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arXiv · 1906.09281

Hierarchical Black Hole Mergers in Active Galactic Nuclei

Yang Yang·Imre Bartos·V. Gayathri·Saavik Ford·Zoltan Haiman·Sergey Klimenko·Bence Kocsis·Szabolcs Márka·Zsuzsa Márka·Barry McKernan·Richard O'Shaugnessy
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Abstract

The origins of the stellar-mass black hole mergers discovered by LIGO/Virgo are still unknown. Here we show that, if migration traps develop in the \add{accretion} disks of Active Galactic Nuclei (AGNs) and promote the mergers of their captive black holes, the majority of black holes within disks will undergo hierarchical mergers---with one of the black holes being the remnant of a previous merger. 40% of AGN-assisted mergers detected by LIGO/Virgo will include a black hole with mass $\gtrsim 50$ M$_\odot$, the mass limit from stellar core collapse. Hierarchical mergers at traps in AGNs will exhibit black hole spins (anti-)aligned with the binary's orbital axis, a distinct property from other hierarchical channels. Our results are suggestive, although not definitive (with Odds ratio of $\sim 1$), that LIGO's heaviest merger so far, GW170729, could have originated from this channel.

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Yang Yang, Imre Bartos, V. Gayathri, Saavik Ford, Zoltan Haiman, Sergey Klimenko, Bence Kocsis, Szabolcs Márka, Zsuzsa Márka, Barry McKernan, Richard O'Shaugnessy. 2019-09-30. Hierarchical Black Hole Mergers in Active Galactic Nuclei. https://doi.org/10.1103/physrevlett.123.181101

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