黑洞粒子的相对论抑制
Relativistic Suppression of Black Hole Recoils
摘要：
数值相对论模拟表明，在双星合并中产生的黑洞相对于初始双星的质心的反冲速度可达v_max ~ 4，000 km/s。这挑战了大多数星系通过等级合并形成的范式，尽管逃逸速度远小于v_max，但在它们的中心仍然保留着超大质量黑洞。与环双星盘的相互作用可以使双星黑洞的自旋与它们的轨道角动量对齐，从而降低在随后的合并中产生的最终黑洞的反冲速度。然而，这种对齐的有效性取决于高度不确定的吸积流附近的双黑洞。在这封信中，我们表明，如果更大质量的二元黑洞的自旋S_1甚至部分与轨道角动量L对齐，亚秒差距尺度上的相对论自旋进动可以使二元黑洞的自旋彼此对齐。即使在没有气体的情况下，这种对准也显著降低了反冲速度。例如，当第二自旋S_2各向同性分布时，在大间距处S_1与L的夹角为10 °时，对于质量比为9/11的最大自旋黑洞，本文所讨论的自旋排列使中位反冲从864 km/s降到273 km/s。这种减少将大大增加保留其超大质量黑洞的星系的比例。
英文摘要：
Numerical-relativity simulations indicate that the black hole produced in a binary merger can recoil with a velocity up to v_max ~ 4,000 km/s with respect to the center of mass of the initial binary. This challenges the paradigm that most galaxies form through hierarchical mergers, yet retain supermassive black holes at their centers despite having escape velocities much less than v_max. Interaction with a circumbinary disk can align the binary black hole spins with their orbital angular momentum, reducing the recoil velocity of the final black hole produced in the subsequent merger. However, the effectiveness of this alignment depends on highly uncertain accretion flows near the binary black holes. In this Letter, we show that if the spin S_1 of the more massive binary black hole is even partially aligned with the orbital angular momentum L, relativistic spin precession on sub-parsec scales can align the binary black hole spins with each other. This alignment significantly reduces the recoil velocity even in the absence of gas. For example, if the angle between S_1 and L at large separations is 10 degrees while the second spin S_2 is isotropically distributed, the spin alignment discussed in this paper reduces the median recoil from 864 km/s to 273 km/s for maximally spinning black holes with a mass ratio of 9/11. This reduction will greatly increase the fraction of galaxies retaining their supermassive black holes.
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