2+2四重系统中低质量和高质量能隙中的黑洞合并
Merging Black Holes in the Low-mass and High-mass Gaps from 2+2 Quadruple Systems
摘要：
LIGO-Virgo观测到的黑洞（BH）双星合并的起源仍然不确定，恒星BH质量函数的边界也是如此。恒星演化模型预测，质量为$\gtrsim 50$ M $_\odot$和$\lesssim 5$ M $_\odot$的黑洞都很缺乏，因此在黑洞质量函数中留下了低质量和高质量的间隙。形成这些质量的黑洞的一种自然方式是通过中子星（NS;对于低质量间隙）或低质量黑洞（对于高质量间隙）的合并;作为合并产物产生的低或高质量间隙黑洞如果再次与新的伴星合并，则可以被LIGO-Virgo检测到。我们发现，2+2四重系统的演化可以自然地导致BH合并的组件质量在低或高质量的差距。在我们的方案中，质量间隙中的BH源自两个NS或两个BH的合并，在两个双星中的一个中，合并产物被赋予反冲反冲（来自各向异性引力波发射），这触发了它与四重系统的另一个双星组件的相互作用。这种三体相互作用的结果通常是一个新的偏心致密双星，其中包含质量间隙中的BH，然后可以再次合并。低质量间隙和高质量间隙中BH的合并率分别为$\sim 10^{-7} - 10^{-2}$ Gpc $^{-3}$ yr $^{-1}$和$\sim 10^{-3} - 10^{-2}$ Gpc $^{-3}$ yr $^{-1}$。随着引力波探测器灵敏度的提高，恒星BH质量函数将很快受到更严格的约束。
英文摘要：
The origin of the black hole (BH) binary mergers observed by LIGO-Virgo is still uncertain, as are the boundaries of the stellar BH mass function. Stellar evolution models predict a dearth of BHs both at masses $\gtrsim 50$ M$_\odot$ and $\lesssim 5$ M$_\odot$, thus leaving low- and high-mass gaps in the BH mass function. A natural way to form BHs of these masses is through mergers of neutron stars (NSs; for the low-mass gap) or lower-mass BHs (for the high-mass gap); the low- or high-mass-gap BH produced as a merger product can then be detected by LIGO-Virgo if it merges again with a new companion. We show that the evolution of a 2+2 quadruple system can naturally lead to BH mergers with component masses in the low- or high-mass gaps. In our scenario, the BH in the mass gap originates from the merger of two NSs, or two BHs, in one of the two binaries and the merger product is imparted a recoil kick (from anisotropic gravitational wave emission), which triggers its interaction with the other binary component of the quadruple system. The outcome of this three-body interaction is usually a new eccentric compact binary containing the BH in the mass gap, which can then merge again. The merger rate is $\sim 10^{-7} - 10^{-2}$ Gpc$^{-3}$ yr$^{-1}$ and $\sim 10^{-3} - 10^{-2}$ Gpc$^{-3}$ yr$^{-1}$ for BHs in the low-mass and high-mass gap, respectively. As the sensitivity of gravitational wave detectors improves, tighter constraints will soon be placed on the stellar BH mass function.
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