活动星系核吸积盘中的EMRIs与IMRIs同步
Synchronizing the EMRIs and IMRIs in AGN accretion disks
AI总结：
本研究发现活动星系核吸积盘中的中等质量黑洞可俘获内侧恒星质量黑洞，二者迁移同步至距中心黑洞约10个史瓦西半径处因引力波辐射解体，提示LISA或能在同个活动星系核中数年内先后探测到EMRI和IMRI，为相关黑洞形成演化研究提供新信息。
摘要：
极端质量比旋近（Extreme-mass-ratio inspirals, EMRIs）和中等质量比旋近（intermediate-mass-ratio inspirals, IMRIs）是激光干涉空间天线（Laser Interferometer Space Antenna, LISA）的重要引力波（gravitational-wave, GW）源。迄今为止，它们的形成与演化一直被认为是相互独立的，但近期理论表明，恒星质量黑洞（stellar-mass black holes, sBHs）和中等质量黑洞（intermediate-mass black hole, IMBHs）可以共存于活动星系核（active galactic nucleus, AGN）的吸积盘中，这意味着EMRIs和IMRIs可能在同一区域形成。受原行星盘中迁移的气态巨行星可将星子俘获在其轨道附近这一现象的启发，本文研究了AGN盘中会开启间隙的IMBH与其周围sBHs之间的类似相互作用。我们分析了吸积盘以及IMBH对sBHs施加的力矩，结果表明，若sBHs位于IMBH的轨道内侧，就可以被IMBH俘获。随后我们将这些力矩纳入数值模拟，研究了同处于AGN盘中的外侧IMBH与内侧sBH的迁移过程。我们发现，二者的迁移会保持同步，直到它们到达距离中心超大质量黑洞约10个史瓦西半径的位置，此时该双星系统会因强烈的引力波辐射而解体。这一结果表明，LISA可能在数年内探测到来自同一个AGN的一个EMRI和一个IMRI。这类引力波源将为研究AGN中sBHs与IMBHs的形成和演化提供丰富的信息。
英文摘要：
Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals (IMRIs) are important gravitational-wave (GW) sources for the Laser Interferometer Space Antenna (LISA). So far, their formation and evolution are considered to be independent, but recent theories suggest that stellar-mass black holes (sBHs) and intermediate-mass black hole (IMBHs) can coexist in the accretion disk of an active galactic nucleus (AGN), which indicates that EMRIs and IMRIs may form in the same place. Motivated by the fact that a gas giant migrating in a protoplanetary disk could trap planetesimals close to its orbit, we study in this paper a similar interaction between a gap-opening IMBH in an AGN disk and the sBHs surrounding it. We analyse the torques imposed on the sBHs by the disk as well as by the IMBH, and show that the sBHs can be trapped by the IMBH if they are inside the orbit of the IMBH. Then we implement the torques in our numerical simulations to study the migration of an outer IMBH and an inner sBH, both embedded in an AGN disk. We find that their migration is synchronized until they reach a distance of about ten Schwarzschild radii from the central supermassive black hole, where the pair breaks up due to strong GW radiation. This result indicates that LISA may detect an EMRI and an IMRI within several years from the same AGN. Such a GW source will bring rich information about the formation and evolution of sBHs and IMBHs in AGNs.
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