Merger Rate Density of Binary Black Holes through Isolated Population I, II, III and Extremely Metal-poor Binary Star Evolution
Merger Rate Density of Binary Black Holes through Isolated Population I, II, III and Extremely Metal-poor Binary Star Evolution
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DOI：
10.3847/1538-4357/ac4247
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发表时间：
2021-10
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影响因子：
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通讯作者：
A. Tanikawa;T. Yoshida;T. Kinugawa;A. Trani;T. Hosokawa;H. Susa;K. Omukai
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文献类型：
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作者：
A. Tanikawa;T. Yoshida;T. Kinugawa;A. Trani;T. Hosokawa;H. Susa;K. Omukai
我们通过孤立的双星演化研究了合并双黑洞（BHs）的形成，进行了双星族合成计算，涵盖了前所未有的金属丰度范围，包括族（Pop） I， II， III和极贫金属（EMP）双星。我们发现预测的合并率密度和初级黑洞质量（m1）分布与引力波（GW）观测结果一致。值得注意的是，星族III和EMP（<10−2 Z⊙）双星产生了大多数的对不稳定性（PI）质量间隙事件，m1 = 65-130 m⊙。星族III双星对PI质量缺口事件的贡献随着红移的增加而增加，所有PI质量缺口事件都有星族III起源，红移为≥8。我们的结果可以通过以下两点的未来GW观测来评估。首先，在我们的结果中不存在m1 = 100-130 m⊙的二元黑洞，因此m1分布应该在m1 = 100-130 m⊙的范围内突然下降。其次，PI质量间隙事件率应该增加到更高的红移至~ 11，因为这些事件主要来自III星族双星。我们发现，要重现当前的GW观测结果，需要以下三个假设：恒星初始质量函数为头重，III星族和EMP双星存在紧密的双星，以及恒星演化主序阶段的低效对流超调。如果没有上述任何一项，PI质量间隙事件的数量将变得太低，无法重现当前的GW观测。
We investigate the formation of merging binary black holes (BHs) through isolated binary evolution, performing binary population synthesis calculations covering an unprecedentedly wide metallicity range of Population (Pop) I, II, III, and extremely metal-poor (EMP) binary stars. We find that the predicted merger rate density and primary BH mass (m 1) distribution are consistent with the gravitational wave (GW) observations. Notably, Population III and EMP (<10−2 Z ⊙) binary stars yield most of the pair instability (PI) mass gap events with m 1 = 65–130 M ⊙. Population III binary stars contribute more to the PI mass gap events with increasing redshift, and all the PI mass gap events have the Population III origin at redshifts ≳8. Our result can be assessed by future GW observations in the following two points. First, there are no binary BHs with m 1 = 100–130 M ⊙ in our result, and thus the m 1 distribution should suddenly drop in the range of m 1 = 100–130 M ⊙. Second, the PI mass gap event rate should increase toward higher redshift up to ∼11, since those events mainly originate from the Population III binary stars. We find that the following three assumptions are needed to reproduce the current GW observations: a top-heavy stellar initial mass function and the presence of close binary stars for Population III and EMP binary stars, and inefficient convective overshoot in the main-sequence phase of stellar evolution. Without any of the above, the number of PI mass gap events becomes too low to reproduce current GW observations.