[论文解读] The origin of low spin of black holes in LIGO/Virgo mergers

K. Belczynski, Jakub Klencki+16 more|arXiv (Cornell University)|Jun 21, 2017

Pulsars and Gravitational Waves Research参考文献 19被引用 55

一句话总结

该论文提出，如果大质量恒星中的角动量输运效率适中，则孤立双星演化可以解释LIGO/Virgo双黑洞并合中观测到的低有效自旋，包括GW170104。然而，该模型预测的高自旋并合比例高于实际观测，表明大质量恒星中的角动量输运效率必须高于模型假设，从而导致黑洞以接近零自旋的状态形成。

ABSTRACT

LIGO/Virgo have reported six binary black hole (BH-BH) mergers. The effective spins of all of them are clustered around Xeff=0. However, the effective spin of one of them, GW170104, has an 82% probability of being negative, which would indicate a significant spin-orbit misalignment and seemingly supporting dynamical formation over isolated binary evolution. We show (i) as a proof-of-principle case, that GW170104 could have been formed through isolated binary evolution, and (ii) that the LIGO/Virgo measurements inform about, thus far unconstrained, angular momentum transport in massive stars. Massive stars can have inner transport of angular momentum and their strong winds may carry away substantial angular momentum, affecting the natal spin of the BHs created at the end of their lives. We present a physically motivated model for BH natal spins based on moderately efficient angular momentum transport. With this model we can explain the low effective spin of GW170104 in the context of isolated binary evolution. However, our predicted effective spin distribution of BH-BH mergers, showing a large fraction of high effective spins, is not consistent with LIGO/Virgo observations. If the effective spins of BHs observed by LIGO/Virgo continue to be small, it will indicate that angular momentum transport in massive stars is more efficient than adopted in our model and that BHs found in BH-BH mergers are born with low spins (a_spin=0).

研究动机与目标

• 研究孤立双星演化是否能够解释LIGO/Virgo双黑洞并合中观测到的低有效自旋，特别是GW170104。
• 评估大质量恒星中角动量输运在决定恒星演化末期形成的黑洞原初自旋中的作用。
• 将观测到的低有效自旋分布与孤立双星演化的理论模型相协调。
• 基于LIGO/Virgo观测结果，约束大质量恒星中角动量输运的效率。

提出的方法

• 基于大质量恒星中角动量输运效率适中，构建了黑洞原初自旋的物理解释模型。
• 利用该模型模拟孤立双星演化，预测双黑洞并合的有效自旋分布。
• 利用LIGO/Virgo观测到的有效自旋分布（包括GW170104中82%的概率为负自旋）检验模型的一致性。
• 将模型预测的有效自旋分布与实际LIGO/Virgo观测结果进行比较，以推断角动量输运效率的约束。
• 将恒星风质量损失和内部角动量输运作为决定黑洞原初自旋的关键驱动力。
• 将模型预测与观测到的有效自旋集中在零附近的趋势进行对比评估。

实验结果

研究问题

• RQ1 孤立双星演化能否重现GW170104及其他LIGO/Virgo双黑洞并合中观测到的低有效自旋？
• RQ2 大质量恒星中角动量输运的效率如何影响核心塌缩形成的黑洞原初自旋？
• RQ3 LIGO/Virgo观测对大质量恒星中角动量输运效率施加了何种约束？
• RQ4 尽管理论预期自旋值较高，为何双黑洞并合的有效自旋分布如此强烈地集中在零附近？
• RQ5 观测到的自旋分布是否意味着双星并合中的黑洞以接近零自旋的状态形成？

主要发现

• 角动量输运效率适中的模型能够通过孤立双星演化解释GW170104中观测到的负有效自旋。
• 该模型预测的有效自旋分布中包含大量高自旋并合事件，与LIGO/Virgo观测结果不一致。
• 观测到的低有效自旋分布表明，大质量恒星中的角动量输运效率必须高于模型假设的水平。
• 如果观测到的自旋分布保持较低水平，则表明双星并合中的黑洞以接近零自旋（a_spin ≈ 0）的状态形成。
• 因此，LIGO/Virgo观测为大质量恒星中角动量输运的物理机制提供了新的约束，而这些机制此前尚未被约束。