标题： 通过年轻星团中的恒星碰撞填补上部黑洞质量间隙 显示英文标题

标题： Populating the upper black hole mass gap through stellar collisions in young star clusters

摘要： 大质量恒星的理论建模预测，在通过单星演化形成的黑洞（BH）的质量函数中，存在一个位于$\sim 40-50\,M_{\odot}$之上的“黑洞质量空隙”。这一空隙源于（脉动）成对不稳定超新星现象。然而，在密集星团中，可能存在动力学通道，允许形成质量超过单星演化所允许范围的黑洞。在所谓的“上质量空隙”中检测到黑洞将为黑洞在最终合并之前的动力学处理提供有力证据。 在此，我们详细探讨了在密集星团中年轻大质量恒星碰撞下形成质量位于或高于成对不稳定空隙内的黑洞的过程。我们运行了一组包含 68 个独立星团模拟的实验，探索了与恒星碰撞增长相关的多种物理假设，包括原始星团的质量分离和碰撞过程中包层剥离的效率。 我们发现，多达$\sim20\%$的所有黑洞前身星在恒星坍缩之前经历了一次或多次碰撞，并且多达$\sim1\%$的所有黑洞通过这些碰撞效应位于或高于成对不稳定空隙内。我们表明，这些黑洞容易与其他黑洞合并，从而在星团中创建一个巨大的黑洞合并群体，其合并速率可能与在其他分析中描述的“多代合并”通道相竞争。这对最近由 LIGO/Virgo 在 GW190521 中探测到的非常大质量黑洞双星的形成具有明确的相关性。 最后，我们描述了星团中的恒星碰撞如何为成对不稳定超新星提供一条独特路径，并简要讨论了这些事件和其他电磁暂现现象的预期发生率。 显示英文摘要

摘要： Theoretical modeling of massive stars predicts a gap in the black hole (BH) mass function above $\sim 40-50\,M_{\odot}$ for BHs formed through single star evolution, arising from (pulsational) pair-instability supernovae. 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 $\sim20\%$ of all BH progenitors undergo one or more collisions prior to stellar collapse and up to $\sim1\%$ 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 LIGO/Virgo in GW190521. Finally, we describe how stellar collisions in clusters may provide a unique pathway to pair-instability supernovae and briefly discuss the expected rate of these events and other electromagnetic transients.