The merger of two carbon-oxygen white dwarfs has long been theorized to lead to a massive carbon-oxygen or oxygen-neon white dwarf, accretion-induced collapse to a neutron star, or a type Ia supernova. Determining which mergers lead to a particular outcome requires hydrodynamic simulations of the merging process. I give a brief overview of the current understanding of mergers and their end-products derived from simulations, and show how temperature, rather than density or mass, most strongly determines a merging binary's subsequent evolution. I then describe recent simulations that show mergers generate strong magnetic fields that could help drive a merger remnant to ignition.
The ELM Survey. V. Merging Massive White Dwarf Binaries
我们在短周期P<1天的双星中发现了17颗低质量白矮星。我们的样本包括四个对象显着的log（g）~5表面重力和轨道的解决方案，要求他们是双退化双星。所有最低的表面重力WD在其光谱中都有金属线，这意味着长的重力沉降时间或正在进行的吸积。值得注意的是，在我们的样本中的六个WD具有二进制合并时间<10 Gyr. Four have >=0.9 Msun同伴。如果伴星是大质量的WD，这四个双星将演化成稳定的质量转移AM CVn系统，并可能爆炸为暗超新星。如果伴星是中子星，那么它们可能是毫秒脉冲星双星。这些发现使ELM巡天中分离的双简并双星的数量增加到54个;其中31个将在哈勃时间内合并。
Binary and multiple stellar systems are numerous in our solar neighborhood with 80 per cent of the solar-type stars being members of systems with high order multiplicity. The Contact Binaries Towards Merging (CoBiToM) Project is a programme that focuses on contact binaries and multiple stellar systems, as a key for understanding stellar nature. The goal is to investigate stellar coalescence and merging processes, as the final state of stellar evolution of low-mass contact binary systems. Obtaining observational data of approximately 100 eclipsing binaries and multiple systems and more than 400…
Unravelling the progenitors of merging black hole binaries
近年来的引力波探测证实了大质量恒星黑洞双星的存在，但黑洞双星的形成通道仍是一个悬而未决的问题。在这里，我们调查的人口BBHs使用我们的新的人口合成代码MOBSE。MOBSE是广泛使用的双星总体合成代码BSE（Hurley et al. 2000，Hurley et al. 2002）的更新版本，包括确定大质量恒星命运的关键要素：最新的恒星风处方和超新星模型。使用MOBSE，我们在低金属丰度下形成总质量高达$\sim{}120$ M $_\odot$的BBH，但只有总质量高达$\sim{}80$ M $_\odot$的系统在不到一个哈勃时间内合并。我们的研究结果表明，只有大质量贫金属星（$Z\lesssim 0.002$）才可能是像GW 150914这样的引力波事件的祖先。此外，我们预测，合并BBH形式更有效地从金属贫比富金属的恒星。
Eccentricity and Inclination Excitation of Stellar Orbits around merging Black-Hole Binaries
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University（南京大学现代天体学与天体物理教育部重点实验室）
Gravitational-wave observations of binary black hole (BBH) systems point to black hole spin magnitudes being relatively low. These measurements appear in tension with high spin measurements for high-mass X-ray binaries (HMXBs). We use grids of MESA simulations combined with the rapid population-synthesis code COSMIC to examine the origin of these two binary populations. It has been suggested that Case-A mass transfer while both stars are on the main sequence can form high-spin BHs in HMXBs. Assuming this formation channel, we show that depending on critical mass ratios for the stability of mas…
寻找独特的签名，这表明不同的形成渠道的双黑洞（BBH），是一个关键的一步，对当前和未来的引力波探测的解释。在这里，我们调查的人口合并BBHs在年轻的星团（SC），这是大质量恒星的托儿所。我们进行了$4\times{} 10^3$ N-体模拟的SC与金属$Z=0.002$，初始二元分数$0.4$和分形初始条件，以模拟恒星形成区的块状。我们的模拟包括一个新的人口合成的基础上的代码MOBSE的方法。我们发现，SC动态并不影响合并率显着，但留下了强大的指纹上的属性合并BBH。在最初的几个百万年中，年轻SC中超过50%的合并BBH通过动态交换形成。动态形成的合并BBH比孤立双星中的合并BBH重得多：在年轻的SC中，合并BBH的总质量高达$\sim{}120$ M $_\odot$形式，而在具有相同金属丰度的孤立双星中，合并BBH的最大总质量仅为$\sim{}70$ M $_\odot$。通过动力学交换产生的合并BBH往往比孤立双星中的BBH具有更小的质量比。此外，SC动力学加速合并：在年轻的SC中，恒星形成和合并之间的延迟时间显着缩短。在我们的模拟中，像GW 170729这样的大质量系统只能通过动力学交换形成。最后，年轻SC中合并BBH的$\sim{}2$ %在对不稳定质量间隙中具有质量（$\sim{}60-120$ M $_\odot$）。这表示在SC中合并BBH的唯一指纹。
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 …
There are few observed high-mass X-ray binaries (HMXBs) that harbor massive black holes, and none are likely to result in a binary black hole (BBH) that merges within a Hubble time; however, we know that massive merging BBHs exist from gravitational-wave observations. We investigate the role that X-ray and gravitational-wave observational selection effects play in determining the properties of their respective detected binary populations. We find that, as a result of selection effects, detectable HMXBs and detectable BBHs form at different redshifts and metallicities, with detectable HMXBs for…
As the number of observed merging binary black holes (BHs) grows, accurate models are required to disentangle multiple formation channels. In models with isolated binaries, important uncertainties remain regarding the stability of mass transfer (MT) and common-envelope (CE) evolution. To study some of these uncertainties, we have computed simulations using MESA of a $30M_\odot$, low metallicity ($Z_\odot/10$) star with a BH companion. We developed a prescription to compute MT rates including possible outflows from outer Lagrangian points, and a method to self-consistently determine the core-en…
The maximum mass of black holes formed in isolated binaries is determined by stellar winds and the interactions between the binary components. We consider for the first time fully self-consistent detailed stellar structure and binary evolution calculations in population-synthesis models and a new, qualitatively different picture emerges for the formation of black-hole binaries, compared to studies employing rapid population synthesis models. We find merging binary black holes can form with a non-negligible rate ($\sim 4\times10^{-7}\,M_\odot^{-1}$) at solar metallicity. Their progenitor stars …
The LIGO and Virgo detectors have directly observed gravitational waves from mergers of pairs of stellar-mass black holes, along with a smaller number of mergers involving neutron stars. These observations raise the hope that compact object mergers could be used as a probe of stellar and binary evolution, and perhaps of stellar dynamics. This colloquium-style article summarises the existing observations, describes theoretical predictions for formation channels of merging stellar-mass black-hole binaries along with their rates and observable properties, and presents some prospects for gravitati…
The progenitors of compact-object binaries: impact of metallicity, common envelope and natal kicks
LIGO-Virgo合作（LVC）已经报道了六个引力波事件，其中五个与黑洞双星（BHB）合并有关，一个与双中子星（DNS）合并有关，而黑洞-中子星（BHNS）双星的合并仍然缺失。我们调查的祖先的双重紧凑的对象二进制与我们的人口合成代码MOBSE。MOBSE包括恒星风造成的质量损失的高级处方（取决于金属丰度和爱丁顿比），以及核心坍缩、电子俘获和（脉动）对不稳定超新星的形式主义。我们研究了祖先的金属丰度，共同包络参数$α$和出生踢的DNSs，BHNSs和BHBs的属性的影响。我们发现，中子星（NS）的质量范围从1.1到2.0 M $_\odot$，与轻NS的偏好，而在合并BHNS NS的NS大多有大的质量（$1.3-2.0$ M $_\odot$）。合并BHN中的BH优先为低质量（$5-15$ M $_\odot$）。合并BHB中的BH质量强烈依赖于祖细胞的金属性，并且从$\sim{}5$跨越到$\sim{}45$ M $_\odot$。从我们的模拟中得出的BHNS和BHB的本地合并率密度与LVC在我们所有的模拟中报告的值是一致的。与此相反，本地合并率密度的DNS匹配的值推断出的LVC只有当低出生踢假定。这一结果为本征踢和DNS形成的复杂谜题增添了另一个部分。
Formation of Merging Black Hole Binaries Inside Massive AGN Stars
Perimeter Institute for Theoretical Physics（Perimeter理论物理研究所）；Department of Astronomy and Astrophysics, University of California, Santa Cruz（加州大学圣克鲁兹分校天体物理学与天文学系）；School of Natural Sciences, Institute for Advanced Study（高等研究院自然科学院）；Department of Astrophysical Sciences, Princeton University（普林斯顿大学天体物理科学系）
Linking high-mass X-ray binaries to binary compact object mergers in Milky Way-like galaxies
Universidad Andres Bello（安德烈斯贝略大学）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio（意大利国家天体物理研究所空间科学与天体物理观测站）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉拉克鲁纳大学）；Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB)（巴塞罗那宇宙科学研究所）；Universität Heidelberg, Zentrum für Astronomie (ZAH), Institut für Theoretische Astrophysik（海德堡大学天文学中心理论天体物理研究所）
2015年9月14日，LIGO干涉仪从两个合并的黑洞（BH）中捕获了引力波（GW）信号，开启了GW天体物理学的时代。到目前为止，已经报告了五个黑洞合并，其中三个涉及大质量黑洞（$\gtrsim{}30$ M $_\odot$）。根据恒星演化模型，这种大质量黑洞可能起源于大质量、相对贫金属的恒星。合并BH双星的形成通道仍然是一个悬而未决的问题：大量的不确定性影响了大质量恒星双星的演化（如共同包层过程）和动力学。这篇评论的目的是讨论有关BH双星的开放性问题，并提出了国家的最先进的知识的天体物理学的BH的非专业人士，在光的第一个LIGO-Virgo检测。
