Remnant Black Hole Kicks and Implications for Hierarchical Mergers
Remnant Black Hole Kicks and Implications for Hierarchical Mergers
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DOI：
10.3847/2041-8213/ac20db
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发表时间：
2021-06
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影响因子：
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通讯作者：
P. Mahapatra;Anuradha Gupta;Marc Favata;K. Arun;B. Sathyaprakash
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作者：
P. Mahapatra;Anuradha Gupta;Marc Favata;K. Arun;B. Sathyaprakash
当双黑洞在密集的星团中合并时，它们的残余物可以与星团中的其他黑洞配对，形成越来越重的黑洞，这一过程被称为分层合并。分层合并发生的最重要条件是合并形成的残余物被主星团保留。利用公开可用的引力波事件数据库，我们推断了由于引力波的各向异性发射而赋予残余黑洞的踢速的大小，并利用它来量化每个事件的保留概率作为星团逃逸速度的函数。在第二次引力波瞬变目录（GWTC-2）事件中，GW190814在90%可信水平上提供了最严格的踢射量级约束，其Vkick=74−7+10 km s−1。我们发现逃逸速度为200 km s−1的星团可以保留GWTC-2中大约50%的事件。利用核星团和球状星团的逃逸速度分布，我们发现，如果所有GWTC-2事件都发生在核（球状）星团中，那么GWTC-2的残留物可能被宿主星团保留了~ 17(2)。我们的研究表明，在未来的分层合并研究中，折叠在踢速推断中的重要性。
When binary black holes merge in dense star clusters, their remnants can pair up with other black holes in the cluster, forming heavier and heavier black holes in a process called hierarchical merger. The most important condition for hierarchical merger to occur is that remnants formed by mergers are retained by the host star cluster. Using the publicly available gravitational-wave event database, we infer the magnitudes of kick velocities imparted to the remnant black holes due to anisotropic emission of gravitational waves and use that to quantify the retention probability of each event as a function of the escape speed of the star cluster. Among the second gravitational-wave transient catalog (GWTC-2) events, GW190814 provides the tightest constraint on the kick magnitude with Vkick=74−7+10 km s−1 at the 90% credible level. We find that star clusters with escape speeds of 200 km s−1 can retain about 50% of the events in the GWTC-2. Using the escape speed distributions of nuclear star clusters and globular clusters, we find that ∼17 (2) remnants of GWTC-2 may be retained by the host star cluster if all GWTC-2 events occurred in nuclear (globular) clusters. Our study demonstrates the importance of folding in kick velocity inferences in future studies of hierarchical mergers.