The Stellar Merger Scenario for Black Holes in the Pair-instability Gap
The Stellar Merger Scenario for Black Holes in the Pair-instability Gap
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DOI：
10.3847/2041-8213/abc6a6
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发表时间：
2020-10
期刊：
影响因子：
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通讯作者：
M. Renzo;M. Cantiello;B. Metzger;Yan-Fei 飞 Jiang 姜燕
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文献类型：
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作者：
M. Renzo;M. Cantiello;B. Metzger;Yan-Fei 飞 Jiang 姜燕
最近对GW 190521的探测激发了关于如何填充预测的黑洞（BH）对不稳定性（PI）质量间隙的想法。一个建议是两颗PI区域以下的恒星动力学合并，形成一颗核心较小、包层过大的星星。我们概述了在差距中形成一个BH所面临的主要挑战。特别是，核心需要避免在合并过程中增长，合并后的产品需要保持足够的质量，包括在随后的进化中，以及在核心崩溃（CC）时。我们探索这种情况下，详细的恒星演化计算，从临时的初始条件强制执行合并过程中没有核心的增长。我们发现，这些大规模的合并产品很可能是氦丰富的，并花费其剩余的大部分寿命内的不稳定区域内的赫兹斯普朗-罗素图，如发光的蓝色变量爆发。忽略星星的反反应，对质量损失量的能量估计表明，在低金属丰度下，可以去除的质量总量为101 M。这是足够小的，在CC我们的模型保留足够的质量，形成BH的PI间隙类似于最近的LIGO/处女座检测到的。然而，在合并时的质量损失，由此产生的核心结构，并在CC的质量损失仍然需要量化这些模型，以确认这种情况下的可行性。
The recent detection of GW190521 stimulated ideas on how to populate the predicted black hole (BH) pair-instability (PI) mass gap. One proposal is the dynamical merger of two stars below the PI regime forming a star with a small core and an oversized envelope. We outline the main challenges this scenario faces to form one BH in the gap. In particular, the core needs to avoid growing during the merger, and the merger product needs to retain enough mass, including in the subsequent evolution, and at core collapse (CC). We explore this scenario with detailed stellar evolution calculations, starting with ad hoc initial conditions enforcing no core growth during the merger. We find that these massive merger products are likely to be helium-rich and spend most of their remaining lifetime within regions of instabilities in the Herzsprung–Russell diagram, such as luminous blue variable eruptions. An energetic estimate of the amount of mass loss neglecting the back reaction of the star suggests that the total amount of mass that can be removed at low metallicity is ≲1 M ⊙. This is small enough that at CC our models are retaining sufficient mass to form BHs in the PI gap similar to the recent ones detected by LIGO/Virgo. However, mass loss at the time of merger, the resulting core structure, and the mass loss at CC still need to be quantified for these models to confirm the viability of this scenario.