Populating the Upper Black Hole Mass Gap through Stellar Collisions in Young Star Clusters
Populating the Upper Black Hole Mass Gap through Stellar Collisions in Young Star Clusters
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DOI：
10.3847/1538-4357/abb945
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发表时间：
2020-06
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影响因子：
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通讯作者：
K. Kremer;M. Spera;Devin R. Becker;S. Chatterjee;U. N. Di Carlo;G. Fragione;C. Rodriguez;Claire S.
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作者：
K. Kremer;M. Spera;Devin R. Becker;S. Chatterjee;U. N. Di Carlo;G. Fragione;C. Rodriguez;Claire S.
大质量恒星的理论模型预测黑洞（BH）的质量函数在1040 -50 M以上的黑洞（BH）质量函数的差距，通过单颗星星演化形成，产生于（脉动）对不稳定超新星（PISNe）。然而，在致密的星星团中，可能存在动力通道，允许建造质量超过单颗星星演化所允许的质量的黑洞。在这个所谓的“上质量间隙”中探测到黑洞，将为黑洞在最终合并之前的动力学过程提供强有力的证据。在这里，我们详细探讨了形成BH的质量内或以上的对不稳定的差距，通过碰撞的年轻大质量恒星在密集的星星集群。我们运行了一套68个独立的集群模拟，探索各种物理假设有关的增长，通过恒星碰撞，包括原始集群质量分离和碰撞过程中的包络剥离效率。我们发现，多达20%的所有BH祖细胞经历一个或多个碰撞之前，恒星坍缩和高达20%的所有BH居住在或以上的对不稳定间隙通过这些碰撞的影响。我们表明，这些BH容易继续合并与其他BH在集群中，创造人口的大规模BH合并的速度，可能会与其他分析中描述的“多代”合并渠道。这与最近在GW 190521中由激光干涉引力波天文台/室女座探测到的超大质量BH双星的形成有明显的相关性。最后，我们描述了如何恒星碰撞集群可能提供一个独特的途径PISNe和简要讨论这些事件和其他电磁瞬变的预期率。
Theoretical modeling of massive stars predicts a gap in the black hole (BH) mass function above ∼40–50 M ⊙ for BHs formed through single star evolution, arising from (pulsational) pair-instability supernovae (PISNe). However, in dense star clusters, dynamical channels may exist that allow construction of BHs with masses in excess of those allowed from single star evolution. The detection of BHs in this so-called “upper-mass gap” would provide strong evidence for the dynamical processing of BHs prior to their eventual merger. Here, we explore in detail the formation of BHs with masses within or above the pair-instability gap through collisions of young massive stars in dense star clusters. We run a suite of 68 independent cluster simulations, exploring a variety of physical assumptions pertaining to growth through stellar collisions, including primordial cluster mass segregation and the efficiency of envelope stripping during collisions. We find that as many as ∼20% of all BH progenitors undergo one or more collisions prior to stellar collapse and up to ∼1% of all BHs reside within or above the pair-instability gap through the effects of these collisions. We show that these BHs readily go on to merge with other BHs in the cluster, creating a population of massive BH mergers at a rate that may compete with the “multiple-generation” merger channel described in other analyses. This has clear relevance for the formation of very massive BH binaries as recently detected by the Laser Interferometer Gravitational-Wave Observatory/Virgo in GW190521. Finally, we describe how stellar collisions in clusters may provide a unique pathway to PISNe and briefly discuss the expected rate of these events and other electromagnetic transients.