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Results for “NEUTRON STAR”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Accreting, Isolated Neutron Stars: Preheated of Infalling Gas and Cometary H II Regions - 3

Nearby, isolated, old neutron stars (IONSs) accreting interstellar material might be detectable as sources of UV and soft X-ray radiation. We investigate the interaction between this radiation field and the surrounding medium, assumed to consist of purely hydrogen and helium. This interaction results in a cometary H II region around the star which we model in detail by including all the relevant time-dependent ionization, recombination, heating, and cooling processes. We find that preheating of the ambient gas to temperatures higher than 10(exp 4) K may significantly quench the accretion rate onto these neutron stars, thereby reducing the IONS number counts in the EUV and soft X-ray bands predicted by previous investigations. However, the reprocessing of hard radiation by the surrounding H II regions may enhance the detectability of IONSs at optical wavelengths. Searches for nearby accreting IONSs are currently being undertaken.

Madau, Piero↗
DOE OSTI2026

Microscopic constraints for the equation of state and structure of neutron stars: A Bayesian model mixing framework

Bayesian model mixing (BMM) is a statistical technique that can combine constraints from different regions of an input space in a principled way. Here we extend our BMM framework for the equation of state (EOS) of strongly interacting matter from symmetric nuclear matter to asymmetric matter, specifically focusing on zero-temperature, charge-neutral, 𝛽-equilibrated matter. We use Gaussian processes (GPs) to infer constraints on the neutron-star matter EOS at intermediate densities from two different microscopic theories: chiral effective-field theory (𝜒⁢EFT) at baryon densities around nuclear saturation, 𝑛 𝐵 ∼ 𝑛 0 , and perturbative QCD at asymptotically high baryon densities, 𝑛 𝐵 ⩾ 20⁢𝑛 0 . The uncertainties of the 𝜒⁢EFT and pQCD EOSs are obtained using the BUQEYE truncation error model. We demonstrate the flexibility of our framework through the use of two categories of GP kernels: conventional stationary kernels and a nonstationary changepoint kernel. We use the latter to explore potential constraints on the dense matter EOS by including exogenous data representing theory predictions and heavy-ion collision measurements at densities ⩾ 2⁢𝑛 0 . We also use our EOSs to obtain neutron-star mass-radius relations and their uncertainties. Finally, our framework, whose implementation will be available through a GitHub repository, provides a prior distribution for the EOS that can be used in large-scale neutron-star inference frameworks.

Bayesian methods↗
DOE OSTI2026

Error quantification and comparison of binary neutron star gravitational waveforms from numerical relativity codes

Future gravitational wave detections of merging binary neutron star systems have the possibility to tightly constrain the equation of state of dense nuclear matter. In order to extract such constraints, gravitational waveform models need to be calibrated to accurate numerical relativity simulations of the late inspiral and merger. In this work, we take an essential step toward classifying the error and potential systematics in current generation numerical relativity simulations of merging binary neutron stars. To this end, we perform a direct comparison of two codes (fil, spec), which differ in many aspects, including the numerical methods and discretizations used and equations solved. We find that despite these different approaches, the codes are—within current numerical resolution bounds—fully consistent, and broadly comparable in cost for a given accuracy level. Our results indicate that the error in the waveforms is primarily dominated by the hydrodynamic evolution, consistent with earlier findings in the literature. Finally, we also discuss current limitations and cost estimates for numerical relativity simulations to reach the accuracies required in the era of next-generation gravitational detectors.

gravitational waves↗
NASA NTRS1979

Neutrinos from neutron stars

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

Helfand, D. J.↗
NASA NTRS1987

Nonradial g-mode oscillations in X-ray bursting neutron stars

The oscillation spectrum of nonradial g-modes in X-ray bursting neutron stars has been studied. The pulsation periods are found to be sensitive to the envelope temperature and range from about 15 ms to about 50 ms for the l = 1 g(1) mode during the X-ray burst. From a quasi-adiabatic stability analysis it is likely that a spectrum of l-pole g-modes is unstable due to the epsilon-mechanism associated with rapid alpha captures. As the thermal structure of the envelope of the neutron star changes on time scales less than 0.2 s during the rise of the X-ray burst, the oscillations are expected to be quasi-coherent during this phase. The calculated period derivatives are large during the burst and are about 1 ms/s. The pulsations are short-lived and are most likely to be seen in the immediate vicinity of the burst peak. Finally, the possible relevance of nonradial g-mode pulsations to the recently discovered quasi-periodic oscillations observed in a number of X-ray sources is discussed.

Mcdermott, P. N.↗
NASA NTRS2008

Neutron Star Interior Composition Explorer (NICE)

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

Gendreau, Keith C.↗
NASA NTRS1974

Quantum crystals in neutron stars

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

Canuto, V.↗
DOE OSTI2025

Interface Modes in Inspiralling Neutron Stars: A Gravitational-Wave Probe of First-Order Phase Transitions

At the extreme densities in neutron stars, a phase transition to deconfined quark matter is anticipated. Yet masses, radii, and tidal deformabilities offer only indirect measures of a first-order phase transition, requiring many detections to resolve or being ineffective observables if the discontinuity exists at lower densities. Here, we report on a smoking-gun gravitational-wave signature of a first-order transition: the resonant tidal excitation of an interface mode. Using relativistic perturbation theory with an equation-of-state family informed by chiral effective field theory, we show that such a resonance may be detectable with next-generation interferometers and possibly already with LIGO A+ for sufficiently loud events.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Tight Bound on the Neutron Star Radius with Quasiperiodic Oscillations in Short Gamma-Ray Bursts

Abstract Quasiperiodic oscillations (QPOs) have been recently discovered in the short gamma-ray bursts (GRBs) 910711 and 931101B. Their frequencies are consistent with those of the quasiradial and quadrupolar oscillations of binary neutron star (BNS) merger remnants, as obtained in numerical relativity simulations. These simulations reveal quasi-universal relations between the remnant oscillation frequencies and the tidal coupling constant of the binaries. Under the assumption that the observed QPOs are due to these postmerger oscillations, we use the frequency–tide relations in a Bayesian framework to infer the source redshift, as well as the chirp mass and the binary tidal deformability of the BNS progenitors for GRBs 910711 and 931101B. We further use this inference to estimate bounds on the mass–radius relation for neutron stars. By combining the estimates from the two GRBs, we find a 68% credible range R 1.4 = 12.4 8 − 0.40 + 0.41 km for the radius of a neutron star with mass M = 1.4 M ⊙ , which is one of the tightest bounds to date.

Guedes, Victor↗
NASA NTRS1988

Spontaneous superfluid unpinning and the inhomogeneous distribution of vortex lines in neutron stars

The equation of motion of the pinned superfluid which couples to the crust of neutron stars via thermal vortex creep is studied. Spontaneous unpinning at locations characterized by a very inhomogeneous distribution of vortex lines is examined as a possible mechanism for the initiation of glitches. It is suggested that structural inhomogeneities in the crust of neutron stars may be responsible for frequent microglitches which lead to pulsar timing noise. A generalization of the model shows promise for explaining the origin of the giant glitches in pulsars.

Cheng, K. S.↗
NASA NTRS2017

Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-Driven Convection

Thermonuclear flashes of hydrogen and helium accreted onto neutron stars produce the frequently observed Type I X-ray bursts. It is the current paradigm that almost all material burns in a burst, after which it takes hours to accumulate fresh fuel for the next burst. In rare cases, however, bursts are observed with recurrence times as short as minutes. We present the first one-dimensional multi-zone simulations that reproduce this phenomenon. Bursts that ignite in a relatively hot neutron star envelope leave a substantial fraction of the fuel unburned at shallow depths. In the wake of the burst, convective mixing events driven by opacity bring this fuel down to the ignition depth on the observed timescale of minutes. There, unburned hydrogen mixes with the metal-rich ashes, igniting to produce a subsequent burst. We find burst pairs and triplets, similar to the observed instances. Our simulations reproduce the observed fraction of bursts with short waiting times of approximately 30%, and demonstrate that short recurrence time bursts are typically less bright and of shorter duration.

nucleosynthesis↗
NASA NTRS2006

Chandra Observations of Neutron Stars: An Overview

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

Weisskopf, Martin C.↗
NASA NTRS2004

Accreting Millisecond Pulsars: Neutron Star Masses and Radii

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

Strohmayer, Tod↗
NASA NTRS1991

Neutron stars and the distance to gamma-ray bursters

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

Dermer, Charles D.↗
NASA NTRS1992

Light curves of rotating, oscillating neutron stars

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.

Strohmayer, T. E.↗