication Sciences, Osaka Gakuin University, Osaka (Japan); Uechi, Schun T. [Research Center for Nuclear Physics (RCNP), Osaka University, Osaka (Japan)

2011-10-21

332

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

333

Tidal excitation of normal modes in eccentric binary neutron stars  

NASA Astrophysics Data System (ADS)

Neutron star binaries offer a rich phenomenology in terms of gravitational waves and merger remnants. However, most general relativistic studies have been performed for nearly circular binaries, with the exception of head-on collisions. We present the first numerical relativity investigation of mergers of eccentric neutron-star binaries that probes the regime between head-on and circular. Upon variation of the initial eccentricity, covering cases from direct plunge to more adiabatic inspiral, we study the outcome of a binary composed of two 1.4M neutron stars. We characterize the gravitational wave emission, the internal dynamics of the stars and the properties of the merger remnant. In addition to gravitational waves generated by the orbital motion, we find that the signal also contains a strong component due to stellar oscillations (f-modes) induced by tidal forces, extending a classical result for Newtonian binaries. Such signatures may be used to constrain the NS equation of state. With the exception of extreme eccentricities (near head-on collisions) the merger leads generically to rather massive disks, which in some cases can be on the order of 10% of the total initial mass. All merger remnants form a black hole making such encounters a plausible SGRB engine.

Gold, Roman; Bernuzzi, Sebastiano; Thierfelder, Marcus; Bruegmann, Bernd; Pretorius, Frans

2012-03-01

334

PSR J1840-1419: A VERY COOL NEUTRON STAR  

SciTech Connect

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

Keane, E. F.; Kramer, M. [Max Planck Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)] [Max Planck Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); McLaughlin, M. A. [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States)] [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States); Stappers, B. W.; Bassa, C. G.; Purver, M. B.; Weltevrede, P. [University of Manchester, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, Manchester M13 9PL (United Kingdom)] [University of Manchester, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, Manchester M13 9PL (United Kingdom)

2013-02-20

335

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment  

NASA Technical Reports Server (NTRS)

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

Lai, Dong; Shapiro, Stuart L.

1995-01-01

336

Investigating Superconductivity in Neutron Star Interiors with Glitch Models  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

337

INVESTIGATING SUPERCONDUCTIVITY IN NEUTRON STAR INTERIORS WITH GLITCH MODELS  

SciTech Connect

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

Haskell, B. [Astronomical Institute ''Anton Pannekoek'', University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands); Pizzochero, P. M.; Seveso, S. [Dipartimento di Fisica, Universita degli Studi di Milano, Via Celoria 16, I-20133 Milano (Italy)

2013-02-20

338

A NEW CODE FOR PROTO-NEUTRON STAR EVOLUTION  

SciTech Connect

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

Roberts, L. F., E-mail: lroberts@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2012-08-20

339

Effective no-hair relations for neutron stars and quark stars: Relativistic results  

NASA Astrophysics Data System (ADS)

Astrophysical charge-free black holes are known to satisfy no-hair relations through which all multipole moments can be specified in terms of just their mass and spin angular momentum. We here investigate the possible existence of no-hair-like relations among multipole moments for neutron stars and quark stars that are independent of their equation of state. We calculate the multipole moments of these stars up to hexadecapole order by constructing uniformly rotating and unmagnetized stellar solutions to the Einstein equations. For slowly rotating stars, we construct stellar solutions to quartic order in spin in a slow-rotation expansion, while for rapidly rotating stars, we solve the Einstein equations numerically with the LORENE and RNS codes. We find that the multipole moments extracted from these numerical solutions are consistent with each other and agree with the quartic-order slow-rotation approximation for spin frequencies below roughly 500 Hz. We also confirm that the current dipole is related to the mass quadrupole in an approximately equation-of-state-independent fashion, which does not break for rapidly rotating neutron stars or quark stars. We further find that the current-octupole and the mass-hexadecapole moments are related to the mass quadrupole in an approximately equation-of-state-independent way to roughly O(10%), worsening in the hexadecapole case. All of our findings are in good agreement with previous work that considered stellar solutions to leading order in a weak-field, Newtonian expansion. In fact, the hexadecapole-quadrupole relation agrees with the Newtonian one quite well even in moderately relativistic regimes. The quartic in spin, slowly rotating solutions found here allows us to estimate the systematic errors in the measurement of the neutron star's mass and radius with future x-ray observations, such as Neutron star Interior Composition ExploreR (NICER) and Large Observatory for X-ray Timing (LOFT). We find that the effect of these quartic-in-spin terms on the quadrupole and hexadecapole moments and stellar eccentricity may dominate the error budget for very rapidly rotating neutron stars. The new universal relations found here should help to reduce such systematic errors.

Yagi, Kent; Kyutoku, Koutarou; Pappas, George; Yunes, Nicolás; Apostolatos, Theocharis A.

2014-06-01

340

Discovery of a Neutron Star Oscillation Mode During a Superburst  

NASA Astrophysics Data System (ADS)

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

Strohmayer, Tod E.; Mahmoodifar, Simin

2014-08-01

341

Axisymmetric Toroidal Modes of General Relativistic Magnetized Neutron Star Models  

NASA Astrophysics Data System (ADS)

We calculate axisymmetric toroidal modes of magnetized neutron stars with a solid crust in the general relativistic Cowling approximation. We assume that the interior of the star is threaded by a poloidal magnetic field, which is continuous at the surface with an outside dipole field. We examine the cases of the field strength B S ~ 1016 G at the surface. Since separation of variables is not possible for the oscillations of magnetized stars, we employ finite series expansions for the perturbations using spherical harmonic functions. We find discrete normal toroidal modes of odd parity, but no toroidal modes of even parity are found. The frequencies of the toroidal modes form distinct mode sequences and the frequency in a given mode sequence gradually decreases as the number of radial nodes of the eigenfunction increases. From the frequency spectra computed for neutron stars of different masses, we find that the frequency is almost exactly proportional to B S and is well represented by a linear function of R/M for a given B S, where M and R are the mass and radius of the star. The toroidal mode frequencies for B S ~ 1015 G are in the frequency range of the quasi-periodic oscillations (QPOs) detected in the soft-gamma-ray repeaters, but we find that the toroidal normal modes cannot explain all the detected QPO frequencies.

Asai, Hidetaka; Lee, Umin

2014-07-01

342

Stellar encounters involving neutron stars in globular cluster cores  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

343

Merger of a Neutron Star with a Newtonian Black Hole  

NASA Technical Reports Server (NTRS)

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

Lee, William H.; Kluzniak, Wlodzimierz

1995-01-01

344

Competition of neutrino and gravitational radiation in neutron star formation  

NASA Technical Reports Server (NTRS)

An investigation is conducted concerning the possibility that neutrino radiation rather than gravitational radiation may be the dominant way by which nonradial pulsations are damped out in a collapsing star. The effects of neutrino radiation on the nonradial oscillations of such objects are examined and damping times corresponding to a particular neutrino production mechanism are evaluated. The obtained results imply that neutrino radiation, by more rapid damping of the nonradial oscillations of a newly formed neutron star in a supernova explosion, would hinder gravitational radiation, thus reducing the possibility of its detection.

Kazanas, D.; Schramm, D. N.

1976-01-01

345

Neutron-star formation in the carbon-detonation supernova.  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

346

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

Microsoft Academic Search

Fusion reactions in the crust of an accreting neutron star are an important\\u000asource of heat, and the depth at which these reactions occur is important for\\u000adetermining the temperature profile of the star. Fusion reactions depend\\u000astrongly on the nuclear charge $Z$. Nuclei with $Z\\\\le 6$ can fuse at low\\u000adensities in a liquid ocean. However, nuclei with Z=8

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

2008-01-01

347

Neutron star properties and the equation of state of neutron-rich matter  

SciTech Connect

We calculate total masses and radii of neutron stars for pure neutron matter and nuclear matter in {beta} equilibrium. We apply a relativistic nuclear matter equation of state derived from Dirac-Brueckner-Hartree-Fock calculations. We use realistic nucleon-nucleon interactions defined in the framework of the meson exchange potential models. Our results are compared with other theoretical predictions and recent observational data. Suggestions for further study are discussed.

Krastev, P. G.; Sammarruca, F. [Physics Department, University of Idaho, Moscow, Idaho 83844 (United States)

2006-08-15

348

Einstein-Maxwell field equations in isotropic coordinates: an application to neutron star and quark star  

NASA Astrophysics Data System (ADS)

We present a new class of static spherically symmetric exact solutions of the Einstein-Maxwell field equations in isotropic coordinates for perfect fluid by considering a specific choice of electrical intensity which involves a parameter K. The resulting solutions represent charged fluid spheres joining smoothly with the Reissner-Nordstrom metric at the pressure free interface. The solutions so obtained are utilized to construct the models for super-dense star like neutron stars ( ? b =2 and 2.7×1014 g/cm3) and Quark stars ( ? b =4.6888×1014 g/cm3). It is observed that the models are well behaved for the restricted value of parameter K (0.141? K?0.159999). Corresponding to K max =0.159999 for which, u max =0.259, the resulting Quark star has a maximum mass M=1.618 M ? and radius R=9.263 km and the neutron star modeling based on the particular solution; corresponding to K=0.15, u=0.238 and by assuming the surface density ? b =2.7×1014 g/cm3 the maximum mass of neutron star M=1.966 M ? and radius R=12.23 km and by assuming the surface density ? b =2×1014 g/cm3 the resulting well behaved solution has a maximum mass of neutron M=2.284 M ? and radius R=14.21 km. The robustness of our result is that it matches with the recent discoveries.

Pradhan, N.; Pant, Neeraj

2014-07-01

349

On radial oscillations in viscous accretion discs surrounding neutron stars  

NASA Technical Reports Server (NTRS)

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding neutron stars in X-ray binary systems have been investigated. Within the framework of the alpha-viscosity model a series of hydrodynamic calculations demonstrates that the oscillations are global for alpha of about 1. On the other hand, for alpha of 0.4 or less, the oscillations are local and confined to the disk boundaries. If viscous stresses acting in the radial direction are included, however, it is found that the disk can be stabilized. The application of such instabilities in accretion disks, without reference to the boundary layer region between the neutron star (or magnetosphere) and the inner edge of the disk, to the phenomenology of quasi-periodic oscillations is brought into question.

Chen, Xingming; Taam, Ronald E.

1992-01-01

350

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

PubMed

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

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

2013-08-01

351

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

352

Systematic Parameter Errors in Inspiraling Neutron Star Binaries  

NASA Astrophysics Data System (ADS)

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

Favata, Marc

2014-03-01

353

Shear viscosity due to phonons in superfluid neutron stars  

NASA Astrophysics Data System (ADS)

We compute the contribution of phonons to the shear viscosity ? in superfluid neutron stars, assuming neutron pairing in a S01 channel. We use a Boltzmann equation amended by a collision term that takes into account the binary collisions of phonons. We use effective field theory techniques to extract the phonon scattering rates, written as a function of the equation of state of the system. Our formulation is rather general, and can be used to extract the shear viscosity due to binary collisions of phonons for other superfluids, such as the cold Fermi gas in the unitarity limit. We find that ??1/T5, the proportionality factor depending on the equation of state of the system. Our results indicate that the phonon contribution to ? cannot be ignored and might have relevant effects in the dynamics of the different oscillation modes of the star.

Manuel, Cristina; Tolos, Laura

2011-12-01

354

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

355

Oscillation spectra of neutron stars with strong magnetic fields  

NASA Technical Reports Server (NTRS)

The effects of strong frozen-in vertical magnetic fields on nonradial oscillation spectra in neutron stars are investigated theoretically, focusing on the surface layers near the polar cap of a cylindrically symmetric neutron-star model with shear-supporting crust and molten-crust oceans. The pulsation equations are derived; analytical estimates are obtained; and the results of numerical experiments are presented in tables and graphs. Significant modifications in the frequencies and displacements of the modes are found when a magnetic field is present: Alfven-like g modes (designated magneto-gravity), pseudotoroidal a modes with periods less than 100 ns for a 1-TG field, p-mode displacements almost totally parallel to the field, and a mode spectrum for periods of 100 microsec or more comprising only t, s, and p modes at 1 TG.

Carroll, B. W.; Savedoff, M. P.; Zweibel, E. G.; Hansen, C. J.; Mcdermott, P. N.

1986-01-01

356

Symmetry energy, unstable nuclei and neutron star crusts  

NASA Astrophysics Data System (ADS)

The phenomenological approach to inhomogeneous nuclear matter is useful to describe fundamental properties of atomic nuclei and neutron star crusts in terms of the equation of state of uniform nuclear matter. We review a series of researches that we have developed by following this approach. We start with more than 200 equations of state that are consistent with empirical masses and charge radii of stable nuclei and then apply them to describe matter radii and masses of unstable nuclei, proton elastic scattering and total reaction cross sections off unstable nuclei, and nuclei in neutron star crusts including nuclear pasta. We finally discuss the possibility of constraining the density dependence of the symmetry energy from experiments on unstable nuclei and even observations of quasi-periodic oscillations in giant flares of soft gamma-ray repeaters.

Iida, Kei; Oyamatsu, Kazuhiro

2014-02-01

357

Measuring neutron-star ellipticity with measurements of the stochastic gravitational-wave background  

NASA Astrophysics Data System (ADS)

Galactic neutron stars are a promising source of gravitational waves in the analysis band of detectors such as Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo. Previous searches for gravitational waves from neutron stars have focused on the detection of individual neutron stars, which are either nearby or highly nonspherical. Here, we consider the stochastic gravitational-wave signal arising from the ensemble of Galactic neutron stars. Using a population synthesis model, we estimate the single-sigma sensitivity of current and planned gravitational-wave observatories to average neutron star ellipticity ? as a function of the number of in-band Galactic neutron stars Ntot. For the plausible case of Ntot?53000, and assuming one year of observation time with colocated initial LIGO detectors, we find it to be ??=2.1×10-7, which is comparable to current bounds on some nearby neutron stars. (The current best 95% upper limits are ? ?7×10-8.) It is unclear if Advanced LIGO can significantly improve on this sensitivity using spatially separated detectors. For the proposed Einstein Telescope, we estimate that ??=5.6×10-10. Finally, we show that stochastic measurements can be combined with measurements of individual neutron stars in order to estimate the number of in-band Galactic neutron stars. In this way, measurements of stochastic gravitational waves provide a complementary tool for studying Galactic neutron stars.

Talukder, Dipongkar; Thrane, Eric; Bose, Sukanta; Regimbau, Tania

2014-06-01

358

Maximum mass of a Neutron star in metric theories of gravitation  

Microsoft Academic Search

A method is proposed of finding approximately the equilibrium configurations of nonrotating neutron stars without choosing any particular field equation for the metric. The method consists in choosing interpolation functions for the metric coefficients inside the star and matching them to that of the external metric at the body surface. In particular, the maximum mass a neutron star may have

Carlos O. Lousto

1987-01-01

359

Effects of Differential Rotation on the Maximum Mass of Neutron Stars  

Microsoft Academic Search

The merger of binary neutron stars is likely to lead to differentially rotating remnants. In this paper, we numerically construct models of differentially rotating neutron stars in general relativity and determine their maximum allowed mass. We model the stars by adopting a polytropic equation of state and tabulate maximum allowed masses as a function of differential rotation and stiffness of

Nicholas D. Lyford; Thomas W. Baumgarte; Stuart L. Shapiro

2003-01-01

360

Maximum mass of a neutron star in metric theories of gravitation  

Microsoft Academic Search

A method is proposed of finding approximately the equilibrium configurations of nonrotating neutron stars without choosing any particular field equation for the metric. The method consists in choosing interpolation functions for the metric coefficients inside the star and matching them to that of the external metric at the body surface. In particular, the maximum mass a neutron star may have

Carlos O. Lousto

1987-01-01

361

On the capture of dark matter by neutron stars  

NASA Astrophysics Data System (ADS)

We calculate the number of dark matter particles that a neutron star accumulates over its lifetime as it rotates around the center of a galaxy, when the dark matter particle is a self-interacting boson but does not self-annihilate. We take into account dark matter interactions with baryonic matter and the time evolution of the dark matter sphere as it collapses within the neutron star. We show that dark matter self-interactions play an important role in the rapid accumulation of dark matter in the core of the neutron star. We consider the possibility of determining an exclusion region of the parameter space for dark matter mass and dark matter interaction cross section with the nucleons as well as dark matter self-interaction cross section, based on the observation of old neutron stars. We show that for a dark matter density of 103 GeV/cm3and dark matter mass m? lesssim 10 GeV, there is a potential exclusion region for dark matter interactions with nucleons that is three orders of magnitude more stringent than without self-interactions. The potential exclusion region for dark matter self-interaction cross sections is many orders of magnitude stronger than the current Bullet Cluster limit. For example, for high dark matter density regions, we find that for m? ~ 10 GeV when the dark matter interaction cross section with the nucleons ranges from ??n ~ 10-52 cm2 to ??n ~ 10-57 cm2, the dark matter self-interaction cross section limit is ??? lesssim 10-33 cm2, which is about ten orders of magnitude stronger than the Bullet Cluster limit.

Güver, Tolga; Emre Erkoca, Arif; Hall Reno, Mary; Sarcevic, Ina

2014-05-01

362

Surface structure of neutron stars with high magnetic fields  

Microsoft Academic Search

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

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

1989-01-01

363

Binary Neutron Stars in General Relativity: Quasiequilibrium Models  

Microsoft Academic Search

We perform fully relativistic calculations of binary neutron stars in\\u000aquasi-equilibrium circular orbits. We integrate Einstein's equations together\\u000awith the relativistic equation of hydrostatic equilibrium to solve the initial\\u000avalue problem for equal-mass binaries of arbitrary separation. We construct\\u000asequences of constant rest mass and identify the innermost stable circular\\u000aorbit and its angular velocity. We find that the quasi-equilibrium

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

1997-01-01

364

Quasiequilibrium black hole-neutron star binaries in general relativity  

Microsoft Academic Search

We construct quasiequilibrium sequences of black hole-neutron star binaries\\u000ain general relativity. We solve Einstein's constraint equations in the\\u000aconformal thin-sandwich formalism, subject to black hole boundary conditions\\u000aimposed on the surface of an excised sphere, together with the relativistic\\u000aequations of hydrostatic equilibrium. In contrast to our previous calculations\\u000awe adopt a flat spatial background geometry and do not

Keisuke Taniguchi; Thomas W. Baumgarte; Joshua A. Faber; Stuart L. Shapiro

2007-01-01

365

A Neutron Star Atmosphere in the Laboratory With Petawatt Lasers  

Microsoft Academic Search

We discuss the preliminary estimates to create Neutron Star atmospheric conditions in the laboratory and the possibility of generating photon bubbles. The minimal requirements for photon-bubble instability could potentially be met with a properly configured 10 ps petawatt laser experiment. The high energy (multi-MeV) electrons generated by an ultra-intense laser interacting with a foil are coupled to the electrons in

S. J. Moon; S. C. Wilks; R. I. Klein; B. A. Remington; D. D. Ryutov; A. J. Mackinnon; P. K. Patel; A. Spitkovsky

2005-01-01

366

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

367

Advection-dominated Accretion: Underfed Black Holes and Neutron Stars  

Microsoft Academic Search

We describe new optically thin solutions for rotating accretion flows around black holes and neutron stars. These solutions are advection dominated, so that most of the viscously dissipated energy is advected radially with the flow. We model the accreting gas as a two-temperature plasma and include cooling by bremsstrahlung, synchrotron, and Comptonization. We obtain electron temperatures Te 108.5-1010 K. The

Ramesh Narayan; Insu Yi

1995-01-01

368

Magnetic field decay and the origin of neutron star binaries  

Microsoft Academic Search

The origin of magnetized neutron stars in binaries and the 1.55 ms pulsar is examined in terms of the magnetic field decay model for radio pulsars with a decay time scale of order 5 x 10 to the 6th yr over 7-10 e-foldings. Observational data of pulsing X-ray sources, nonpulsing X-ray sources, and binary radio pulsars are analyzed. Evolutionary scenarios

R. E. Taam; E. P. J. Van De Heuvel

1986-01-01

369

Uncovering the Properties of Young Neutron Stars and Their Surroundings  

NASA Technical Reports Server (NTRS)

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

Oliversen, Ronald (Technical Monitor); Slane, Patrick

2005-01-01

370

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

371

Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars  

Microsoft Academic Search

A Lagrangian, fully implicit, one-dimensional hydrodynamic computer code is used to evolve thermonuclear runaways in the accreted hydrogen-rich envelopes of 1.0-solar-mass neutron stars with radii of 10 km and 20 km. The simulations produce outbursts lasting from approximately 750 seconds to approximately one week. The peak effective temperatures and luminosities are 2.6 x 10 to the 7th K and 8

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

1982-01-01

372

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

373

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

Microsoft Academic Search

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

F. Douchin; P. Haensel

2001-01-01

374

Dragging of Inertial Frames inside the Rotating Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Chakraborty, Chandrachur; Prasad Modak, Kamakshya; Bandyopadhyay, Debades

2014-07-01

375

The Neutron Star Interior Composition Explorer Mission of Opportunity  

NASA Astrophysics Data System (ADS)

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

Gendreau, Keith

2014-08-01

376

The Oscillations and Stability of Differentially Rotating Neutron Stars  

NASA Technical Reports Server (NTRS)

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

Watts, A.

2004-01-01

377

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

378

Detecting neutrinos from black hole-neutron star mergers  

SciTech Connect

While it is well known that neutrinos are emitted from standard core collapse protoneutron star supernovae, less attention has been focused on neutrinos from accretion disks. These disks occur in some supernovae (i.e. collapsars) as well as in compact object mergers, and they emit neutrinos with similar properties to those from protoneutron star supernovae. These disks and their neutrinos play an important role in our understanding of gamma ray bursts as well as the nucleosynthesis they produce. We study a disk that forms in the merger of a black hole and a neutron star and examine the neutrino fluxes, luminosities and neutrino surfaces for the disk. We also estimate the number of events that would be registered in current and proposed supernova neutrino detectors if such an event were to occur in the Galaxy.

Caballero, O. L.; McLaughlin, G. C.; Surman, R. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States); Department of Physics and Astronomy, Union College, Schenectady, New York 12308 (United States)

2009-12-15

379

The hydrodynamic origin of neutron star kicks  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

380

Neutron stars and white dwarfs in galactic halos  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

381

Focused Study of Thermonuclear Bursts on Neutron Stars  

NASA Astrophysics Data System (ADS)

X-ray bursters form a class of Low Mass X-Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric radius expansion bursts likely eject nuclear burning ashes into the interstellar medium, and may make possible the detection of photoionization edges. Indeed, theoretical models predict that absorption edges from 58Fe at 9.2 keV, 60Zn and 62Zn at 12.2 keV should be detectable by the future missions Simbol-X and NuSTAR. A positive detection would thus probe the nuclear burning as well as the gravitational redshift from the neutron star. Moreover, likely observations of atomic X-ray spectral components reflected from the inner accretion disk have been reported. The high spectral resolution capabilities of the focusing X-ray telescopes may therefore make possible to differentiate between the potential interpretations of the X-ray bursts spectral features.

Chenevez, Jérôme

2009-05-01

382

Time Evolution of Relativistic Force-Free Fields Connecting a Neutron Star and its Disk  

NASA Astrophysics Data System (ADS)

We study the magnetic interaction between a neutron star and its disk by solving the time-dependent relativistic force-free equations. At the initial state, we assumed that the dipole magnetic field of the neutron star connects the neutron star and its equatorial disk, which deeply enters into the magnetosphere of the neutron star. Magnetic fields were assumed to be frozen to the star and the disk. The rotations of the neutron star and the disk were imposed as boundary conditions. We applied the Harten-Lax-van Leer (HLL) method to simulate the evolution of the star-disk system. We carried out simulations for (1) a disk inside the corotation radius, in which the disk rotates faster than the star, and (2) a disk outside the corotation radius, in which the neutron star rotates faster than the disk. The numerical results indicate that for both models, the magnetic field lines connecting the disk and the star inflate as they are twisted by the differential rotation between the disk and the star. When the twist angle exceeds ? radian, the magnetic field lines expand with a speed close to the speed of light. This mechanism can be the origin of the relativistic outflows observed in binaries containing a neutron star.

Asano, Eiji; Uchida, Toshio; Matsumoto, Ryoji

2005-04-01

383

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

384

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

PubMed

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

Ho, Wynn C G; Heinke, Craig O

2009-11-01

385

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

386

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

387

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

388

Distinguishing newly born strange stars from neutron stars with g-mode oscillations.  

PubMed

The gravity-mode (g-mode) eigenfrequencies of newly born strange quark stars (SQSs) and neutron stars (NSs) are studied. It is found that the eigenfrequencies in SQSs are much lower than those in NSs by almost 1 order of magnitude, since the components of a SQS are all extremely relativistic particles while nucleons in a NS are nonrelativistic. We therefore propose that newly born SQSs can be distinguished from the NSs by detecting the eigenfrequencies of the g-mode pulsations of supernovae cores through gravitational radiation by LIGO-class detectors. PMID:18999812

Fu, Wei-Jie; Wei, Hai-Qing; Liu, Yu-Xin

2008-10-31

389

Distinguishing Newly Born Strange Stars from Neutron Stars with g-Mode Oscillations  

SciTech Connect

The gravity-mode (g-mode) eigenfrequencies of newly born strange quark stars (SQSs) and neutron stars (NSs) are studied. It is found that the eigenfrequencies in SQSs are much lower than those in NSs by almost 1 order of magnitude, since the components of a SQS are all extremely relativistic particles while nucleons in a NS are nonrelativistic. We therefore propose that newly born SQSs can be distinguished from the NSs by detecting the eigenfrequencies of the g-mode pulsations of supernovae cores through gravitational radiation by LIGO-class detectors.

Fu Weijie [Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Wei Haiqing [oLambda, Inc., Sunnyvale, California 94089 (United States); 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)

2008-10-31

390

Compression of matter in the center of accreting neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

391

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

392

Collapse of differentially rotating neutron stars and cosmic censorship  

NASA Astrophysics Data System (ADS)

We present new results on the dynamics and gravitational-wave emission from the collapse of differentially rotating neutron stars. We have considered a number of polytropic stellar models having different values of the dimensionless angular momentum J/M2, where J and M are the asymptotic angular momentum and mass of the star, respectively. For neutron stars with J/M2<1, i.e. “sub-Kerr” models, we were able to find models that are dynamically unstable and that collapse promptly to a rotating black hole. Both the dynamics of the collapse and the consequent emission of gravitational waves resemble those seen for uniformly rotating stars, although with an overall decrease in the efficiency of gravitational-wave emission. For stellar models with J/M2>1, i.e. “supra-Kerr” models, on the other hand, we were not able to find models that are dynamically unstable and all of the computed supra-Kerr models were found to be far from the stability threshold. For these models a gravitational collapse is possible only after a very severe and artificial reduction of the pressure, which then leads to a torus developing nonaxisymmetric instabilities and eventually contracting to a stable axisymmetric stellar configuration. While this does not exclude the possibility that a naked singularity can be produced by the collapse of a differentially rotating star, it also suggests that cosmic censorship is not violated and that generic conditions for a supra-Kerr progenitor do not lead to a naked singularity.

Giacomazzo, Bruno; Rezzolla, Luciano; Stergioulas, Nikolaos

2011-07-01

393

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

394

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

NASA Technical Reports Server (NTRS)

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

1995-01-01

395

Kaon condensation in neutron stars with Skyrme-Hartree-Fock models  

NASA Astrophysics Data System (ADS)

We investigate nuclear-matter equations of state in neutron stars with kaon condensation. It is generally known that the existence of kaons in neutron star makes the equation of state soft so that the maximum mass of a neutron star is not likely to be greater than 2.0M?, the maximum mass constrained by current observations. With existing Skyrme force model parameters, we calculate nuclear equations of state and check the possibility of kaon condensation in the core of neutron stars. The results show that, even with the kaon condensation, the nuclear equation of state satisfies both the maximum mass and the allowed ranges of mass and radius.

Lim, Yeunhwan; Kwak, Kyujin; Hyun, Chang Ho; Lee, Chang-Hwan

2014-05-01

396

QuakeSim 2.0  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

397

Observational constraints on the masses of neutron stars  

NASA Technical Reports Server (NTRS)

The present state of empirical knowledge about neutron-star masses is reviewed. It is shown how the mass function of a pulsar-containing binary system can be inferred from measurements of the pulsation period and the projected semimajor axis of the pulsar orbit plus independent information concerning the inclination of the orbital plane, the mass of the companion star, or both. Relevant observational properties, the type of information used to constrain the pulsar mass, and the range of allowable pulsar masses are summarized for the binary systems 3U 0900-40, Cen X-3, SMC X-1, Her X-1, and PSR 1913+16. It is found that as long as the general theory of relativity is correct, neutron-star masses should range from about 1.4 to 1.9 solar masses if the companion is a normal white dwarf or should be less than about 1.9 solar masses if the companion is some other object. It is concluded that these mass estimates are entirely consistent with the predictions of nuclear physics theory.

Joss, P. C.; Rappaport, S. A.

1976-01-01

398

GB 790305 as a very strongly magnetized neutron star  

NASA Technical Reports Server (NTRS)

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

Paczynski, Bohdan

1992-01-01

399

Evolution of Binary Neutron Stars and Their White Dwarf Companions  

NASA Astrophysics Data System (ADS)

Understanding the age and evolutionary history of millisecond pulsars can be greatly enhanced by careful multi-color photometry of the white dwarf companions to binary millisecond pulsars. Twenty two millisecond pulsars have been identified with low-mass companions, the majority being 0.1 to 0.6 Msun white dwarfs. We have selected the six most promising pulsar-white dwarf systems for study with HST. Photometry in B, V, and I filters will be used to determine the cooling age of the dwarf star independent of evolutionary arguments made from timing measurements of the pulsar. In several cases the estimated companion mass, determined from the luminosity, will place significant upper bounds on the neutron star mass, potentially revealing clues about both the supernova explosion which created the neutron star, and the later accretion which spun it up to millisecond periods. Astrometric observations of the white dwarfs will serve as a first epoch of proper motion measurements important for distinguishing between supernova and accretion induced collapse models for millisecond pulsar formation. Finally, the astrometry will enable us to measure the rotation of the optical reference frame relative to the radio and dynamical reference frames made from independent pulsar observations.

Foster, Roger

1995-07-01

400

Magnetic field evolution from neutron star crust breaking.  

NASA Astrophysics Data System (ADS)

Spinning-down (or up) neutron star crusts may be stressed beyond their yield strengths by crust neutron superfluid vortex line pinning. Such stresses may then move crustal plates and the magnetic field imbedded in them. Consequences can include continued magnetic moment decrease in dead spinning-down pulsars. Subsequent spin-up (e.g. by accretion from a companion) can lead to a variety of final spin periods and further reduction in magnetic dipole moment depending upon the initial pulsar magnetic field configuration. If the crust stress is relaxed by large scale cracking events, these could cause pulsar timing glitches with magnitude and recurrence rates near those observed. In old or dead radio pulsars the sudden releases of stored elastic energy could give bursts of X-ray and gamma-rays whose number, energy, and rise time suggest those of gamma-ray burst sources. The surface magnetic field of a spinning-down crust cracking neutron star may break up into large surface patches which move apart from each other but retain the original surface magnetic field. Pulsar spin-down torque observations would then reflect the decrease in average surface dipole field, while the field strength inferred from a cyclotron resonance spectral feature above a platelet would remain high and independent of stellar age.

Ruderman, M.

401

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

402

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

SciTech Connect

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

Hakan Erkut, M. [Physics Department, Istanbul Kueltuer University, Atakoey Campus, Bakirkoey 34156, Istanbul (Turkey)

2011-09-21

403

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

404

Gravitational wave asteroseismology with fast rotating neutron stars  

SciTech Connect

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

Gaertig, Erich [Theoretical Astrophysics, Eberhard-Karls University of Tuebingen, Tuebingen 72076 (Germany); Kokkotas, Kostas D. [Theoretical Astrophysics, Eberhard-Karls University of Tuebingen, Tuebingen 72076 (Germany); Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece)

2011-03-15

405

Constraints on neutron star crusts from oscillations in giant flares.  

PubMed

We show that the fundamental seismic shear mode, observed as a quasiperiodic oscillation in giant flares emitted by highly magnetized neutron stars, is particularly sensitive to the nuclear physics of the crust. The identification of an oscillation at approximately 30 Hz as the fundamental crustal shear mode requires a nuclear symmetry energy that depends very weakly on density near saturation. If the nuclear symmetry energy varies more strongly with density, then lower frequency oscillations, previously identified as torsional Alfvén modes of the fluid core, could instead be associated with the crust. If this is the case, then future observations of giant flares should detect oscillations at around 18 Hz. An accurate measurement of the neutron-skin thickness of lead will also constrain the frequencies predicted by the model. PMID:19905795

Steiner, Andrew W; Watts, Anna L

2009-10-30

406

Constraints on Natal Kicks in Galactic Double Neutron Star Systems  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

407

General Relativistic Equilibrium Models of Magnetized Neutron Stars  

NASA Astrophysics Data System (ADS)

Magnetic fields play a crucial role in many astrophysical scenarios and, in particular, are of paramount importance in the emission mechanism and evolution of Neutron Stars (NSs). To understand the role of the magnetic field in compact objects it is important to obtain, as a first step, accurate equilibrium models for magnetized NSs. Using the conformally flat approximation we solve the Einstein's equations together with the GRMHD equations in the case of a static axisymmetric NS taking into account different types of magnetic configuration. This allows us to investigate the effect of the magnetic field on global properties of NSs such as their deformation.

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

2014-03-01

408

Transport coefficients of nuclear matter in neutron star cores  

NASA Astrophysics Data System (ADS)

We calculate thermal conductivity and shear viscosity of nucleons in the dense nuclear matter of neutron star cores in the nonrelativistic Brueckner-Hartree-Fock framework. The nucleon-nucleon interaction is described by the Argonne v18 potential with addition of the Urbana IX effective three-body forces. We find that this three-body force leads to a decrease of the kinetic coefficients with respect to the two-body case. The results of calculations are compared with electron and muon transport coefficients as well as with the results of other authors.

Shternin, P. S.; Baldo, M.; Haensel, P.

2013-12-01

409

On the moment of inertia of a proto neutron star  

NASA Astrophysics Data System (ADS)

The influences of ?* and ? mesons, temperature and coupling constants of nucleons on the moment of inertia of the proto neutron star (PNS) are examined in the framework of relativistic mean field theory for the baryon octet {n, p, ?, ?-, ?0, ?+, ?-, ?0} system. It is found that, compared with that without considering ?* and ? mesons, the moment of inertia decreases. It is also found that the higher the temperature, the larger the incompressibility and symmetry energy coefficient, and the larger the moment of inertia of a PNS. The influence of temperature and coupling constants of the nucleons on the moment of inertia of a PNS is larger than that of the ?* and ? mesons.

Zhao, Xian-Feng; Zhang, Hua; Jia, Huan-Yu

2010-10-01

410

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

411

Cyclotron line resonant transfer through neutron star atmospheres  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

412

Soft gamma rays from black holes versus neutron stars  

NASA Technical Reports Server (NTRS)

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

Liang, Edison P.

1992-01-01

413

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

414

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

415

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

416

Gravitational light bending near neutron stars. I - Emission from columns and hot spots  

Microsoft Academic Search

The beam shapes, pulse profiles, and spectral transmission function at infinity for the radiation originating in columns or hot spots on slowly rotating neutron stars, represented by the Schwarzschild metric, are calculated. These are used for models for binary accreting pulsars and may apply to isolated neutron stars as well. The shadowing effects and their interplay with the frequency changes

H. Riffert; P. Meszaros

1988-01-01

417

Prospects for Measuring Neutron-star Masses and Radii with X-Ray Pulse Profile Modeling  

NASA Astrophysics Data System (ADS)

Modeling the amplitudes and shapes of the X-ray pulsations observed from hot, rotating neutron stars provides a direct method for measuring neutron-star properties. This technique constitutes an important part of the science case for the forthcoming NICER and proposed LOFT X-ray missions. In this paper, we determine the number of distinct observables that can be derived from pulse profile modeling and show that using only bolometric pulse profiles is insufficient for breaking the degeneracy between inferred neutron-star radius and mass. However, we also show that for moderately spinning (300-800 Hz) neutron stars, analysis of pulse profiles in two different energy bands provides additional constraints that allow a unique determination of the neutron-star properties. Using the fractional amplitudes of the fundamental and the second harmonic of the pulse profile in addition to the amplitude and phase difference of the spectral color oscillations, we quantify the signal-to-noise ratio necessary to achieve a specified measurement precision for neutron star radius. We find that accumulating 106 counts in a pulse profile is sufficient to achieve a <~ 5% uncertainty in the neutron star radius, which is the level of accuracy required to determine the equation of state of neutron-star matter. Finally, we formally derive the background limits that can be tolerated in the measurements of the various pulsation amplitudes as a function of the system parameters.

Psaltis, Dimitrios; Özel, Feryal; Chakrabarty, Deepto

2014-06-01

418

Effect of Differential Rotation on the Maximum Mass of Neutron Stars: Realistic Nuclear Equations of State  

Microsoft Academic Search

The merger of binary neutron stars is likely to lead to differentially rotating remnants. In this paper, we survey several cold nuclear equations of state (EOSs) and numerically construct models of differentially rotating neutron stars in general relativity. For each EOS we tabulate maximum allowed masses as a function of the degree of differential rotation. We also determine effective polytropic

Ian A. Morrison; Thomas W. Baumgarte; Stuart L. Shapiro

2004-01-01

419

Detecting Quasi-Normal Modes from Neutron Stars and Black Holes  

NASA Astrophysics Data System (ADS)

The properties of relativistic perturbations of neutron stars and black holes are discussed. They are of great relevance in the study of gravitational wave astronomy. In this work, we review the properties of quasi-normal modes of neutron stars and Schwarzschild black holes and the main features of their detection by actual gravitational wave interferometers.

Marranghello, G. F.

420

Velocity-dependent energy gaps and dynamics of superfluid neutron stars  

NASA Astrophysics Data System (ADS)

We show that suppression of the baryon energy gaps, caused by the relative motion of superfluid and normal liquid components, can substantially influence dynamical properties and evolution of neutron stars. This effect has been previously ignored in the neutron star literature.

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

2013-01-01

421

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

422

Astrophysical measurement of the equation of state of neutron star matter  

SciTech Connect

We present the first astrophysical measurement of the pressure of cold matter above nuclear saturation density, based on recently determined masses and radii of three neutron stars. The pressure at higher densities is below the predictions of equations of state that account only for nucleonic degrees of freedom, and thus present a challenge to the microscopic theory of neutron star matter.

Oezel, Feryal; Guever, Tolga [Department of Astronomy and Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, Arizona 85721 (United States); Baym, Gordon [Department of Physics, University of Illinois, 1110 W. Green Street, Urbana, Illinois 61801 (United States)

2010-11-15

423

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

PubMed

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

Vallisneri, M

2000-04-17

424

Universal three-body repulsion suggested by neutron stars  

SciTech Connect

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

Takatsuka, T.; Nishizaki, S. [Faculty of Humanities and Social Sciences, Iwate University, Morioka 020-8550 (Japan); Tamagaki, R. [Kamitakano Maeda-Cho 26-5, Kyoto 606-0097 (Japan)

2008-04-29

425

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

426

Formation of Stable Magnetars from Binary Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

By performing fully general relativistic magnetohydrodynamic simulations of binary neutron star mergers, we investigate the possibility that the end result of the merger is a stable magnetar. In particular, we show that, for a binary composed of two equal-mass neutron stars (NSs) of gravitational mass M ~ 1.2 M ? and equation of state similar to Shen et al. at high densities, the merger product is a stable NS. Such NS is found to be differentially rotating and ultraspinning with spin parameter J/M2 ~ 0.86, where J is its total angular momentum, and it is surrounded by a disk of ?0.1 M ?. While in our global simulations the magnetic field is amplified by about two orders of magnitude, local simulations have shown that hydrodynamic instabilities and the onset of the magnetorotational instability could further increase the magnetic field strength up to magnetar levels. This leads to the interesting possibility that, for some NS mergers, a stable and magnetized NS surrounded by an accretion disk could be formed. We discuss the impact of these new results for the emission of electromagnetic counterparts of gravitational wave signals and for the central engine of short gamma-ray bursts.

Giacomazzo, Bruno; Perna, Rosalba

2013-07-01

427

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

PubMed

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

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

2012-08-24

428

FORMATION OF STABLE MAGNETARS FROM BINARY NEUTRON STAR MERGERS  

SciTech Connect

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

Giacomazzo, Bruno [JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309 (United States); Perna, Rosalba [JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)

2013-07-10

429