黑洞（BH）自旋的起源仍然是黑洞最不为人理解的方面之一。尽管存在许多不确定性，人们通常认为，如果黑洞起源于孤立的大质量恒星双星系统，它们的自旋应当与双星系统的轨道角动量方向一致。这一假设源于黑洞会继承其前身恒星自旋的观点。在本研究中，我们放宽了这一长期存在的观点，并探讨了在黑洞形成之前或形成期间能够使其自旋加快的各种机制。除出生自旋外，我们还讨论了能够使黑洞自旋各向同性、平行于 natal kick（出生反冲）以及垂直于 natal kick（出生反冲）的物理过程。这些不同机制会在可观测的自旋大小、自旋—轨道失配角以及并合双星的有效旋进自旋分布上留下独特印记。特别是，这些机制甚至允许起源于场星环境的双星表现出进动和逆行自旋（$χ_{\ m eff}<0$）。这将孤立双星演化所允许的参数空间扩展到了此前被认为专属于动力学组装双星的区域。
英文摘要：
The origin of black hole (BH) spins remains one of the least understood aspects of BHs. Despite many uncertainties, it is commonly assumed that if BHs originated from isolated massive star binaries, their spins should be aligned with the orbital angular momentum of the binary system. This assumption stems from the notion that BHs inherit their spins from their progenitor stars. In this study, we relax this long-held viewpoint and explore various mechanisms that can spin up BHs before or during their formation. In addition to natal spins, we discuss physical processes that can spin BHs isotropically, parallel to natal kicks, and perpendicular to natal kicks. These different mechanisms leave behind distinct imprints on the observable distributions of spin magnitudes, spin-orbit misalignments and the effective inspiral spin of merging binaries. In particular, these mechanisms allow even the binaries originating in the field to exhibit precession and retrograde spin ($χ_{\rm eff}<0$). This broadens the parameter space allowed for isolated binary evolution into regimes which were previously thought to be exclusive to dynamically assembled binaries.
Natal kicks are matter of debate and significantly affect the merger rate density of compact objects. Here, we present a new simple formalism for natal kicks of neutron stars (NSs) and black holes (BHs). We describe the magnitude of the kick as $v_{\rm kick}\propto{}f_{\rm H05}\,{}\,{}m_{\rm ej}\,{}\,{}m_{\rm rem}^{-1}$, where $f_{\rm H05}$ is a normalization factor, drawn from a Maxwellian distribution with one-dimensional root-mean-square velocity $σ=265$~km~s$^{-1}$, $m_{\rm ej}$ is the mass of the supernova (SN) ejecta and $m_{\rm rem}$ is the mass of the compact object. This formalism mat…
Current prescriptions for supernova natal kicks in rapid binary population synthesis simulations are based on fits of simple functions to single pulsar velocity data. We explore a new parameterization of natal kicks received by neutron stars in isolated and binary systems developed by Mandel & Müller, which is based on 1D and 3D supernova simulations and accounts for the physical correlations between progenitor properties, remnant mass, and the kick velocity. We constrain two free parameters in this model using very long baseline interferometry velocity measurements of Galactic single pulsars.…
We compare binary evolution models with different assumptions about black-hole natal kicks to the first gravitational-wave observations performed by the LIGO detectors. Our comparisons attempt to reconcile merger rate, masses, spins, and spin-orbit misalignments of all current observations with state-of-the-art formation scenarios of binary black holes formed in isolation. We estimate that black holes (BHs) should receive natal kicks at birth of the order of $σ\simeq 200$ (50) km/s if tidal processes do (not) realign stellar spins. Our estimate is driven by two simple factors. The natal kick d…
Advanced LIGO and Advanced Virgo's newly-released GWTC-2 catalog of gravitational-wave detections offers unprecedented information about the spin magnitudes and orientations of merging binary black holes (BBHs). Notably, analysis of the BBH population suggests the presence of binaries whose component spins are significantly misaligned with respect to their orbital angular momenta. Significantly misaligned spins are typically predicted to be at odds with isolated field formation via standard common envelope (CE) evolution, and hence a "smoking gun" signature of dynamical binary formation inside…
A population of more than 50 binary black hole mergers has now been observed by the LIGO and Virgo gravitational-wave observatories. While neutron stars are known to have large velocities associated with impulsive kicks imparted to them at birth in supernovae, whether black holes receive similar kicks, and of what magnitude, remains an open question. Recently, Callister et al. (2021) analysed the binary black hole population under the hypothesis that they were all formed through isolated binary evolution and claimed that large black hole kicks (greater than 260 km/s at 99% confidence) were req…
The speeds of young isolated pulsars are generally inferred from their observed 2-d velocities on the plane of the sky under the assumption that the unobserved radial velocity is not special, i.e., that the measured 2-d velocity is an isotropic projection of the full 3-d velocity. However, if pulsar spins are preferentially aligned with kicks, then the observer's viewing angle relative to the pulsar velocity vector is in fact special because the direction of the spin impacts the detectability of the pulsar. This means that the measured 2-d velocity of observable pulsars is not an isotropic pro…
Understanding the natal kicks received by neutron stars (NSs) during formation is a critical component of modelling the evolution of massive binaries. Natal kicks are an integral input parameter for population synthesis codes, and have implications for the formation of double NS systems and their subsequent merger rates. However, many of the standard observational kick distributions that are used are obtained from samples created only from isolated NSs. Kick distributions derived in this way overestimate the intrinsic NS kick distribution. For NSs in binaries, we can only directly estimate the…
The inferred parameters of the binary black hole GW151226 are consistent with nonzero spin for the most massive black hole, misaligned from the binary's orbital angular momentum. If the black holes formed through isolated binary evolution from an initially aligned binary star, this misalignment would then arise from a natal kick imparted to the first-born black hole at its birth during stellar collapse. We use simple kinematic arguments to constrain the characteristic magnitude of this kick, and find that a natal kick $v_k \gtrsim 50$ km/s must be imparted to the black hole at birth to produce…
The spin precession of binary black holes (BBHs) that originate from isolated high-mass binary stars is determined by the interplay of phenomena such as tides, winds, accretion, common-envelope evolution, natal kicks, and stellar core-envelope coupling. In previous work, we identified regions of the parameter space that may produce BBHs with large misalignments from natal kicks and high spin magnitudes from three mechanisms - tides, accretion, or inheritance via minimal core-envelope coupling. Here, we explore the spin precession of such BBHs using five parameters that describe the amplitude a…
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…
Binary black holes (BBHs) can form from the collapsed cores of isolated high-mass binary stars. The masses and spins of these BBHs are determined by the complicated interplay of phenomena such as tides, winds, accretion, common-envelope evolution (CEE), supernova natal kicks, and stellar core-envelope coupling. The gravitational waves emitted during the mergers of BBHs depend on their masses and spins and can thus constrain these phenomena. We present a simplified model of binary stellar evolution and identify regions of the parameter space that produce BBHs with large spins misaligned with th…
Some fraction of compact binaries that merge within a Hubble time may have formed from two massive stars in isolation. For this isolated-binary formation channel, binaries need to survive two supernova (SN) explosions in addition to surviving common-envelope evolution. For the SN explosions, both the mass loss and natal kicks change the orbital characteristics, producing either a bound or unbound binary. We show that gravitational waves (GWs) may be produced not only from the core-collapse SN process, but also from the SN mass loss and SN natal kick during the pre-SN to post-SN binary transiti…
We show that a black-hole binary with an external companion can undergo Lidov-Kozai cycles that cause a close pericenter passage, leading to a rapid merger due to gravitational-wave emission. This scenario occurs most often for systems in which the companion has mass comparable to the reduced mass of the binary and the companion orbit has semi-major axis within a factor of $\sim 10$ of the binary semi-major axis. Using a simple population-synthesis model and 3-body simulations, we estimate the rate of mergers in triple black hole systems in the field to be about six per Gpc$^3$ per year in the…
Based on their relatively isolated environments, we argue that LBVs must be primarily the product of binary evolution, challenging the traditional single-star view wherein LBVs mark a brief transition between massive O stars and Wolf-Rayet (WR) stars. If the latter were true, then LBVs should be concentrated in young clusters and found alongside main-sequence stars with similarly high inferred initial mass. This is decidedly not the case. Examining locations of LBVs compared to O stars in our Galaxy and the Magellanic Clouds reveals that LBVs systematically avoid clusters of O stars, and many …
In this work we study the formation of the first two black hole-neutron star (BHNS) mergers detected in gravitational waves (GW200115 and GW200105) from massive stars in wide isolated binary systems - the isolated binary evolution channel. We use 560 BHNS binary population synthesis model realizations from Broekgaarden et al. (2021a) and show that the system properties (chirp mass, component masses and mass ratios) of both GW200115 and GW200105 match predictions from the isolated binary evolution channel. We also show that most model realizations can account for the local BHNS merger rate dens…
Multiple pieces of evidence suggest that neutron stars receive large kicks when formed from the remnant of a collapsing star. However, the evidence for whether black holes (BH) receive natal kicks is less clear, reliant on weak constraints from the analysis of BH X-ray binaries and massive runaway and walkaway stars. Here we show for the first time that recent microlensing detections offer a new method for measuring the kicks BHs receive at birth. When a BH is identified through both photometric and astrometric microlensing and when the lensed star has a known distance and proper motion, the m…
High-velocity neutron stars (HVNSs) that were kicked out from their birth location can be potentially identified with their large proper motions, and possibly with large parallax, when they come across the solar neighborhood. In this paper, we study the feasibility of hunting isolated HVNSs in wide-area optical surveys by modeling the evolution of NS luminosity taking into account spin-down and thermal radiation. Assuming the upcoming 10-year VRO LSST observation, our model calculations predict that about 10 HVNSs mainly consisting of pulsars with ages of $10^4$--$10^5$ yr and thermally emitti…
According to the recycling model, neutron stars in low-mass X-ray binaries were spun up to millisecond pulsars (MSPs), which indicates that all MSPs in the Galactic plane ought to be harbored in binaries. However, about $20\%$ Galactic field MSPs are found to be solitary. To interpret this problem, we assume that the accreting neutron star in binaries may collapse and become a strange star when it reaches some critical mass limit. Mass loss and a weak kick induced by asymmetric collapse during the phase transition (PT) from neutron star to strange star can result in isolated MSPs. In this work…
Observations of binary pulsars and pulsars in globular clusters suggest that at least some pulsars must receive weak natal kicks at birth. If all pulsars received strong natal kicks above \unit[50]{\kms}, those born in globular clusters would predominantly escape, while wide binaries would be disrupted. On the other hand, observations of transverse velocities of isolated radio pulsars indicate that only $5\pm2\%$ have velocities below \unit[50]{\kms}. We explore this apparent tension with rapid binary population synthesis modelling. We propose a model in which supernovae with characteristicall…
California Institute of Technology（加州理工学院）；University of California, Los Angeles（加州大学洛杉矶分校）；Mani L. Bhaumik Institute for Theoretical Physics（马尼·L·巴乌米克理论物理研究所）
Mergers of black hole (BH) and neutron star (NS) binaries are expected to be observed by gravitational wave observatories in the coming years. Until now, LIGO has only set an upper limit on this merger rate. BH-NS binaries are expected to merge in isolation, as their formation is suppressed in star clusters by the mass segregation and the strong heating by BHs in the cluster core. Another viable scenario to BH-NS mergers is in triple systems. In this paper, we carry out a systematic statistical study of the dynamical evolution of triples comprised of an inner BH-NS binary by means of high-prec…
The Galactic Centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we investigate the role of supernova (SN) explosions occurring in massive binary systems lying in a disc-like structure within the innermost parsec. We use a regularized algorithm to simulate 30,000 isolated three-body systems composed of a stellar binary orbiting the SMBH. We start the integration when the primary member undergoes a SN explosion, and we analyze the impact of SN kicks on the orbits of stars and compact remnants. We find that SN explosions s…
We study evolution of isolated neutron stars on long time scale and calculate distribution of these sources in the main evolutionary stages: Ejector, Propeller, Accretor, and Georotator. We compare different initial magnetic field distributions taking into account a possibility of magnetic field decay, and include in our calculations the stage of subsonic Propeller. It is shown that though the subsonic propeller stage can be relatively long, initially highly magnetized neutron stars ($B_0\ga 10^{13}$ G) reach the accretion regime within the Galactic lifetime if their kick velocities are not to…
Astrometric microlensing probes of the isolated neutron star population with Roman
Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心）；Space Science Institute, Lawrence Livermore National Laboratory（空间科学研究所，劳伦斯利弗莫尔国家实验室）；Georgia Institute of Technology（佐治亚理工学院）
GW200115 is one of the first two confidently detected gravitational-wave events of neutron star-black hole mergers. An interesting property of this merger is that the black hole, if spinning rapidly, has its spin axis negatively aligned (with a misalignment angle $> 90^{\circ}$) with the binary orbital angular momentum vector. Although such a large spin-orbit misalignment angle naturally points toward a dynamical origin, the measured neutron star-black hole merger rate exceeds theoretical predictions of the dynamical formation channel. In the canonical isolated binary formation scenario, the i…
This paper uses population synthesis to investigate the possible origin of isolated millisecond pulsars (IMSPs) as born from the coalescence of a neutron star (NS) and a white dwarf (WD). Results show that the galactic birth - rate of IMSPs is likely to lie between $5.8\times10^{-5}$ $\rm yr^{-1}$ and $2.0\times10^{-4}$ $\rm yr^{-1}$, depending on critical variables, such as the stability of mass transfer via the Roche lobe and the value of kick velocity. In addition to this, this paper estimates that the solar mass of IMSPs can range from $1.5$ and 2.0 $M_{\odot}$, making them more massive th…
Isolated millisecond pulsars (IMSPs) are a topic of academic contention. There are various models to explain their formation. We explore the formation of IMSP via quark novae (QN). During this formation process, low-mass X-ray binaries (LMXBs) are disrupted when the mass of the neutron star (NS) reaches 1.8 $\rm M_\odot$. Using population synthesis, this work estimates that the Galactic birthrate of QN-produced IMSPs lies between $\sim 9.5\times10^{-6}$ and $\sim1.7\times10^{-4}$ $\rm yr^{-1}$. The uncertainties shown in our experiment model is due to the QN's kick velocity. Furthermore, our f…
Detectability of isolated black holes (IBHs) without a companion star but emitting X-rays by accretion from dense interstellar medium (ISM) or molecular cloud gas is investigated. We calculate orbits of IBHs in the Galaxy to derive a realistic spatial distribution of IBHs, for various mean values of kick velocity at their birth $\upsilon_{\rm avg}$. X-ray luminosities of these IBHs are then calculated considering various phases of ISM and molecular clouds, for a wide range of the accretion efficiency $λ$ (a ratio of the actual accretion rate to the Bondi rate) that is rather uncertain. It is f…
The isolated binary evolution model for merging neutron stars (NSs) involves processes such as mass transfer, common-envelope evolution, and natal kicks, all of which are poorly understood. Also, the predicted NS-NS merger rates are typically lower than the rates inferred from the LIGO GW170817 event. Here, we investigate merger rates of NS and black hole (BH)-NS binaries in hierarchical triple-star systems. In such systems, the tertiary can induce Lidov-Kozai (LK) oscillations in the inner binary, accelerating its coalescence, and potentially enhancing compact object merger rates. However, si…
Neutron stars receive velocity kicks at birth in supernovae. Those formed in electron-capture supernovae from super asymptotic giant branch stars -- the lowest mass stars to end their lives in supernovae -- may receive significantly lower kicks than typical neutron stars. Given that many massive stars are members of wide binaries, this suggests the existence of a population of low-mass ($1.25 < M_\mathrm{psr} / $M$_\odot < 1.3$), wide ($P_\mathrm{orb} \gtrsim 10^{4}$\,day), eccentric ($e \sim 0.7$), unrecycled ($P_\mathrm{spin} \sim 1$\,s) binary pulsars. The formation rate of such binaries is…
Binary radio pulsars are generally believed to have been spun up to millisecond periods (i.e. recycling) via mass accretion from their donor stars, and they are the descendants of neutron star low-mass X-ray binaries. However, some studies indicate that the formation of pulsars from the accretion-induced collapse (AIC) of accreting white dwarfs (WDs) cannot be excluded. In this work, we use a population synthesis code to examine if the AIC channel can produce eccentric binary millisecond pulsars (BMSPs) in the Galaxy. Our simulated results indicate that, only when the natal MSPs receive a rela…
The identification of the first confirmed neutron star - black hole (NS-BH) binary mergers by the LIGO, Virgo and KAGRA collaboration provides the opportunity to investigate the properties of the early sample of confirmed and candidate events. Here, we focus primarily on the tilt angle of the black hole's spin relative to the orbital angular momentum vector of the binary, and the implications for the physical processes that determine this tilt. The posterior tilt distributions of GW200115 and the candidate events GW190426_152155 and GW190917_114630 peak at significantly anti-aligned orientatio…
Binary black holes (BBHs) are one of the endpoints of isolated binary evolution, and their mergers a leading channel for gravitational wave events. Here, using the evolutionary code \textsc{StarTrack}, we study the statistical properties of the BBH population from isolated binary evolution for a range of progenitor star metallicities and BH natal kicks. We compute the mass function and the distribution of the primary BH spin $a$ as a result of mass accretion during the binary evolution, and find that this is not an efficient process to spin up BHs, producing an increase by at most $a\sim$~0.2-…
The role of accretion efficiency, natal kicks, and angular momentum transport in the formation of the Gaia black holes
Universität Heidelberg（海德堡大学）；University of Padova（帕多瓦大学）；INAF - Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Universitat de Barcelona（巴塞罗那大学）
Astrometric satellite Gaia is expected to observe non-interacting black hole (BH) binaries with luminous companions (LCs) (hereafter BH-LC binaries), a different population from BH X-ray binaries previously discovered. The detectability of BH-LC binaries with Gaia might be dependent on binary evolution models. We investigated the Gaia's detectability of BH-LC binaries formed through isolated binary evolution by means of binary population synthesis technique, and examined its dependence on single and binary star models: supernova models, common envelope (CE) ejection efficiency $α$, and BH nata…
We perform population synthesis studies of different types of neutron stars taking into account the magnetic field decay. For the first time, we confront our results with observations using {\it simultaneously} the Log N -- Log S distribution for nearby isolated neutron stars, the Log N -- Log L distribution for magnetars, and the distribution of radio pulsars in the $P$ -- $\dot P$ diagram. We find that our theoretical model is consistent with all sets of data if the initial magnetic field distribution function follows a log-normal law with $<\log (B_0/[G]) > \sim 13.25$ and $σ_{\log B_0}\sim…
Gravitational waves (GWs) from binary black hole (BBH) mergers provide a new probe of massive-star evolution and the formation channels of binary compact objects. By coupling the growing sample of BBH systems with population synthesis models, we can begin to constrain the parameters of such models and glean unprecedented knowledge about the inherent physical processes that underpin binary stellar evolution. In this study, we apply a hierarchical Bayesian model to mass measurements from a synthetic GW sample to constrain the physical prescriptions in population models and the relative fraction …
The merger of two massive 30 Msun black holes has been detected in gravitational waves (1,GW150914). This discovery validates recent predictions (2-4) that massive binary black holes would constitute the first detection. However, previous calculations have not sampled the relevant binary black hole progenitors---massive, low-metallicity binary stars---with sufficient accuracy and input physics to enable robust predictions to better than several orders of magnitude (5-10). Here we report a suite of high-precision numerical simulations of binary black hole formation via the evolution of isolated…
High-mass binary black hole mergers from detailed binary evolution models
Université de Genève（日内瓦大学）；Gravitational Wave Science Center (GWSC), Université de Genève（引力波科学中心（GWSC），日内瓦大学）；Bilkent University（比尔肯特大学）；Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University（西北大学天体物理学跨学科探索与研究中心（CIERA））；The NSF-Simons AI Institute for the Sky (NSF-Simons SkAI)（NSF-Simons 天空人工智能研究所（NSF-Simons SkAI））；Department of Physics and Astronomy, Northwestern University（西北大学物理与天文系）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Harvard Society of Fellows（哈佛学者学会）
