arXiv subjects

Xiang-Dong Li

Publications and source records attributed to Xiang-Dong Li.

At least 73 records · Page 4Linked to original sources

arXiv2023

Can cosmologically-coupled mass growth of black holes solve the mass gap problem?

Observations of elliptical galaxies suggest that black holes (BHs) might serve as dark energy candidates, coupled to the expansion of the Universe. According to this hypothesis, the mass of a BH could increase as the Universe expands. BH low-mass X-ray binaries (LMXBs) in the Galactic disk were born several gigayears ago, making the coupling effect potentially significant. In this work, we calculate the evolution of BH binaries with a binary population synthesis method to examine the possible influence of cosmologically-coupled growth of BHs, if it really exists. The measured masses of the compact objects in LMXBs show a gap around $\sim 2.5-5~{\rm M_\odot}$, separating the most massive neutron stars from the least massive BHs. Our calculated results indicate that, considering the mass growth seem to (partially) account for the mass gap and the formation of compact BH LMXBs, alleviating the challenges in modeling the formation and evolution of BH LMXBs with traditional theory. However, critical observational evidence like the detection of intermediate-mass black hole binaries is required to test this hypothesis.

astro-ph.HE↗

arXiv2023

Detection Prospects of Fast-merging Gravitational Wave Sources in M31

It is widely accepted that quite a number of double compact objects (DCOs) in the Milky Way can be identified by future space-based gravitational wave (GW) detectors, while systematic investigations on the detection of the GW sources in nearby galaxies are still lacking. In this paper, we present calculations of potential populations of GW sources for all types of DCOs in the Local Group galaxy M31. For M31, we use an age-dependent model for the evolution of the metallicity and the star-formation rate. By varying assumptions of common-envelope ejection efficiencies and supernova-explosion mechanisms during binary evolution, we make predictions on the properties of DCOs that can be detected by the Laser Interferometer Space Antenna (LISA). Our calculations indicate that a few (a dozen) DCOs are likely to be observed by LISA during its 4 (10) yr mission. We expect that the sources with black-hole components are more likely to be firstly identified during a 4-yr mission since these binaries have relatively large chirp masses, while the systems with white-dwarf components dominate the overall population of detectable GW sources during a 10-yr mission. LISA can only detect very tight fast-merging systems in M31, corresponding to the peak of orbital period distribution from $\sim 2$ min for double white dwarfs to $\sim 20$~min for double black holes.

astro-ph.HE↗

arXiv2023

An XMM-Newton View of the ANdromeda Galaxy as Explored in a Legacy Survey (New-ANGELS) I: the X-ray Source Catalogue

We introduce the New-ANGELS program, an XMM-Newton survey of $\sim7.2\rm~deg^2$ area around M 31, which aims to study the X-ray populations in M 31 disk and the X-ray emitting hot gas in the inner halo of M 31 up to 30 kpc. In this first paper, we report the catalogue of 4506 detected X-ray sources, and attempt to cross-identify or roughly classify them. We identify 352 single stars in the foreground, 35 globular clusters and 27 supernova remnants associated with M 31, as well as 62 AGNs, 59 galaxies, and 1 galaxy clusters in the background. We uniquely classify 236 foreground stars and 17 supersoft sources based on their X-ray colors. X-ray binaries (83 LMXBs, 1 HMXBs) are classified based on their X-ray colors and X-ray variabilities. The remaining X-ray sources either have too low S/N to calculate their X-ray colors or do not have a unique classification, so are regarded as unclassified. The X-ray source catalogue is published online. Study of the X-ray source populations and the contribution of X-ray sources in the unresolved X-ray emissions based on this catalogue will be published in companion papers.

astro-ph.HE↗

arXiv2023

On the Formation of GW190521-like Binary Black Hole Merger Systems

GW190521 is the most massive merging binary black hole (BBH) system detected so far. At least one of the component BHs was measured to lie within the pair-instability supernova (PISN) mass gap ($\sim 50-135\;{\rm M}_{\odot}$), making its formation a mystery. However, the transient observed signal allows alternative posterior distributions. There was suggestion that GW190521 could be an intermediate-mass ratio inspiral (IMRI), with the component masses $m_1\sim 170\;{\rm M}_{\odot}$ and $m_2\sim 16 \;{\rm M}_{\odot}$, happening to straddle the PISN mass gap. Under this framework, we perform binary population synthesis to explore the formation of GW190521-like systems via isolated binary evolution. We numerically calculate the binding energy parameter for massive stars at different metallicities, and employ them in our calculation for common envelope evolution. Our results prefer that the progenitor binaries formed in metal-poor environment with $\rm Z\leq0.0016$. The predicted merger rate density within redshift $z=1.1$ is $\sim 4\times 10^{-5}-5\times 10^{-2} \,\rm Gpc^{-3}yr^{-1}$. We expect that such events are potentially observable by upcoming both space and ground-based gravitational wave detectors.

astro-ph.HE↗

arXiv2023

Back to the Starting Point: on the Simulation of Initial Magnetic Fields and Spin Periods of Non-accretion Pulsars

Neutron stars (NSs) play essential roles in modern astrophysics. Magnetic fields and spin periods of newborn (zero age) NSs have large impact on the further evolution of NSs, which are however poorly explored in observation due to the difficulty of finding newborn NSs. In this work, we aim to infer the magnetic fields and spin periods (Bi and Pi) of zero-age NSs from the observed properties of NS population. We select non-accretion NSs (NANSs) whose evolution is solely determined by magnetic dipole radiation. We find that both Bi and Pi can be described by log-normal distribution and the fitting sensitively depends on our parameters.

astro-ph.HE↗

arXiv2023

Magnetic Inclination Evolution of Accreting Neutron Stars in Intermediate/Low-Mass X-ray Binaries

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 $χ$ depends not only on the initial parameters of the binary systems, but also on the mass transfer history and the efficiency of pulsar loss. Based on the calculated results we present the characteristic distribution of $χ$ for various types of systems including ultracompact X-ray binaries, binary millisecond pulsars, and ultraluminous X-ray sources, and discuss their possible observational implications.

astro-ph.HE↗

arXiv2023

Simulations of the progenitors of black hole-neutron star gravitational wave sources

Recent discoveries of gravitational wave (GW) events most likely originating from black hole (BH) + neutron star (NS) mergers reveal the existence of BH+NS binaries. The formation of BH+NS binaries and their merger rates through isolated binary evolution have been investigated extensively with population synthesis simulations. A detailed stellar evolution modelings of the formation of this population, however, is missing in the literature. In this work, we perform the first complete 1D model of more than 30 BH+NS progenitor systems which are calculated self-consistently until the iron core collapse with infall velocity exceeds 1000 km s^-1. Focusing on the progenitors of BH- NS GW sources, we apply the MESA code starting from a post-common envelope binary with short orbital period (< 1 day) consisting of a BH and a zero-age main-sequence helium star that experiences stable mass transfer. These NS masses could be significantly larger depending on the exact mass cut during the supernova explosion. These BH+NS systems are likely to merge and produce GW events within a Hubble time. System C is a potential progenitor of a GW200115-like event, while Systems A and B are possible candidates for a GW200105-like event and may represent the final destiny of the X-ray binary SS433.

astro-ph.HE↗

arXiv2022

Impact of Asymmetrical Mass Ejection from Proto-White Dwarfs on the Properties of Binary Millisecond Pulsars

The standard formation theory of binary millisecond pulsars (BMSPs) predicts efficient orbital circularization due to tidal interaction during the previous mass transfer phase. Therefore, BMSPs are expected to have a circular orbit. However, the discovery of several eccentric BMSPs (eBMSPs) with a white dwarf (WD) companion has challenged this picture. In particular, recent observation reveals that the spin angular momentum of the eBMSP J0955$-$6150 is tilted at an angle $>4.8^{\rm \degree}$ from the orbital angular momentum. This is the first time that a tilt angle is deduced for eBMSPs, which provides an important clue to their formation mechanism. Both the orbital eccentricity and tilt angle could be qualitatively accounted for by asymmetrical mass ejection during thermonuclear flashes from proto-WDs (so-called the thermonuclear rocket model), but detailed studies are still lacking. In this paper, we simulate the impact of the kick caused by asymmetrical mass ejection on the properties of BMSPs. We find that the thermonuclear rocket model can potentially explain the observational characteristics of both eBMSPs and normal BMSPs under reasonable input parameters. In addition, our results predict a wide range of the orbital period (from less than one day to more than several hundred days) for eBMSPs, which can be tested by future observations.

astro-ph.HE↗

arXiv2022

A long-period pre-ELM system discovered from LAMOST medium-resolution survey

We present LAMOST~J041920.07+072545.4 (hereafter J0419), a close binary consisting of a bloated extremely low mass pre-white dwarf (pre-ELM WD) and a compact object with an orbital period of 0.607189~days. The large-amplitude ellipsoidal variations and the evident Balmer and He~I emission lines suggest a filled Roche lobe and ongoing mass transfer. No outburst events were detected in the 15 years of monitoring of J0419, indicating a very low mass transfer rate. The temperature of the pre-ELM, $T_\mathrm{eff} = 5793_{-133}^{+124}\,\rm K$, is cooler than the known ELMs, but hotter than most CV donors. Combining the mean density within the Roche lobe and the radius constrained from our SED fitting, we obtain the mass of the pre-ELM, $M_1 = 0.176\pm 0.014\,M_\odot$. The joint fitting of light and radial velocity curves yields an inclination angle of $i = 66.5_{-1.7}^{+1.4}$ degrees, corresponding to the compact object mass of $M_2 = 1.09\pm 0.05\,M_\odot$. The very bloated pre-ELM has a smaller surface gravity ($\log g = 3.9\pm 0.01$, $R_1 = 0.78 \pm 0.02\,R_\odot$) than the known ELMs or pre-ELMs. The temperature and the luminosity ($L_\mathrm{bol} = 0.62_{-0.10}^{+0.11}\,L_\odot$) of J0419 are close to the main sequence, which makes the selection of such systems through the HR diagram inefficient. Based on the evolutionary model, the relatively long period and small $\log g$ indicate that J0419 could be close to the "bifurcation period" in the orbit evolution, which makes J0419 to be a unique source to connect ELM/pre-ELM WD systems, wide binaries and cataclysmic variables.

astro-ph.SR↗

arXiv2022

A dynamically discovered and characterized non-accreting neutron star -- M dwarf binary candidate

Optical time-domain surveys can unveil and characterize exciting but less-explored non-accreting and/or non-beaming neutron stars (NS) in binaries. Here we report the discovery of such a NS candidate using the LAMOST spectroscopic survey. The candidate, designated LAMOST J112306.9+400736 (hereafter J1123), is in a single-lined spectroscopic binary containing an optically visible M star. The star's large radial velocity variation and ellipsoidal variations indicate a relatively massive unseen companion. Utilizing follow-up spectroscopy from the Palomar 200-inch telescope and high-precision photometry from TESS, we measure a companion mass of $1.24_{-0.03}^{+0.03}~M_{\odot}$. Main-sequence stars with this mass are ruled out, leaving a NS or a massive white dwarf (WD). Although a massive WD cannot be ruled out, the lack of UV excess radiation from the companion supports the NS hypothesis. Deep radio observations with FAST yielded no detections of either pulsed or persistent emission. J1123 is not detected in numerous X-ray and gamma-ray surveys. These non-detections suggest that the NS candidate is not presently accreting and pulsing. Our work exemplifies the capability of discovering compact objects in non-accreting close binaries by synergizing the optical time-domain spectroscopy and high-cadence photometry.

astro-ph.SR↗

arXiv2022

Formation of Mass-gap Black Holes from Neutron Star X-ray Binaries with Super-Eddington Accretion

Electromagnetic and gravitational wave observations indicate that there is dearth of compact objects with mass $\sim 2.5-5~{\rm M_\odot}$. This so-called "mass gap" may be linked to the supernova explosion mechanisms that produce neutron stars (NSs) and black holes (BHs). However, the existence of a few mass-gap compact objects, some of which have been confirmed to be BHs, poses a challenge to the traditional theory of black hole formation. In this work we investigate the possible formation channel of BHs from accretion-induced collapse (AIC) of NSs in X-ray binaries. In particular, we consider the influence of super-Eddington accretion of NSs. Recent observations of ultraluminous X-ray pulsars suggest that their apparent luminosities may reflect the true accretion luminosities of the accreting NSs, even exceeding the Eddington limit by a factor of $\gtrsim 100$. Thus, NSs accreting at a super-Eddington accretion rate may rapidly grow into BHs in intermediate/low-mass X-ray binaries. Based on the super-Eddington accretion disk models, we have investigated the evolution of NSs in intermediate/low-mass X-ray binaries by combining binary population synthesis and detailed stellar evolutionary calculations. We show that super-Eddington accretion plays a critical role in mass growth of NSs, and the final masses of the descendant BHs are heavily dependent on the NS magnetic fields, the metallicity of the donor star, and the bifurcation period of the binaries. AIC of NSs may account for some of the observed mass-gap BHs like GRO J0422+32. We also present the parameter distributions of the potential mass-gap BHs in a Milky Way-like galaxy, and point out that future space-based gravitational wave observations may provide important test of or constraints on the formation of mass-gap BHs from the AIC channel.

astro-ph.HE↗

arXiv2022

Stable mass transfer can explain massive binary black hole mergers with a high spin component

Recent gravitational wave observations showed that binary black hole (BBH) mergers with massive components are more likely to have high effective spins. In the model of isolated binary evolution, BH spins mainly originate from the angular momenta of the collapsing cores before BH formation. Both observations and theories indicate that BHs tend to possess relatively low spins, the origin of fast-spinning BHs remains a puzzle. We investigate an alternative process that stable Case A mass transfer may significantly increase BH spins during the evolution of massive BH binaries. We present detailed binary evolution calculations and find that this process can explain observed high spins of some massive BBH mergers under the assumption of mildly super-Eddington accretion.

astro-ph.HE↗

arXiv2021

$W$-entropy formulas and Langevin deformation of flows on Wasserstein space over Riemannian manifolds

We introduce Perelman's $W$-entropy and prove the $W$-entropy formula along the geodesic flow on the $L^2$-Wasserstein space over compact Riemannian manifolds equipped with Otto's Riemannian metric, which allows us to recapture a previous result due to Lott and Villani on the displacement convexity of $s{\rm Ent}+ns\log s$ on $P^\infty_2(M)$ over Riemannian manifolds with non-negative Ricci curvature. To better understand the similarity between the $W$-entropy formula for the geodesic flow on the Wasserstein space and the $W$-entropy formula for the heat equation of the Witten Laplacian on the underlying manifolds, we introduce the Langevin deformation of flows on the Wasserstein space over Riemannian manifold, which interpolates the gradient flow and the geodesic flow on the Wasserstein space over Riemannian manifolds, and can be regarded as the potential flow of the compressible Euler equation with damping on manifolds. We prove the existence, uniqueness and regularity of the Langevin deformation on the Wasserstein space over the Euclidean space and compact Riemannian manifolds, and prove the convergence of the Langevin deformation for $c\rightarrow 0$ and $c\rightarrow \infty$ respectively. We prove an analogue of the Perelman type $W$-entropy formula along the Langevin deformation on the Wasserstein space on Riemannian manifolds. A rigidity theorem is proved for the $W$-entropy for the geodesic flow, and a rigidity model is also provided for the Langevin deformation on the Wasserstein space over complete Riemannian manifolds with the $CD(0, m)$-condition.

math.PR↗

arXiv2021

New Laplacian comparison theorem and its applications to diffusion processes on Riemannian manifolds

Let $L=Δ-\nablaϕ\cdot \nabla$ be a symmetric diffusion operator with an invariant measure $μ({\rm} d x)=e^{-ϕ(x)}{\mathfrak m}({\rm d} x)$ on a complete non-compact smooth Riemannian manifold $(M,g)$ with its volume element ${\mathfrak m}={\rm vol}_g$, and $ϕ\in C^2(M)$ a potential function. In this paper, we prove a Laplacian comparison theorem on weighted complete Riemannian manifolds with ${\rm CD}(K, m)$-condition for $m\leq 1$ and a continuous function $K$. As consequences, we give the optimal conditions on $m$-Bakry-Émery Ricci tensor for $m\leq1$ such that the (weighted) Myers' theorem, Bishop-Gromov volume comparison theorem, Ambrose-Myers' theorem, and the Cheeger-Gromoll type splitting theorem, stochastic completeness and Feller property of $L$-diffusion processes hold on weighted complete Riemannian manifolds. Some of these results were well-studied for $m$-Bakry-Émery Ricci curvature for $m\geq n$ (\!\!\cite{Lot,Qian,XDLi05, WeiWylie}) or $m=1$ (\!\!\cite{Wylie:WarpedSplitting, WylieYeroshkin}). When $m<1$, our results are new in the literature.

math.DG↗

arXiv2021

A Study of Magnetized White Dwarf + Helium Star Binary Evolution to Type Ia Supernovae

The white dwarf (WD) + helium (He) star binary channel plays an important role in the single degenerate scenario for the progenitors of type Ia supernovae (SNe Ia). Previous studies on the WD + main sequence star evolution have shown that the magnetic fields of WDs may significantly influence their accretion and nuclear burning processes. In this work we focus on the evolution of magnetized WD + He star binaries with detailed stellar evolution and binary population synthesis (BPS) calculations. In the case of magnetized WDs, the magnetic fields may disrupt the inner regions of the accretion disk, funnel the accretion flow onto the polar caps, and even confine helium burning within the caps.We find that, for WDs with sufficiently strong magnetic fields, the parameter space of the potential SN Ia progenitor systems shrinks toward shorter orbital periods and lower donor masses compared with that in the non-magnetized WD case. The reason is that the magnetic confinement usually works with relatively high mass transfer rates, which can trigger strong wind mass loss from the WD, thus limiting the He-rich mass accumulation efficiency. The surviving companion stars are likely of low-mass at the moment of the SN explosions, which can be regarded as a possible explanation for the non-detection of surviving companions after the SNe or inside the SN remnants. However, the corresponding birthrate of Galactic SNe Ia in our high-magnetic models is estimated to be ~(0.08-0.13) * 10^{-3} yr^{-1}( ~0.17-0.28 * 10^{-3}yr^{-1} for the non-magnetic models), significantly lower than the observed Galactic SN Ia birthrate.

astro-ph.SR↗

arXiv2021

Are there magnetars in high-mass X-ray binaries?

Magnetars form a special population of neutron stars with strong magnetic fields and long spin periods. About 30 magnetars and magnetar candidates known currently are probably isolated. But the possibility that magnetars are in binaries hasn't been excluded. In this work, we perform spin evolution of neutron stars with different magnetic fields in wind-fed high-mass X-ray binaries and compare the spin period distribution with observations, aiming to find magnetars in binaries. Our simulation shows that some of the neutron stars, which have long spin periods or in wide-separation systems, need strong magnetic fields to explain their spin evolution. This implies that there are probably magnetars in high-mass X-ray binaries. Moreover, this can further provide a theoretical basis for some unclear astronomical phenomena, such as the possible origin of periodic fast radio bursts from magnetars in binary systems.

astro-ph.HE↗

arXiv2021

On the effect of pulsar evaporation on the cooling of white dwarfs

Evolution of a large part of low-mass X-ray binaries (LMXBs) leads to the formation of rapidly rotating pulsars with a helium white dwarf (He WD) companion. Observations indicate that some He WDs in binary pulsar systems are ultracool (with the effective temperatures $T_{\rm eff}\lesssim$ 4000\, K). It is hard to cool down a He WD to such low temperatures within the Hubble time, because a thick hydrogen envelope was left behind around the He core after the mass transfer process. A possible mechanism that can accelerate the WD cooling is the evaporative wind mass loss from the He WD driven by the high-energy radiation from the recycled pulsar. In this paper, we evolve a large number of LMXBs and investigate the influence of the pulsar's high-energy radiation on the WD cooling with different input parameters, including the neutron star's spin-down luminosity, the evaporation efficiency and the metallicity of the companion star. By comparing our results with observations we note that, for relatively hot He WDs (with $T_{\rm eff}> 7000$ K), standard WD cooling without evaporation considered is able to reproduce their temperatures, while evaporation is probably required for the He WDs with relatively low temperatures ($T_{\rm eff}$ <5000 K).

astro-ph.HE↗

arXiv2021

Population Synthesis of Black Hole Binaries with Compact Star Companions

We perform a systematic study of merging black hole (BH) binaries with compact star (CS) companions, including black hole--white dwarf (BH--WD), black hole--neutron star (BH--NS) and black hole--black hole (BH--BH) systems. Previous studies have shown that mass transfer stability and common envelope evolution can significantly affect the formation of merging BH--CS binaries through isolated binary evolution. With detailed binary evolution simulations, we obtain easy-to-use criteria for the occurrence of the common envelope phase in mass-transferring BH binaries with a nondegenerate donor, and incorporate into population synthesis calculations. To explore the impact of possible mass gap between NSs and BHs on the properties of merging BH--CS binary population, we adopt different supernova mechanisms involving the \textit{rapid}, \textit{delayed} and \textit{stochastic} prescriptions to deal with the compact remnant masses and the natal kicks. Our calculations show that there are $ \sim 10^{5} -10^{6}$ BH--CS binaries in the Milky Way, among which dozens are observable by future space-based gravitational wave detectors. We estimate that the local merger rate density of all BH--CS systems is $ \sim 60-200 \,\rm Gpc^{-3}yr^{-1}$. While there are no low-mass BHs formed via \textit{rapid} supernovae, both \textit{delayed} and \textit{stochastic} prescriptions predict that $ \sim 100\% $/$ \sim 70\% $/$ \sim 30\% $ of merging BH--WD/BH--NS/BH--BH binaries are likely to have BH components within the mass gap.

astro-ph.HE↗