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Sample records for neutron star spin

  1. Burst Oscillations: Watching Neutron Stars Spin

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2010-01-01

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

  2. Equilibrium spin pulsars unite neutron star populations

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  3. Spin paramagnetic deformation of a neutron star

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  4. Burst Oscillations: A New Spin on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2007-01-01

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

  5. Burst Oscillations: A New Spin on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2007-01-01

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

  6. Compact Object Binaries with Spinning Neutron Stars in Numerical Relativity

    NASA Astrophysics Data System (ADS)

    Tacik, Nicholas A.

    The inspiral and merger of binary neutron stars (BNS) is one of the most promising potential sources of gravitational waves for ground-based detectors like Advanced LIGO. BNS mergers are also likely a source of counterpart electromagnetic radiation. It is important to perform simulations of BNS to better understand and model their gravitational wave emission as well as their electromagnetic emission. The parameter space of BNS binaries is quite large, and one aspect that has not been well studied in neutron star spin. In this thesis, we focus on investigating spinning neutron stars in compact object binaries. Using the SpEC code, developed by the SXS collaboration, we begin by presenting a new code to create initial data for binary neutron stars with arbitrary spins. We introduce a novel method of measuring neutron star spin, and show that it is accurate and robust. We evolve several spinning binary configurations and show that their properties agree remarkably well with Post-Newtonian predictions. We also show that we are able to control the eccentricity of the binaries to 0.1%. Thereafter, we proceed to extend our code to black hole.neutron star (BHNS) binaries. We create many data sets across the BHNS parameter space, varying neutron star spin magnitude, spin direction, compactness, and black hole mass, spin and spin direction. We are able to create initial data sets with neutron star spins near the mass shedding limit, and nearly extremal black hole spins. Finally, we investigate spurious gravitational radiation in binary black hole systems. We study its parameter space dependence, by introducing three diagnostics, investigating them as a function of black hole spin and black hole separation, and comparing two different methods of constructing initial data.

  7. NARROW ATOMIC FEATURES FROM RAPIDLY SPINNING NEUTRON STARS

    SciTech Connect

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    SciTech Connect

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

    2012-02-10

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

  10. Gravitational Waves and the Maximum Spin Frequency of Neutron Stars

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  11. Persistent crust-core spin lag in neutron stars

    NASA Astrophysics Data System (ADS)

    Glampedakis, Kostas; Lasky, Paul D.

    2015-06-01

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

  12. Tidal Love numbers of a slowly spinning neutron star

    NASA Astrophysics Data System (ADS)

    Pani, Paolo; Gualtieri, Leonardo; Ferrari, Valeria

    2015-12-01

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

  13. ECCENTRIC MERGERS OF BLACK HOLES WITH SPINNING NEUTRON STARS

    SciTech Connect

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

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Van Doesburgh, Marieke; van der Klis, Michiel

    2016-07-01

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

  15. SPIN-PRECESSION: BREAKING THE BLACK HOLE-NEUTRON STAR DEGENERACY

    SciTech Connect

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

  17. Quark Deconfinement in Neutron Star Cores: The Effects of Spin-down

    NASA Astrophysics Data System (ADS)

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

    2006-07-01

    We study the role of spin-down in driving quark deconfinement in the high-density cores of isolated neutron stars. Assuming spin-down to be solely due to magnetic braking, we obtain typical timescales to quark deconfinement for neutron stars that are born with Keplerian frequencies. Employing different equations of state (EOSs), we determine the minimum and maximum neutron star masses that will allow for deconfinement via spin-down only. We find that the time to reach deconfinement is strongly dependent on the magnetic field and that this time is least for EOSs that support the largest minimum mass at zero spin, unless rotational effects on stellar structure are large. For a fiducial critical density of 5ρ0 for the transition to the quark phase (ρ0=2.5×1014 g cm-3 is the saturation density of nuclear matter), we find that neutron stars lighter than 1.5 Msolar cannot reach a deconfined phase. Depending on the EOS, neutron stars of more than 1.5 Msolar can enter a quark phase only if they are spinning faster than about 3 ms as observed now, whereas larger spin periods imply either that they are already quark stars or that they will never become them.

  18. The masses and spins of neutron stars and stellar-mass black holes

    NASA Astrophysics Data System (ADS)

    Miller, M. Coleman; Miller, Jon M.

    2015-01-01

    Stellar-mass black holes and neutron stars represent extremes in gravity, density, and magnetic fields. They therefore serve as key objects in the study of multiple frontiers of physics. In addition, their origin (mainly in core-collapse supernovae) and evolution (via accretion or, for neutron stars, magnetic spindown and reconfiguration) touch upon multiple open issues in astrophysics. In this review, we discuss current mass and spin measurements and their reliability for neutron stars and stellar-mass black holes, as well as the overall importance of spins and masses for compact object astrophysics. Current masses are obtained primarily through electromagnetic observations of binaries, although future microlensing observations promise to enhance our understanding substantially. The spins of neutron stars are straightforward to measure for pulsars, but the birth spins of neutron stars are more difficult to determine. In contrast, even the current spins of stellar-mass black holes are challenging to measure. As we discuss, major inroads have been made in black hole spin estimates via analysis of iron lines and continuum emission, with reasonable agreement when both types of estimate are possible for individual objects, and future X-ray polarization measurements may provide additional independent information. We conclude by exploring the exciting prospects for mass and spin measurements from future gravitational wave detections, which are expected to revolutionize our understanding of strong gravity and compact objects.

  19. Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars.

    PubMed

    Chakrabarty, Deepto; Morgan, Edward H; Muno, Michael P; Galloway, Duncan K; Wijnands, Rudy; Van Der Klis, Michiel; Markwardt, Craig B

    2003-07-03

    Millisecond pulsars are neutron stars that are thought to have been spun-up by mass accretion from a stellar companion. It is not known whether there is a natural brake for this process, or if it continues until the centrifugal breakup limit is reached at submillisecond periods. Many neutron stars that are accreting mass from a companion star exhibit thermonuclear X-ray bursts that last tens of seconds, caused by unstable nuclear burning on their surfaces. Millisecond-period brightness oscillations during bursts from ten neutron stars (as distinct from other rapid X-ray variability that is also observed) are thought to measure the stellar spin, but direct proof of a rotational origin has been lacking. Here we report the detection of burst oscillations at the known spin frequency of an accreting millisecond pulsar, and we show that these oscillations always have the same rotational phase. This firmly establishes burst oscillations as nuclear-powered pulsations tracing the spin of accreting neutron stars, corroborating earlier evidence. The distribution of spin frequencies of the 11 nuclear-powered pulsars cuts off well below the breakup frequency for most neutron-star models, supporting theoretical predictions that gravitational radiation losses can limit accretion torques in spinning up millisecond pulsars.

  20. Spin evolution of a proto-neutron star

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  1. A RAY-TRACING ALGORITHM FOR SPINNING COMPACT OBJECT SPACETIMES WITH ARBITRARY QUADRUPOLE MOMENTS. II. NEUTRON STARS

    SciTech Connect

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

    2012-07-10

    A moderately spinning neutron star acquires an oblate shape and a spacetime with a significant quadrupole moment. These two properties affect its apparent surface area for an observer at infinity, as well as the light curve arising from a hot spot on its surface. In this paper, we develop a ray-tracing algorithm to calculate the apparent surface areas of moderately spinning neutron stars making use of the Hartle-Thorne metric. This analytic metric allows us to calculate various observables of the neutron star in a way that depends only on its macroscopic properties and not on the details of its equation of state. We use this algorithm to calculate the changes in the apparent surface area, which could play a role in measurements of neutron-star radii and, therefore, in constraining their equation of state. We show that whether a spinning neutron star appears larger or smaller than its non-rotating counterpart depends primarily on its equatorial radius. For neutron stars with radii {approx}10 km, the corrections to the Schwarzschild spacetime cause the apparent surface area to increase with spin frequency. In contrast, for neutron stars with radii {approx}15 km, the oblateness of the star dominates the spacetime corrections and causes the apparent surface area to decrease with increasing spin frequency. In all cases, the change in the apparent geometric surface area for the range of observed spin frequencies is {approx}<5% and hence only a small source of error in the measurement of neutron-star radii.

  2. Pulse profiles from spinning neutron stars in the Hartle-Thorne approximation

    SciTech Connect

    Psaltis, Dimitrios; Özel, Feryal E-mail: fozel@email.arizone.edu

    2014-09-10

    We present a new numerical algorithm for the calculation of pulse profiles from spinning neutron stars in the Hartle-Thorne approximation. Our approach allows us to formally take into account the effects of Doppler shifts and aberration, of frame dragging, as well as of the oblateness of the stellar surface and of its quadrupole moment. We confirm an earlier result that neglecting the oblateness of the neutron-star surface leads to ≅ 5%-30% errors in the calculated profiles and further show that neglecting the quadrupole moment of its spacetime leads to ≅ 1%-5% errors at a spin frequency of ≅ 600 Hz. We discuss the implications of our results for the measurements of neutron-star masses and radii with upcoming X-ray missions, such as NASA's NICER and ESA's LOFT.

  3. Neutron Stars

    NASA Technical Reports Server (NTRS)

    Cottam, J.

    2007-01-01

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

  4. Spin evolution of neutron stars: Nonlinear development of the r-mode instability

    NASA Astrophysics Data System (ADS)

    Bondarescu, Ruxandra

    2008-08-01

    Rotating neutron stars have modes that are driven unstable by gravitational radiation reaction, principally the r-mode, a Rossby wave with n = 3, m = 2, and hence large gravitational radiation reaction. Here n and m label the Legendre functions associated with the mode. The r-mode instability is active when gravitational driving dominates viscous dissipation. It has been suggested that this instability can (1) set the largest angular frequency of rotation of accreting neutron stars and (2) significantly spin down newborn neutron stars preventing them from reaching millisecond periods. Both the maximum frequency that neutron stars can reach and the frequency to which newborn stars can be spun down to in the first few years after formation depend on the neutron star composition via viscous dissipation and neutrino cooling. The nonlinear development of the instability plays a very important role in determining how the saturation process works, and also illustrates how instabilities can saturate at low amplitudes as a consequence of nearly resonant excitation of other modes. We model the nonlinear interactions between modes together with basic neutron star physics including viscous heating, cooling and spin evolution of the star. The nonlinear effects are included via three-mode couplings. We show that in most scenarios one triplet of modes is sufficient to stop the growth of the instability. To explore possible nonlinear behaviors we parameterize uncertain properties of neutron stars such as the superfluid transition temperature and the rate at which the star cools via neutrino emission. The average evolution of the mode amplitudes can usually be approximated by quasi-stationary states that change slowly with spin frequency and temperature and can be determined algebraically. The spin and temperature evolution follow or oscillate around trajectories along sequences of quasi-stationary states. In the Low Mass X-ray Binary (LMXB) case (Chapter 2), after some brief

  5. Mergers of magnetized neutron stars with spinning black holes: disruption, accretion, and fallback.

    PubMed

    Chawla, Sarvnipun; Anderson, Matthew; Besselman, Michael; Lehner, Luis; Liebling, Steven L; Motl, Patrick M; Neilsen, David

    2010-09-10

    We investigate the merger of a neutron star in orbit about a spinning black hole in full general relativity with a mass ratio of 5:1, allowing the star to have an initial magnetization of 10(12)  G. We present the resulting gravitational waveform and analyze the fallback accretion as the star is disrupted. We see no significant dynamical effects in the simulations or changes in the gravitational waveform resulting from the initial magnetization. We find that only a negligible amount of matter becomes unbound; 99% of the neutron star material has a fallback time of 10 seconds or shorter to reach the region of the central engine and that 99.99% of the star will interact with the central disk and black hole within 3 hours.

  6. Parameter Estimation on Gravitational Waves from Neutron-star Binaries with Spinning Components

    NASA Astrophysics Data System (ADS)

    Farr, Ben; Berry, Christopher P. L.; Farr, Will M.; Haster, Carl-Johan; Middleton, Hannah; Cannon, Kipp; Graff, Philip B.; Hanna, Chad; Mandel, Ilya; Pankow, Chris; Price, Larry R.; Sidery, Trevor; Singer, Leo P.; Urban, Alex L.; Vecchio, Alberto; Veitch, John; Vitale, Salvatore

    2016-07-01

    Inspiraling binary neutron stars (BNSs) are expected to be one of the most significant sources of gravitational-wave signals for the new generation of advanced ground-based detectors. We investigate how well we could hope to measure properties of these binaries using the Advanced LIGO detectors, which began operation in September 2015. We study an astrophysically motivated population of sources (binary components with masses 1.2\\quad {M}⊙ {--}1.6\\quad {M}⊙ and spins of less than 0.05) using the full LIGO analysis pipeline. While this simulated population covers the observed range of potential BNS sources, we do not exclude the possibility of sources with parameters outside these ranges; given the existing uncertainty in distributions of mass and spin, it is critical that analyses account for the full range of possible mass and spin configurations. We find that conservative prior assumptions on neutron-star mass and spin lead to average fractional uncertainties in component masses of ˜16%, with little constraint on spins (the median 90% upper limit on the spin of the more massive component is ˜0.7). Stronger prior constraints on neutron-star spins can further constrain mass estimates but only marginally. However, we find that the sky position and luminosity distance for these sources are not influenced by the inclusion of spin; therefore, if LIGO detects a low-spin population of BNS sources, less computationally expensive results calculated neglecting spin will be sufficient for guiding electromagnetic follow-up.

  7. Modeling the Spin Equilibrium of Neutron Stars in LMXBs Without Gravitational Radiation

    NASA Technical Reports Server (NTRS)

    Andersson, N.; Glampedakis, K.; Haskell, B.; Watts, A. L.

    2004-01-01

    In this paper we discuss the spin-equilibrium of accreting neutron stars in LMXBs. We demonstrate that, when combined with a naive spin-up torque, the observed data leads to inferred magnetic fields which are at variance with those of galactic millisecond radiopulsars. This indicates the need for either additional spin-down torques (eg. gravitational radiation) or an improved accretion model. We show that a simple consistent accretion model can be arrived at by accounting for radiation pressure in rapidly accreting systems (above a few percent of the Eddington accretion rate). In our model the inner disk region is thick and significantly sub-Keplerian, and the estimated equilibrium periods are such that the LMXB neutron stars have properties that accord well with the galactic millisecond radiopulsar sample. The implications for future gravitational-wave observations are also discussed briefly.

  8. Modeling the Spin Equilibrium of Neutron Stars in LMXBs Without Gravitational Radiation

    NASA Technical Reports Server (NTRS)

    Andersson, N.; Glampedakis, K.; Haskell, B.; Watts, A. L.

    2004-01-01

    In this paper we discuss the spin-equilibrium of accreting neutron stars in LMXBs. We demonstrate that, when combined with a naive spin-up torque, the observed data leads to inferred magnetic fields which are at variance with those of galactic millisecond radiopulsars. This indicates the need for either additional spin-down torques (eg. gravitational radiation) or an improved accretion model. We show that a simple consistent accretion model can be arrived at by accounting for radiation pressure in rapidly accreting systems (above a few percent of the Eddington accretion rate). In our model the inner disk region is thick and significantly sub-Keplerian, and the estimated equilibrium periods are such that the LMXB neutron stars have properties that accord well with the galactic millisecond radiopulsar sample. The implications for future gravitational-wave observations are also discussed briefly.

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

    NASA Astrophysics Data System (ADS)

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

    2006-08-01

    The present study is mainly addressed to the coupled spin, mass, magnetic field, orbital separation, and orbital period evolution of a neutron star entering a close binary system with a low mass main sequence companion, which loses mass in form of homogenous stellar wind. We apply flux expulsion of the magnetic field from the superfluid superconductive core of a neutron star , based on different equation of states, and its subsequent decay in the crust , which also depends on conductivity of the crust, and hence on the temperature, T, and the neutron star age. The initial core and surface magnetic field are of the same order of magnitude. To derive the rate of expulsion of the magnetic flux out of the core we consider various forces which act on the fluxoids in the interior of a neutron star, including a force due to their pinning interaction with the moving neutron vortices, buoyancy force, curvature force, and viscous drag force due to magnetic scattering of electrons. Various effects accompanying mass exchange in binaries can influence the evolution of spin and magnetic field of the neutron star. The orbital separation of the binary clearly affects the estimated value of , and it itself evolves due to mass exchange between the components, mass loss from the system, and two other sinks of the orbital angular momentum namely magnetic braking and gravitational waves. The neutron star passes through four evolutionary phases ( isolated pulsar- propeller- accretion from the wind of a companion- accretion resulting from Roche-lobe overflow). Models for a range of parameters, and initial orbital period, magnetic field and spin period are constructed. The impurity parameter, Q, is assumed to be constant during the whole evolution of the star and range from 1 to 0.001. Final magnetic field, spin and orbital period are presented in this paper. The surface magnetic field weakens by a factor of .The suggested mechanism can explain the lower magnetic field and faster spins of

  10. Simulating a High-Spin Black Hole-Neutron Star Binary

    NASA Astrophysics Data System (ADS)

    Derby, John; Lovelace, Geoffrey; Duez, Matt; Foucart, Francois; Simulating Extreme Spacetimes (SXS) Collaboration

    2017-01-01

    During their first observing run (fall 2015) Advanced LIGO detected gravitational waves from merging black holes. In its future observations LIGO could detect black hole neutron star binaries (BHNS). It is important to have numerical simulations to predict these waves, to help find as many of these waves as possible and to estimate the sources properties, because at times near merger analytic approximations fail. Also, numerical models of the disk formed when the black hole tears apart the neutron star can help us learn about these systems' potential electromagnetic counterparts. One area of the parameter space for BHNS systems that is particularly challenging is simulations with high black hole spin. I will present results from a new BHNS simulation that has a black hole spin of 90% of the theoretical maximum. We are part of SXS but not all.

  11. Aligned spin neutron star-black hole mergers: A gravitational waveform amplitude model

    NASA Astrophysics Data System (ADS)

    Pannarale, Francesco; Berti, Emanuele; Kyutoku, Koutarou; Lackey, Benjamin D.; Shibata, Masaru

    2015-10-01

    The gravitational radiation emitted during the merger of a black hole with a neutron star is rather similar to the radiation from the merger of two black holes when the neutron star is not tidally disrupted. When tidal disruption occurs, gravitational waveforms can be broadly classified in two groups, depending on the spatial extent of the disrupted material. Extending previous work by some of us, here we present a phenomenological model for the gravitational waveform amplitude in the frequency domain encompassing the three possible outcomes of the merger: no tidal disruption, and "mild" and "strong" tidal disruption. The model is calibrated to 134 general-relativistic numerical simulations of binaries where the black hole spin is either aligned or antialigned with the orbital angular momentum. All simulations were produced using the SACRA code and piecewise polytropic neutron star equations of state. The present model can be used to determine when black-hole binary waveforms are sufficient for gravitational-wave detection, to extract information on the equation of state from future gravitational-wave observations, to obtain more accurate estimates of black hole-neutron star merger event rates, and to determine the conditions under which these systems are plausible candidates as central engines of gamma-ray bursts and macronovae/kilonovae.

  12. Evolution of the Spin Periods of Neutron Stars in Low-mass X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Xu, X. T.; Zhu, Z. L.

    2016-11-01

    We present numerical analysis of the spin evolution of the neutron stars in low-mass X-ray binaries, trying to explain the discrepancy in the spin period distribution between observations of millisecond pulsars and theoretical results. In our calculations, we take account of possible effect of radiation pressure, and irradiation-induced instability on the structure of the disk, and the evolution of the mass transfer rate, respectively. We report the following results: (1) Radiation pressure leads to a slight increase of the spin periods, and irradiation-induced mass transfer cycles can shorten the spin-down phase of evolution. (2) The calculated results in the model combining radiation pressure and irradiation-induced mass transfer cycles show that accretion is strongly limited by radiation pressure in high mass transfer phase. (3) The accreted mass and the critical fastness parameter can affect the number of systems in equilibrium state.

  13. Discovery of the Neutron Star Spin Frequency in EXO 0748-676

    NASA Technical Reports Server (NTRS)

    Villarreal, Adam R.; Strohmayer, Tod E.

    2004-01-01

    We report the results of a search for burst oscillations during thermonuclear X-ray bursts from the low mass X-ray binary (LMXB) EXO 0748-676. With the proportional counter array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) we have detected a 45 Hz oscillation in the average power spectrum of 38 thermonuclear X-ray bursts from this source. We computed power spectra with 1 Hz frequency resolution for both the rising and decaying portions of 38 X-ray bursts from the public RXTE archive. We averaged the 1 Hz power spectra and detected a significant signal at 45 Hz in the decaying phases of the bursts. The signal is detected at a significance level of 4 x 10 (exp -8) similar signal was detected in the rising intervals. The oscillation peak is unresolved at 1 Hz frequency resolution, indicating an oscillation quality factor, Q = nu (sub 0)/Delta nu (sub fwhm) greater than 45, and the average signal amplitude is approximately equal to 3% (rms) The detection of 45 Hz burst oscillations from EXO 0748-676 provides compelling evidence that this is the neutron star spin frequency in this system. We use the inferred spin frequency to model the widths of absorption lines from the neutron star surface and show that the widths of the absorption lines from EXO 0748-676 recently reported by Cottam et al. are consistent with a 45 Hz spin frequency as long as the neutron star radius is in the range from about 9.5 - 15 km. With a known spin frequency, precise modelling of the line profiles from EXO 0748-676 holds great promise for constraining the dense matter equation of state.

  14. Structure of stable binary neutron star merger remnants: Role of initial spin

    NASA Astrophysics Data System (ADS)

    Kastaun, W.; Ciolfi, R.; Endrizzi, A.; Giacomazzo, B.

    2017-08-01

    We present general relativistic numerical simulations of binary neutron star (BNS) mergers with different initial spin configurations. We focus on models with stars of mass 1.4 M⊙ each, which employ the equation of state (EOS) by Shen, Horowitz, and Teige, and which result in stable NSs as merger remnants. For comparison, we consider two irrotational equal mass (M =1.35 M⊙) and unequal mass (M =1.29 , 1.42 M⊙ ) BNS models using the APR4 EOS, which result in a supramassive merger remnant. We present visualizations of the fluid flow and temperature distribution and find a strong impact of the spin on vortex structure and nonaxisymmetric deformation. We compute the radial mass distribution and the rotation profile in the equatorial plane using recently developed measures independent of spatial gauge, revealing slowly rotating cores that can be well approximated by the cores of spherical stars. We also study the influence of the spin on the inspiral phase and the gravitational wave (GW) signal. Using a newly developed analysis method, we further show that gravitational waveforms from BNS mergers can exhibit one or more phase jumps after merger, which occur together with minima of the strain amplitude. We provide a natural explanation in terms of the remnant's quadrupole moment, and show that cancellation effects due to phase jumps can have a strong impact on the GW power spectrum. Finally, we discuss the impact of the spin on the amount of ejected matter.

  15. Spinning down newborn neutron stars: Nonlinear development of the r-mode instability

    SciTech Connect

    Bondarescu, Ruxandra; Teukolsky, Saul A.; Wasserman, Ira

    2009-05-15

    We model the nonlinear saturation of the r-mode instability via three-mode couplings and the effects of the instability on the spin evolution of young neutron stars. We include one mode triplet consisting of the r-mode and two near-resonant inertial modes that couple to it. We find that the spectrum of evolutions is more diverse than previously thought. We start our evolutions with a star of temperature {approx}10{sup 10} K and a spin frequency close to the Kepler break-up frequency. We assume that hyperon bulk viscosity dominates at high temperatures (T{approx}10{sup 9}-10{sup 10} K) and boundary layer viscosity dominates at lower temperatures ({approx}a fewx10{sup 8} K). To explore possible nonlinear behavior, we vary properties of the star such as the hyperon superfluid transition temperature, the strength of the boundary layer viscosity, and the fraction of the star that cools via direct URCA reactions. The evolution of the star is dynamic and initially dominated by fast neutrino cooling. Nonlinear effects become important when the r-mode amplitude grows above its first parametric instability threshold. The balance between neutrino cooling and viscous heating plays an important role in the evolution. Depending on the initial r-mode amplitude, and on the strength of the viscosity and of the cooling this balance can occur at different temperatures. If thermal equilibrium occurs on the r-mode stability curve, where gravitational driving equals viscous damping, the evolution may be adequately described by a one-mode model. Otherwise, nonlinear effects are important and lead to various more complicated scenarios. Once thermal balance occurs, the star spins down oscillating between thermal equilibrium states until the instability is no longer active. The average evolution of the mode amplitudes can be approximated by quasistationary states that are determined algebraically. For lower viscosity we observe runaway behavior in which the r-mode amplitude passes several

  16. Spin-Down Mechanisms in Neutron Stars with ``Anomalous'' Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rogers, Adam; Safi-Harb, Samar

    2015-08-01

    Energy losses from isolated neutron stars are attributed to a number of factors, the most common assumption being the emission of electromagnetic radiation from a rotating point-like magnetic dipole in vacuum. This energy loss mechanism predicts a braking index n = 3, which is not observed in highly magnetized neutron stars. Despite this fact, the assumptions of a dipole field and rapid early rotation are often assumed a priori. This typically causes a discrepancy in the characteristic age of these objects and the age of their associated Supernova Remnants (SNRs). In this work we consider neutron stars with ``anomalous'' magnetic fields - namely magnetars, high-B radio pulsars, and the Central Compact Objects (proposed to be `anti-magnetars’) that are securely associated with SNRs. Without making any assumptions about the initial spin periods of these objects and by constraining the SNR ages to match their associated pulsar ages, we compare the predictions of distinct energy loss mechanisms, such as field decay and the emission of relativistic winds using all observed data on the braking indices. This study has important implications on the proposed emission models for these exotic objects and helps in resolving the PSR-SNR age discrepancy.

  17. CONSTRAINING THE SPIN-DOWN OF THE NEARBY ISOLATED NEUTRON STAR RX J0806.4-4123, AND IMPLICATIONS FOR THE POPULATION OF NEARBY NEUTRON STARS

    SciTech Connect

    Kaplan, D. L.; Van Kerkwijk, M. H. E-mail: mhvk@astro.utoronto.c

    2009-11-01

    The nearby isolated neutron stars (INSs) are a group of seven relatively slowly rotating neutron stars that show thermal X-ray spectra, most with broad absorption features. They are interesting both because they may allow one to determine fundamental neutron-star properties by modeling their spectra, and because they appear to be a large fraction of the overall neutron-star population. Here, we describe a series of XMM -Newton observations of the nearby INS RX J0806.4-4123, taken as part of larger program of timing studies. From these, we limit the spin-down rate to nu-dot=(-4.3+-2.3)x10{sub -16}Hz s{sup -1}. This constrains the dipole magnetic field to be <3.7 x 10{sup 13} G at 2sigma, significantly less than the field of approx10{sup 14} G implied by simple models for the X-ray absorption found at 0.45 keV. We confirm that the spectrum is thermal and stable (to within a few percent), but find that the 0.45 keV absorption feature is broader and more complex than previously thought. Considering the population of INSs, we find that magnetic field decay from an initial field of approx<3 x 10{sup 14} G accounts most naturally for their timing and spectral properties, both qualitatively and in the context of the models for field decay of Pons and collaborators.

  18. Spin evolution of accreting neutron stars: Nonlinear development of the r-mode instability

    SciTech Connect

    Bondarescu, Ruxandra; Teukolsky, Saul A.; Wasserman, Ira

    2007-09-15

    The nonlinear saturation of the r-mode instability and its effects on the spin evolution of low mass x-ray binaries (LMXBs) are modeled using the triplet of modes at the lowest parametric instability threshold. We solve numerically the coupled equations for the three modes in conjunction with the spin and temperature evolution equations. We observe that very quickly the mode amplitudes settle into quasistationary states that change slowly as the temperature and spin of the star evolve. Once these states are reached, the mode amplitudes can be found algebraically and the system of equations is reduced from eight to two equations: spin and temperature evolution. The evolution of the neutron star angular velocity and temperature follow easily calculated trajectories along these sequences of quasistationary states. The outcome depends on whether or not the star will reach thermal equilibrium, where the viscous heating by the three modes is equal to the neutrino cooling (H=C curve). If, when the r-mode becomes unstable, the star spins at a frequency below the maximum of the H=C curve, then it will reach a state of thermal equilibrium. It can then either (1) undergo a cyclic evolution with a small cycle size with a frequency change of at most 10% (2) evolve toward a full equilibrium state in which the accretion torque balances the gravitational radiation emission, or (3) enter a thermogravitational runaway on a very long time scale of {approx_equal}10{sup 6} years. If the star does not reach a state of thermal equilibrium, then a faster thermal runaway (time scale of {approx_equal}100 years) occurs and the r-mode amplitude increases above the second parametric instability threshold. Following this evolution requires more inertial modes to be included. The sources of damping considered are shear viscosity, hyperon bulk viscosity, and viscosity within the core-crust boundary layer. We vary proprieties of the star such as the hyperon superfluid transition temperature T

  19. Spin evolution of accreting neutron stars: Nonlinear development of the r-mode instability

    NASA Astrophysics Data System (ADS)

    Bondarescu, Ruxandra; Teukolsky, Saul A.; Wasserman, Ira

    2007-09-01

    The nonlinear saturation of the r-mode instability and its effects on the spin evolution of low mass x-ray binaries (LMXBs) are modeled using the triplet of modes at the lowest parametric instability threshold. We solve numerically the coupled equations for the three modes in conjunction with the spin and temperature evolution equations. We observe that very quickly the mode amplitudes settle into quasistationary states that change slowly as the temperature and spin of the star evolve. Once these states are reached, the mode amplitudes can be found algebraically and the system of equations is reduced from eight to two equations: spin and temperature evolution. The evolution of the neutron star angular velocity and temperature follow easily calculated trajectories along these sequences of quasistationary states. The outcome depends on whether or not the star will reach thermal equilibrium, where the viscous heating by the three modes is equal to the neutrino cooling (H=C curve). If, when the r-mode becomes unstable, the star spins at a frequency below the maximum of the H=C curve, then it will reach a state of thermal equilibrium. It can then either (1) undergo a cyclic evolution with a small cycle size with a frequency change of at most 10%, (2) evolve toward a full equilibrium state in which the accretion torque balances the gravitational radiation emission, or (3) enter a thermogravitational runaway on a very long time scale of ≈106years. If the star does not reach a state of thermal equilibrium, then a faster thermal runaway (time scale of ≈100years) occurs and the r-mode amplitude increases above the second parametric instability threshold. Following this evolution requires more inertial modes to be included. The sources of damping considered are shear viscosity, hyperon bulk viscosity, and viscosity within the core-crust boundary layer. We vary proprieties of the star such as the hyperon superfluid transition temperature Tc, the fraction of the star that

  20. Neutron Star Phenomena

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin

    1998-01-01

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

  1. Long-term evolution of the neutron-star spin period of SXP 1062

    NASA Astrophysics Data System (ADS)

    Sturm, R.; Haberl, F.; Oskinova, L. M.; Schurch, M. P. E.; Hénault-Brunet, V.; Gallagher, J. S.; Udalski, A.

    2013-08-01

    Context. The Be/X-ray binary SXP 1062 is of especial interest owing to the large spin period of the neutron star, its large spin-down rate, and the association with a supernova remnant constraining its age. This makes the source an important probe for accretion physics. Aims: To investigate the long-term evolution of the spin period and associated spectral variations, we performed an XMM-Newton target-of-opportunity observation of SXP 1062 during X-ray outburst. Methods: Spectral and timing analysis of the XMM-Newton data was compared with previous studies, as well as complementary Swift/XRT monitoring and optical spectroscopy with the SALT telescope were obtained. Results: The spin period was measured to be Ps = (1071.01 ± 0.16) s on 2012 Oct. 14. The X-ray spectrum is similar to that of previous observations. No convincing cyclotron absorption features, which could be indicative for a high magnetic field strength, are found. The high-resolution RGS spectra indicate the presence of emission lines, which may not completely be accounted for by the SNR emission. The comparison of multi-epoch optical spectra suggest an increasing size or density of the decretion disc around the Be star. Conclusions: SXP 1062 showed a net spin-down with an average of Ṗs = (2.27 ± 0.44) s yr-1 over a baseline of 915 days. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA and on observations made with the Southern African Large Telescope (SALT).The reduced SALT spectra is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/556/A139

  2. Hidden Markov model tracking of continuous gravitational waves from a neutron star with wandering spin

    NASA Astrophysics Data System (ADS)

    Suvorova, S.; Sun, L.; Melatos, A.; Moran, W.; Evans, R. J.

    2016-06-01

    Gravitational wave searches for continuous-wave signals from neutron stars are especially challenging when the star's spin frequency is unknown a priori from electromagnetic observations and wanders stochastically under the action of internal (e.g., superfluid or magnetospheric) or external (e.g., accretion) torques. It is shown that frequency tracking by hidden Markov model (HMM) methods can be combined with existing maximum likelihood coherent matched filters like the F -statistic to surmount some of the challenges raised by spin wandering. Specifically, it is found that, for an isolated, biaxial rotor whose spin frequency walks randomly, HMM tracking of the F -statistic output from coherent segments with duration Tdrift=10 d over a total observation time of Tobs=1 yr can detect signals with wave strains h0>2 ×10-26 at a noise level characteristic of the Advanced Laser Interferometer Gravitational Wave Observatory (Advanced LIGO). For a biaxial rotor with randomly walking spin in a binary orbit, whose orbital period and semimajor axis are known approximately from electromagnetic observations, HMM tracking of the Bessel-weighted F -statistic output can detect signals with h0>8 ×10-26. An efficient, recursive, HMM solver based on the Viterbi algorithm is demonstrated, which requires ˜103 CPU hours for a typical, broadband (0.5-kHz) search for the low-mass x-ray binary Scorpius X-1, including generation of the relevant F -statistic input. In a "realistic" observational scenario, Viterbi tracking successfully detects 41 out of 50 synthetic signals without spin wandering in stage I of the Scorpius X-1 Mock Data Challenge convened by the LIGO Scientific Collaboration down to a wave strain of h0=1.1 ×10-25, recovering the frequency with a root-mean-square accuracy of ≤4.3 ×10-3 Hz .

  3. Neutron Stars

    NASA Astrophysics Data System (ADS)

    van den Heuvel, Ed

    Radio pulsars are unique laboratories for a wide range of physics and astrophysics. Understanding how they are created, how they evolve and where we find them in the Galaxy, with or without binary companions, is highly constraining of theories of stellar and binary evolution. Pulsars' relationship with a recently discovered variety of apparently different classes of neutron stars is an interesting modern astrophysical puzzle which we consider in Part I of this review. Radio pulsars are also famous for allowing us to probe the laws of nature at a fundamental level. They act as precise cosmic clocks and, when in a binary system with a companion star, provide indispensable venues for precision tests of gravity. The different applications of radio pulsars for fundamental physics will be discussed in Part II. We finish by making mention of the newly discovered class of astrophysical objects, the Fast Radio Bursts, which may or may not be related to radio pulsars or neutron stars, but which were discovered in observations of the latter.

  4. Role of nuclear spin-orbit coupling on the constitution of the outer crust of a nonaccreting neutron star

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    The role of the nuclear spin-orbit coupling on the equilibrium composition and on the equation of state of the outer crust of a nonaccreting neutron star is studied by employing a series of three different nuclear mass models based on the self-consistent Hartree-Fock-Bogoliubov method.

  5. Black hole from merging binary neutron stars: How fast can it spin?

    NASA Astrophysics Data System (ADS)

    Kastaun, Wolfgang; Galeazzi, Filippo; Alic, Daniela; Rezzolla, Luciano; Font, José A.

    2013-07-01

    The merger of two neutron stars will in general lead to the formation of a torus surrounding a black hole whose rotational energy can be tapped to potentially power a short gamma-ray burst. We have studied the merger of equal-mass binaries with spins aligned with the orbital angular momentum to determine the maximum spin the black hole can reach. Our initial data consists of irrotational binaries to which we add various amounts of rotation to increase the total angular momentum. Although the initial data violates the constraint equations, the use of the constraint-damping conformal and covariant Z4 formulation yields evolutions with violations smaller than those with irrotational initial data and standard formulations. Interestingly, we find that a limit of J/M2≃0.89 exists for the dimensionless spin and that any additional angular momentum given to the binary ends up in the torus rather than in the black hole, thus providing another nontrivial example supporting the cosmic censorship hypothesis.

  6. Planets Around Neutron Stars

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  7. SXP 1062, a young Be X-ray binary pulsar with long spin period. Implications for the neutron star birth spin

    NASA Astrophysics Data System (ADS)

    Haberl, F.; Sturm, R.; Filipović, M. D.; Pietsch, W.; Crawford, E. J.

    2012-01-01

    Context. The Small Magellanic Cloud (SMC) is ideally suited to investigating the recent star formation history from X-ray source population studies. It harbours a large number of Be/X-ray binaries (Be stars with an accreting neutron star as companion), and the supernova remnants can be easily resolved with imaging X-ray instruments. Aims: We search for new supernova remnants in the SMC and in particular for composite remnants with a central X-ray source. Methods: We study the morphology of newly found candidate supernova remnants using radio, optical and X-ray images and investigate their X-ray spectra. Results: Here we report on the discovery of the new supernova remnant around the recently discovered Be/X-ray binary pulsar CXO J012745.97-733256.5 = SXP 1062 in radio and X-ray images. The Be/X-ray binary system is found near the centre of the supernova remnant, which is located at the outer edge of the eastern wing of the SMC. The remnant is oxygen-rich, indicating that it developed from a type Ib event. From XMM-Newton observations we find that the neutron star with a spin period of 1062 s (the second longest known in the SMC) shows a very high average spin-down rate of 0.26 s per day over the observing period of 18 days. Conclusions: From the currently accepted models, our estimated age of around 10 000-25 000 years for the supernova remnant is not long enough to spin down the neutron star from a few 10 ms to its current value. Assuming an upper limit of 25 000 years for the age of the neutron star and the extreme case that the neutron star was spun down by the accretion torque that we have measured during the XMM-Newton observations since its birth, a lower limit of 0.5 s for the birth spin period is inferred. For more realistic, smaller long-term average accretion torques our results suggest that the neutron star was born with a correspondingly longer spin period. This implies that neutron stars in Be/X-ray binaries with long spin periods can be much younger

  8. Banks of templates for directed searches of gravitational waves from spinning neutron stars

    SciTech Connect

    Pisarski, Andrzej; Jaranowski, Piotr; Pietka, Maciej

    2011-02-15

    We construct efficient banks of templates suitable for directed searches of almost monochromatic gravitational waves originating from spinning neutron stars in our Galaxy in data being collected by currently operating interferometric detectors. We thus assume that the position of the gravitational-wave source in the sky is known, but we do not assume that the wave's frequency and its derivatives are a priori known. In the construction we employ a simplified model of the signal with constant amplitude and phase which is a polynomial function of time. All our template banks enable usage of the fast Fourier transform algorithm in the computation of the maximum-likelihood F-statistic for nodes of the grids defining the bank. We study and employ the dependence of the grid's construction on the choice of the position of the observational interval with respect to the origin of time axis. We also study the usage of the fast Fourier transform algorithms with nonstandard frequency resolutions achieved by zero padding or folding the data. In the case of the gravitational-wave signal with one spin-down parameter included we have found grids with covering thicknesses which are only 0.1-16% larger than the thickness of the optimal 2-dimensional hexagonal covering.

  9. Quark deconfinement in Neutron stars

    NASA Astrophysics Data System (ADS)

    Staff, Jan E.; Ouyed, R.; Jaikumar, P.

    2006-06-01

    We study the role of spin-down of isolated neutron stars in driving quark deconfinement in their high density core. Assuming spin-down to be solely due to magnetic braking, we obtain typical timescales to quark deconfinement for neutron stars that are born with Keplerian frequencies. Employing different equations of state (EOS), we determine the minimum and maximum neutron star masses that will allow for deconfinement via spin-down only. We find that the time to reach deconfinement is strongly dependent on the magnetic field and that this time is least for EOS that support the largest minimum mass at zero spin, unless rotational effects on stellar structure are large. For a fiducial critical density of five times nuclear saturation density for the transition to the quark phase, we find that neutron stars lighter than 1.5 solar masses cannot reach a deconfined phase. Depending on the EOS, neutron stars of more than 1.5 solar masses can enter a quark phase only if they are spinning faster than about 3 milliseconds as observed now, whereas larger spin periods imply that they are either already quark stars or will never become one.

  10. ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS

    SciTech Connect

    Lamb, Frederick K.; Boutloukos, Stratos; Van Wassenhove, Sandor; Chamberlain, Robert T.; Lo, Ka Ho; Coleman Miller, M.

    2009-11-01

    We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this 'nearly aligned moving spot model' may also explain the intermittent accretion-powered pulsations that have been detected in three weakly magnetic accreting neutron stars. We show that movement of the emitting area from very close to the spin axis to approx10 deg. away can increase the fractional rms amplitude from approx<0.5%, which is usually undetectable with current instruments, to a few percent, which is easily detectable. The second harmonic of the spin frequency usually would not be detected, in agreement with observations. The model produces intermittently detectable oscillations for a range of emitting area sizes and beaming patterns, stellar masses and radii, and viewing directions. Intermittent oscillations are more likely in stars that are more compact. In addition to explaining the sudden appearance of accretion-powered millisecond oscillations in some neutron stars with millisecond spin periods, the model explains why accretion-powered millisecond oscillations are relatively rare and predicts that the persistent accretion-powered millisecond oscillations of other stars may become undetectable for brief intervals. It suggests why millisecond oscillations are frequently detected during the X-ray bursts of some neutron stars but not others and suggests mechanisms that could explain the occasional temporal association of intermittent accretion-powered oscillations with thermonuclear X-ray bursts.

  11. Neutron skins and neutron stars

    SciTech Connect

    Piekarewicz, J.

    2013-11-07

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

  12. Dibaryons in neutron stars

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  13. Probing the neutron star spin evolution in the young Small Magellanic Cloud Be/X-ray binary SXP 1062

    NASA Astrophysics Data System (ADS)

    Popov, S. B.; Turolla, R.

    2012-03-01

    The newly discovered Be/X-ray binary in the Small Magellanic Cloud, SXP 1062, provides the first example of a robust association with a supernova remnant (SNR). The short age estimated for the SNR qualifies SXP 1062 as the youngest known source in its class, ?. As such, it allows us to test current models of magnetorotational evolution of neutron stars in a still unexplored regime. Here we discuss possible evolutionary scenarios for SXP 1062 in an attempt to reconcile its long spin period, ?, and short age. Although several options can be considered, like an anomalously long initial period or the presence of a fossil disc, our results indicate that SXP 1062 may host a neutron star born with a large initial magnetic field, typically in excess of ˜ 1014 G, which then decayed to ˜ 1013 G.

  14. The Fate of Merging Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-08-01

    A rapidly spinning, highly magnetized neutron star is one possible outcome when two smaller neutron stars merge. [Casey Reed/Penn State University]When two neutron stars collide, the new object that they make can reveal information about the interior physics of neutron stars. New theoretical work explores what we should be seeing, and what it can teach us.Neutron Star or Black Hole?So far, the only systems from which weve detected gravitational waves are merging black holes. But other compact-object binaries exist and are expected to merge on observable timescales in particular, binary neutron stars. When two neutron stars merge, the resulting object falls into one of three categories:a stable neutron star,a black hole, ora supramassive neutron star, a large neutron star thats supported by its rotation but will eventually collapse to a black hole after it loses angular momentum.Histograms of the initial (left) and final (right) distributions of objects in the authors simulations, for five different equations of state. Most cases resulted primarily in the formation of neutron stars (NSs) or supramassive neutron stars (sNSs), not black holes (BHs). [Piro et al. 2017]Whether a binary-neutron-star merger results in another neutron star, a black hole, or a supramassive neutron star depends on the final mass of the remnant and what the correct equation of state is that describes the interiors of neutron stars a longstanding astrophysical puzzle.In a recent study, a team of scientists led by Anthony Piro (Carnegie Observatories) estimated which of these outcomes we should expect for mergers of binary neutron stars. The teams results along with future observations of binary neutron stars may help us to eventually pin down the equation of state for neutron stars.Merger OutcomesPiro and collaborators used relativistic calculations of spinning and non-spinning neutron stars to estimate the mass range that neutron stars would have for several different realistic equations of

  15. Binary neutron stars with generic spin, eccentricity, mass ratio, and compactness: Quasi-equilibrium sequences and first evolutions

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Information about the last stages of a binary neutron star inspiral and the final merger can be extracted from quasiequilibrium configurations and dynamical evolutions. In this article, we construct quasiequilibrium configurations for different spins, eccentricities, mass ratios, compactnesses, and equations of state. For this purpose we employ the sgrid code, which allows us to construct such data in previously inaccessible regions of the parameter space. In particular, we consider spinning neutron stars in isolation and in binary systems; we incorporate new methods to produce highly eccentric and eccentricity-reduced data; we present the possibility of computing data for significantly unequal-mass binaries with mass ratios q ≃2 ; and we create equal-mass binaries with individual compactness up to C ≃0.23 . As a proof of principle, we explore the dynamical evolution of three new configurations. First, we simulate a q =2.06 mass ratio which is the highest mass ratio for a binary neutron star evolved in numerical relativity to date. We find that mass transfer from the companion star sets in a few revolutions before merger and a rest mass of ˜10-2M⊙ is transferred between the two stars. This amount of mass accretion corresponds to ˜1051 ergs of accretion energy. This configuration also ejects a large amount of material during merger (˜7.6 ×1 0-2M⊙), imparting a substantial kick to the remnant neutron star. Second, we simulate the first merger of a precessing binary neutron star. We present the dominant modes of the gravitational waves for the precessing simulation, where a clear imprint of the precession is visible in the (2,1) mode. Finally, we quantify the effect of an eccentricity-reduction procedure on the gravitational waveform. The procedure improves the waveform quality and should be employed in future precision studies. However, one also needs to reduce other errors in the waveforms, notably truncation errors, in order for the improvement due to

  16. Gravitational Waves from Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kokkotas, Konstantinos

    2016-03-01

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

  17. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Supid

    2007-01-01

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

  18. Old and new neutron stars

    SciTech Connect

    Ruderman, M.

    1984-09-01

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

  19. Introduction to neutron stars

    SciTech Connect

    Lattimer, James M.

    2015-02-24

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

  20. Rapidly rotating neutron star progenitors

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  1. Superfluidity in the Core of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Page, Dany

    2013-04-01

    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.

  2. Thermally driven neutron star glitches

    SciTech Connect

    Link, B. |; Epstein, R.I.

    1996-02-01

    We examine the thermal and dynamical response of a neutron star to a sudden perturbation of the inner crust temperature. During the star{close_quote}s evolution, starquakes and other processes may deposit {approx_gt}10{sup 42} ergs, causing significant internal heating and increased frictional coupling between the crust and the more rapidly rotating neutron superfluid the star is expected to contain. Through numerical simulation we study the propagation of the thermal wave created by the energy deposition, the induced motion of the interior superfluid, and the resulting spin evolution of the crust. We find that energy depositions of {approximately}10{sup 40} ergs produce gradual spin-ups above the timing noise level, while larger energy depositions produce sudden spin jumps resembling pulsar glitches. For a star with a temperature in the observed range of the Vela pulsar, an energy deposition of {approximately}10{sup 42} ergs produces a large spin-up taking place over minutes, similar to the Vela {open_quote}{open_quote}Christmas{close_quote}{close_quote} glitch. Comparable energy deposition in a younger and hotter {open_quote}{open_quote}Crab-like{close_quote}{close_quote} star produces a smaller spin-up taking place over {approximately}1{sup d}, similar to that seen during the partially time-resolved Crab glitch of 1989. {copyright} {ital 1996 The American Astronomical Society.}

  3. The Guitar nebula - A bow shock from a slow-spin, high-velocity neutron star

    NASA Technical Reports Server (NTRS)

    Cordes, James M.; Romani, Roger W.; Lundgren, Scott C.

    1993-01-01

    The discovery is reported of a prominent nebula produced by the motion of a high-velocity pulsar, PSR 2224 + 65, through partially neutral gas. The pulsar's transverse speed of over about 800 km/s makes it arguably the fastest known star in the Galaxy and guarantees that it will ultimately escape the Galactic potential well. A deep H-alpha image reveals a bright head and a giant limb-brightened 'body' whose variable width suggests that the ambient interstellar gas has density variations on length scales less than 0.1 pc. Thermalization of shock energy occurs at a rate of about 0.01 times the pulsar's spindown loss rate. These observations provide some insights into the likelihood of finding shocks around other pulsars and the use of nebulae to find high-velocity neutron stars either not acting as pulsars or with their radiation beamed away from the earth.

  4. The Guitar nebula - A bow shock from a slow-spin, high-velocity neutron star

    NASA Astrophysics Data System (ADS)

    Cordes, James M.; Romani, Roger W.; Lundgren, Scott C.

    1993-03-01

    The discovery is reported of a prominent nebula produced by the motion of a high-velocity pulsar, PSR 2224 + 65, through partially neutral gas. The pulsar's transverse speed of over about 800 km/s makes it arguably the fastest known star in the Galaxy and guarantees that it will ultimately escape the Galactic potential well. A deep H-alpha image reveals a bright head and a giant limb-brightened 'body' whose variable width suggests that the ambient interstellar gas has density variations on length scales less than 0.1 pc. Thermalization of shock energy occurs at a rate of about 0.01 times the pulsar's spindown loss rate. These observations provide some insights into the likelihood of finding shocks around other pulsars and the use of nebulae to find high-velocity neutron stars either not acting as pulsars or with their radiation beamed away from the earth.

  5. Orbital Decay of a Binary System Consisting of Spin-Down Neutron Stars

    NASA Astrophysics Data System (ADS)

    Cheng, K. S.; Harko, T.; Yuan, Y. F.; Tang, P. S.

    2004-12-01

    {W}e consider the gravitational radiation from two time variable mass stars, orbiting around each other under the influence of gravity. The total rates of the variation of the energy, angular momentum, semimajor axis, eccentricity and orbital period are obtained. The results could be important for the understanding of general relativistic effects in the case of the variation of the gravitational mass due to spinning down of the compact stars, which sensitively depends on the equations of state. The cases of the binary systems PSR 1913+16 and PSR 1534+12 are analyzed in detail, and, for different equations of state of nuclear matter, the corrections to the orbital decay due to gravitational radiation and to the spinning down of the pulsars are calculated. The results show that a future significant improvement in the observational techniques could lead to the observation of the specific general relativistic effect of mass variation of pulsars due to spinning down, via the study of orbital decay, even in slowly rotating binary systems.

  6. Neutron Stars are Follicly Challenged

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Black holes satisfy certain no-hair relations through which all multipole moments of the spacetime can be specified in terms of just a few quantities, like their mass and spin angular momentum. I will describe how neutron stars and quark stars also satisfy similar no-hair relations that are approximately independent of their equation of state. I will show how these results hold for both slowly- and rapidly-rotating stars in full General Relativity, provided the stars are uniformly rotating and uncharged. I will then explain why such relations may be relevant to observations of the pulse profile of hot spots on rotating neutron stars with NICER, as well as how they could be used to test General Relativity with binary pulsar and gravitational wave observations. I acknowledge support from the NSF CAREER Award PHY-1250636.

  7. Hyperons in neutron stars

    SciTech Connect

    Glendenning, N.K.

    1986-04-01

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

  8. Neutron stars - General review

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  9. Probing the accretion disc structure by the twin kHz QPOs and spins of neutron stars in LMXBs

    NASA Astrophysics Data System (ADS)

    Wang, D. H.; Zhang, C. M.; Lei, Y. J.; Chen, L.; Qu, J. L.; Zhi, Q. J.

    2017-04-01

    We analyse the relation between the emission radii of twin kilohertz quasi-periodic oscillations (kHz QPOs) and the co-rotation radii of the 12 neutron star low-mass X-ray binaries (NS-LMXBs), which are simultaneously detected with the twin kHz QPOs and NS spins. We find that the average co-rotation radius of these sources is ∼ 32 km, and all the emission positions of twin kHz QPOs lie inside the co-rotation radii, indicating that the twin kHz QPOs are formed in the spin-up process. It is noticed that the upper frequency of twin kHz QPOs is higher than NS spin frequency by ≥10 per cent, which may account for a critical velocity difference between the Keplerian motion of accretion matter and NS spin that is corresponding to the production of twin kHz QPOs. In addition, we also find that ∼83 per cent of twin kHz QPOs cluster around the radius range of 15-20 km, which may be affected by the hard surface or the local strong magnetic field of the NS. As a special case, SAX J1808.4-3658 shows the larger emission radii of twin kHz QPOs of r ∼ 21-24 km, which may be due to its low accretion rate or small measured NS mass (<1.4 M⊙).

  10. Directed searches for continuous gravitational waves from spinning neutron stars in binary systems

    NASA Astrophysics Data System (ADS)

    Meadors, Grant David

    2014-09-01

    Gravitational wave detectors such as the Laser Interferometer Gravitational-wave Observatory (LIGO) seek to observe ripples in space predicted by General Relativity. Black holes, neutron stars, supernovae, the Big Bang and other sources can radiate gravitational waves. Original contributions to the LIGO effort are presented in this thesis: feedforward filtering, directed binary neutron star searches for continuous waves, and scientific outreach and education, as well as advances in quantum optical squeezing. Feedforward filtering removes extraneous noise from servo-controlled instruments. Filtering of the last science run, S6, improves LIGO's astrophysical range (+4.14% H1, +3.60% L1: +12% volume) after subtracting noise from auxiliary length control channels. This thesis shows how filtering enhances the scientific sensitivity of LIGO's data set during and after S6. Techniques for non-stationarity and verifying calibration and integrity may apply to Advanced LIGO. Squeezing is planned for future interferometers to exceed the standard quantum limit on noise from electromagnetic vacuum fluctuations; this thesis discusses the integration of a prototype squeezer at LIGO Hanford Observatory and impact on astrophysical sensitivity. Continuous gravitational waves may be emitted by neutron stars in low-mass X-ray binary systems such as Scorpius X-1. The TwoSpect directed binary search is designed to detect these waves. TwoSpect is the most sensitive of 4 methods in simulated data, projecting an upper limit of 4.23e-25 in strain, given a year-long data set at an Advanced LIGO design sensitivity of 4e-24 Hz. (-1/2). TwoSpect is also used on real S6 data to set 95% confidence upper limits (40 Hz to 2040 Hz) on strain from Scorpius X-1. A millisecond pulsar, X-ray transient J1751-305, is similarly considered. Search enhancements for Advanced LIGO are proposed. Advanced LIGO and fellow interferometers should detect gravitational waves in the coming decade. Methods in these

  11. Search of S3 LIGO data for gravitational wave signals from spinning black hole and neutron star binary inspirals

    NASA Astrophysics Data System (ADS)

    Abbott, B.; Abbott, R.; Adhikari, R.; Agresti, J.; Ajith, P.; Allen, B.; Amin, R.; Anderson, S. B.; Anderson, W. G.; Arain, M.; Araya, M.; Armandula, H.; Ashley, M.; Aston, S.; Aufmuth, P.; Aulbert, C.; Babak, S.; Ballmer, S.; Bantilan, H.; Barish, B. C.; Barker, C.; Barker, D.; Barr, B.; Barriga, P.; Barton, M. A.; Bayer, K.; Betzwieser, J.; Beyersdorf, P. T.; Bhawal, B.; Bilenko, I. A.; Billingsley, G.; Biswas, R.; Black, E.; Blackburn, K.; Blackburn, L.; Blair, D.; Bland, B.; Bogenstahl, J.; Bogue, L.; Bork, R.; Boschi, V.; Bose, S.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Brinkmann, M.; Brooks, A.; Brown, D. A.; Bullington, A.; Bunkowski, A.; Buonanno, A.; Burmeister, O.; Busby, D.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Camp, J. B.; Cannizzo, J.; Cannon, K.; Cantley, C. A.; Cao, J.; Cardenas, L.; Castaldi, G.; Cepeda, C.; Chalkley, E.; Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Chiadini, F.; Christensen, N.; Clark, J.; Cochrane, P.; Cokelaer, T.; Coldwell, R.; Conte, R.; Cook, D.; Corbitt, T.; Coyne, D.; Creighton, J. D. E.; Croce, R. P.; Crooks, D. R. M.; Cruise, A. M.; Cumming, A.; Dalrymple, J.; D'Ambrosio, E.; Danzmann, K.; Davies, G.; Debra, D.; Degallaix, J.; Degree, M.; Demma, T.; Dergachev, V.; Desai, S.; Desalvo, R.; Dhurandhar, S.; Díaz, M.; Dickson, J.; di Credico, A.; Diederichs, G.; Dietz, A.; Doomes, E. E.; Drever, R. W. P.; Dumas, J.-C.; Dupuis, R. J.; Dwyer, J. G.; Ehrens, P.; Espinoza, E.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Fan, Y.; Fazi, D.; Fejer, M. M.; Finn, L. S.; Fiumara, V.; Fotopoulos, N.; Franzen, A.; Franzen, K. Y.; Freise, A.; Frey, R.; Fricke, T.; Fritschel, P.; Frolov, V. V.; Fyffe, M.; Galdi, V.; Garofoli, J.; Gholami, I.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Goda, K.; Goetz, E.; Goggin, L. M.; González, G.; Gossler, S.; Grant, A.; Gras, S.; Gray, C.; Gray, M.; Greenhalgh, J.; Gretarsson, A. M.; Grosso, R.; Grote, H.; Grunewald, S.; Guenther, M.; Gustafson, R.; Hage, B.; Hammer, D.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G.; Harstad, E.; Hayler, T.; Heefner, J.; Heng, I. S.; Heptonstall, A.; Heurs, M.; Hewitson, M.; Hild, S.; Hirose, E.; Hoak, D.; Hosken, D.; Hough, J.; Hoyland, D.; Huttner, S. H.; Ingram, D.; Innerhofer, E.; Ito, M.; Itoh, Y.; Ivanov, A.; Johnson, B.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kasprzyk, D.; Katsavounidis, E.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Keppel, D. G.; Khalili, F. Ya.; Kim, C.; King, P.; Kissel, J. S.; Klimenko, S.; Kokeyama, K.; Kondrashov, V.; Kopparapu, R. K.; Kozak, D.; Krishnan, B.; Kwee, P.; Lam, P. K.; Landry, M.; Lantz, B.; Lazzarini, A.; Lei, M.; Leiner, J.; Leonhardt, V.; Leonor, I.; Libbrecht, K.; Lindquist, P.; Lockerbie, N. A.; Longo, M.; Lormand, M.; Lubiński, M.; Lück, H.; Machenschalk, B.; Macinnis, M.; Mageswaran, M.; Mailand, K.; Malec, M.; Mandic, V.; Marano, S.; Márka, S.; Markowitz, J.; Maros, E.; Martin, I.; Marx, J. N.; Mason, K.; Matone, L.; Matta, V.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McHugh, M.; McKenzie, K.; McWilliams, S.; Meier, T.; Melissinos, A.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messaritaki, E.; Messenger, C. J.; Meyers, D.; Mikhailov, E.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Mohanty, S.; Moreno, G.; Mossavi, K.; Mowlowry, C.; Moylan, A.; Mudge, D.; Mueller, G.; Mukherjee, S.; Müller-Ebhardt, H.; Munch, J.; Murray, P.; Myers, E.; Myers, J.; Nash, T.; Newton, G.; Nishizawa, A.; Numata, K.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pan, Y.; Papa, M. A.; Parameshwaraiah, V.; Patel, P.; Pedraza, M.; Penn, S.; Pierro, V.; Pinto, I. M.; Pitkin, M.; Pletsch, H.; Plissi, M. V.; Postiglione, F.; Prix, R.; Quetschke, V.; Raab, F.; Rabeling, D.; Radkins, H.; Rahkola, R.; Rainer, N.; Rakhmanov, M.; Ramsunder, M.; Ray-Majumder, S.; Re, V.; Rehbein, H.; Reid, S.; Reitze, D. H.; Ribichini, L.; Riesen, R.; Riles, K.; Rivera, B.; Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Rodriguez, A.; Rogan, A. M.; Rollins, J.; Romano, J. D.; Romie, J.; Route, R.; Rowan, S.; Rüdiger, A.; Ruet, L.; Russell, P.; Ryan, K.; Sakata, S.; Samidi, M.; Sancho de La Jordana, L.; Sandberg, V.; Sannibale, V.; Saraf, S.; Sarin, P.; Sathyaprakash, B. S.; Sato, S.; Saulson, P. R.; Savage, R.; Savov, P.; Schediwy, S.; Schilling, R.; Schnabel, R.; Schofield, R.; Schutz, B. F.; Schwinberg, P.; Scott, S. M.; Searle, A. C.; Sears, B.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Shawhan, P.; Shoemaker, D. H.; Sibley, A.; Sidles, J. A.; Siemens, X.; Sigg, D.; Sinha, S.; Sintes, A. M.; Slagmolen, B. J. J.; Slutsky, J.; Smith, J. R.; Smith, M. R.; Somiya, K.; Strain, K. A.; Strom, D. M.; Stuver, A.; Summerscales, T. Z.; Sun, K.-X.; Sung, M.; Sutton, P. J.; Takahashi, H.; Tanner, D. B.; Taylor, R.; Taylor, R.; Thacker, J.; Thorne, K. A.; Thorne, K. S.; Thüring, A.; Tokmakov, K. V.; Torres, C.; Torrie, C.; Traylor, G.; Trias, M.; Tyler, W.; Ugolini, D.; Urbanek, K.; Vahlbruch, H.; Vallisneri, M.; van den Broeck, C.; Varvella, M.; Vass, S.; Vecchio, A.; Veitch, J.; Veitch, P.; Villar, A.; Vorvick, C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Ward, H.; Ward, R.; Watts, K.; Weidner, A.; Weinert, M.; Weinstein, A.; Weiss, R.; Wen, S.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; Whiting, B. F.; Wilkinson, C.; Willems, P. A.; Williams, L.; Willke, B.; Wilmut, I.; Winkler, W.; Wipf, C. C.; Wise, S.; Wiseman, A. G.; Woan, G.; Woods, D.; Wooley, R.; Worden, J.; Wu, W.; Yakushin, I.; Yamamoto, H.; Yan, Z.; Yoshida, S.; Yunes, N.; Zanolin, M.; Zhang, J.; Zhang, L.; Zhao, C.; Zotov, N.; Zucker, M.; Zur Mühlen, H.; Zweizig, J.

    2008-08-01

    We report on the methods and results of the first dedicated search for gravitational waves emitted during the inspiral of compact binaries with spinning component bodies. We analyze 788 hours of data collected during the third science run (S3) of the LIGO detectors. We searched for binary systems using a detection template family specially designed to capture the effects of the spin-induced precession of the orbital plane. We present details of the techniques developed to enable this search for spin-modulated gravitational waves, highlighting the differences between this and other recent searches for binaries with nonspinning components. The template bank we employed was found to yield high matches with our spin-modulated target waveform for binaries with masses in the asymmetric range 1.0M⊙spin of the binary’s components to have a significant effect. We find that our search of S3 LIGO data has good sensitivity to binaries in the Milky Way and to a small fraction of binaries in M31 and M33 with masses in the range 1.0M⊙spinning components and Gaussian distribution of masses representing a prototypical neutron star black hole system with m1≃1.35M⊙ and m2≃5M⊙, we calculate the 90%-confidence upper limit on the rate of coalescence of these systems to be 15.9yr-1L10-1, where L10 is 1010 times the blue light luminosity of the Sun.

  12. Converting neutron stars into strange stars

    NASA Technical Reports Server (NTRS)

    Olinto, A. V.

    1991-01-01

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

  13. Extracting equation of state parameters from black hole-neutron star mergers: Aligned-spin black holes and a preliminary waveform model

    NASA Astrophysics Data System (ADS)

    Lackey, Benjamin D.; Kyutoku, Koutarou; Shibata, Masaru; Brady, Patrick R.; Friedman, John L.

    2014-02-01

    Information about the neutron-star equation of state is encoded in the waveform of a black hole-neutron star system through tidal interactions and the possible tidal disruption of the neutron star. During the inspiral this information depends on the tidal deformability Λ of the neutron star, and we find that the best-measured parameter during the merger and ringdown is consistent with Λ as well. We performed 134 simulations where we systematically varied the equation of state as well as the mass ratio, neutron star mass, and aligned spin of the black hole. Using these simulations we develop an analytic representation of the full inspiral-merger-ringdown waveform calibrated to these numerical waveforms; we use this analytic waveform and a Fisher matrix analysis to estimate the accuracy to which Λ can be measured with gravitational-wave detectors. We find that although the inspiral tidal signal is small, coherently combining this signal with the merger-ringdown matter effect improves the measurability of Λ by a factor of ˜3 over using just the merger-ringdown matter effect alone. However, incorporating correlations between all the waveform parameters then decreases the measurability of Λ by a factor of ˜3. The uncertainty in Λ increases with the mass ratio, but decreases as the black hole spin increases. Overall, a single Advanced LIGO detector can only marginally measure Λ for mass ratios Q =2-5, black hole spins JBH/MBH2=-0.5-0.75, and neutron star masses MNS=1.2M⊙-1.45M⊙ at an optimally oriented distance of 100 Mpc. For the proposed Einstein Telescope, however, the uncertainty in Λ is an order of magnitude smaller.

  14. Exploration of spin-down rate of neutron stars in high-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Dai, Hai-Lang; Liu, Xi-Wei; Li, Xiang-Dong

    2016-04-01

    We use the evolutionary population synthesis method to investigate the statistical properties of the wind-fed neutron-star (NS) compact (Porb < 10 d) high-mass X-ray binaries (HMXBs) in our Galaxy, based on different spin-down models. Model 1 assumes that the surrounding material is treated as forming a quasi-static atmosphere. Model 2 assumes that the characteristic velocity of matter and the typical Alfvén velocity of material in the magnetospheric boundary layer are comparable to the sound speed in the external medium. We find that the spin-down rate in the supersonic propeller phase in either model 1 or model 2 is too low to produce the observed number of compact HMXBs. Model 3 assumes that the infalling material is ejected with the corotation velocity at the magnetospheric radius when the magnetospheric radius is larger than the corotation radius. Model 4 uses simple integration of the magnetic torque over the magnetosphere. Both models 3 and 4 have a larger spin down rate than that given by model 1 or 2. We also find that models 3 and 4 can predict a reasonable number of observed wind-fed NS compact HMXBs. By comparing our calculated results with the observed particular distributions of wind-fed NS compact HMXBs in a Ps versus Porb diagram, we find that the subsonic propeller phase may not exist at all. However, the spin-down rates in models 3 and 4 both seem reasonable to produce the observed distribution of wind-fed NS compact HMXBs in the Ps versus Porb diagram. We cannot find which spin-down rate seems more reasonable from our calculations.

  15. The Neutron Star Zoo

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2014-01-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not

  16. Neutron Star Compared to Manhattan

    NASA Image and Video Library

    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...

  17. Cooling of neutron stars

    NASA Technical Reports Server (NTRS)

    Pethick, C. J.

    1992-01-01

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

  18. Cooling of neutron stars

    NASA Technical Reports Server (NTRS)

    Pethick, C. J.

    1992-01-01

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

  19. Matter accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

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

  20. TESTING MODELS OF MAGNETIC FIELD EVOLUTION OF NEUTRON STARS WITH THE STATISTICAL PROPERTIES OF THEIR SPIN EVOLUTIONS

    SciTech Connect

    Zhang Shuangnan; Xie Yi

    2012-10-01

    We test models for the evolution of neutron star (NS) magnetic fields (B). Our model for the evolution of the NS spin is taken from an analysis of pulsar timing noise presented by Hobbs et al.. We first test the standard model of a pulsar's magnetosphere in which B does not change with time and magnetic dipole radiation is assumed to dominate the pulsar's spin-down. We find that this model fails to predict both the magnitudes and signs of the second derivatives of the spin frequencies ({nu}-double dot). We then construct a phenomenological model of the evolution of B, which contains a long-term decay (LTD) modulated by short-term oscillations; a pulsar's spin is thus modified by its B-evolution. We find that an exponential LTD is not favored by the observed statistical properties of {nu}-double dot for young pulsars and fails to explain the fact that {nu}-double dot is negative for roughly half of the old pulsars. A simple power-law LTD can explain all the observed statistical properties of {nu}-double dot. Finally, we discuss some physical implications of our results to models of the B-decay of NSs and suggest reliable determination of the true ages of many young NSs is needed, in order to constrain further the physical mechanisms of their B-decay. Our model can be further tested with the measured evolutions of {nu}-dot and {nu}-double dot for an individual pulsar; the decay index, oscillation amplitude, and period can also be determined this way for the pulsar.

  1. Neutron Star Structure From Observations

    NASA Astrophysics Data System (ADS)

    Lattimer, James

    2006-10-01

    Neutron stars are laboratories for dense matter physics. Observations of neutron stars, in the form of radio pulsars, X-ray binaries, X-ray bursters, and thermally-emitting isolated stars, are rapidly accumulating. Especially interesting are the radio pulsars PSR J0751+1807, Terzan 5 I and Terzan 5 J (with suprisingly large measured masses of 2.1±0.2, 1.69±0.1 and 1.85±0.05 solar masses, respectively), the pulsar PSR J1748-2446ad with the most rapid spin rate of 716 Hz, and the radio pulsar binary PSR J0737-3039 for which a moment of inertia of one of the neutron stars might be measured within a few years. Extremely massive neutron stars are important because they set limits to the maximum mass and upper limits to the maximum density found in cold, static, objects, and might limit the appearance of exotic matter such as hyperons, Bose condensates or deconfined quarks in a star's interior. The spin rate sets an upper limit to the radius of a star of a given mass, and the moment of inertia, being roughly proportional to M R^2, is a sensitive measure of neutron star radius. While the maximum mass speaks to the relative stiffness of the high-density equation of state at several times nuclear matter density, the radius is a measure of the relative stiffness of the low-density equation of state in the vicinity of the nuclear saturation density. For the nearly pure neutron matter found in neutron stars, it is a direct measure of the density dependence of the nuclear symmetry energy. Other promising observational constraints might be obtained from neutron star seismology (which limits the relative crustal thickness) and Eddington limited fluxes observed from bursting sources, and from thermal emissions from cooling neutron stars. The latter have the potential of constraining R∞=R/√1-2GM/Rc^2 if the source's distance can be accurately assessed. The distances of two nearby isolated sources, RX J1856-3754 and Geminga, have been determined by parallax. However, there

  2. Banks of templates for all-sky narrow-band searches of gravitational waves from spinning neutron stars

    NASA Astrophysics Data System (ADS)

    Pisarski, Andrzej; Jaranowski, Piotr

    2015-07-01

    We construct efficient banks of templates suitable for all-sky narrow-band searches of almost monochromatic gravitational waves originating from spinning neutron stars in our Galaxy in data collected by interferometric detectors. We consider waves with one spindown parameter included, and we assume that both the position of the gravitational-wave source in the sky and the wave's frequency, together with spindown parameter, are unknown. In the construction we employ a simplified model of the signal with constant amplitude and phase which is a linear function of unknown parameters. Our template banks enable the usage of the fast Fourier transform algorithm in the computation of the maximum-likelihood {F}-statistic for nodes of the grids defining the bank, and fulfill an additional constraint needed to resample the data to barycentric time efficiently. All these template bank features were employed in the recent all-sky {F}-statistic-based search for continuous gravitational waves in Virgo VSR1 data (Aasi et al 2014 Class. Quantum Grav. 31 165014). Here we improve that template bank by constructing templates suitable for a larger range of search parameters and of smaller thicknesses for certain values of search parameters. One of our template banks has a thickness 12% smaller than that of the template bank used in the all-sky search of Virgo VSR1 data and only 4% larger than the thickness of the four-dimensional optimal lattice covering {A}4\\star .

  3. Quark Deconfinement in Rotating Neutron Stars

    NASA Astrophysics Data System (ADS)

    Mellinger, Richard; Weber, Fridolin; Spinella, William; Contrera, Gustavo; Orsaria, Milva

    2017-01-01

    In this paper, we use a three flavor non-local Nambu--Jona-Lasinio (NJL) model, an~improved effective model of Quantum Chromodynamics (QCD) at low energies, to investigate the existence of deconfined quarks in the cores of neutron stars. Particular emphasis is put on the possible existence of quark matter in the cores of rotating neutron stars (pulsars). In contrast to non-rotating neutron stars, whose particle compositions do not change with time (are frozen in), the type and structure of the matter in the cores of rotating neutron stars depends on the spin frequencies of these stars, which opens up a possible new window on the nature of matter deep in the cores of neutron stars. Our study shows that, depending on mass and rotational frequency, up to around 8% of the mass of a massive neutron star may be in the mixed quark-hadron phase, if the phase transition is treated as a Gibbs transition. We also find that the gravitational mass at which quark deconfinement occurs in rotating neutron stars varies quadratically with spin frequency, which can be fitted by a simple formula.

  4. Neutron star evolutionary sequences

    NASA Technical Reports Server (NTRS)

    Richardson, M. B.; Van Horn, H. M.; Ratcliff, K. F.; Malone, R. C.

    1982-01-01

    Detailed numerical calculations which are solutions of the full set of general relativistic equations describing the evolution of a spherical star are presented, for the case of the evolution of neutron stars that are cooling over the central temperatures range of 10 to the 10th to 10 to the 7th K. The effects of nucleon superfluidity in the inner crust and core are included, and models are constructed with and without a pion condensate at high densities. It is found that the localized neutrino cooling which dominates the early evolution of neutron stars is so rapid that heat transport within the star cannot keep pace, and temperature distribution is not isothermal. The residual contraction of the neutron star during the early cooling phase contributes little to the heat budget of the star, and most of the gravitational energy released raises the Fermi energy of the degenerate nucleons. It is concluded that since calculations with and without pion condensate are consistent with the upper limits of current observations, these are not sufficient in distinguishing between the various models of neutron star cooling.

  5. Discovery of a Neutron Star with Spin Frequency 530 Hz in A1744-361

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip; Strohmayer, Tod E.; Markwardt, Craig B.; Swank, Jean H.; Bhattacharyya, Sudip

    2005-01-01

    We report the detection with the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) of 530 Hz burst oscillations in a thermonuclear (Type I) burst from the transient X-ray source A1744-361. This is only the second burst ever observed from this source, and the first to be seen in any detail. Our results confirm that A1744-361 is a low mass X-ray binary (LMXB) system harboring a rapidly rotating neutron star. The oscillations are first detected along the rising edge of the burst, and show evidence for frequency evolution of a magnitude similar to that seen in other burst sources. The modulation amplitude and its increase with photon energy are also typical of burst oscillations. The lack of any strong indication of photospheric radius expansion during the burst suggests a 9 kpc upper limit of the source distance. We also find energy dependent dips, establishing A1744-361 as a high inclination, dipping LMXB. The timescale between the two episodes of observed dips suggests an orbital period of approx. 97 min. We have also detected a 2 - 4 Hz quasi-periodic-oscillation (QPO) for the first time from this source. This QPO appears consistent with approx. 1 Hz QPOs seen from other high inclination systems. We searched for kilohertz QPOs, and found a suggestive 2.3 sigma feature at 800 Hz in one observation. The frequency, strength and quality factor are consistent with that of a lower frequency kilohertz QPO, but the relatively low significance argues for caution, so we consider this a tentative detection requiring confirmation.

  6. Origin of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Brecher, K.

    1999-12-01

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

  7. Neutron star crusts

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    We calculate properties of neutron star matter at subnuclear densities using an improved nuclear Hamiltonian. Nuclei disappear and the matter becomes uniform at a density of about 0.6n(s), where n(s) of about 0.16/cu fm is the saturation density of nuclear matter. As a consequence, the mass of matter in the crusts of neutron stars is only about half as large as previously estimated. In about half of that crustal mass, nuclear matter occurs in shapes very different from the roughly spherical nuclei familiar at lower densities. The thinner crust and the unusual nuclear shape have important consequences for theories of the rotational and thermal evolution of neutron stars, especialy theories of glitches.

  8. Neutrinos from neutron stars

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.

    1979-01-01

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

  9. The neutron star zoo

    NASA Astrophysics Data System (ADS)

    Harding, Alice K.

    2013-12-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission.

  10. The breaking strain of neutron star crust

    SciTech Connect

    Kadau, Kai; Horowitz, C J

    2009-01-01

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

  11. Neutron matter, symmetry energy and neutron stars

    SciTech Connect

    Stefano, Gandolfi; Steiner, Andrew W

    2016-01-01

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

  12. Neutron matter, symmetry energy and neutron stars

    NASA Astrophysics Data System (ADS)

    Gandolfi, S.; Steiner, A. W.

    2016-01-01

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

  13. Hyperons and neutron stars

    NASA Astrophysics Data System (ADS)

    Vidaña, Isaac

    2015-02-01

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

  14. Hyperons in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Vidaña, Isaac

    2016-01-01

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

  15. Hyperons and neutron stars

    SciTech Connect

    Vidaña, Isaac

    2015-02-24

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

  16. Initial data for black hole-neutron star binaries, with rotating stars

    NASA Astrophysics Data System (ADS)

    Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Muhlberger, Curran; Kidder, Lawrence E.; Scheel, Mark A.; Szilágyi, Béla

    2016-11-01

    The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole-neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as {S}{BH}/{M}{BH}2=0.99.

  17. Black hole-neutron star binary merger: Dependence on black hole spin orientation and equation of state

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Kyohei; Kyutoku, Koutarou; Nakano, Hiroyuki; Okawa, Hirotada; Shibata, Masaru; Taniguchi, Keisuke

    2015-07-01

    We systematically performed numerical-relativity simulations for black hole-neutron star (BH-NS) binary mergers with a variety of the BH spin orientation and nuclear-theory-based equations of state (EOS) of the NS. The initial misalignment angles of the BH spin measured from the direction of the orbital angular momentum are chosen in the range of itilt,0≈30 ° -90 ° . We employed four models of nuclear-theory-based zero-temperature EOS for the NS in which the compactness of the NS is in the range of C =MNS/RNS=0.138 -0.180 , where MNS and RNS are the mass and the radius of the NS, respectively. The mass ratio of the BH to the NS, Q =MBH/MNS , and the dimensionless spin parameter of the BH, χ , are chosen to be Q =5 and χ =0.75 , together with MNS=1.35 M⊙ so that the BH spin misalignment has a significant effect on tidal disruption of the NS. We obtain the following results: (i) The inclination angles of itilt,0<70 ° and itilt,0<50 ° are required for the formation of a remnant disk with its mass larger than 0.1 M⊙ for the cases C =0.140 and C =0.160 , respectively, while the disk mass is always smaller than 0.1 M⊙ for C ≳0.175 . The ejecta with its mass larger than 0.01 M⊙ is obtained for itilt,0<85 ° with C =0.140 , for itilt,0<65 ° with C =0.160 , and for itilt,0<30 ° with C =0.175 . (ii) The rotational axis of the dense part of the remnant disk with its rest-mass density larger than 109 g /cm3 is approximately aligned with the remnant BH spin for itilt,0≈30 ° . On the other hand, the disk axis is misaligned initially with ˜30 ° for itilt,0≈60 ° , and the alignment with the remnant BH spin is achieved at ˜50 - 60 ms after the onset of merger. The accretion time scale of the remnant disk is typically ˜100 ms and depends only weakly on the misalignment angle and the EOS. (iii) The ejecta velocity is typically ˜0.2 - 0.3 c and depends only weakly on the misalignment angle and the EOS of the NS, while the morphology of the ejecta depends

  18. Can neutron stars have auroras ? : electromagnetic coupling process between neutron star and magnetized accretion disk

    NASA Astrophysics Data System (ADS)

    Kimura, T.; Iwakiri, W. B.; Enoto, T.; Wada, T.; Tao, C.

    2015-12-01

    In the binary neutron star system, angular momentum transfer from accretion disk to a star is essential process for spin-up/down of stars. The angular momentum transfer has been well formulated for the accretion disk strongly magnetized by the neutron star [e.g., Ghosh and Lamb, 1978, 1979a, b]. However, the electromagnetic (EM) coupling between the neutron star and accretion disk has not been self-consistently solved in the previous studies although the magnetic field lines from the star are strongly tied with the accretion disk. In this study, we applied the planet-magnetosphere coupling process established for Jupiter [Hill, 1979] to the binary neutron star system. Angular momentum distribution is solved based on the torque balance between the neutron star's surface and accretion disk coupled by the magnetic field tensions. We found the EM coupling can transfer significantly larger fraction of the angular momentum from the magnetized accretion disk to the star than the unmagnetized case. The resultant spin-up rate is estimated to ~10^-14 [sec/sec] for the nominal binary system parameters, which is comparable with or larger than the other common spin-down/up processes: e.g., the magnetic dipole radiation spin-down. The Joule heating energy dissipated in the EM coupling is estimated to be up to ~10^36 [erg/sec] for the nominal binary system parameters. The release is comparable to that of gravitation energy directly caused by the matters accreting onto the neutron star. This suggests the EM coupling at the neutron star can accompany the observable radiation as auroras with a similar manner to those at the rotating planetary magnetospheres like Jupiter, Saturn, and other gas giants.

  19. Neutron Stars and NuSTAR

    NASA Astrophysics Data System (ADS)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses

  20. Plasma physics of accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Ghosh, Pranab; Lamb, Frederick K.

    1991-01-01

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

  1. Compactness of Neutron Stars.

    PubMed

    Chen, Wei-Chia; Piekarewicz, J

    2015-10-16

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

  2. The physics of neutron stars.

    PubMed

    Lattimer, J M; Prakash, M

    2004-04-23

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

  3. Orbital Decay of the PSR J0045-7319 Binary System: Age of Radio Pulsar and Initial Spin of Neutron Star

    NASA Astrophysics Data System (ADS)

    Lai, Dong

    1996-07-01

    Recent timing observations of PSR J0045-7319 reveal that the neutron star/B star binary orbit is decaying on a timescale of |P_{{orb}}/P dot _{{orb}}| = 0.5 Myr, shorter than the characteristic age ( tau c = 3 Myr) of the pulsar. We study mechanisms for the orbital decay. The standard weak-friction theory based on static tide requires far too short a viscous time to explain the observed P dot _{{orb}} . We show that dynamical tidal excitation of g-modes in the B star can be responsible for the orbital decay. However, to explain the observed short decay timescale, the B star must have some significant retrograde rotation with respect to the orbit---the retrograde rotation brings lower order g-modes, which couple much more strongly to the tidal potential, into closer "resonances" with the orbital motion, thus significantly enhancing the dynamical tide. A much less likely possibility is that the g-mode damping time is much shorter than the ordinary radiative damping time. The observed orbital decay timescale combined with a generic orbital evolution model based on dynamical tide can be used as a "timer," yielding an upper limit of 1.4 Myr on the age of the binary system since the neutron star's formation. Thus the characteristic age of the pulsar is not a good age indicator. Assuming standard magnetic dipole braking for the pulsar and no significant magnetic field decay on a timescale <~1 Myr, the upper limit for the age implies that the initial spin of the neutron star at birth was close to its current value.

  4. Dark neutron stars

    NASA Astrophysics Data System (ADS)

    Jones, P. B.

    2017-06-01

    There is good evidence that electron-positron pair formation is not present in that section of the pulsar open magnetosphere, which is the source of coherent radio emission, but the possibility of two-photon pair creation in an outer gap remains. Calculation of transition rates for this process based on measured whole-surface temperatures, combined with a survey of γ-ray, X-ray and optical luminosities, expressed per primary beam lepton, shows that few Fermi-LAT pulsars have significant outer-gap pair creation. For radio-loud pulsars with positive polar-cap corotational charge density and an ion-proton plasma, there must be an outward flow of electrons from some other part of the magnetosphere to maintain a constant net charge on the star. In the absence of pair creation, it is likely that this current is the source of GeV γ-emission observed by the Fermi-LAT and its origin is in the region of the outer gap. With negative polar-cap corotational charge density, the compensating current in the absence of pair creation can consist only of ions or protons. These neutron stars are likely to be radio-quiet, have no observable γ-emission, and hence can be described as dark neutron stars.

  5. On magnetized neutron stars

    SciTech Connect

    Lopes, Luiz; Menezes, Debora E-mail: debora.p.m@ufsc.br

    2015-08-01

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

  6. Does mass accretion lead to field decay in neutron stars?

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    Adopting the hypothesis of accretion-induced magnetic field decay in neutron stars, the consequent evolution of a neutron star's spin and magnetic field are calculated. The results are consistent with observations of binary and millisecond radio pulsars. Thermomagnetic effects could provide a possible physical mechanism for such accretion-induced field decay.

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

    PubMed

    Schilling, G

    2000-09-01

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

  8. Magnetic Fields of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Konar, Sushan

    2017-09-01

    This article briefly reviews our current understanding of the evolution of magnetic fields in neutron stars, which basically defines the evolutionary pathways between different observational classes of neutron stars. The emphasis here is on the evolution in binary systems and the newly emergent classes of millisecond pulsars.

  9. KAON CONDENSATION IN NEUTRON STARS.

    SciTech Connect

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

    2001-04-24

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

  10. Grand unification of neutron stars.

    PubMed

    Kaspi, Victoria M

    2010-04-20

    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.

  11. Grand unification of neutron stars

    PubMed Central

    Kaspi, Victoria M.

    2010-01-01

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

  12. QPO Constraints on Neutron Stars

    NASA Technical Reports Server (NTRS)

    Miller, M. Coleman

    2005-01-01

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

  13. Neutron Star Mass Distribution in Binaries

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hwan; Kim, Young-Min

    2016-05-01

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

  14. Neutron Stars and Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip

    2007-01-01

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

  15. Understanding Neutron Stars using Thermonuclear X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, S.

    2007-01-01

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

  16. Neutron star structure from QCD

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  17. Gravitational wave background from rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Rosado, Pablo A.

    2012-11-01

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

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

    PubMed

    Yagi, Kent; Yunes, Nicolás

    2013-07-26

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

  19. Chandra Captures Neutron Star Action

    NASA Image and Video Library

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

  20. Neutron stars : Seen my way

    NASA Astrophysics Data System (ADS)

    Kundt, Wolfgang

    2001-09-01

    An unconventional survey is presented of the observable properties of neutron stars and of all astrophysical phenomena possibly related to them, such as their pulsing, clock irregularities, bursting, flickering, and occasional super-Eddington brightness, the generation of cosmic rays, of gamma-ray bursts, of jets, and of synchrotron nebulae, their birth, and their occasional transient appearance as 'supersoft' X-ray sources. The msec pulsars are argued to be born fast, the black-hole candidates to be neutron stars inside of massive disks, and the gamma-ray bursts to be sparks from dense 'blades' accreting spasmodically onto the surfaces of (generally old) neutron stars within " 0.3 Kpc from the Sun. Supernovae - the likely birth events of neutron stars - are thick-walled explosions, not to be described by Sedov-Taylor waves, which illuminate their gaseous environs via collisions of their 'splinters'.

  1. Cracking on anisotropic neutron stars

    NASA Astrophysics Data System (ADS)

    Setiawan, A. M.; Sulaksono, A.

    2017-07-01

    We study the effect of cracking of a local anisotropic neutron star (NS) due to small density fluctuations. It is assumed that the neutron star core consists of leptons, nucleons and hyperons. The relativistic mean field model is used to describe the core of equation of state (EOS). For the crust, we use the EOS introduced by Miyatsu et al. [1]. Furthermore, two models are used to describe pressure anisotropic in neutron star matter. One is proposed by Doneva-Yazadjiev (DY) [2] and the other is proposed by Herrera-Barreto (HB) [3]. The anisotropic parameter of DY and HB models are adjusted in order the predicted maximum mass compatible to the mass of PSR J1614-2230 [4] and PSR J0348+0432 [5]. We have found that cracking can potentially present in the region close to the neutron star surface. The instability due cracking is quite sensitive to the NS mass and anisotropic parameter used.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  3. Neutron star news and puzzles

    NASA Astrophysics Data System (ADS)

    Prakash, Madappa

    2014-08-01

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

  4. The Zoo of neutron stars

    NASA Astrophysics Data System (ADS)

    Popov, S. B.

    2008-12-01

    In these lecture notes, I briefly discuss the present day situation and new discoveries in astrophysics of neutron stars focusing on isolated objects. The latter include soft gamma repeaters, anomalous x-ray pulsars, central compact objects in supernova remnants, the Magnificent Seven, and rotating radio transients. In the last part of the paper, I describe available tests of cooling curves of neutron stars and discuss different additional constraints that can help to confront theoretical calculations of cooling with observational data.

  5. Neutron Star - Magnetosphere Interactions

    NASA Astrophysics Data System (ADS)

    Ponce, Marcelo; Anderson, Matthew; Lehner, Luis; Liebling, Steven L.; Palenzuela, Carlos

    2012-03-01

    In this work we report results of the interaction of a neutron star magnetosphere in both collapsing and moving scenarios interacting with an ambient magnetic field. In recent works [1,2], it has been shown the important role and realism associated with studies of electromagnetic environments in some particular regimes, such as: ideal-MHD, force-free, and electro-vacuum. Motivated by this and their astrophysical implications for BBH and hybrid BH-NS mergers [3,4], we study the following cases: collapse of a magnetized NS, head-on collision of a BH-NS, and orbiting merger of a BH-NS. Based in the results from our simulations, we draw some relevant conclusions to the production of jets as described within the force-free formalism. [4pt] [1] C.Palenzuela, L.Lehner and S.Liebling, Science 329, 927 (2010).[0pt] [2] C.Palenzuela, T.Garrett, et al., Phys.Rev.D 82, 044045 (2010).[0pt] [3] L.Lehner, C.Palenzuela, et al., 2011.[0pt] [4] S.Liebling, L.Lehner, et al., Phys.Rev.D 81, 124023 (2010).

  6. Spin-orbit splitting in neutron drops

    SciTech Connect

    Pieper, S.C.; Pandharipande, V.R.; Ravenhall, D.G.

    1995-08-01

    Hartree-Fock calculations of very neutron-rich nuclei are an essential source of input for calculations of the properties of neutron-star crusts. The Hartree-Fock calculations often use Skyrme models whose parameters are determined by fits to known (hence not neutron-rich) nuclei and extrapolations to the N >> Z case. The Vautherin and Brink (VB) prescription for the isospin dependence of the spin-orbit potential, V{sub so}, is usually used; this is based on the assumption that most of V{sub so} comes from a short-range L{center_dot}S nucleon-nucleon interaction. In 1993 we showed that more than half of the spin-orbit splitting in {sup 15}N comes from long-range three-nucleon potentials and correlations, which violate the VB assumption. To investigate the isospin dependence of the spin-orbit splitting, we made calculations of the type described in Sec. B.d for systems of 7 (p-wave splitting) and 19 (d-wave) neutrons. The neutrons were confined in external potentials that were adjusted to give physically reasonable densities. We find that the spin-orbit splitting of these drops is less than half the {sup 15}N value. These values can be used to determine an isospin dependence of V{sub so} that is very different from that of VB. Hartree-Fock calculations of known spin-orbit splittings in nuclei with N significantly different from Z are now being made with this new prescription.

  7. Neutron star moments of inertia

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  8. The nuclear physics of neutron stars

    NASA Astrophysics Data System (ADS)

    Piekarewicz, J.

    2014-05-01

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

  9. The nuclear physics of neutron stars

    SciTech Connect

    Piekarewicz, J.

    2014-05-09

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

  10. Neutron stars structure in the context of massive gravity

    NASA Astrophysics Data System (ADS)

    Hendi, S. H.; Bordbar, G. H.; Eslam Panah, B.; Panahiyan, S.

    2017-07-01

    Motivated by the recent interests in spin-2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

  11. Neutron Star Seismology with Accreting Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    conduct the first targeted searches for X-ray modulations induced by non-radial oscillation modes (including r- and g-modes) in neutron stars using RXTE and XMM-Newton data from the eleven AMXPs which have not yet been searched. This includes the first AMXP discovered, SAX J1808.4-3658, which because of its large RXTE data set ( 2 M-sec) will yield one of the most sensitive searches to date. To widen the range of neutron star spin frequencies probed we will also conduct similar searches in two ``slow'' LMXB pulsars, IGR J17480-2466 (11 Hz), and the ``bursting pulsar,'' GRO J1744-28 (2 Hz). We will explore for potentially coherent signals in the neutron star's inertial frame by first removing the phase delays associated with the star's binary motion and computing FFT power spectra of long, continuous light curves. We will search a range of frequencies in which both r- and g-modes are theoretically expected to reside. We will also characterize, interpret and model any detected oscillation mode frequencies, or in the case of no detections we will set upper limits on the X-ray modulation amplitudes that can be present. This will include efforts to constrain the physical properties of the neutron stars, for example, their masses and radii, based on any detected frequencies.

  12. Dynamics of microemulsions bridged with hydrophobically end-capped star polymers studied by neutron spin-echo

    NASA Astrophysics Data System (ADS)

    Hoffmann, I.; de Molina, Paula Malo; Farago, B.; Falus, P.; Herfurth, Christoph; Laschewsky, André; Gradzielski, M.

    2014-01-01

    The mesoscopic dynamical properties of oil-in-water microemulsions (MEs) bridged with telechelic polymers of different number of arms and with different lengths of hydrophobic stickers were studied with neutron spin-echo (NSE) probing the dynamics in the size range of individual ME droplets. These results then were compared to those of dynamicic light scattering (DLS) which allow to investigate the dynamics on a much larger length scale. Studies were performed as a function of the polymer concentration, number of polymer arms, and length of the hydrophobic end-group. In general it is observed that the polymer bridging has a rather small influence on the local dynamics, despite the fact that the polymer addition leads to an increase of viscosity by several orders of magnitude. In contrast to results from rheology and DLS, where the dynamics on much larger length and time scales are observed, NSE shows that the linear polymer is more efficient in arresting the motion of individual ME droplets. This finding can be explained by a simple simulation, merely by the fact that the interconnection of droplets becomes more efficient with a decreasing number of arms. This means that the dynamics observed on the short and on the longer length scale depend in an opposite way on the number of arms and hydrophobic stickers.

  13. Dynamics of microemulsions bridged with hydrophobically end-capped star polymers studied by neutron spin-echo

    SciTech Connect

    Hoffmann, I.; Malo de Molina, Paula; Gradzielski, M.; Farago, B.; Falus, P.; Herfurth, Christoph; Laschewsky, André

    2014-01-21

    The mesoscopic dynamical properties of oil-in-water microemulsions (MEs) bridged with telechelic polymers of different number of arms and with different lengths of hydrophobic stickers were studied with neutron spin-echo (NSE) probing the dynamics in the size range of individual ME droplets. These results then were compared to those of dynamicic light scattering (DLS) which allow to investigate the dynamics on a much larger length scale. Studies were performed as a function of the polymer concentration, number of polymer arms, and length of the hydrophobic end-group. In general it is observed that the polymer bridging has a rather small influence on the local dynamics, despite the fact that the polymer addition leads to an increase of viscosity by several orders of magnitude. In contrast to results from rheology and DLS, where the dynamics on much larger length and time scales are observed, NSE shows that the linear polymer is more efficient in arresting the motion of individual ME droplets. This finding can be explained by a simple simulation, merely by the fact that the interconnection of droplets becomes more efficient with a decreasing number of arms. This means that the dynamics observed on the short and on the longer length scale depend in an opposite way on the number of arms and hydrophobic stickers.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  15. Neutron stars are gold mines

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    Neutron stars are not only mines for clues to dense matter physics but may also be the auspicious sources of half of all nuclei heavier than A = 60 in the universe, including the auric isotopes. Although the cold dense matter above the nuclear saturation density cannot be directly explored in the laboratory, gilded constraints on the properties of matter from 1 to 10 times higher density can now be panned from neutron star observations. We show how upcoming observations, such as gravitational wave from mergers, precision timing of pulsars, neutrinos from neutron star birth and X-rays from bursts and thermal emissions, will provide the bullion from which further advances can be smelted.

  16. Tidal polarizability effects in neutron star mergers

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  17. BLACK HOLE-NEUTRON STAR MERGERS WITH A HOT NUCLEAR EQUATION OF STATE: OUTFLOW AND NEUTRINO-COOLED DISK FOR A LOW-MASS, HIGH-SPIN CASE

    SciTech Connect

    Deaton, M. Brett; Duez, Matthew D.; Foucart, Francois; O'Connor, Evan; Ott, Christian D.; Scheel, Mark A.; Szilagyi, Bela; Kidder, Lawrence E.; Muhlberger, Curran D. E-mail: m.duez@wsu.edu

    2013-10-10

    Neutrino emission significantly affects the evolution of the accretion tori formed in black hole-neutron star mergers. It removes energy from the disk, alters its composition, and provides a potential power source for a gamma-ray burst. To study these effects, simulations in general relativity with a hot microphysical equation of state (EOS) and neutrino feedback are needed. We present the first such simulation, using a neutrino leakage scheme for cooling to capture the most essential effects and considering a moderate mass (1.4 M{sub ☉} neutron star, 5.6 M{sub ☉} black hole), high-spin (black hole J/M {sup 2} = 0.9) system with the K{sub 0} = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 M{sub ☉} of nuclear matter is ejected from the system, while another 0.3 M{sub ☉} forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (1) to make the disk much denser and more compact, (2) to cause the average electron fraction Y{sub e} of the disk to rise to about 0.2 and then gradually decrease again, and (3) to gradually cool the disk. The disk is initially hot (T ∼ 6 MeV) and luminous in neutrinos (L{sub ν} ∼ 10{sup 54} erg s{sup –1}), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution.

  18. Superfluidity and Superconductivity in Neutron Stars

    NASA Astrophysics Data System (ADS)

    Chamel, N.

    2017-09-01

    Neutron stars, the compact stellar remnants of core-collapse supernova explosions, are unique cosmic laboratories for exploring novel phases of matter under extreme conditions. In particular, the occurrence of superfluidity and superconductivity in neutron stars will be briefly reviewed.

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

    PubMed

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

    2014-04-18

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

  20. Theory of cooling neutron stars versus observations

    SciTech Connect

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

    2008-02-27

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

  1. Breaking strain of neutron star crust and gravitational waves.

    PubMed

    Horowitz, C J; Kadau, Kai

    2009-05-15

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

  2. Neutrino Processes in Neutron Stars

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  3. r-MODE Runaway and Rapidly Rotating Neutron Stars

    NASA Astrophysics Data System (ADS)

    Stergioulas, Nikolaos; Kokkotas, Kostas D.; Andersson, Nils; Jones, David Ian

    2002-12-01

    We present a simple spin evolution model that predicts that rapidly rotating accreting neutron stars will mainly be confined to a narrow range of spin-frequencies; P = 1.5 - 5 ms. This is in agreement with current observations of both neutron stars in the Low-Mass X-ray Binaries and millisecond radio pulsars. The main ingredients in the model are: i) the instability of r-modes above a critical spin rate, ii) thermal runaway due to heat released as viscous damping mechanisms counteract the r-mode growth, and iii) a revised estimate of the strength of dissipation due to the presence of a viscous boundary layer at the base of the crust in an old and relatively cold neutron star...

  4. Jets from Merging Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-06-01

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

  5. Hypernuclei and massive neutron stars

    NASA Astrophysics Data System (ADS)

    Fortin, M.; Avancini, S. S.; Providência, C.; Vidaña, I.

    2017-06-01

    Background: The recent accurate measurement of the mass of two pulsars close to or above 2 M⊙ has raised the question of whether such large pulsar masses allow for the existence of exotic degrees of freedom, such as hyperons, inside neutron stars. Purpose: In the present work, we will investigate, within a phenomenological relativistic mean field approach, how the existing hypernuclei properties may constrain the neutron star equation of state and confront the neutron star maximum masses obtained with equations of state calibrated to hypernuclei properties with the astrophysical 2 M⊙ constraint. Method: The study is performed using a relativistic mean field approach to describe both the hypernuclei and the neutron star equations of state. Unified equations of state are obtained. A set of five models that describe 2 M⊙ when only nucleonic degrees of freedom are employed. Some of these models also satisfy other well-established laboratory or theoretical constraints. Results: The Λ -meson couplings are determined for all the models considered, and the Λ potential in symmetric nuclear matter and Λ matter at saturation are calculated. Maximum neutron star masses are determined for two values of the Λ -ω meson coupling, gω Λ=2 gω N/3 and gω Λ=gω N , and a wide range of values for gϕ Λ. Hyperonic stars with the complete baryonic octet are studied, restricting the coupling of the Σ and Ξ hyperons to the ω ,ρ , and σ mesons due to the lack of experimental data, and maximum star masses calculated. Conclusions: We conclude that, within a phenomenological relativistic mean field approach, the currently available hypernuclei experimental data and the lack of constraints on the asymmetric equation of state of nuclear matter at high densities set only a limited number of constraints on the neutron star matter equation of state using the recent 2 M⊙ observations. It is shown that the Λ potential in symmetric nuclear matter takes a value of ˜30 -32 Me

  6. NSCool: Neutron star cooling code

    NASA Astrophysics Data System (ADS)

    Page, Dany

    2016-09-01

    NSCool is a 1D (i.e., spherically symmetric) neutron star cooling code written in Fortran 77. The package also contains a series of EOSs (equation of state) to build stars, a series of pre-built stars, and a TOV (Tolman- Oppenheimer-Volkoff) integrator to build stars from an EOS. It can also handle “strange stars” that have a huge density discontinuity between the quark matter and the covering thin baryonic crust. NSCool solves the heat transport and energy balance equations in whole GR, resulting in a time sequence of temperature profiles (and, in particular, a Teff - age curve). Several heating processes are included, and more can easily be incorporated. In particular it can evolve a star undergoing accretion with the resulting deep crustal heating, under a steady or time-variable accretion rate. NSCool is robust, very fast, and highly modular, making it easy to add new subroutines for new processes.

  7. Accuracy and precision of gravitational-wave models of inspiraling neutron star-black hole binaries with spin: Comparison with matter-free numerical relativity in the low-frequency regime

    NASA Astrophysics Data System (ADS)

    Kumar, Prayush; Barkett, Kevin; Bhagwat, Swetha; Afshari, Nousha; Brown, Duncan A.; Lovelace, Geoffrey; Scheel, Mark A.; Szilágyi, Béla

    2015-11-01

    Coalescing binaries of neutron stars and black holes are one of the most important sources of gravitational waves for the upcoming network of ground-based detectors. Detection and extraction of astrophysical information from gravitational-wave signals requires accurate waveform models. The effective-one-body and other phenomenological models interpolate between analytic results and numerical relativity simulations, that typically span O (10 ) orbits before coalescence. In this paper we study the faithfulness of these models for neutron star-black hole binaries. We investigate their accuracy using new numerical relativity (NR) simulations that span 36-88 orbits, with mass ratios q and black hole spins χBH of (q ,χBH)=(7 ,±0.4 ),(7 ,±0.6 ) , and (5 ,-0.9 ). These simulations were performed treating the neutron star as a low-mass black hole, ignoring its matter effects. We find that (i) the recently published SEOBNRv1 and SEOBNRv2 models of the effective-one-body family disagree with each other (mismatches of a few percent) for black hole spins χBH≥0.5 or χBH≤-0.3 , with waveform mismatch accumulating during early inspiral; (ii) comparison with numerical waveforms indicates that this disagreement is due to phasing errors of SEOBNRv1, with SEOBNRv2 in good agreement with all of our simulations; (iii) phenomenological waveforms agree with SEOBNRv2 only for comparable-mass low-spin binaries, with overlaps below 0.7 elsewhere in the neutron star-black hole binary parameter space; (iv) comparison with numerical waveforms shows that most of this model's dephasing accumulates near the frequency interval where it switches to a phenomenological phasing prescription; and finally (v) both SEOBNR and post-Newtonian models are effectual for neutron star-black hole systems, but post-Newtonian waveforms will give a significant bias in parameter recovery. Our results suggest that future gravitational-wave detection searches and parameter estimation efforts would benefit

  8. Magnetically driven crustquakes in neutron stars

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  9. Unifying neutron stars getting to GUNS

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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 of ≲ 104-105 yr, significant contribution of non-dipolar fields, and appropriate initial parameter distributions. We present our results on the initial spin period distribution, and suggest that inconsistencies 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 of 8× 104-3.5 × 105 yr with a time scale of ˜ 5 × 105 yr. We discuss several issues related to the unifying scenario. At first, we note that the dichotomy, among local thermally emitting neutron stars, between normal pulsars and the Magnificent Seven remains unexplained. Then we discuss the role of high-mass X-ray binaries in the unification of neutron star evolution. We note, that such systems allow to check evolutionary effects on a time scale longer than what can be probed with normal pulsars alone. We conclude with a brief discussion of the importance of discovering old neutron stars accreting from the interstellar medium.

  10. Neutron Stars in Binaries and in Isolation

    NASA Astrophysics Data System (ADS)

    Yancopoulos, Sophia

    1996-01-01

    This thesis is a study of neutron stars in three distinct classes. After a brief overview of neutron stars in Chapter 1, the three systems are discussed in order of decreasing luminosity. In Chapter 2, we present a new model for the normal branch of a class of low mass X-ray binaries which show quasiperiodic oscillations: a quasi -periodic modulation in the intensity of their X-ray signal. Chapter 3 discusses a particular radio pulsar which we observed in X-rays with the ROSAT PSPC. Chapter 4 rounds out the thesis with a discussion of a class of neutron stars which have not, to date, been definitively shown to exist. We describe a search for these isolated old neutron stars in the Einstein database, and present the results of our finds. As part of a search for thermal surface radiation from nearby neutron stars, we have carried out a 45,000 s observation of the nearby radio pulsar PSR 1929+10 with the ROSAT PSPC. After background subtraction, a net of 420+/-25 photons in the 0.1-2.0 keV band were detected at the position of the pulsar, corresponding to a luminosity of position of the pulsar, corresponding to a luminosity of 1.2 times 1030 erg/s for a source distance of 250 pc, or {~}3 times 10^{-4} of the pulsar's spin-down luminosity. We find coherent pulsations from PSR 1929+10 at the radio period of 0.2265 s. The folded light curve is well fit by a sinusoidal oscillation with a pulsed fraction of about 30%. The total spectrum is fit by a blackbody with a temperature T_ infty~3.2times10^6 K; the implied emitting area has a radius of less than 50 meters. The maximum of the X-ray light curve coincides with the radio pulse, suggesting we are detecting the hot magnetic polar cap of the star. We discuss the implications of our results for the temperature distribution over the surface of the star, and use this detection to constrain various heating mechanisms for rotation-powered neutron stars. We also use a simple model of general relativistic light bending near the

  11. Approximate universal relations for neutron stars and quark stars

    NASA Astrophysics Data System (ADS)

    Yagi, Kent; Yunes, Nicolás

    2017-04-01

    Neutron stars and quark stars are ideal laboratories to study fundamental physics at supra nuclear densities and strong gravitational fields. Astrophysical observables, however, depend strongly on the star's internal structure, which is currently unknown due to uncertainties in the equation of state. Universal relations, however, exist among certain stellar observables that do not depend sensitively on the star's internal structure. One such set of relations is between the star's moment of inertia (I), its tidal Love number (Love) and its quadrupole moment (Q), the so-called I-Love-Q relations. Similar relations hold among the star's multipole moments, which resemble the well-known black hole no-hair theorems. Universal relations break degeneracies among astrophysical observables, leading to a variety of applications: (i) X-ray measurements of the nuclear matter equation of state, (ii) gravitational wave measurements of the intrinsic spin of inspiraling compact objects, and (iii) gravitational and astrophysical tests of General Relativity that are independent of the equation of state. We here review how the universal relations come about and all the applications that have been devised to date.

  12. r-Mode Runaway and Rapidly Rotating Neutron Stars.

    PubMed

    Andersson; Jones; Kokkotas; Stergioulas

    2000-05-01

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

  13. Accreting neutron stars by QFT

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Guang

    layer with thickness of 1 km then q = 1 (N1S1), the gravity from N1S1 inside and exterior will be completely shielded. Because of net nuν _{0} flux is the medium to produce and transmit gravity, q obstructed by the shielding layer lie on the density of layer matter and the section of single nucleon to electronic neutrino obtained by nuclear physics experiments is about 1.1*10 ({-) 43} cm (2) . The mass inside N1S1 for exterior has not gravity interaction, it equivalent to has not inertia as the mass vanish. The neutron star is as a empty shell thereby may rapidly rotating and has not upper limit of mass and radii by the gravity accretion of N1S1, which will influence the mechanisms of pulsars, quasars and X-rays generated. At N1S1 interior the mass for exterior has not gravity which is just we searching dark matter. The mass each part will each other shielding and gravity decrease to less than the pressure of the degenerate neutron gas. The neutron star cannot collapse into a singular point with infinite density, i.e., the black hole with infinite gravity cannot be formed or the neutron star is jest the black hole in observational meaning. By the gravity accrete of N1S1 the neutron star may enlarge its shell radii but thickness keep. Only a shell gravity may be not less than any a observed value which to be deemed as black hole. The neutron star has powerful gravity certainly accompany with great surface negative charge and it may rapidly to rotate, so that there is a powerful magnetic field surround it. The accreting neutron star is as a slowly expand empty shell with fixed thickness of 1 km, its spin period depend on its radii or total accretion mass.

  14. Journey to the Center of a Neutron Star

    NASA Technical Reports Server (NTRS)

    Wanjek, Christopher

    2003-01-01

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

  15. Journey to the Center of a Neutron Star

    NASA Technical Reports Server (NTRS)

    Wanjek, Christopher

    2003-01-01

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

  16. Quark-hadron composition of rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Mellinger, Richard D., Jr.

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

  17. Properties of neutron star critical collapses

    NASA Astrophysics Data System (ADS)

    Wan, Mew-Bing

    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.

  18. Properties of Neutron Star Critical Collapses

    NASA Astrophysics Data System (ADS)

    Wan, Mew-Bing

    2010-01-01

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

  19. Birth accelerations of neutron stars

    NASA Astrophysics Data System (ADS)

    Heras, Ricardo

    2013-03-01

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

  20. Role of correlations in spin-polarized neutron matter

    NASA Astrophysics Data System (ADS)

    Vidaña, Isaac; Polls, Artur; Durant, Victoria

    2016-11-01

    Background: The possible existence of a phase transition to a ferromagnetic state in neutron matter as origin of the extremely high magnetic fields of neutron stars is still an open issue. Whereas many phenomenological interactions predict this transition at densities accessible in neutron stars, microscopic calculations based on realistic interactions show no indication of it. The existence or non-existence of this transition is a consequence of the different role of nucleon-nucleon correlations in polarized and unpolarized neutron matter. Therefore, to give a definite answer to this issue it is necessary to analyze the behavior of these correlations. Purpose: Using the Hellmann-Feynman theorem we analyze the contribution of the different terms of the nucleon-nucleon interaction to the spin symmetry energy of neutron matter with the purpose of identifying the nature and role of correlations in polarized and unpolarized neutron matter. Methods: The analysis is performed within the microscopic Brueckner-Hartree-Fock approach using the Argonne V18 realistic potential plus the Urbana IX three-body force. Results: Our results show no indication of a ferromagnetic transition as the spin symmetry energy of neutron matter is always an increasing function of density. They show also that the main contribution to it comes from the S =0 channel, acting only in non-polarized neutron matter, in particular from the 1S0 and the 1D2 partial waves. Three-body forces are found to play a secondary role in the determination of the spin symmetry energy. Conclusions: By evaluating the kinetic energy difference between the correlated system and the underlying Fermi sea to estimate the importance of correlations in spin-polarized neutron matter, we conclude that non-polarized neutron matter is more correlated than totally polarized one.

  1. Parameters of rotating neutron stars with and without hyperons

    NASA Astrophysics Data System (ADS)

    Bejger, M.

    2013-04-01

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

  2. Limits on Anomalous Spin-Spin Couplings between Neutrons

    NASA Astrophysics Data System (ADS)

    Glenday, Alexander G.; Cramer, Claire E.; Phillips, David F.; Walsworth, Ronald L.

    2008-12-01

    We report experimental limits on new spin-dependent macroscopic forces between neutrons. We measured the nuclear Zeeman frequencies of a He3/Xe129 maser while modulating the nuclear spin polarization of a nearby He3 ensemble in a separate glass cell. We place limits on the coupling strength of neutron spin-spin interactions mediated by light pseudoscalar particles like the axion [gpgp/(4πℏc)] at the 3×10-7 level for interaction ranges longer than about 40 cm. This limit is about 10-5 the size of the magnetic dipole-dipole interaction between neutrons.

  3. Gravitational waves from neutron star binaries

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hwan

    With H. A. Bethe, G. E. Brown worked on the merger rate of neutron star binaries for the gravitational wave detection. Their prediction has to be modified significantly due to the observations of 2M⊙ neutron stars and the detection of gravitational waves. There still, however, remains a possibility that neutron star-low mass black hole binaries are significant sources of gravitational waves for the ground-based detectors. In this paper, I review the evolution of neutron star binaries with super-Eddington accretion and discuss the future prospect.

  4. Testing the relativistic precession model using low-frequency and kHz quasi-periodic oscillations in neutron star low-mass X-ray binaries with known spin

    NASA Astrophysics Data System (ADS)

    van Doesburgh, Marieke; van der Klis, Michiel

    2017-03-01

    We analyse all available RXTE data on a sample of 13 low-mass X-ray binaries with known neutron star spin that are not persistent pulsars. We carefully measure the correlations between the centroid frequencies of the quasi-periodic oscillations (QPOs). We compare these correlations to the prediction of the relativistic precession model that, due to frame dragging, a QPO will occur at the Lense-Thirring precession frequency νLT of a test-particle orbit whose orbital frequency is the upper kHz QPO frequency νu. Contrary to the most prominent previous studies, we find two different oscillations in the range predicted for νLT that are simultaneously present over a wide range of νu. Additionally, one of the low-frequency noise components evolves into a (third) QPO in the νLT range when νu exceeds 600 Hz. The frequencies of these QPOs all correlate to νu following power laws with indices between 0.4 and 3.3, significantly exceeding the predicted value of 2.0 in 80 per cent of the cases (at 3 to >20σ). Also, there is no evidence that the neutron star spin frequency affects any of these three QPO frequencies, as would be expected for frame dragging. Finally, the observed QPO frequencies tend to be higher than the νLT predicted for reasonable neutron star specific moment of inertia. In the light of recent successes of precession models in black holes, we briefly discuss ways in which such precession can occur in neutron stars at frequencies different from test-particle values and consistent with those observed. A precessing torus geometry and other torques than frame dragging may allow precession to produce the observed frequency correlations, but can only explain one of the three QPOs in the νLT range.

  5. White Dwarfs, Neutron Stars and Black Holes

    ERIC Educational Resources Information Center

    Szekeres, P.

    1977-01-01

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

  6. White Dwarfs, Neutron Stars and Black Holes

    ERIC Educational Resources Information Center

    Szekeres, P.

    1977-01-01

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

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

    SciTech Connect

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

    2012-05-20

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

  8. Mergers of Black Hole -- Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Rantsiou, Emmanouela

    Motivated by the scenario that black hole-neutron star (BH-NS) mergers are viable progenitors of observed short Gamma-ray Bursts, we have used a 3D relativistic SPH (smoothed particle hydrodynamics) code to study mergers of such binary systems (with relatively low mass ratios). We have investigated a wide range of parameters for those binaries: mass ratio, Equation of State (EOS) for the NS, compactness of the NS. Most importantly, the BH's spin was varied in our simulations (from non-spinning to maximally spinning BHs), and so was the orbital inclination of the NS. We have found that the outcome of such mergers depends sensitively on both the magnitude of the BH spin and its obliquity (i.e., the inclination of the binary orbit with respect to the equatorial plane of the BH). In particular, only systems with sufficiently high BH spin parameter a and sufficiently low orbital inclinations allow any NS matter to escape or to form a long-lived disk outside the BH horizon after disruption. Mergers of binaries with orbital inclinations above ˜60° lead to complete prompt accretion of the entire NS by the BH, even for the case of an extreme Kerr BH. We find that the formation of a significant disk or torus of NS material around the BH always requires a near-maximal BH spin and a low initial inclination of the NS orbit just prior to merger. Furthermore, we have investigated and we are presenting the gravitational waveforms and gravitational wave energy spectra from some representative cases. Despite using simply the quadrupole formula with post-Newtonian extensions (up to 3.5 terms) for radiation reaction, we were able to clearly see the impact of the BH's spin and NS's orbital inclination on the spectra and waveforms produced in our simulations.

  9. Magnetic fields in Neutron Stars

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  11. Planetary Systems Around Neutron Stars

    NASA Astrophysics Data System (ADS)

    Wolszczan, Alexander

    1997-01-01

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

  12. Planetary Systems Around Neutron Stars

    NASA Technical Reports Server (NTRS)

    Wolszczan, Alexander

    1997-01-01

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

  13. Many faces of young neutron stars

    NASA Astrophysics Data System (ADS)

    Vasisht, Gautam

    The hardware aspect of this thesis consists in the design, fabrication and assembly of twin analog Flexible Filter Banks at Caltech. These are user-friendly, workhorse, radio-pulsar search and timing instruments. Novel features include the flexibility in configuring channel center-frequencies and widths, the rapid sampling down to 25 μs and a total instrument bandwidth ranging from a narrow 0.2 MHz to a mammoth 100 MHz. Frequency synthesis is used to downconvert, detect and sample the telescope receiver bandpass as 32 separate time-series in each polarization. The collected data are later subjected to standard pulsar search and timing algorithms in software.The vital scientific issue addressed here is the nature of young neutron stars. In the standard picture, young neutron stars are rapidly spinning radio-luminous pulsars, which may also display pulsed emission at high X-ray and γ-ray energies. However there is no evidence that all neutron stars are born according to this standard picture. We present radio or X-ray investigations of steady nebular emission produced by three clearly non-standard and ill-understood objects. In all likelihood, these are young neutron stars, a notion upheld by their association with young Galactic supernova remnants.Based on its display of high energy transients, the soft γ-ray repeater SGR 1806-20 is posited to be a seismically active "magnetar", i.e., a neutron star with a super-strong magnetic field (10[superscript 15] G) nearly three orders of magnitude greater than pulsar dipolar fields. Our VLA observations of fleeting small-scale structure around SGR 1806-20 provide intriguing, although preliminary, support for the magnetar model. In time, similar observations could unravel the riddle of soft γ-ray repeaters and possibly establish the reality of magnetars.X-ray observations of the remnant of the historical supernova of 386 A.D., SNR G 11.2-0.3 are presented. The nature of an embedded underlumnious plerion discovered in

  14. (3) He Spin Filter for Neutrons.

    PubMed

    Batz, M; Baeßler, S; Heil, W; Otten, E W; Rudersdorf, D; Schmiedeskamp, J; Sobolev, Y; Wolf, M

    2005-01-01

    The strongly spin-dependent absorption of neutrons in nuclear spin-polarized (3)He opens up the possibility of polarizing neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. This paper gives a report on the neutron spin filter (NSF) development program at Mainz. The polarization technique is based on direct optical pumping of metastable (3)He atoms combined with a polarization preserving mechanical compression of the gas up to a pressure of several bar, necessary to run a NSF. The concept of a remote type of operation using detachable NSF cells is presented which requires long nuclear spin relaxation times of order 100 hours. A short survey of their use under experimental conditions, e.g. large solid-angle polarization analysis, is given. In neutron particle physics NSFs are used in precision measurements to test fundamental symmetry concepts.

  15. Data analysis of gravitational-wave signals from spinning neutron stars. V. A narrow-band all-sky search

    SciTech Connect

    Astone, Pia; Borkowski, Kazimierz M.; Jaranowski, Piotr; Pietka, Maciej; Krolak, Andrzej

    2010-07-15

    We present theory and algorithms to perform an all-sky coherent search for periodic signals of gravitational waves in narrow-band data of a detector. Our search is based on a statistic, commonly called the F-statistic, derived from the maximum-likelihood principle in Paper I of this series. We briefly review the response of a ground-based detector to the gravitational-wave signal from a rotating neuron star and the derivation of the F-statistic. We present several algorithms to calculate efficiently this statistic. In particular our algorithms are such that one can take advantage of the speed of fast Fourier transform in calculation of the F-statistic. We construct a grid in the parameter space such that the nodes of the grid coincide with the Fourier frequencies. We present interpolation methods that approximately convert the two integrals in the F-statistic into Fourier transforms so that the fast Fourier transform algorithm can be applied in their evaluation. We have implemented our methods and algorithms into computer codes and we present results of the Monte Carlo simulations performed to test these codes.

  16. How loud are neutron star mergers?

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  18. Neutron Star Interior Composition Explorer (NICE)

    NASA Technical Reports Server (NTRS)

    Gendreau, Keith C.; Arzoumanian, Zaven

    2008-01-01

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

  19. Systematic parameter errors in inspiraling neutron star binaries.

    PubMed

    Favata, Marc

    2014-03-14

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

  20. Neutrinos from Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Anchordoqui, Luis A.; Torres, Diego F.; McCauley, Thomas P.; Romero, Gustavo E.; Aharonian, Felix A.

    2003-05-01

    The magnetospheres of accreting neutron stars develop electrostatic gaps with huge potential drops. Protons and ions, accelerated in these gaps along the dipolar magnetic field lines to energies greater than 100 TeV, can impact onto the surrounding accretion disk. A proton-induced cascade develops, and charged pion decays produce ν emission. With extensive disk shower simulations using DPMJET and GEANT4, we have calculated the resulting ν spectrum. We show that the spectrum produced out of the proton beam is a power law. We use this result to propose accretion-powered X-ray binaries (with highly magnetized neutron stars) as a new population of pointlike ν sources for kilometer-scale detectors such as ICECUBE. As a particular example, we discuss the case of A0535+26. We show that ICECUBE should find A0535+26 to be a periodic ν source, one for which the formation and loss of its accretion disk can be fully detected. Finally, we comment briefly on the possibility that smaller telescopes such as AMANDA could also detect A0535+26 by folding observations with the orbital period.

  1. Thermonuclear runaways on neutron stars

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

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

  2. Close binary neutron star systems

    NASA Astrophysics Data System (ADS)

    Marronetti, Pedro

    1999-12-01

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

  3. Magnetic field devices for neutron spin transport and manipulation in precise neutron spin rotation measurements

    NASA Astrophysics Data System (ADS)

    Maldonado-Velázquez, M.; Barrón-Palos, L.; Crawford, C.; Snow, W. M.

    2017-05-01

    The neutron spin is a critical degree of freedom for many precision measurements using low-energy neutrons. Fundamental symmetries and interactions can be studied using polarized neutrons. Parity-violation (PV) in the hadronic weak interaction and the search for exotic forces that depend on the relative spin and velocity, are two questions of fundamental physics that can be studied via the neutron spin rotations that arise from the interaction of polarized cold neutrons and unpolarized matter. The Neutron Spin Rotation (NSR) collaboration developed a neutron polarimeter, capable of determining neutron spin rotations of the order of 10-7 rad per meter of traversed material. This paper describes two key components of the NSR apparatus, responsible for the transport and manipulation of the spin of the neutrons before and after the target region, which is surrounded by magnetic shielding and where residual magnetic fields need to be below 100 μG. These magnetic field devices, called input and output coils, provide the magnetic field for adiabatic transport of the neutron spin in the regions outside the magnetic shielding while producing a sharp nonadiabatic transition of the neutron spin when entering/exiting the low-magnetic-field region. In addition, the coils are self contained, forcing the return magnetic flux into a compact region of space to minimize fringe fields outside. The design of the input and output coils is based on the magnetic scalar potential method.

  4. Analytic description of neutron star cooling

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    We have derived analytic expressions that describe cooling of isolated neutron stars with nucleon cores after reaching the state of internal thermal relaxation. The results are valid for a wide class of equations of state of nucleonic matter and, in this sense, are universal. Moreover, they accurately reproduce the evolution of neutron stars at the neutrino and photon cooling stages as well as during transition from one stage to the other. These results greatly simplify theoretical analysis of internal structure of cooling neutron stars. For illustration, we analyse the thermal state of the bright nearby neutron star RX J1856.5-3754 and present arguments that this star has already left the neutrino cooling stage and contains superfluidity of neutrons and protons inside. We discuss possible efficiency of its neutrino cooling and heat capacity of its core.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  6. Where a Neutron Star's Accretion Disk Ends

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    In X-ray binaries that consist of a neutron star and a companion star, gas funnels from the companion into an accretion disk surrounding the neutron star, spiraling around until it is eventually accreted. How do the powerful magnetic fields threading through the neutron star affect this accretion disk? Recent observations provide evidence that they may push the accretion disk away from the neutron stars surface.Truncated DisksTheoretical models have indicated that neutron star accretion disks may not extend all the way in to the surface of a neutron star, but may instead be truncated at a distance. This prediction has been difficult to test observationally, however, due to the challenge of measuring the location of the inner disk edge in neutron-star X-ray binaries.In a new study, however, a team of scientists led by Ashley King (Einstein Fellow at Stanford University) has managed to measure the location of the inner edge of the disk in Aquila X-1, a neutron-star X-ray binary located 17,000 light-years away.Iron line feature detected by Swift (red) and NuSTAR (black). The symmetry of the line is one of the indicators that the disk is located far from the neutron star; if the inner regions of the disk were close to the neutron star, severe relativistic effects would skew the line to be asymmetric. [King et al. 2016]Measurements from ReflectionsKing and collaborators used observations made by NuSTAR and Swift/XRT both X-ray space observatories of Aquila X-1 during the peak of an X-ray outburst. By observing the reflection of Aquila X-1s emission off of the inner regions of the accretion disk, the authors were able to estimate the location of the inner edge of the disk.The authors find that this inner edge sits at ~15 gravitational radii. Since the neutron stars surface is at ~5 gravitational radii, this means that the accretion disk is truncated far from the stars surface. In spite of this truncation, material still manages to cross the gap and accrete onto the

  7. Axion cooling of neutron stars

    NASA Astrophysics Data System (ADS)

    Sedrakian, Armen

    2016-03-01

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

  8. ROTATIONAL CORRECTIONS TO NEUTRON-STAR RADIUS MEASUREMENTS FROM THERMAL SPECTRA

    SciTech Connect

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

    2015-01-20

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

  9. Accreting Millisecond Pulsars: Neutron Star Masses and Radii

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2004-01-01

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

  10. Physics in strong magnetic fields near neutron stars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    1991-01-01

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

  11. Transient phenomena from accreting magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Klochkov, Dmitry

    In this contribution, I will review the recent progress in the research of accreting magnetized neutron stars (observed as X-ray pulsars) based on the study of their variability on different time scales. Specifically, I will focus on the properties of the X-ray emitting region. In recent years, the high-quality observational data accumulated with the new generation of X-ray observatories have triggered a renewed interest in these systems. The new studies are primarily focused on the detailed structure of the two physical regions of the objects: (i) the emitting area above the polar caps of the neutron star and (ii) the magnetospheric boundary, where the infalling matter couples to the accretoŕs magnetic field. The modulation of the matter supply from the binary companion as well as the instabilities in the accretion flow lead to the transient character of the majority of X-ray pulsars. The observations show that the "persistent" pulsars also exhibit numerous types of variabilities over a broad range of time scales (off-states, pulse-to-pulse variability, switches of spectral states, alternation of the pulsar's spin-up/spin-down episodes etc.). Of particular importance are the observed variations of the cyclotron absorption features (cyclotron lines), whose centroid energies are directly proportional to the magnetic field strength at the site of the line formation. The detailed studies of these variabilities have lead to the development of new theoretical models describing the physics in the emitting region and at the magnetospheric boundary. It has been proposed that the configuration and geometry of the two areas may change abruptly when the mass accretion rate reaches certain critical values. Such changes cause transitions between different accretion modes. A particular mode is expected to be characterized by certain variability patterns and can thus be inferred from the observations. I will describe these recent observations and the models which are aimed at

  12. Fully self-consistent thermal evolution studies of rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Negreiros, Rodrigo; Schramm, Stefan; Weber, Fridolin

    2017-07-01

    In this work we study the thermal evolution of rotating, axis-symmetric neutron stars, which are subjected to structural and compositional changes during spin-down. Our aim is to go beyond standard thermal evolution calculations where neutron stars are considered spherically-symmetric and with a static, "frozen-in" composition. Building on previous work, we carry out fully self-consistent thermal evolution calculations where the neutron star has an axis-symmetric, time-dependent structure. Such an approach allows us to consider, during the thermal evolution, changes of the star's geometry as well as its microscopic particle population. As a proof-of-concept, we study the thermal evolution of a neutron star subjected to magnetic braking spin-down. We show that the spin-evolution, combined with the accompanying structural and compositional changes lead to a substantially distinct thermal evolution scenario.

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

    NASA Astrophysics Data System (ADS)

    Falcke, Heino; Rezzolla, Luciano

    2014-02-01

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

  14. Neutron spin echo scattering angle measurement (SESAME)

    SciTech Connect

    Pynn, R.; Fitzsimmons, M.R.; Fritzsche, H.; Gierlings, M.; Major, J.; Jason, A.

    2005-05-15

    We describe experiments in which the neutron spin echo technique is used to measure neutron scattering angles. We have implemented the technique, dubbed spin echo scattering angle measurement (SESAME), using thin films of Permalloy electrodeposited on silicon wafers as sources of the magnetic fields within which neutron spins precess. With 30-{mu}m-thick films we resolve neutron scattering angles to about 0.02 deg. with neutrons of 4.66 A wavelength. This allows us to probe correlation lengths up to 200 nm in an application to small angle neutron scattering. We also demonstrate that SESAME can be used to separate specular and diffuse neutron reflection from surfaces at grazing incidence. In both of these cases, SESAME can make measurements at higher neutron intensity than is available with conventional methods because the angular resolution achieved is independent of the divergence of the neutron beam. Finally, we discuss the conditions under which SESAME might be used to probe in-plane structure in thin films and show that the method has advantages for incident neutron angles close to the critical angle because multiple scattering is automatically accounted for.

  15. A propelling neutron star in the enigmatic Be-star γ Cassiopeia

    NASA Astrophysics Data System (ADS)

    Postnov, K.; Oskinova, L.; Torrejón, J. M.

    2017-02-01

    γ Cassiopeia (γ Cas), is known to be a binary system consisting of a Be-type star and a low-mass (M ˜ 1 M⊙) companion of unknown nature orbiting in the Be-disc plane. Here, we apply the quasi-spherical accretion theory on to a compact magnetized star and show that if the low-mass companion of γ Cas is a fast spinning neutron star, the key observational signatures of γ Cas are remarkably well reproduced. Direct accretion on to this fast rotating neutron star is impeded by the propeller mechanism. In this case, around the neutron star magnetosphere a hot shell is formed which emits thermal X-rays in qualitative and quantitative agreement with observed properties of the X-ray emission from γ Cas. We suggest that γ Cas and its analogues constitute a new subclass of Be-type X-ray binaries hosting rapidly rotating neutron stars formed in supernova explosions with small kicks. The subsequent evolutionary stage of γ Cas and its analogues should be the X Per-type binaries comprising low-luminosity slowly rotating X-ray pulsars. The model explains the enigmatic X-ray emission from γ Cas, and also establishes evolutionary connections between various types of rotating magnetized neutron stars in Be-binaries.

  16. Observations of Millisecond Variability from Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    1997-04-01

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

  17. Measuring Neutron Star Radii via Pulse Profile Modeling with NICER

    NASA Astrophysics Data System (ADS)

    Özel, Feryal; Psaltis, Dimitrios; Arzoumanian, Zaven; Morsink, Sharon; Bauböck, Michi

    2016-11-01

    The Neutron-star Interior Composition Explorer is an X-ray astrophysics payload that will be placed on the International Space Station. Its primary science goal is to measure with high accuracy the pulse profiles that arise from the non-uniform thermal surface emission of rotation-powered pulsars. Modeling general relativistic effects on the profiles will lead to measuring the radii of these neutron stars and to constraining their equation of state. Achieving this goal will depend, among other things, on accurate knowledge of the source, sky, and instrument backgrounds. We use here simple analytic estimates to quantify the level at which these backgrounds need to be known in order for the upcoming measurements to provide significant constraints on the properties of neutron stars. We show that, even in the minimal-information scenario, knowledge of the background at a few percent level for a background-to-source countrate ratio of 0.2 allows for a measurement of the neutron star compactness to better than 10% uncertainty for most of the parameter space. These constraints improve further when more realistic assumptions are made about the neutron star emission and spin, and when additional information about the source itself, such as its mass or distance, are incorporated.

  18. Validating Neutron Star Radius Measurements

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Deepto

    2010-09-01

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

  19. Formation of Double Neutron Star Systems

    NASA Astrophysics Data System (ADS)

    Tauris, T. M.; Kramer, M.; Freire, P. C. C.; Wex, N.; Janka, H.-T.; Langer, N.; Podsiadlowski, Ph.; Bozzo, E.; Chaty, S.; Kruckow, M. U.; van den Heuvel, E. P. J.; Antoniadis, J.; Breton, R. P.; Champion, D. J.

    2017-09-01

    Double neutron star (DNS) systems represent extreme physical objects and the endpoint of an exotic journey of stellar evolution and binary interactions. Large numbers of DNS systems and their mergers are anticipated to be discovered using the Square Kilometre Array searching for radio pulsars, and the high-frequency gravitational wave detectors (LIGO/VIRGO), respectively. Here we discuss all key properties of DNS systems, as well as selection effects, and combine the latest observational data with new theoretical progress on various physical processes with the aim of advancing our knowledge on their formation. We examine key interactions of their progenitor systems and evaluate their accretion history during the high-mass X-ray binary stage, the common envelope phase, and the subsequent Case BB mass transfer, and argue that the first-formed NSs have accreted at most ∼ 0.02 {M}ȯ . We investigate DNS masses, spins, and velocities, and in particular correlations between spin period, orbital period, and eccentricity. Numerous Monte Carlo simulations of the second supernova (SN) events are performed to extrapolate pre-SN stellar properties and probe the explosions. All known close-orbit DNS systems are consistent with ultra-stripped exploding stars. Although their resulting NS kicks are often small, we demonstrate a large spread in kick magnitudes that may, in general, depend on the past interaction history of the exploding star and thus correlate with the NS mass. We analyze and discuss NS kick directions based on our SN simulations. Finally, we discuss the terminal evolution of close-orbit DNS systems until they merge and possibly produce a short γ-ray burst.

  20. Magnetic fields in superconducting neutron stars.

    PubMed

    Lander, S K

    2013-02-15

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

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

    PubMed

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

    2006-04-06

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

  2. Experimental approach to neutron stars

    SciTech Connect

    Leifels, Yvonne

    2014-05-09

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

  3. Pulsar observations and neutron star models

    NASA Technical Reports Server (NTRS)

    Boerner, G.; Cohen, J. M.

    1972-01-01

    Information about the physical parameters of neutron stars is obtained from pulsar observations. The energy balance of the Crab nebula and the Vela X remnant allows derivation of limits for the masses of the Crab and Vela pulsars. Glitch observations provide further clues on the masses of these two pulsars. The degree of confidence in the derived numbers is pointed out. The possibility of observing neutron stars in binary systems as pulsating X-ray sources is discussed. The importance of observing redshifted gamma ray lines from the surface of neutron stars, and thus directly measuring either individual or statistical properties of these objects is pointed out.

  4. Observations of Neutron Stars with NICER

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko

    2016-07-01

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

  5. Position annihilation radiation from neutron stars

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  6. Positron-annihilation radiation from neutron stars.

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  7. Stability of precessing superfluid neutron stars.

    PubMed

    Glampedakis, K; Andersson, N; Jones, D I

    2008-02-29

    We discuss a new superfluid instability occurring in the interior of mature neutron stars with implications for free precession. This instability is similar to the instability which is responsible for the formation of turbulence in superfluid helium. We demonstrate that the instability is unlikely to affect slowly precessing systems with weak superfluid coupling. In contrast, fast precession in systems with strong coupling appears to be generically unstable. This raises serious questions about our understanding of neutron star precession and complicates attempts to constrain neutron star interiors using such observations.

  8. Cyclotron Lines in Accreting Neutron Star Spectra

    NASA Astrophysics Data System (ADS)

    Wilms, Jörn; Schönherr, Gabriele; Schmid, Julia; Dauser, Thomas; Kreykenbohm, Ingo

    2009-05-01

    Cyclotron lines are formed through transitions of electrons between discrete Landau levels in the accretion columns of accreting neutron stars with strong (1012 G) magnetic fields. We summarize recent results on the formation of the spectral continuum of such systems, describe recent advances in the modeling of the lines based on a modification of the commonly used Monte Carlo approach, and discuss new results on the dependence of the measured cyclotron line energy from the luminosity of transient neutron star systems. Finally, we show that Simbol-X will be ideally suited to build and improve the observational database of accreting and strongly magnetized neutron stars.

  9. Optical Pumping / Spin Exchange ^3He Neutron Spin Filter Development

    NASA Astrophysics Data System (ADS)

    Hwang, Shenq-Rong; Coulter, Kevin P.; Chupp, Timothy E.; Welsh, Robert C.

    1998-04-01

    We have instrumented a thermal neutron beam line at the 2MW Ford reactor at the University of Michigan to develop a ^3He neutron spin filter test stand. Due to a large, spin depedent neutron cross section at low energies, polarized ^3He can be used as a neutron spin filter. Our ^3He spin filter is a 10 amagat-cm ^3He cell polarized via optical pumping/spin exchange with Rb. The filter is made of Corning 7056 glass filled with Rb , several atmosphere of ^3He and a few hundred torr nitrogen as buffer gas. We apply two 15W diode array lasers to optically pump Rb. In this presentation we will discuss some progress of this development, including a rotating oven design and a stepping motor driven neutron chopper. Preliminary results of the 10 amagat-cm filter will be presented and compared with theoretical calculations. A study of systematic errors from the data acquisition system and the neutron chopper will also be discussed.

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

    SciTech Connect

    Strohmayer, Tod; Mahmoodifar, Simin

    2014-10-01

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

  11. Neutron Stars in X-ray Binaries and their Environments

    NASA Astrophysics Data System (ADS)

    Paul, Biswajit

    2017-09-01

    Neutron stars in X-ray binary systems are fascinating objects that display a wide range of timing and spectral phenomena in the X-rays. Not only parameters of the neutron stars, like magnetic field strength and spin period evolve in their active binary phase, the neutron stars also affect the binary systems and their immediate surroundings in many ways. Here we discuss some aspects of the interactions of the neutron stars with their environments that are revelaed from their X-ray emission. We discuss some recent developments involving the process of accretion onto high magnetic field neutron stars: accretion stream structure and formation, shape of pulse profile and its changes with accretion torque. Various recent studies of reprocessing of X-rays in the accretion disk surface, vertical structures of the accretion disk and wind of companion star are also discussed here. The X-ray pulsars among the binary neutron stars provide excellent handle to make accurate measurement of the orbital parameters and thus also evolution of the binray orbits that take place over time scale of a fraction of a million years to tens of millions of years. The orbital period evolution of X-ray binaries have shown them to be rather complex systems. Orbital evolution of X-ray binaries can also be carried out from timing of the X-ray eclipses and there have been some surprising results in that direction, including orbital period glitches in two X-ray binaries and possible detection of the most massive circum-binary planet around a Low Mass X-ray Binary.

  12. Neutron spin evolution through broadband current sheet spin flippers

    NASA Astrophysics Data System (ADS)

    Stonaha, P.; Hendrie, J.; Lee, W. T.; Pynn, Roger

    2013-10-01

    Controlled manipulation of neutron spin is a critical tool for many neutron scattering techniques. We have constructed current-sheet, neutron spin flippers for use in Spin Echo Scattering Angle Measurement (SESAME) that comprise pairs of open-faced solenoids which introduce an abrupt field reversal at a shared boundary. The magnetic fields generated by the coils have been mapped and compared with both an analytical approximation and a numerical boundary integral calculation. The agreement is generally good, allowing the former method to be used for rapid calculations of the Larmor phase acquired by a neutron passing through the flipper. The evolution of the neutron spin through the current sheets inside the flipper is calculated for various geometries of the current-carrying conductors, including different wire shapes, arrangements, and common imperfections. The flipping efficiency is found to be sensitive to gaps between wires and between current sheets. SESAME requires flippers with high fields and flipping planes inclined to the neutron beam. To avoid substantial neutron depolarization, such flippers require an interdigitated arrangement of wires.

  13. Neutron spin evolution through broadband current sheet spin flippers.

    PubMed

    Stonaha, P; Hendrie, J; Lee, W T; Pynn, Roger

    2013-10-01

    Controlled manipulation of neutron spin is a critical tool for many neutron scattering techniques. We have constructed current-sheet, neutron spin flippers for use in Spin Echo Scattering Angle Measurement (SESAME) that comprise pairs of open-faced solenoids which introduce an abrupt field reversal at a shared boundary. The magnetic fields generated by the coils have been mapped and compared with both an analytical approximation and a numerical boundary integral calculation. The agreement is generally good, allowing the former method to be used for rapid calculations of the Larmor phase acquired by a neutron passing through the flipper. The evolution of the neutron spin through the current sheets inside the flipper is calculated for various geometries of the current-carrying conductors, including different wire shapes, arrangements, and common imperfections. The flipping efficiency is found to be sensitive to gaps between wires and between current sheets. SESAME requires flippers with high fields and flipping planes inclined to the neutron beam. To avoid substantial neutron depolarization, such flippers require an interdigitated arrangement of wires.

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

    NASA Astrophysics Data System (ADS)

    2011-02-01

    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

  15. Numerical Relativity Simulations of Black Holes Binaries, Neutron Star Binaries, and Neutron Star Oscillations

    NASA Astrophysics Data System (ADS)

    Rosofsky, Shawn; Gold, Roman; Chirenti, Cecilia; Miller, Cole

    2017-01-01

    We present the results of numerical relativity simulations, using the Einstein Toolkit, of black hole binaries, neutron star binaries, and neutron star oscillations. The black hole binary simulations represent the source of LIGO's first gravitational wave detection, GW150914. We compare the gravitational wave output of this simulation with the LIGO data LIGO on GW150914. The neutron star binaries we simulated have different mass ratios and equations of state. These simulations were compared with each other to illustrate the effect of different mass ratios and equations of state on binary evolution and gravitational wave emission. To perform the neutron star oscillation simulations, we applied pressure and density perturbations to the star using specific eigenmodes. These evolutions of the stars were then compared to the expected oscillation frequencies of those excited eigemodes and contrasted with simulations of unperturbed neutron stars.

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

    SciTech Connect

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

    2015-02-24

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

  17. Neutron Star Science with the NuSTAR

    SciTech Connect

    Vogel, J. K.

    2015-10-16

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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

  19. Young Neutron Stars in Extragalactic Supernovae

    NASA Astrophysics Data System (ADS)

    Tehrani, Nathan; Lorimer, D. R.

    2012-01-01

    Pulsars are compact remnants of stellar cores left behind by supernova explosions. They spin rapidly and emit electromagnetic radiation from their magnetic poles, and gradually lose rotational energy. This project tests and expands upon a previous prediction by Perna et al. for the initial spin rates of neutron stars by attempting to model the x-ray emission from extragalactic supernovae. A computer simulation generated a set of pulsars of known initial rotational periods, magnetic field strengths, and ages, and will calculate the expected x-ray luminosities from the known relationship between magnetic field strengths, slow-down rates, and radio luminosities. This experiment expanded upon the original research by incorporating variability in the angle between the magnetic and rotational axes of each pulsar as well as the braking index value, which in the original publication were kept constant. This examines the effect of the angle on pulsars’ x-ray luminosities. The simulated x-ray luminosities were compared to the known x-ray luminosities of known supernova explosions, which served as an upper limit to determine the highest possible initial rotation speeds. Funding was provided through the WVU Summer Undergraduate Research Program.

  20. The Neutron Star Interior Composition Explorer

    NASA Technical Reports Server (NTRS)

    Gendreau, Keith C.

    2008-01-01

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

  1. Transport coefficients in superfluid neutron stars

    SciTech Connect

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

    2016-01-22

    We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.

  2. The Neutron Star Interior Composition Explorer

    NASA Technical Reports Server (NTRS)

    Gendreau, Keith C.

    2008-01-01

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

  3. Early neutron stars and quark matter

    NASA Astrophysics Data System (ADS)

    Li, You-chen; Kong, Xiao-jun; Wei, Cheng-wen; Ge, Yun-zhao

    1988-03-01

    There may exist quark matter inside early hot neutron stars. Using the general method of Baym and Chin, we evaluated the pressure and density at neutron matter — quark matter phase transition for different temperatures and compared the values for stable hot neutron stars. We found (1) that whenever the neutron star temperature exceeds (+10)K, there will be a core of quark matter; (2) that the bag constant B is the most important determining factor of the quark core size. For a given temperature, the core is the larger, the smaller B is; (3) that by the conservation of baryon number, the total energy released by a star during its cooling is about (+53) ergs.

  4. Disruption of light He companions in accreting neutron star binaries

    NASA Astrophysics Data System (ADS)

    Ruderman, M. A.; Shaham, J.

    1985-02-01

    An old neutron star, being spun up to become a radio pulsar by accretion from a very low-mass He secondary, will ultimately tidally disrupt the secondary before the latter's mass reaches 4×10-3M_sun;. Even if angular momentum loss from the binary is carried away only by gravitational radiation, the formation of an isolated, rapidly spinning pulsar in this way will take less than 1010yr.

  5. Direct URCA process in neutron stars

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  6. Chandra Observations of Isolated Neutron Stars

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin

    2006-01-01

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

  7. Astronomers Discover Most Massive Neutron Star Yet Known

    NASA Astrophysics Data System (ADS)

    2010-10-01

    Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered the most massive neutron star yet found, a discovery with strong and wide-ranging impacts across several fields of physics and astrophysics. "This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out," said Paul Demorest, of the National Radio Astronomy Observatory (NRAO). "This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics," he added. Neutron stars are the superdense "corpses" of massive stars that have exploded as supernovae. With all their mass packed into a sphere the size of a small city, their protons and electrons are crushed together into neutrons. A neutron star can be several times more dense than an atomic nucleus, and a thimbleful of neutron-star material would weigh more than 500 million tons. This tremendous density makes neutron stars an ideal natural "laboratory" for studying the most dense and exotic states of matter known to physics. The scientists used an effect of Albert Einstein's theory of General Relativity to measure the mass of the neutron star and its orbiting companion, a white dwarf star. The neutron star is a pulsar, emitting lighthouse-like beams of radio waves that sweep through space as it rotates. This pulsar, called PSR J1614-2230, spins 317 times per second, and the companion completes an orbit in just under nine days. The pair, some 3,000 light-years distant, are in an orbit seen almost exactly edge-on from Earth. That orientation was the key to making the mass measurement. As the orbit carries the white dwarf directly in front of the pulsar, the radio waves from the pulsar that reach Earth must travel very close to the white dwarf. This close passage causes them to be delayed in their arrival by the distortion of

  8. The decompression of cold neutron star matter

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  9. Magnetic field decay in isolated neutron stars

    NASA Technical Reports Server (NTRS)

    Goldreich, Peter; Reisenegger, Andreas

    1992-01-01

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

  10. The decompression of cold neutron star matter

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  11. Neutron star cooling: effects of envelope physics

    SciTech Connect

    Van Riper, K.A.

    1982-01-01

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

  12. Theoretical Studies of Accreting Neutron Stars

    NASA Technical Reports Server (NTRS)

    Taam, Ronald E.

    2003-01-01

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

  13. Neutron stars as laboratories for gravity physics

    SciTech Connect

    Deliduman, Cemsinan

    2014-01-01

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

  14. ULXs: Neutron stars versus black holes

    NASA Astrophysics Data System (ADS)

    King, Andrew; Lasota, Jean-Pierre

    2016-05-01

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

  15. Cooling of Accretion-Heated Neutron Stars

    NASA Astrophysics Data System (ADS)

    Wijnands, Rudy; Degenaar, Nathalie; Page, Dany

    2017-09-01

    We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

  16. Carbon Atmosphere Discovered On Neutron Star

    NASA Astrophysics Data System (ADS)

    2009-11-01

    Evidence for a thin veil of carbon has been found on the neutron star in the Cassiopeia A supernova remnant. This discovery, made with NASA's Chandra X-ray Observatory, resolves a ten-year mystery surrounding this object. "The compact star at the center of this famous supernova remnant has been an enigma since its discovery," said Wynn Ho of the University of Southampton and lead author of a paper that appears in the latest issue of Nature. "Now we finally understand that it can be produced by a hot neutron star with a carbon atmosphere." By analyzing Chandra's X-ray spectrum - akin to a fingerprint of energy - and applying it to theoretical models, Ho and his colleague Craig Heinke, from the University of Alberta, determined that the neutron star in Cassiopeia A, or Cas A for short, has an ultra-thin coating of carbon. This is the first time the composition of an atmosphere of an isolated neutron star has been confirmed. The Chandra "First Light" image of Cas A in 1999 revealed a previously undetected point-like source of X-rays at the center. This object was presumed to be a neutron star, the typical remnant of an exploded star, but researchers were unable to understand its properties. Defying astronomers' expectations, this object did not show any X-ray or radio pulsations or any signs of radio pulsar activity. By applying a model of a neutron star with a carbon atmosphere to this object, Ho and Heinke found that the region emitting X-rays would uniformly cover a typical neutron star. This would explain the lack of X-ray pulsations because -- like a lightbulb that shines consistently in all directions -- this neutron star would be unlikely to display any changes in its intensity as it rotates. Scientists previously have used a neutron star model with a hydrogen atmosphere giving a much smaller emission area, corresponding to a hot spot on a typical neutron star, which should produce X-ray pulsations as it rotates. Interpreting the hydrogen atmosphere model

  17. Dynamical stability of nascent neutron stars

    NASA Astrophysics Data System (ADS)

    Liu, Yuk Tung

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

  18. Relativistic tidal properties of neutron stars

    SciTech Connect

    Damour, Thibault; Nagar, Alessandro

    2009-10-15

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

  19. Neutron Stars and the Discovery of Pulsars.

    ERIC Educational Resources Information Center

    Greenstein, George

    1985-01-01

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

  20. Neutron Stars and the Discovery of Pulsars.

    ERIC Educational Resources Information Center

    Greenstein, George

    1985-01-01

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

  1. Upper Limits on the Rates of Binary Neutron Star and Neutron Star-Black Hole Mergers from Advanced LIGO’s First Observing Run

    NASA Astrophysics Data System (ADS)

    Abbott, B. P.; Abbott, R.; Abbott, T. D.; Abernathy, M. R.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X.; Adya, V. B.; Affeldt, C.; Agathos, M.; Agatsuma, K.; Aggarwal, N.; Aguiar, O. D.; Aiello, L.; Ain, A.; Ajith, P.; Allen, B.; Allocca, A.; Altin, P. A.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Araya, M. C.; Arceneaux, C. C.; Areeda, J. S.; Arnaud, N.; Arun, K. G.; Ascenzi, S.; Ashton, G.; Ast, M.; Aston, S. M.; Astone, P.; Aufmuth, P.; Aulbert, C.; Babak, S.; Bacon, P.; Bader, M. K. M.; Baker, P. T.; Baldaccini, F.; Ballardin, G.; Ballmer, S. W.; Barayoga, J. C.; Barclay, S. E.; Barish, B. C.; Barker, D.; Barone, F.; Barr, B.; Barsotti, L.; Barsuglia, M.; Barta, D.; Bartlett, J.; Bartos, I.; Bassiri, R.; Basti, A.; Batch, J. C.; Baune, C.; Bavigadda, V.; Bazzan, M.; Bejger, M.; Bell, A. S.; Berger, B. K.; Bergmann, G.; Berry, C. P. L.; Bersanetti, D.; Bertolini, A.; Betzwieser, J.; Bhagwat, S.; Bhandare, R.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Birney, R.; Biscans, S.; Bisht, A.; Bitossi, M.; Biwer, C.; Bizouard, M. A.; Blackburn, J. K.; Blair, C. D.; Blair, D. G.; Blair, R. M.; Bloemen, S.; Bock, O.; Boer, M.; Bogaert, G.; Bogan, C.; Bohe, A.; Bond, C.; Bondu, F.; Bonnand, R.; Boom, B. A.; Bork, R.; Boschi, V.; Bose, S.; Bouffanais, Y.; Bozzi, A.; Bradaschia, C.; Brady, P. R.; Braginsky, V. B.; Branchesi, M.; Brau, J. E.; Briant, T.; Brillet, A.; Brinkmann, M.; Brisson, V.; Brockill, P.; Broida, J. E.; Brooks, A. F.; Brown, D. A.; Brown, D. D.; Brown, N. M.; Brunett, S.; Buchanan, C. C.; Buikema, A.; Bulik, T.; Bulten, H. J.; Buonanno, A.; Buskulic, D.; Buy, C.; Byer, R. L.; Cabero, M.; Cadonati, L.; Cagnoli, G.; Cahillane, C.; Calderón Bustillo, J.; Callister, T.; Calloni, E.; Camp, J. B.; Cannon, K. C.; Cao, J.; Capano, C. D.; Capocasa, E.; Carbognani, F.; Caride, S.; Casanueva Diaz, J.; Casentini, C.; Caudill, S.; Cavaglià, M.; Cavalier, F.; Cavalieri, R.; Cella, G.; Cepeda, C. B.; Cerboni Baiardi, L.; Cerretani, G.; Cesarini, E.; Chamberlin, S. J.; Chan, M.; Chao, S.; Charlton, P.; Chassande-Mottin, E.; Cheeseboro, B. D.; Chen, H. Y.; Chen, Y.; Cheng, C.; Chincarini, A.; Chiummo, A.; Cho, H. S.; Cho, M.; Chow, J. H.; Christensen, N.; Chu, Q.; Chua, S.; Chung, S.; Ciani, G.; Clara, F.; Clark, J. A.; Cleva, F.; Coccia, E.; Cohadon, P.-F.; Colla, A.; Collette, C. G.; Cominsky, L.; Constancio., M., Jr.; Conte, A.; Conti, L.; Cook, D.; Corbitt, T. R.; Cornish, N.; Corsi, A.; Cortese, S.; Costa, C. A.; Coughlin, M. W.; Coughlin, S. B.; Coulon, J.-P.; Countryman, S. T.; Couvares, P.; Cowan, E. E.; Coward, D. M.; Cowart, M. J.; Coyne, D. C.; Coyne, R.; Craig, K.; Creighton, J. D. E.; Cripe, J.; Crowder, S. G.; Cumming, A.; Cunningham, L.; Cuoco, E.; Dal Canton, T.; Danilishin, S. L.; D'Antonio, S.; Danzmann, K.; Darman, N. S.; Dasgupta, A.; Da Silva Costa, C. F.; Dattilo, V.; Dave, I.; Davier, M.; Davies, G. S.; Daw, E. J.; Day, R.; De, S.; DeBra, D.; Debreczeni, G.; Degallaix, J.; De Laurentis, M.; Deléglise, S.; Del Pozzo, W.; Denker, T.; Dent, T.; Dergachev, V.; De Rosa, R.; DeRosa, R. T.; DeSalvo, R.; Devine, R. C.; Dhurandhar, S.; Díaz, M. C.; Di Fiore, L.; Di Giovanni, M.; Di Girolamo, T.; Di Lieto, A.; Di Pace, S.; Di Palma, I.; Di Virgilio, A.; Dolique, V.; Donovan, F.; Dooley, K. L.; Doravari, S.; Douglas, R.; Downes, T. P.; Drago, M.; Drever, R. W. P.; Driggers, J. C.; Ducrot, M.; Dwyer, S. E.; Edo, T. B.; Edwards, M. C.; Effler, A.; Eggenstein, H.-B.; Ehrens, P.; Eichholz, J.; Eikenberry, S. S.; Engels, W.; Essick, R. C.; Etzel, T.; Evans, M.; Evans, T. M.; Everett, R.; Factourovich, M.; Fafone, V.; Fair, H.; Fairhurst, S.; Fan, X.; Fang, Q.; Farinon, S.; Farr, B.; Farr, W. M.; Favata, M.; Fays, M.; Fehrmann, H.; Fejer, M. M.; Fenyvesi, E.; Ferrante, I.; Ferreira, E. C.; Ferrini, F.; Fidecaro, F.; Fiori, I.; Fiorucci, D.; Fisher, R. P.; Flaminio, R.; Fletcher, M.; Fournier, J.-D.; Frasca, S.; Frasconi, F.; Frei, Z.; Freise, A.; Frey, R.; Frey, V.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Gabbard, H. A. G.; Gair, J. R.; Gammaitoni, L.; Gaonkar, S. G.; Garufi, F.; Gaur, G.; Gehrels, N.; Gemme, G.; Geng, P.; Genin, E.; Gennai, A.; George, J.; Gergely, L.; Germain, V.; Ghosh, Abhirup; Ghosh, Archisman; Ghosh, S.; Giaime, J. A.; Giardina, K. D.; Giazotto, A.; Gill, K.; Glaefke, A.; Goetz, E.; Goetz, R.; Gondan, L.; González, G.; Gonzalez Castro, J. M.; Gopakumar, A.; Gordon, N. A.; Gorodetsky, M. L.; Gossan, S. E.; Gosselin, M.; Gouaty, R.; Grado, A.; Graef, C.; Graff, P. B.; Granata, M.; Grant, A.; Gras, S.; Gray, C.; Greco, G.; Green, A. C.; Groot, P.; Grote, H.; Grunewald, S.; Guidi, G. M.; Guo, X.; Gupta, A.; Gupta, M. K.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hacker, J. J.; Hall, B. R.; Hall, E. D.; Hammond, G.; Haney, M.; Hanke, M. M.; Hanks, J.; Hanna, C.; Hannam, M. D.; Hanson, J.; Hardwick, T.; Harms, J.; Harry, G. M.; Harry, I. W.; Hart, M. J.; Hartman, M. T.; Haster, C.-J.; Haughian, K.; Heidmann, A.; Heintze, M. C.; Heitmann, H.; Hello, P.; Hemming, G.; Hendry, M.; Heng, I. S.; Hennig, J.; Henry, J.; Heptonstall, A. W.; Heurs, M.; Hild, S.; Hoak, D.; Hofman, D.; Holt, K.; Holz, D. E.; Hopkins, P.; Hough, J.; Houston, E. A.; Howell, E. J.; Hu, Y. M.; Huang, S.; Huerta, E. A.; Huet, D.; Hughey, B.; Husa, S.; Huttner, S. H.; Huynh-Dinh, T.; Indik, N.; Ingram, D. R.; Inta, R.; Isa, H. N.; Isac, J.-M.; Isi, M.; Isogai, T.; Iyer, B. R.; Izumi, K.; Jacqmin, T.; Jang, H.; Jani, K.; Jaranowski, P.; Jawahar, S.; Jian, L.; Jiménez-Forteza, F.; Johnson, W. W.; Jones, D. I.; Jones, R.; Jonker, R. J. G.; Ju, L.; K, Haris; Kalaghatgi, C. V.; Kalogera, V.; Kandhasamy, S.; Kang, G.; Kanner, J. B.; Kapadia, S. J.; Karki, S.; Karvinen, K. S.; Kasprzack, M.; Katsavounidis, E.; Katzman, W.; Kaufer, S.; Kaur, T.; Kawabe, K.; Kéfélian, F.; Kehl, M. S.; Keitel, D.; Kelley, D. B.; Kells, W.; Kennedy, R.; Key, J. S.; Khalili, F. Y.; Khan, I.; Khan, S.; Khan, Z.; Khazanov, E. A.; Kijbunchoo, N.; Kim, Chi-Woong; Kim, Chunglee; Kim, J.; Kim, K.; Kim, N.; Kim, W.; Kim, Y.-M.; Kimbrell, S. J.; King, E. J.; King, P. J.; Kissel, J. S.; Klein, B.; Kleybolte, L.; Klimenko, S.; Koehlenbeck, S. M.; Koley, S.; Kondrashov, V.; Kontos, A.; Korobko, M.; Korth, W. Z.; Kowalska, I.; Kozak, D. B.; Kringel, V.; Krishnan, B.; Królak, A.; Krueger, C.; Kuehn, G.; Kumar, P.; Kumar, R.; Kuo, L.; Kutynia, A.; Lackey, B. D.; Landry, M.; Lange, J.; Lantz, B.; Lasky, P. D.; Laxen, M.; Lazzarini, A.; Lazzaro, C.; Leaci, P.; Leavey, S.; Lebigot, E. O.; Lee, C. H.; Lee, H. K.; Lee, H. M.; Lee, K.; Lenon, A.; Leonardi, M.; Leong, J. R.; Leroy, N.; Letendre, N.; Levin, Y.; Lewis, J. B.; Li, T. G. F.; Libson, A.; Littenberg, T. B.; Lockerbie, N. A.; Lombardi, A. L.; London, L. T.; Lord, J. E.; Lorenzini, M.; Loriette, V.; Lormand, M.; Losurdo, G.; Lough, J. D.; Lück, H.; Lundgren, A. P.; Lynch, R.; Ma, Y.; Machenschalk, B.; MacInnis, M.; Macleod, D. M.; Magaña-Sandoval, F.; Magaña Zertuche, L.; Magee, R. M.; Majorana, E.; Maksimovic, I.; Malvezzi, V.; Man, N.; Mandic, V.; Mangano, V.; Mansell, G. L.; Manske, M.; Mantovani, M.; Marchesoni, F.; Marion, F.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martelli, F.; Martellini, L.; Martin, I. W.; Martynov, D. V.; Marx, J. N.; Mason, K.; Masserot, A.; Massinger, T. J.; Masso-Reid, M.; Mastrogiovanni, S.; Matichard, F.; Matone, L.; Mavalvala, N.; Mazumder, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McGuire, S. C.; McIntyre, G.; McIver, J.; McManus, D. J.; McRae, T.; McWilliams, S. T.; Meacher, D.; Meadors, G. D.; Meidam, J.; Melatos, A.; Mendell, G.; Mercer, R. A.; Merilh, E. L.; Merzougui, M.; Meshkov, S.; Messenger, C.; Messick, C.; Metzdorff, R.; Meyers, P. M.; Mezzani, F.; Miao, H.; Michel, C.; Middleton, H.; Mikhailov, E. E.; Milano, L.; Miller, A. L.; Miller, A.; Miller, B. B.; Miller, J.; Millhouse, M.; Minenkov, Y.; Ming, J.; Mirshekari, S.; Mishra, C.; Mitra, S.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Moggi, A.; Mohan, M.; Mohapatra, S. R. P.; Montani, M.; Moore, B. C.; Moore, C. J.; Moraru, D.; Moreno, G.; Morriss, S. R.; Mossavi, K.; Mours, B.; Mow-Lowry, C. M.; Mueller, G.; Muir, A. W.; Mukherjee, Arunava; Mukherjee, D.; Mukherjee, S.; Mukund, N.; Mullavey, A.; Munch, J.; Murphy, D. J.; Murray, P. G.; Mytidis, A.; Nardecchia, I.; Naticchioni, L.; Nayak, R. K.; Nedkova, K.; Nelemans, G.; Nelson, T. J. N.; Neri, M.; Neunzert, A.; Newton, G.; Nguyen, T. T.; Nielsen, A. B.; Nissanke, S.; Nitz, A.; Nocera, F.; Nolting, D.; Normandin, M. E. N.; Nuttall, L. K.; Oberling, J.; Ochsner, E.; O'Dell, J.; Oelker, E.; Ogin, G. H.; Oh, J. J.; Oh, S. H.; Ohme, F.; Oliver, M.; Oppermann, P.; Oram, Richard J.; O'Reilly, B.; O'Shaughnessy, R.; Ottaway, D. J.; Overmier, H.; Owen, B. J.; Pai, A.; Pai, S. A.; Palamos, J. R.; Palashov, O.; Palomba, C.; Pal-Singh, A.; Pan, H.; Pankow, C.; Pannarale, F.; Pant, B. C.; Paoletti, F.; Paoli, A.; Papa, M. A.; Paris, H. R.; Parker, W.; Pascucci, D.; Pasqualetti, A.; Passaquieti, R.; Passuello, D.; Patricelli, B.; Patrick, Z.; Pearlstone, B. L.; Pedraza, M.; Pedurand, R.; Pekowsky, L.; Pele, A.; Penn, S.; Perreca, A.; Perri, L. M.; Phelps, M.; Piccinni, O. J.; Pichot, M.; Piergiovanni, F.; Pierro, V.; Pillant, G.; Pinard, L.; Pinto, I. M.; Pitkin, M.; Poe, M.; Poggiani, R.; Popolizio, P.; Post, A.; Powell, J.; Prasad, J.; Predoi, V.; Prestegard, T.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prodi, G. A.; Prokhorov, L.; Puncken, O.; Punturo, M.; Puppo, P.; Pürrer, M.; Qi, H.; Qin, J.; Qiu, S.; Quetschke, V.; Quintero, E. A.; Quitzow-James, R.; Raab, F. J.; Rabeling, D. S.; Radkins, H.; Raffai, P.; Raja, S.; Rajan, C.; Rakhmanov, M.; Rapagnani, P.; Raymond, V.; Razzano, M.; Re, V.; Read, J.; Reed, C. M.; Regimbau, T.; Rei, L.; Reid, S.; Reitze, D. H.; Rew, H.; Reyes, S. D.; Ricci, F.; Riles, K.; Rizzo, M.; Robertson, N. A.; Robie, R.; Robinet, F.; Rocchi, A.; Rolland, L.; Rollins, J. G.; Roma, V. J.; Romano, R.; Romanov, G.; Romie, J. H.; Rosińska, D.; Rowan, S.; Rüdiger, A.; Ruggi, P.; Ryan, K.; Sachdev, S.; Sadecki, T.; Sadeghian, L.; Sakellariadou, M.; Salconi, L.; Saleem, M.; Salemi, F.; Samajdar, A.; Sammut, L.; Sanchez, E. J.; Sandberg, V.; Sandeen, B.; Sanders, J. R.; Sassolas, B.; Sathyaprakash, B. S.; Saulson, P. R.; Sauter, O. E. S.; Savage, R. L.; Sawadsky, A.; Schale, P.; Schilling, R.; Schmidt, J.; Schmidt, P.; Schnabel, R.; Schofield, R. M. S.; Schönbeck, A.; Schreiber, E.; Schuette, D.; Schutz, B. F.; Scott, J.; Scott, S. M.; Sellers, D.; Sengupta, A. S.; Sentenac, D.; Sequino, V.; Sergeev, A.; Setyawati, Y.; Shaddock, D. A.; Shaffer, T.; Shahriar, M. S.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Sheperd, A.; Shoemaker, D. H.; Shoemaker, D. M.; Siellez, K.; Siemens, X.; Sieniawska, M.; Sigg, D.; Silva, A. D.; Singer, A.; Singer, L. P.; Singh, A.; Singh, R.; Singhal, A.; Sintes, A. M.; Slagmolen, B. J. J.; Smith, J. R.; Smith, N. D.; Smith, R. J. E.; Son, E. J.; Sorazu, B.; Sorrentino, F.; Souradeep, T.; Srivastava, A. K.; Staley, A.; Steinke, M.; Steinlechner, J.; Steinlechner, S.; Steinmeyer, D.; Stephens, B. C.; Stone, R.; Strain, K. A.; Straniero, N.; Stratta, G.; Strauss, N. A.; Strigin, S.; Sturani, R.; Stuver, A. L.; Summerscales, T. Z.; Sun, L.; Sunil, S.; Sutton, P. J.; Swinkels, B. L.; Szczepańczyk, M. J.; Tacca, M.; Talukder, D.; Tanner, D. B.; Tápai, M.; Tarabrin, S. P.; Taracchini, A.; Taylor, R.; Theeg, T.; Thirugnanasambandam, M. P.; Thomas, E. G.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Tiwari, S.; Tiwari, V.; Tokmakov, K. V.; Toland, K.; Tomlinson, C.; Tonelli, M.; Tornasi, Z.; Torres, C. V.; Torrie, C. I.; Töyrä, D.; Travasso, F.; Traylor, G.; Trifirò, D.; Tringali, M. C.; Trozzo, L.; Tse, M.; Turconi, M.; Tuyenbayev, D.; Ugolini, D.; Unnikrishnan, C. S.; Urban, A. L.; Usman, S. A.; Vahlbruch, H.; Vajente, G.; Valdes, G.; van Bakel, N.; van Beuzekom, M.; van den Brand, J. F. J.; Van Den Broeck, C.; Vander-Hyde, D. C.; van der Schaaf, L.; van Heijningen, J. V.; van Veggel, A. A.; Vardaro, M.; Vass, S.; Vasúth, M.; Vaulin, R.; Vecchio, A.; Vedovato, G.; Veitch, J.; Veitch, P. J.; Venkateswara, K.; Verkindt, D.; Vetrano, F.; Viceré, A.; Vinciguerra, S.; Vine, D. J.; Vinet, J.-Y.; Vitale, S.; Vo, T.; Vocca, H.; Vorvick, C.; Voss, D. V.; Vousden, W. D.; Vyatchanin, S. P.; Wade, A. R.; Wade, L. E.; Wade, M.; Walker, M.; Wallace, L.; Walsh, S.; Wang, G.; Wang, H.; Wang, M.; Wang, X.; Wang, Y.; Ward, R. L.; Warner, J.; Was, M.; Weaver, B.; Wei, L.-W.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Weßels, P.; Westphal, T.; Wette, K.; Whelan, J. T.; Whiting, B. F.; Williams, R. D.; Williamson, A. R.; Willis, J. L.; Willke, B.; Wimmer, M. H.; Winkler, W.; Wipf, C. C.; Wittel, H.; Woan, G.; Woehler, J.; Worden, J.; Wright, J. L.; Wu, D. S.; Wu, G.; Yablon, J.; Yam, W.; Yamamoto, H.; Yancey, C. C.; Yu, H.; Yvert, M.; Zadrożny, A.; Zangrando, L.; Zanolin, M.; Zendri, J.-P.; Zevin, M.; Zhang, L.; Zhang, M.; Zhang, Y.; Zhao, C.; Zhou, M.; Zhou, Z.; Zhu, X. J.; Zucker, M. E.; Zuraw, S. E.; Zweizig, J.; LIGO Scientific Collaboration; Virgo Collaboration

    2016-12-01

    We report here the non-detection of gravitational waves from the merger of binary-neutron star systems and neutron star-black hole systems during the first observing run of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). In particular, we searched for gravitational-wave signals from binary-neutron star systems with component masses \\in [1,3] {M}⊙ and component dimensionless spins <0.05. We also searched for neutron star-black hole systems with the same neutron star parameters, black hole mass \\in [2,99] {M}⊙ , and no restriction on the black hole spin magnitude. We assess the sensitivity of the two LIGO detectors to these systems and find that they could have detected the merger of binary-neutron star systems with component mass distributions of 1.35 ± 0.13 M ⊙ at a volume-weighted average distance of ˜70 Mpc, and for neutron star-black hole systems with neutron star masses of 1.4 M ⊙ and black hole masses of at least 5 M ⊙, a volume-weighted average distance of at least ˜110 Mpc. From this we constrain with 90% confidence the merger rate to be less than 12,600 Gpc-3 yr-1 for binary-neutron star systems and less than 3600 Gpc-3 yr-1 for neutron star-black hole systems. We discuss the astrophysical implications of these results, which we find to be in conflict with only the most optimistic predictions. However, we find that if no detection of neutron star-binary mergers is made in the next two Advanced LIGO and Advanced Virgo observing runs we would place significant constraints on the merger rates. Finally, assuming a rate of {10}-7+20 Gpc-3 yr-1, short gamma-ray bursts beamed toward the Earth, and assuming that all short gamma-ray bursts have binary-neutron star (neutron star-black hole) progenitors, we can use our 90% confidence rate upper limits to constrain the beaming angle of the gamma-ray burst to be greater than 2\\buildrel{\\circ}\\over{.} {3}-1.1+1.7 (4\\buildrel{\\circ}\\over{.} {3}-1.9+3.1).

  2. Local distribution of old neutron stars

    NASA Technical Reports Server (NTRS)

    Frei, Szolt; Huang, Xiaolan; Paczynski, Bohdan

    1992-01-01

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

  3. Spin equilibrium in strongly magnetized accreting stars

    NASA Astrophysics Data System (ADS)

    D'Angelo, C. R.

    2017-09-01

    Strongly magnetized accreting stars are often hypothesized to be in 'spin equilibrium' with their surrounding accretion flows, which requires that the accretion rate changes more slowly than it takes the star to reach spin equilibrium. This is not true for most magnetically accreting stars, which have strongly variable accretion outbursts on time-scales much shorter than the time it would take to reach spin equilibrium. This paper examines how accretion outbursts affect the time a star takes to reach spin equilibrium and its final equilibrium spin period. I consider several different models for angular momentum loss - either carried away in an outflow, lost to a stellar wind, or transferred back to the accretion disc (the 'trapped disc'). For transient sources, the outflow scenario leads to significantly longer times to reach spin equilibrium (∼10 ×), and shorter equilibrium spin periods than would be expected from spin equilibrium arguments, while the 'trapped disc' does not. The results suggest that disc trapping plays a significant role in the spin evolution of strongly magnetic stars, with some caveats for young stellar objects.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  5. Equation-of-state-independent relations in neutron stars

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  6. Flux-Vortex Pinning and Neutron Star Evolution

    NASA Astrophysics Data System (ADS)

    Alpar, M. Ali

    2017-09-01

    G. Srinivasan et al. (1990) proposed a simple and elegant explanation for the reduction of the neutron star magnetic dipole moment during binary evolution leading to low mass X-ray binaries and eventually to millisecond pulsars: Quantized vortex lines in the neutron star core superfluid will pin against the quantized flux lines of the proton superconductor. As the neutron star spins down in the wind accretion phase of binary evolution, outward motion of vortex lines will reduce the dipole magnetic moment in proportion to the rotation rate. The presence of a toroidal array of flux lines makes this mechanism inevitable and independent of the angle between the rotation and magnetic axes. The incompressibility of the flux-line array (Abrikosov lattice) determines the epoch when the mechanism will be effective throughout the neutron star. Flux vortex pinning will not be effective during the initial young radio pulsar phase. It will, however, be effective and reduce the dipole moment in proportion with the rotation rate during the epoch of spindown by wind accretion as proposed by Srinivasan et al. The mechanism operates also in the presence of vortex creep.

  7. Cyg X-1 - A massive neutron star

    NASA Technical Reports Server (NTRS)

    Goldman, I.

    1981-01-01

    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.

  8. Forecasting neutron star temperatures: predictability and variability.

    PubMed

    Page, Dany; Reddy, Sanjay

    2013-12-13

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

  9. Outer crust of nonaccreting cold neutron stars

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

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

  10. Outer crust of nonaccreting cold neutron stars

    SciTech Connect

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

    2006-03-15

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

  11. Neutron single target spin asymmetries in SIDIS

    SciTech Connect

    Cisbani, Evaristo

    2010-04-01

    The experiment E06-010 in Hall A at Jefferson Lab took data between November 2008 and February 2009 to directly measure, for the first time, the pion (and kaon) single "neutron" target-spin asymmetry (SSA) in semi-inclusive DIS from a polarized 3He target. Collins, Sivers (and Pretzelosity) neutron asymmetries are going to be extracted from the measured SSA. Details of the experiment are described together with the preliminary results of the ongoing analysis. Near future Hall A experiments on transverse nucleon spin structure are shorty reviewed.

  12. HYPERACCRETING NEUTRON STAR DISKS AND NEUTRINO ANNIHILATION

    SciTech Connect

    Zhang Dong; Dai, Z. G. E-mail: dzg@nju.edu.c

    2009-09-20

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

  13. Neutron stars including the effects of chaotic magnetic fields and anomalous magnetic moments

    NASA Astrophysics Data System (ADS)

    Wu, Fei; Wu, Chen; Ren, Zhong-Zhou

    2017-04-01

    The relativistic mean field (RMF) FSUGold model extended to include hyperons is employed to study the properties of neutron stars with strong magnetic fields. The chaotic magnetic field approximation is utilized. The effect of anomalous magnetic moments (AMMs) is also investigated. It is shown that the equation of state (EOS) of neutron star matter is stiffened by the presence of the magnetic field, which increases the maximum mass of a neutron star by around 6%. The AMMs only have a small influence on the EOS of neutron star matter, and increase the maximum mass of a neutron star by 0.02M sun. Neutral particles are spin polarized due to the presence of the AMMs. Supported by National Natural Science Foundation of China (11535004, 11375086, 11120101005, 11175085, 11235001), 973 National Major State Basic Research and Development of China (2013CB834400), and Science and Technology Development Fund of Macau (068/2011/A)

  14. Limiting rotational period of neutron stars

    NASA Astrophysics Data System (ADS)

    Glendenning, Norman K.

    1992-11-01

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

  15. Limiting rotational period of neutron stars

    SciTech Connect

    Glendenning, N.K. )

    1992-11-15

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

  16. Spin distribution in neutron induced preequilibrium reactions

    SciTech Connect

    Dashdorj, D; Kawano, T; Chadwick, M; Devlin, M; Fotiades, N; Nelson, R O; Mitchell, G E; Garrett, P E; Agvaanluvsan, U; Becker, J A; Bernstein, L A; Macri, R; Younes, W

    2005-10-04

    The preequilibrium reaction mechanism makes an important contribution to neutron-induced reactions above E{sub n} {approx} 10 MeV. The preequilibrium process has been studied exclusively via the characteristic high energy neutrons produced at bombarding energies greater than 10 MeV. They are expanding the study of the preequilibrium reaction mechanism through {gamma}-ray spectroscopy. Cross-section measurements were made of prompt {gamma}-ray production as a function of incident neutron energy (E{sub n} = 1 to 250 MeV) on a {sup 48}Ti sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center facility. The prompt-reaction {gamma} rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Residual state population was predicted using the GNASH reaction code, enhanced for preequilibrium. The preequilibrium reaction spin distribution was calculated using the quantum mechanical theory of Feshback, Kerman, and Koonin (FKK). The multistep direct part of the FKK theory was calculated for a one-step process. The FKK preequilibrium spin distribution was incorporated into the GNASH calculations and the {gamma}-ray production cross sections were calculated and compared with experimental data. The difference in the partial {gamma}-ray cross sections using spin distributions with and without preequilibrium effects is significant.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  19. Neutron star accretion and the neutrino fireball

    NASA Astrophysics Data System (ADS)

    Colgate, Stirling A.; Herant, Marc; Benz, Willy

    1993-05-01

    We suggest a mechanism for driving supernova explosions through neutrino energy deposition beyond the formation and the cooling of the neutron star. The mechanism depends upon convection next to the neutron star and terminates when the entropy of buoyant bubbles increases sufficiently due to neutrino heating to shut off the down flow of low entropy matter. This convection is initially caused by the heat deposited from neutrinos emitted by the cooling neutron star in a region gravitationally dominated by the neutron star. This convection by providing an efficient heat transport mechanism avoids the overheating and excessive neutrino energy losses in the regions close to the neutron stars and has been recently modeled by Herant, Benz and Colgate. In this model the explosion shock, initially driven by the bounce followed by neutron star derived neutrino heating is further driven by the up flow of the bouyant, high entropy bubbles. The down flow between the bubbles of low entropy matter originating from behind the bounce and later the explosion shock will build up a modest entropy atmosphere in pressure equilibrium with the surface of the cooling neutron star. For modest entropies, Srad ~ 10 or Stotal ~ 18 and condensed neutron stars, R/M ~ 10 km per solar mass, the total mass of such an atmosphere is small, 1.7 × 10-3 Msolar, but the temperature at the base of such an atmosphere is extremely high, T ~ 10 MeV. The paradoxical result of neutrino emission is to further condense the atmosphere and increase the temperature until the compression heating is exceeded by the neutrino emission. The absolute limit of compression heating is free fall collapse, which may be approached but not exceeded. Such an accretion event approaching this limit may reach a temperature high enough to create a neutrino ``fireball'', a region hot enough, ~ 11 MeV, so as to be partially opaque to its own (neutrino) radiation. The further heating of the already high entropy bubbles by the neutrino

  20. The population of highly magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Gomes, R. O.; Dexheimer, V.; Franzon, B.; Schramm, S.

    2017-06-01

    In this work, we study the effects of strong magnetic field configurations on the population of neutron stars. The stellar matter is described within a relativistic mean field formalism which considers many-body force contributions in the scalar couplings. We choose the parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive hyperon stars. Hadronic matter is modeled at zero temperature, in beta-equilibrium, charge neutral and populated by the baryonic octet, electrons and muons. Magnetic effects are taken into account in the structure of stars by the solution of the Einstein-Maxwell equations with the assumption of a poloidal magnetic field distribution. Our results show that magnetic neutron stars are populated essencialy by nucleons and leptons, due to the fact that strong magnetic fields decrease the central density of stars and, hence, supress the appearance of exotic particles.

  1. Dissipative processes in superfluid neutron stars

    SciTech Connect

    Mannarelli, Massimo; Colucci, Giuseppe; Manuel, Cristina

    2011-05-23

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

  2. Higher spin states in neutron rich nuclei

    NASA Astrophysics Data System (ADS)

    Zhu, S.; Zhao, X.; Hamilton, J. H.; Ramayya, A. V.; Ma, W. C.; Peker, L. K.; Kormicki, J.; Hong, X.; Gao, W. B.; Deng, J. K.

    Nuclei on the neutron rich side of beta stability have long been of interest for nuclear structure studies because they probe different regions of the single particle spectrum and different shell gap combinations for both spherical and deformed shapes. However, such nuclei have been a difficult challenge experimentally. Much information has been gained about the properties of neutron rich nuclei at low spin from the study of radioactive isotopes produced in neutron induced, and more recently, proton induced fission of uranium. Such studies have been made possible by the use of isotope separators on line to reactors and more recently to low energy proton accelerators. However, to test many of the theoretical predictions of nuclear models one needs information about the higher spin states in nuclei in addition to their low spin states populated in radioactive decays. Higher spin states in neutron rich nuclei have been an even more difficult challenge than the lower spin states accessible through decay studies. One cannot reach the higher spin states in these nuclei by heavy ion fusion evaporation in reactions as carried out extensively for proton rich nuclei. Many years ago prompt spontaneous fission studies were used to suggest for the first time that Sr-98 and Zr-100 had unusually large ground state of deformations. The availability of higher efficiency multi-detector arrays of Compton suppressed Ge detectors has brought on a renewed interest in studies of the prompt gamma rays of the fragments from spontaneous and induced fission. Groups at Argonne, Daresbury, and a Vanderbilt-Oak Ridge-Idaho-Dubna collaboration have carried out several such studies from spontaneous and heavy-ion induced fission which have revealed new insights into our knowledge of neutron rich nuclei. This paper is primarily a review of these studies, including recent, unpublished results.

  3. The spectra of weakly magnetized neutron stars

    NASA Technical Reports Server (NTRS)

    Fu, Albert; Taam, Ronald E.

    1990-01-01

    The continuum spectrum of a rotating equatorial emitting region on the surface of an accreting neutron star is investigated within the Schwarzschild spacetime. It is found that the dominant general relativistic effect is the increase in apparent emission area from the neutron star surface due to gravitational light bending. For typical neutron star parameters, the apparent area of the accretion belt is remarkably independent of the viewing angle and, hence, the contribution for a boundary layer to the total X-ray luminosity is found to depend only weakly on the inclination angle of the binary system. For a blackbody spectrum in the local rest frame of the emitting surface, the distortion of the spectral shape by longitudinal and transverse Doppler shifts is minimal for neutron stars rotating at periods greater than about 2 ms. It is shown that the failure to detect a blackbody component from the weakly magnetized neutron star surface in some X-ray burst sources during their quiescent state may be related to the presence of temperature variations along the vertical extent of the boundary layer.

  4. From ultracold Fermi Gases to Neutron Stars

    NASA Astrophysics Data System (ADS)

    Salomon, Christophe

    2012-02-01

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

  5. ^3He neutron spin filters for polarized neutron scattering.

    NASA Astrophysics Data System (ADS)

    Chen, Wangchun; Borchers, Julie; Chen, Ying; O'Donovan, Kevin; Erwin, Ross; Lynn, Jeffrey; Majkrzak, Charles; McKenney, Sarah; Gentile, Thomas

    2006-03-01

    Polarized neutron scattering (PNS) is a powerful tool that probes the magnetic structures in a wide variety of magnetic materials. Polarized ^3He gas, produced by optical pumping, can be used to polarize or analyze neutron beams because of the strong spin dependence of the neutron absorption cross section for ^3He. Polarized ^3He neutron spin filters (NSF) have been of great interest in PNS community due to recent significant improvement of their performance. Here I will discuss successful applications using ^3He NSFs in polarized neutron reflectometry (PNR) and triple-axis spectrometry (TAS). In PNR, a ^3He NSF in conjunction with a position-sensitive detector allows for efficient polarization analysis of off-specular scattering over a broad range of reciprocal space. In TAS, a ^3He NSF in combination with a double focusing pyrolytic graphite monochromator provides greater versatility and higher intensity compared to a Heusler polarizer. Finally I will present the results from patterned magnetically-coupled thin films in PNR and our first ``proof-of-principle'' experiment in TAS, both of which were performed using ^3He NSF(s) at the NIST Center for Neutron Research.

  6. Evolutions of magnetized and rotating neutron stars

    SciTech Connect

    Liebling, Steven L.; Lehner, Luis; Neilsen, David; Palenzuela, Carlos

    2010-06-15

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

  7. Effective spin-spin interaction in neutron matter

    SciTech Connect

    Zverev, M.V.; Khafizov, R.U.; Khodel, V.A.; Shaginyan, V.R.

    1995-09-01

    A set of equations for calculating the effective-interaction matrix R{sup ik}(q, {omega}) and the response function X{sup ik}(q, {omega}) is derived. These equations take into account the spin degrees of freedom of infinite neutron matter. For isotropic neutron matter with the Bethe interaction, the effective spin-spin interaction g(k) is calculated in the local approximation of the functional approach in the density range from {rho} = 0.17 to 25 fm{sup -3}. It is shown that this interaction weakly depends on the density within the range under consideration and that neither ferromagnetic nor antiferromagnetic phase transitions occur in the system. 7 refs., 2 figs.

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

    SciTech Connect

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

    2014-06-01

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

  9. Hybrid stars that masquerade as neutron stars

    SciTech Connect

    Mark Paris; Mark Alford; Matt Braby; Sanjay Reddy

    2004-11-01

    We show that a hybrid (nuclear + quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state, and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M{sub solar} for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.

  10. Gravitational Waves from Rotating Neutron Stars and Evaluation of fast Chirp Transform Techniques

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    X-ray observations suggest that neutron stars in low mass X-ray binaries (LMXB) are rotating with frequencies from 300 - 600 Hz. These spin rates are significantly less than the break-up rates for essentially all realistic neutron star equations of state, suggesting that some process may limit the spin frequencies of accreting neutron stars to this range. If the accretion induced spin up torque is in equilibrium with gravitational radiation losses, these objects could be interesting sources of gravitational waves. I present a brief summary of current measurements of neutron star spins in LMXBs based on the observations of high-Q oscillations during thermonuclear bursts (so called 'burst oscillations'). Further measurements of neutron star spins will be important in exploring the gravitational radiation hypothesis in more detail. To this end I also present a study of fast chirp transform (FCT) techniques as described by Jenet and Prince in the context of searching for the chirping signals observed during X-ray bursts.

  11. Gravitational waves from rotating neutron stars and evaluation of fast chirp transform techniques

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod E.

    2002-04-01

    X-ray observations suggest that neutron stars in low mass x-ray binaries (LMXB) are rotating with frequencies in the range 300-600 Hz. These spin rates are significantly less than the break-up rates for essentially all realistic neutron star equations of state, suggesting that some process may limit the spin frequencies of accreting neutron stars to this range. If the accretion-induced spin up torque is in equilibrium with gravitational radiation losses, these objects could be interesting sources of gravitational waves. I present a brief summary of current measurements of neutron star spins in LMXBs based on the observations of high-Q oscillations during thermonuclear bursts (so-called 'burst oscillations'). Further measurements of neutron star spins will be important in exploring the gravitational radiation hypothesis in more detail. To this end, I also present a study of fast chirp transform (FCT) techniques as described by Jenet and Prince (Prince T A and Jenet F A 2000 Phys. Rev. D 62 122001) in the context of searching for the chirping signals observed during x-ray bursts.

  12. Magnetorotational instability in neutron star mergers: impact of neutrinos

    NASA Astrophysics Data System (ADS)

    Guilet, Jérôme; Bauswein, Andreas; Just, Oliver; Janka, Hans-Thomas

    2017-10-01

    The merger of two neutron stars may give birth to a long-lived hypermassive neutron star. If it harbours a strong magnetic field of magnetar strength, its spin-down could explain several features of short gamma-ray burst afterglows. The magnetorotational instability (MRI) has been proposed as a mechanism to amplify the magnetic field to the required strength. Previous studies have, however, neglected neutrinos that may have an important impact on the MRI by inducing a viscosity and drag. We investigate the impact of these neutrinos effects on the linear growth of the MRI by applying a local stability analysis to snapshots of a neutron star merger simulation. We find that neutrinos have a significant impact inside the hypermassive neutron star, but have at most a marginal effect in the torus surrounding it. Inside the hypermassive neutron star, the MRI grows in different regimes depending on the radius and on the initial magnetic-field strength. For magnetic fields weaker than 1013-1014 G, the growth rate of the MRI is significantly reduced due to the presence of neutrinos. We conclude that neutrinos should be taken into account when studying the growth of the MRI from realistic initial magnetic fields. Current numerical simulations, which neglect neutrino viscosity, are only consistent, i.e. in the adopted ideal regime, if they start from artificially strong initial magnetic fields above ∼1014 G. One should be careful when extrapolating these results to lower initial magnetic fields, where the MRI growth is strongly affected by neutrino viscosity or drag.

  13. Neutron Star Mass-Radius Constraints Using Evolutionary Optimization

    NASA Astrophysics Data System (ADS)

    Stevens, A. L.; Fiege, J. D.; Leahy, D. A.; Morsink, S. M.

    2016-12-01

    The equation of state of cold supra-nuclear-density matter, such as in neutron stars, is an open question in astrophysics. A promising method for constraining the neutron star equation of state is modeling pulse profiles of thermonuclear X-ray burst oscillations from hot spots on accreting neutron stars. The pulse profiles, constructed using spherical and oblate neutron star models, are comparable to what would be observed by a next-generation X-ray timing instrument like ASTROSAT, NICER, or a mission similar to LOFT. In this paper, we showcase the use of an evolutionary optimization algorithm to fit pulse profiles to determine the best-fit masses and radii. By fitting synthetic data, we assess how well the optimization algorithm can recover the input parameters. Multiple Poisson realizations of the synthetic pulse profiles, constructed with 1.6 million counts and no background, were fitted with the Ferret algorithm to analyze both statistical and degeneracy-related uncertainty and to explore how the goodness of fit depends on the input parameters. For the regions of parameter space sampled by our tests, the best-determined parameter is the projected velocity of the spot along the observer’s line of sight, with an accuracy of ≤3% compared to the true value and with ≤5% statistical uncertainty. The next best determined are the mass and radius; for a neutron star with a spin frequency of 600 Hz, the best-fit mass and radius are accurate to ≤5%, with respective uncertainties of ≤7% and ≤10%. The accuracy and precision depend on the observer inclination and spot colatitude, with values of ˜1% achievable in mass and radius if both the inclination and colatitude are ≳60°.

  14. The Neutron Star Interior Composition Explorer (NICER)

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  15. Ultrahigh energy neutrinos from galactic neutron stars

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.

    1979-01-01

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

  16. Ultrahigh energy neutrinos from galactic neutron stars

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.

    1979-01-01

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

  17. TOPICAL REVIEW: Coalescing binary neutron stars

    NASA Astrophysics Data System (ADS)

    Rasio, Frederic A.; Shapiro, Stuart L.

    1999-06-01

    Coalescing compact binaries with neutron star or black hole components provide the most promising sources of gravitational radiation for detection by the LIGO/VIRGO/GEO/TAMA laser interferometers now under construction. This fact has motivated several different theoretical studies of the inspiral and hydrodynamic merging of compact binaries. Analytic analyses of the inspiral waveforms have been performed in the post-Newtonian approximation. Analytic and numerical treatments of the coalescence waveforms from binary neutron stars have been performed using Newtonian hydrodynamics and the quadrupole radiation approximation. Numerical simulations of coalescing black hole and neutron star binaries are also underway in full general relativity. Recent results from each of these approaches will be described and their virtues and limitations summarized.

  18. Magnetic field evolution in neutron stars

    NASA Astrophysics Data System (ADS)

    Castillo, F.; Reisenegger, A.; Valdivia, J. A.

    2017-07-01

    Neutron stars contain the strongest magnetic fields known in the Universe. Using numerical simulations restricted to axially symmetric geometry, we study the long-term evolution of the magnetic field in the interior of an isolated neutron star under the effect of ambipolar diffusion, i.e. the drift of the magnetic field and the charged particles relative to the neutrons. We model the stellar interior as an electrically neutral fluid composed of neutrons, protons and electrons; these species can be converted into each other by weak interactions (beta decays), suffer binary collisions, and be affected by each other's macroscopic electromagnetic fields. We show that, in the restricted case of pure ambipolar diffusion, neglecting weak interactions, the magnetic fields evolves towards a stable MHD equilibria configuration, in the timescales analytically expected.

  19. Symmetry energy: nuclear masses and neutron stars

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  20. Neutron stars as type-I superconductors.

    PubMed

    Buckley, Kirk B W; Metlitski, Max A; Zhitnitsky, Ariel R

    2004-04-16

    In a recent paper by Link, it was pointed out that the standard picture of the neutron star core composed of a mixture of a neutron superfluid and a proton type-II superconductor is inconsistent with observations of a long period precession in isolated pulsars. In the following we will show that an appropriate treatment of the interacting two-component superfluid (made of neutron and proton Cooper pairs), when the structure of proton vortices is strongly modified, may dramatically change the standard picture, resulting in a type-I superconductor. In this case the magnetic field is expelled from the superconducting regions of the neutron star, leading to the formation of the intermediate state when alternating domains of superconducting matter and normal matter coexist.

  1. Towards a metallurgy of neutron star crusts.

    PubMed

    Kobyakov, D; Pethick, C J

    2014-03-21

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

  2. Vortex Pinning and Dynamics in the Neutron Star Crust

    NASA Astrophysics Data System (ADS)

    Wlazłowski, Gabriel; Sekizawa, Kazuyuki; Magierski, Piotr; Bulgac, Aurel; Forbes, Michael McNeil

    2016-12-01

    The nature of the interaction between superfluid vortices and the neutron star crust, conjectured by Anderson and Itoh in 1975 to be at the heart vortex creep and the cause of glitches, has been a long-standing question in astrophysics. Using a qualitatively new approach, we follow the dynamics as superfluid vortices move in response to the presence of "nuclei" (nuclear defects in the crust). The resulting motion is perpendicular to the force, similar to the motion of a spinning top when pushed. We show that nuclei repel vortices in the neutron star crust, and characterize the force per unit length of the vortex line as a function of the vortex element to the nucleus separation.

  3. Vortex Pinning and Dynamics in the Neutron Star Crust.

    PubMed

    Wlazłowski, Gabriel; Sekizawa, Kazuyuki; Magierski, Piotr; Bulgac, Aurel; Forbes, Michael McNeil

    2016-12-02

    The nature of the interaction between superfluid vortices and the neutron star crust, conjectured by Anderson and Itoh in 1975 to be at the heart vortex creep and the cause of glitches, has been a long-standing question in astrophysics. Using a qualitatively new approach, we follow the dynamics as superfluid vortices move in response to the presence of "nuclei" (nuclear defects in the crust). The resulting motion is perpendicular to the force, similar to the motion of a spinning top when pushed. We show that nuclei repel vortices in the neutron star crust, and characterize the force per unit length of the vortex line as a function of the vortex element to the nucleus separation.

  4. Improved Universal No-Hair Relations for Neutron Stars

    NASA Astrophysics Data System (ADS)

    Majumder, Barun; Yagi, Kent; Yunes, Nicolas

    2016-03-01

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

  5. Physics in Strong Magnetic Fields Near Neutron Stars.

    ERIC Educational Resources Information Center

    Harding, Alice K.

    1991-01-01

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

  6. Physics in Strong Magnetic Fields Near Neutron Stars.

    ERIC Educational Resources Information Center

    Harding, Alice K.

    1991-01-01

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

  7. Instability of superfluid flow in the neutron star core

    NASA Astrophysics Data System (ADS)

    Link, B.

    2012-04-01

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

  8. Neutron stars. [quantum mechanical processes associated with magnetic fields

    NASA Technical Reports Server (NTRS)

    Canuto, V.

    1978-01-01

    Quantum-mechanical processes associated with the presence of high magnetic fields and the effect of such fields on the evolution of neutron stars are reviewed. A technical description of the interior of a neutron star is presented. The neutron star-pulsar relation is reviewed and consideration is given to supernovae explosions, flux conservation in neutron stars, gauge-invariant derivation of the equation of state for a strongly magnetized gas, neutron beta-decay, and the stability condition for a neutron star.

  9. An instability in neutron stars at birth.

    PubMed

    Burrows, A; Fryxell, B A

    1992-10-16

    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 supemova explosion may be inadequate. Whether this "convective" instability is pivotal to the supemova mechanism, pulsar magnetic 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.

  10. An instability in neutron stars at birth

    NASA Technical Reports Server (NTRS)

    Burrows, Adam; Fryxell, Bruce A.

    1992-01-01

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

  11. An instability in neutron stars at birth

    NASA Technical Reports Server (NTRS)

    Burrows, Adam; Fryxell, Bruce A.

    1992-01-01

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

  12. Chandra Observations of Neutron Stars: An Overview

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

  13. Holographic Quark Matter and Neutron Stars.

    PubMed

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

    2016-07-15

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

  14. Early neutron stars and quark matter

    NASA Astrophysics Data System (ADS)

    Li, You-Chen; Kong, Xiao-Jun; Wei, Cheng-Wen; Ge, Yun-Zhao

    1988-03-01

    The existence of quark matter (QM) in hot early neutron stars is considered theoretically, using the method of Baym and Chin (1976) to calculate the pressure and density at the phase transition between neutron and quark matter for various temperatures. The results are presented in tables and graphs and discussed in detail. It is found that QM cores can exist whenever the temperature exceeds 10 to the 10th K, and that their radii increase with decreasing QM bag constant. The total energy emitted by a star during cooling is estimated as 10 to the 53rd erg, assuming conservation of baryon number.

  15. Neutron Star Cooling with Various Superfluid and Superconducting States

    NASA Astrophysics Data System (ADS)

    Noda, Tsuneo; Hashimoto, Masa-aki; Matsuo, Yasuhide; Yasutake, Nobutoshi; Maruyama, Toshiki; Tatsumi, Toshitaka

    A neutron star is a highly dense object which lasts after a supernova explosion. The density of a neutron star overcomes the nuclear density, and the temperature is high at the beginning of its history. An isolated neutron star does not have any heat sources, and it cools down emitting thermal energy by neutrinos. The neutrino emission process depends on the state of interior matter of the neutron star. To compare theoretical simulations and observations of neutron stars, it can constrain the nuclear theory of high density region. We create a model of neutron stars with colour superconducting quark matter and nucleon superfluidity/superconductivity, to satisfy recent observations, including two 2M ⊙ neutron stars. We parameterize these super-states and demonstrate the cooling curves, which show heavy stars do not always cool faster than lighter stars.

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

    SciTech Connect

    Cheng, Quan; Yu, Yun-Wei

    2014-05-10

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

  17. Accreting neutron stars, black holes, and degenerate dwarf stars.

    PubMed

    Pines, D

    1980-02-08

    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.

  18. Electric field in neutron stars

    SciTech Connect

    Adam, R. I. Sulaksono, A.

    2016-04-19

    In a compact star, an electric field is generated by the charge polarization effect. We investigate the charge polarization effect due to a significant difference of core and crust densities in the form of a combination of two Gaussian functions. The results indicate that the electric field only occurs significantly on the crust of the compact star. As a consequence, the mass-radius relationship only affects compact stars with mass ≤ 1.0 M{sub ⊙}.

  19. Gravitational waves and mass ejecta from binary neutron star mergers: Effect of the stars' rotation

    NASA Astrophysics Data System (ADS)

    Dietrich, Tim; Bernuzzi, Sebastiano; Ujevic, Maximiliano; Tichy, Wolfgang

    2017-02-01

    We present new (3 +1 )-dimensional numerical relativity simulations of the binary neutron star (BNS) mergers that take into account the NS spins. We consider different spin configurations, aligned or antialigned to the orbital angular momentum, for equal- and unequal-mass BNSs and for two equations of state. All the simulations employ quasiequilibrium circular initial data in the constant rotational velocity approach, i.e. they are consistent with the Einstein equations and in hydrodynamical equilibrium. We study the NS rotation effect on the energetics, the gravitational waves (GWs) and on the possible electromagnetic (EM) emission associated to dynamical mass ejecta. For dimensionless spin magnitudes of χ ˜0.1 we find that both spin-orbit interactions and spin-induced quadrupole deformations affect the late-inspiral merger dynamics. The latter is, however, dominated by finite-size effects. Spin (tidal) effects contribute to GW phase differences up to ˜5 (20) radians accumulated during the last eight orbits to merger. Similarly, after merger the collapse time of the remnant and the GW spectrogram are affected by the NSs rotation. Spin effects in dynamical ejecta are clearly observed in unequal-mass systems in which mass ejection originates from the tidal tail of the companion. Consequently kilonovae and other EM counterparts are affected by spins. We find that spin aligned to the orbital angular momentum leads to brighter EM counterparts than antialigned spin with luminosities up to a factor of 2 higher.

  20. Neutron stars: A cosmic hadron physics laboratory

    NASA Technical Reports Server (NTRS)

    Pines, David

    1989-01-01

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

  1. Neutron stars - A cosmic hadron physics laboratory

    NASA Technical Reports Server (NTRS)

    Pines, David

    1989-01-01

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

  2. Constraining Neutron Star Matter with Quantum Chromodynamics

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  3. Constraining neutron star matter with quantum chromodynamics

    SciTech Connect

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

    2014-07-10

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

  4. PULSE PROFILES FROM THERMALLY EMITTING NEUTRON STARS

    SciTech Connect

    Turolla, R.; Nobili, L.

    2013-05-10

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

  5. Neutron star crustal plate tectonics. I. Magnetic dipole evolution in millisecond pulsars and low-mass X-ray binaries

    SciTech Connect

    Ruderman, M. )

    1991-01-01

    Crust lattices in spinning-up or spinning-down neutron stars have growing shear stresses caused by neutron superfluid vortex lines pinned to lattice nuclei. For the most rapidly spinning stars, this stress will break and move the crust before vortex unpinning occurs. In spinning-down neutron stars, crustal plates will move an equatorial subduction zone in which the plates are forced into the stellar core below the crust. The opposite plate motion occurs in spinning-up stars. Magnetic fields which pass through the crust or have sources in it move with the crust. Spun-up neutron stars in accreting low-mass X-ray binaries LMXBs should then have almost axially symmetric magnetic fields. Spun-down ones with very weak magnetic fields should have external magnetic fields which enter and leave the neutron star surface only near its equator. The lowest field millisecond radiopulsars seem to be orthogonal rotators implying that they have not previously been spun-up in LMXBs but are neutron stars initially formed with periods near 0.001 s that subsequently spin down to their present periods. Accretion-induced white dwarf collapse is then the most plausible genesis for them. 29 refs.

  6. Neutron star kicks and their relationship to supernovae ejecta mass

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  7. Few-Body Effects in Neutron Star Matter

    NASA Astrophysics Data System (ADS)

    Takibayev, N.

    2017-03-01

    Neutron resonances in systems of few nuclei, electron capture reactions with formation of excited nuclei, and density oscillation in the neutron star envelopes are investigated. These results allow to propose the special experiments to verify the neutron resonances in the few-body systems and understand the origin of some processes that are going in the neutron star crusts.

  8. Measuring Ejecta from Inspiralling Binary Neutron Stars using Smoothed-particle Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Rizzo, Monica; O'Shaughnessy, Richard; Faber, Joshua

    2017-01-01

    Gravitational waves, detectable perturbations in spacetime, can arise from astrophysical systems such as inspiralling binary neutron stars, the remnants of the core collapse of massive stars. In the inspiral process, neutron stars, composed of highly dense nuclear matter, are torn apart by each others gravity and eject matter. Using both gravitational waves and direct observations of ejected matter, we may gain valuable new information about the composition of neutron stars. Using several previously studied test cases, we seek to determine how the amount of ejected matter depends on the physical parameters of these systems. To do this, we use a particle-based hydrodynamics code which can accurately simulate binary neutron star systems with variable equation of state, spin, mass ratio, and eccentricity, and includes the lowest-order effects from gravitational wave emission. I would like to thank RIT's College of Science as well as the Center for Computational Relativity and Gravitation for support and funding.

  9. Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru; Kiuchi, Kenta

    2017-06-01

    Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

  10. The Mystery of the Lonely Neutron Star

    NASA Astrophysics Data System (ADS)

    2000-09-01

    The VLT Reveals Bowshock Nebula around RX J1856.5-3754 Deep inside the Milky Way, an old and lonely neutron star plows its way through interstellar space. Known as RX J1856.5-3754 , it measures only ~ 20 km across. Although it is unusually hot for its age, about 700,000 °C, earlier observations did not reveal any activity at all, contrary to all other neutron stars known so far. In order to better understand this extreme type of object, a detailed study of RX J1856.5-3754 was undertaken by Marten van Kerkwijk (Institute of Astronomy of the University of Utrecht, The Netherlands) and Shri Kulkarni (California Institute of Technology, Pasadena, California, USA). To the astronomers' delight and surprise, images and spectra obtained with the ESO Very Large Telescope (VLT) now show a small nearby cone-shaped ("bowshock") nebula. It shines in the light from hydrogen atoms and is obviously a product of some kind of interaction with this strange star. Neutron stars - remnants of supernova explosions Neutron stars are among the most extreme objects in the Universe. They are formed when a massive star dies in a "supernova explosion" . During this dramatic event, the core of the star suddenly collapses under its own weight and the outer parts are violently ejected into surrounding space. One of the best known examples is the Crab Nebula in the constellation Taurus (The Bull). It is the gaseous remnant of a star that exploded in the year 1054 and also left behind a pulsar , i.e., a rotating neutron star [1]. A supernova explosion is a very complex event that is still not well understood. Nor is the structure of a neutron star known in any detail. It depends on the extreme properties of matter that has been compressed to incredibly high densities, far beyond the reach of physics experiments on Earth [2]. The ultimate fate of a neutron star is also unclear. From the observed rates of supernova explosions in other galaxies, it appears that several hundred million neutron stars

  11. Nuclear physics problems for accreting neutron stars

    SciTech Connect

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

    1983-01-01

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

  12. Temperature effects in pulsating superfluid neutron stars

    SciTech Connect

    Kantor, Elena M.; Gusakov, Mikhail E.

    2011-05-15

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

  13. Quantitative radiography of magnetic fields using neutron spin phase imaging.

    PubMed

    Piegsa, F M; van den Brandt, B; Hautle, P; Kohlbrecher, J; Konter, J A

    2009-04-10

    We report on a novel neutron radiography technique that uses the Ramsey principle, a method similar to neutron spin echo. For the first time quantitative imaging measurements of magnetic objects and fields could be performed. The strength of the spin-dependent magnetic interaction is detected by a change in the Larmor precession frequency of the neutron spins. Hence, one obtains in addition to the normal attenuation radiography image a so-called neutron spin phase image, which provides a two-dimensional projection of the magnetic field integrated over the neutron flight path.

  14. Tuning up for Gravitational Wave Detection in Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Galloway, Duncan; Steeghs, Danny; Ransom, Scott

    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.

  15. Tidal Love Numbers of Neutron Stars

    SciTech Connect

    Hinderer, Tanja

    2008-04-20

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

  16. Fallback Disks, Magnetars and Other Neutron Stars

    NASA Astrophysics Data System (ADS)

    Alpar, M. Ali; Çalışkan, Ş.; Ertan, Ü.

    2013-02-01

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

  17. The Fate of Neutron Star Binary Mergers

    NASA Astrophysics Data System (ADS)

    Piro, Anthony L.; Giacomazzo, Bruno; Perna, Rosalba

    2017-08-01

    Following merger, a neutron star (NS) binary can produce roughly one of three different outcomes: (1) a stable NS, (2) a black hole (BH), or (3) a supramassive, rotationally supported NS, which then collapses to a BH following angular momentum losses. Which of these fates occur and in what proportion has important implications for the electromagnetic transient associated with the mergers and the expected gravitational wave (GW) signatures, which in turn depend on the high density equation of state (EOS). Here we combine relativistic calculations of NS masses using realistic EOSs with Monte Carlo population synthesis based on the mass distribution of NS binaries in our Galaxy to predict the distribution of fates expected. For many EOSs, a significant fraction of the remnants are NSs or supramassive NSs. This lends support to scenarios in which a quickly spinning, highly magnetized NS may be powering an electromagnetic transient. This also indicates that it will be important for future GW observatories to focus on high frequencies to study the post-merger GW emission. Even in cases where individual GW events are too low in signal to noise to study the post merger signature in detail, the statistics of how many mergers produce NSs versus BHs can be compared with our work to constrain the EOS. To match short gamma-ray-burst (SGRB) X-ray afterglow statistics, we find that the stiffest EOSs are ruled out. Furthermore, many popular EOSs require a significant fraction of ˜60%-70% of SGRBs to be from NS-BH mergers rather than just binary NSs.

  18. R modes and neutron star recycling scenario

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    To put new constraints on the r-mode instability window, we analyse the formation of millisecond pulsars (MSPs) within the recycling scenario, making use of three sets of observations: (a) X-ray observations of neutron stars (NSs) in low-mass X-ray binaries; (b) timing of MSPs and (c) X-ray and UV observations of MSPs. As shown in previous works, r-mode dissipation by shear viscosity is not sufficient to explain observational set (a), and enhanced r-mode dissipation at the redshifted internal temperatures T ∞ ˜ 108 K is required to stabilize the observed NSs. Here, we argue that models with enhanced bulk viscosity can hardly lead to a self-consistent explanation of observational set (a) due to strong neutrino emission, which is typical for these models (unrealistically powerful energy source is required to keep NSs at the observed temperatures.). We also demonstrate that the observational set (b), combined with the theory of internal heating and NS cooling, provides evidence of enhanced r-mode dissipation at low temperatures, T ∞ ˜ 2 × 107 K. Observational set (c) allows us to set an upper limit on the internal temperatures of MSPs, T ∞ < 2 × 107 K (assuming a canonical NS with the accreted crust). Recycling scenario can produce MSPs at these temperatures only if r-mode instability is suppressed in the whole MSP spin frequency range (ν ≲ 750 Hz) at temperatures 2 × 107 ≲ T ∞ ≲ 3 × 107 K, providing thus a new constraint on the r-mode instability window. These observational constraints are analysed in more details in application to the resonance uplift scenario of Gusakov et al.

  19. Neutrino scattering rates in neutron star matter with {delta} isobars

    SciTech Connect

    Chen Yanjun; Guo Hua; Liu Yuxin

    2007-03-15

    We take the {delta}-isobar degrees of freedom into account in neutron star matter and evaluate their contributions to neutrino scattering cross sections and mean free paths. The neutron star matter is described by means of an effective hadronic model in the relativistic mean-field approximation. It is found that {delta} isobars may be present in neutron stars. The electron chemical potential does not decrease and the neutrino abundance does not increase with the increase of the density when neutrinos are trapped in the matter with {delta} isobars. The large vector coupling constant between the {delta}{sup -} and neutrino and the high spin of the {delta} influence significantly the neutrino scattering cross section and lead the contribution of the {delta}{sup -} to the dominance of the scattering rates. In neutrino-trapped case, the presence of {delta}s causes the neutrino mean free path to decrease drastically compared to that in the matter in which baryons are only nucleons.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  1. Antikaon condensation and deconfinement phase transition in neutron stars

    SciTech Connect

    Gu Jianfa; Guo Hua; Xu Furong; Li Xiguo; Liu Yuxin

    2006-05-15

    Antikaon condensation and deconfinement phase transition in neutron stars are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase and in the MIT bag model for the deconfined quark matter phase. It is shown that the existence of quark matter phase makes antikaon condensation impossible in neutron stars. The properties of neutron stars are sensitive to the bag constant. For the small values of the bag constant, the pure quark matter core appears and hyperons are strongly suppressed in neutron stars, whereas for the large bag constant, the hadron-quark mixed phase exists in the center of neutron stars. The maximum masses of neutron stars with the quark matter phase are lower than those without the quark matter phase; meanwhile, the maximum masses of neutron stars with the quark matter phase increase with the bag constant.

  2. Confirming a substellar companion candidate around a neutron star

    NASA Astrophysics Data System (ADS)

    Posselt, Bettina; Luhman, Kevin

    2014-08-01

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

  3. Probing thermonuclear burning on accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Keek, L.

    2008-12-01

    Neutron stars are the most compact stars that can be directly observed, which makes them ideal laboratories to study physics at extreme densities. Neutron stars in low-mass X-ray binaries accrete hydrogen and helium from a lower-mass companion star through Roche lobe overflow. This matter undergoes thermonuclear burning in the neutron star envelope, creating carbon and heavier elements. The fusion process may proceed in an unstable manner, resulting in a thermonuclear runaway. Within one second the entire surface is burned, which is observable as a sharp rise in the emitted X-ray flux: a type I X-ray burst. Afterwards the neutron star surface cools down on a timescale of ten to one hundred seconds. During these bursts the surface of an accreting neutron star can be observed directly, which makes them instrumental for studying this type of stars. We have studied rare kinds of X-ray bursts. One such rare burst is the superburst, which lasts a thousand times longer than an ordinary burst. Superbursts are thought to result from the explosive burning of a thick carbon layer, which lies deeper inside the neutron star, close to a layer known as the crust. A prerequisite for the occurrence of a superburst is a high enough temperature, which is set by the temperature of the crust and the heat conductivity of the envelope. The latter is lowered by the presence of heavy elements that are produced during normal X-ray bursts. Using a large set of observations from the Wide Field Camera's onboard the BeppoSAX satellite, we find that, at high accretion rate, sources which do not exhibit normal bursts likely have a longer superburst recurrence time, than the observed superburst recurrence time of one burster. We analyze in detail the first superburst from a transient source, which went into outburst only 55 days before the superburst. Recent models of the neutron star crust predict that this is too small a time to heat the crust sufficiently for superburst ignition, indicating

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    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.

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

    SciTech Connect

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

    2011-09-21

    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.

  6. Non-identical neutron star twins

    SciTech Connect

    Glendenning, Norman K.; Kettner, Christiane

    1998-07-01

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

  7. Strange Stars, Neutron Stars and Pulsar Emission

    NASA Astrophysics Data System (ADS)

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

    1990-11-01

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

  8. Oscillations During Thermonuclear X-ray Bursts: A New Probe of Neutron Stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    Observations of thermonuclear (also called Type 1) X-ray bursts from neutron stars in low mass X-ray binaries (LMXB) with the Rossi X-ray Timing Explorer (RXTE) have revealed large amplitude, high coherence X-ray brightness oscillations with frequencies in the 300 - 600 Hz range. Substantial spectral and timing evidence point to rotational modulation of the X-ray burst flux as the cause of these oscillations, and it is likely that they reveal the spin frequencies of neutron stars in LMXB from which they are detected. Here we review the status of our knowledge of these oscillations and describe how they can be used to constrain the masses and radii of neutron stars as well as the physics of thermonuclear burning on accreting neutron stars.

  9. Cooling of neutron stars with diffusive envelopes

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  10. Free fall onto magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Salpeter, E. E.

    Some compact X-ray sources show evidence of cyclotron line radiation from excited electron Landau orbits, powered by hydrogen and helium falling onto a neutron star atmosphere along the magnetic field. The slowing of the incident matter is discussed, including the spread in energy loss due to Coulomb scattering and direct nuclear reactions for disintegrating the α particles. The α disintegrations, followed by neutron capture, lead to nuclear γ rays; the γ-ray intensity is (indirectly) coupled to the Coulomb energy loss and the cyclotron line emission.

  11. THE ANGULAR MOMENTA OF NEUTRON STARS AND BLACK HOLES AS A WINDOW ON SUPERNOVAE

    SciTech Connect

    Miller, J. M.; Miller, M. C.; Reynolds, C. S.

    2011-04-10

    It is now clear that a subset of supernovae displays evidence for jets and is observed as gamma-ray bursts (GRBs). The angular momentum distribution of massive stellar endpoints provides a rare means of constraining the nature of the central engine in core-collapse explosions. Unlike supermassive black holes, the spin of stellar-mass black holes in X-ray binary systems is little affected by accretion and accurately reflects the spin set at birth. A modest number of stellar-mass black hole angular momenta have now been measured using two independent X-ray spectroscopic techniques. In contrast, rotation-powered pulsars spin down over time, via magnetic braking, but a modest number of natal spin periods have now been estimated. For both canonical and extreme neutron star parameters, statistical tests strongly suggest that the angular momentum distributions of black holes and neutron stars are markedly different. Within the context of prevalent models for core-collapse supernovae, the angular momentum distributions are consistent with black holes typically being produced in GRB-like supernovae with jets and with neutron stars typically being produced in supernovae with too little angular momentum to produce jets via magnetohydrodynamic processes. It is possible that neutron stars are with high spin initially and rapidly spun down shortly after the supernova event, but the available mechanisms may be inconsistent with some observed pulsar properties.

  12. Why neutron stars have three hairs

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  13. Colloquium: Measuring the neutron star equation of state using x-ray timing

    NASA Astrophysics Data System (ADS)

    Watts, Anna L.; Andersson, Nils; Chakrabarty, Deepto; Feroci, Marco; Hebeler, Kai; Israel, Gianluca; Lamb, Frederick K.; Miller, M. Coleman; Morsink, Sharon; Özel, Feryal; Patruno, Alessandro; Poutanen, Juri; Psaltis, Dimitrios; Schwenk, Achim; Steiner, Andrew W.; Stella, Luigi; Tolos, Laura; van der Klis, Michiel

    2016-04-01

    One of the primary science goals of the next generation of hard x-ray timing instruments is to determine the equation of state of matter at supranuclear densities inside neutron stars by measuring the radius of neutron stars with different masses to accuracies of a few percent. Three main techniques can be used to achieve this goal. The first involves waveform modeling. The flux observed from a hotspot on the neutron star surface offset from the rotational pole will be modulated by the star's rotation, and this periodic modulation at the spin frequency is called a pulsation. As the photons propagate through the curved spacetime of the star, information about mass and radius is encoded into the shape of the waveform (pulse profile) via special and general-relativistic effects. Using pulsations from known sources (which have hotspots that develop either during thermonuclear bursts or due to channeled accretion) it is possible to obtain tight constraints on mass and radius. The second technique involves characterizing the spin distribution of accreting neutron stars. A large collecting area enables highly sensitive searches for weak or intermittent pulsations (which yield spin) from the many accreting neutron stars whose spin rates are not yet known. The most rapidly rotating stars provide a clean constraint, since the limiting spin rate where the equatorial surface velocity is comparable to the local orbital velocity, at which mass shedding occurs, is a function of mass and radius. However, the overall spin distribution also provides a guide to the torque mechanisms in operation and the moment of inertia, both of which can depend sensitively on dense matter physics. The third technique is to search for quasiperiodic oscillations in x-ray flux associated with global seismic vibrations of magnetars (the most highly magnetized neutron stars), triggered by magnetic explosions. The vibrational frequencies depend on stellar parameters including the dense matter equation of

  14. Colloquium: Measuring the neutron star equation of state using x-ray timing

    DOE PAGES

    Watts, Anna L.; Andersson, Nils; Chakrabarty, Deepto; ...

    2016-04-13

    One of the primary science goals of the next generation of hard x-ray timing instruments is to determine the equation of state of matter at supranuclear densities inside neutron stars by measuring the radius of neutron stars with different masses to accuracies of a few percent. Three main techniques can be used to achieve this goal. The first involves waveform modeling. The flux observed from a hotspot on the neutron star surface offset from the rotational pole will be modulated by the star s rotation, and this periodic modulation at the spin frequency is called a pulsation. As the photonsmore » propagate through the curved spacetime of the star, information about mass and radius is encoded into the shape of the waveform (pulse profile) via special and general-relativistic effects. Using pulsations from known sources (which have hotspots that develop either during thermo- nuclear bursts or due to channeled accretion) it is possible to obtain tight constraints on mass and radius. The second technique involves characterizing the spin distribution of accreting neutron stars. A large collecting area enables highly sensitive searches for weak or intermittent pulsations (which yield spin) from the many accreting neutron stars whose spin rates are not yet known. The most rapidly rotating stars provide a clean constraint, since the limiting spin rate where the equatorial surface velocity is comparable to the local orbital velocity, at which mass shedding occurs, is a function of mass and radius. However, the overall spin distribution also provides a guide to the torque mechanisms in operation and the moment of inertia, both of which can depend sensitively on dense matter physics. The third technique is to search for quasiperiodic oscillations in x-ray flux associated with global seismic vibrations of magnetars (the most highly magnetized neutron stars), triggered by magnetic explosions. The vibrational frequencies depend on stellar parameters including the dense matter

  15. Colloquium: Measuring the neutron star equation of state using x-ray timing

    SciTech Connect

    Watts, Anna L.; Andersson, Nils; Chakrabarty, Deepto; Feroci, Marco; Hebeler, Kai; Israel, Gianluca; Miller, M. Coleman; Morsink, Sharon; Ozel, Feryal; Patruno, Alessandro; Poutanen, Juri; Psaltis, Dimitrios; Schwenk, Achim; Steiner, Andrew W.; Stella, Luigi; van der Klis, Michiel

    2016-04-13

    One of the primary science goals of the next generation of hard x-ray timing instruments is to determine the equation of state of matter at supranuclear densities inside neutron stars by measuring the radius of neutron stars with different masses to accuracies of a few percent. Three main techniques can be used to achieve this goal. The first involves waveform modeling. The flux observed from a hotspot on the neutron star surface offset from the rotational pole will be modulated by the star s rotation, and this periodic modulation at the spin frequency is called a pulsation. As the photons propagate through the curved spacetime of the star, information about mass and radius is encoded into the shape of the waveform (pulse profile) via special and general-relativistic effects. Using pulsations from known sources (which have hotspots that develop either during thermo- nuclear bursts or due to channeled accretion) it is possible to obtain tight constraints on mass and radius. The second technique involves characterizing the spin distribution of accreting neutron stars. A large collecting area enables highly sensitive searches for weak or intermittent pulsations (which yield spin) from the many accreting neutron stars whose spin rates are not yet known. The most rapidly rotating stars provide a clean constraint, since the limiting spin rate where the equatorial surface velocity is comparable to the local orbital velocity, at which mass shedding occurs, is a function of mass and radius. However, the overall spin distribution also provides a guide to the torque mechanisms in operation and the moment of inertia, both of which can depend sensitively on dense matter physics. The third technique is to search for quasiperiodic oscillations in x-ray flux associated with global seismic vibrations of magnetars (the most highly magnetized neutron stars), triggered by magnetic explosions. The vibrational frequencies depend on stellar parameters including the dense matter equation

  16. FAST FOSSIL ROTATION OF NEUTRON STAR CORES

    SciTech Connect

    Melatos, A.

    2012-12-10

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

  17. Super-Eddington winds from neutron stars

    NASA Technical Reports Server (NTRS)

    Paczynski, Bohdan

    1990-01-01

    Results are presented from a study of winds driven by a super-Eddington rate of energy deposition near the surface of a neutron star, a condition which may develop following a collision between two neutron stars when more than 10 to the 53rd ergs is radiated during a few seconds. A fraction of that energy, perhaps as large as 10 to the 50th ergs, may be transformed into electron-positron pairs and drive a powerful wind. Using a model of the highly super-Eddington wind, the fraction of energy injected into a wind that emerges as gamma rays is estimated. It is shown that it is possible to reach gamma-ray temperatures with the optically thick winds, provided the energy injection rate is sufficiently high.

  18. Quasinormal modes of superfluid neutron stars

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    NASA Technical Reports Server (NTRS)

    Michel, F. Curtis

    1988-01-01

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

  20. Fast Fossil Rotation of Neutron Star Cores

    NASA Astrophysics Data System (ADS)

    Melatos, A.

    2012-12-01

    It is argued that the superfluid core of a neutron star super-rotates relative to the crust, because stratification prevents the core from responding to the electromagnetic braking torque, until the relevant dissipative (viscous or Eddington-Sweet) timescale, which can exceed ~103 yr and is much longer than the Ekman timescale, has elapsed. Hence, in some young pulsars, the rotation of the core today is a fossil record of its rotation at birth, provided that magnetic crust-core coupling is inhibited, e.g., by buoyancy, field-line topology, or the presence of uncondensed neutral components in the superfluid. Persistent core super-rotation alters our picture of neutron stars in several ways, allowing for magnetic field generation by ongoing dynamo action and enhanced gravitational wave emission from hydrodynamic instabilities.

  1. Light curves of rotating, oscillating neutron stars

    NASA Technical Reports Server (NTRS)

    Strohmayer, T. E.

    1992-01-01

    A technique has been developed for computing the light curve produced by a rotating, oscillating neutron star that emits radiation from circular polar cap regions, as are thought to exist in pulsars, X-ray binaries, and perhaps X-ray bursters. Several examples of light curves produced by single, low-order (l = 1, 2) oscillation modes are given. A Gaussian beaming function is used to simulate typical radio pulsar beam widths in order to investigate a neutron star oscillation model for subpulse drift in pulsars. X-ray bursts and X-ray pulsars have also been simulated to assess the possibility of detecting such oscillations in these sources with XTE and AXAF.

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

    NASA Technical Reports Server (NTRS)

    Michel, F. Curtis

    1988-01-01

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

  3. The Origin of Neutron Star Kicks

    NASA Astrophysics Data System (ADS)

    Lai, Dong

    2000-05-01

    Despite decades of theoretical investigations, our understanding of core-collapse supernovae remains significantly incomplete. Recent observations show that many supernovae are asymmetric and newly-formed neutron stars have large space velocities. I will discuss the physics of different mechanisms for generating asymmetric explosions and pulsar velocities, including hydrodynamically driven, neutrino and magnetically driven kicks. References: D. Lai and Y.-Z. Qian 1998, ApJ, 505, 844. P. Arras and D. Lai 1999, ApJ, 519, 745. P. Arras and D. Lai 1999, Phys. Rev. D60, 043001. D. Lai 1999, "Physics of Neutron Star Kicks", in press (astro-ph/9912522). D. Lai and P. Goldreich 2000, ApJ, in press (astro-ph/9906400). D. Lai 2000, ApJ, in press (astro-ph/0004066). This research is supported by NASA Grants NAG 5-8484 and NAG 5-8356, and by a research fellowship from the Alfred P. Sloan foundation.

  4. AFTERGLOW OF A BINARY NEUTRON STAR MERGER

    SciTech Connect

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

    2011-06-20

    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.

  5. Physics of systems containing neutron stars

    NASA Technical Reports Server (NTRS)

    Shaham, Jacob

    1989-01-01

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

  6. Neutron star inner crust: Nuclear physics input

    SciTech Connect

    Steiner, Andrew W.

    2008-03-15

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

  7. Instability of superfluid flow in the neutron star inner crust

    NASA Astrophysics Data System (ADS)

    Link, B.

    2012-05-01

    Pinning of superfluid vortices to the nuclear lattice of the inner crust of a neutron star supports a velocity difference between the superfluid and the solid as the star spins down. Under the Magnus force that arises on the vortex lattice, vortices undergo vortex creep through thermal activation or quantum tunnelling. We examine the hydrodynamic stability of this situation. Vortex creep introduces two low-frequency modes, one of which is unstable above a critical wavenumber for any non-zero flow velocity of the superfluid with respect to the solid. For typical pinning parameters of the inner crust, the superfluid flow is unstable over length scales ≲10 m and over time-scales as fast as months. The vortex lattice could degenerate into a tangle, and the superfluid flow could become turbulent. Unexpectedly large dissipation would suppress this instability.

  8. Dissipation in relativistic superfluid neutron stars

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  9. Quasi-static winds from neutron stars

    NASA Technical Reports Server (NTRS)

    Joss, Paul C.; Melia, Fulvio

    1987-01-01

    A series of numerical models is constructed for radiatively driven, quasi-static winds from the surfaces of hot neutron stars. A mathematical technique is devised that in many cases facilitates the integration of the fluid equations in the vicinity of the sonic point, and an improved treatment of radiative transfer is developed that is appropriate to the exotic physical conditions encountered in the models. Boundary conditions which are more realistic than previous ones are used in these models. In agreement with earlier studies, it is found that radiatively driven winds are likely to be directly relevant to the existence of precursors in fast X-ray transients and to apparent radius variations during the course of some type I bursts, and that the presence of such a wind should prevent the bolometric luminosity of a neutron star from exceeding the Eddington limit by more than a small fractional amount. Formulas describing the wind models are presented which are usable as boundary conditions for calculations of the evolution of the deeper, hydrostatic layers of a neutron-star envelope.

  10. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    Many of NICER’s 56 X-ray “concentrators” seen from within the instrument optical bench. Light reflected from the gold surfaces of the 24 concentric foils in each concentrator is focused onto detectors slightly more than 1 meter (3.5 feet) away. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  11. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    NICER’s X-ray concentrator optics are inspected under a black light for dust and foreign object debris that could impair functionality once in space. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  12. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    NICER Optics Lead Takashi Okajima makes a fine adjustment to the orientation of one X-ray “concentrator” optic. The 56 optics must point in the same direction in order for NICER to achieve its science goals. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  13. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    NICER engineer Steven Kenyon prepares seven of the 56 X-ray concentrators for installation in the NICER instrument. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  14. Numerical relativity simulations of binary neutron stars

    NASA Astrophysics Data System (ADS)

    Thierfelder, Marcus; Bernuzzi, Sebastiano; Brügmann, Bernd

    2011-08-01

    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.

  15. Quasi-static winds from neutron stars

    NASA Technical Reports Server (NTRS)

    Joss, Paul C.; Melia, Fulvio

    1987-01-01

    A series of numerical models is constructed for radiatively driven, quasi-static winds from the surfaces of hot neutron stars. A mathematical technique is devised that in many cases facilitates the integration of the fluid equations in the vicinity of the sonic point, and an improved treatment of radiative transfer is developed that is appropriate to the exotic physical conditions encountered in the models. Boundary conditions which are more realistic than previous ones are used in these models. In agreement with earlier studies, it is found that radiatively driven winds are likely to be directly relevant to the existence of precursors in fast X-ray transients and to apparent radius variations during the course of some type I bursts, and that the presence of such a wind should prevent the bolometric luminosity of a neutron star from exceeding the Eddington limit by more than a small fractional amount. Formulas describing the wind models are presented which are usable as boundary conditions for calculations of the evolution of the deeper, hydrostatic layers of a neutron-star envelope.

  16. An Exoplanet Spinning Up Its Star

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-11-01

    We know that the large masses of stars govern the orbits of the planets that circle them but a large, close-in planet can also influence the rotation of its host star. A recently discovered, unusual hot Jupiter may be causing its star to spin faster than it should.Exotic PlanetsHot Jupiters are gas giants of roughly Jupiters size that orbit close in to their host stars. Though these planets are easy to detect their large sizes and frequent transits mean surveys have a good chance of catching them we havent found many of them, suggesting that planetary systems containing hot Jupiters are fairly unusual.The period-folded light curve of HATS-18, revealing the transit of the hot Jupiter HATS-18b. The period is P=0.8378 days. [Penev et al. 2016]Studying this exotic population of planets, however, can help us to better understand how gas giants form and evolve in planetary systems. New observations of hot Jupiters may also reveal how stars and close-in planets interact through radiation, gravity, and magnetic fields.The recent discovery of a transiting hot Jupiter a little over 2000 light-years away therefore presents an exciting opportunity!A Speeding GiantThe discovery of HATS-18b, a planet of roughly 2 times Jupiters mass and 1.3 times its radius, was announced in a study led by Kaloyan Penev (Princeton University). The planet was discovered using the HATSouth transit survey network, which includes instruments in Chile, Namibia, and Australia, and follow-up photometry and spectroscopy was conducted at a variety of ground-based observatories.HATS-18bs properties are particularly unusual: this hot Jupiter is zipping around its host star which is very similar to the Sun at the incredible pace of one orbit every 0.84 days. HATS-18bs orbit is more than 20 times closer to its host star than Mercurys is to the Sun, bringing it so close it nearly grazes the stars surface!Size of the planetary orbit relative to the stellar radius as a function of the stellar rotation period

  17. Neutron stars interiors: Theory and reality

    NASA Astrophysics Data System (ADS)

    Stone, J. R.

    2016-03-01

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

  18. Magnetic field evolution of accreting neutron stars

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    The flow of a matter, accreting on to a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the superconducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transverse conductivity. As a result, the current begins to flow mainly in the toroidal direction, creating a strong longitudinal magnetic field, far exceeding an initial dipole field. This field exists only in the narrow polar tube of r width, narrowing with the depth, i.e. with increasing of the crust density ρ, r ∝ ρ-1/4. Accordingly, the magnetic field B in the tube increases with the depth, B∝ρ1/2, and reaches the value of about 1017 Gauss in the core. It destroys superconducting vortices in the core of a star in the narrow region of the size of the order of 10 cm. Because of generated density gradient of vortices, they constantly flow into this dead zone and the number of vortices decreases, the magnetic field of a star decreases as well. The attenuation of the magnetic field is exponential, B = B0(1 + t/τ)-1. The characteristic time of decreasing of the magnetic field τ is equal to τ ≃ 103 yr. Thus, the magnetic field of accreted neutron stars decreases to values of 108-109 Gauss during 107-106 yr.

  19. Searching for gravitational waves from neutron stars

    NASA Astrophysics Data System (ADS)

    Idrisy, Ashikuzzaman

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

  20. From neutron stars to quark stars in mimetic gravity

    NASA Astrophysics Data System (ADS)

    Astashenok, Artyom V.; Odintsov, Sergei D.

    2016-09-01

    Realistic models of neutron and quark stars in the framework of mimetic gravity with a Lagrange multiplier constraint are presented. We discuss the effect of a mimetic scalar aiming to describe dark matter on the mass-radius relation and the moment of inertia for slowly rotating relativistic stars. The mass-radius relation and moment of inertia depend on the value of the mimetic scalar in the center of the star. This fact leads to the ambiguity in the mass-radius relation for a given equation of state. Such ambiguity allows us to explain some observational facts better than in standard general relativity. The case of mimetic potential V (ϕ )˜A eC ϕ2 is considered in detail. The relative deviation of the maximal moment of inertia is approximately twice as large as the relative deviation of the maximal stellar mass. We also briefly discuss the mimetic f (R ) gravity. In the case of f (R )=R +a R2 mimetic gravity, it is expected that the increase of maximal mass and maximal moment of inertia due to the mimetic scalar becomes much stronger with bigger parameter a . The influence of the scalar field in mimetic gravity can lead to the possible existence of extreme neutron stars with large masses.

  1. Lattice Waves, Spin Waves, and Neutron Scattering

    DOE R&D Accomplishments Database

    Brockhouse, Bertram N.

    1962-03-01

    Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)

  2. Merging neutron stars. 1. Initial results for coalescence of noncorotating systems

    NASA Technical Reports Server (NTRS)

    Davies, M. B.; Benz, W.; Piran, T.; Thielemann, F. K.

    1994-01-01

    We present three-dimensional Newtonian simulations of the coalescence of two neutron stars, using a smoothed particle hydrodynamics (SPH) code. We begin the simulations with the two stars in a hard, circular binary, and have them spiral together as angular momentum is lost through gravitational radiation at the rate predicted by modeling the system as two point masses. We model the neutron stars as hard polytropes (gamma = 2.4) of equal mass, and investigate the effect of the initial spin of the two stars on the coalescence. The process of coalescence, from initial contact to the formation of an axially symmetric object, takes only a few orbital periods. Some of the material from the two neutron stars is shed, forming a thick disk around the central, coalesced object. The mass of this disk is dependent on the initial neutron star spins; higher spin rates result in greater mass loss and thus more massive disks. For spin rates that are most likely to be applicable to real systems, the central coalesced object has a mass of 2.4 solar mass, which is tantalizingly close to the maximum mass allowed by any neutron star equation of state for an object that is supported in part by rotation. Using a realistic nuclear equation of state, we estimate the temperature of the material after the coalescence. We find that the central object is at a temperature of approximately 10 MeV, while the disk is heated by shocks to a temperature of 2 to 4 MeV.

  3. Isolated neutron stars in the galaxy: from magnetars to antimagnetars

    SciTech Connect

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

    2012-07-15

    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.

  4. Accuracy in measuring the neutron star mass in the gravitational wave parameter estimation for black hole-neutron star binaries

    NASA Astrophysics Data System (ADS)

    Cho, Hee-Suk

    2016-09-01

    Recently, two gravitational wave (GW) signals, named as GW150914 and GW151226, have been detected by the two LIGO detectors. Although both signals were identified as originating from merging black hole (BH) binaries, GWs from systems containing neutron stars (NSs) are also expected to be detected in the near future by the advanced detector network. In this work, we assess the accuracy in measuring the NS mass ( M NS) for the GWs from BH-NS binaries adopting the Advanced LIGO sensitivity with a signal-to-noise ratio of 10. By using the Fisher matrix method, we calculate the measurement errors ( σ) in M NS assuming a NS mass of 1 ≤ M NS/ M ⊙ ≤ 2 and low-mass BHs with masses in the range of 4 ≤ M BH/ M ⊙ ≤ 10. We use the TaylorF2 waveform model in which the spins are aligned with the orbital angular momentum, but here we only consider the BH spins. We find that the fractional errors ( σ/ M NS × 100) are in the range of 10% - 50% in our mass region for a given dimensionless BH spin χBH = 0. The errors tend to increase as the BH spin increases, and this tendency is stronger for higher NS masses (or higher total masses). In particular, for the highest mass NSs ( M NS = 2 M ⊙), the errors σ can be larger than the true value of M NS if the dimensionless BH spin exceeds ~ 0.6.

  5. Nonequilibrium Dynamics and the Evolution of Superfluid Neutron Stars

    NASA Astrophysics Data System (ADS)

    Sauls, Jame

    2016-07-01

    The interior crust and the liquid core of neutron stars are predicted to be a mixture of neutron and proton superfluids and a liquid of relativistic electrons and muons. Quantized vortices in the neutron superfluid and quantized flux lines in the proton superconductor are topological defects of these hadronic condensates. I discuss the roles of nucleation, interaction and evolution of topological defects under non-equilibrium conditions in the context of our current understanding and models of the rotational dynamics of pulsars, as well as thermal and magnetic field evolution of neutron stars. I include some speculative ideas on possibile turbulent vortex states in neutron star interiors.

  6. Cooling rates of neutron stars and the young neutron star in the Cassiopeia A supernova remnant

    NASA Astrophysics Data System (ADS)

    Yakovlev, Dmitry G.; Ho, Wynn C. G.; Shternin, Peter S.; Heinke, Craig O.; Potekhin, Alexander Y.

    2011-03-01

    We explore the thermal state of the neutron star in the Cassiopeia A supernova remnant using the recent result of Ho & Heinke that the thermal radiation of this star is well described by a carbon atmosphere model and the emission comes from the entire stellar surface. Starting from neutron star cooling theory, we formulate a robust method to extract neutrino cooling rates of thermally relaxed stars at the neutrino cooling stage from observations of thermal surface radiation. We show how to compare these rates with the rates of standard candles - stars with non-superfluid nucleon cores cooling slowly via the modified Urca process. We find that the internal temperature of standard candles is a well-defined function of the stellar compactness parameter x=rg/R, irrespective of the equation of state of neutron star matter (R and rg are circumferential and gravitational radii, respectively). We demonstrate that the data on the Cassiopeia A neutron star can be explained in terms of three parameters: fℓ, the neutrino cooling efficiency with respect to the standard candle; the compactness x; and the amount of light elements in the heat-blanketing envelope. For an ordinary (iron) heat-blanketing envelope or a low-mass (≲ 10-13 M⊙) carbon envelope, we find the efficiency fℓ˜ 1 (standard cooling) for x≲ 0.5 and fℓ˜ 0.02 (slower cooling) for a maximum compactness x≈ 0.7. A heat blanket containing the maximum mass (˜10-8 M⊙) of light elements increases fℓ by a factor of 50. We also examine the (unlikely) possibility that the star is still thermally non-relaxed.

  7. Gamma-ray bursts from extinct neutron stars

    NASA Technical Reports Server (NTRS)

    Michel, F. C.

    1990-01-01

    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.

  8. Merger of binary neutron stars: Gravitational waves and electromagnetic counterparts

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru

    2016-12-01

    Late inspiral and merger phases of binary neutron stars are the valuable new experimental fields for exploring nuclear physics because (i) gravitational waves from them will bring information for the neutron-star equation of state and (ii) the matter ejected after the onset of the merger could be the main site for the r-process nucleosynthesis. We will summarize these aspects of the binary neutron stars, describing the current understanding for the merger process of binary neutron stars that has been revealed by numerical-relativity simulations.

  9. Measuring neutron star tidal deformability with Advanced LIGO: A Bayesian analysis of neutron star-black hole binary observations

    NASA Astrophysics Data System (ADS)

    Kumar, Prayush; Pürrer, Michael; Pfeiffer, Harald P.

    2017-02-01

    The pioneering discovery of gravitational waves (GWs) by Advanced LIGO has ushered us into an era of observational GW astrophysics. Compact binaries remain the primary target sources for GW observation, of which neutron star-black hole (NSBH) binaries form an important subset. GWs from NSBH sources carry signatures of (a) the tidal distortion of the neutron star by its companion black hole during inspiral, and (b) its potential tidal disruption near merger. In this paper, we present a Bayesian study of the measurability of neutron star tidal deformability ΛNS∝(R /M )NS5 using observation(s) of inspiral-merger GW signals from disruptive NSBH coalescences, taking into account the crucial effect of black hole spins. First, we find that if nontidal templates are used to estimate source parameters for an NSBH signal, the bias introduced in the estimation of nontidal physical parameters will only be significant for loud signals with signal-to-noise ratios greater than ≃30 . For similarly loud signals, we also find that we can begin to put interesting constraints on ΛNS (factor of 1-2) with individual observations. Next, we study how a population of realistic NSBH detections will improve our measurement of neutron star tidal deformability. For an astrophysically likely population of disruptive NSBH coalescences, we find that 20-35 events are sufficient to constrain ΛNS within ±25 %- 50 % , depending on the neutron star equation of state. For these calculations we assume that LIGO will detect black holes with masses within the astrophysical mass gap. In case the mass gap remains preserved in NSBHs detected by LIGO, we estimate that approximately 25% additional detections will furnish comparable ΛNS measurement accuracy. In both cases, we find that it is the loudest 5-10 events that provide most of the tidal information, and not the combination of tens of low-SNR events, thereby facilitating targeted numerical-GR follow-ups of NSBHs. We find these results

  10. Astronomers Find the First 'Wind Nebula' Around a Rare Ultra-Magnetic Neutron Star

    NASA Image and Video Library

    2016-06-21

    Astronomers have discovered a vast cloud of high-energy particles called a wind nebula around a rare ultra-magnetic neutron star, or magnetar, for the first time. The find offers a unique window into the properties, environment and outburst history of magnetars, which are the strongest magnets in the universe. A neutron star is the crushed core of a massive star that ran out of fuel, collapsed under its own weight, and exploded as a supernova. Each one compresses the equivalent mass of half a million Earths into a ball just 12 miles (20 kilometers) across, or about the length of New York's Manhattan Island. Neutron stars are most commonly found as pulsars, which produce radio, visible light, X-rays and gamma rays at various locations in their surrounding magnetic fields. When a pulsar spins these regions in our direction, astronomers detect pulses of emission, hence the name. Credit: ESA/XMM-Newton/Younes et al. 2016

  11. Probing Neutron Star Evolution with Gamma Rays

    NASA Astrophysics Data System (ADS)

    Wijers, Ralph A. M. J.

    1996-02-01

    The research sponsored by this grant was conducted in two fields of high-energy astrophysics: gamma-ray bursts and evolution of neutron stars. It is unknown at this time whether they are related. The work performed in each area is discussed followed by a full list of publications supported by the grant. My research (with E. Fenimore, L. Lubin, B. Paczyiiski, and A. Ulmer) has focussed on devising tests that could distinguish between BATSE and galactic-halo distance scales using the available data. In the first instance, the issue was whether the early BATSE peak flux distribution could be used to extract more than just a slope of the log N(greater than P) distribution, and whether it joined smoothly to the steeper peak flux distribution of bright bursts. To this end, we analysed the peak flux distribution for the presence of a change in slope. This was done both by fitting models with a core radius to see whether a significant value for it could be found, and by developing a completely model-independent test to search for slope changes in arbitrary distributions that are nearly power laws. A slope change was marginally detected in the first-year BATSE data. Good progress has been made in understanding the evolution of neutron stars and their magnetic fields. Having shown in earlier work that magnetic fields in some neutron stars, particularly Her X-1, do not decay spontaneously on million-year time scales, we set out to check whether such spontaneous decay was needed in isolated radio pulsars, as claimed by many. We found that it is not; rather long decay times or no decay are preferred. Since there are neutron stars with low magnetic fields, one must conclude that there is something in their past that distinguishes them from most pulsars. These so-called recycled pulsars are in binaries much more often than normal pulsars. My research concentrates on the class of scenarios in which the recycled pulsars are initially the same as ordinary high-field radio pulsars

  12. Future Probes of the Neutron Star Equation of State Using X-ray Bursts

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.

    2004-01-01

    Observations with NASA s Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast (200 - 600 Hz), coherent X-ray intensity oscillations (hereafter, %urstoscillations ) during thermonuclear X-ray bursts from 12 low mass X-ray binaries (LMXBs). Although many of their detailed properties remain to be fully understood, it is now beyond doubt that these oscillations result from spin modulation of the thermonuclear burst flux from the neutron star surface. Among the new timing phenomena revealed by RXTE the burst oscillations are perhaps the best understood, in the sense that many of their properties can be explained in the framework of this relatively simple model. Because of this, detailed modelling of burst oscillations can be an extremely powerful probe of neutron star structure, and thus the equation of state (EOS) of supra-nuclear density matter. Both the compactness parameter beta = GM/c(sup 2)R, and the surface velocity, nu(sub rot) = Omega(sub spin)R, are encoded in the energy-dependent amplitude and shape of the modulation pulses. The new discoveries have spurred much new theoretical work on thermonuclear burning and propagation on neutron stars, so that in the near future it is not unreasonable to think that detailed physical models of the time dependent flux from burning neutron stars will be available for comparison with the observed pulse profiles from a future, large collecting area X-ray timing observatory. In addition, recent high resolution burst spectroscopy with XMM/Newton suggests the presence of redshifted absorption lines from the neutron star surface during bursts. This leads to the possibility of using large area, high spectral resolution measurements of X-ray bursts as a precise probe of neutron star structure. In this work I will explore the precision with which constraints on neutron star structure, and hence the dense matter EOS, can be made with the implementation of such programs.

  13. Statistical theory of thermal evolution of neutron stars

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  14. Dynamics of dissipative multifluid neutron star cores

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  15. Probing the possibility of hotspots on the central neutron star in HESS J1731-347

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    The X-ray spectra of the neutron stars located in the centers of supernova remnants Cas A and HESS J1731-347 are well fit with carbon atmosphere models. These fits yield plausible neutron star sizes for the known or estimated distances to these supernova remnants. The evidence in favor of the presence of a pure carbon envelope at the neutron star surface is rather indirect and is based on the assumption that the emission is generated uniformly by the entire stellar surface. Although this assumption is supported by the absence of pulsations, the observational upper limit on the pulsed fraction is not very stringent. In an attempt to quantify this evidence, we investigate the possibility that the observed spectrum of the neutron star in HESS J1731-347 is a combination of the spectra produced in a hydrogen atmosphere of the hotspots and of the cooler remaining part of the neutron star surface. The lack of pulsations in this case has to be explained either by a sufficiently small angle between the neutron star spin axis and the line of sight, or by a sufficiently small angular distance between the hotspots and the neutron star rotation poles. As the observed flux from a non-uniformly emitting neutron star depends on the angular distribution of the radiation emerging from the atmosphere, we have computed two new grids of pure carbon and pure hydrogen atmosphere model spectra accounting for Compton scattering. Using new hydrogen models, we have evaluated the probability of a geometry that leads to a pulsed fraction below the observed upper limit to be about 8.2%. Such a geometry thus seems to be rather improbable but cannot be excluded at this stage.

  16. Neutron Stars: Laboratories for Fundamental Physics Under Extreme Astrophysical Conditions

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Debades

    2017-09-01

    We discuss different exotic phases and components of matter from the crust to the core of neutron stars based on theoretical models for equations of state relevant to core collapse supernova simulations and neutron star merger. Parameters of the models are constrained from laboratory experiments. It is observed that equations of state involving strangeness degrees of freedom such as hyperons and Bose-Einstein condensates are compatible with 2{M}_{solar} neutron stars. The role of hyperons is explored on the evolution and stability of the protoneutron star in the context of SN1987A. Moment of inertia, mass and radius which are direct probes of neutron star interior are computed and their observational consequences are discussed. We continue our study on the dense matter under strong magnetic fields and its application to magnetoelastic oscillations of neutron stars.

  17. Is there a propeller neutron star in γ Cas?

    NASA Astrophysics Data System (ADS)

    Smith, M. A.; Lopes de Oliveira, R.; Motch, C.

    2017-08-01

    γ Cas is the prototype of a small population of B0-B1.5 III-V classical Be (cBe) stars that emit anomalous and hard X-rays with a unique array of properties. γ Cas is known to host, like other cBe stars, a decretion disc and also a low-mass companion. Recently, Postnov et al. have posited that this companion is a magnetized rapidly spinning neutron star that deflects direct gravitational accretion from a stellar/disc wind via the 'propeller mechanism'. These authors state that the key X-ray observations are 'remarkably well produced' in this scenario. We re-examine this mechanism in detail and conclude that there are a number of fatal objections in its application to the γ Cas case. Among other considerations these issues include the prediction under the propeller scenario of a much smaller population of γ Cas stars than is observed and the lack of allowance for observed correlations of X-ray and UV and/or optical properties over a variety of time-scales.

  18. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    NICER Optics Lead Takashi Okajima installs one of NICER’s 56 X-ray “concentrators,” each consisting of 24 concentric foils. To minimize the effects of Earth’s gravity on their alignment, the concentrator assemblies were installed from the outside edges toward the center of the plate that houses them. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  19. Sound Velocity Bound and Neutron Stars

    SciTech Connect

    Bedaque, Paulo; Steiner, Andrew W.

    2015-01-21

    A conjecture 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. Moreover, the bound has been demonstrated in several classes of strongly coupled theories with gravity duals and is saturated only in conformal theories. Here, 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.

  20. Neutron star cooling and pion condensation

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  1. Quark matter droplets in neutron stars

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  2. Quark matter droplets in neutron stars

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  3. Sound Velocity Bound and Neutron Stars

    DOE PAGES

    Bedaque, Paulo; Steiner, Andrew W.

    2015-01-21

    A conjecture 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. Moreover, the bound has been demonstrated in several classes of strongly coupled theories with gravity duals and is saturated only in conformal theories. Here, we point out that the existence of neutron stars with masses around two solar masses combined with the knowledge of the equation of state of hadronic matter at low densities is in strong tension with this bound.

  4. Nonthermal accretion disk models around neutron stars

    NASA Technical Reports Server (NTRS)

    Tavani, M.; Liang, Edison P.

    1994-01-01

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

  5. Supernovae, neutron stars and biomolecular chirality.

    PubMed

    Bonner, W A; Rubenstein, E

    1987-01-01

    Recent theoretical and experimental investigations of the origin of biomolecular chirality are reviewed briefly. Biotic and abiotic theories are evaluated critically with the conclusion that asymmetric photochemical processes with circulary polarized light (CPL), particularly asymmetric photolyses, constitute the most viable mechanisms. Solar CPL sources appear too weak and random to be effective. We suggest an alternative CPL source, namely, the synchrotron radiation from the neutron star remnants of supernova explosions. This could asymmetrically process racemic compounds in the organic mantles of the dust grains in interstellar clouds, and the resulting chiral molecules could be transferred to Earth by cold accretion as the solar system periodically traverses these interstellar clouds.

  6. Sound velocity bound and neutron stars.

    PubMed

    Bedaque, Paulo; Steiner, Andrew W

    2015-01-23

    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.

  7. Magneto-thermal evolution of neutron stars

    NASA Astrophysics Data System (ADS)

    Pons, J. A.; Miralles, J. A.; Geppert, U.

    2009-03-01

    Context: The presence of magnetic fields in the crust of neutron stars (NSs) causes a non-spherically symmetric temperature distribution. The strong temperature dependence of the magnetic diffusivity and thermal conductivity, together with the heat generated by magnetic dissipation, couple the magnetic and thermal evolution of NSs, which can no longer be formulated as separated one-dimensional problems. Aims: We study the mutual influence of thermal and magnetic evolution in a neutron star's crust in axial symmetry. Taking realistic microphysical inputs into account, we find the heat released by Joule effect consistent with the circulation of currents in the crust, and we incorporate its effects in 2D cooling calculations. Methods: We solve the induction equation numerically using a hybrid method (spectral in angles, but a finite-differences scheme in the radial direction), coupled to the thermal diffusion equation. To improve the boundary conditions, we also revisit the envelope stationary solutions updating the well known T_b-T_s-relations to include the effect of 2D heat transfer calculations and new microphysical inputs. Results: We present the first longterm 2D simulations of the coupled magneto-thermal evolution of neutron stars. This substantially improves previous works in which a very crude approximation in at least one of the parts (thermal or magnetic diffusion) has been adopted. Our results show that the feedback between Joule heating and magnetic diffusion is strong, resulting in a faster dissipation of the stronger fields during the first 10^5-106 years of an NS's life. As a consequence, all neutron stars born with fields over a critical value (>5 × 1013 G) reach similar field strengths (≈2-3 × 1013 G) at late times. Irrespective of the initial magnetic field strength, the temperature becomes so low after 106 years that the magnetic diffusion timescale becomes longer than the typical ages of radiopulsars, thus apparently resulting in no

  8. Neutron star binaries, pulsars and burst sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1981-01-01

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

  9. Theory of Radiation Transfer in Neutron Star Atmospheres

    NASA Technical Reports Server (NTRS)

    Zavlin, Vyacheslav

    2006-01-01

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

  10. A SECOND NEUTRON STAR IN M4?

    SciTech Connect

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

    2012-05-01

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

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

    SciTech Connect

    Chatterjee, Debarati; Bandyopadhyay, Debades

    2009-07-15

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

  12. TeV mu neutrinos from young neutron stars.

    PubMed

    Link, Bennett; Burgio, Fiorella

    2005-05-13

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

  13. Effect of radiation forces on disk accretion by weakly magnetic neutron stars

    NASA Technical Reports Server (NTRS)

    Miller, M. C.; Lamb, Frederick K.

    1993-01-01

    Radiation forces are shown to be more important than general relativistic corrections to Newtonian gravitational forces in determining the motion of particles accreting onto a slowly rotating neutron star if the luminosity of the star is greater than about 1 percent of the Eddington critical luminosity (ECL). This is so even if the radius of the star is less than the radius of the innermost stable orbit. In particular, radiation drag causes matter accreting from a disk to lose angular momentum and spiral inward. At luminosities greater than about 0.2 ECL, a substantial fraction of the accreting matter can transfer most of its angular momentum and gravitational binding energy to the radiation field before reaching the stellar surface. These results have important implications for the X-ray spectra, time variability, and spin evolution of neutron stars with very weak magnetic fields and the prospects for detecting general relativistic effects near such stars.

  14. Impact of phase transition from neutrons to hyperons in neutron star properties

    NASA Astrophysics Data System (ADS)

    Alrizal, Sulaksono, A.

    2017-07-01

    We revisit the impact of phase transition from neutrons to hyperons in the properties of neutron star using BSP parameter set of relativistic mean field (RMF) model. Similar to the work reported in Reference [1], the significance of the phase transition is observed from the impact gσ∗Λ/gσN variation on the corresponding neutron stars equation of state and mass versus radius relation. The impact of anisotropic pressure on equation of state and mass versus radius relation of neutron stars is also investigated. It is found that equation of state of neutron stars is very sensitive to gσ∗Λ/gσN coupling constant variation. However, different to the result of Reference [1], we do not obtain hyperon stars with very small radii R˜ 8 km. We do not also find significant effect of anisotropic pressure to change the behavior of neutron star properties due to phase transition.

  15. Stars Can't Spin Out of Control (Artist's Animation)

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Click on the image for QuickTime Movie of Stars Can't Spin Out of Control

    This artist's animation demonstrates how a dusty planet-forming disk can slow down a whirling young star, essentially saving the star from spinning itself to death. Evidence for this phenomenon comes from NASA's Spitzer Space Telescope.

    The movie begins by showing a developing star (red ball). The star is basically a giant ball of gas that is collapsing onto itself. As it shrinks, it spins faster and faster, like a skater folding in his or her arms. The green lines represent magnetic fields.

    As gravity continues to pull matter inward, the star spins so fast, it starts to flatten out. The same principle applies to the planet Saturn, whose spin has caused it to be slightly squashed or oblate.

    A forming star can theoretically whip around fast enough to overcome gravity and flatten itself into a state where it can no longer become a full-fledged star. But stars don't spin out of control, possibly because swirling disks of dust slow them down. Such disks can be found orbiting young stars, and are filled with dust that might ultimately stick together to form planets.

    The second half of the animation demonstrates how a disk is thought to keep its star's speed in check. A developing star is shown twirling inside its disk. As it turns, its magnetic fields pass through the disk and get bogged down like a spoon in molasses. This locks the star's rotation to the slower-turning disk, so the star, while continuing to shrink, does not spin faster.

    Spitzer found evidence for star-slowing disks in a survey of nearly 500 forming stars in the Orion nebula. It observed that slowly spinning stars are five times more likely to host disks than rapidly spinning stars.

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

    SciTech Connect

    Gandolfi, Stefano

    2015-01-13

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

  17. Spectral Models of Neutron Star Magnetospheres

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.

    1997-01-01

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

  18. Rapidly rotating neutron stars in general relativity: Realistic equations of state

    NASA Technical Reports Server (NTRS)

    Cook, Gregory B.; Shapiro, Stuart L.; Teukolsky, Saul A.

    1994-01-01

    We construct equilibrium sequences of rotating neutron stars in general relativity. We compare results for 14 nuclear matter equations of state. We determine a number of important physical parameters for such stars, including the maximum mass and maximum spin rate. The stability of the configurations to quasi-radial perturbations is assessed. We employ a numerical scheme particularly well suited to handle rapid rotation and large departures from spherical symmetry. We provide an extensive tabulation of models for future reference. Two classes of evolutionary sequences of fixed baryon rest mass and entropy are explored: normal sequences, which behave very much like Newtonian sequences, and supramassive sequences, which exist for neutron stars solely because of general relativistic effects. Adiabatic dissipation of energy and angular momentum causes a star to evolve in quasi-stationary fashion along an evolutionary sequence. Supramassive sequences have masses exceeding the maximum mass of a nonrotating neutron star. A supramassive star evolves toward eventual catastrophic collapse to a black hole. Prior to collapse, the star actually spins up as it loses angular momentum, an effect that may provide an observable precursor to gravitational collapse to a black hole.

  19. Rapidly rotating neutron stars in general relativity: Realistic equations of state

    NASA Technical Reports Server (NTRS)

    Cook, Gregory B.; Shapiro, Stuart L.; Teukolsky, Saul A.

    1994-01-01

    We construct equilibrium sequences of rotating neutron stars in general relativity. We compare results for 14 nuclear matter equations of state. We determine a number of important physical parameters for such stars, including the maximum mass and maximum spin rate. The stability of the configurations to quasi-radial perturbations is assessed. We employ a numerical scheme particularly well suited to handle rapid rotation and large departures from spherical symmetry. We provide an extensive tabulation of models for future reference. Two classes of evolutionary sequences of fixed baryon rest mass and entropy are explored: normal sequences, which behave very much like Newtonian sequences, and supramassive sequences, which exist for neutron stars solely because of general relativistic effects. Adiabatic dissipation of energy and angular momentum causes a star to evolve in quasi-stationary fashion along an evolutionary sequence. Supramassive sequences have masses exceeding the maximum mass of a nonrotating neutron star. A supramassive star evolves toward eventual catastrophic collapse to a black hole. Prior to collapse, the star actually spins up as it loses angular momentum, an effect that may provide an observable precursor to gravitational collapse to a black hole.

  20. Consequences of a strong phase transition in the dense matter equation of state for the rotational evolution of neutron stars

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    Aims: We explore the implications of a strong first-order phase transition region in the dense matter equation of state in the interiors of rotating neutron stars, and the resulting creation of two disjoint families of neutron-star configurations (the so-called high-mass twins). Methods: We numerically obtained rotating, axisymmetric, and stationary stellar configurations in the framework of general relativity, and studied their global parameters and stability. Results: The instability induced by the equation of state divides stable neutron star configurations into two disjoint families: neutron stars (second family) and hybrid stars (third family), with an overlapping region in mass, the high-mass twin-star region. These two regions are divided by an instability strip. Its existence has interesting astrophysical consequences for rotating neutron stars. We note that it provides a natural explanation for the rotational frequency cutoff in the observed distribution of neutron star spins, and for the apparent lack of back-bending in pulsar timing. It also straightforwardly enables a substantial energy release in a mini-collapse to another neutron-star configuration (core quake), or to a black hole.

  1. Neutron Resonance Spin Determination Using Multi-Segmented Detector DANCE

    SciTech Connect

    Baramsai, B.; Mitchell, G. E.; Chyzh, A.; Dashdorj, D.; Walker, C.; Agvaanluvsan, U.; Becvar, F.; Krticka, M.; Bredeweg, T. A.; Couture, A.; Haight, R. C.; Jandel, M.; Keksis, A. L.; O'Donnell, J. M.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.

    2011-06-01

    A sensitive method to determine the spin of neutron resonances is introduced based on the statistical pattern recognition technique. The new method was used to assign the spins of s-wave resonances in {sup 155}Gd. The experimental neutron capture data for these nuclei were measured with the DANCE (Detector for Advanced Neutron Capture Experiment) calorimeter at the Los Alamos Neutron Science Center. The highly segmented calorimeter provided detailed multiplicity distributions of the capture {gamma}-rays. Using this information, the spins of the neutron capture resonances were determined. With these new spin assignments, level spacings are determined separately for s-wave resonances with J{sup {pi}} = 1{sup -} and 2{sup -}.

  2. Neutron star Interior Composition ExploreR (NICER), Takashi Okaj

    NASA Image and Video Library

    2015-07-09

    Neutron star Interior Composition ExploreR (NICER) is an approved NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational and nuclear-physics environments embodied by neutron stars. NICER achieves these goals by deploying an X-ray timing and spectroscopy instrument as an attached payload aboard the International Space Station (ISS). Takashi Okajima installs optics.

  3. Neutron Star Structure in the Presence of Scalar Fields

    NASA Technical Reports Server (NTRS)

    Kazanas, Demosthenes

    2004-01-01

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

  4. Relativistic Processes and the Internal Structure of Neutron Stars

    SciTech Connect

    Alvarez-Castillo, D. E.; Kubis, S.

    2011-10-14

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

  5. Microscopic vortex velocity and implications for neutron star dynamics

    NASA Astrophysics Data System (ADS)

    Gügercinoǧlu, Erbil; Alpar, Mehmet Ali

    2016-07-01

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

  6. SELF-TRAPPING OF DISKOSEISMIC CORRUGATION MODES IN NEUTRON STAR SPACETIMES

    SciTech Connect

    Tsang, David; Pappas, George

    2016-02-10

    We examine the effects of higher-order multipole contributions of rotating neutron star (NS) spacetimes on the propagation of corrugation (c-)modes within a thin accretion disk. We find that the Lense–Thirring precession frequency, which determines the propagation region of the low-frequency fundamental corrugation modes, can experience a turnover allowing for c-modes to become self-trapped for sufficiently high dimensionless spin j and quadrupole rotational deformability α. If such self-trapping c-modes can be detected, e.g., through phase-resolved spectroscopy of the iron line for a high-spin low-mass accreting neutron star, this could potentially constrain the spin-induced NS quadrupole and the NS equation of state.

  7. RELATIONS BETWEEN NEUTRON-STAR PARAMETERS IN THE HARTLE-THORNE APPROXIMATION

    SciTech Connect

    Bauböck, Michi; Psaltis, Dimitrios; Özel, Feryal; Berti, Emanuele E-mail: dpsaltis@email.arizona.edu E-mail: berti@phy.olemiss.edu

    2013-11-01

    Using stellar structure calculations in the Hartle-Thorne approximation, we derive analytic expressions connecting the ellipticity of the stellar surface to the compactness, the spin angular momentum, and the quadrupole moment of the spacetime. We also obtain empirical relations between the compactness, the spin angular momentum, and the spacetime quadrupole. Our formulae reproduce the results of numerical calculations to within a few percent and help reduce the number of parameters necessary to model the observational appearance of moderately spinning neutron stars. This is sufficient for comparing theoretical spectroscopic and timing models to observations that aim to measure the masses and radii of neutron stars and to determine the equation of state prevailing in their interiors.

  8. Physics of systems containing neutron stars

    NASA Technical Reports Server (NTRS)

    Ruderman, Malvin

    1996-01-01

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

  9. Neutron star accretion and the neutrino fireball

    SciTech Connect

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

    1991-11-26

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

  10. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    A photo taken during the NICER range-of-motion test at NASA’s Goddard Space Flight Center shows the photographer’s reflection in the mirror-like radiator surface of the detector plate. Teflon-coated silver tape is used to keep NICER’s detectors cool. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  11. Simulations of binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Kiuchi, Kenta

    2017-01-01

    The merger of a binary composed of a neutron star and/or a black hole is one of the most promising sources of gravitational waves. If we detected gravitational waves from them, it could tell us a validity of the general relativity in a strong gravitational field and the equation of state of neutron star matter. Furthermore, if gravitational waves from a compact binary merger and a short-hard gamma-ray burst are observed simultaneously, a long-standing puzzle on the central engine of short gamma-ray bursts could be resolved. In addition, compact binary mergers are a theoretical candidate of the rapid process nucleosynthesis site. Motivated by these facts, it is mandatory to build a physically reliable model of compact binary mergers and numerical relativity is a unique approach for this purpose. We are tackling this problem from several directions; the magneto-hydrodynamics, the neutrino radiation transfer, and a comprehensive study with simplified models. I will talk a current status of Kyoto Numerical Relativity group and future prospect on the compact binary mergers.

  12. Gravitomagnetic tidal currents in rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Poisson, Eric; Douçot, Jean

    2017-02-01

    It was recently revealed that a rotating compact body responds dynamically when it is subjected to a gravitomagnetic tidal field, even when this field is idealized as time independent. The dynamical response is characterized by time-changing internal currents, and it was suspected to originate from zero-frequency g -modes and r -modes driven by the tidal forces. In this paper, we provide additional insights into the phenomenon by examining the tidal response of a rotating body within the framework of post-Newtonian gravity. This approach allows us to develop an intuitive picture for the phenomenon, which relies on the close analogy between post-Newtonian gravity and Maxwell's theory of electromagnetism. In this picture, the coupling between the gravitomagnetic tidal field and the body's rotational velocity is naturally expected to produce an unbalanced Lorentz-like force within the body, and it is this force that is responsible for the tidal currents. The simplicity of the fluid equations in the post-Newtonian setting allows us to provide a complete description of the zero-frequency modes and demonstrate their precise role in the establishment of the tidal currents. We estimate the amplitude of these currents, and find that for neutron-star binaries of relevance to LIGO, the scale of the velocity perturbation is measured in kilometers per second when the rotation period is comparable to 100 milliseconds. This estimate indicates that the tidal currents may have a significant impact on the physics of neutron stars near merger.

  13. Gravitomagnetic effect in magnetized neutron stars

    NASA Astrophysics Data System (ADS)

    Chatterjee, Debarati; Chakraborty, Chandrachur; Bandyopadhyay, Debades

    2017-01-01

    Rotating bodies in General Relativity produce frame dragging, also known as the gravitomagnetic effect in analogy with classical electromagnetism. In this work, we study the effect of magnetic field on the gravitomagnetic effect in neutron stars with poloidal geometry, which is produced as a result of its rotation. We show that the magnetic field has a non-negligible impact on frame dragging. The maximum effect of the magnetic field appears along the polar direction, where the frame-dragging frequency decreases with increase in magnetic field, and along the equatorial direction, where its magnitude increases. For intermediate angles, the effect of the magnetic field decreases, and goes through a minimum for a particular angular value at which magnetic field has no effect on gravitomagnetism. Beyond that particular angle gravitomagnetic effect increases with increasing magnetic field. We try to identify this `null region' for the case of magnetized neutron stars, both inside and outside, as a function of the magnetic field, and suggest a thought experiment to find the null region of a particular pulsar using the frame dragging effect.

  14. Constraining decaying dark matter with neutron stars

    NASA Astrophysics Data System (ADS)

    Pérez-García, M. Ángeles; Silk, Joseph

    2015-05-01

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

  15. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-27

    NICER engineer Steven Kenyon installs an X-ray detector onto the payload’s detector plate. The detectors are protected by red caps during installation because they are very sensitive to dust and other foreign object debris. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  16. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-27

    A NICER team member measures the focused optical power of each X-ray concentrator in a clean tent at NASA’s Goddard Space Flight Center. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  17. Neutron star Interior Composition Explorer (NICER)

    NASA Image and Video Library

    2017-09-28

    The NICER payload, blanketed and waiting for launch in the Space Station Processing Facility at NASA’s Kennedy Space Center in Cape Canaveral, Florida. The instrument is in its stowed configuration for launch. The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons. Credit: NASA/Goddard/ Keith Gendreau NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  18. Transient radio bursts from rotating neutron stars.

    PubMed

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

    2006-02-16

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

  19. Matter effects on binary neutron star waveforms

    NASA Astrophysics Data System (ADS)

    Read, Jocelyn S.; Baiotti, Luca; Creighton, Jolien D. E.; Friedman, John L.; Giacomazzo, Bruno; Kyutoku, Koutarou; Markakis, Charalampos; Rezzolla, Luciano; Shibata, Masaru; Taniguchi, Keisuke

    2013-08-01

    Using an extended set of equations of state and a multiple-group multiple-code collaborative effort to generate waveforms, we improve numerical-relativity-based data-analysis estimates of the measurability of matter effects in neutron-star binaries. We vary two parameters of a parametrized piecewise-polytropic equation of state (EOS) to analyze the measurability of EOS properties, via a parameter Λ that characterizes the quadrupole deformability of an isolated neutron star. We find that, to within the accuracy of the simulations, the departure of the waveform from point-particle (or spinless double black-hole binary) inspiral increases monotonically with Λ and changes in the EOS that did not change Λ are not measurable. We estimate with two methods the minimal and expected measurability of Λ in second- and third-generation gravitational-wave detectors. The first estimate using numerical waveforms alone shows that two EOSs which vary in radius by 1.3 km are distinguishable in mergers at 100 Mpc. The second estimate relies on the construction of hybrid waveforms by matching to post-Newtonian inspiral and estimates that the same EOSs are distinguishable in mergers at 300 Mpc. We calculate systematic errors arising from numerical uncertainties and hybrid construction, and we estimate the frequency at which such effects would interfere with template-based searches.

  20. On the electrostatic structure of neutron stars

    SciTech Connect

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

    2010-03-24

    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 beta-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.

  1. Geminga: A cooling superfluid neutron star

    NASA Technical Reports Server (NTRS)

    Page, Dany

    1994-01-01

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

  2. Geminga: A cooling superfluid neutron star

    NASA Technical Reports Server (NTRS)

    Page, Dany

    1994-01-01

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

  3. Spin measurement and neutron resonance spectroscopy for ^155Gd

    NASA Astrophysics Data System (ADS)

    Baramsai, Bayarbadrakh; Mitchell, G. E.; Chyzh, A.; Dashdorj, D.; Walker, C.; Bredeweg, T. A.; Couture, A.; Haight, R. C.; Jandel, M.; Keksis, A. L.; O'Donnell, J. M.; Rundberg, R. S.; Wouters, J. M.; Ullmann, J. L.; Viera, D. J.; Agvaanluvsan, U.; Becvar, F.; Krticka, M.

    2009-05-01

    The ^155Gd(n,γ) reaction has been measured with the DANCE calorimeter at Los Alamos Neutron Science Center. The highly segmented calorimeter provided detailed multiplicity distributions of the capture γ - rays. With this information the spins of the neutron capture resonances have been determined. The improved sensitivity of this method allowed the determination of the spins of even weak and unresolved resonances. With these new spin assignments as well as previously determined resonance parameters, level spacings and neutron strength functions are determined separately for s-wave resonances with J = 1 and 2.

  4. Revisiting Field Burial by Accretion onto Neutron Stars

    NASA Astrophysics Data System (ADS)

    Mukherjee, Dipanjan

    2017-09-01

    The surface magnetic field strength of millisecond pulsars (MSPs) is found to be about 4 orders of magnitude lower than that of garden variety radio pulsars (with a spin of {˜ }0.5-5 s and B{˜ }10^{12} G). The exact mechanism of the apparent reduction of field strength in MSPs is still a subject of debate. One of the proposed mechanisms is burial of the surface magnetic field under matter accreted from a companion. In this article we review the recent work on magnetic confinement of accreted matter on neutron stars poles. We present the solutions of the magneto-static equations with a more accurate equation of state of the magnetically confined plasma and discuss its implications for the field burial mechanism.

  5. A Coincident Search for Radio and Gravitational Waves from Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Cardena, Brett

    2011-05-01

    The merger of neutron star-neutron star binary pairs may be accompanied by the prompt emission of a coherent low-frequency radio pulse. This radio transient is produced as synchrotron radiation caused by the spin and rotation of the surface charge density of a pulsar through the magnetosphere of a larger neutron star, usually referred to as a Magnetar . This type of merger event would also result in the release of a gravitational coalescence wave-form. We will discuss a coincident radio transient and gravitational wave search. This search is being conducted by two radio telescope arrays: The Long Wave Array (LWA) and the Eight-meter-wavelength Transient Array (ETA) in coordination with the Laser Interferometer Gravitational-Wave Observatory (LIGO). We will outline this ongoing coincident search and discuss some preliminary results.

  6. On the Variability of the Isolated Neutron Star RX J0720.4-3125

    NASA Astrophysics Data System (ADS)

    Hambaryan, V.; Neuhäuser, R.

    2017-07-01

    A significant flux and spectral variability over a time scale of years in the X-ray emission of the isolated neutron star RX J0720.4-3125 has been studied based on the all observations conducted by XMM-Newton (2000-2012) years. This first ever detected non-stationary phenomenon in one of the seven radio-quiet, X-ray pulsating isolated neutron stars (INSs) discovered by ROSAT shows long-term variations in its spectral (black body temperature, size of the emitting area, the depth of the absorption feature) and timing parameters (spin period, pulse profile). The reason of this enigmatic behaviour is still unclear: cyclic variations are expected if the neutron star precesses while a sudden event like a glitch or an episode of a clumpy accretion from ambient medium may cause a gradual evolution after a relatively fast change.

  7. General Relativistic Radiation MHD Simulations of Supercritical Accretion onto a Magnetized Neutron Star: Modeling of Ultraluminous X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Takahashi, Hiroyuki R.; Ohsuga, Ken

    2017-08-01

    By performing 2.5-dimensional general relativistic radiation magnetohydrodynamic simulations, we demonstrate supercritical accretion onto a non-rotating, magnetized neutron star, where the magnetic field strength of dipole fields is 1010 G on the star surface. We found the supercritical accretion flow consists of two parts: the accretion columns and the truncated accretion disk. The supercritical accretion disk, which appears far from the neutron star, is truncated at around ≃3 R * (R * = 106 cm is the neutron star radius), where the magnetic pressure via the dipole magnetic fields balances with the radiation pressure of the disks. The angular momentum of the disk around the truncation radius is effectively transported inward through magnetic torque by dipole fields, inducing the spin up of a neutron star. The evaluated spin-up rate, ˜-10-11 s s-1, is consistent with the recent observations of the ultraluminous X-ray pulsars. Within the truncation radius, the gas falls onto a neutron star along the dipole fields, which results in a formation of accretion columns onto the northern and southern hemispheres. The net accretion rate and the luminosity of the column are ≃66 L Edd/c 2 and ≲10 L Edd, where L Edd is the Eddington luminosity and c is the light speed. Our simulations support a hypothesis whereby the ultraluminous X-ray pulsars are powered by the supercritical accretion onto the magnetized neutron stars.

  8. Probing crustal structures from neutron star compactness

    NASA Astrophysics Data System (ADS)

    Sotani, Hajime; Iida, Kei; Oyamatsu, Kazuhiro

    2017-10-01

    With various sets of the parameters that characterize the equation of state (EOS) of nuclear matter, we systematically examine the thickness of a neutron star crust and of the pasta phases contained therein. Then, with respect to the thickness of the phase of spherical nuclei, the thickness of the cylindrical phase and the crust thickness, we successfully derive fitting formulas that express the ratio of each thickness to the star's radius as a function of the star's compactness, the incompressibility of symmetric nuclear matter and the density dependence of the symmetry energy. In particular, we find that the thickness of the phase of spherical nuclei has such a strong dependence on the stellar compactness as the crust thickness, but both of them show a much weaker dependence on the EOS parameters. Thus, via determination of the compactness, the thickness of the phase of spherical nuclei as well as the crust thickness can be constrained reasonably, even if the EOS parameters remain to be well-determined.

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

    NASA Astrophysics Data System (ADS)

    2006-08-01

    Astronomers using radio telescopes from around the world have discovered a spinning neutron star with a superpowerful magnetic field -- called a magnetar -- doing things no magnetar has been seen to do before. The strange behavior has forced them to scrap previous theories about radio pulsars and promises to give new insights on the physics behind these extreme objects. Magnetar Artist's Conception of Magnetar With Radio Beams ALL IMAGES AND ANIMATIONS CREDIT: Bill Saxton, NRAO/AUI/NSF Image and Animation Files Magnetar Graphic (above image, JPEG, 32K) Animation With Sound From GBT Detection of XTE J1810-197 (8.6M) Animation With Sound From GBT Detection of XTE J1810-197 (Full Size, 29M) The magnetar, approximately 10,000 light-years from Earth in the direction of the constellation Sagittarius, is emitting powerful, regularly-timed pulses of radio waves just like radio pulsars, which are neutron stars with far less intense magnetic fields. Usually, magnetars are visible only in X-rays and sometimes very weakly in optical and infrared light. "No one has ever found radio pulses coming from a magnetar before. We thought that magnetars didn't do this," said Fernando Camilo of Columbia University. "This object is going to teach us new things about magnetar physics that we would never have learned otherwise," Camilo added. Neutron stars are the remnants of massive stars that have exploded as supernovae. Containing more mass than the Sun, they are compressed to a diameter of only about 15 miles, making them as dense as atomic nuclei. Ordinary pulsars are neutron stars that emit "lighthouse beams" of radio waves along the poles of their magnetic fields. As the star spins, the beam of radio waves is flung around, and when it passes the direction of Earth, astronomers can detect it with radio telescopes. Scientists have found about 1700 pulsars since their first discovery in 1967. While pulsars have strong magnetic fields, about a dozen neutron stars have been dubbed

  10. 3He spin filter based polarized neutron capability at the NIST Center for Neutron Research

    NASA Astrophysics Data System (ADS)

    Chen, W. C.; Gentile, T. R.; Erwin, R.; Watson, S.; Ye, Q.; Krycka, K. L.; Maranville, B. B.

    2014-07-01

    A 3He neutron spin filter (NSF) program for polarized neutron scattering was launched in 2006 as part of the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) Expansion Initiative. The goal of the project was to enhance the NCNR polarized neutron measurement capabilities. Benefitting from more than a decade's development of spin-exchange optical pumping (SEOP) at NIST, we planned to employ SEOP based 3He neutron spin filters for the polarized neutron scattering community. These 3He NSF devices were planned for use on different classes of polarized neutron instrumentation at the NCNR, including triple-axis spectrometers (TAS), small-angle neutron scattering instruments (SANS), reflectometers, and wide-angle polarization analysis. Among them, the BT-7 thermal TAS, NG-3 SANS, and MAGIK reflectometer have already been in the user program for routine polarized beam experiments. Wide-angle polarization analysis on Multi-Axis Crystal Spectrometer (MACS) has been developed for user experiments. We describe briefly the SEOP systems dedicated for polarized beam experiments and polarizing neutron development for each instrument class. We summarize the current status and polarized neutronic performance for each instrument. We present a 3He NSF hardware and software interface to allow for synchronization of 3He polarization inversion (neutron spin flipping) and free-induction decay (FID) nuclear magnetic resonance (NMR) measurements with neutron data collection.

  11. Dynamical Tidal Response of a Rotating Neutron Star

    NASA Astrophysics Data System (ADS)

    Landry, Philippe; Poisson, Eric

    2017-01-01

    The gravitational wave phase of a neutron star (NS) binary is sensitive to the deformation of the NS that results from its companion's tidal influence. In a perturbative treatment, the tidal deformation can be characterized by a set of dimensionless constants, called Love numbers, which depend on the NS equation of state. For static NSs, one type of Love number encodes the response to gravitoelectric tidal fields (associated with mass multipole moments), while another does likewise for gravitomagnetic fields (associated with mass currents). A NS subject to a gravitomagnetic tidal field develops internal fluid motions through gravitomagnetic induction; the fluid motions are irrotational, provided the star is non-rotating. When the NS is allowed to rotate, the situation is complicated by couplings between the tidal field and the star's spin. The problem becomes tractable in the slow-rotation limit. In this case, the fluid motions induced by an external gravitomagnetic field are fully dynamical, even if the tidal field is stationary: interior metric and fluid variables are time-dependent, and vary on the timescale of the rotation period. Remarkably, the exterior geometry of the NS remains time-independent.

  12. Spin echo small angle neutron scattering using a continuously pumped {sup 3}He neutron polarisation analyser

    SciTech Connect

    Parnell, S. R.; Li, K.; Yan, H.; Stonaha, P.; Li, F.; Wang, T.; Baxter, D. V.; Snow, W. M.; Washington, A. L.; Walsh, A.; Chen, W. C.; Parnell, A. J.; Fairclough, J. P. A.; Pynn, R.

    2015-02-15

    We present a new instrument for spin echo small angle neutron scattering (SESANS) developed at the Low Energy Neutron Source at Indiana University. A description of the various instrument components is given along with the performance of these components. At the heart of the instrument are a series of resistive coils to encode the neutron trajectory into the neutron polarisation. These are shown to work well over a broad range of neutron wavelengths. Neutron polarisation analysis is accomplished using a continuously operating neutron spin filter polarised by Rb spin-exchange optical pumping of {sup 3}He. We describe the performance of the analyser along with a study of the {sup 3}He polarisation stability and its implications for SESANS measurements. Scattering from silica Stöber particles is investigated and agrees with samples run on similar instruments.

  13. Stars Cant Spin Out of Control Artist Animation

    NASA Image and Video Library

    2006-07-24

    This artist concept demonstrates how a dusty planet-forming disk can slow down a whirling young star, essentially saving the star from spinning itself to death. Evidence for this phenomenon comes from NASA Spitzer Space Telescope.

  14. GRAVITATIONAL WAVES FROM FALLBACK ACCRETION ONTO NEUTRON STARS

    SciTech Connect

    Piro, Anthony L.

    2012-12-10

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

  15. Measuring neutron star tidal deformability with Advanced LIGO: black hole - neutron star binaries

    NASA Astrophysics Data System (ADS)

    Kumar, Prayush; Pürrer, Michael; Pfeiffer, Harald

    2017-01-01

    The pioneering observations of gravitational waves (GW) by Advanced LIGO have ushered us into an era of observational GW astrophysics. Compact binaries remain the primary target sources for GW observations, of which black hole - neutron star (BHNS) binaries form an important subset. GWs from coalescing BHNS systems carry signatures of the tidal distortion of the neutron star by its companion black hole during inspiral, as well as of its disruption close to merger. In this talk, I will discuss how well we can measure tidal effects from individual and populations of LIGO observations of disruptive BHNS mergers. I will also talk about how our measurements of non-tidal parameters can get affected by ignoring tidal effects in BHNS parameter estimation.

  16. Evidence for a Broad Relativistic Iron Line from the Neutron Star LMXB Ser X-1

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip; Strohmayer, Tod E.

    2007-01-01

    We report on an analysis of XMM-Newton data from the neutron star low mass X-ray binary (LMXB) Serpens X-1 (Ser X-1). Spectral analysis of EPIC PN data indicates that the previously known broad iron Ka emission line in this source has a significantly skewed structure with a moderately extended red wing. The asymmetric shape of the line is well described with the laor and diskline models in XSPEC, which strongly supports an inner accretion disk origin of the line. To our knowledge this is the first strong evidence for a relativistic line in a neutron star LMXB. This finding suggests that the broad lines seen in other neutron star LMXBs likely originate from the inner disk as well. Detailed study of such lines opens up a new way to probe neutron star parameters and their strong gravitational fields. The laor model describes the line from Ser X-1 somewhat better than diskline, and suggests that the inner accretion disk radius is less than 6GM/c(exp 2). This is consistent with the weak magnetic fields of LMXBs, and may point towards a high compactness and rapid spin of the neutron star. Finally, the inferred source inclination angle in the approximate range 50-60 deg is consistent with the lack of dipping from Ser X-1.

  17. A NuSTAR observation of disc reflection from close to the neutron star in 4U 1608-52

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Miller, J. M.; Chakrabarty, D.; Harrison, F. A.; Kara, E.; Fabian, A. C.

    2015-07-01

    Studying the reflection of X-rays off the inner edge of the accretion disc in a neutron star low-mass X-ray binary allows us to investigate the accretion geometry and to constrain the radius of the neutron star. We report on a NuSTAR observation of 4U 1608-52 obtained during a faint outburst in 2014 when the neutron star, which has a known spin frequency of ν = 620 Hz, was accreting at ≃1-2 per cent of the Eddington limit. The 3-79 keV continuum emission was dominated by a Γ ≃ 2 power law, with an ≃1-2 per cent contribution from a kTbb ≃ 0.3-0.6 keV blackbody component. The high-quality NuSTAR spectrum reveals the hallmarks of disc reflection; a broad iron-line peaking near 7 keV and a Compton back-scattering hump around ≃20-30 keV. Modelling the disc reflection spectrum points to a binary inclination of i ≃30°-40° and a small `coronal' height of h ≲8.5GM/c2. Furthermore, our spectral analysis suggests that the inner disc radius extended to Rin ≃ 7-10GM/c2, close to the innermost stable circular orbit. This constrains the neutron star radius to R ≲21 km and the redshift from the stellar surface to z ≳0.12, for a mass of M = 1.5 M⊙ and a spin parameter of a = 0.29.

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

    PubMed

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

    2009-03-06

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

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

    SciTech Connect

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

    2009-03-06

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

  20. Rotational and magnetic field instabilities in neutron stars

    SciTech Connect

    Kokkotas, Kostas D.

    2014-01-14

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

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

    SciTech Connect

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

    2008-01-01

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

  2. Lev Landau and the concept of neutron stars

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  4. General relativistic viscous hydrodynamics of differentially rotating neutron stars

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru; Kiuchi, Kenta; Sekiguchi, Yu-ichiro

    2017-04-01

    Employing a simplified version of the Israel-Stewart formalism for general-relativistic shear-viscous hydrodynamics, we perform axisymmetric general-relativistic simulations for a rotating neutron star surrounded by a massive torus, which can be formed from differentially rotating stars. We show that with our choice of a shear-viscous hydrodynamics formalism, the simulations can be stably performed for a long time scale. We also demonstrate that with a possibly high shear-viscous coefficient, not only viscous angular momentum transport works but also an outflow could be driven from a hot envelope around the neutron star for a time scale ≳100 ms with the ejecta mass ≳10-2 M⊙ , which is comparable to the typical mass for dynamical ejecta of binary neutron-star mergers. This suggests that massive neutron stars surrounded by a massive torus, which are typical outcomes formed after the merger of binary neutron stars, could be the dominant source for providing neutron-rich ejecta, if the effective shear viscosity is sufficiently high, i.e., if the viscous α parameter is ≳10-2. The present numerical result indicates the importance of a future high-resolution magnetohydrodynamics simulation that is the unique approach to clarify the viscous effect in the merger remnants of binary neutron stars by the first-principle manner.

  5. NEUTRON STAR STRUCTURE IN THE PRESENCE OF SCALAR FIELDS

    SciTech Connect

    Crawford, James P.; Kazanas, Demosthenes

    2009-08-20

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

  6. Hall Effect in Neutron Star Crusts

    NASA Astrophysics Data System (ADS)

    Gourgouliatos, K. N.; Cumming, A.

    2014-08-01

    The crust of Neutron Stars can be approximated by a highly conducting solid crystal lattice. The evolution of the magnetic field in the crust is mediated through Hall effect, namely the electric current is carried by the free electrons of the lattice and the magnetic field lines are advected by the electron fluid. Here, we present the results of a time-dependent evolution code which shows the effect Hall drift has in the large-scale evolution of the magnetic field. In particular we link analytical predictions with simulation results. We find that there are two basic evolutionary paths, depending on the initial conditions compared to Hall equilibrium. We also show the effect axial symmetry combined with density gradient have on suppressing turbulent cascade.

  7. Neutron Star Discovered Where a Black Hole Was Expected

    NASA Astrophysics Data System (ADS)

    2005-11-01

    A very massive star collapsed to form a neutron star and not a black hole as expected, according to new results from NASA's Chandra X-ray Observatory. This discovery shows that nature has a harder time making black holes than previously thought. Scientists found this neutron star -- a dense whirling ball of neutrons about 12 miles in diameter -- in an extremely young star cluster. Astronomers were able to use well-determined properties of other stars in the cluster to deduce that the progenitor of this neutron star was at least 40 times the mass of the Sun. ESO Optical Image of Westerlund 1 ESO Optical Image of Westerlund 1 "Our discovery shows that some of the most massive stars do not collapse to form black holes as predicted, but instead form neutron stars," said Michael Muno, a UCLA postdoctoral Hubble Fellow and lead author of a paper to be published in The Astrophysical Journal Letters. When very massive stars make neutron stars and not black holes, they will have a greater influence on the composition of future generations of stars. When the star collapses to form the neutron star, more than 95% of its mass, much of which is metal-rich material from its core, is returned to the space around it. "This means that enormous amounts of heavy elements are put back into circulation and can form other stars and planets," said J. Simon Clark of the Open University in the United Kingdom. Animation: Dissolve from Optical to X-ray Image of Westerlund 1 Animation: Dissolve from Optical to X-ray Image of Westerlund 1 Astronomers do not completely understand how massive a star must be to form a black hole rather than a neutron star. The most reliable method for estimating the mass of the progenitor star is to show that the neutron star or black hole is a member of a cluster of stars, all of which are close to the same age. Because more massive stars evolve faster than less massive ones, the mass of a star can be estimated from if its evolutionary stage is known. Neutron

  8. Model Atmospheres for X-Ray Bursting Neutron Stars

    NASA Astrophysics Data System (ADS)

    Medin, Zach; von Steinkirch, Marina; Calder, Alan C.; Fontes, Christopher J.; Fryer, Chris L.; Hungerford, Aimee L.

    2016-12-01

    The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Observations from X-ray telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.

  9. MODEL ATMOSPHERES FOR X-RAY BURSTING NEUTRON STARS

    SciTech Connect

    Medin, Zachary James; Steinkirch, Marina von; Calder, Alan C.; Fontes, Christopher J.; Fryer, Chris L.; Hungerford, Aimee L.

    2016-11-21

    The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Also, observations from X-ray telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Lastly, here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.

  10. Neutron star dynamos and the origins of pulsar magnetism

    NASA Technical Reports Server (NTRS)

    Thompson, Christopher; Duncan, Robert C.

    1993-01-01

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

  11. Neutron star dynamos and the origins of pulsar magnetism

    NASA Technical Reports Server (NTRS)

    Thompson, Christopher; Duncan, Robert C.

    1993-01-01

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

  12. Neutron detection in the frame of spatial magnetic spin resonance

    NASA Astrophysics Data System (ADS)

    Jericha, Erwin; Bosina, Joachim; Geltenbort, Peter; Hino, Masahiro; Mach, Wilfried; Oda, Tatsuro; Badurek, Gerald

    2017-02-01

    This work is related to neutron detection in the context of the polarised neutron optics technique of spatial magnetic spin resonance. By this technique neutron beams may be tailored in their spectral distribution and temporal structure. We have performed experiments with very cold neutrons (VCN) at the high-flux research reactor of the Institut Laue Langevin (ILL) in Grenoble to demonstrate the potential of this method. A combination of spatially and temporally resolving neutron detection allowed us to characterize a prototype neutron resonator. With this detector we were able to record neutron time-of-flight spectra, assess and minimise neutron background and provide for normalisation of the spectra owing to variations in reactor power and ambient conditions at the same time.

  13. Neutrino flavor evolution in neutron star mergers

    NASA Astrophysics Data System (ADS)

    Tian, James Y.; Patwardhan, Amol V.; Fuller, George M.

    2017-08-01

    We examine the flavor evolution of neutrinos emitted from the disklike remnant (hereafter called "neutrino disk") of a binary neutron star (BNS) merger. We specifically follow the neutrinos emitted from the center of the disk, along the polar axis perpendicular to the equatorial plane. We carried out two-flavor simulations using a variety of different possible initial neutrino luminosities and energy spectra and, for comparison, three-flavor simulations in specific cases. In all simulations, the normal neutrino mass hierarchy was used. The flavor evolution was found to be highly dependent on the initial neutrino luminosities and energy spectra; in particular, we found two broad classes of results depending on the sign of the initial net electron neutrino lepton number (i.e., the number of neutrinos minus the number of antineutrinos). In the antineutrino-dominated case, we found that the matter-neutrino resonance effect dominates, consistent with previous results, whereas in the neutrino-dominated case, a bipolar spectral swap develops. The neutrino-dominated conditions required for this latter result have been realized, e.g., in a BNS merger simulation that employs the "DD2" equation of state for neutron star matter [Phys. Rev. D 93, 044019 (2016), 10.1103/PhysRevD.93.044019]. For this case, in addition to the swap at low energies, a collective Mikheyev-Smirnov-Wolfenstein mechanism generates a high-energy electron neutrino tail. The enhanced population of high-energy electron neutrinos in this scenario could have implications for the prospects of r -process nucleosynthesis in the material ejected outside the plane of the neutrino disk.

  14. Superconducting magnetic Wollaston prism for neutron spin encoding.

    PubMed

    Li, F; Parnell, S R; Hamilton, W A; Maranville, B B; Wang, T; Semerad, R; Baxter, D V; Cremer, J T; Pynn, R

    2014-05-01

    A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ~30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ~98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.

  15. Superconducting magnetic Wollaston prism for neutron spin encoding

    NASA Astrophysics Data System (ADS)

    Li, F.; Parnell, S. R.; Hamilton, W. A.; Maranville, B. B.; Wang, T.; Semerad, R.; Baxter, D. V.; Cremer, J. T.; Pynn, R.

    2014-05-01

    A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ˜30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ˜98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.

  16. Superconducting magnetic Wollaston prism for neutron spin encoding

    SciTech Connect

    Li, F. Parnell, S. R.; Wang, T.; Baxter, D. V.; Hamilton, W. A.; Maranville, B. B.; Semerad, R.; Cremer, J. T.; Pynn, R.

    2014-05-15

    A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ∼30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ∼98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.

  17. Universality of the acceleration due to gravity on the surface of a rapidly rotating neutron star

    SciTech Connect

    AlGendy, Mohammad; Morsink, Sharon M.

    2014-08-20

    On the surface of a rapidly rotating neutron star, the effective centrifugal force decreases the effective acceleration due to gravity (as measured in the rotating frame) at the equator while increasing the acceleration at the poles due to the centrifugal flattening of the star into an oblate spheroid. We compute the effective gravitational acceleration for relativistic rapidly rotating neutron stars and show that for a star with mass M, equatorial radius R{sub e} , and angular velocity Ω, the deviations of the effective acceleration due to gravity from the nonrotating case take on a universal form that depends only on the compactness ratio M/R{sub e} , the dimensionless square of the angular velocity Ω{sup 2}R{sub e}{sup 3}/GM, and the latitude on the star's surface. This dependence is universal, in that it has very little dependence on the neutron star's equation of state. The effective gravity is expanded in the slow-rotation limit to show the dependence on the effective centrifugal force, oblate shape of the star, and the quadrupole moment of the gravitational field. In addition, an empirical fit and simple formula for the effective gravity is found. We find that the increase in the acceleration due to gravity at the poles is of the same order of magnitude as the decrease in the effective acceleration due to gravity at the equator for all realistic value of mass, radius, and spin. For neutron stars that spin with frequencies near 600 Hz, the difference between the effective gravity at the poles and the equator is about 20%.

  18. Probing thermonuclear flame spreading on neutron stars using burst rise oscillations

    NASA Astrophysics Data System (ADS)

    Chakraborty, Manoneeta; Bhattacharyya, Sudip

    2016-07-01

    Intense X-ray bursts (type-I bursts), originated from runaway thermonuclear processes, are observed from the surfaces of many accreting neutron star Low Mass X-ray Binary (LMXB) systems and they provide an important tool to constrain the neutron star equation of state. Periodic intensity variations during these bursts, termed burst oscillations, are observed in about 10% of thermonuclear bursts. Oscillations during the rising phases of thermonuclear bursts are hypothesized to originate from an expanding hot-spot on the surface of the neutron star. We studied the evolution of oscillations during the rising phase of a large sample of thermonuclear bursts from 10 bursting neutron stars in order to probe the process of burning front propagation during an X-ray burst. Our results show observational evidences of expanding hot-spot with spin modulated flame speeds, possibly due to the effects of the Coriolis force present as a result of the high stellar spin (270-620 Hz). This implies that the flame propagation is latitude-dependent and we address the factors affecting the detection and non-detection of burst rise oscillations in the light of this Coriolis force modulated flame spreading scenario.

  19. Testing the Young Neutron Star Scenario with Persistent Radio Emission Associated with FRB 121102

    NASA Astrophysics Data System (ADS)

    Kashiyama, Kazumi; Murase, Kohta

    2017-04-01

    Recently a repeating fast radio burst (FRB) 121102 has been confirmed to be an extragalactic event and a persistent radio counterpart has been identified. While other possibilities are not ruled out, the emission properties are broadly consistent with Murase et al. that theoretically proposed quasi-steady radio emission as a counterpart of both FRBs and pulsar-driven supernovae. Here, we constrain the model parameters of such a young neutron star scenario for FRB 121102. If the associated supernova has a conventional ejecta mass of M ej ≳ a few M ⊙, a neutron star with an age of t age ∼ 10–100 years, an initial spin period of P i ≲ a few ms, and a dipole magnetic field of B dip ≲ a few × 1013 G can be compatible with the observations. However, in this case, the magnetically powered scenario may be favored as an FRB energy source because of the efficiency problem in the rotation-powered scenario. On the other hand, if the associated supernova is an ultra-stripped one or the neutron star is born by the accretion-induced collapse with M ej ∼ 0.1 M ⊙, a younger neutron star with t age ∼ 1–10 years can be the persistent radio source and might produce FRBs with the spin-down power. These possibilities can be distinguished by the decline rate of the quasi-steady radio counterpart.

  20. Bow Shocks from Neutron Stars: Scaling Laws and Hubble Space Telescope Observations of the Guitar Nebula

    NASA Astrophysics Data System (ADS)

    Chatterjee, S.; Cordes, J. M.

    2002-08-01

    The interaction of high-velocity neutron stars with the interstellar medium produces bow shock nebulae, in which the relativistic neutron star wind is confined by ram pressure. We present multiwavelength observations of the Guitar Nebula, including narrowband Hα imaging with Hubble Space Telescope (HST) WFPC2, which resolves the head of the bow shock. The HST observations are used to fit for the inclination of the pulsar velocity vector to the line of sight and to determine the combination of spin-down energy loss, velocity, and ambient density that sets the scale of the bow shock. We find that the velocity vector is most likely in the plane of the sky. We use the Guitar Nebula and other observed neutron star bow shocks to test scaling laws for their size and Hα emission, discuss their prevalence, and present criteria for their detectability in targeted searches. The set of Hα bow shocks shows remarkable consistency, in spite of the expected variation in ambient densities and orientations. Together, they support the assumption that a pulsar's spin-down energy losses are carried away by a relativistic wind that is indistinguishable from being isotropic. Comparison of Hα bow shocks with X-ray and nonthermal radio-synchrotron bow shocks produced by neutron stars indicates that the overall shape and scaling is consistent with the same physics. It also appears that nonthermal radio emission and Hα emission are mutually exclusive in the known objects and perhaps in all objects.

  1. Neutron star structure with chiral interactions

    NASA Astrophysics Data System (ADS)

    Logoteta, Domenico; Bombaci, Ignazio

    2017-06-01

    We use two-body and three-body nuclear interactions derived in the framework of chiral perturbation theory (ChPT) with and without the explicit ∆ isobar contributions to calculate the energy per particle of symmetric nuclear matter and pure neutron matter employing the microscopic Brueckner-Hartree-Fock approach. In particular, we present nuclear matter calculations using the new fully local in coordinate-space two-nucleon interaction at the next-to-next-to-next-to-leading-order (N3LO) of ChPT with ∆ isobar intermediate states (N3LO∆) recently developed by Piarulli et al. [1]. We compute the β-equilibrium equation of state and determine the neutron star mass-radius and mass-central density sequences. We find that the adopted interactions are able to provide satisfactory properties of nuclear matter at saturation density as well as to fulfill the limit of two-solar mass for the maximum mass configuration as required by recent observations.

  2. Resonant Shattering of Neutron Star Crusts

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    The resonant excitation of neutron star (NS) modes by tides is investigated as a source of short gamma-ray burst (sGRB) precursors. We find that the driving of a crust-core interface mode can lead to shattering of the NS crust, liberating ~10^46-10^47 erg of energy 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.

  3. Surface composition of magnetic neutron stars.

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

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

  4. A Second Neutron Star in M4?

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    We show that the optical counterpart of the X-ray source CX 1 in M4 is a ~20th magnitude star, located in the color-magnitude diagram on (or very close to) the main sequence of the cluster, and exhibiting sinusoidal variations of the flux. We find the X-ray flux to be also periodically variable, with X-ray and optical minima coinciding. Stability of the optical light curve, lack of UV-excess, and unrealistic mean density resulting from period-density relation for semidetached systems speak against the original identification of CX 1 as a cataclysmic variable. We argue that the X-ray active component of this system is a neutron star (probably a millisecond pulsar). Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

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

    NASA Astrophysics Data System (ADS)

    Ludwig, Hendrik; Ruffini, Remo

    2014-09-01

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

  6. Internal heating and ultraviolet emission of old neutron stars

    NASA Astrophysics Data System (ADS)

    Reisenegger, Andreas

    Non-rotating neutron stars are expected to cool down to unobservably low temperatures within less than 10 Myr. However, all known neutron stars are rotating at a slowly decreasing rate, which has been proposed to re-heat old neutron stars by two proceses: 1) Vortex creep, the dissipative motion of superfluid vortices through the neutron superfluid expected to exist in the neutron star crust (Alpar et al. 1984), and 2) Rotochemical heating, the energy released by non-equilibrium beta decays due to the slow contraction of the neutron star as its centrifugal force decreases (Reisenegger 1995, 1997; Fernandez & Reisenegger 2005; Petrovich & Reisenegger 2010, 2011). Both processes are quite model-dependent, but can naturally keep millisecond pulsars at a surface temperature ˜ 10(5mathrm{K}) , at which their thermal radiation should be observed in the far ultraviolet, as appears to be the case in HST observations of the closest millisecond pulsar, PSR J0437-4715 (Kargaltsev et al. 2004; Durant et al. 2012). Far-ultraviolet observations of other old pulsars, which unfortunately have not been attempted so far, should allow to distinguish between the two plausible heating processes and constrain the internal structure of neutron stars and the physics of very dense matter (Gonzalez & Reisenegger 2010).

  7. Precision exploration of neutron spin structure at Jefferson Lab

    SciTech Connect

    Nilanga Liyanage

    2003-08-01

    Spin structure functions provide basic information about the spin of the quark distributions inside the nucleon. Experimental understanding of the nucleon spin in the kinematic region where the three basic (''valence'') quarks dominate the nucleon wave function is still rather poor. Jefferson lab, with its high quality, high polarization continuous electron beam, and a high density polarized 3He target in experimental Hall A, provides the ideal opportunity to gather neutron spin structure data in the valence region with unprecedented precision. Two high precision neutron spin structure measurements were completed in Hall A last summer. The first experiment measured the spin asymmetry A1(N) in the valence region while in second experiment higher-twist effects were studied via measurements of gn2. The planed upgrade of Jefferson lab CEBAF accelerator to 12 GeV will significantly increase the accessible kinematic range and the precision of these measurements.

  8. Measurement of the spin-rotation coupling in neutron polarimetry

    NASA Astrophysics Data System (ADS)

    Demirel, Bülent; Sponar, Stephan; Hasegawa, Yuji

    2015-02-01

    The effect of spin-rotation coupling is measured for the first time with neutrons. The coupling of spin with the angular velocity of a rotating spin turner can be observed as a phase shift in a neutron polarimeter set-up. After the neutron’s spin is rotated by 2π through a rotating magnetic field, different phase shifts are induced for ‘up’ and ‘down’ spin eigenstates. This phase difference results in the rotation of the neutron’s spin-vector, which turns out to depend solely on the frequency of the rotation of the magnetic field. The experimental results agree well with the solutions acquired by the Pauli-Schrödinger equation.

  9. Neutron-capture nucleosynthesis in the first stars

    SciTech Connect

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

    2014-04-01

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

  10. Parity nonconserving spin rotation in weak neutron-proton scattering

    NASA Astrophysics Data System (ADS)

    Avishai, Y.

    1984-07-01

    Parity nonconservation in weak n-p scattering is studied at threshold wehre neutron spin rotation might occur. We use the DDH weak NN force and a separable form with S, P and D partial waves in the strong NN interaction. The contribution of various spin-isospin components to the weak NN scattering amplitude is evaluated and the spin rotation angle is found to be -2.35 × 10 -9 rad/cm. The sources of possible errors are indicated.

  11. Polarized (3) He Spin Filters for Slow Neutron Physics.

    PubMed

    Gentile, T R; Chen, W C; Jones, G L; Babcock, E; Walker, T G

    2005-01-01

    Polarized (3)He spin filters are needed for a variety of experiments with slow neutrons. Their demonstrated utility for highly accurate determination of neutron polarization are critical to the next generation of betadecay correlation coefficient measurements. In addition, they are broadband devices that can polarize large area and high divergence neutron beams with little gamma-ray background, and allow for an additional spin-flip for systematic tests. These attributes are relevant to all neutron sources, but are particularly well-matched to time of flight analysis at spallation sources. There are several issues in the practical use of (3)He spin filters for slow neutron physics. Besides the essential goal of maximizing the (3)He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments. We are currently employing spin-exchange (SE) and metastability-exchange (ME) optical pumping to polarize (3)He, but will focus on SE. We will discuss the recent demonstration of 75 % (3)He polarization, temperature-dependent relaxation mechanism of unknown origin, cell development, spectrally narrowed lasers, and hybrid spin-exchange optical pumping.

  12. Polarized 3He Spin Filters for Slow Neutron Physics

    PubMed Central

    Gentile, T. R.; Chen, W. C.; Jones, G. L.; Babcock, E.; Walker, T. G.

    2005-01-01

    Polarized 3He spin filters are needed for a variety of experiments with slow neutrons. Their demonstrated utility for highly accurate determination of neutron polarization are critical to the next generation of betadecay correlation coefficient measurements. In addition, they are broadband devices that can polarize large area and high divergence neutron beams with little gamma-ray background, and allow for an additional spin-flip for systematic tests. These attributes are relevant to all neutron sources, but are particularly well-matched to time of flight analysis at spallation sources. There are several issues in the practical use of 3He spin filters for slow neutron physics. Besides the essential goal of maximizing the 3He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments. We are currently employing spin-exchange (SE) and metastability-exchange (ME) optical pumping to polarize 3He, but will focus on SE. We will discuss the recent demonstration of 75 % 3He polarization, temperature-dependent relaxation mechanism of unknown origin, cell development, spectrally narrowed lasers, and hybrid spin-exchange optical pumping. PMID:27308140

  13. Neutron spin structure results from JLab Hall A

    SciTech Connect

    Zein-Eddine Meziani

    2004-02-01

    My presentation will focus on some of the latest results of the neutron spin physics program at Jefferson Laboratory in Hall A using a polarized 3He target. This program includes several completed experiments in which the spin structure functions of 3He were measured. The covered kinematic regions were these measurements were performed include the low Q2 resonance and inelastic regions and the high Q2 deep inelastic region. These experiments offer a ground for testing our understanding of the strong regime of quantum chromodynamics (QCD) through the determination of the neutron spin-dependent structure functions and their moments.

  14. Using a Neutron Star as a Stellar Wind Probe

    NASA Astrophysics Data System (ADS)

    Gregory, P. C.; Neish, C.

    2002-12-01

    LS I+61o303 is a remarkable X-ray and γ -ray emitting Be + neutron star binary, with periodic (26.5 day) radio outbursts. A recent Bayesian analysis demonstrates that the orbital phase and peak flux density of the radio outbursts exhibit a 4.6 year periodic modulation. We present a model that accounts for the radio properties of LS I+61o303 in terms of variable accretion by the neutron star in an eccentric orbit embedded within the dense equatorial wind from the rapidly rotating Be star. The neutron star thus acts as a probe of the wind speed and density. The analysis indicates that the 4.6 year modulation in radio properties results from an outward moving density enhancement or shell in the Be star equatorial disk. We propose that each new shell ejection may be triggered by the interaction of a short lived relativistic wind (ejector phase) from the neutron star, with the rapidly rotating Be star. Our best estimates of the mass accretion rate of the neutron star are in the range ~ 0.001 to ~ 0.01 of the Eddington accretion limit. This translates to an expected luminosity range of ~ 1035 to ~ 1036 ergs s-1 which is comparable to estimates of the total X-ray and γ -ray luminosity for LS I +61o 303. This research was supported in part by a grant from the Canadian Natural Sciences and Engineering Research Council at the University of British Columbia.

  15. Strong hyperon-nucleon pairing in neutron stars.

    PubMed

    Zhou, Xian-Rong; Schulze, H-J; Pan, Feng; Draayer, J P

    2005-07-29

    We explore the possibilities of hyperon-nucleon pairing, involving lambda or sigma- hyperons, using different Nijmegen hyperon-nucleon potentials. We find possible very large nsigma- gaps and estimate their relevance for neutron star physics.

  16. Larmor labeling of neutron spin using superconducting Wollaston prisms

    NASA Astrophysics Data System (ADS)

    Li, Fankang

    Neutron spin Larmor labeling using magnetic Wollaston prisms (WP) provides a way to overcome some of the limitations arising from the nature of neutron beams: low flux and divergence. Using superconducting films and tapes, a series of strong, well-defined shaped magnetic fields can be produced due to both the zero-resistance and Meissner effect in superconductors. Using finite element simulations, the criterion to build a superconducting magnetic Wollaston prism with high encoding efficiency and low Larmor phase aberrations are presented. To achieve a high magnetic field and simplify the maintenance, we optimize the design using careful thermal analysis. The measured neutron spin flipping efficiency is measured to be independent of both the neutron wavelength and energizing current, which is a significant improvement over other devices with similar functions. A highly linear variation of the Larmor phase is measured across the device, which ensures a highly uniform encoding of scattering angles into the neutron spin Larmor phase. Using two WPs, the correlation function for a colloidal silica sample was measured by spin echo modulated small angle neutron scattering (SEMSANS) and agrees well with other techniques. Using Monte Carlo code (McStas), we further investigated the SEMSANS setup and showed the requirements to improve its performance. We have proposed a new technique to implement neutron spin echo on a triple axis neutron spectrometer to achieve high resolution measurements of the lifetime of dispersive phonon excitations. The spin echo is tuned by appropriate choice of magnetic fields instead of physically tilting the coils used in traditional methods. This new approach allows a higher energy resolution and a larger effective tilting angle and hence larger group velocity to be measured.

  17. CCO Pulsars as Anti-Magnetars: Evidence of Neutron Stars Weakly Magnetized at Birth

    NASA Astrophysics Data System (ADS)

    Gotthelf, E. V.; Halpern, J. P.

    2008-02-01

    Our new study of the two central compact object pulsars, PSR J1210-5226 (P = 424 ms) and PSR J1852+0040 (P = 105 ms), leads us to conclude that a weak natal magnetic field shaped their unique observational properties. In the dipole spin-down formalism, the 2-sigma upper limits on their period derivatives, <2×10-16 for both pulsars, implies surface magnetic field strengths of Bs<3×1011 G and spin periods at birth equal to their present periods to three significant digits. Their X-ray luminosities exceed their respective spin-down luminosities, implying that their thermal spectra are derived from residual cooling and perhaps partly from accretion of supernova debris. For sufficiently weak magnetic fields an accretion disk can penetrate the light cylinder and interact with the magnetosphere while resulting torques on the neutron star remain within the observed limits. We propose the following as the origin of radio-quiet CCOs: the magnetic field, derived from a turbulent dynamo, is weaker if the NS is formed spinning slowly, which enables it to accrete SN debris. Accretion excludes neutron stars born with both Bs<1011 G and P>0.1 s from radio pulsar surveys, where such weak fields are not encountered except among very old (>40 Myr) or recycled pulsars. We predict that these birth properties are common, and may be attributes of the youngest detected neutron star, the CCO in Cassiopeia A, as well as an undetected infant neutron star in the SN 1987A remnant. In view of the far-infrared light echo discovered around Cas A and attributed to an SGR-like outburst, it is especially important to determine via timing whether Cas A hosts a magnetar or not. If not a magnetar, the Cas A NS may instead have undergone a one-time phase transition (corequake) that powered the light echo.

  18. The dynamics and outcomes of rapid infall onto neutron stars

    SciTech Connect

    Fryer, C.L.; Benz, W.; Herant, M.

    1996-04-01

    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 10{sup 4} {ital M}{sub {circle_dot}} yr{sup 1}. Two types of initial conditions are considered for a range of entropies and chemical compositions: an atmosphere in pressure equilibrium above the neutron star, and a freely falling inflow of matter from infinity (also parameterized by the infall rate). We then evolve the system with one- and two-dimensional hydrodynamic codes to determine the outcome. For most cases, hypercritical (also termed ``super Eddington``) accretion caused by rapid neutrino cooling allows the neutron star to accrete above the Bondi-Hoyle rate as previously pointed out by Chevalier. However, for a subset of simulations which corresponds to evolutionarily common events, convection driven by neutrino heating can lead to explosions by a mechanism similar to that found in core-collapse supernovae. Armed with the results from our calculations, we are in a position to predict the fate of a range of rapid-infall neutron star accretors present in certain low-mass X-ray binaries, common envelope systems, supernova fallbacks, and Thorne-Zytkow objects (TZOs). A majority of the common envelope systems that we considered led to explosions expelling the envelope, halting the neutron star{close_quote}s inward spiral, and allowing the formation of close binary systems. As a result, the smothered neutron stars produced in the collisions studied by Davies & Benz may also explode, probably preventing them from forming millisecond pulsars. For the most massive supernovae, in which the fallback of material toward the neutron star after a successful explosion is large, we find that a black hole is formed in a few seconds. Finally, we argue that the current set of TZO formation scenarios is inadequate and leads instead to hypercritical accretion and black hole formation.

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

    SciTech Connect

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

    2012-09-20

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

  20. MHD Stability of Polar Caps of Accreting Neutron Stars

    NASA Astrophysics Data System (ADS)

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

    2000-12-01

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

  1. Searching for substellar companions of young isolated neutron stars

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

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

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

    PubMed

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

    2007-06-01

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

  3. Structured mixed phase is favored in neutron stars

    SciTech Connect

    Christiansen, Michael B.; Glendenning, Norman K.

    2003-01-01

    We give a general thermodynamical argument showing that in neutron stars, the Coulomb structured mixed phase is always favored for any first order phase transition involving systems in equilibrium with baryon number and electric charge as the two independent components. This finding is likely to have important consequences for many neutron star properties, e.g., glitch phenomena, transport and superfluid properties, r-mode instabilities, and the braking index.

  4. Crust-core coupling in rotating neutron stars

    SciTech Connect

    Glampedakis, Kostas; Andersson, Nils

    2006-08-15

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

  5. Phase separation in the crust of accreting neutron stars

    SciTech Connect

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

    2007-06-15

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

  6. Gravitational waves from surface inhomogeneities of neutron stars

    NASA Astrophysics Data System (ADS)

    Konar, Sushan; Mukherjee, Dipanjan; Bhattacharya, Dipankar; Sarkar, Prakash

    2016-11-01

    Surface asymmetries of accreting neutron stars are investigated for their mass quadrupole moment content. Though the amplitude of the gravitational waves from such asymmetries seems to be beyond the limit of detectability of the present generation of detectors, it appears that rapidly rotating neutron stars with strong magnetic fields residing in high-mass x-ray binaries would be worth considering for a targeted search for continuous gravitational waves with the next generation of instruments.

  7. X-ray studies of neutron stars and their magnetic fields

    NASA Astrophysics Data System (ADS)

    Makishima, K.

    2016-05-01

    Utilizing results obtained over the past quarter century mainly with Japanese X-ray astronomy satellites, a review is given to some aspects of neutron stars (NSs), with a particular emphasis on the magnetic fields (MFs) of mass-accreting NSs and magnetars. Measurements of electron cyclotron resonance features in binary X-ray pulsars, using the Ginga and Suzaku observatories, clarified that their surface MFs are concentrated in a narrow range of (1?7) × 10^8 T. Extensive studies of magnetars with Suzaku reinforced their nature as neutron stars with truly strong MFs, and revealed several important clues to their formation, evolution, and physical states. Taking all these results into account, a discussion is made on the origin and evolution of these strong MFs. One possible scenario is that the MF of NSs is a manifestation of some fundamental physics, e.g., neutron spin alignment or chirality violation, and the MF makes transitions from strong to weak states.

  8. X-ray studies of neutron stars and their magnetic fields.

    PubMed

    Makishima, Kazuo

    2016-01-01

    Utilizing results obtained over the past quarter century mainly with Japanese X-ray astronomy satellites, a review is given to some aspects of neutron stars (NSs), with a particular emphasis on the magnetic fields (MFs) of mass-accreting NSs and magnetars. Measurements of electron cyclotron resonance features in binary X-ray pulsars, using the Ginga and Suzaku observatories, clarified that their surface MFs are concentrated in a narrow range of (1-7) × 10(8) T. Extensive studies of magnetars with Suzaku reinforced their nature as neutron stars with truly strong MFs, and revealed several important clues to their formation, evolution, and physical states. Taking all these results into account, a discussion is made on the origin and evolution of these strong MFs. One possible scenario is that the MF of NSs is a manifestation of some fundamental physics, e.g., neutron spin alignment or chirality violation, and the MF makes transitions from strong to weak states.

  9. Mean free paths of non-degenerate neutrinos in neutron star matter

    NASA Astrophysics Data System (ADS)

    Haensel, P.; Jerzak, A. J.

    1987-06-01

    The authors calculate the neutrino mean free path in the hot interior of neutron stars in the case when the neutrinos are non-degenerate. The calculations are performed for realistic models of the nucleon-nucleon interaction based on the Reid soft core potential. The scattering rate is calculated within the framework of the Fermi liquid theory using a realistic model of the quasiparticle interaction in nuclear matter. The contribution from the spin-zero sound collective excitations of the nucleon medium is important near normal nuclear matter density, but its importance decreases with increasing density. The effect of the tensor component of the quasiparticle interaction in the nucleon medium on the neutrino scattering rate is negligible. The absorption rate is calculated using a realistic description of the nucleon-nucleon correlations in the initial and final state. The tensor correlation of the neutron-proton pair plays a decisive role in determining the neutrino absorption rate in neutron star matter.

  10. X-ray studies of neutron stars and their magnetic fields

    PubMed Central

    MAKISHIMA, Kazuo

    2016-01-01

    Utilizing results obtained over the past quarter century mainly with Japanese X-ray astronomy satellites, a review is given to some aspects of neutron stars (NSs), with a particular emphasis on the magnetic fields (MFs) of mass-accreting NSs and magnetars. Measurements of electron cyclotron resonance features in binary X-ray pulsars, using the Ginga and Suzaku observatories, clarified that their surface MFs are concentrated in a narrow range of (1–7) × 108 T. Extensive studies of magnetars with Suzaku reinforced their nature as neutron stars with truly strong MFs, and revealed several important clues to their formation, evolution, and physical states. Taking all these results into account, a discussion is made on the origin and evolution of these strong MFs. One possible scenario is that the MF of NSs is a manifestation of some fundamental physics, e.g., neutron spin alignment or chirality violation, and the MF makes transitions from strong to weak states. PMID:27169348