The application of standard accretion theory to observations of X-ray binaries provides valuable insights into neutron star properties, such as their spin period and magnetic field. However, most studies concentrate on relatively old systems, where the neutron star is in its late propeller, accretor, or nearly spin equilibrium phase. Here we use an analytic model from standard accretion theory to illustrate the evolution of high-mass X-ray binaries early in their life. We show that a young neutron star is unlikely to be an accretor because of the long duration of ejector and propeller phases. We apply the model to the recently discovered ~4000 yr old high-mass X-ray binary XMMU J051342.6-672412 and find that the system's neutron star, with a tentative spin period of 4.4 s, cannot be in the accretor phase and has a magnetic field B > (a few)x10^13 G, which is comparable to the magnetic field of many older high-mass X-ray binaries and is much higher than the spin equilibrium inferred value of (a few)x10^11 G. The observed X-ray luminosity could be the result of thermal emission from a young cooling magnetic neutron star or a small amount of accretion that can occur in the propeller phase.
The author presented the results on the evolution of NS LMXBs and the formation of UCXBs(Ma & Li 2009 for details), and proposed a scenario for the formation of UCXBs from L/IMXBs with the aid of a CB disk in this work.
As neutron star - black hole binaries are expected to be discovered through future pulsar surveys using upcoming facilities, it is necessary to understand various observable properties of such systems. In the present work, we study the advance of the periastron of such binaries under the post-Newtonian formalism over a wide range of parameters. We find that the first and second order post-Newtonian effects and the leading order spin-orbit coupling effects are significant for such binaries but higher order effects can be neglected.
Binary systems with neutron stars and double degenerate systems are crucial objects to test current stellar evolution models and Einstein's general relativity. In this study, we present angular momentum loss mechanism via gravitational radiation and magnetized stellar winds for some selected systems with a neutron star. We calculated and plotted their time scales for angular momentum loss. Gravitational wave amplitudes of binary systems with a neutron star components are also estimated and their detectability with a gravitational wave detector (LISA) has been plotted.
We investigate evolutionary pathways leading to neutron star formation through the collapse of oxygen-neon white dwarf (ONe WD) stars in interacting binaries. We consider (1) non-dynamical mass transfer where an ONe WD approaches the Chandrasekhar mass leading to accretion-induced collapse (AIC) and (2) dynamical timescale merger-induced collapse (MIC) between an ONe WD and another WD. We present rates, delay times, and progenitor properties for two different treatments of common envelope evolution. We show that AIC neutron stars are formed via many different channels and the most dominant cha…
Neutron star-helium white dwarf (NS+He WD) binaries are important evolutionary products of close-orbit binary star systems. They are often observed as millisecond pulsars and may continue evolving into ultra-compact X-ray binaries (UCXBs) and continuous gravitational wave (GW) sources that will be detected by space-borne GW observatories, such as LISA, TianQin and Taiji. Nevertheless, the stability of NS+He WD binaries undergoing mass transfer is not well studied and still under debate. In this paper, we model the evolution of NS+He WD binaries with WD masses ranging from 0.17-0.45 $M_{\odot}$…
In this chapter, I present the main X-ray observational characteristics of black-hole binaries and low magnetic field neutron-star binaries, concentrating on what can be considered similarities or differences, with particular emphasis on their fast-timing behaviour.
The powerful wind-wind collision in massive star binaries creates a region of high temperature plasma and accelerates particles to relativistic energies. I briefly summarize the hydrodynamics of the wind-wind interaction and the observational evidence, including recent $γ$-ray detections, of non-thermal emission from such systems. I then discuss existing models of the non-thermal emission and their application to date, before concluding with some future prospects.
We consider fallback accretion after an ultra-stripped supernova (USSN) that accompanies formation of a binary neutron star (BNS) or a neutron star-black hole binary (NS-BH). The fallback matter initially accretes directly to the nascent NS, while it starts to accrete to the circumbinary disk, typically $0.1\mbox{-}1\, \mathrm{day}$ after the onset of the USSN explosion. The circumbinary disk mass further accretes, forming mini disks around each compact object, with a super-Eddington rate up to a few years. We show that such a system constitutes a binary ultraluminous X-ray source (ULX), and a…
Recent X-ray observations have revealed the complexity and diversity of high-mass X-ray binaries (HMXBs). This diversity challenges a classical understanding of the accretion process onto the compact objects. In this study, we reinforce the conventional concept of the nature of wind-fed accretion onto a neutron star considering the geometrical effect of radiatively accelerated wind, and re-evaluate the transported angular momentum by using a simple wind model. Our results suggest that even in an OB-type HMXB fed by stellar wind, a large amount of angular momentum could be transported to form a…
The third observing run of the LIGO/Virgo/KARGA collaboration reported a few neutron star - black hole (NSBH) merger events. While NSBH mergers have yet to receive extensive theoretical attention, they may have a promising electromagnetic signature in the form of short gamma - ray bursts. Here we show that NSBH dynamical mergers can naturally form from ultra - wide binaries in the field. Flyby gravitational interactions with other neighbors in the galaxy in these ultra - wide systems may result in high eccentricity that drives the binary into a merger. We show that this process can result in a…
In this study, we examine the properties of donor stars of the three recently discovered ultraluminous X-ray sources (ULXs) powered by rotating neutron stars. For this purpose, we constructed a theoretical relation between the X-ray luminosity ($L_{\rm{X}}$) and the orbital period ($P_{\rm{orb}}$) suitable for ULXs with neutron stars. By using this new $L_{\rm{X}} - P_{\rm{orb}}$ relation, we attempt to determine the currently unknown nature of donor stars in ULXs associated with neutron stars. Especially, comparing the observed properties with the stellar evolution tracks, we suggest that the…
Supernova explosion and the associated neutron star natal kicks are important events on a pathway of a binary to become a gravitational wave source, an X-ray binary or a millisecond radio pulsar. Weak natal kicks often lead to binary survival, while strong kicks frequently disrupt the binary. In this article, we aim to further constrain neutron star natal kicks in binaries. We explore binary population synthesis models by varying prescription for natal kick, remnant mass and mass accretion efficiency. We introduce a robust statistical technique to analyse combined observations of different nat…
Merging neutron star (NS) binaries may be detected by ground-based gravitational wave (GW) interferometers (e.g. LIGO/VIRGO) within this decade and may also generate electromagnetic radiation detectable by wide-field, fast imaging telescopes that are coming online. The GWs can provide new constraint on the NS equation of state (including mass-radius relation and the related nuclear symmetry energy through resonant g-modes). This paper reviews various hydrodynamical (including equilibrium and dynamical/resonant tides) and electrodynamical processes in coalescing NS binaries, with focus on the p…
The prime candidate sources for the upcoming space-borne gravitational wave (GW) observatory LISA are the numerous Galactic tight binaries of white dwarfs (WDs) and neutron stars (NSs), many of which will coalesce and undergo mass transfer, leading to simultaneous emission of X-rays and GWs. Here, detailed and coherent numerical stellar models are explored for the formation and evolution of these systems, including finite-temperature effects and complete calculations of mass transfer from a WD to a NS accretor. Evolutionary tracks of characteristic strain amplitude are computed, and the unique…
We investigate the effects of mass transfer and gravitational wave (GW) radiation on the orbital evolution of contact neutron-star-white-dwarf (NS-WD) binaries, and the detectability of these binaries by space GW detectors (e.g., Laser Interferometer Space Antenna, LISA; Taiji; Tianqin). A NS-WD binary becomes contact when the WD component fills its Roche lobe, at which the GW frequency ranges from ~0.0023 to 0.72 Hz for WD with masses ~0.05-1.4 Msun. We find that some high-mass NS-WD binaries may undergo direct coalescence after unstable mass transfer. However, the majority of NS-WD binaries …
Population synthesis of low-mass binaries with wind-accreting neutron stars
Sternberg Astronomical Institute, Lomonosov Moscow State University（莫斯科国立大学列昂诺夫天文研究所）；Department of Physics, Lomonosov Moscow State University（莫斯科国立大学物理系）
Axion stars could form binaries with neutron stars. Given the extremely strong external magnetic field exhibited by individual neutron stars, there can be a substantial conversion of axions to photons in these binaries. The photon emission is doubly modulated due to the neutron star spinning and the axion star orbiting, yielding a unique discovery signal. Similar features are also generated in binaries between a neutron star and an axion-clouded black hole. Encouragingly, such binaries are found to be within the reach of ongoing and upcoming experiments (e.g., the Five hundred meter Aperture S…
We report the existence of a gravitational-wave-driven secular instability in neutron star binaries, acting on the equilibrium tide. The instability is similar to the classic Chandrasekhar-Friedman-Schutz (CFS) instability of normal modes and is active when the spin of the primary star exceeds the orbital frequency of the companion. Modeling the neutron star as a Newtonian n=1 polytrope, we calculate the instability time scale, which can be as low as a few seconds at small orbital separations but still larger than the inspiral time scale. The implications for orbital and spin evolution are als…
We analyze the distinguishability of populations of coalescing binary neutron stars, neutron-star black-hole binaries, and binary black holes, whose gravitational-wave signatures are expected to be observed by the advanced network of ground-based interferometers LIGO and Virgo. We consider population-synthesis predictions for plausible merging binary distributions in mass space, along with measurement accuracy estimates from the main gravitational-wave parameter-estimation pipeline. We find that for our model compact-object binary mass distribution, we can always distinguish binary neutron sta…
Neutron star X-ray binaries (NS XRBs) associated with supernova remnants (SNRs) are the youngest X-ray binaries that can provide insights into the early evolution of X-ray binaries and the formation properties of neutron stars. There are an increasing number of NS XRBs discovered to be harbored in SNRs in our and nearby galaxies. In this work, we perform binary population synthesis calculations to simulate the population of NS XRBs associated with SNRs for different types of companions, including Roche-lobe overfilling main-sequence stars, Be stars and supergiants. We estimate their birthrates…
We review the current status of general relativistic studies for coalescences of black hole--neutron star binaries. First, high-precision computations of black hole--neutron star binaries in quasiequilibrium circular orbits are summarized, focusing on the quasiequilibrium sequences and the mass-shedding limit. Next, the current status of numerical-relativity simulations for the merger of black hole--neutron star binaries is described. We summarize our understanding for the merger process, tidal disruption and its criterion, properties of the merger remnant and ejected material, gravitational w…
We have numerically solved the Grad-Shafranov equation for axisymmetric static MHD equilibria of matter confined at the polar cap of neutron stars. From the equilibrium solutions we explore the stability of the accretion mounds using the PLUTO MHD code. We find that pressure driven modes disrupt the equilibria beyond a threshold mound mass, forming dynamic structures, as matter spreads over the neutron star surface. Our results show that local variation of magnetic field will significantly affect the shape and nature of the cyclotron features observed in the spectra of High Mass X-ray Binaries…
Measurement of at least three independent parameters, for example, mass, radius and spin frequency, of a neutron star is probably the only way to understand the nature of its supranuclear core matter. Such a measurement is extremely difficult because of various systematic uncertainties. The lack of knowledge of several system parameter values gives rise to such systematics. Low-mass X-ray binaries, which contain neutron stars, provide a number of methods to constrain the stellar parameters. Joint application of these methods has a great potential to significantly reduce the systematic uncertai…
A substantial fraction of the known neutron stars resides in X-ray binaries -- systems in which one compact object accretes matter from a companion star. Neutron stars in X-ray binaries have magnetic fields among the highest found in the Universe, spanning at least the range from $\sim10^8$ to several 10$^{13}$ G. The magnetospheres around these neutron stars have a strong influence on the accretion process, which powers most of their emission. The magnetic field intensity and geometry, are among the main factors responsible for the large variety of spectral and timing properties observed in t…
White dwarf-neutron star binaries generate detectable gravitational radiation. We construct Newtonian equilibrium models of corotational white dwarf-neutron star (WDNS) binaries in circular orbit and find that these models terminate at the Roche limit. At this point the binary will undergo either stable mass transfer (SMT) and evolve on a secular time scale, or unstable mass transfer (UMT), which results in the tidal disruption of the WD. The path a given binary will follow depends primarily on its mass ratio. We analyze the fate of known WDNS binaries and use population synthesis results to e…
Relativistic Lense-Thirring precession of a tilted inner accretion disk around a compact object has been proposed as a mechanism for low-frequency (~0.01-70 Hz) quasi-periodic oscillations (QPOs) in the light curves of X-ray binaries. A substantial misalignment angle (~15-20 degrees) between the inner-disk rotation axis and the compact-object spin axis is required for the effects of this precession to produce observable modulations in the X-ray light curve. A consequence of this misalignment is that in high-inclination X-ray binaries the precessing inner disk will quasi-periodically intercept …
We report on the long-term average spin period, rate of change of spin period and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the Small Magellanic Cloud. We also collect and calculate parameters of each system and use these data to determine that all systems contain a neutron star which is accreting via a disc, rather than a wind, and that if these neutron stars are near spin equilibrium, then over half of them, including all with spin periods over about 100 s, have magnetic fields over the quantum critical level of 4.4x10^13 G. If these neutron stars are not close to s…
The merger of black hole-neutron star binaries can eject substantial material with the mass ~0.01-0.1M_sun when the neutron star is disrupted prior to the merger. The ejecta shows significant anisotropy, and travels in a particular direction with the bulk velocity ~0.2c. This is drastically different from the binary neutron star merger, for which ejecta is nearly isotropic. Anisotropic ejecta brings electromagnetic-counterpart diversity which is unique to black hole-neutron star binaries, such as viewing-angle dependence, polarization, and proper motion. The kick velocity of the black hole, gr…
A close high-mass binary system consisting of a neutron star (NS) and a massive OB supergiant companion is expected to lead to a TZO structure, which consists of a NS core and a stellar envelope. We use the scenario machine program to calculate the formation tracks of TZOs in close high mass NS binaries and their subsequent evolution. We propose and demonstrate that the explosion and instant contraction of a TZO structure leave its stellar remnant as a soft gamma ray repeater and an anomalous X-ray pulsar respectively.
We propose a novel method to examine whether Galactic double neutron star binaries are formed in the LISA band. In our method, we assign an effective time fraction $τ$ to each double neutron star binary detected by LISA. This fraction is given as a function of the observed orbital period and eccentricity and should be uniformly distributed in the absence of in-band binary formation. Applying statistical techniques such as the Kolmogorov-Smirnov test to the actual list of $τ$, we can inspect the signature of the in-band binary formation. We discuss the prospects of this method, paying close att…
The discovery of two neutron star-black hole coalescences by LIGO and Virgo brings the total number of likely neutron stars observed in gravitational waves to six. We perform the first inference of the mass distribution of this extragalactic population of neutron stars. In contrast to the bimodal Galactic population detected primarily as radio pulsars, the masses of neutron stars in gravitational-wave binaries are thus far consistent with a uniform distribution, with a greater prevalence of high-mass neutron stars. The maximum mass in the gravitational-wave population agrees with that inferred…
We perform a hierarchical Bayesian inference to investigate the population properties of the coalescing compact binaries involving at least one neutron star (NS). With the current observation data, we can not rule out either of the Double Gaussian, Single Gaussian and Uniform NS mass distribution models, although the mass distribution of the Galactic NSs is slightly preferred by the gravitational wave (GW) observations. The mass distribution of black holes (BHs) in the neutron star-black hole (NSBH) population is found to be similar to that for the Galactic X-ray binaries. Additionally, the ra…
Neutron stars accreting matter from low-mass binary companions are observed to undergo bursts of X-rays due to the thermonuclear explosion of material on the neutron star surface. We use recent results on superfluid and superconducting properties to show that the core temperature in these neutron stars may not be uniquely determined for a range of observed accretion rates. The degeneracy in inferred core temperatures could contribute to explaining the difference between neutron stars which have very short recurrence times between multiple bursts and those which have long recurrence times betwe…
X-ray polarimetry missions like IXPE will be able to measure for the first time the polarization properties of accreting, weakly magnetized neutron stars in Low Mass X-ray Binaries. In this work we present simulations of the expected X-ray polarized signal including the coronal emission for different geometries of the corona itself, i.e. a slab above the accretion disc and a spherical shell around the neutron star. The simulations are performed with the fully relativistic Monte Carlo code monk capable of computing the X-ray polarization degree and angle for various physical input parameters of…
We study the current sample of rapidly rotating neutron stars in both accreting and non-accreting binaries in order to determine whether the spin distribution of accreting neutron stars in low-mass X-ray binaries can be reconciled with current accretion torque models. We perform a statistical analysis of the spin distributions and show that there is evidence for two sub-populations among low-mass X-ray binaries, one at relatively low spin frequency, with an average of ~300 Hz and a broad spread, and a peaked population at higher frequency with average spin frequency of ~575 Hz. We show that th…
We investigate the kilohertz quasi-periodic oscillations of low-mass X-ray binaries within the Hartle-Thorne spacetime. On the basis the relativistic precession model we extract the total mass $M$, angular momentum $J$, and quadrupole moment $Q$ of a compact object in a low-mass X-ray binary by analyzing the data of the Z -source GX 5-1. In view of the recent neutron star model we compute the radius, angular velocity and other parameters of this source by imposing the observational and theoretical constraints on the mass-radius relation.
Neutron star X-ray binaries emit a compact, optically thick, relativistic radio jet during low-luminosity, usually hard states, as Galactic black-hole X-ray binaries do. When radio emission is bright, a hard power-law tail without evidence for an exponential cutoff is observed in most systems. We have developed a jet model that explains many spectral and timing properties of black-hole binaries in the states where a jet is present. Our goal is to investigate whether our jet model can reproduce the hard tail, with the correct range of photon index and the absence of a high-energy cutoff, in neu…
Merging neutron star binaries are prime candidate sources for heavy r-process nucleosynthesis. The amount of heavy r-process material is consistent with the mass ejection and rates of mergers, and abundances of relic radioactive materials suggest that heavy r-process material is produced in rare events. Observations of possible macronovae provide further support for this model. Still, some concerns remain. One is the observation of heavy r-process elements in Ultra Faint Dwarf (UFD) galaxies. The escape velocities from UFDs are so small that the natal kicks, taking place at neutron stars birth…
The dust properties of the line-of-sight materials in neutron star low-mass X-ray binaries (LMXBs) can be probed by X-ray observations and laboratory experiments. We use a Markov chain Monte Carlo (MCMC) method to conduct a spectral analysis of Chandra ACIS-S/HETG archival data of a sample of LMXBs, including GX 5-1 and GX 13+1. Our MCMC-based analysis puts constraints on the Si K-edge dust properties of the outflowing disk winds in this sample. Further X-ray observations of other LMXBs will help us better understand the grain features of dense outflows and accretion flows in neutron star bina…
Using 250 neutron star merger simulations with microphysics, we explore for the first time the role of nuclear incompressibility in the prompt collapse threshold for binaries with different mass ratios. We demonstrate that observations of prompt collapse thresholds, either from binaries with two different mass ratios or with one mass ratio but combined with the knowledge of the maximum neutron star mass or compactness, will constrain the incompressibility at the maximum neutron star density, $K_{\rm max}$, to within tens of percent. This, otherwise inaccessible, measure of $K_{\rm max}$ can po…
We search the literature for reports on the spectral properties of neutron-star low-mass X-ray binaries when they have accretion luminosities between 1E34 and 1E36 ergs/s. We found that in this luminosity range the photon index (obtained from fitting a simple absorbed power-law in the 0.5-10 keV range) increases with decreasing 0.5-10 keV X-ray luminosity (i.e., the spectrum softens). Such behaviour has been reported before for individual sources, but here we demonstrate that very likely most (if not all) neutron-star systems behave in a similar manner and possibly even follow a universal rela…
Mergers of binary neutron stars and black hole-neutron star binaries are one of the most promising sources for the ground-based gravitational-wave (GW) detectors and also a high-energy astrophysical phenomenon as illustrated by the observations of gravitational waves and electromagnetic (EM) waves in the event of GW170817. Mergers of these neutron-star binaries are also the most promising site for r-process nucleosynthesis. Numerical simulation in full general relativity (numerical relativity) is a unique approach to the theoretical prediction of the merger process, GWs emitted, mass ejection …
We discuss mass transfer in eccentric binaries containing a white dwarf and a neutron star (WD--NS binaries). We show that such binaries are produced from field binaries following a series of mass transfer episodes that allow the white dwarf to form before the neutron star. We predict the orbital properties of binaries similar to the observed WD--NS binary J1141+6545, and show that they will undergo episodic mass transfer from the white dwarf to the neutron star. Furthermore, we describe oil-on-water, a two-phase SPH formalism that we have developed in order to model mass transfer in such bina…
This article gives a very brief introduction about measuring the mass and radius of neutron star from X-ray observations. The masses and radii of neutron stars can be determined from photospheric radius expansion bursts in low-mass X-ray binaries, X-ray pulse profile modeling in accreting X-ray pulsars, gravitational redshift measurement in low-mass X-ray binaries and thermal X-ray spectral fitting in quiescent low-mass X-ray binaries.
We discuss the prospects of LISA for detecting neutron star binaries (NSBs) in the local group galaxies such as LMC and M31. Using the recently estimated merger rate $ {\rm 1540 \, Gpc^{-3}yr^{-1}}$ and inversely applying the conventional arguments based on the $B$-band galaxy luminosities, we estimate the frequency distributions of NSBs in the local galaxies. We find that, after 10 year observation with its current design sensitivity, LISA might detect $\sim 5$ NSBs both in LMC and M31 with signal-to-noise ratios larger than 10. Some of the NSBs might be three-dimensionally localized well wit…
Young star clusters are likely the most common birthplace of massive stars across cosmic time and influence the formation of compact binaries in several ways. Here, we simulate the formation of black hole -- neutron star binaries (BHNSs) in young star clusters, by means of the binary population synthesis code \texttt{MOBSE} interfaced with the $N$-body code \texttt{NBODY6++GPU}. BHNSs formed in young star clusters (dynamical BHNSs) are significantly more massive than BHNSs formed from isolated binaries (isolated BHNSs): $\sim{}40$~\% of the dynamical BHNS mergers have total mass $>15$ M$_\odot…
We develop a method to compute low-eccentricity initial data of black hole--neutron star binaries in the puncture framework extending previous work on other types of compact binaries. In addition to adjusting the orbital angular velocity of the binary, the approaching velocity of a neutron star is incorporated by modifying the helical Killing vector used to derive equations of the hydrostationary equilibrium. The approaching velocity of the black hole is then induced by requiring the vanishing of the total linear momentum of the system, differently from the case of binary black holes in the pu…
We perform a systematic analysis of neutron star radius constraints from five quiescent low-mass X-ray binaries and examine how they depend on measurements of their distances and amounts of intervening absorbing material, as well as their assumed atmospheric compositions. We construct and calibrate to published results a semi-analytic model of the neutron star atmosphere which approximates these effects for the predicted masses and radii. Starting from mass and radius probability distributions established from hydrogen-atmosphere spectral fits of quiescent sources, we apply this model to compu…
Gravitational waveforms from numerical simulations are a critical tool to test and analytically calibrate the waveform models used to study the properties of merging compact objects. In this paper, we present a series of high-accuracy waveforms produced with the SpEC code for systems involving at least one neutron star. We provide for the first time waveforms with sub-radian accuracy over more than twenty cycles for low-mass black hole-neutron star binaries, including binaries with non-spinning objects, and binaries with rapidly spinning neutron stars that maximize the impact on the gravitatio…
Neutron stars are the densest objects known in the Universe. Being the final product of stellar evolution, their internal composition and structure is rather poorly constrained by measurements. It is the purpose of this paper to put some constrains on the mass and moment of inertia of neutron stars based on the interpretation of kHz quasi-periodic oscillations observed in low mass X-ray binaries. We use observations of high-frequency quasi-periodic observations (HF-QPOs) in low mass X-ray binaries (LMXBs) to look for the average mass and moment of inertia of neutron stars. This is done by appl…
There are over 100 Be stars that are known to have neutron star companions but only one such system with a black hole. Previous theoretical work suggests this is not due to their formation but due to differences in X-ray luminosity. It has also been proposed that the truncation of the Be star's circumstellar disc is dependent on the mass of the compact object. Hence, Be star discs in black hole binaries are smaller. Since accretion onto the compact object from the Be star's disc is what powers the X-ray luminosity, a smaller disc in black hole systems leads to a lower luminosity. In this paper…
Gravitational wave detectors in the LIGO/Virgo frequency band are able to measure the individual masses and the composite tidal deformabilities of neutron-star binary systems. This paper demonstrates that high accuracy measurements of these quantities from an ensemble of binary systems can in principle be used to determine the high density neutron-star equation of state exactly. This analysis assumes that all neutron stars have the same thermodynamically stable equation of state, but does not use simplifying approximations for the composite tidal deformability or make additional assumptions ab…
The magnetic inclination angle $χ$, namely the angle between the spin and magnetic axes of a neutron star (NS), plays a vital role in its observational characteristics. However, there are few systematic investigations on its long-term evolution, especially for accreting NSs in binary systems. Applying the model of \citet{2021MNRAS.505.1775B} and the binary evolution code \mesa{}, we simultaneously simulate the evolution of the accretion rate, spin period, magnetic field, and magnetic inclination angle of accreting NSs in intermediate/low X-ray binaries (I/LMXBs). We show that the evolution of …
The fundamental constituent of matter at high temperature and density has intrigued physicists for quite some time. Recent results from heavy-ion colliders have enriched the Quantum Chromodynamics phase diagram at high temperatures and low baryon density. However, the phase at low temperatures and finite (mostly intermediate) baryon density remain unexplored. Theoretical Quantum Chromodynamics calculation predicts phase transition from hadronic matter to quark matter at such densities. Presently, the best laboratories available to probe such densities lie at the core of neutron stars. Recent r…
We perform hydrodynamic simulations of mass transfer in binaries that contain a white dwarf and a neutron star (WD-NS binaries), and measure the specific angular momentum of material lost from the binary in disc winds. By incorporating our results within a long-term evolution model we measure the long-term stability of mass transfer in these binaries. We find that only binaries containing helium white dwarfs with masses less than a critical mass of $M_{\rm WD,crit}=0.2\,M_\odot$ undergo stable mass transfer and evolve into ultra-compact $X$-ray binaries. Systems with higher-mass white dwarfs e…
