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arXiv 2204.06002astro-ph.HEgr-qc
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AGN黑洞中逃逸共振的偏心并合

Eccentric Mergers of Intermediate-Mass Black Holes from Evection Resonances in AGN Disks

Diego J. Muñoz, Nicholas C. Stone, Cristobal Petrovich, Frederic A. Rasio

摘要:

本文应用非线性共振俘获理论研究了一个黑洞双星(BHB)嵌入活动星系核(AGN)吸积盘中并围绕一个超大质量黑洞(SMBH)运动的问题。如果成功的话,共振捕获可以触发BHB偏心率的急剧增长,对BHB合并的时间尺度以及这种偏心合并的引力波(GW)签名产生重要影响。当SMBH(“外双星”)的轨道周期和BHB(“内双星”)的拱点进动处于1:1的比例时,可能会发生共振捕获。这种效应类似于早期日-地-月系统中的月球偏移共振现象,区别在于,在目前的情况下,BHB拱点进动是由于广义相对论,而不是旋转引起的扭曲。然而,与月球逃逸的情况相反,内双星经历由GW发射驱动的轨道衰减,而不是由潮汐耗散驱动的轨道膨胀。这种区别从根本上改变了三体动力学,禁止共振捕获,并限制偏心率的增长。然而,如果BHB迁移通过的气态活动星系盘,在外部的二元的变化可以抵消的抑制效果的BHB衰变,允许偏转共振捕获和偏心BHB合并的生产。我们计算共振捕获的可能性假设一个不可知的参数分布的三个机构参与和AGN磁盘的属性。我们发现,中等质量比的BHB(涉及一个中等质量的黑洞和一个恒星质量的黑洞)是最有可能被捕获到的逃逸共振,从而进行偏心合并。我们还计算GW签名的这些合并,表明他们可以进入LISA带,而偏心。

英文摘要:

We apply the theory of nonlinear resonance capture to the problem of a black hole binary (BHB) orbiting a supermassive black hole (SMBH) while embedded in the accretion disk of an active galactic nucleus (AGN). If successful, resonance capture can trigger dramatic growth in the BHB eccentricity, with important consequences for the BHB merger timescale, as well as for the gravitational wave (GW) signature of such an eccentric merger. This resonance capture may occur when the orbital period around the SMBH (the "outer binary") and the apsidal precession of the BHB (the "inner binary") are in a 1:1 commensurability. This effect is analogous to the phenomenon of lunar evection resonance in the early Sun-Earth-Moon system, with the distinction that in the present case, the BHB apsidal precession is due to general relativity, rather than rotationally-induced distortion. In contrast to the case of lunar evection, however, the inner binary undergoes orbital decay driven by GW emission, rather than orbital expansion driven by tidal dissipation. This distinction fundamentally alters the three-body dynamics, forbidding resonance capture, and limiting eccentricity growth. However, if the BHB migrates through of a gaseous AGN disk, the change in the outer binary can counterbalance the suppressing effect of BHB decay, permitting evection resonance capture and the production of eccentric BHB mergers. We compute the likelihood of resonance capture assuming an agnostic distribution of parameters for the three bodies involved and for the properties of the AGN disk. We find that intermediate-mass ratio BHBs (involving an intermediate-mass black hole and a stellar-mass black hole) are the most likely to be captured into evection resonance and thus undergo an eccentric merger. We also compute the GW signature of these mergers, showing that they can enter the LISA band while eccentric.

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