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1

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

2

Neutron stars as cosmic neutron matter laboratories.  

NASA Astrophysics Data System (ADS)

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

Pines, D.

3

Dibaryons in neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

4

Superfluidity in neutron stars  

NASA Astrophysics Data System (ADS)

Astrophysical evidence is reviewed for the existence of at least three distinct superfluids inside neutron stars from the observed relaxation of the rotation and spin-down rates of the pulsars Vela, Crab, and PSR0525 + 21, following sudden jumps or glitches in these quantities. Theoretical aspects of neutron and proton superfluids in neutron stars and core neutron communication, glitches and post-glitch relaxation, neutron star coupling, and vortex creep theory are discussed. The effects of the superfluid interior in the accreting neutron star X-ray sources are also considered.

Pines, D.; Alpar, M. A.

1985-07-01

5

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.

Dave Bock

1999-01-21

6

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

PubMed Central

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

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

2012-01-01

7

Neutron stars as cosmic neutron matter laboratories  

SciTech Connect

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

Pines, D.

1986-01-01

8

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

9

Hyperons in neutron stars  

E-print Network

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

Katayama, Tetsuya

2015-01-01

10

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

11

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

NASA Technical Reports Server (NTRS)

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

Pines, D.; Shaham, J.

1972-01-01

12

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

13

Neutron Star Phenomena  

NASA Technical Reports Server (NTRS)

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

Ruderman, Malvin

1998-01-01

14

Neutron Stars and NuSTAR  

NASA Astrophysics Data System (ADS)

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

Bhalerao, Varun

2012-05-01

15

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

16

The physics of neutron stars.  

PubMed

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

Lattimer, J M; Prakash, M

2004-04-23

17

Hubble Sees a Neutron Star Alone in Space Nearest Known Neutron Star  

E-print Network

Hubble Sees a Neutron Star Alone in Space Nearest Known Neutron Star #12;Birth of a Neutron Star & neutrinos. The birth temperature of a neutron star is ~5Ã?1011 K, but neutrino emission cools it to `only' 106 to 107 K. #12;Sizes of Neutron Stars Google Maps: Oahu #12;Sizes of Neutron Stars Artist

Barnes, Joshua Edward

18

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.

2012-08-03

19

Neutron Stars for Undergraduates  

E-print Network

Calculating the structure of white dwarf and neutron stars would be a suitable topic for an undergraduate thesis or an advanced special topics or independent study course. The subject is rich in many different areas of physics accessible to a junior or senior physics major, ranging from thermodynamics to quantum statistics to nuclear physics to special and general relativity. The computations for solving the coupled structure differential equations (both Newtonian and general relativistic) can be done using a symbolic computational package, such as Mathematica. In doing so, the student will develop computational skills and learn how to deal with dimensions. Along the way he or she will also have learned some of the physics of equations of state and of degenerate stars.

Richard R. Silbar; Sanjay Reddy

2003-09-16

20

Physics of Neutron Star Crusts  

E-print Network

The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

N. Chamel; P. Haensel

2008-12-20

21

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

22

Grand unification of neutron stars  

PubMed Central

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

Kaspi, Victoria M.

2010-01-01

23

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

24

Neutron stars with dark energy  

NASA Astrophysics Data System (ADS)

After a short review on the possible experimental observations to verify pseudocomplex General Relativity, neutron stars as a particular object of interest are investigated. Dark energy is added to the structure of a neutron star, while for the nuclear part the chiral SU(3) model is used. For the coupling of matter to dark energy a special assumption is made. The consequences are discussed. We show that neutron stars of up to six solar masses are obtained, which already behave similar to a black hole.

Hess, P. O.; Rodríguez, I.; Greiner, W.; Boller, T.

2015-01-01

25

Neutron stars as cosmic hadron physics laboratories.  

NASA Astrophysics Data System (ADS)

Recent developments have radically changed our understanding of both the dynamics of neutron-star superfluids and the free precession of neutron stars. Astrophysical constraints on neutron matter are derived from observation and compared with microscopic theory.

Pines, D.

26

Neutron star evolution and emission  

SciTech Connect

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

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

1997-08-01

27

The Neutron Star Zoo  

NASA Technical Reports Server (NTRS)

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

Harding, Alice K.

2014-01-01

28

Helium Detonations on Neutron Stars  

Microsoft Academic Search

We present the results of a numerical study of helium detonations on the surfaces of neutron stars. We describe two-dimensional simulations of the evolution of a detonation as it breaks through the accreted envelope of the neutron star and propagates laterally through the accreted material. The detonation front propagates laterally at nearly the Chapman-Jouguet velocity, v=1.3×109 cm s-1. A series

M. Zingale; F. X. Timmes; B. Fryxell; D. Q. Lamb; K. Olson; A. C. Calder; L. J. Dursi; P. Ricker; R. Rosner; P. MacNeice; H. M. Tufo

2001-01-01

29

Complexity and neutron star structure  

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

30

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

31

Binary Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the formation channels of merging binaries and we discuss the most recent theoretical predictions for merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for fully dynamical simulations. The quasi-equilibrium approximation has played a key role in developing our understanding of the physics of binary coalescence and, in particular, of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. We then turn to the numerical techniques used in dynamical simulations, including relativistic formalisms, (magneto-)hydrodynamics, gravitational-wave extraction techniques, and nuclear microphysics treatments. This is followed by a summary of the simulations performed across the field to date, including the most recent results from both fully relativistic and microphysically detailed simulations. Finally, we discuss the likely directions for the field as we transition from the first to the second generation of gravitational-wave interferometers and while supercomputers reach the petascale frontier.

Faber, Joshua A.; Rasio, Frederic A.

2012-07-01

32

The nuclear physics of neutron stars  

SciTech Connect

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. [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

2014-05-09

33

Populus tremuloides (quaking aspen)  

NSDL National Science Digital Library

Populus tremuloides (quaking aspen) Laterally compressed petioles allow any breeze to cause leaves to vibrate or ""quake"". This movement makes it difficult for insects to land on or crawl on leaf surfaces.

John Curtis (University of Wisconsin ADR; POSTAL)

2004-03-09

34

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

35

Nuclear Physics of Neutron Stars  

E-print Network

Understanding the equation of state (EOS) of cold nuclear matter, namely, the relation between the pressure and energy density, is a central goal of nuclear physics that cuts across a variety of disciplines. Indeed, the limits of nuclear existence, the collision of heavy ions, the structure of neutron stars, and the dynamics of core-collapse supernova, all depend critically on the equation of state of hadronic matter. In this contribution I will concentrate on the special role that nuclear physics plays in constraining the EOS of cold baryonic matter and its impact on the properties of neutron stars.

J. Piekarewicz

2009-01-28

36

Quark matter in neutron stars  

E-print Network

According to quantum chromodynamics, matter at ultra-high density and low temperature is a quark liquid, with a condensate of Cooper pairs of quarks near the Fermi surface ("color superconductivity"). This paper reviews the physics of color superconductivity, and discusses some of the proposed signatures by which we might detect quark matter in neutron stars.

Mark G. Alford

2009-09-18

37

Be/neutron Star Transients  

NASA Astrophysics Data System (ADS)

The Be/neutron star systems form the largest sub-class of the high mass X-ray binary category. While some individual members have been studied in detail, a full understanding of these objects can only come from a study of the class as a whole. This proposal is aimed at increasing the number of well studied objects by proposing for two sets of TOO observations of newly discovered Be/neutron star binaries. One short period (pulse and orbit) system will be observed repeatedly to obtain a good measurement of its orbit. In addition, one long period system will be observed for an extended time to obtain a single good pulse period measurement - the orbital period will come from the ASM. Cyclotron lines will be searched for from both systems using PCA/HEXTE data.

Corbet, Robin

38

From Nuclei to Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Reddy, Sanjay

2007-10-01

39

Properties of neutron star critical collapses  

NASA Astrophysics Data System (ADS)

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

Wan, Mew-Bing

40

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.

41

Neutron stars as cosmic hadron physics laboratories  

NASA Astrophysics Data System (ADS)

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

Pines, D.

1985-05-01

42

The HST contribution to neutron star astronomy  

E-print Network

While isolated neutron stars (INSs) are among the brightest gamma-ray sources, they are among the faintest ones in the optical, and their study is a challenging task which require the most powerful telescopes. HST has lead neutron star optical astronomy yielding nearly all the identifications achieved since the early 1990s. Here, the major HST contributions in the optical studies of INSs and their relevance for neutron stars' astronomy are reviewed.

R. P. Mignani

2007-10-29

43

Gravitational Waves From Low Mass Neutron Stars  

E-print Network

Low mass neutron stars may be uniquely strong sources of gravitational waves (GW). 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 $Q_{22}$ over 100 times larger, for low mass stars than for 1.4 $M_\\odot$ neutron stars. Indeed, we calculate that the crust can support an $\\epsilon$ as large as 0.01 for a minimum mass neutron star. A 0.12 $M_\\odot$ star, that is maximally strained and rotating at 100 Hz, will produce a characteristic gravitational wave strain of $h_0=2.1\\times 10^{-24}$ at a distance of 1 kpc. The GW detector Advanced LIGO should be sensitive to such objects through out the Milky Way Galaxy.

C. J. Horowitz

2009-12-08

44

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

45

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

46

Superfluidity in the Core of Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Page, Dany

2013-04-01

47

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

48

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

49

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

50

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

51

Superfluid dynamics in neutron star crusts  

E-print Network

A simple description of superfluid hydrodynamics in the inner crust of a neutron star is given. Particular attention is paid to the effect of the lattice of nuclei on the properties of the superfluid neutrons, and the effects of entrainment, the fact that some fraction of the neutrons are locked to the motion of the protons in nuclei.

C. J. Pethick; N. Chamel; S. Reddy

2010-09-13

52

Neutron Star Crust and Molecular Dynamics Simulation  

E-print Network

In this book chapter we review plasma crystals in the laboratory, in the interior of white dwarf stars, and in the crust of neutron stars. We describe a molecular dynamics formalism and show results for many neutron star crust properties including phase separation upon freezing, diffusion, breaking strain, shear viscosity and dynamics response of nuclear pasta. We end with a summary and discuss open questions and challenges for the future.

C. J. Horowitz; J. Hughto; A. Schneider; D. K. Berry

2011-09-23

53

Electron-neutron scattering and transport properties of neutron stars  

E-print Network

We show that electrons can couple to the neutron excitations in neutron stars and find that this can limit their contribution to the transport properties of dense matter, especially the shear viscosity. The coupling between electrons and neutrons is induced by protons in the core, and by ions in the crust. We calculate the effective electron-neutron interaction for the kinematics of relevance to the scattering of degenerate electrons at high density. We use this interaction to calculate the electron thermal conductivity, electrical conductivity, and shear viscosity in the neutron star inner crust, and in the core where we consider both normal and superfluid phases of neutron-rich matter. In some cases, particularly when protons are superconducting and neutrons are in their normal phase, we find that electron-neutron scattering can be more important than the other scattering mechanisms considered previously.

Bridget Bertoni; Sanjay Reddy; Ermal Rrapaj

2014-09-27

54

Quark Matter in Neutron Stars: An apercu  

E-print Network

The existence of deconfined quark matter in the superdense interior of neutron stars is a key question that has drawn considerable attention over the past few decades. Quark matter can comprise an arbitrary fraction of the star, from 0 for a pure neutron star to 1 for a pure quark star, depending on the equation of state of matter at high density. From an astrophysical viewpoint, these two extreme cases are generally expected to manifest different observational signatures. An intermediate fraction implies a hybrid star, where the interior consists of mixed or homogeneous phases of quark and nuclear matter, depending on surface and Coulomb energy costs, as well as other finite size and screening effects. In this brief review article, we discuss what we can deduce about quark matter in neutron stars in light of recent exciting developments in neutron star observations. We state the theoretical ideas underlying the equation of state of dense quark matter, including color superconducting quark matter. We also highlight recent advances stemming from re-examination of an old paradigm for the surface structure of quark stars and discuss possible evolutionary scenarios from neutron stars to quark stars, with emphasis on astrophysical observations.

Prashanth Jaikumar; Sanjay Reddy; Andrew W. Steiner

2006-08-16

55

The many lives of magnetized neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

56

Anisotropic pressure and hyperons in neutron stars  

E-print Network

We study the effects of anisotropic pressure on properties of the neutron stars with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of anisotropic pressure on neutron star matter is to increase the stiffness of the equation of state, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of anisotropic pressure model $h \\le 0.8$[1] and $\\Lambda \\le -1.15$ [2]. The radius of the corresponding neutron star at $M$=1.4 $M_\\odot$ is more than 13 km, while the effect of anisotropic pressure on the minimum mass of neutron star is insignificant. Furthermore, due to the anisotropic pressure in the neutron star, the maximum mass limit of higher than 2.1 $M_\\odot$ cannot rule out the presence of hyperons in the neutron star core.

A. Sulaksono

2014-12-23

57

Atmospheres and radiating surfaces of neutron stars  

NASA Astrophysics Data System (ADS)

The early 21st century is witnessing a breakthrough in the study of the thermal radiation of neutron stars. Observations with modern space telescopes have provided a wealth of valuable information, which, when properly interpreted, can elucidate the physics of superdense matter in the interior of these stars. This interpretation is underlain by the theory of formation of the neutron star thermal spectra, which is in turn based on plasma physics and on the understanding of radiative processes in stellar photospheres. In this paper, the current status of the theory is reviewed, with particular emphasis on neutron stars with strong magnetic fields. In addition to the conventional deep (semi-infinite) atmospheres, radiative condensed surfaces of neutron stars and 'thin' (finite) atmospheres are considered.

Potekhin, A. Yu

2014-08-01

58

The breaking strain of neutron star crust  

SciTech Connect

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

Kadau, Kai [Los Alamos National Laboratory; Horowitz, C J [INDIANA UNIV

2009-01-01

59

Experimental approach to neutron stars  

SciTech Connect

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 [GSI Helmholtzzentrum für Schwerionenforschung, Planckstr. 1, 64291 Darmstadt (Germany)

2014-05-09

60

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

61

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

62

THE ROLE OF HELIUM STARS IN THE FORMATION OF DOUBLE NEUTRON STARS N. Ivanova,1  

E-print Network

THE ROLE OF HELIUM STARS IN THE FORMATION OF DOUBLE NEUTRON STARS N. Ivanova,1 K. Belczynski,1,2 V:5 6 M with a 1.4 M neutron star companion to investigate the formation of double neutron star systems phase) leads to the formation of extremely short-period double neutron star systems (with Pd0:1 days

Rasio, Frederic A.

63

Rotation and cooling of neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

64

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

65

Neutron Star Compared to Manhattan - Duration: 0:11.  

NASA Video Gallery

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

66

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

67

Optical Observations of Isolated Neutron Stars  

E-print Network

Only 1% of the Isolated Neutron Star (INS) population has been identified in the optical, albeit with different degrees of confidence. Optical observations of INSs are reviewed and their emission properties discussed in an evolutionary framework.

R. Mignani

1998-10-02

68

Direct URCA process in neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

69

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

70

Carbon Atmosphere Discovered On Neutron Star  

NASA Astrophysics Data System (ADS)

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

2009-11-01

71

The decompression of cold neutron star matter  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

72

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

73

Which Stars Form Black Holes and Neutron Stars?  

E-print Network

I describe the current state of our knowledge of the mapping between the initial masses of stars and the compact objects -- particularly neutron stars and black holes -- that they produce. Most of that knowledge is theoretical in nature, and relies on uncertain assumptions about mass loss through winds, binary mass transfer, and the amount of mass ejected during a supernovae. Observational constraints on the initial masses of stars that produce neutron stars and black holes is scarce. They fall into three general categories: (1) models of the stars that produced the supernova remnants associated with known compact objects, (2) scenarios through with high mass X-ray binaries were produced, and (3) associations between compact objects and coeval clusters of stars for which the minimum masses of stars that have undergone supernovae are known. I focus on the last category as the most promising in the near term. I describe three highly-magnetized neutron stars that have been associated with progenitors that had initial masses of $>$30\\msun, and evaluate the prospects of finding further associations between star clusters and compact objects.

Michael P. Muno

2006-11-18

74

Cyg X-1 - A massive neutron star  

NASA Technical Reports Server (NTRS)

The expected X-ray emission from Cyg X-1, considered a massive neutron star (8-15 solar masses) according to some gravity theories, is studied within the framework of Rosen's bimetric gravity theory (1973, 1974). It is shown that in such massive neutron stars, the innermost stable orbit lies far outside the star surface, and therefore the X-ray spectrum consists of two components: a soft one emitted from a cold accretion disk and a hard one emitted by the matter striking the neutron star surface after spiraling down freely from the disk. The proposed model is shown to be in good agreement with the observed luminosities. The model predicts a surface gravitational redshift of 3.16 which could be tested by the future X- and gamma-ray detectors.

Goldman, I.

1981-01-01

75

Population Synthesis of Double Neutron Stars  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

76

TeV mu Neutrinos from Young Neutron Stars  

E-print Network

Neutron stars are efficient accelerators for bringing charges up to relativistic energies. We show that if positive ions are accelerated to ~1 PeV near the surface of a young neutron star (t_age Earth; the star would be a ``neutrino pulsar''. Looking for muon neutrino emission from young neutron stars will provide a valuable probe of the energetics of the neutron star magnetosphere.

B. Link; Fiorella Burgio

2004-12-20

77

Encounters between binaries and neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

78

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

79

Quasiparticle interactions in neutron matter for applications in neutron stars  

NASA Astrophysics Data System (ADS)

A microscopic model for the quasiparticle interaction in neutron matter is presented. Both particle-particle (pp) and particle-hole (ph) correlations are included. The pp correlations are treated in a 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 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 1S 0 gap parameter for neutron superfluidity and comment briefly on neutron-star implications.

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

1993-04-01

80

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

81

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

82

Non-Identical Neutron Star Twins  

E-print Network

The work of J. A. Wheeler in the mid 1960's showed that for smooth equations of state no stable stellar configurations with central densities above that corresponding to the limiting mass of ``neutron stars'' (in the generic sense) were stable against acoustical vibrational modes. A perturbation would cause any such star to collapse to a black hole or explode. Accordingly, there has been no reason to expect that a stable degenerate family of stars with higher density than the known white dwarfs and neutron stars might exist. We have found a class of exceptions corresponding to certain equations of state that describe a first order phase transition. We discuss how such a higher density family of stars could be formed in nature, and how the promising new exploration of oscillations in the X-ray brightness of accreting neutron stars might provide a means of identifying them. Our proof of the possible existence of a third family of degenerate stars is one of principle and rests on general principles like causality, microstability of matter and General Relativity.

Norman K. Glendenning; Christiane Kettner

1998-10-22

83

Accreting neutron stars, black holes, and degenerate dwarf stars  

NASA Astrophysics Data System (ADS)

During the past 8 years, extended temporal and broadband spectroscopic studies carried out by X-ray astronomical satellites have led to the identification of specific compact X-ray sources as accreting neutron stars, black holes, and degenerate dwarf stars in close binary systems. Such sources provide a unique opportunity to study matter under extreme conditions not accessible in the terrestrial laboratory. Quantitative theoretical models have been developed which demonstrate that detailed studies of these sources will lead to a greatly increased understanding of dense and superdense hadron matter, hadron superfluidity, high-temperature plasma in superstrong magnetic fields, and physical processes in strong gravitational fields. Through a combination of theory and observation such studies will make possible the determination of the mass, radius, magnetic field, and structure of neutron stars and degenerate dwarf stars and the identification of further candidate black holes, and will contribute appreciably to our understanding of the physics of accretion by compact astronomical objects.

Pines, D.

1980-02-01

84

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

85

Hot Neutron and Quark Star Evolution  

E-print Network

The physics of compact objects is one of the very actively developing branches of theoretical investigations, since the careful analysis of different models for the internal structure of these objects, their evolutionary characteristics and the comparison with modern observational data give access to discriminate among various speculations about the state of matter under extreme conditions. The lecture provides an overview to the problem of neutron star cooling evolution. We discuss the scheme and necessary inputs for neutron star cooling simulations from the background of a microscopic modeling in order to present the surface temperature - age characteristics of hybrid neutron stars including the determination of main regulators of the cooling process, the question of neutrino production and diffusion.

Hovik Grigorian

2005-06-16

86

The Neutron Star Interior Composition Explorer (NICER)  

NASA Technical Reports Server (NTRS)

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

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

2014-01-01

87

Towards a metallurgy of neutron star crusts  

E-print Network

In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic (bcc) lattice of nuclei immersed in an essentially uniform electron gas. We show that at densities above that for neutron drip ($\\sim4\\times10^11$) g cm$^{-3}$ or roughly one thousandth of nuclear matter density, the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO$_3$. As a consequence, properties of matter in the inner crust are expected to be much richer than previously appreciated and we mention consequences for observable neutron star properties.

Kobyakov, D

2013-01-01

88

Towards a metallurgy of neutron star crusts  

E-print Network

In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic (bcc) lattice of nuclei immersed in an essentially uniform electron gas. We show that at densities above that for neutron drip ($\\sim4\\times10^11$) g cm$^{-3}$ or roughly one thousandth of nuclear matter density, the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as BaTiO$_3$. As a consequence, properties of matter in the inner crust are expected to be much richer than previously appreciated and we mention consequences for observable neutron star properties.

D. Kobyakov; C. J. Pethick

2013-09-07

89

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

90

Dense hadronic matter in neutron stars  

E-print Network

The existence of stars with masses up to $2 M_{\\odot}$ and the hints of the existence of stars with radii smaller than $\\sim 11$ km seem to require, at the same time, a stiff and a soft hadronic equation of state at large densities. We argue that these two apparently contradicting constraints are actually an indication of the existence of two families of compact stars: hadronic stars which could be very compact and quark stars which could be very massive. In this respect, a crucial role is played, in the hadronic equation of state, by the delta isobars whose early appearance shifts to large densities the formation of hyperons. We also discuss how recent experimental information on the symmetry energy of nuclear matter at saturation indicate, indirectly, an early appearance of delta isobars in neutron star matter.

Giuseppe Pagliara; Alessandro Drago; Andrea Lavagno; Daniele Pigato

2014-04-24

91

Dark-Matter Admixed Neutron Stars  

E-print Network

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

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

2011-11-08

92

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

93

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

94

Pulse Profiles from Thermally Emitting Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Turolla, R.; Nobili, L.

2013-05-01

95

The Influence of the ?-FIELD on Neutron Stars  

NASA Astrophysics Data System (ADS)

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

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

2008-02-01

96

QPO constraints on neutron stars M. Coleman Miller  

E-print Network

reliable of the constraints. Double neutron star systems have masses up to 1.44M (e.g., ThorsettQPO constraints on neutron stars M. Coleman Miller University of Maryland, Department of Astronomy a b s t r a c t The kilohertz frequencies of QPOs from accreting neutron star systems imply

Miller, Cole

97

Neutron stars: a cosmic hadron physics laboratory.  

NASA Astrophysics Data System (ADS)

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 post-glitch behaviour. 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 SN 1987A are discussed.

Pines, D.

98

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

99

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

E-print Network

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

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

2012-07-25

100

Emission processes in quiescent neutron star transients  

E-print Network

We review the observational properties of transient systems made by a neutron star primary and a late dwarf companion (known also as Soft X-ray Transients) during their quiescent state. We focus on the several emission mechanisms proposed and try to compare them with observations. Finally, we review new tools to improve our comprehension of the physics of the emission processes.

Sergio Campana

2003-11-10

101

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

102

Neutron star solutions in perturbative quadratic gravity  

SciTech Connect

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

Deliduman, Cemsinan [Department of Physics, Mimar Sinan Fine Arts University, Bomonti 34380, ?stanbul (Turkey); Ek?i, K.Y.; Kele?, Vildan, E-mail: cemsinan@msgsu.edu.tr, E-mail: eksi@itu.edu.tr, E-mail: kelesvi@itu.edu.tr [?stanbul Technical University, Faculty of Science and Letters, Physics Engineering Department, Maslak 34469, ?stanbul (Turkey)

2012-05-01

103

Measurement of the Radius of Neutron Stars  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

104

Measurement of the Radius of Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Guillot, Sebastien

2012-07-01

105

RELATIVISTIC IRON EMISSION LINES IN NEUTRON STAR LOW-MASS X-RAY BINARIES AS PROBES OF NEUTRON STAR RADII  

E-print Network

RELATIVISTIC IRON EMISSION LINES IN NEUTRON STAR LOW-MASS X-RAY BINARIES AS PROBES OF NEUTRON STAR redshift, but these lines appear to be extremely rare and difficult to observe, and the only detection for placing upper limits on neutron star radii using relativistic iron emission lines (see Miller 2007

Miller, Cole

106

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

107

Tidal Love numbers of neutron stars  

E-print Network

For a variety of fully relativistic polytropic neutron star models we calculate the star's tidal Love number k2. Most realistic equations of state for neutron stars can be approximated as a polytrope with an effective index n~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_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 ~24%. The Love number is potentially measurable in gravitational wave signals from inspiralling binary neutron stars.

Tanja Hinderer

2009-03-07

108

Induced Pairing Interaction in Neutron Star Matter  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

109

Neutron stars and quark stars: Two coexisting families of compact stars?  

E-print Network

The mass-radius relation of compact stars is discussed with relation to the presence of quark matter in the core. The existence of a new family of compact stars with quark matter besides white dwarfs and ordinary neutron stars is outlined.

J. Schaffner-Bielich

2006-12-29

110

A Statistical Study on Neutron Star Masses  

NASA Astrophysics Data System (ADS)

We investigate the measurement of neutron star masses in different population of binaries. Based on the collection of the orbital parameters of 40 systems (46 sources), we apply the boot-strap method together with the Monte Carlo method to reconstruct the likelihood curves for each source separately. The cumulative analysis of the simulation result shows that the neutron star masses in X-ray systems and radio systems obey different distributions, and no evidence for the bimodal distribution could be found. Employing the Bayesian statistical techniques, we find that the most likely distributions for the high mass X-ray binaries (HMXBs), low mass X-ray binaries (LMXBs), double neutron star (DNS) systems, and neutron star-white dwarf (NS-WD) binary systems are (1.340±0.230) M_{?}, (1.505±0.125) M_{?}, (1.335±0.055) M_{?}, and (1.495±0.225) M_{?}, respectively. The statistical distribution has no significant deviation from the standard neutron star formation mechanism. It is noticed that the statistical results of the center masses of LMXBs and NS-WD systems are significantly higher than the other groups by about 0.16 M_{?}, which could be regarded as the evidence of accretion episodes. And if we regard the HMXBs and LMXBs as the progenitors of DNS and NS-WD systems, then we can draw the conclusion that the accretion effect must be very week during the evolution trajectory from HMXBs to DNS systems, and this could be the reason why the masses of DNS systems have such a narrow distribution.

Cheng, Z.; Zhang, C. M.; Zhao, Y. H.; Wang, D. H.; Pan, Y. Y.; Lei, Y. J.

2013-11-01

111

Shear viscosity in neutron star cores  

E-print Network

We calculate the shear viscosity $\\eta = \\eta_{e\\mu}+\\eta_{n}$ in a neutron star core composed of nucleons, electrons and muons ($\\eta_{e\\mu}$ being the electron-muon viscosity, mediated by collisions of electrons and muons with charged particles, and $\\eta_{n}$ the neutron viscosity, mediated by neutron-neutron and neutron-proton collisions). Deriving $\\eta_{e\\mu}$, we take into account the Landau damping in collisions of electrons and muons with charged particles via the exchange of transverse plasmons. It lowers $\\eta_{e\\mu}$ and leads to the non-standard temperature behavior $\\eta_{e\\mu}\\propto T^{-5/3}$. The viscosity $\\eta_{n}$ is calculated taking into account that in-medium effects modify nucleon effective masses in dense matter. Both viscosities, $\\eta_{e\\mu}$ and $\\eta_{n}$, can be important, and both are calculated including the effects of proton superfluidity. They are presented in the form valid for any equation of state of nucleon dense matter. We analyze the density and temperature dependence of $\\eta$ for different equations of state in neutron star cores, and compare $\\eta$ with the bulk viscosity in the core and with the shear viscosity in the crust.

P. S. Shternin; D. G. Yakovlev

2008-08-21

112

General Relativistic Decompression of Binary Neutron Stars During Dynamic Inspiral  

E-print Network

We investigate the dynamic stability of inspiraling neutron stars by performing multiple-orbit numerical relativity simulations of the binary neutron star inspiral process. By introducing eccentricities in the orbits of the neutron stars, significant changes in orbital separation are obtained within orbital timescales. We find that as the binary system evolves from apastron to periastron (as the binary separation decreases), the central rest mass density of each star decreases, thus stabilizing the stars against individual prompt collapse. As the binary system evolves from periastron to apastron, the central rest mass density increases; the neutron stars re-compress as the binary separation increases.

Mark Miller

2005-10-05

113

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.

Alan McConnell

1990-07-10

114

Observational constrains on the EoS of neutron stars.  

NASA Astrophysics Data System (ADS)

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

Jonker, Peter

115

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

116

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.

Pamela ONeil

1994-02-12

117

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.

Pamela ONeil

1994-02-12

118

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

Microsoft Academic Search

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

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

2003-01-01

119

Rotational parameters of strange stars in comparison with neutron stars  

NASA Astrophysics Data System (ADS)

I study stellar structures, i.e. the mass, the radius, the moment of inertia and the oblateness parameter at different spin frequencies for strange stars and neutron stars in a comparative manner. I also calculate the values of the radii of the marginally stable orbits and Keplerian orbital frequencies. By equating kHz QPO frequencies to Keplerian orbital frequencies, I find corresponding orbital radii. Knowledge about these parameters might be useful in further modeling of the observed features from LMXBs with advanced and improved future techniques for observations and data analysis.

Bagchi, Manjari

2010-01-01

120

Neutron stars and the coherent nuclear interaction.  

NASA Astrophysics Data System (ADS)

In the framework of a novel approach to the dynamics of nuclei and large collections of nucleons, which fully exploits the coherent interaction among ?'s, nucleons and ?'s, the authors derive a new equation of state for neutronic matter. By introducing it in the Tolman-Oppenheimer-Volkof equations they derive the masses and radii of neutron stars as a function of the central density. The authors obtain a maximum mass Mmax ? 2.7 Msun and a minimum period of rotation Tmin = 0.8 msec.

Del Giudice, E.; Mele, R.; Preparata, G.; Gualdi, C.; Mangano, G.; Miele, G.

1995-08-01

121

Symmetry energy, neutron skin, and neutron star radius from chiral effective field theory interactions  

E-print Network

We discuss neutron matter calculations based on chiral effective field theory interactions and their predictions for the symmetry energy, the neutron skin of 208 Pb, and for the radius of neutron stars.

Hebeler, K

2014-01-01

122

Constraining decaying dark matter with neutron stars  

E-print Network

The amount of decaying dark matter, accumulated in the central regions in neutron stars together with the energy deposition rate from decays, may set a limit on the neutron star survival rate against transitions to more compact objects and, correspondingly, on the dark matter particle decay time, $\\tau_{\\chi}$. We find that for masses $(m_{\\chi}/ \\rm TeV) \\gtrsim 9 \\times 10^{-4}$ or $(m_{\\chi}/ \\rm TeV) \\gtrsim 5 \\times 10^{-2}$ in the bosonic or fermionic decay cases respectively, lifetimes ${\\tau_{\\chi}}\\lesssim 10^{55}$ s and ${\\tau_{\\chi}}\\lesssim 10^{53}$ s can be excluded. Our result significantly improves on other current constraints if nuclear matter is metastable to percolation.

M. Angeles Perez-Garcia; J. Silk

2014-03-24

123

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

124

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

125

'Tertiary' nuclear burning - Neutron star deflagration?  

NASA Technical Reports Server (NTRS)

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

Michel, F. Curtis

1988-01-01

126

Physics of systems containing neutron stars  

NASA Technical Reports Server (NTRS)

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

Shaham, Jacob

1989-01-01

127

Neutron star inner crust and symmetry energy  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

128

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

129

Numerical relativity simulations of binary neutron stars  

NASA Astrophysics Data System (ADS)

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

Thierfelder, Marcus; Bernuzzi, Sebastiano; Brügmann, Bernd

2011-08-01

130

Evolution of Close Neutron Star Binaries  

E-print Network

We have calculated evolution of neutron star binaries towards the coalescence driven by gravitational radiation. The hydrodynamical effects as well as the general relativistic effects are important in the final phase. All corrections up to post$^{2.5}$-Newtonian order and the tidal effect are included in the orbital motion. The star is approximated by a simple Newtonian stellar model called affine star model. Stellar spins and angular momentum are assumed to be aligned. We have showed how the internal stellar structure affects the stellar deformation, variations of the spins, and the orbital motion of the binary just before the contact. The gravitational wave forms from the last a few revolutions significantly depend on the stellar structure.

W. Ogawaguchi; Y. Kojima

1996-10-17

131

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

132

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

133

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

134

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

135

Gamma-ray bursts from extinct neutron stars  

NASA Technical Reports Server (NTRS)

The paper concentrates on disks around old extinct pulsars, that can produce gamma-ray bursts owing to viscous evolution of the disk bringing it into the near vicinity of the neutron star, with runaway ionization of the disk and simultaneous precipitation of this plasma onto the neutron star. An old extinct pulsar is modeled as a magnetized neutron star circled by a ring of cold dense matter with an orbital period approximately equal to the rotational period of the neutron star. The numerical estimates produced are found to be consistent with the observed properties of gamma-ray bursters.

Michel, F. C.

1990-01-01

136

Mutual Friction in Superfluid Neutron Stars  

E-print Network

We discuss vortex-mediated mutual friction in the two-fluid model for superfluid neutron star cores. Our discussion is based on the general formalism developed by Carter and collaborators, which makes due distinction between transport velocity and momentum for each fluid. This is essential for an implementation of the so-called entrainment effect, whereby the flow of one fluid imparts momentum in the other and vice versa. The mutual friction follows by balancing the Magnus force that acts on the quantised neutron vortices with a resistive force due to the scattering of electrons off of the magnetic field with which each vortex core is endowed. We derive the form of the macroscopic mutual friction force which is relevant for a model based on smooth-averaging over a collection of vortices. We discuss the coefficients that enter the expression for this force, and the timescale on which the two interpenetrating fluids in a neutron star core are coupled. This discussion confirms that our new formulation accords well with previous work in this area.

N. Andersson; T. Sidery; G. L. Comer

2005-10-03

137

Statistical theory of thermal evolution of neutron stars  

NASA Astrophysics Data System (ADS)

Thermal evolution of neutron stars is known to depend on the properties of superdense matter in neutron star cores. We suggest a statistical analysis of isolated cooling middle-aged neutron stars and old transiently accreting quasi-stationary neutron stars warmed up by deep crustal heating in low-mass X-ray binaries. The method is based on simulations of the evolution of stars of different masses and on averaging the results over respective mass distributions. This gives theoretical distributions of isolated neutron stars in the surface temperature-age plane and of accreting stars in the photon thermal luminosity-mean mass accretion rate plane to be compared with observations. This approach permits to explore not only superdense matter but also the mass distributions of isolated and accreting neutron stars. We show that the observations of these stars can be reasonably well explained by assuming the presence of the powerful direct Urca process of neutrino emission in the inner cores of massive stars, introducing a slight broadening of the direct Urca threshold (for instance, by proton superfluidity), and by tuning mass distributions of isolated and accreted neutron stars.

Beznogov, M. V.; Yakovlev, D. G.

2015-02-01

138

Gravitational Waves from Rapidly Rotating Neutron Stars  

NASA Astrophysics Data System (ADS)

Rapidly rotating neutron stars in Low Mass X-ray Binaries have been proposed as an interesting source of gravitational waves. In this chapter we present estimates of the gravitational wave emission for various scenarios, given the (electromagnetically) observed characteristics of these systems. First of all we focus on the r-mode instability and show that a "minimal" neutron star model (which does not incorporate exotica in the core, dynamically important magnetic fields or superfluid degrees of freedom), is not consistent with observations. We then present estimates of both thermally induced and magnetically sustained mountains in the crust. In general magnetic mountains are likely to be detectable only if the buried magnetic field of the star is of the order of B ? 10^{12} G. In the thermal mountain case we find that gravitational wave emission from persistent systems may be detected by ground based interferometers. Finally we re-asses the idea that gravitational wave emission may be balancing the accretion torque in these systems, and show that in most cases the disc/magnetosphere interaction can account for the observed spin periods.

Haskell, Brynmor; Andersson, Nils; D`Angelo, Caroline; Degenaar, Nathalie; Glampedakis, Kostas; Ho, Wynn C. G.; Lasky, Paul D.; Melatos, Andrew; Oppenoorth, Manuel; Patruno, Alessandro; Priymak, Maxim

139

Rotational and magnetic field instabilities in neutron stars  

SciTech Connect

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

Kokkotas, Kostas D. [Theoretical Astrophysics, IAAT, Eberhard Karls University of Tübingen, Tübingen 72076 (Germany)

2014-01-14

140

Dark matter transport properties and rapidly rotating neutron stars  

E-print Network

Neutron stars are attractive places to look for dark matter because their high densities allow repeated interactions. Weakly interacting massive particles (WIMPs) may scatter efficiently in the core or in the crust of a neutron star. In this paper we focus on WIMP contributions to transport properties, such as shear viscosity or thermal conductivity, because these can be greatly enhanced by long mean free paths. We speculate that WIMPs increase the shear viscosity of neutron star matter and help stabilize r-mode oscillations. These are collective oscillations where the restoring force is the Coriolis force. At present r-modes are thought to be unstable in many observed rapidly rotating stars. If WIMPs stabilize the r-modes, this would allow neutron stars to spin rapidly. This likely requires WIMP-nucleon cross sections near present experimental limits and an appropriate density of WIMPs in neutron stars.

C. J. Horowitz

2012-05-16

141

Relativistic superfluid models for rotating neutron stars  

E-print Network

This article starts by providing an introductory overview of the theoretical mechanics of rotating neutron stars as developped to account for the frequency variations, and particularly the discontinuous glitches, observed in pulsars. The theory suggests, and the observations seem to confirm, that an essential role is played by the interaction between the solid crust and inner layers whose superfluid nature allows them to rotate independently. However many significant details remain to be clarified, even in much studied cases such as the Crab and Vela. The second part of this article is more technical, concentrating on just one of the many physical aspects that needs further development, namely the provision of a satisfactorily relativistic (local but not microscopic) treatment of the effects of the neutron superfluidity that is involved.

Brandon Carter

2001-01-16

142

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

143

Coalescence of Magnetized Binary Neutron Star Systems  

NASA Astrophysics Data System (ADS)

We present simulations of the merger of binary neutron star systems calculated with full general relativity and incorporating the global magnetic field structure for the stars evolved with resistive magnetohydrodynamics. Our simulation tools have recently been improved to incorporate the effects of neutrino cooling and have been generalized to allow for tabular equations of state to describe the degenerate matter. Of particular interest are possible electromagnetic counterparts to the gravitational radiation that emerges from these systems. We focus on magnetospheric interactions that ultimately tap into the gravitational potential energy of the binary to power a Poynting flux and deposition of energy through Joule heating and magnetic reconnection. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

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

2015-01-01

144

A SECOND NEUTRON STAR IN M4?  

SciTech Connect

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

Kaluzny, J.; Rozanska, A.; Rozyczka, M.; Krzeminski, W. [Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw (Poland); Thompson, Ian B. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2012-05-01

145

Neutron star cooling and pion condensation  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

146

Holographic cold nuclear matter and neutron star  

E-print Network

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/$\\overline{\\rm D8}$ 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.

Kazuo Ghoroku; Kouki Kubo; Motoi Tachibana; Fumihiko Toyoda

2014-02-19

147

Quark matter droplets in neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

148

Sound velocity bound and neutron stars.  

PubMed

It has been conjectured that the velocity of sound in any medium is smaller than the velocity of light in vacuum divided by sqrt[3]. Simple arguments support this bound in nonrelativistic and/or weakly coupled theories. The bound has been demonstrated in several classes of strongly coupled theories with gravity duals and is saturated only in conformal theories. We point out that the existence of neutron stars with masses around two solar masses combined with the knowledge of the equation of state of hadronic matter at "low" densities is in strong tension with this bound. PMID:25658990

Bedaque, Paulo; Steiner, Andrew W

2015-01-23

149

Diffusive Nuclear Burning in Neutron Star Envelopes  

E-print Network

We present a new mode of hydrogen burning on neutron stars (NSs) called diffusive nuclear burning (DNB). In DNB, the burning occurs in the exponentially suppressed tail of hydrogen that extends to the hotter regions of the envelope where protons are readily captured. Diffusive nuclear burning changes the compositional structure of the envelope on timescales $\\sim 10^{2-4} {\\rm yrs}$, much shorter than otherwise expected. This mechanism is applicable to the physics of young pulsars, millisecond radio pulsars (MSPs) and quiescent low mass X-ray binaries (LMXBs).

P. Chang; L. Bildsten

2002-11-02

150

Sound Velocity Bound and Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Bedaque, Paulo; Steiner, Andrew W.

2015-01-01

151

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

152

Probing dense matter in neutron stars with axial w modes  

SciTech Connect

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

Chatterjee, Debarati; Bandyopadhyay, Debades [Theory Division and Centre for Astroparticle Physics, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064 (India)

2009-07-15

153

Axisymmetric toroidal modes of magnetized neutron stars  

E-print Network

We calculate axisymmetric toroidal modes of magnetized neutron stars with a solid crust. We assume the interior of the star is threaded by a poloidal magnetic field that is continuous at the surface with the outside dipole field whose strength $B_p$ at the magnetic pole is $B_p\\sim 10^{16}$G. Since separation of variables is not possible for oscillations of magnetized stars, we employ finite series expansions of the perturbations using spherical harmonic functions to represent the angular dependence of the oscillation modes. For $B_p\\sim 10^{16}$G, we find distinct mode sequences, in each of which the oscillation frequency of the toroidal mode slowly increases as the number of radial nodes of the eigenfunction increases. The frequency spectrum of the toroidal modes for $B_p\\sim 10^{16}$G is largely different from that of the crustal toroidal modes of the non-magnetized model, although the frequency ranges are overlapped each other. This suggests that an interpretation of the observed QPOs based on the magnetic toroidal modes may be possible if the field strength of the star is as strong as $B_p\\sim 10^{16}$G.

U. Lee

2007-10-26

154

Neutron stars in the Starobinsky model  

NASA Astrophysics Data System (ADS)

We study the structure of neutron stars in the f(R)=R+?R2 theory of gravity (the Starobinsky model) in an exact and nonperturbative approach. In this model, apart from the standard general relativistic junction conditions, two extra conditions—namely, the continuity of the curvature scalar and its first derivative—need to be satisfied. For an exterior Schwarzschild solution, the curvature scalar and its derivative must be zero at the stellar surface. We show that for some equation of state (EoS) of matter, matching all conditions at the surface of the star is impossible. Hence the model brings two major fine-tuning problems: (i) only some particular classes of EoS are consistent with Schwarzschild at the surface, and (ii) given the EoS, only a very particular set of boundary conditions at the center of the star will satisfy the given boundary conditions at the surface. Hence we show that this model [and subsequently many other f(R) models where the uniqueness theorem is valid] is highly unnatural for the existence of compact astrophysical objects. This is because the EoS of a compact star should be completely determined by the physics of nuclear matter at high density and not the theory of gravity.

Ganguly, Apratim; Gannouji, Radouane; Goswami, Rituparno; Ray, Subharthi

2014-03-01

155

RADIATION FROM CONDENSED SURFACE OF MAGNETIC NEUTRON STARS  

E-print Network

RADIATION FROM CONDENSED SURFACE OF MAGNETIC NEUTRON STARS Matthew van Adelsberg,1 Dong Lai,1 metallic condensed surface, without going through a gaseous atmosphere. Here we discuss emission properties of condensed Fe and H surfaces of magnetic neutron stars in the regimes where such condensation may be possible

156

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

157

A Neutron Star in F-sharp  

E-print Network

In this short introductory commentary on the paper (Hessels et al 2006, Science, 311, 1901) reporting the discovery of the shortest spin period millisecond pulsar (MSP) Ter5-ad in the globular cluster Terzan 5, I also point out a new explanation for possible minimum spin periods, P, of MSPs without requiring gravitational radiation (or other) slow-down torques. If the accretion of matter required to spinup a MSP also reduces (buries) the neutron star (NS) magnetic field, B, as commonly believed, an inverse correlation between neutron star mass, M, and B is expected together with a positive correlation between P and B. Both are suggested for the 4 MSPs with NS mass measures reported (Latimer and Prakash 2004, Science, 304, 536) to have <~10% uncertainties. The correlations imply the Ter5-ad NS has ~2.5 Msun, B ~5 x 10^7 G and thus Pdot ~3 x 10^-21 s/s -- which can be tested when a timing solution is found. If confirmed, the highest spin frequency NSs do not pulse simply because their B fields are too low.

Jonathan E. Grindlay

2006-05-04

158

NSMAXG: A new magnetic neutron star spectral model in XSPEC  

NASA Astrophysics Data System (ADS)

The excellent sensitivity of X-ray telescopes, such as Chandra and XMM-Newton, is ideal for the study of cooling neutron stars, which can emit at these energies. In order to exploit the wealth of information contained in the high quality data, a thorough knowledge of the radiative properties of neutron star atmospheres is necessary. A key factor affecting photon emission is magnetic fields, and neutron stars are known to have strong surface magnetic fields. Here I briefly describe our latest work on constructing magnetic (B >= 1010 G) atmosphere models of neutron stars and the NSMAXG implementation of these models in XSPEC. Our results allow for more robust extractions of neutron star parameters from observations.

Ho, Wynn C. G.

2014-08-01

159

NARROW ATOMIC FEATURES FROM RAPIDLY SPINNING NEUTRON STARS  

SciTech Connect

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

Bauboeck, Michi; Psaltis, Dimitrios; Oezel, Feryal, E-mail: mbaubock@email.arizona.edu, E-mail: dpsaltis@email.arizona.edu, E-mail: fozel@email.arizona.edu [Astronomy Department, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)] [Astronomy Department, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2013-04-01

160

Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State  

E-print Network

With central densities way above the density of atomic nuclei, neutron stars contain matter in one of the densest forms found in the universe. Depending of the density reached in the cores of neutron stars, they may contain stable phases of exotic matter found nowhere else in space. This article gives a brief overview of the phases of ultra-dense matter predicted to exist deep inside neutron stars and discusses the equation of state associated with such matter.

Fridolin Weber; Matthew Meixner; Rodrigo P. Negreiros; Manuel Malheiro

2006-06-05

161

On the electrostatic structure of neutron stars  

NASA Astrophysics Data System (ADS)

We consider neutron stars composed by, (1) a core of degenerate neutrons, protons, and electrons above nuclear density; (2) an inner crust of nuclei in a gas of neutrons and electrons; and (3) an outer crust of nuclei in a gas of electrons. We use for the strong interaction model for the baryonic matter in the core an equation of state based on the phenomenological Weizsacker mass formula, and to determine the properties of the inner and the outer crust below nuclear saturation density we adopt the well-known equation of state of Baym-Bethe-Pethick. The integration of the Einstein-Maxwell equations is carried out under the constraints of ?-equilibrium and global charge neutrality. We obtain baryon densities that sharply go to zero at nuclear density and electron densities matching smoothly the electron component of the crust. We show that a family of equilibrium configurations exists fulfilling overall neutrality and characterized by a non-trivial electrodynamical structure at the interface between the core and the crust. We find that the electric field is overcritical and that the thickness of the transition surface-shell separating core and crust is of the order of the electron Compton wavelength.

Rueda, Jorge A.; Ruffini, Remo; Xue, S.-S.

2010-03-01

162

Tidal Stablization of Neutron Stars and White Dwarfs  

E-print Network

What happens to a neutron star or white dwarf near its maximum mass limit when it is brought into a close binary orbit with a companion? Such situation may occur in the progenitors of Type Ia supernovae and in coalescing neutron star binaries. Using an energy variational principle, we show that tidal field reduces the central density of the compact object, making it more stable against radial collapse. For a cold white dwarf, the tidal field increases the maximum stable mass only slightly, but can actually lower the maximum central density by as much as $30\\%$. Thus a white dwarf in a close binary may be more susceptible to general relativistic instability than the instability associated with electron capture and pycronuclear reaction (depending on the white dwarf composition). We analyse the radial stability of neutron star using post-Newtonian approximation with an ideal degenerate neutron gas equation of state. The tidal stablization effect implies that the neutron star in coalescing neutron star-neutron star or neutron star-black hole binaries does not collapse prior to merger or tidal disruption.

Dong Lai

1996-05-16

163

Mass and radius formulas for low-mass neutron stars  

E-print Network

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) 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 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 the 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.

Hajime Sotani; Kei Iida; Kazuhiro Oyamatsu; Akira Ohnishi

2013-12-31

164

Gravitational waves from neutron stars described by modern EOS  

E-print Network

The frequencies and damping times of neutron star (and quark star) oscillations have been computed using the most recent equations of state available in the literature. We find that some of the empirical relations that connect the frequencies and damping times of the modes to the mass and radius of the star, and that were previously derived in the literature need to be modified.

O. Benhar; V. Ferrari; L. Gualtieri

2004-10-28

165

Journey to the Center of a Neutron Star  

NASA Technical Reports Server (NTRS)

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

Wanjek, Christopher

2003-01-01

166

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

167

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

168

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

169

Superfluid Heat Conduction and the Cooling of Magnetized Neutron Stars  

E-print Network

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

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

2008-07-29

170

Superfluid heat conduction and the cooling of magnetized neutron stars  

SciTech Connect

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

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

2008-01-01

171

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

PubMed

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

Yagi, Kent; Yunes, Nicolás

2013-07-26

172

Magnetic field evolution in neutron stars  

NASA Astrophysics Data System (ADS)

I will discuss our current theoretical understanding of the physical effects and processes governing the evolution of magnetic fields, likely starting from stable MHD-equilibrium configurations in newborn neutron stars, which then slowly evolve through non-ideal MHD processes such as resistive dissipation and Hall drift in the crust, non-equilibrium beta decays and ambipolar diffusion in the core. The energy dissipated by these processes and their temperature-dependence lead to an interplay between the thermal and magnetic evolution. I will give our current best guesses for their effects in magnetars, classical pulsars, long-lived accreting low-mass X-ray binaries, and their final state as millisecond pulsars.

Reisenegger, Andreas

173

Magnetic Fields of Neutron Stars in X-Ray Binaries  

NASA Astrophysics Data System (ADS)

A substantial fraction of the known neutron stars resides in X-ray binaries -- systems in which one compact object accretes matter from a companion star. Neutron stars in X-ray binaries have magnetic fields among the highest found in the Universe, spanning at least the range from $\\sim10^8$ to several 10$^{13}$ G. The magnetospheres around these neutron stars have a strong influence on the accretion process, which powers most of their emission. The magnetic field intensity and geometry, are among the main factors responsible for the large variety of spectral and timing properties observed in the X-ray energy range, making these objects unique laboratories to study the matter behavior and the radiation processes in magnetic fields unaccessible on Earth. In this paper we review the main observational aspects related to the presence of magnetic fields in neutron star X-ray binaries and some methods that are used to estimate their strength.

Revnivtsev, Mikhail; Mereghetti, Sandro

2014-12-01

174

The Breaking Strain of Neutron Star Crust and Gravitational Waves  

E-print Network

Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of neutron star crust. With multi-million ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Due to the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their 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 and micro flares.

C. J. Horowitz; Kai Kadau

2009-04-13

175

Neutron star dynamos and the origins of pulsar magnetism  

NASA Technical Reports Server (NTRS)

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

Thompson, Christopher; Duncan, Robert C.

1993-01-01

176

Solar flare leaves sun quaking  

NASA Astrophysics Data System (ADS)

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

1998-05-01

177

Evolution of Young Neutron Star Envelopes  

E-print Network

We extend our initial study of diffusive nuclear burning (DNB) for neutron stars (NSs) with Hydrogen atmospheres and an underlying layer of proton capturing nuclei. Our initial study showed that DNB can alter the photospheric abundance of Hydrogen on surprisingly short timescales ($10^{2-4}\\yrs$). Significant composition evolution impacts the radiated thermal spectrum from the NS as well as its overall cooling rate. In this paper, we consider the case when the rate limiting step for the H consumption is diffusion to the burning layer, rather than the local nuclear timescale. This is relevant for NSs with surface temperatures in excess of $10^6 {\\rm K}$, such as young ($<10^5$ yr) radio pulsars and accreting NSs in quiescence. When downward diffusion is the limiting rate in DNB, the rate of H consumption is suppressed by 1-2 orders of magnitude compared to a DNB estimate that assumes diffusive equilibrium. In order to apply our ongoing study to young neutron stars, we also include the important effects of strong magnetic fields ($B \\sim 10^{12} {\\rm G}$). In this initial study of magnetic modifications to DNB, we find that the H burning time is lengthened by 2-3 orders of magnitude for a $10^{12} {\\rm G}$ field. However, even for NSs with dipole field strengths of $10^{12}$ G, we find that all of the H can be burned before the pulsar reaches an age of $\\sim 10^5 \\ {\\rm yr}$, thus potentially revealing the underlying proton-capturing elements. Finally, we conclude by providing an overview of what can be learned about fallback and pulsar winds from measuring the surface composition of a young NS.

P. Chang; L. Bildsten

2003-12-22

178

The neutron stars of Soft X-ray Transients  

NASA Astrophysics Data System (ADS)

Soft X-ray Transients (SXRTs) have long been suspected to contain old, weakly magnetic neutron stars that have been spun up by accretion torques. After reviewing their observational properties, we analyse the different regimes that likely characterise the neutron stars in these systems across the very large range of mass inflow rates, from the peak of the outbursts to the quiescent emission. While it is clear that close to the outburst maxima accretion onto the neutron star surface takes place, as the mass inflow rate decreases, accretion might stop at the magnetospheric boundary because of the centrifugal barrier provided by the neutron star. For low enough mass inflow rates (and sufficiently short rotation periods), the radio pulsar mechanism might turn on and sweep the inflowing matter away. The origin of the quiescent emission, observed in a number of SXRTs at a level of ~1032-1033 erg s-1, plays a crucial role in constraining the neutron star magnetic field and spin period. Accretion onto the neutron star surface is an unlikely mechanism for the quiescent emission of SXRTs, as it requires very low magnetic fields and/or long spin periods. Thermal radiation from a cooling neutron star surface in between the outbursts can be ruled out as the only cause of the quiescent emission. We find that accretion onto the neutron star magnetosphere and shock emission powered by an enshrouded radio pulsar provide far more plausible models. In the latter case the range of allowed neutron star spin periods and magnetic fields is consistent with the values recently inferred from the properties of kHz quasi-periodic oscillation in low mass X-ray binaries. If quiescent SXRTs contain enshrouded radio pulsars, they provide a missing link between X-ray binaries and millisecond pulsars.

Campana, S.; Colpi, M.; Mereghetti, S.; Stella, L.; Tavani, M.

179

A Statistical Study of the Mass Distribution of Neutron Stars  

NASA Astrophysics Data System (ADS)

By reviewing the methods of mass measurements of neutron stars in four different kinds of systems, i.e., the high-mass X-ray binaries (HMXBs), low-mass X-ray binaries (LMXBs), double neutron star systems (DNSs) and neutron star-white dwarf (NS-WD) binary systems, we have collected the orbital parameters of 40 systems. By using the boot-strap method and the Monte-Carlo method, we have rebuilt the likelihood probability curves of the measured masses of 46 neutron stars. The statistical analysis of the simulation results shows that the masses of neutron stars in the X-ray neutron star systems and those in the radio pulsar systems exhibit different distributions. Besides, the Bayes statistics of these four different kind systems yields the most-probable probability density distributions of these four kind systems to be (1.340 ± 0.230)M8, (1, 505 ± 0.125)M8,(1.335 ± 0.055)M8 and (1.495 ± 0.225)M8, respectively. It is noteworthy that the masses of neutron stars in the HMXB and DNS systems are smaller than those in the other two kind systems by approximately 0.16M8. This result is consistent with the theoretical model of the pulsar to be accelerated to the millisecond order of magnitude via accretion of approximately 0.2M8. If the HMXBs and LMXBs are respectively taken to be the precursors of the BNS and NS-WD systems, then the influence of the accretion effect on the masses of neutron stars in the HMXB systems should be exceedingly small. Their mass distributions should be very close to the initial one during the formation of neutron stars. As for the LMXB and NS-WD systems, they should have already under- gone the process of suffcient accretion, hence there arises rather large deviation from the initial mass distribution.

Cheng, Zheng; Zhang, Cheng-Min; Zhao, Yong-Heng; Wang, De-Hua; Pan, Yuan-Yue; Lei, Ya-Juan

2014-07-01

180

ccsd00004644, Observing Quantum Vacuum Lensing in a Neutron Star Binary System  

E-print Network

of the recently discovered double neutron star system J0737-3039. PACS numbers: Keywords: Neutron stars have beenccsd­00004644, version 1 ­ 6 Apr 2005 Observing Quantum Vacuum Lensing in a Neutron Star Binary of magnetised neutron stars. Thanks to the optical properties of quantum vacuum in the presence of a magnetic

181

Kaon condensation in neutron star using relativistic mean field models  

E-print Network

We use the modified quark-meson coupling and the quantum hadrodynamics models to study the properties of neutron star. Coupling constants of both models are adjusted to reproduce the same saturation properties. The onset of kaon condensation in neutron star matter is studied in detail over a wide range of kaon optical potential values. Once the kaon condensation takes place, the population of kaons increases very rapidly, and kaons become the dominant component, possibly making the neutron star matter a kaonic matter if the kaon optical potential is large.

S. W. Hong; C. H. Hyun; C. Y. Ryu

2007-02-08

182

The Possible White Dwarf-Neutron Star Connection  

E-print Network

The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.

R. Canal; J. Gutierrez

1997-01-29

183

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

184

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

185

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

186

Resonant Shattering of Neutron Star Crusts  

NASA Astrophysics Data System (ADS)

The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (sGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ~10^46-10^47 erg of energy secondsbefore the merger of a NS-NS or NS-black hole binary. Such properties are consistent with Swift/BAT detections of sGRB precursors, and we use the timing of the observed precursors to place weak constraints on the crust equation of state. We describe how a larger sample of precursor detections could be used alongside coincident gravitational wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure. These two types of observations nicely complement one another, since the former constrains the equation of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state. I will also discuss shattering flares as electromagnetic counterparts to gravitational wave bursts during parabolic and elliptic encounters in dense star clusters.

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

2014-08-01

187

Surface composition of magnetic neutron stars.  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

188

Gamow's Calculation of the Neutron Star's Critical Mass Revised  

E-print Network

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

Hendrik Ludwig; Remo Ruffini

2014-09-05

189

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

Microsoft Academic Search

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

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

2003-01-01

190

Isovector potential of $?$ in nuclei and neutron star matter  

E-print Network

We determine the coupling constants of $\\Sigma$ hyperon with mesons in relativistic mean field (RMF) models using $\\Sigma^-$ atomic shift data and examine the effects of $\\Sigma$ on the neutron star maximum mass. We find that we need to reduce the vector-isovector meson coupling with $\\Sigma$ ($g_{\\rho\\Sigma}$) from the value constrained by the SU(3)v symmetry in order to explain the $\\Sigma^-$ atomic shifts for light symmetric and heavy asymmetric nuclei simultaneously. With the atomic shift fit value of $g_{\\rho\\Sigma}$, $\\Sigma^-$ can emerge in neutron star matter overcoming the repulsive isoscalar potential for $\\Sigma$ hyperons. Admixture of $\\Sigma^-$ in neutron stars is found to reduce the neutron star maximum mass slightly.

K. Tsubakihara; A. Ohnishi; T. Harada

2014-02-05

191

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

192

A Definitive Test of Relativistic Disk Lines in Neutron Stars  

NASA Astrophysics Data System (ADS)

Accretion disks around neutron stars must be truncated at the stellar surface. If neutron star spectra contain relativistic lines from the inner disk, these lines could then give constraints on stellar radii and the neutron star equation of state. Such lines have recently been claimed in many sources. However, other work has brought the nature of these lines into question, largely owing to instrumental effects such as photon pile-up. The resolution of the HETG is ideally suited to testing the nature of such lines, and it is uniquely resistant to photon pile-up when the ACIS array is run in 'CC' mode. As a unified group of six teams, we request a 300 ksec observation of Serpens X-1 to definitively resolve the nature of iron lines in neutron star low-mass X-ray binaries.

Cackett, Edward

2013-09-01

193

Neutrino-pair bremsstrahlung in a neutron star crust  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

194

Temperature-dependent pulsations of superfluid neutron stars  

E-print Network

We examine radial oscillations of superfluid neutron stars at finite internal temperatures. For this purpose we generalize the description of relativistic superfluid hydrodynamics to the case of superfluid mixtures. We show that in a neutron star at hydrostatic and beta-equilibrium the red-shifted temperature gradient is smoothed out by neutron superfluidity (but not by proton superfluidity). We calculate radial oscillation modes of neutron stars assuming "frozen" nuclear composition in the pulsating matter. The resulting pulsation frequencies show a strong temperature dependence in the temperature range (0.1-1) T_cn, where T_cn is the critical temperature of neutron superfluidity. Combining our results with thermal evolution, we obtain a significant evolution of the pulsation spectrum, associated with highly efficient Cooper pairing neutrino emission, for 20 years after superfluidity onset.

M. E. Gusakov; N. Andersson

2006-02-13

195

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

SciTech Connect

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

Nomoto, K.

1986-01-01

196

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

197

Phase separation in the crust of accreting neutron stars.  

PubMed

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

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

2007-06-01

198

Short Gamma-Ray Bursts from Binary Neutron Star Mergers  

E-print Network

We present the results from new relativistic hydrodynamic simulations of binary neutron star mergers using realistic non-zero temperature equations of state. We vary several unknown parameters in the system such as the neutron star (NS) masses, their spins and the nuclear equation of state. The results are then investigated with special focus on the post-merger torus-remnant system. Observational implications on the Gamma-ray burst (GRB) energetics are discussed and compared with recent observations.

Roland Oechslin; Thomas Janka

2006-04-27

199

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

200

Gravitational waves from newly born, hot neutron stars  

E-print Network

We study the gravitational radiation associated to the non--radial oscillations of newly born, hot neutron stars. The frequencies and damping times of the relevant quasi--normal modes are computed for two different models of proto--neutron stars, at different times of evolution, from its birth until it settles down as a cold neutron star. We find that the oscillation properties of proto--neutron stars are remarkably different from those of their cold, old descendants and that this affects the characteristic features of the gravitational signal emitted during the post-collapse evolution. The consequences on the observability of these signals by resonant--mass and interferometric detectors are analyzed. We find that gravitational waves from the pulsations of a newborn proto--neutron star in the galaxy could be detected with a signal to noise ratio of 5 by the first generation interferometers, if the energy stored in the modes is greater than $\\sim 10^{-8} M_\\odot c^2$, or by a resonant antenna if it is greater than $\\sim 10^{-4} M_\\odot c^2$. In addition since at early times the frequency of the spacetime modes is much lower than that of a cold neutron star, they would be also detectable with the same signal to noise ratio if a comparable amount of energy is radiated into these modes.

Valeria Ferrari; Giovanni Miniutti; Jose' A. Pons

2002-10-26

201

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

202

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment  

Microsoft Academic Search

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

Dong Lai; Stuart L. Shapiro

1995-01-01

203

Neutron-Capture Element Abundances in Halo Stars  

E-print Network

We present new abundance observations of neutron-capture elements in Galactic stars. These include new Hubble Space Telescope (HST) detections of the elements Ge, Zr and Pt in a group of 11 halo stars. Correlations between these elements and Eu (obtained with ground-based observations), and with respect to metallicity, are also presented.

John J. Cowan; Christopher Sneden

2004-09-22

204

Resonant shattering of neutron star crusts.  

PubMed

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

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

2012-01-01

205

Unifying neutron stars: getting to GUNS  

E-print Network

The variety of the observational appearance of young isolated neutron stars must find an explanation in the framework of some unifying approach. Nowadays it is believed that such scenario must include magnetic field decay, the possibility of magnetic field emergence on a time scale $\\lesssim 10^4$--$10^5$ yrs, significant contribution of non-dipolar fields, and appropriate initial parameter distributions. We present our results on the initial spin period distribution, and suggest that inconsistences between distributions derived by different methods for samples with different average ages can uncover field decay or/and emerging field. We describe a new method to probe the magnetic field decay in normal pulsars. The method is a modified pulsar current approach, where we study pulsar flow along the line of increasing characteristic age for constant field. Our calculations, performed with this method, can be fitted with an exponential decay for ages in the range $8\\times 10^4$--$3.5 \\times 10^5$ yrs with a time ...

Igoshev, A P; Turolla, R

2013-01-01

206

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

207

Gravitational radiation during coalescence of neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

208

Simulations of Axisymmetric Magnetospheres of Neutron Stars  

E-print Network

In this paper we present the results of time-dependent simulations of dipolar axisymmetric magnetospheres of neutron stars carried out both within the framework of relativistic magnetohydrodynamics and within the framework of resistive force-free electrodynamics. The results of force-free simulations reveal the inability of our numerical method to accommodate the equatorial current sheets of pulsar magnetospheres and raise a question mark over the robustness of this approach. On the other hand, the MHD approach allows to make a significant progress. We start with a nonrotating magnetically dominated dipolar magnetospheres and follow its evolution as the stellar rotation is switched on. We find that the time-dependent solution gradually approaches the steady state that is very close to the stationary solution of the Pulsar Equation found by Contopoulos et al.(1999). This result suggests that other stationary solutions that have the y-point located well inside the light cylinder are unstable. The role of the particle inertia and pressure on the structure and dynamics of MHD magnetospheres is studied in details, as well as the potential implications of the dissipative processes in the equatorial current sheet. We argue that pulsars may have differentially rotating magnetospheres which develop noticeable structural oscillations and that this may help to explain the nature of the sub-pulse phenomena.

S. S. Komissarov

2005-10-11

209

Diffusive Nuclear Burning on Neutron Star Envelopes  

E-print Network

We calculate the rate of hydrogen burning for neutron stars (NSs) with hydrogen atmospheres and an underlying reservoir of nuclei capable of proton capture. This burning occurs in the exponentially suppressed diffusive tail of H that extends to the hotter depths of the envelope where protons are rapidly captured. This process, which we call diffusive nuclear burning (DNB), can change the H abundance at the NS photosphere on timescales as short as $10^{2-4}$ years. In the absence of diffusion, the hydrogen at the photosphere (where $T\\approx 10^6 {\\rm K}$ and $\\rho\\sim 0.1 {\\rm g cm^{-2}}$) would last for far longer than a Hubble time. Our work impacts the understanding of the evolution of surface abundances of isolated NSs, which is important to their thermal spectrum and their effective temperature-core temperature relation. In this paper, we calculate the rate of H burning when the overall consumption rate is controlled by the nuclear timescales, rather than diffusion timescales. The immediate application is for H burning on millisecond radio pulsars and in quiescence for the accreting NS Cen X-4. We will apply this work to young radio pulsars and magnetars once we have incorporated the effects of strong $B>10^{12} {\\rm G}$ magnetic fields.

P. Chang; L. Bildsten

2002-10-09

210

Early appearance of ? isobars in neutron stars  

NASA Astrophysics Data System (ADS)

We discuss the formation of ? isobars in neutron star matter. We show that their threshold density strictly correlates with the density derivative of the symmetry energy of nuclear matter: the L parameter. By restricting L to the range of values indicated by recent experimental and theoretical analysis, i.e., 40 MeV?L ?62 MeV , we find that ? isobars appear at a density of the order of 2 to 3 times the nuclear matter saturation density, i.e., the same range as for the appearance of hyperons. The range of values of the couplings of the ? s with the mesons is restricted by the analysis of the data obtained from photoabsorption, electron and pion scattering on nuclei. If the potential of the ? in nuclear matter is close to the one indicated by the experimental data then the equation of state becomes soft enough that a "? puzzle" exists, similar to the "hyperon puzzle" widely discussed in the literature. Possible solutions to this puzzle are also discussed.

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

2014-12-01

211

Neutron specific heat in the crust of neutron stars from the nuclear band theory  

E-print Network

The inner crust of neutron stars, formed of a crystal lattice of uclear clusters immersed in a sea of unbound neutrons, may be the nique example of periodic nuclear systems. We have calculated the neutron specific heat in the shallow part of the crust using the band theory of solids with Skyrme nucleon-nucleon interactions. We have also tested the validity of various approximations. We have found that the neutron specific heat is well described by that of a Fermi gas, while the motion of the unbound neutrons is strongly affected by the nuclear lattice. These apparently contradictory results are explained by the particular properties of the neutron Fermi surface.

Nicolas Chamel; Jérôme Margueron; Elias Khan

2008-12-23

212

Neutron Stars Join The Black Hole Jet Set  

NASA Astrophysics Data System (ADS)

NASA's Chandra X-ray Observatory has revealed an X-ray jet blasting away from a neutron star in a binary system. This discovery may help astronomers understand how neutron stars as well as black holes can generate powerful beams of relativistic particles. The jet was found in Circinus X-1, a system where a neutron star is in orbit around a star several times the mass of the Sun, about 20,000 light years from Earth. A neutron star is an extremely dense remnant of an exploded star consisting of tightly packed neutrons. Many jets have been found originating near black holes - both the supermassive and stellar-mass variety - but the Circinus X-1 jet is the first extended X-ray jet associated with a neutron star in a binary system. This detection shows that the unusual properties of black holes - such as presence of an event horizon and the lack of an actual surface - may not be required to form powerful jets. "Gravity appears to be the key to creating these jets, not some trick of the event horizon," said Sebastian Heinz of the University of Wisconsin at Madison, who led the study. The discovery of this jet with Chandra also reveals how efficient neutron stars can be as cosmic power factories. Heinz and his colleagues estimate that a surprisingly high percentage of the energy available from material falling onto the neutron star is converted into powering the jet. "In terms of energy efficiency across the Universe, this result shows that neutron stars are near the top of the list," said Norbert Schulz, a coauthor from the Massachusetts Institute of Technology in Cambridge. "This jet is almost as efficient as one from a black hole." The Chandra results also help to explain the origin of diffuse lobes of radio emission previously detected around Circinus X-1. The team found the X-ray jets of high-energy particles are powerful enough to create and maintain these balloons of radio-emitting gas. "We've seen enormous radio clouds around supermassive black holes at the centers of galaxies," said Heinz. "What's unusual here is that this pocket-sized version, relatively speaking, is being powered by a neutron star, not a black hole." The main evidence for the newly found jet comes in two extended features in the Chandra data. These two fingers of X-ray emission are separated by about 30 degrees and may represent the outer walls of a wide jet. When overlapped with radio images, these X-ray features, which are at least five light years from the neutron star, closely trace the outline of the radio jet. Another interpretation is that these two features represent two separate, highly collimated jets produced at different times by a precessing neutron star. That is, the neutron star wobbles like a top as it spins and the jet fires at different angles at different times. Jet precession is also consistent with radio observations taken at different times, which show varying orientation angles of the jet. If the precession scenario is correct, Circinus X-1 would possess one of the longest, narrowest jets found in X-ray binary systems to date, representing yet another way in which neutron stars can rival and even outdo their larger black hole relatives. These results will appear in an upcoming issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

2007-06-01

213

Neutron Stars And The Oppenheimer-Volkoff Limit  

NASA Astrophysics Data System (ADS)

Generalized Yukawa-Maxwell Theory combines a generalized Maxwell electromagnetic field theory with a generalized Yukawa interaction (valid for all four fundamental forces), with the fermion-degeneracy energy, and with the size-dependence of mass. Two versions of the theory are considered, where the fermions can be neutrons-protons or u-d-quarks. Mass density, nuclear compressibility and symmetry energy of a neutron star like that associated with the Crab Pulsar show a marked preference for the quark version. The mass stability limit of a quark (neutron) star becoming a black hole is predicted to be 3.6M?.

Kumar, Krishna

2005-07-01

214

Cosmic superfluidity: the evidence for superfluidity in neutron stars.  

NASA Astrophysics Data System (ADS)

Neutron stars are expected to be superfluid on quite general grounds. Following a brief historical review of theoretical calculations which have suggested the existence of at least three distinct superfluids inside neutron stars, the astrophysical evidence for their existence, which comes from the agreement between theory and observation for the observed relaxation of the rotation and spindown rates of the Vela and Crab pulsars, and of PSR 0525+21, following sudden jumps (glitches) in these quantities, is reviewed. The prospects for observing similar consequences of the pinned crustal neutron superfluid in the recently-discovered millisecond pulsars are examined.

Pines, D.

215

Mass and radius formulas for low-mass neutron stars  

E-print Network

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) 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 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 the 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 equat...

Sotani, Hajime; Oyamatsu, Kazuhiro; Ohnishi, Akira

2014-01-01

216

Thermal evolution of neutron stars with internal frictional heating  

NASA Technical Reports Server (NTRS)

It has been suggested that the frictional interaction of neutron superfluids with normal matter in the inner crust of neutron stars dissipates rotational energy of superfluids and generates heat. Incorporating a general formula of internal heating into the detailed numerical codes of thermal evolution, we examine the effects of the internal heating on thermal evolution of neutron stars. We find that when a very stiff equation of state is used, it takes as long as about 2 x 10 exp 4 yr for the interior of a neutron star to reach the isothermal state, even if a strong heat source is placed in a thin layer of the inner crust. This time scale reduces to a few hundred years or less when medium to soft equations of state are used. A neutron star cools by neutrino emissions during the earlier stages referred to as the neutrino cooling era, while during the later photon cooling era it cools primarily by emission of photons from its surface. We show that heating rates expected in the current superfluid-crust interaction model can greatly increase the surface temperature in the photon cooling era, significantly changing the thermal evolution of relatively old neutron stars if a stiff equation of state is adopted.

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

1993-01-01

217

Hydromagnetic Equilibria and their Evolution in Neutron Stars  

NASA Astrophysics Data System (ADS)

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

Reisenegger, Andreas

2014-08-01

218

Self-similarity relations for cooling superfluid neutron stars  

NASA Astrophysics Data System (ADS)

We consider models of cooling neutron stars with nucleon cores which possess moderately strong triplet-state superfluidity of neutrons. When the internal temperature drops below the maximum of the critical temperature over the core, TC, this superfluidity sets in. It produces a neutrino outburst due to Cooper pairing of neutrons which greatly accelerates the cooling. We show that the cooling of the star with internal temperature T within 0.6 TC ? T ? TC is described by analytic self-similar relations. A measurement of the effective surface temperature of the star and its decline, supplemented by assumptions on star's mass, radius and composition of heat-blanketing envelope, allows one to construct a family of cooling models parametrized by the value of TC. Each model reconstructs cooling history of the star including its neutrino emission level before neutron superfluidity onset and the intensity of Cooper pairing neutrinos. The results are applied to interpret the observations of the neutron star in the Cassiopeia A supernova remnant.

Shternin, P. S.; Yakovlev, D. G.

2015-02-01

219

Constraining neutron star tidal Love numbers with gravitational wave detectors  

E-print Network

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

Eanna E. Flanagan; Tanja Hinderer

2007-12-07

220

Ferromagnetism of dense matter and magnetic properties of neutron stars  

E-print Network

Possible consequences of ferromagnetic transition in dense matter suggested recently by Kutschera and W{\\'o}jcik, for the magnetic properties of neutron stars, are studied. Specific model of dense matter, in which a small admixture of protons is completely polarized due to their interaction with neutrons, is considered. Magnetic field of neutron stars with a ferromagnetic core is calculated within the framework of general relativity. Two types of boundary conditions at the ferromagnetic core edge are considered, corresponding to normal and superconducting liquid envelope, respectively. Numerical results for the neutron star magnetic dipole moment are confronted with pulsar timing. To be consistent with observations, ferromagnetic cores surrounded by a non-superconducting envelope, should consist of weakly ordered ferromagnetic domains. If domains are highly ordered, ferromagnetic core should be screened by a superconducting envelope.

P. Haensel; S. Bonazzola

1996-05-24

221

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

222

The Dynamics and Outcomes of Rapid Infall onto Neutron Stars  

E-print Network

We present an extensive study of accretion onto neutron stars in which the velocity of the neutron star and structure of the surrounding medium is such that the Bondi-Hoyle accretion exceeds .001 Msun/y. For most cases, hypercritical accretion due to rapid neutrino cooling allows the neutron star to accrete above the Bondi-Hoyle rate as previously pointed out by Chevalier. However, for a subset of simulations which corresponds to evolutionarily common events, convection driven by neutrino heating can lead to explosions by a mechanism similar to that found in core-collapse supernovae. Armed with the results from our calculations, we are in a position to predict the fate of a range of rapid-infall neutron star accretors present in certain low-mass X-ray binaries, common envelope systems, supernova fallbacks and Thorne-Zytkow objects (TZOs). A majority of the common envelope systems that we considered led to explosions expelling the envelope, halting the neutron star's inward spiral, and allowing the formation of close binary systems. Smothered neutron stars produced in collisions also lead to explosions, preventing them from forming millisecond pulsars. For supernovae in which the fallback of material towards the neutron star is large, we find that a black hole is formed within a few seconds. Finally, we argue that the current set of TZO formation scenarios is inadequate and leads instead to hypercritical accretion and black hole formation. Moreover, it appears that many of the current TZ models have structures ill-suited for modeling by mixing length convection. This has prompted us to develop a simple test to determine the viability of this approximation for a variety of convective systems.

Chris L. Fryer; Willy Benz; Marc Herant

1995-09-27

223

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

224

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

225

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

226

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

227

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

228

Spin-down of neutron stars by neutrino emission  

SciTech Connect

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

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

2010-08-15

229

Effects of fermionic dark matter on properties of neutron stars  

E-print Network

By assuming that only gravitation exists between dark matter (DM) and normal matter (NM), we study the effects of fermionic DM on the properties of neutron stars using the two-fluid Tolman-Oppenheimer-Volkoff formalism. It is found that the mass-radius relationship of the DM admixed neutron stars (DANSs) depends sensitively on the mass of DM candidates, the amount of DM, and interactions among DM candidates. The existence of DM in DANSs results in a spread of mass-radius relationships that cannot be interpreted with a unique equilibrium sequence. In some cases, the DM distribution can surpass the NM distribution to form DM halo. In particular, it is favorable to form an explicit DM halo, provided the repulsion of DM exists. It is interesting to find that the difference in particle number density distributions in DANSs and consequently in star radii caused by various density dependencies of nuclear symmetry energy tends to disappear as long as the repulsion of accumulated DM is sufficient. These phenomena indicate that the admixture of DM in neutron stars can significantly affect the astrophysical extraction of nuclear equation of state by virtue of neutron star measurements. In addition, the effect of the DM admixture on the star maximum mass is also investigated.

Qian-Fei Xiang; Wei-Zhou Jiang; Dong-Rui Zhang; Rong-Yao Yang

2014-02-02

230

Universality in Quasi-normal Modes of Neutron Stars  

E-print Network

We study the universality in gravitational waves emitted from non-rotating neutron stars characterized by different equations of state (EOS). We find that the quasi-normal mode frequencies of such waves, including the $w$-modes and the $f$-mode, display similar universal scaling behaviours that hold for most EOS. Such behaviours are shown to stem from the mathematical structure of the axial and the polar gravitational wave equations, and the fact that the mass distribution function can be approximated by a cubic-quintic polynomial in radius. As a benchmark for other realistic neutron stars, a simple model of neutron stars is adopted here to reproduce the pulsation frequencies and the generic scaling behaviours mentioned above with good accuracy.

L. K. Tsui; P. T. Leung

2004-12-06

231

Direct Detection of Gravity Waves from Neutron Stars  

E-print Network

In light of the discovery of the first-ever double pulsar system, PSR J0737-3039, we re-examine an earlier proposal to directly detect gravity waves from neutron stars, which was predicated on a hypothetical system almost identical to the later discovered double pulsar. We re-derive the effect in more detail, and confirm the initial estimate--sometimes doubted in the literature--that it includes a 1/b dependence, where b is the impact parameter of a pulsar with respect to its foreground, gravity-wave emitting, neutron star companion. A coherent modulation in pulsar time-of-arrival measurements of 10 nano-sec/sec is possible. A one-year intermittent experiment on an instrument comparable to the SKA could thus detect the exceedingly faint gravity waves from individual neutron stars.

Redouane Al Fakir; William G. Unruh

2008-05-24

232

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

233

Narrow Lines from a Slowly Rotating Neutron Star  

NASA Astrophysics Data System (ADS)

The detection and identification of photospheric absorption lines from a neutron star would allow measurement of its gravitational redshift and hence the neutron star compactness. In principle, the line shape allows unique determination of mass and radius separately. X-ray bursters are, in most respects, the ideal targets for this search, but most rotate so rapidly that any lines are too broadened to detect. However, the recently discovered X-ray burster Terzan 5 X-2 spins at only 11 Hz, 20 times slower than the next slowest rotator. We propose a TOO observation with HETGS to search for narrow lines of ionized Fe when this X-ray transient next becomes active. This is the best chance ever to detect a narrow atomic line in a neutron star.

Chakrabarty, Deepto

2014-09-01

234

Thermonuclear burning as a probe of neutron stars  

NASA Astrophysics Data System (ADS)

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

235

Magnetic Energy Production by Turbulence in Binary Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

The simultaneous detection of electromagnetic and gravitational wave emission from merging neutron star binaries would greatly aid in their discovery and interpretation. By studying turbulent amplification of magnetic fields in local high-resolution simulations of neutron star merger conditions, we demonstrate that magnetar-level (gsim 1016 G) fields are present throughout the merger duration. We find that the small-scale turbulent dynamo converts 60% of the randomized kinetic energy into magnetic fields on a merger timescale. Since turbulent magnetic energy dissipates through reconnection events that accelerate relativistic electrons, turbulence may facilitate the conversion of orbital kinetic energy into radiation. If 10-4 of the ~1053 erg of orbital kinetic available gets processed through reconnection and creates radiation in the 15-150 keV band, then the fluence at 200 Mpc would be 10-7 erg cm-2, potentially rendering most merging neutron stars in the advanced LIGO and Virgo detection volumes detectable by Swift BAT.

Zrake, Jonathan; MacFadyen, Andrew I.

2013-06-01

236

Rapidly rotating neutron stars in $R$-squared gravity  

E-print Network

$f(R)$ theories of gravity are one of the most popular alternative explanations for dark energy and therefore studying the possible astrophysical implications of these theories is an important task. In the present paper we make a substantial advance in this direction by considering rapidly rotating neutron stars in $R^2$ gravity. The results are obtained numerically and the method we use is non-perturbative and self-consistent. The neutron star properties, such as mass, radius and moment of inertia, are studied in detail and the results show that rotation magnifies the deviations from general relativity and the maximum mass and moment of inertia can reach very high values. This observation is similar to previous studies of rapidly rotating neutron stars in other alternative theories of gravity, such as the scalar-tensor theories, and it can potentially lead to strong astrophysical manifestations.

Yazadjiev, Stoytcho S; Kokkotas, Kostas D

2015-01-01

237

X-rays from neutron stars: recent Chandra results  

NASA Astrophysics Data System (ADS)

The outstanding capabilities of the Chandra X-ray Observatory have provided excel- lent observational data on many radio pulsars and radio-quiet neutron stars. We will present an overview of the recent results on the spectral and timing observations of var- ious types of neutron stars observed with Chandra and discuss the inferred properties of thermal radiation from the surfaces of neutron stars and nonthermal radiation from pulsar magnetospheres. In particular, we will present the analysis and interpretation of the absorption features in the spectrum of the central source of the SNR G296.5+10.0, the periodicities in the X-ray emission of the central source of the SNR RCW 103, and the phase-resolved spectroscopy of the radio pulsars B0656+14 and B1055-52.

Pavlov, G.; Zavlin, V.; Sanwal, D.; Teter, M.; Garmire, G.

238

Effects of hyperons in binary neutron star mergers.  

PubMed

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

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

2011-11-18

239

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

E-print Network

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

Contenta, Filippo; Heggie, Douglas C

2015-01-01

240

Magnetohydrodynamic processes in strongly magnetized young neutron stars  

NASA Astrophysics Data System (ADS)

We examine the early evolution of a neutron star with a very strong magnetic field (B >= 4 x 10^13 G) that occupies a significant fraction of the core volume. The electrical conductivity of the core matter is a strong function of the magnetic field, therefore the evolution of magnetized neutron stars (magnetars) may well be different from that of ordinary radiopulsars. We consider magnetohydrodynamic processes in the core for two possible models of nuclear matter, with normal and superfluid neutrons. In the case of the normal matter, an enhancement of the resistivity perpendicular to the magnetic field can result in rapid field decay during the early evolutionary stage. If neutrons are in the superfluid state, we find that the Hall effect can lead to oscillatory behaviour of the magnetic field. This oscillatory behaviour is caused by the generation of large-scale helicoid modes resulting from non-linear coupling between the different field components.

Urpin, V.; Shalybkov, D.

1999-04-01

241

PROSPECTS FOR MEASURING NEUTRON-STAR MASSES AND RADII WITH X-RAY PULSE PROFILE MODELING  

E-print Network

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 ...

Psaltis, Dimitrios

242

Neutron star matter in an effective model  

E-print Network

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

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

2007-11-13

243

Diagnostics of disk-magnetosphere interaction in neutron star binaries  

NASA Technical Reports Server (NTRS)

The interaction between the magnetospheres of accreting neutron stars and accretion disks plays at key role in determining the properties of many accretion-powered neutron star X-ray sources and the recycled binary and millisecond rotation-powered pulsars. Here we show that the behavior of the horizontal branch quasi-periodic intensity oscillations in low mass X-ray binaries and the correlation between the magnetic fields and periods of binary and millisecond pulsars are sensitive probes of the state of the inner disk.

Ghosh, Pranab; Lamb, Frederick K.

1992-01-01

244

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

245

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

246

Isospin-dependent clusterization of Neutron-Star Matter  

E-print Network

Because of the presence of a liquid-gas phase transition in nuclear matter, compact-star matter can present a region of instability against the formation of clusters. We investigate this phase separation in a matter composed of neutrons, protons and electrons, within a Skyrme-Lyon mean-field approach. Matter instability and phase properties are characterized through the study of the free-energy curvature. The effect of beta-equilibrium is also analyzed in detail, and we show that the opacity to neutrinos has an influence on the presence of clusterized matter in finite-temperature proto-neutron stars.

Camille Ducoin; Philippe Chomaz; Francesca Gulminelli

2006-12-11

247

Observing quantum vacuum lensing in a neutron star binary system.  

PubMed

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

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

2005-04-29

248

Gamma-Ray Bursts from Decompressing Neutron Star Material()  

NASA Astrophysics Data System (ADS)

We explore the possibility that decompressing neutron star material may be a source for the isotropic gamma-ray bursts observed by the Compton Gamma Ray Observatory. Such material might be ejected during the collision or tidal disruption of a neutron star in a binary sytem or as a result of neutron star seismic activity. Without gravitational confinement, this extremely neutron-rich material will decompress and heat up through a series of fissions, beta (-) decays, and photodissociations. It will then recombine in an r-process like environment. As the density drops and the material becomes optically thin, short-lived nuclei decay back to stability emitting a burst of gamma rays on a time scale of msec to sec. The resulting gamma-ray spectrum will be directly observable if the burst luminosity is low enough that a pair-dominated photosphere which would reprocess the gamma-ray spectrum is not formed. We report on efforts to model the resulting gamma-ray spectrum, which requires estimates of beta (-) decay, gamma emission, beta -delayed neutron emission, and photodissociation rates for many neutron rich nuclei. This work will eventually be coupled to hydrodynamic and radiation transport codes, in an effort to explain some of the observed gamma-ray bursts. () Work at Lawrence Livermore National Laboratory was performed under the auspices of the U.S. DoE under contract No. W-7405-ENG-48 and DOE Nuclear Theory Grant SF-ENG-48.

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

1992-12-01

249

A Hot Water Bottle for Aging Neutron Stars  

E-print Network

The gapless color-flavor locked (gCFL) phase is the second-densest phase of matter in the QCD phase diagram, making it a plausible constituent of the core of neutron stars. We show that even a relatively small region of gCFL matter in a star will dominate both the heat capacity C_V and the heat loss by neutrino emission L_\

Alford, M; Kouvaris, C; Kundu, J; Rajagopal, K; Alford, Mark; Jotwani, Pooja; Kouvaris, Chris; Kundu, Joydip; Rajagopal, Krishna

2004-01-01

250

A Hot Water Bottle for Aging Neutron Stars  

E-print Network

The gapless color-flavor locked (gCFL) phase is the second-densest phase of matter in the QCD phase diagram, making it a plausible constituent of the core of neutron stars. We show that even a relatively small region of gCFL matter in a star will dominate both the heat capacity C_V and the heat loss by neutrino emission L_\

Mark Alford; Pooja Jotwani; Chris Kouvaris; Joydip Kundu; Krishna Rajagopal

2005-04-01

251

Gamma-Ray Bursts from Neutron Star Binaries  

E-print Network

We report on general relativistic hydrodynamic studies which indicate several new physical processes which may contribute to powering gamma-ray bursts in neutron star binaries. Relativistically driven compression, heating, and collapse of the individual stars can occur many seconds before inspiral and merger. This compression may produce a neutrino burst of $\\sim 10^{53}$ ergs lasting several seconds. The associated thermal neutrino emission produces an $e^+-e^-$ pair plasma by $\

G. J. Mathews; J. R. Wilson; J. Salmonson

1997-10-21

252

Lightning Stars: Anomalous Photoproduction in Neutron Stars via Parametric Resonance Mechanism  

E-print Network

In this work we propose a new mechanism for photoproduction inside a neutron star based on Parametric Resonance phenomenon as firstly applied to Inflationary Cosmology. Our assumptions are based on the pion condensation model by Harrington and Shepard. We show that a huge number of photons are created which, on turns, reheats the matter in the star's core. Thus, we argue that Parametric Resonance can be effective during a brief period out of an neutron star lifetime leading to an anomalous uprising variation of its brightness departing from the black body radiation at regularly spaced frequencies. In adition, a time periodic signal is obtained in moderate (not exponential) regimes. We argue also that our PR mechanism offers a simple and feasible explanation for some recent observations of giant flares from neutron stars.

S. D. Campos; A. Maia Jr

2005-06-29

253

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

SciTech Connect

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

Weber, F.; Glendenning, N.K.

1992-11-02

254

Extreme neutron stars from Extended Theories of Gravity  

NASA Astrophysics Data System (ADS)

We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(Script G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant Script G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M? can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ?c ~ 1.5-2.0 GeV/fm3) are possible considering quadratic corrections of f(Script G) gravity. The magnetic field strength in the star center is of order 6-8 × 1018 G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.

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

2015-01-01

255

1Tracy K. Steinbach April 5, 2014 The outer crust of an accreting neutron star is  

E-print Network

1Tracy K. Steinbach April 5, 2014 ² The outer crust of an accreting neutron star is an unique) Haensel et al., Neutron Stars 1, 2007 Cumming et al., Astrophys. J. Lett. 559, L127 (2001) Strohmayer et al., Astrophys. J. 566, 1045 (2002) Tracy K. Steinbach Indiana University Accreting Neutron Stars #12

de Souza, Romualdo T.

256

Novel Phases at High Density and their Roles in the Structure and Evolution of Neutron Stars  

E-print Network

We present a pedagogic discussion on the role of novel phases of dense baryonic matter in ``neutron'' stars. Qualitative aspects of the physics that drives phase transitions and some of its astrophysical consequences are discussed. Observable aspects of neutron star structure and early evolution of the newly born neutron star are discussed in some detail.

Sanjay Reddy

2002-11-14

257

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

SciTech Connect

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

Weber, F.; Glendenning, N.K.

1992-11-02

258

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

259

Dark matter, neutron stars and strange quark matter  

E-print Network

We show that self-annihilating neutralino 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.

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

2010-09-04

260

Gamma-burst emission from neutron-star accretion  

SciTech Connect

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

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

1983-08-30

261

Developing a model for neutron star oscillations following starquakes  

NASA Astrophysics Data System (ADS)

Glitches - sudden increases in spin rate - are observed in many pulsars. One mechanism advanced to explain glitches in the youngest pulsars is that they are caused by a starquake, a sudden rearrangement of the crust of the neutron star. Starquakes have the potential to excite some of the oscillation modes of the neutron star, which means that they are of interest as a source of gravitational waves. These oscillations could also have an impact on radio emission. In this paper, we make upper estimates of the amplitude of the oscillations produced by a starquake, and the corresponding gravitational wave emission. We then develop a more detailed framework for calculating the oscillations excited by the starquake, using a toy model of a solid, incompressible star where all strain is lost instantaneously from the star at the glitch. For this toy model, we give plots of the amplitudes of the modes excited, as the shear modulus and rotation rate of the star are varied. We find that for our specific model, the largest excitation is generally of a mode similar to the f-mode of an incompressible fluid star, but that other modes of the star are excited to a significant degree over small parameter ranges of the rotation rate.

Keer, L.; Jones, D. I.

2015-01-01

262

Thermal conductivity of ions in a neutron star envelope  

E-print Network

We analyze the thermal conductivity of ions (equivalent to the conductivity of phonons in crystalline matter) in a neutron star envelope. We calculate the ion/phonon thermal conductivity in a crystal of atomic nuclei using variational formalism and performing momentum-space integration by Monte Carlo method. We take into account phonon-phonon and phonon-electron scattering mechanisms and show that phonon-electron scattering dominates at not too low densities. We extract the ion thermal conductivity in ion liquid or gas from literature. Numerical values of the ion/phonon conductivity are approximated by analytical expressions, valid for T>10^5 K and 10^5 g cm^-3 conductivity although they strongly reduce the electron thermal conductivity across the magnetic field. The ion thermal conductivity remains much smaller than the electron conductivity along the magnetic field. However, in the outer neutron star envelope it can be larger than the electron conductivity across the field, that is important for heat transport across magnetic field lines in cooling neutron stars. The ion conductivity can greatly reduce the anisotropy of heat conduction in outer envelopes of magnetized neutron stars.

A. I. Chugunov; P. Haensel

2007-07-31

263

Very massive neutron stars in Ni's theory of gravity  

NASA Technical Reports Server (NTRS)

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

Mikkelsen, D. R.

1977-01-01

264

Comparison of Neutron Star Models Using Various EOS  

NASA Astrophysics Data System (ADS)

In this work we discuss the solutions of the Tolman-Oppenheimer-Volkov equation for different inputs of Equation Of State (EOS). These solutions represent static models of Neutron Stars (NS). Modern EOS are used for this purpose, based on recent research on nuclear matter. The resulting NS models are compared to recent observations.

Naizer, Michael; Newton, William; Bertulani, Carlos

2012-10-01

265

Statistics of Neutron Stars at the Stage of Supersonic Propeller  

E-print Network

We analyze the statistical distribution of neutron stars at the stage of a supersonic propeller. An important point of our analysis is allowance for the evolution of the angle of inclination of the magnetic axis to the spin axis of the neutron star for the boundary of the transition to the supersonic propeller stage for two models: the model with hindered particle escape from the stellar surface and the model with free particle escape. As a result, we have shown that a consistent allowance for the evolution of the inclination angle in the region of extinct radio pulsars for the two models leads to an increase in the total number of neutron stars at the supersonic propeller stage. This increase stems from he fact that when allowing for the evolution of the inclination angle $\\chi$ for neutron stars in the region of extinct radio pulsars and, hence, for the boundary of the transition to the propeller stage, this transition is possible at shorter spin periods (P~5-10 s) than assumed in the standard model.

V. S. Beskin; S. A. Eliseeva

2005-09-15

266

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

267

Virtual Trips to Black Holes and Neutron Stars  

NSDL National Science Digital Library

This web-site contains descriptions and movies that take users into black holes and neutron stars. The movies are scientifically accurate computer animations made with adherence to Einstein's General Theory of Relativity. Descriptions of visual distortions that occur near these objects as well as the principles of gravity and mathematics are written to be understandable on a variety of levels.

Nemiroff, Robert

268

Gravitational Radiation from a Solid Crust Neutron Star  

NASA Astrophysics Data System (ADS)

A rapidly rotating neutron star with a solid crust will have a rotationally induced oblateness that is constrained by the rigidity of the solid. It is shown that the effective triaxiality and the gravitational radiation output are small, in agreement with the very small Pof PSR 1937+21.

Alpar, A.; Pines, D.

269

Probing the interior of neutron stars with gravitational waves  

E-print Network

We show here how the internal structure of a neutron star can be inferred from its gravitational wave spectrum. Under the premise that the frequencies and damping rates of a few $w$-mode oscillations are found, we apply an inversion scheme to determine its mass, radius and density distribution. In addition, accurate equation of state of nuclear matter can also be determined.

L. K. Tsui; P. T. Leung

2005-06-28

270

Magnetar activity mediated by plastic deformations of neutron star crust  

NASA Astrophysics Data System (ADS)

We advance a `solar flare' model of magnetar activity, whereas a slow evolution of the magnetic field in the upper crust, driven by electron magnetohydrodynamic flows, twists the external magnetic flux tubes, producing persistent emission, bursts, and flares. At the same time, the neutron star crust plastically relieves the imposed magnetic field stress, limiting the strain ?t to values well below the critical strain ?crit of a brittle fracture, ?t ˜ 10-2?crit. Magnetar-like behaviour, occurring near the magnetic equator, takes place in all neutron stars, but to a different extent. The persistent luminosity is proportional to cubic power of the magnetic field (at a given age), and hence is hardly observable in most rotationally powered neutron stars. Giant flares can occur only if the magnetic field exceeds some threshold value, while smaller bursts and flares may take place in relatively small magnetic fields. Bursts and flares are magnetospheric reconnection events that launch Alfvén shocks which convert into high-frequency whistlers upon hitting the neutron star surface. The resulting whistler pulse induces a strain that increases with depth both due to the increasing electron density (and the resulting slowing of the waves), and due to the increasing coherence of a whistler pulse with depth. The whistler pulse is dissipated on a time-scale of approximately a day at shallow depths corresponding to ? ˜ 1010 g cm-3; this energy is detected as enhanced post-flare surface emission.

Lyutikov, Maxim

2015-02-01

271

Constraints on perturbative f(R) gravity via neutron stars  

SciTech Connect

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

Arapo?lu, Sava?; Ek?i, K. Yavuz [?stanbul Technical University, Faculty of Science and Letters, Physics Engineering Department, Maslak 34469, ?stanbul (Turkey); Deliduman, Cemsinan, E-mail: arapoglu@itu.edu.tr, E-mail: cemsinan@msgsu.edu.tr, E-mail: eksi@itu.edu.tr [Mimar Sinan Fine Arts University, Department of Physics, Be?ikta? 34349, ?stanbul (Turkey)

2011-07-01

272

Bulk viscosity and r-modes of neutron stars  

E-print Network

The bulk viscosity due to the non-leptonic process involving hyperons in $K^-$ condensed matter is discussed here. We find that the bulk viscosity is modified in a superconducting phase. Further, we demonstrate how the exotic bulk viscosity coefficient influences $r$-modes of neutron stars which might be sources of detectable gravitational waves.

Debarati Chatterjee; Debades Bandyopadhyay

2008-08-08

273

NEUTRON STAR BIRTH RATES D.R. LORIMER  

E-print Network

NEUTRON STAR BIRTH RATES D.R. LORIMER National Astronomy and Ionospheric Center Arecibo Observatory. Abstract. A crucial test any proposed evolutionary scenario must pass is can the birth rate of the sources used to determine the birth rates of normal and millisecond radio pulsars and sum­ marise recent

Lorimer, Dunc

274

Astronomers Discover Most Massive Neutron Star Yet Known  

NASA Astrophysics Data System (ADS)

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

2010-10-01

275

Slowly rotating neutron and strange stars in R2 gravity  

NASA Astrophysics Data System (ADS)

In the present paper we investigate self-consistently slowly rotating neutron and strange stars in R-squared gravity with Lagrangian f(R) = R + aR2, where a is a parameter. For this purpose we first derive the equations describing the structure of the slowly rotating compact stars in f(R)-gravity and then simultaneously solve numerically the exterior and the interior problem. The structure of the slowly rotating neutron stars is studied for two different hadronic equations of state and a strange matter equation of state. The moment of inertia and its dependence on the stellar mass and the R-squared gravity parameter a is also examined in details. The numerical results show that the neutron star moment of inertia can be up to 30% larger compared to the corresponding general relativistic models. This is much higher than the change in the maximum mass induced by R-squared gravity and is beyond the EOS uncertainty. In this way the future observations of the moment of inertia of compact stars could allow us to distinguish between general relativity and f(R) gravity, and more generally to test the strong field regime of gravity.

Staykov, Kalin V.; Doneva, Daniela D.; Yazadjiev, Stoytcho S.; Kokkotas, Kostas D.

2014-10-01

276

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

Microsoft Academic Search

We study the merger of black hole-neutron star binaries with a variety of black hole spins aligned or antialigned with the orbital angular momentum, and with the mass ratio in the range MBH\\/MNS=2-5, where MBH and MNS are the mass of the black hole and neutron star, respectively. We model neutron-star matter by systematically parametrized piecewise polytropic equations of state.

Koutarou Kyutoku; Hirotada Okawa; Masaru Shibata; Keisuke Taniguchi

2011-01-01

277

Type II superconductivity and magnetic flux transport in neutrons stars  

E-print Network

The transition to a type II proton superconductor which is believed to occur in a cooling neutron star is accompanied by changes in the equation of hydrostatic equilibrium and by the formation of proton vortices with quantized magnetic flux. Analysis of the electron Boltzmann equation for this system and of the proton supercurrent distribution formed at the transition leads to the derivation of a simple expression for the transport velocity of magnetic flux in the liquid interior of a neutron star. This shows that flux moves easily as a consequence of the interaction between neutron and proton superfluid vortices during intervals of spin-down or spin-up in binary systems. The differences between the present analysis and those of previous workers are reviewed and an error in the paper of Jones (1991) is corrected.

P. B. Jones

2005-10-13

278

Recent Breakthroughs in Detecting Neutron Star Binaries in Globular Clusters  

E-print Network

Binary stars have long been considered to play a crucial role in globular cluster evolution, and offer the advantages of studying systems at the same, well-determined distances. However, early search attempts were consistently thwarted by crowding (particularly in the optical) and initial detections were limited to small numbers of low-mass X-ray binaries (LMXBs) and a handful of other systems. This resolution hurdle has been dramatically overcome by the superb spatial resolution and sensitivity of HST and Chandra (supported by advances in radio observations), enabling the detection in individual clusters of more than 10, and in some cases more than 100, binaries. This review will focus on detections of neutron star binaries, including recent optical identifications, the exciting discoveries of multiple LMXBs in quiescence (with the potential to constrain neutron star equations of state) and the detections of millisecond pulsars (MSPs) in X-ray and optical images.

Peter D. Edmonds

2002-10-23

279

Neutron star equations of state with optical potential constraint  

E-print Network

Nuclear matter and neutron stars are studied in the framework of an extended relativistic mean-field (RMF) model with higher-order derivative and density dependent couplings of nucleons to the meson fields. The derivative couplings lead to an energy dependence of the scalar and vector self-energies of the nucleons. It can be adjusted to be consistent with experimental results for the optical potential in nuclear matter. Several parametrisations, which give identical predictions for the saturation properties of nuclear matter, are presented for different forms of the derivative coupling functions. The stellar structure of spherical, non-rotating stars is calculated for these new equations of state (EoS). A substantial softening of the EoS and a reduction of the maximum mass of neutron stars is found if the optical potential constraint is satisfied.

Antic, Sofija

2015-01-01

280

The Properties of Matter in White Dwarfs and Neutron Stars  

E-print Network

White dwarfs and neutron stars are stellar objects with masses comparable to that of our sun. However, as the endpoint stages of stellar evolution, these objects do not sustain any thermonuclear burning and therefore can no longer support the gravitational load of their own mass by generating thermal pressure. Rather, matter in their interiors is compressed to much higher densities than commonly found in normal stars, and pressure is created by degenerate fermion kinetic energy and particle interactions. As a result, white dwarfs and neutron stars offer unique cosmic laboratories for studying matter at very high densities. In this review we discuss the basic properties of condensed matter at extreme densities and summarize the extent to which these properties can be examined by observations of compact objects.

Shmuel Balberg; Stuart L. Shapiro

2000-04-24

281

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

282

Radiation from condensed surface of magnetic neutron stars  

E-print Network

Recent observations show that the thermal X-ray spectra of many isolated neutron stars are featureless and in some cases (e.g., RX J1856.5-3754) well fit by a blackbody. Such a perfect blackbody spectrum is puzzling since radiative transport through typical neutron star atmospheres causes noticeable deviation from blackbody. Previous studies have shown that in a strong magnetic field, the outermost layer of the neutron star may be in a condensed solid or liquid form because of the greatly enhanced cohesive energy of the condensed matter. The critical temperature of condensation increases with the magnetic field strength, and can be as high as 10^6 K (for Fe surface at B \\sim 10^{13} G or H surface at B \\sim a few times 10^{14} G). Thus the thermal radiation can directly emerge from the degenerate metallic condensed surface, without going through a gaseous atmosphere. Here we calculate the emission properties (spectrum and polarization) of the condensed Fe and H surfaces of magnetic neutron stars in the regimes where such condensation may be possible. For a smooth condensed surface, the overall emission is reduced from the blackbody by less than a factor of 2. The spectrum exhibits modest deviation from blackbody across a wide energy range, and shows mild absorption features associated with the ion cyclotron frequency and the electron plasma frequency in the condensed matter. The roughness of the solid condensate (in the Fe case) tends to decrease the reflectivity of the surface, and make the emission spectrum even closer to blackbody. We discuss the implications of our results for observations of dim, isolated neutron stars and magnetars.

Matthew van Adelsberg; Dong Lai; Alexander Y. Potekhin; Phil Arras

2004-06-01

283

QPO observations related to neutron star equations of state  

NASA Astrophysics Data System (ADS)

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

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

284

Neutron star equation of state and QPO observations  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

285

Thermal evolution of neutron stars with global and local neutrality  

E-print Network

Globally neutral neutron stars, obtained from the solution of the called Einstein-Maxwell-Thomas-Fermi equations that account for all the fundamental interactions, have been recently introduced. These configurations have a more general character than the ones obtained with the traditional Tolman-Oppenheimer-Volkoff, which impose the condition of local charge neutrality. The resulting configurations have a less massive and thinner crust, leading to a new mass-radius relation. Signatures of this new structure of the neutron star on the thermal evolution might be a potential test for this theory. We compute the cooling curves by integrating numerically the energy balance and transport equations in general relativity, for globally neutral neutron stars with crusts of different masses and sizes, according to this theory for different core-crust transition interfaces. We compare and contrast our study with known results for local charge neutrality. We found a new behavior for the relaxation time, depending upon the density at the base of the crust, $\\rho_{\\rm crust}$. In particular, we find that the traditional increase of the relaxation time with the crust thickness holds only for configurations whose density of the base of the crust is greater than $\\approx 5\\times 10^{13}$ g cm$^{-3}$. The reason for this is that neutron star crusts with very thin or absent inner crust have some neutrino emission process blocked which keep the crust hotter for longer times. Therefore, accurate observations of the thermal relaxation phase of neutron stars might give crucial information on the core-crust transition which may aid us in probing the inner composition/structure of these objects.

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

2014-11-19

286

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

287

Effective No-Hair Relations for Neutron Stars and Quark Stars: Relativistic Results  

E-print Network

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. We 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 $\\sim 10%$, 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 expansion. The quartic in spin, slowly-rotating solutions found here allow us to estimate the systematic errors in the measurement of the neutron star's mass and radius with future X-ray observations, such as NICER and 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.

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

2014-03-25

288

The shear modulus of the neutron star crust and nonradial oscillations of neutron stars  

NASA Technical Reports Server (NTRS)

Shear moduli are calculated for bcc crystalline and rapidly quenched Coulomb solids produced by the Monte Carlo simulation method. The shear moduli are calculated up to the transition temperature and include the effects of thermal fluctuations. An effective shear modulus appropriate to an approximate 'isotropic' body is introduced. It is found that the values of the 'average shear modulus' for the quenched solids remain about the same as those for the corresponding bcc crystals, although the individual shear moduli of the former, disordered solids deviate considerably from the cubic symmetry of the latter. These results are applied to analyses of neutron star oscillations. It is found that the periods of the two interfacial modes are increased by about 10 percent compared to previous results, and that s-mode periods are increased by about 30 percent. The periods of the f and p modes are hardly affected at all. The surface g-mode periods are not greatly affected, while the t-mode periods are increased by 20-25 percent.

Strohmayer, T.; Van Horn, H. M.; Ogata, S.; Iyetomi, H.; Ichimaru, S.

1991-01-01

289

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

290

The mass of the neutron star in SMC X-1  

E-print Network

We present new optical spectroscopy of the eclipsing binary pulsar Sk 160/SMC X-1. From the He I absorption lines, taking heating corrections into account, we determine the radial velocity semi-amplitude of Sk 160 to be 21.8 +/- 1.8 km/s. Assuming Sk 160 fills its Roche-lobe, the inclination angle of the system is i=65.3 deg +/- 1.3 deg and in this case we obtain upper limits for the mass of the neutron star as Mx = 1.21 +/- 0.10 Msolar and for Sk 160 as Mo= 16.6 +/- 0.4 Msolar. However if we assume that the inclination angle is i=90 deg, then the ratio of the radius of Sk 160 to the radius of its Roche-lobe is beta = 0.79 +/- 0.02, and the lower limits for the masses of the two stars are Mx = 0.91 +/- 0.08 Msolar and Mo = 12.5 +/- 0.1 Msolar. We also show that the HeII 4686A emission line tracks the motion of the neutron star, but with a radial velocity amplitude somewhat less than that of the neutron star itself. We suggest that this emission may arise from a hotspot where material accreting via Roche lobe overflow impacts the outer edge of an accretion disc.

A. K. F. Val Baker; A. J. Norton; H. Quaintrell

2005-07-08

291

The companion candidate near Fomalhaut - a background neutron star?  

E-print Network

The directly detected planetary mass companion candidate close to the young, nearby star Fomalhaut is a subject of intense discussion. While the detection of common proper motion led to the interpretation as Jovian-mass companion, later non-detections in the infrared raised doubts. Recent astrometric measurements indicate a belt crossing or highly eccentric orbit for the object, if a companion, making the planetary interpretation potentially even more problematic. In this study we discuss the possibility of Fomalhaut\\,b being a background object with a high proper motion. By analysing the available photometric and astrometric data of the object, we show that they are fully consistent with a neutron star: Neutron stars are faint, hot (blue), and fast moving. Neutron stars with an effective temperature of the whole surface area being 112,000 K to 126,500 K (with small to negligible extinction) at a distance of roughly 11 pc (best fit) would be consistent with all observables, namely with the photometric detecti...

Neuhaeuser, Ralph; Ginski, Christian; Schmidt, Janos; Hambaryan, Valeri; Schmidt, Tobias

2015-01-01

292

Hydrodynamic Instability and Coalescence of Binary Neutron Stars  

E-print Network

We study the importance of hydrodynamic effects on the evolution of coalescing binary neutron stars. Using an approximate energy functional constructed from equilibrium solutions for polytropic binary configurations, we incorporate hydrodynamic effects into the calculation of the orbital decay driven by gravitational wave emission. In particular, we follow the transition between the quasi-static, secular decay of the orbit at large separation and the rapid dynamical evolution of configurations approaching contact. We show that a purely Newtonian hydrodynamic instability can significantly accelerate the coalescence at small separation. Such an instability occurs in all close binary configurations containing sufficiently incompressible stars. Calculations are performed for various neutron star masses, radii, spins, and effective polytropic indices. Typically, we find that the radial infall velocity just prior to contact is about 10\\% of the tangential orbital velocity. Post-Newtonian effects can move the stability limit to a larger binary separation, and may induce an even larger radial velocity. We also consider the possibility of mass transfer from one neutron star to the other. We show that stable mass transfer is impossible except when the mass of one of the components is very small (less than about 0.4 solar mass) and the viscosity is high enough to maintain corotation.

D. Lai; F. A. Rasio; S. L. Shapiro

1993-04-28

293

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.

Pamela ONeil

1994-02-12

294

Supernova Explosions and the Birth of Neutron Stars  

SciTech Connect

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

Janka, H.-Thomas; Marek, Andreas; Mueller, Bernhard; Scheck, Leonhard [Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85741 Garching (Germany)

2008-02-27

295

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

296

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

297

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

298

Numerical relativity simulations of binary neutron stars  

Microsoft Academic Search

We present a new numerical relativity code designed for simulations of compact binaries involving matter. The code is an upgrade of the BAM code to include general relativistic hydrodynamics and implements state-of-the-art high-resolution-shock-capturing schemes on a hierarchy of mesh refined Cartesian grids with moving boxes. We test and validate the code in a series of standard experiments involving single neutron

Marcus Thierfelder; Sebastiano Bernuzzi; Bernd Brügmann

2011-01-01

299

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

SciTech Connect

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

Todd-Rutel, B.G.; Piekarewicz, J. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)

2005-09-16

300

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

301

Unexpected Dynamical Instabilities in Differentially Rotating Neutron Stars  

NASA Astrophysics Data System (ADS)

A one-armed spiral instability has been found to develop in differentially rotating stellar models that have a relatively stiff, n=1 polytropic equation of state and a wide range of rotational energies. This suggests that such instabilities can arise in neutron stars that are differentially, although not necessarily rapidly, rotating. The instability seems to be directly triggered by the presence of a corotation resonance inside the star. Our analysis also suggests that a resonant cavity resulting from a local minimum in the radial vortensity profile of the star plays an important role in amplifying the unstable mode. Hence, it appears as though this instability is closely related to the so-called Rossby wave instability (see work of Lovelace et al.) that has been found to arise in accretion disks. In addition to the one-armed (m=1) spiral mode, we have found that higher order (m=2 and 3) nonaxisymmetric modes also can become unstable if corotation points that resonate with the eigenfrequencies of these higher order modes also appear inside the star. The growth rate of each mode seems to depend on the location of its corotation radius with respect to the vortensity profile (or on the depth of its corotation radius inside the vortensity well). The existence of such instabilities makes the stability criterion for differentially rotating neutron stars nonunique. Also, the gravitational waves emitted from such unstable systems generally will not have a monochromatic frequency spectrum.

Ou, Shangli; Tohline, Joel E.

2006-11-01

302

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

303

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

304

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

E-print Network

Gravitational waves from spinning black hole-neutron star binaries: dependence on black hole spins the compactness of the neutron star and an appropriately defined ``cutoff frequency'' in the gravitational-wave promising sources of gravitational waves for ground-based laser- interferometric gravitational-wave

Shibata, Masaru

305

Thermal conductivity of ions in a neutron star envelope  

E-print Network

We analyze the thermal conductivity of ions (equivalent to the conductivity of phonons in crystalline matter) in a neutron star envelope. We calculate the ion/phonon thermal conductivity in a crystal of atomic nuclei using variational formalism and performing momentum-space integration by Monte Carlo method. We take into account phonon-phonon and phonon-electron scattering mechanisms and show that phonon-electron scattering dominates at not too low densities. We extract the ion thermal conductivity in ion liquid or gas from literature. Numerical values of the ion/phonon conductivity are approximated by analytical expressions, valid for T>10^5 K and 10^5 g cm^-3 conductivity although they strongly reduce the electron thermal conductivity across the magnetic field. The ion thermal conductivity remains much smaller than the electron conductivity along the magnetic field. However, in the outer neutron star...

Chugunov, A I

2007-01-01

306

Newtonian and post-Newtonian binary neutron star mergers  

E-print Network

We present two of our efforts directed toward the numerical analysis of neutron star mergers, which are the most plausible sources for gravitational wave detectors that should begin operating in the near future. First we present Newtonian 3D simulations including radiation reaction (2.5PN) effects. We discuss the gravitational wave signals and luminosity from the merger with/without radiation reaction effects. Second we present the matching problem between post-Newtonian formulations and general relativity in numerical treatments. We prepare a spherical, static neutron star in a post-Newtonian matched spacetime, and find that discontinuities at the matching surface become smoothed out during fully relativistic evolution if we use a proper slicing condition.

Hisa-aki Shinkai; Wai-Mo Suen; F. Douglas Swesty; Malcolm Tobias; Edward Y. M. Wang; Clifford M. Will

1997-10-14

307

Long-term evolution of dim isolated neutron stars  

E-print Network

The dim isolated neutron stars (XDINs) have periods in the same range as the anomalous X-ray pulsars (AXPs) and the soft gamma-ray repeaters (SGRs). We apply the fallback disk model, which explains the period clustering and other properties of AXP/SGRs, to the six XDINs with measured periods and period derivatives. Present properties of XDINs are obtained in evolutionary scenarios with surface dipole magnetic fields $B_0 \\sim 10^{12}$ G. The XDINs have gone through an accretion epoch with rapid spin-down earlier, and have emerged in their current state, with the X-ray luminosity provided by neutron star cooling and no longer by accretion. Our results indicate that the known XDINs are not likely to be active radio pulsars, as the low $B_0$, together with their long periods place these sources clearly below the "death valley".

Ertan, U; Benli, O; Alpar, M A

2014-01-01

308

Gravitational waves from r-mode oscillations of neutron stars  

NASA Astrophysics Data System (ADS)

Gravitational wave can directly see the innermost part of core collapse supernova and helps us understand the explosion mechanism. The numerical simulation on this event was focused on understanding the influence of rigid rotation, differential rotation, equation of state and others. The initial mass range 8 -20 solar mass eventually produces a hot and rapidly spinning neutron star, which is unstable to r-mode emission. The evolution of r-mode instability in hot new born neutron star is investigated. It is found that the centrifugal force may play a decisive role in this mode. Further it is realized that magnetic field may cause the r-mode instability window to shrink and as such it may suppress the gravitational wave strain amplitude. It may be necessary for the future to develop more sensitive Gravitational wave detectors to classify the effect of magnetic fields.

Duorah, Hiralal

309

Electromagnetic and Gravitational Outputs from Binary-Neutron-Star Coalescence  

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

310

Systematic parameter errors in inspiraling neutron star binaries.  

PubMed

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

Favata, Marc

2014-03-14

311

Colored condensates deep inside neutron stars  

E-print Network

It is demonstrated how in the absence of solutions for QCD under conditions deep inside compact stars an equation of state can be obtained within a model that is built on the basic symmetries of the QCD Lagrangian, in particular chiral symmetry and color symmetry. While in the vacuum the chiral symmetry is spontaneously broken, it gets restored at high densities. Color symmetry, however, gets broken simultaneously by the formation of colorful diquark condensates. It is shown that a strong diquark condensate in cold dense quark matter is essential for supporting the possibility that such states could exist in the recently observed pulsars with masses of 2 $M_\\odot$.

David Blaschke

2014-07-28

312

Neutron star evolution with internal heating  

NASA Technical Reports Server (NTRS)

The thermal evolution predicted by current models of the superfluid-crust interaction is noted to differ substantially from the thermal evolution predicted by models without internal heating as well as previous models of heating. Heating rates approaching the maximum predicted by current models enhance the photon luminosity of the star in the neutrino cooling era, and dramatically alter the thermal evolution in the photon cooling era. Standard cooling models are consistent with current pulsar temperature estimates and upper limits, except those for the Vela pulsar, which are lower than predicted.

Shibazaki, Noriaki; Lamb, Frederick K.

1989-01-01

313

Singlet pairing gaps of neutrons and protons in hyperonic neutron stars  

E-print Network

The $^{1}S_{0}$ nucleonic superfluids are investigated within the relativistic mean-field model and Bardeen-Cooper-Schrieffer theory in hyperonic neutron stars. The $^{1}S_{0}$ pairing gaps of neutrons and protons are calculated based on the Reid soft-core interaction as the nucleon-nucleon interaction. We have studied particularly the influence of hyperons degrees of freedom on the $^{1}S_{0}$ nucleonic pairing gap in neutron star matter. It is found that the appearance of hyperons has little impact on baryonic density range and size for the $^{1}S_{0}$ neutronic pairing gap, the $^{1}S_{0}$ protonic pairing gap also decreases slightly in this region $\\rho_B=0.0-0.393$ fm$^{-3}$. However, if baryonic density becomes greater than 0.393 fm${^{-3}}$, the $^{1}S_{0}$ protonic pairing gap obviously increases. In addition, the protonic superfluid range is obviously enlarged due to the presence of hyperons. In our results, the hyperons change the $^{1}S_{0}$ protonic pairing gap which must change the cooling properties of neutron stars.

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

2014-08-13

314

A Hydrodynamical Analysis of the Burning of a Neutron Star  

E-print Network

The burning of a neutron star by strange matter is analyzed using relativistic combustion theory with a planar geometry. It is shown that such burning is probably neither slow combustion nor simple detonation. Fast combustion without detonation is possible under certain circumstances, but would involve very efficient heat transfer mechanisms. It is found, however, that the burning is most likely absolutely unstable with no well defined burn front.

H. T. Cho; K. -W. Ng; Achilles D. Speliotopoulos

1993-05-07

315

SHATTERING FLARES DURING CLOSE ENCOUNTERS OF NEUTRON STARS  

SciTech Connect

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

Tsang, David, E-mail: dtsang@physics.mcgill.ca [Department of Physics, McGill University, Montreal, QC (Canada)

2013-11-10

316

Neutron star mergers and gamma-ray bursts  

NASA Technical Reports Server (NTRS)

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

Narayan, Ramesh

1993-01-01

317

The Cosmic Coalescence Rates for Double Neutron Star Binaries  

Microsoft Academic Search

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

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

2004-01-01

318

Neutron star deformation due to multipolar magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

319

Simulations of black hole-neutron star binary coalescence  

E-print Network

We show the results of dynamical simulations of the coalescence of black hole-neutron star binaries. We use a Newtonian Smooth Particle Hydrodynamics code, and include the effects of gravitational radiation back reaction with the quadrupole approximation for point masses, and compute the gravitational radiation waveforms. We assume a polytropic equation of state determines the structure of the neutron star in equilibrium, and use an ideal gas law to follow the dynamical evolution. Three main parameters are explored: (i) The distribution of angular momentum in the system in the initial configuration, namely tidally locked systems vs. irrotational binaries; (ii) The stiffness of the equation of state through the value of the adiabatic index Gamma (ranging from Gamma=5/3 to Gamma=3); (iii) The initial mass ratio q=M(NS)/M(BH). We find that it is the value of Gamma that determines how the coalescence takes place, with immediate and complete tidal disruption for Gamma less than 2, while the core of the neutron star survives and stays in orbit around the black hole for Gamma=3. This result is largely independent of the initial mass ratio and spin configuration, and is reflected directly in the gravitational radiation signal. For a wide range of mass ratios, massive accretion disks are formed (M(disk)~0.2 solar masses), with baryon-free regions that could possibly give rise to gamma ray bursts.

William H. Lee

2001-01-09

320

MAGNETIC ENERGY PRODUCTION BY TURBULENCE IN BINARY NEUTRON STAR MERGERS  

SciTech Connect

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

Zrake, Jonathan; MacFadyen, Andrew I. [Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003 (United States)

2013-06-01

321

Dense baryonic matter: constraints from recent neutron star observations  

E-print Network

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

Thomas Hell; Wolfram Weise

2014-02-17

322

Universality in oscillation modes of superfluid neutron stars?  

E-print Network

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

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

2009-03-20

323

Dense baryonic matter: Constraints from recent neutron star observations  

NASA Astrophysics Data System (ADS)

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

Hell, Thomas; Weise, Wolfram

2014-10-01

324

Two Dimensional Cooling Simulations of Rotating Neutron Stars  

E-print Network

The effect of rotation on the cooling of neutron stars is investigated. The thermal evolution equations are solved in two dimensions with full account of general relativistic effects. It is found that rotation is particularly important in the early epoch when the neutron star's interior is not yet isothermal. The polar surface temperature is up to 63% higher than the equatorial temperature. This temperature difference might be observable if the thermal radiation of a young, rapidly rotating neutron star is detected. In the intermediate epoch (10^2 < t < 10^5 yr), when the interior becomes isothermal, the polar temperature is still up to 31% higher than the equatorial temperature. Afterwards photon surface radiation dominates the cooling, and the surface becomes isothermal on a timescale of 10^7 yr. Furthermore, the transition between the early and the intermediate epochs is delayed by several hundred years. An additional effect of rotation is the reduction of the neutrino luminosity due to the reduction of the central density with respect to the non-rotating case.

Ch. Schaab; M. K. Weigel

1998-06-12

325

Linking electromagnetic and gravitational radiation in coalescing binary neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

326

Neutron Star Binaries as Central Engines of GRBs  

E-print Network

We describe the results high resolution, hydrodynamic calculations of neutron star mergers. The model makes use of a new, nuclear equation of state, accounts for multi-flavour neutrino emission and solves the equations of hydrodynamics using the smoothed particle hydrodynamics method with more than $10^6$ particles. The merger leaves behind a strongly differentially rotating central object of $\\sim 2.5$ M$_{\\odot}$ together with a distribution of hot debris material. For the most realistic case of initial neutron star spins, no sign of a collapse to a black hole can be seen. We argue that the differential rotation stabilizes the central object for $\\sim 10^2$ s and leads to superstrong magnetic fields. We find the neutrino emission from the hot debris around the freshly-formed, supermassive neutron star to be substantially lower than predicted previously. Therefore the annihilation of neutrino anti-neutrino pairs will have difficulties to power very energetic bursts ($\\gg 10^{49}$ erg).

S. Rosswog

2002-04-29

327

Evolutionary Channels for the Formation of Double Neutron Stars  

E-print Network

We analyze binary population models of double-neutron stars and compare results to the accurately measured orbital periods and eccentricities of the eight known such systems in our Galaxy. In contrast to past similar studies, we especially focus on the dominant evolutionary channels (we identify three); for the first time, we use a detailed understanding of the evolutionary history of three double neutron stars as actual constraints on the population models. We find that the evolutionary constraints derived from the double pulsar are particularly tight, and less than half of the examined models survive the full set of constraints. The top-likelihood surviving models yield constraints on the key binary evolution parameters, but most interestingly reveal (i) the need for electron-capture supernovae from relatively low-mass degenerate, progenitor cores, and (ii) the most likely evolutionary paths for the rest of the known double neutron stars. In particular, we find that J1913+16 likely went through a phase of C...

Andrews, Jeff J; Kalogera, Vicky; Willems, Bart

2014-01-01

328

Dynamical mass ejection from black hole-neutron star binaries  

E-print Network

We investigate properties of material ejected dynamically in the merger of black hole-neutron star binaries by numerical-relativity simulations. We systematically study dependence of ejecta properties on the mass ratio of the binary, spin of the black hole, and equation of state of the neutron-star matter. Dynamical mass ejection is driven primarily by tidal torque, and the ejecta is much more anisotropic than that from binary neutron star mergers. In particular, the dynamical ejecta is concentrated around the orbital plane with a half opening angle of 10deg--20deg and often sweeps only a half of the plane. The ejecta mass can be as large as ~0.1M_sun, and the velocity is subrelativistic with ~0.2--0.3c for typical cases. The ratio of the ejecta mass to the bound mass (disk and fallback components) becomes high and the ejecta velocity is large when the binary mass ratio is large, i.e., the black hole is massive. The remnant black hole-disk system receives a kick velocity of O(100)km/s due to the ejecta linear...

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

2015-01-01

329

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

330

Hydrodynamic instability and coalescence of binary neutron stars  

NASA Technical Reports Server (NTRS)

We study the importance of hydrodynamic effects on the evolution of coalescing binary neutron stars. Using an approximate energy functional constructed from equilibrium solutions for polytropic binary configuration, we incorporate hydrodynamic effects into the calculation of the orbital decay driven by gravitational wave emission. In particular, we follow the transition between the quasi-static, secular decay of the orbit at large separation and the rapid dynamical evolution of confirgurations approaching contact. We show that a purely Newtonian hydrodynamic instability can significantly accelerate the coalescence at small separation. Such an instability occurs in all close binary configurations containing sufficiently incompressible stars. Calculations are performed for various neutron star masses, radii, and spins. The influence of the stiffness of the equation of state is also explored by varying the effective polytopic index. Typically, we find that the radial infall velocity just prior to contact is about 10% of the tangential orbital velocity. Once the stability limit is reached, the final evolution only takes another orbit. Post-Newtonian effects can move the stability limit to a larger binary separation, and may induce an even larger radial velocity. We also consider the possibiltiy of mass transfer form one neutron star to the other. We show that stable mass transfer is unlikely except when the mass of one of the components is very small (M is less than or approximately 0.4 solar mass) and the viscosity is high enough to maintain corotation. Otherwise, either the two stars come into contact or the dynamical instability sets in before a Roche limit can be reached.

Lai, Dong; Rasio, Frederic A.; Shapiro, Stuart L.

1994-01-01

331

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

332

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

333

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

1990-01-01

334

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

335

Magnetized neutron-star mergers and gravitational-wave signals.  

PubMed

We investigate the influence of magnetic fields upon the dynamics of, and resulting gravitational waves from, a binary neutron-star merger in full general relativity coupled to ideal magnetohydrodynamics. We consider two merger scenarios: one where the stars have aligned poloidal magnetic fields and one without. Both mergers result in a strongly differentially rotating object. In comparison to the nonmagnetized scenario, the aligned magnetic fields delay the full merger of the stars. During and after merger we observe phenomena driven by the magnetic field, including Kelvin-Helmholtz instabilities in shear layers, winding of the field lines, and transition from poloidal to toroidal magnetic fields. These effects not only mediate the production of electromagnetic radiation, but also can have a strong influence on the gravitational waves. Thus, there are promising prospects for studying such systems with both types of waves. PMID:18518432

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

2008-05-16

336

A Christmas comet falling onto a neutron star  

NASA Astrophysics Data System (ADS)

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

Campana, S.

337

Superfluid phases of triplet pairing and rapid cooling of the neutron star in Cassiopeia A  

E-print Network

In a simple model it is demonstrated that the neutron star surface temperature evolution is sensitive to the phase state of the triplet superfluid condensate. A multicomponent triplet pairing of superfluid neutrons in the core of a neutron star with participation of several magnetic quantum numbers leads to neutrino energy losses exceeding the losses from the unicomponent pairing. A phase transition of the neutron condensate into the multicomponent state triggers more rapid cooling of superfluid core in neutron stars. This makes it possible to simulate an anomalously rapid cooling of neutron stars within the minimal cooling paradigm without employing any exotic scenarios suggested earlier for rapid cooling of isolated neutron star in Cassiopeia A.

Lev B. Leinson

2014-11-25

338

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.

John Blondin

1990-07-10

339

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.

Alan McConnell

1990-07-10

340

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.

Alan McConnell

1990-07-10

341

Bulk viscosity coefficients due to phonons in superfluid neutron stars  

SciTech Connect

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

Manuel, Cristina; Tolos, Laura [Institut de Ciències del Espai (IEEC/CSIC), Facultat de Ciències, Campus Universitat Autònoma de Barcelona, Torre C5, E-08193 Bellaterra (Spain); Tarrús, Jaume, E-mail: cmanuel@ieec.uab.es, E-mail: tarrus@ecm.ub.edu, E-mail: tolos@ice.csic.es [Departament d'Estructura i Constituents de la Matèria, Universitat de Barcelona, Diagonal 647, E-08028 Barcelona (Spain)

2013-07-01

342

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

NASA Technical Reports Server (NTRS)

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

Chakkalakal, D. A.; Yang, C.

1973-01-01

343

Gamma-Ray Bursts via Pair Plasma Fireballs from Heated Neutron Stars  

E-print Network

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

Jay D. Salmonson; James R. Wilson; Grant J. Mathews

2000-01-22

344

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

SciTech Connect

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

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

2000-01-11

345

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

346

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

347

Advection of magnetic flux by accretion disks around neutron stars  

NASA Astrophysics Data System (ADS)

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

Flores-Tulian, S.; Reisenegger, A.

348

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.

349

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

NASA Astrophysics Data System (ADS)

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

Radice, David; Rezzolla, Luciano; Kellerman, Thorsten

2010-12-01

350

Gravitational Wave Background of Neutron Star-White Dwarf Binaries  

E-print Network

We discuss the stochastic background of gravitational waves from ultra compact neutron star-white dwarf (NS-WD) binaries at cosmological distances. Under the assumption that accreting neutron stars and donor white dwarf stars form most of the low mass X-ray binaries (LMXBs), our calculation makes use of recent results related to the luminosity function determined from X-ray observations. Even after accounting for detached NS-WD binaries not captured in X-ray data, the NS-WD background is at least an order of magnitude below that due to extragalactic white dwarf-white dwarf binaries and below the detectability level of the Laser Interferometer Space Antenna (LISA) at frequencies between 10^-5 Hz and 10^-1 Hz. While the extragalactic background is unlikely to be detected, we suggest that around one to ten galactic NS-WD binaries may be resolved with LISA such that their positions are determined to an accuracy of several degrees on the sky.

Asantha Cooray

2004-06-21

351

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

352

White Dwarfs, Neutron Stars, Black Holes and the EUV  

NASA Astrophysics Data System (ADS)

White dwarfs are recognized as formally analogous to neutron stars being stellar configurations where the thermal contribution to support is secondary. Both stellar types exist with various intrinsic parameters (spin mass magnetic field temperature/age) and environmental parameters (accretion environment if any characterized by overall rate and flow geometry). Comparison of analogous systems using scalings of these parameters can be fruitful e.g. comparison of stars with similar magnetic moments. Source class characterization is mature enough that such analogies can be used to compare theoretical ideas across a wide dynamic range in parameters one example being theories of quasiperioic oscillations. However the white dwarf side of this program is limited by available high resolution spectroscopy and photometry in the EUV. EUV observation is challenging but this is where white dwarf spectral energy distributions often reach maximum values. (For neutron stars the same role is played by X-rays.) Two types of cataclysmic variable systems exemplified by AM Her and EX Hya are used to illustrate these ideas in detail. Dynamical timescales and envisioned spectroscopic performance parameters of next-generation EUV satellites make possible a new level of source modeling that blends timing and spectroscopic tests. Extensions to include black holes are also considered.

Wood, Kent S.

353

Variability in the Thermal Emission from Accreting Neutron Star Transients  

E-print Network

The composition of the outer 100 m of a neutron star sets the heat flux that flows outwards from the core. For an accreting neutron star in an X-ray transient, the thermal quiescent flux depends sensitively on the amount of hydrogen and helium remaining on the surface after an accretion outburst and on the composition of the underlying ashes of previous H/He burning. Because H/He has a higher thermal conductivity, a larger mass of H/He implies a shallower thermal gradient through the low density envelope and hence a higher effective temperature for a given core temperature. The mass of residual H and He varies from outburst to outburst, so the thermal quiescent flux is variable even though the core temperature is constant for timescales < 10 000 yr. Heavy elements settle from a H/He envelope in a few hours; we therefore model the quiescent envelope as two distinct layers, H/He over heavier elements, and treat the mass of H/He as a free parameter. We find that the emergent thermal quiescent flux can vary by a factor of 2 to 3 between different quiescent epochs. The variation is more pronounced at lower interior temperatures, making systems with low quiescent luminosities and frequent outbursts, such as SAX J1808.4-3658, ideal candidates from which to observe this effect. We compute, for different ash compositions, the interior temperatures of Cen X-4, Aql X-1, and SAX J1808.4-3658. In the case of Aql X-1, the inferred high interior temperature suggests that neutrino cooling contributes to the neutron star's thermal balance.

Edward F. Brown; Lars Bildsten; Philip Chang

2002-04-05

354

White dwarfs, black holes and neutron stars in close binaries  

NASA Astrophysics Data System (ADS)

In this thesis some aspects of the formation and evolution of binaries containing white dwarfs, black holes and neutron stars are investigated. In the first part the formation of observed single undermassive white dwarfs and double helium white dwarfs is studied. I conclude that the formation of single undermassive white dwarfs can be explained by the evolution of `binaries' consisting of a solar-like star and a massive planet or brown dwarf. A tidal instability causes the low-mass companion to be drawn into the solar-like star when it evolves up the giant branch, expelling the giants envelope, leaving a single undermassive white dwarf. I reconstructed the evolution of three observed double helium white dwarfs, using the unique core mass -- radius relation for giants with degenerate cores, to find the pre-mass-transfer orbital separations and came to the following conclusions: (i) The last mass-transfer phase can be described with the spiral-in formalism with high common-envelope efficiency. (ii) The first mass-transfer phase cannot be described by a spiral-in nor by stable mass transfer but can be described very well with a formalism based on the angular momentum balance, with one free parameter which for the three observed systems has a very similar value. Further, I calculated the current population of close double white dwarfs and interacting white dwarfs (AM CVn stars) and concluded: (i) The recently proposed cooling curves for helium white dwarfs overestimate the luminosity for the lowest mass helium white dwarfs (ii) The fraction of double white dwarfs among all white dwarfs can only be brought into agreement with observations if the initial binary fraction is not above 50 % (iii) The model with an exponentially decaying star formation rate gives a slightly better fit to the observed period distribution for double white dwarfs than a constant star formation rate. For the AM CVn stars I conclude that in order to distinguish between different models and formation channels both the theory of helium accretion disks and the homogeneity and completeness of the observations (particularly regarding the distances to the AM CVn stars) need to be improved. I already started this by reducing and analyzing high-speed spectroscopic data of AM CVn itself and found, for the first time, a clear direct signature of the binary nature of AM CVn in its spectrum. The study of black hole binaries led to two conclusions. The first is that the observed space velocities of black hole binaries imply that in the supernova in which the black hole was produced, some 30 -- 50% of the mass of the exploding helium star was ejected from the system if the explosion was symmetric. The second is that the mass-loss rates for for Wolf-Rayet stars currently used in stellar evolution calculations still overestimate the mass loss, yielding very low masses for massive stars when they explode. A mass-loss law more in agreement with the observed values significantly increases these final masses, improving the possibility for the formation of black holes in binaries. Finally I describe the population of binaries consisting of two compact objects, either white dwarfs, neutron stars or black holes and use these to calculate the unresolved noise background produced by double white dwarfs and calculate the population of resolved binaries and binaries with signals sufficiently strong that they may be detected above the noise level for the low-frequency gravitational wave detector in space (LISA).

Nelemans, G.

2001-03-01

355

NetQuakes Instrument in Place  

USGS Multimedia Gallery

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

356

Effects of pseudoscalar condensation on the cooling of neutron stars  

E-print Network

In this work we consider the effect that the appearance of pseudoscalar condensates in a neutron star can have on its cooling rate. We make no particular assumption on the origin and characteristics of these possible condensates and only assume that in regions where the pseudoscalar density varies the propagation of photons is governed by modified Maxwell-Chern-Simons electrodynamics. We find that this gives non-trivial reflection coefficients between regions of different pseudoscalar density and may affect very substantially the star cooling rate. While quantitative results do depend on precise details that can only be answered once a proper equation of state is determined, the general trend is quite universal and serious consideration should be given to this possibility.

Andrianov, A A; Kolevatov, S S

2015-01-01

357

Axion cyclotron emissivity of magnetized white dwarfs and neutron stars  

E-print Network

The energy loss rate of a magnetized electron gas emitting axions a due to the process $e^- \\to e^- +a$ is derived for arbitrary magnetic field strength B. Requiring that for a strongly magnetized neutron star the axion luminosity is smaller than the neutrino luminosity we obtain the bound $g_{ae}\\lsim 10^{-10}$ for the axion electron coupling constant. This limit is considerably weaker than the bound derived earlier by Borisov and Grishina using the same method. Applying a similar argument to magnetic white dwarf stars results in the more stringent bound $g_{ae}\\lsim 9x10^{-13} (T/10^7 K)^{5/4} (B/10^{10} G)^{-2}$ where T is the internal temperature of the white dwarf.

M. Kachelriess; C. Wilke; G. Wunner

1997-04-08

358

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

359

Unstable g-modes in Proto-Neutron Stars  

E-print Network

In this article we study the possibility that, due to non-linear couplings, unstable g-modes associated to convective motions excite stable oscillating g-modes. This problem is of particular interest, since gravitational waves emitted by a newly born proto-neutron star pulsating in its stable g-modes would be in the bandwidth of VIRGO and LIGO. Our results indicate that nonlinear saturation of unstable modes occurs at relatively low amplitudes, and therefore, even if there exists a coupling between stable and unstable modes, it does not seem to be sufficiently effective to explain, alone, the excitation of the oscillating g-modes found in hydrodynamical simulations.

V. Ferrari; L. Gualtieri; J. A. Pons

2007-09-04

360

Relativistic outflow from two thermonuclear shell flashes on neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

361

Electrical Conductivity of the Neutron Star Crust at Low Temperatures  

E-print Network

Abstract—The electrical conductivity of the neutron star crust at low temperatures is calculated by taking into account the mixing of the electron wave functions due to the interaction with the crystal lattice of atomic nuclei. We show that the previously existed model of exponential reduction of the electron–ion scattering rate can lead to an overestimation of the electrical conductivity by several orders of magnitude. We propose a simple interpolation formula for use in applications that joins the previously known results of calculating the electrical conductivity at high temperatures with the low-temperature asymptotics found here. DOI: 10.1134/S1063773712010021

A. I. Chugunov

2011-01-01

362

Transition density and pressure in hot neutron stars  

E-print Network

PHYSICAL REVIEW C 81, 055805 (2010) Transition density and pressure in hot neutron stars Jun Xu,1 Lie-Wen Chen,2,3 Che Ming Ko,4 and Bao-An Li5 1Cyclotron Institute, Texas A&M University, College Station, Texas 77843-3366, USA 2Department...-2813/2010/81(5)/055805(7) 055805-1 ?2010 The American Physical Society JUN XU, LIE-WEN CHEN, CHE MING KO, AND BAO-AN LI PHYSICAL REVIEW C 81, 055805 (2010) II. THE MDI The MDI is an effective nuclear interaction with its density and momentum dependence constrained from...

Xu, Jun; Chen, Lie-Wen; Ko, Che Ming; Li, Bao-An.

2010-01-01

363

Quasiequilibrium sequences of binary neutron stars undergoing dynamical scalarization  

NASA Astrophysics Data System (ADS)

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

Taniguchi, Keisuke; Shibata, Masaru; Buonanno, Alessandra

2015-01-01

364

Comment on "Instabilities in Close Neutron Star Binaries"  

E-print Network

In a recent Physical Review Letter, Wilson and Mathews presented some interesting numerical calculations of a system of two equally massive neutron stars in strong-field gravity. In particular they estimated the innermost stable circular orbit in their system. Here we point out a possibly important consequence of their results: Their calculated configurations have total angular momentum $J$ and total mass $M$ too large to form any Kerr black hole: $J>M^2$, in constrast to previous calculations of the innermost stable circular orbit.

Douglas M. Eardley; Eric W. Hirschmann

1996-01-11

365

CONSTRAINTS ON NATAL KICKS IN GALACTIC DOUBLE NEUTRON STAR SYSTEMS  

SciTech Connect

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

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

2010-10-01

366

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

367

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.

Alan McConnell

1990-07-10

368

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

369

Slowly rotating neutron stars in scalar-tensor theories  

NASA Astrophysics Data System (ADS)

We construct models of slowly rotating, perfect-fluid neutron stars by extending the classical Hartle—Thorne formalism to generic scalar-tensor theories of gravity. Working at second order in the dimensionless angular momentum, we compute the mass M, radius R, scalar charge q, moment of inertia I, and spin-induced quadrupole moment Q, as well as the tidal and rotational Love numbers. Our formalism applies to generic scalar-tensor theories, but we focus in particular on theories that allow for spontaneous scalarization. It was recently discovered that the moment of inertia, quadrupole moment, and Love numbers are connected by approximately universal (i.e., equation-of-state independent) "I-Love-Q" relations. We find that similar relations hold also for spontaneously scalarized stars. More interestingly, the I-Love-Q relations in scalar-tensor theories coincide with the general relativistic ones within less than a few percent, even for spontaneously scalarized stars with the largest couplings allowed by current binary-pulsar constraints. This implies that astrophysical measurements of these parameters cannot be used to discriminate between general relativity and scalar-tensor theories, even if spontaneous scalarization occurs in nature. Because of the well-known equivalence between f(R) theories and scalar-tensor theories, the theoretical framework developed in this paper can be used to construct rotating compact stellar models in f(R) gravity. Our slow-rotation expansion can also be used as a benchmark for numerical calculations of rapidly spinning neutron stars in generic scalar-tensor theories.

Pani, Paolo; Berti, Emanuele

2014-07-01

370

Isospin asymmetric nuclear matter and properties of axisymmetric neutron stars  

SciTech Connect

Pure hadronic compact stars that are above a limiting value (approx =1.6M{sub c}entre dot) of their gravitational masses, to which predictions of most of other equations of state are restricted, can be reached from the equation of state (EOS) obtained using the density-dependent M3Y (DDM3Y) effective interaction. This effective interaction is found to be quite successful in providing a unified description of elastic and inelastic scattering, various radioactivities, and nuclear matter properties. We present a systematic study of the properties of pure hadronic compact stars. The beta-equilibrated neutron star matter using this EOS with a thin crust is able to describe highly massive compact stars, such as PSR B1516+02B with a mass M=1.94{sub -0.19}{sup +0.17}M{sub c}entre dot and PSR J0751+1807 with a mass M=2.1+-0.2M{sub c}entre dot to a 1sigma confidence level.

Chowdhury, Partha Roy; Bhattacharyya, Abhijit [Department of Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009 (India); Basu, D. N. [Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700 064 (India)

2010-06-15

371

Neutron star models in frames of f (R) gravity  

SciTech Connect

Neutron star models in perturbative f (R) gravity are considered with realistic equations of state. In particular, we consider the FPS and SLy equations of state. The mass-radius relations for f(R)?=?R+?R(e{sup ?R/R{sub 0}}?1) model and for R{sup 2} models with cubic corrections are obtained. In the case of R2 gravity with cubic corrections, we obtain that at high central densities (? > 10 ?{sub ns} = 2.7 × 10{sup 14} g/cm{sup 3} is the nuclear saturation density), stable star configurations exist. The minimal radius of such stars is close to 9 km with maximal mass ? 1.9M{sub ?}(SLy equation) or to 8.5 km with mass ? 1.7M{sub ?} (FPS equation). This effect can give rise to more compact stars than in GR. If observationally identified, such objects could constitute a formidable signature for modified gravity at astrophysical level.

Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, 236041, 14, Nevsky st., Kaliningrad (Russian Federation)

2014-07-23

372

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

SciTech Connect

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

Leonard, P.J.T. [Los Alamos National Lab., NM (United States); Davies, M.B. [California Inst. of Tech., Pasadena, CA (United States)

1993-12-31

373

Intense electromagnetic outbursts from collapsing hypermassive neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

374

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

375

RADIATION FROM CONDENSED SURFACE OF MAGNETIC NEUTRON STARS Matthew van Adelsberg,1  

E-print Network

RADIATION FROM CONDENSED SURFACE OF MAGNETIC NEUTRON STARS Matthew van Adelsberg,1 Dong Lai,1 the thermal radiation can directly emerge from the degenerate metallic condensed surface without going through Fe and H surfaces of magnetic neutron stars in the regimes in which such condensation may be possible

376

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

E-print Network

Gravitational waves from nonspinning black hole-neutron star binaries: Dependence on equations. The tidal disruption is reflected in a cutoff frequency of the gravitational-wave spectrum, above which of the gravitational-wave spectrum and the compactness of the neutron star. This relation also depends weakly

Shibata, Masaru

377

Computation of gravitational waves from inspiraling binary neutron stars in quasiequilibrium circular orbits: Formulation and calibration  

E-print Network

Computation of gravitational waves from inspiraling binary neutron stars in quasiequilibrium 2001# Gravitational waves from binary neutron stars in quasiequilibrium circular orbits are computed gravitational waves. We adopt the so­called conformal flatness approximation for a three­metric to obtain

Shibata, Masaru

378

Sti equation-of-state of neutron star due to antikaon condensation  

E-print Network

Sti¤ equation-of-state of neutron star due to antikaon condensation K. Miyazaki E-mail: miyazakiro@rio.odn.ne.jp Abstract We re-examine the antikaon condensation in neutron star (NS) matter within the extended Zimanyi experimental information on K atom and deeply bound kaonic states. Consequently, the antikaon condensed phase

379

Antikaon condensation in neutron stars by a new nonlinear mean-...eld model  

E-print Network

Antikaon condensation in neutron stars by a new nonlinear mean-...eld model K. Miyazaki Abstract We have investigated both the K and K0 condensations in -equilibrated neutron star (NS) matter using optical potential of 120 MeV, our model predicts the K condensation as the second-order phase transition

380

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

381

The nuclear symmetry energy and stability of matter in neutron star  

E-print Network

It is shown that behavior of the nuclear symmetry energy is the key quantity in the stability consideration in neutron star matter. The symmetry energy controls the position of crust-core transition and also may lead to new effects in the inner core of neutron star.

Sebastian Kubis

2006-11-23

382

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

383

Resonant Cyclotron Scattering and Comptonization in Neutron Star Magnetospheres  

E-print Network

Resonant cyclotron scattering of the surface radiation in the magnetospheres of neutron stars may considerably modify the emergent spectra and impede efforts to constraint neutron star properties. Resonant cyclotron scattering by a non-relativistic warm plasma in an inhomogeneous magnetic field has a number of unusual characteristics: (i) in the limit of high resonant optical depth, the cyclotron resonant layer is half opaque, in sharp contrast to the case of non-resonant scattering. (ii) The transmitted flux is on average Compton up-scattered by ~ $1+ 2 beta_T$, where $\\beta_T$ is the typical thermal velocity in units of the velocity of light; the reflected flux has on average the initial frequency. (iii) For both the transmitted and reflected fluxes the dispersion of intensity decreases with increasing optical depth. (iv) The emergent spectrum is appreciably non-Plankian while narrow spectral features produced at the surface may be erased. We derive semi-analytically modification of the surface Plankian emission due to multiple scattering between the resonant layers and apply the model to anomalous X-ray pulsar 1E 1048.1--5937. Our simple model fits just as well as the ``canonical'' magnetar spectra model of a blackbody plus power-law.

Maxim Lyutikov; Fotis P. Gavriil

2005-07-22

384

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

385

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

386

Magnetised Neutron Star Crusts and Torsional Shear Modes of Magnetars  

NASA Astrophysics Data System (ADS)

We discuss outer and inner crusts of neutron stars in strong magnetic fields. Here, we demonstrate the effect of Landau quantization of electrons on the ground state properties of matter in outer and inner crusts in magnetars. This effect leads to the enhancement of the electron number density in strong magnetic fields with respect to the zero field case. For the outer crust, we adopt the magnetic Baym-Pethick-Sutherland model and obtain the sequence of nuclei and equation of state (EoS). The properties of nuclei in the inner crust in the presence of strong magnetic fields are investigated using the Thomas-Fermi model. The coexistence of two phases of nuclear matter - liquid and gas, is assumed in this case. The proton number density in the Wigner-Seitz cell is affected in strong magnetic fields through the charge neutrality. We perform this calculation using the Skyrme nucleon-nucleon interaction with different parameterisations. We find nuclei with larger mass and atomic numbers in the inner crust in the presence of strong magnetic fields than those of the zero field case for all those parameter sets. Further we investigate torsional shear mode frequencies using the results of magnetised neutron star crusts and compare those with observations.

Nandi, Rana; Bandyopadhyay, Debades

2013-03-01

387

Phenomenological QCD equation of state for massive neutron stars  

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

388

Fundamental oscillation modes of neutron stars: validity of universal relations  

E-print Network

We study the $f$-mode frequencies and damping times of nonrotating neutron stars (NS) in general relativity (GR) by solving the linearized perturbation equations, with the aim to establish "universal" relations that depend only weakly on the equations of state (EOS). Using a more comprehensive set of EOSs, we re-examine some proposed linearizations that describe the $f$-mode parameters in terms of mass and radius of the neutron star (NS), and we test a more recent proposal for expressing the $f$-mode parameters as quadratic functions of the effective compactness. Our extensive results for each equation of state considered allow us to study the accuracy of each proposal. In particular, we find that the damping time deviates quite considerably from the proposed linearization. We introduce a new universal relation for the product of the $f$-mode frequency and damping time as a function of the (ordinary) compactness, which proved to be more accurate. The relations using the effective compactness on the other hand...

Chirenti, Cecilia; Kastaun, Wolfgang

2015-01-01

389

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

390

Tuning up for Gravitational Wave Detection in Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

Rapidly-rotating neutron stars are the only candidates for persistent gravitational wave emis-sion, for which a targeted search can be performed based on the spin period measured from electromagnetic (e.g. radio and X-ray) observations. Apart from the expected weakness of the emission, the principal difficulty for such searches is the lack of precision in measurements of the spin as well as the other physical parameters of the system. I present a pilot program of optical and infra-red observations of the stellar counterparts to X-ray bright accreting neutron stars, in order to measure (or improve the precision of) the binary parameters. These measurements will allow optimisation of future gravitational wave searches, and will also facilitate searches of the extensive X-ray timing data from NASA's Rossi X-ray Timing Explorer, to measure the spin frequency (for those systems where it is not precisely known). Observations such as these will provide the best possible chance for detecting the gravitational wave emission from these systems.

Galloway, Duncan; Steeghs, Danny; Ransom, Scott

391

From Neutron Star Binaries to Gamma-ray bursts  

E-print Network

I summarize recent results about how a neutron star binary coalescence can produce short gamma-ray bursts (GRBs). Two possibilities are discussed: the annihilation of neutrino anti-neutrino pairs above the merged remnant and the exponential amplification of magnetic fields in the central object up to values close to equipartition. We find that the neutrino annihilation drives bipolar, relativistic outflows with Lorentz-factors large enough to circumvent the GRB 'compactness problem'. The total energy within these outflows is moderate by GRB-standards ($\\sim 10^{48}-10^{49}$ ergs), but the interaction with the baryonic material blown-off by the neutrinos collimates the outflows into opening angles of typically 0.1 sterad, yielding isotropic energies close to $10^{51}$ ergs. We further want to stress the plausibility of the central object resisting the immediate collapse to a black hole. In this case the central object will --similar to a proto-neutron star-- be subject to neutrino driven convection that --together with the rapid, differential rotation-- will lead to a drastic amplification of pre-existing magnetic fields. Within fractions of a second, field strengths comparable to equipartition field strength ($> 10^{17}$ G) will be reached. These will produce large torques that will spin-down the object within about 0.2 s, and would thus naturally explain the duration of short GRBs.

S. Rosswog

2005-04-17

392

Nuclear fusion and carbon flashes on neutron stars  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

393

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

E-print Network

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

Manjari Bagchi; Diego F. Torres

2014-07-29

394

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

NASA Astrophysics Data System (ADS)

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

Bagchi, Manjari; Torres, Diego F.

2014-08-01

395

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

396

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

397

Electromagnetic and Radiative Properties of Neutron Star Magnetospheres  

NASA Astrophysics Data System (ADS)

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

Li, Jason G.

2014-05-01

398

INNER CRUSTS OF NEUTRON STARS IN STRONGLY QUANTIZING MAGNETIC FIELDS  

SciTech Connect

We study the ground-state properties of inner crusts of neutron stars in the presence of strong magnetic fields of {approx}10{sup 17} G. Nuclei coexist with a neutron gas and reside in a uniform gas of electrons in the inner crust. This problem is investigated within the Thomas-Fermi model. We extract the properties of nuclei based on the subtraction procedure of Bonche, Levit, and Vautherin. The phase space modification of electrons due to Landau quantization in the presence of strong magnetic fields leads to the enhancement of electron as well as proton fractions at lower densities of {approx}0.001 fm{sup -3}. We find the equilibrium nucleus at each average baryon density by minimizing the free energy and show that, in the presence of strong magnetic fields, it is lower than that in the field-free case. The size of the spherical cell that encloses a nucleus along with the neutron and electron gases becomes smaller in strong magnetic fields compared to the zero-field case. Nuclei with larger mass and atomic numbers are obtained in the presence of strong magnetic fields compared with cases of zero field.

Nandi, Rana; Bandyopadhyay, Debades [Astroparticle Physics and Cosmology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Mishustin, Igor N.; Greiner, Walter [Frankfurt Institute for Advanced Studies (FIAS), J. W. Goethe Universitaet, Ruth Moufang Strasse 1, 60438 Frankfurt am Main (Germany)

2011-08-01

399

Inner Crusts of Neutron Stars in Strongly Quantizing Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

400

Neutron star tidal disruption in mixed binaries: The imprint of the equation of state  

SciTech Connect

We study the tidal disruption of neutron stars in black hole-neutron star coalescing binaries. We calculate the critical orbital separation at which the star is disrupted by the black hole tidal field for several equations of state describing the matter inside the neutron star, and for a large set of the binary parameters. When the disruption occurs before the star reaches the innermost stable circular orbit, the gravitational wave (GW) signal emitted by the system is expected to exhibit a cutoff frequency {nu}{sub GW}-tilde, which is a distinctive feature of the waveform. We evaluate {nu}{sub GW}-tilde and show that, if this frequency will be found in a detected gravitational wave, it will allow one to determine the neutron star radius with an error of a few percent, providing valuable information on the behavior of matter in the stellar core.

Ferrari, V.; Gualtieri, L. [Dipartimento di Fisica, 'Sapienza' Universita di Roma and Sezione INFN Roma1, Piazzale Aldo Moro 5, 00185, Roma (Italy); Pannarale, F. [Dipartimento di Fisica, 'Sapienza' Universita di Roma and Sezione INFN Roma1, Piazzale Aldo Moro 5, 00185, Roma (Italy); Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Potsdam (Germany)

2010-03-15

401

Neutron star tidal disruption in mixed binaries: the imprint of the equation of state  

E-print Network

We study the tidal disruption of neutron stars in black hole-neutron star coalescing binaries. We calculate the critical orbital separation at which the star is disrupted by the black hole tidal field for several equations of state describing the matter inside the neutron star, and for a large set of the binary parameters. When the disruption occurs before the star reaches the innermost stable circular orbit, the gravitational wave (GW) signal emitted by the system is expected to exhibit a cutoff frequency nu_GWtide, which is a distinctive feature of the waveform. We evaluate nu_GWtide and show that, if this frequency will be found in a detected gravitational wave, it will allow to determine the neutron star radius with an error of a few percent, providing valuable information on the behaviour of matter in the stellar core.

V. Ferrari; L. Gualtieri; F. Pannarale

2009-12-18

402

Neutron star structure in the presence of conformally coupled scalar fields  

NASA Astrophysics Data System (ADS)

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

Sultana, Joseph; Bose, Benjamin; Kazanas, Demosthenes

2014-10-01

403

Initial data for binary neutron stars with adjustable eccentricity  

NASA Astrophysics Data System (ADS)

Binary neutron stars in circular orbits can be modeled as helically symmetric, i.e., stationary in a rotating frame. This symmetry gives rise to a first integral of the Euler equation, often employed for constructing equilibrium solutions via iteration. For eccentric orbits, however, the lack of helical symmetry has prevented the use of this method, and the numerical relativity community has often resorted to constructing initial data by superimposing boosted spherical stars without solving the Euler equation. The spuriously excited neutron star oscillations seen in evolutions of such data arise because such configurations lack the appropriate tidal deformations and are stationary in a linearly comoving—rather than rotating—frame. We consider eccentric configurations at apoapsis that are instantaneously stationary in a rotating frame. We extend the notion of helical symmetry to eccentric orbits, by approximating the elliptical orbit of each companion as instantaneously circular, using the ellipse's inscribed circle. The two inscribed helical symmetry vectors give rise to approximate instantaneous first integrals of the Euler equation throughout each companion. We use these integrals as the basis of a self-consistent iteration of the Einstein constraints to construct conformal thin-sandwich initial data for eccentric binaries. We find that the spurious stellar oscillations are reduced by at least an order of magnitude, compared with those found in evolutions of superposed initial data. The tidally induced oscillations, however, are physical and qualitatively similar to earlier evolutions. Finally, we show how to incorporate radial velocity due to radiation reaction in our inscribed helical symmetry vectors, which would allow one to obtain truly noneccentric initial data when our eccentricity parameter e is set to zero.

Moldenhauer, Niclas; Markakis, Charalampos M.; Johnson-McDaniel, Nathan K.; Tichy, Wolfgang; Brügmann, Bernd

2014-10-01

404

Gravitational Radiation and Rotation of Accreting Neutron Stars  

NASA Astrophysics Data System (ADS)

Recent discoveries by the Rossi X-Ray Timing Explorer indicate that most of the rapidly accreting (?>~10-11 Msolar yr-1) weakly magnetic (B<<1011 G) neutron stars in the Galaxy are rotating at spin frequencies ?s>~250 Hz. Remarkably, they all rotate in a narrow range of frequencies (no more than a factor of 2, with many within 20% of 300 Hz). I suggest that these stars rotate fast enough so that, on average, the angular momentum added by accretion is lost to gravitational radiation. The strong ?s-dependence of the angular momentum loss rate from gravitational radiation then provides a natural reason for similar spin frequencies. Provided that the interior temperature has a large-scale asymmetry misaligned from the spin axis, then the temperature-sensitive electron captures in the deep crust can provide the quadrupole needed (~10-7MR2) to reach this limiting situation at ?s~300 Hz. This quadrupole is only present during accretion and makes it difficult to form radio pulsars with ?s>(600-800) Hz by accreting at ?>~10-10 Msolar yr-1. The gravity wave strength is hc~(0.5-1)×10-26 from many of these neutron stars and greater than 2×10-26 for Sco X-1. Prior knowledge of the position, spin frequency, and orbital periods will allow for deep searches for these periodic signals with gravitational wave interferometers (LIGO, VIRGO, and the ``dual-recycled'' GEO 600 detector), and experimenters need to take such sources into account. Sco X-1 will most likely be detected first.

Bildsten, Lars

1998-07-01

405

Excitation of neutron star normal modes during binary inspiral  

NASA Technical Reports Server (NTRS)

As a compact binary inspirals due to the emission of gravitational waves, its orbital period decreases continuously down to approximately 1 ms, its value at coalescence. During the last part of the inspiral, the two stars are close together, and their tidal interactions become strong. Neutron stars have many normal modes (core g-modes, crustal discontinuity modes, shear modes, etc.) whose periods lie in the range (approximately several ms) swept by the orbital period. Some of these modes are resonantly excited by the tidal force. The amount of energy a mode absorbs is proportional to the square of the overlap integral between its displacement field and the tidal force field. For all modes of interest, this overlap is poor, resulting in relatively weak excitation. For the best case, the absorbed energy is only a small fraction (approximately 10(exp -6)) of the orbital energy, so the orbital phase shift is too weak to be detected by observations of the gravitational wave signal emitted by the inspiraling binary. However, with displacement amplitudes of excited quadrupole modes ranging up to 0.5% of the stellar radius, the possibility of a detectable electromagnetic signature cannot be dismissed. Both the periods of the modes and the energy they absorb depend quite strongly on the internal structure of the star. Their observation could shed light on the correct high-density equation of state.

Reisenegger, Andreas; Goldreich, Peter

1994-01-01

406

Neutron conduction in the inner crust of a neutron star in the framework of the band theory of solids  

NASA Astrophysics Data System (ADS)

Even though the “free” neutrons in the inner crust of a neutron star are superfluid, they are still strongly coupled to nuclei due to nondissipative entrainment effects. These effects have been systematically studied in all regions of the inner crust in the framework of the band theory of solids. Using concepts from solid-state physics, it is shown that the density of conduction neutrons, i.e., neutrons that are effectively free, can be much smaller than the density of unbound neutrons (by an order of magnitude in some layers) due to Bragg scattering. These results suggest that a revision of the interpretation of various observable neutron-star phenomena might be necessary.

Chamel, N.

2012-03-01

407

Neutron conduction in the inner crust of a neutron star in the framework of the band theory of solids  

E-print Network

Even though the "free" neutrons in the inner crust of a neutron star are superfluid, they are still strongly coupled to nuclei due to non-dissipative entrainment effects. These effects have been systematically studied in all regions of the inner crust in the framework of the band theory of solids. Using concepts from solid-state physics, it is shown that the density of conduction neutrons, i.e. neutrons that are effectively "free", can be much smaller than the density of unbound neutrons (by an order of magnitude in some layers) due to Bragg scattering. These results suggest that a revision of the interpretation of various observable neutron-star phenomena may be necessary.

Nicolas Chamel

2012-03-01

408

Possible implications of asymmetric fermionic dark matter for neutron stars  

NASA Astrophysics Data System (ADS)

We consider the implications of fermionic asymmetric dark matter (ADM) for a “mixed neutron star” composed of ordinary baryons and dark fermions. We find examples, where for a certain range of dark fermion mass - when it is less than that of ordinary baryons - such systems can reach higher masses than the maximal values allowed for ordinary (“pure”) neutron stars. This is shown both within a simplified, heuristic Newtonian analytic framework with non-interacting particles and via a general relativistic numerical calculation, under certain assumptions for the dark matter equation of state. Our work applies to various dark fermion models such as mirror matter models and to other models where the dark fermions have self-interactions. Dark matter is accreted onto ordinary stellar objects at various stages of the evolution of the latter, or conversely, ordinary matter is accreted onto pre-existing dark stars, and dark and ordinary matter jointly cluster forming the mixed stars. 1. Accretion of DM onto stars has been discussed in the past [17,19,18]. It was motivated by noting that even tiny (?X=NX/N˜10-11) admixtures inside the Sun of dark matter of mass mX˜5-10 GeV can modify heat convection from the solar core and help explain some apparent anomalies. If the density of dark matter near the star has the average value of 0.4 GeV/mX cm, then to generate ?X˜10-11 over a Hubble time we need that ?, the cross-section for scattering of dark and normal nucleons, exceed 10-37 cm. This is excluded for heavy DM by direct searches - but not for the case of mX=1/2 GeV that we focus on in this Letter. Furthermore once ?X exceeds the ratio of ?/? (which can be as small as 10-15), the non-linear process of scattering the incoming DM on already captured X particles in the star dominates and further accelerates the accretion [18]. There is however an upper “unitarity” limit on the accretion rate fixed by the area of the star ?R2 (possibly with a “focusing” ( enhancement ˜10 for the Sun) corresponding to the case of complete capture of all X particles which hit the stellar surface. Even at this maximal rate if a solar type star were to accrete in Hubble time a solar mass of dark matter, we need that the DM density in its neighborhood will be 109 times larger than the local halo density of 0.4 GeV cm-3. In general CDM starts clustering before baryons and our star may naturally be situated in a dark matter mini-halo. If this dark mini-halo formed at redshift z its density can be enhanced in comparison with the cosmological DM density of KeV/cm3 by (6˜2×108 for z˜100. The CMB spectrum and simulations [20], certainly exclude forming mini-halos of solar mass at larger redshifts. Even then this achieves at most a 103 enhancement relative to the local halo density. It seems that only if DM was dissipative it could have clustered more effectively reaching the 109 enhancement required.In passing, we note that the total DM accretion is not enhanced for bigger, more massive red/blue giant stars. The surface density M/R2 of the such giant stars is smaller making it difficult to accrete the minimal amount of X particles required in order to initiate the non-linear regime and hence reach the unitarity limit. Furthermore the lifetime of these stars scales like M-3 making them live considerably shorter than solar systems. Also for more compact objects such as white dwarfs /neutron stars the enhanced focusing is offset by the far smaller areas.Turning to collider constraints on dark matter (DM) properties in our model, the Atlas and CMS detectors at the LHC accelerator operate at unexplored energies and unprecedented rates. Their implications for DM properties stem from the fact that the detectors, triggered by large transverse momenta are ideal for detecting missing (transverse) energy. This underlies the remarkable, extensive SUSY searches at LHC as pair production of SUSY particles yields, often via spectacular decay chains, stable neutral lightest SUSY partner (LSP)s which escape the detector leaving an extra signature of mis

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

2013-10-01

409

Short gamma-ray bursts from binary neutron star mergers in globular clusters  

E-print Network

ARTICLES Short gamma-ray bursts from binary neutron star mergers in globular clusters JONATHAN produced in globular clusters, in which extreme densities of very old stars can create and exchange compact) mission located short GRBs in (or near) elliptical galaxies, that are no longer active in star formation

Loss, Daniel

410

Finite size effects in neutron star and nuclear matter simulations  

NASA Astrophysics Data System (ADS)

In this work we study molecular dynamics simulations of symmetric nuclear and neutron star matter using a semi-classical nucleon interaction model. Our aim is to gain insight on the nature of the so-called 'finite size effects', unavoidable in this kind of simulations, and to understand what they actually affect. To do so, we explore different geometries for the periodic boundary conditions imposed on the simulation cell: cube, hexagonal prism and truncated octahedron. For nuclear matter simulations we show that, at sub-saturation densities and low temperatures, the solutions are non-homogeneous structures reminiscent of the 'nuclear pasta' phases expected in neutron star matter simulations, but only one structure per cell and shaped by specific artificial aspects of the simulations-for the same physical conditions (i.e. number density and temperature) different cells yield different solutions. The particular shape of the solution at low enough temperature and a given density can be predicted analytically by surface minimization. We also show that even if this behavior is due to the imposition of periodic boundary conditions on finite systems, this does not mean that it vanishes for very large systems, and it is actually independent of the system size. We conclude that, for nuclear matter simulations, the cells' size sets the only characteristic length scale for the inhomogeneities, and the geometry of the periodic cell determines the shape of those inhomogeneities. To model neutron star matter we add a screened Coulomb interaction between protons, and perform simulations in the three cell geometries. Our simulations indeed produce the well known nuclear pasta, with (in most cases) several structures per cell. However, we find that for systems not too large results are affected by finite size in different ways depending on the geometry of the cell. In particular, at the same certain physical conditions and system size, the hexagonal prism yields a single structure per cell while the cubic and truncated octahedron show consistent results, with more than one structure per cell. For systems of the size studied in this work these effects are still noticeable, but we find evidence to support that the dependence of the results on the cell geometry becomes smaller as the system size is increased. When the Coulomb interaction is present, the competition between opposing interactions of different range results in a proper, physically meaningful length scale that is independent of the system size and periodic cell of choice. Only under these conditions 'finite size effects' will vanish for large enough systems (i.e. cells much larger than this characteristic length). Larger simulations are in order, but our computational capabilities forbid it for the time being.

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

2015-01-01

411

The effects of strong magnetic and gravitational fields on emission properties of neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars offer us a unique medium to study the physics of intense magnetic and gravitational fields. They can be magnetized so strongly that exotic quantum electrodynamical processes become important. With their strong gravity, they can gravitationally lens radiation from their own surfaces. In this thesis, I study how these fields affect the physical processes and the interactions of photons with matter on the surfaces of neutron stars and shape their observable properties. Confining magnetic fields alter the properties of electrons, protons, and atoms present in the atmospheres of neutron stars. Therefore, they modify the interactions and propagation of photons through this medium. In particular, strong fields render the interactions anisotropic and polarization-dependent. In addition, the magnetic vacuum becomes polarized due to the presence of virtual electron-positron pairs in strong fields. I study the transfer of radiation in the atmospheres of neutron stars taking into account the resonances that arise because of the polarization of vacuum and the presence of the protons and electron in the plasma. The emission from the surface of neutron stars is also modified by general relativistic effects in strong gravitational fields. I determine the signatures of gravitational lensing and identify new effects introduced by the stellar gravity on the observable properties of neutron stars. I study the uncertainties these effects introduce to the inferred properties of such sources and discuss the importance of timing studies in constraining the processes that occur in the stellar interiors and surfaces. There are several classes of neutron star sources that are thought to show thermal emission from their surfaces, offering us a window into these extreme processes. Of these, I study in detail the intriguing anomalous X-ray pulsars, the young isolated neutron stars, and the accreting stars that show thermonuclear bursts on their surfaces, in an attempt to reveal the nature of these sources and understand the physical processes that take place on the surfaces of neutron stars.

Ozel, Feryal

2002-10-01

412

Complete equation of state for neutron stars using the relativistic Hartree-Fock approximation  

SciTech Connect

We construct the equation of state in a wide-density range for neutron stars within relativistic Hartree-Fock approximation. The properties of uniform and nonuniform nuclear matter are studied consistently. The tensor couplings of vector mesons to baryons due to exchange contributions (Fock terms) are included, and the change of baryon internal structure in matter is also taken into account using the quark-meson coupling model. The Thomas-Fermi calculation is adopted to describe nonuniform matter, where the lattice of nuclei and the neutron drip out of nuclei are considered. Even if hyperons exist in the core of a neutron star, we obtain the maximum neutron-star mass of 1.95M{sub ?}, which is consistent with the recently observed massive pulsar, PSR J1614-2230. In addition, the strange vector (?) meson also plays a important role in supporting a massive neutron star.

Miyatsu, Tsuyoshi; Cheoun, Myung-Ki [Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Yamamuro, Sachiko; Nakazato, Ken'ichiro [Department of Physics, Faculty of Science and Technology, Tokyo University of Science (TUS), Noda 278-8510 (Japan)

2014-05-02

413

[Nucleosynthesis, Rotation and Magnetism in Accreting Neutron Stars  

NASA Technical Reports Server (NTRS)

This is my final report on the NASA ATP grant on nucleosynthesis, rotation and magnetism in accreting neutron stars (NAG5-8658). In my last two reports, I summarized the science that I have accomplished, which covered a large range of topics. For this report, I want to point out the graduate students that were partially supported on this grant and where they are now. Andrew Cumming is an Assistant Professor of Physics at McGill University, Greg Ushomirsky is a researcher at MIT s Lincoln Laboratories, Dean Townsley is a postdoctoral researcher at Univ. of Chicago, Chris Deloye is a postdoctoral researcher at Northwestern University. The other two students, Phil Chang and Tony Piro, are still at UCSB and will be completing their PhD s in Summer 05 and Summer 06.

Bildsten, Lars

2004-01-01

414

Gravitational Lensing of Gravitational Waves from Merging Neutron Star Binaries  

E-print Network

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

Yun Wang; Albert Stebbins; Edwin L. Turner

1996-05-22

415

Maximum mass of neutron stars with quark matter core  

SciTech Connect

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

Takatsuka, Tatsuyuki; Hatsuda, Tetsuo; Masuda, Kota [Iwate University, Morioka 020-8550 (Japan); Department of Physics, University of Tokyo, Tokyo 113-0033, Japan and Theoretical Research Division, Nishina Center, RIKEN, Wako 351-0198 (Japan); Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan)

2012-11-12

416

Neutrino Energetics of Black Hole--Neutron Star Mergers  

NASA Astrophysics Data System (ADS)

We present simulations of black hole--neutron star mergers solving the coupled Einstein-hydrodynamics equations, including radiative cooling and chemical evolution. To this end we have added a leakage approximation to the Spectral Einstein Code (SpEC). The nuclear matter is modeled by the Lattimer & Swesty equation of state. This first in a set of binary configurations uses a low mass ratio (q=4) and high spin (a=0.9). Our choice of parameters is astrophysically optimistic and provides an approximate upper bound on radiation energetics due to the large (initial mass ˜0.15 M), long-lived (>150 ms) disk. We examine the energy of neutrino radiation, the dynamics of the remnant disk, and the characteristics of the tidally ejected fluid.

Deaton, M. Brett

2013-04-01

417

Effective field theory for neutron stars with strong ?--hyperon repulsion  

NASA Astrophysics Data System (ADS)

We investigate the role of many-body correlations in the maximum mass of neutron stars using the effective relativistic QHD-model with parameterized couplings which represents an extended compilation of other effective models found in the literature. Our model exhausts the whole fundamental baryon octet (n, p, ?-, ?0, ?+, ?, ?-, ?0) and simulates corrections to the minimal Yukawa couplings by considering many-body nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (?, ?*), vector-isoscalar (?, ?), vector-isovector (?rrho) and scalar-isovector (?). Following recent experimental results, we consider in our calculations the extreme case where the ?- experiences such a strong repulsion that it does not appear at all in nuclear matter.

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

2014-09-01

418

Searches for Gravitational Waves from Binary Neutron Stars: A Review  

E-print Network

A new generation of observatories is looking for gravitational waves. These waves, emitted by highly relativistic systems, will open a new window for ob- servation of the cosmos when they are detected. Among the most promising sources of gravitational waves for these observatories are compact binaries in the final min- utes before coalescence. In this article, we review in brief interferometric searches for gravitational waves emitted by neutron star binaries, including the theory, instru- mentation and methods. No detections have been made to date. However, the best direct observational limits on coalescence rates have been set, and instrumentation and analysis methods continue to be refined toward the ultimate goal of defining the new field of gravitational wave astronomy.

Warren G. Anderson; Jolien D. E. Creighton

2007-12-15

419

FURTHER EVIDENCE FOR THE BIMODAL DISTRIBUTION OF NEUTRON-STAR MASSES  

SciTech Connect

We use a collection of 14 well-measured neutron-star masses to strengthen the case that a substantial fraction of these neutron stars were formed via electron-capture (e-capture) supernovae (SNe) as opposed to Fe core-collapse SNe. The e-capture SNe are characterized by lower resultant gravitational masses and smaller natal kicks, leading to lower orbital eccentricities when the e-capture SN has led to the formation of the second neutron star in a binary system. Based on the measured masses and eccentricities, we identify four neutron stars, which have a mean post-collapse gravitational mass of {approx}1.25 M {sub sun}, as the product of e-capture SNe. We associate the remaining 10 neutron stars, which have a mean mass of {approx}1.35 M {sub sun}, with Fe core-collapse SNe. If the e-capture SN occurs during the formation of the first neutron star, then this should substantially increase the formation probability for double neutron stars, given that more systems will remain bound with the smaller kicks. However, this does not appear to be the case for any of the observed systems and we discuss possible reasons for this.

Schwab, J.; Rappaport, S. [37-602B, M.I.T., Department of Physics and Kavli Institute for Astrophysics and Space Research, 70 Vassar St., Cambridge, MA, 02139 (United States); Podsiadlowski, Ph., E-mail: sar@mit.ed, E-mail: jschwab@mit.ed, E-mail: jwschwab@berkeley.ed, E-mail: podsi@astro.ox.ac.u [Department of Astrophysics, University of Oxford, Oxford OX1 3RH (United Kingdom)

2010-08-10

420

On the compatibility of observable grand unified monopole fluxes and neutron stars  

NASA Astrophysics Data System (ADS)

We consider the possibility that the constraints on grand unified monopole fluxes derived from limits on the X-ray background due to hot neutron stars, contain a window in the range 10-15 <~ F?0 <~ 10-13 cm-2 s-1 s-1. The appearance of this window is due primarily to three effects: (1) neutron stars with large numbers of monopoles catalyzing baryon decay in their interiors are mainly producing neutrinos rather than photons; (2) the photons radiated are hard X-rays or ?-rays in which the background limits are slightly less restrictive, and (3) the lifetime of the neutron star is drastically reduced through disintegration (i.e., all the nucleons in the star will have been processed by monopoles). All of the arguments are sensitive to the equation of state inside the neutron star, leading to uncertainties which should not dissuade experimenters from monopole searches.

Olive, Keith A.; Schramm, David N.

1983-10-01

421

Spin-Precession: Breaking the Black Hole--Neutron Star Degeneracy  

E-print Network

Mergers of compact stellar remnant are prime targets for the LIGO/Virgo gravitational wave detectors. One hopes that the gravitational wave signals from these merger events can be used to study the mass and spin distribution of stellar remnants, and provide information about black hole horizons and the material properties of neutron stars. However, it has been suggested that degeneracies in the way that the star's mass and spin are imprinted in the waveforms may make it impossible to distinguish between black holes and neutron stars. Here we show that the precession of the orbital plane due to spin-orbit coupling breaks the mass-spin degeneracy, and allows us to distinguish between standard neutron stars and alternative possibilities, such as black holes or exotic neutron stars with large masses and spins.

Chatziioannou, Katerina; Klein, Antoine; Yunes, Nicolas

2014-01-01

422

Spin-precession: Breaking the Black Hole-Neutron Star Degeneracy  

NASA Astrophysics Data System (ADS)

Mergers of compact stellar remnants are prime targets for the LIGO/Virgo gravitational wave detectors. The gravitational wave signals from these merger events can be used to study the mass and spin distribution of stellar remnants, and provide information about black hole horizons and the material properties of neutron stars. However, it has been suggested that degeneracies in the way that the star's mass and spin are imprinted in the waveforms may make it impossible to distinguish between black holes and neutron stars. Here we show that the precession of the orbital plane due to spin-orbit coupling breaks the mass-spin degeneracy, and allows us to distinguish between standard neutron stars and alternative possibilities, such as black holes or exotic neutron stars with large masses and spins.

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

2015-01-01

423

Spin-Precession: Breaking the Black Hole--Neutron Star Degeneracy  

E-print Network

Mergers of compact stellar remnant are prime targets for the LIGO/Virgo gravitational wave detectors. One hopes that the gravitational wave signals from these merger events can be used to study the mass and spin distribution of stellar remnants, and provide information about black hole horizons and the material properties of neutron stars. However, it has been suggested that degeneracies in the way that the star's mass and spin are imprinted in the waveforms may make it impossible to distinguish between black holes and neutron stars. Here we show that the precession of the orbital plane due to spin-orbit coupling breaks the mass-spin degeneracy, and allows us to distinguish between standard neutron stars and alternative possibilities, such as black holes or exotic neutron stars with large masses and spins.

Katerina Chatziioannou; Neil Cornish; Antoine Klein; Nicolas Yunes

2014-12-18

424

Finite size effects in Neutron Star and Nuclear matter simulations  

E-print Network

In this work we study molecular dynamics simulations of symmetric nuclear matter using a semi-classical nucleon interaction model. We show that, at sub-saturation densities and low temperatures, the solutions are non-homogeneous structures reminiscent of the ``nuclear pasta'' phases expected in Neutron Star Matter simulations, but shaped by artificial aspects of the simulations. We explore different geometries for the periodic boundary conditions imposed on the simulation cell: cube, hexagonal prism and truncated octahedron. We find that different cells may yield different solutions for the same physical conditions (i.e. density and temperature). The particular shape of the solution at a given density can be predicted analytically by energy minimization. We also show that even if this behavior is due to finite size effects, it does not mean that it vanishes for very large systems and it actually is independent of the system size: The system size sets the only characteristic length scale for the inhomogeneities. We then include a screened Coulomb interaction, as a model of Neutron Star Matter, and perform simulations in the three cell geometries. In this case, the competition between competing interactions of different range produces the well known nuclear pasta, with (in most cases) several structures per cell. However, we find that the results are affected by finite size in different ways depending on the geometry of the cell. In particular, at the same physical conditions and system size, the hexagonal prism yields a single structure per cell while the cubic and truncated octahedron show consistent results with more than one structure per cell. In this case, the results in every cell are expected to converge for systems much larger than the characteristic length scale that arises from the competing interactions.

P. A. Giménez Molinelli; C. O. Dorso

2014-03-23

425

Rotating proto-neutron stars: spin evolution, maximum mass and I-Love-Q relations  

E-print Network

Shortly after its birth in a gravitational collapse, a proto-neutron star enters in a phase of quasi-stationary evolution characterized by large gradients of the thermodynamical variables and intense neutrino emission. In few tens of seconds the gradients smooth out while the star contracts and cools down, until it becomes a neutron star. In this paper we study this phase of the proto-neutron star life including rotation, and employing finite temperature equations of state. We model the evolution of the rotation rate, and determine the relevant quantities characterizing the star. Our results show that an isolated neutron star cannot reach, at the end of the evolution, the maximum values of mass and rotation rate allowed by the zero-temperature equation of state. Moreover, a mature neutron star evolved in isolation cannot rotate too rapidly, even if it is born from a proto-neutron star rotating at the mass-shedding limit. We also show that the I-Love-Q relations are violated in the first second of life, but they are satisfied as soon as the entropy gradients smooth out.

Grégoire Martinon; Andrea Maselli; Leonardo Gualtieri; Valeria Ferrari

2014-06-30

426

Rotational Corrections to Neutron-star Radius Measurements from Thermal Spectra  

NASA Astrophysics Data System (ADS)

We calculate the rotational broadening in the observed thermal spectra of neutron stars spinning at moderate rates in the Hartle-Thorne approximation. These calculations accurately account for the effects of the second-order Doppler boosts as well as for the oblate shapes and the quadrupole moments of the neutron stars. We find that fitting the spectra and inferring the bolometric fluxes under the assumption that a star is not rotating causes an underestimate of the inferred fluxes and, thus, radii. The correction depends on the stellar spin, mass, radius, and the observer's inclination. For a 10 km, 1.4 M ? neutron star spinning at 600 Hz, the rotational correction to the flux is ~1%-4%, while for a 15 km neutron star with the same spin period, the correction ranges from 2% for pole-on sources to 12% for edge-on sources. We calculate the inclination-averaged corrections to inferred radii as a function of the neutron-star radius and mass and provide an empirical formula for the corrections. For realistic neutron-star parameters (1.4 M ?, 12 km, 600 Hz), the stellar radius is on the order of 4% larger than the radius inferred under the assumption that the star is not spinning.

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

2015-01-01

427

Realistic fission model and the r-process in neutron star mergers  

SciTech Connect

About half of heavy elements are considered to be produced by the rapid neutron-capture process, r-process. The neutron star merger is one of the viable candidates for the astrophysical site of r-process nucleosynthesis. Nuclear fission reactions play an important role in the r-process of neutron star mergers. However theoretical predictions about fission properties of neutron-rich nuclei have some uncertainties. Especially, their fission fragment distributions are totally unknown and the phenomenologically extrapolated distribution was often applied to nucleosynthesis calculations. In this study, we have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions. We discuss the effects on the r-process in neutron star mergers from the nuclear fission of heavy neutron-rich actinide elements. We also discuss how variations in the fission fragment distributions affect the abundance pattern.

Shibagaki, S.; Kajino, T. [Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan and National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Chiba, S. [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8850 (Japan); Mathews, G. J. [Center for Astrophysics, Department of Physics, University of Notre Dame, IN 46556, U.S.A. and National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2014-05-09

428

On the number of accreting and cooling isolated neutron stars detectable with the ROSAT All-Sky Survey  

E-print Network

We present limits to the log N - log S curve for isolated neutron stars, both cooling and accreting neutron stars, which are not active as radio pulsars, as observed with the ROSAT All-Sky Survey and compare it with theoretical expectations. So far, only one isolated neutron star is identified optically among ROSAT sources, namely RXJ185635-3754 (Walter & Matthews 1997). Three more promising candidates have been suggested. In addition, several upper limit estimates are available on the space density of such neutron stars from different optical follow-up studies. We show that the log N - log S curve according to the current observations, including the identified neutron star, the three additional candidates, and the upper limits, lies between the theoretical expectations for middle-aged cooling neutron stars and old accreting neutron stars. At least one of the neutron star candidates found so far with ROSAT may be cooling instead of accreting. We suggest that the fact that more accreting isolated old neutron stars were expected (e.g., Madau & Blaes 1994) than observed is mostly due to the velocity distribution used in those calculations. More recent radio observations indicate that there are fewer slow neutron stars, ie., fewer accreting X-ray bright old neutron stars. At the X-ray bright end of the log N - log S curve, however, the ROSAT observations agree well with the theoretical expectations.

Ralph Neuhaeuser; Joachim Truemper

1998-12-28

429

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

430

Bulk viscosity of strange matter and r-modes in neutron stars  

E-print Network

We discuss bulk viscosity due to non-leptonic processes involving hyperons and Bose-Einstein condensate of negatively charged kaons in neutron stars. It is noted that the hyperon bulk viscosity coefficient is a few order of magnitude larger than that of the case with the condensate. Further it is found that the hyperon bulk viscosity is suppressed in a superconducting phase. The hyperon bulk viscosity efficiently damps the r-mode instability in neutron stars irrespective of whether a superconducting phase is present or not in neutron star interior.

Debarati Chatterjee; Debades Bandyopadhyay

2008-12-30

431

Neutrino Scattering in a Newly Born Neutron Star  

E-print Network

We calculate neutrino cross sections from neutral current reactions in the dense matter encountered in the evolution of a newly born neutron star. Effects of composition and of strong interactions in the deleptonization and cooling phases of the evolution are studied. The influence of the possible presence of strangeness-rich hyperons on the neutrino scattering cross sections is explored. Due to the large vector couplings of the Sigma-minus and Cascade-minus, |C_V|~2, these particles, if present in protoneutron star matter, give significant contributions to neutrino scattering. In the deleptonization phase, the presence of strangeness leads to large neutrino energies, which results in large enhancements in the cross sections compared to those in matter with nucleons only. In the cooling phase, in which matter is nearly neutrino free, the response of the Sigma-minus hyperons to thermal neutrinos is the most significant. Neutrinos couple relatively weakly to the Lambda hyperons and, hence, their contributions are significant only at high density.

Sanjay Reddy; Madappa Prakash

1996-10-15

432

Maximum mass of neutron stars and strange neutron-star cores  

NASA Astrophysics Data System (ADS)

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