Gravitational waves emitted by merging black holes between ∼104 and 107 M⊙ will be detectable by the Laser Interferometer Space Antenna (LISA) with signal-to-noise ratios of several hundred out to redshift 20. Supermassive black hole (107–1010 M⊙) binary formation, coalescence, and merger within massive galaxies is well-studied. However, intermediate-mass black holes (IMBHs) between ∼104 and 106 M⊙ are hosted by low mass and dwarf galaxies; it is not trivial to extrapolate black hole merger time-scales to this IMBH binary regime, due to the starkly different host galaxy structure, kinematics, and morphology compared to massive galaxy hosts. We perform ultrahigh resolution N-body simulations to study IMBH dynamics in nucleated dwarf galaxies whose structural parameters are obtained from observations of nearby dwarf galaxies. Starting from 50 pc, an IMBH quickly forms a binary. Thereafter, the binary orbit shrinks rapidly due to the high central stellar densities furnished by nuclear star clusters (NSCs). We find high eccentricities (e ∼ 0.4–0.99) in our suite of IMBH binaries, and residual eccentricity may persist to the LISA regime. IMBH merger times are typically a few hundred million years, with a few exceptionally short merger times for high eccentricities. We find that IMBH-stellar encounters originate pre-dominantly from NSCs, if the NSC-to-IMBH binary mass ratio is greater than 10; otherwise, bulge stars contribute significantly. As the IMBH binary ejects stars, however, the NSCs are disrupted. We conclude that comparable-mass IMBHs merge very efficiently in nucleated dwarf galaxies, making them promising LISA sources, as well as a channel for IMBH growth.

中文翻译：

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有核矮星系中中等质量黑洞双星的极有效合并

激光干涉仪空间天线 (LISA) 可以检测到 ∼104 到 107 M⊙ 合并黑洞发出的引力波，其信噪比为几百到红移 20。 超大质量黑洞 (107-1010 M⊙ ) 大质量星系内的二元形成、合并和合并已得到充分研究。然而，~104 和 106 M⊙ 之间的中等质量黑洞 (IMBH) 由低质量和矮星系托管；由于与大质量星系宿主相比，宿主星系的结构、运动学和形态截然不同，因此将黑洞合并的时间尺度外推到这个 IMBH 二元状态并非易事。我们进行超高分辨率 N 体模拟以研究有核矮星系中的 IMBH 动力学，其结构参数是从对附近矮星系的观测中获得的。50个起，一个 IMBH 很快就形成了一个二进制文件。此后，由于核星团（NSC）提供的高中心恒星密度，双星轨道迅速缩小。我们在我们的 IMBH 双星套件中发现了高偏心率（e ~ 0.4-0.99），并且剩余的偏心率可能会持续存在于 LISA 机制中。IMBH 合并时间通常为几亿年，对于高离心率，合并时间极短。我们发现，如果 NSC 与 IMBH 双星质量比大于 10，则 IMBH 与恒星的相遇主要来自 NSC；否则，膨胀星的贡献很大。然而，随着 IMBH 双星喷射恒星，NSC 被破坏。我们得出结论，相当质量的 IMBH 在有核矮星系中非常有效地合并，使它们成为有希望的 LISA 来源，以及 IMBH 增长的渠道。