Population III binary black holes: effects of convective overshooting on formation of GW190521
Population III binary black holes: effects of convective overshooting on formation of GW190521
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DOI：
10.1093/mnras/stab1421
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发表时间：
2020-10
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影响因子：
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通讯作者：
A. Tanikawa;T. Kinugawa;T. Yoshida;K. Hijikawa;H. Umeda
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作者：
A. Tanikawa;T. Kinugawa;T. Yoshida;K. Hijikawa;H. Umeda
GW 190521是两个黑洞（BH）的合并，其中至少一个处于所谓的对不稳定（PI）质量间隙中，并且由于PI超新星（SNe）和脉动PI（PPI）的影响，应该很难形成。我们研究了GW 190521-like BH-BH在Pop. III环境的二进制人口合成（BPS）计算。我们揭示了恒星演化过程中的对流过冲强烈影响了类GW 190521 BH-BH的形成。具有小过冲参数的模型（类似于GENEC）可以形成类似GW 190521的BH-BH。在红移为0.82$时，推导出的合并速率为4 * 10^{-2}$ yr$^{-1}$ Gpc$^{-3}$，与引力波观测推断的类GW 190521 BH-BH的合并速率相当。在这个模型中，一颗$\sim 90 M_\odot$星星可以坍缩成一颗$\sim 90 M_\odot$ BH，避免PPI和PISN，即使它是一颗双星星星的成员。这是因为它会膨胀到$\sim 10^2 R_\odot$，并且在双星演化过程中几乎没有质量损失。然而，具有大的超调参数的模型（类似于Stern）根本不能形成类似GW 190521的BH-BH。我们不能断定第三类双星是GW 190521的起源，因为正确的过冲参数是高度不确定的。如果GW 190521的起源是一颗Pop. III双星，那么包含100 -135 M_（odot）$ BH的BH-BH的合并率远小于类GW 190521的BH-BH的合并率。这将在不久的将来通过引力波观测进行评估。
GW190521 is a merger of two black holes (BHs), at least one of which is in so-called the pair-instability (PI) mass gap, and should be hard to form due to effects of PI supernovae (SNe) and pulsational PI (PPI). We study the formation of GW190521-like BH-BHs under Population (Pop.) III environments by binary population synthesis (BPS) calculations. We reveal that convective overshooting in stellar evolution strongly affects the formation of GW190521-like BH-BHs. A model with a small overshoot parameter (similar to GENEC) can form GW190521-like BH-BHs. The derived merger rate is $4 \times 10^{-2}$ yr$^{-1}$ Gpc$^{-3}$ at redshift of $\sim 0.82$, comparable to the merger rate of GW190521-like BH-BHs inferred by gravitational wave observations. In this model, a $\sim 90 M_\odot$ star can collapse to a $\sim 90 M_\odot$ BH avoiding PPI and PISN even if it is a member of a binary star. This is because it expands up to $\sim 10^2 R_\odot$, and lose little mass through binary evolution. However, a model with a large overshoot parameter (similar to Stern) cannot form GW190521-like BH-BHs at all. We cannot conclude that a Pop. III binary is the origin of GW190521, since the correct overshoot parameter is highly uncertain. If a Pop. III binary is the origin of GW190521, the merger rate of BH-BHs including a $100-135 M_\odot$ BH is much smaller than that of GW190521-like BH-BHs. This will be assessed by gravitational wave observations in the near future.