Hierarchical Black Hole Mergers are Common in AGN Disks. (arXiv:1906.09281v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Yang Yang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bartos_I/0/1/0/all/0/1">Imre Bartos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gayathri_V/0/1/0/all/0/1">V. Gayathri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ford_S/0/1/0/all/0/1">Saavik Ford</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haiman_Z/0/1/0/all/0/1">Zoltan Haiman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Klimenko_S/0/1/0/all/0/1">Sergey Klimenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kocsis_B/0/1/0/all/0/1">Bence Kocsis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marka_S/0/1/0/all/0/1">Szabolcs Márka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marka_Z/0/1/0/all/0/1">Zsuzsa Márka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McKernan_B/0/1/0/all/0/1">Barry McKernan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+OShaugnessy_R/0/1/0/all/0/1">Richard O'Shaugnessy</a>
The origins of the stellar-mass black hole mergers discovered by LIGO and
Virgo are still unknown. The masses and spins of merging black holes, which can
be reconstructed from gravitational-wave observations, are characteristic of
the formation mechanism. Here we show that the majority of black hole mergers
within the disks of active galactic nuclei (AGNs) will be hierarchical
mergers—with one of the black holes being the remnant of a previous merger.
This results in black hole properties distinct from other channels. Such black
holes will be significantly heavier than their initial mass distribution, with
30% of AGN binaries expected to include one black hole with mass $gtrsim 50$
M$_odot$, the mass limit from stellar core collapse. As orbital planes are
aligned with the AGN disk, the heavier black hole’s spin in hierarchical
mergers will be aligned or anti-aligned with the binary’s orbital axis. We find
that LIGO’s the heaviest black hole merger so far, GW170729, could have
originated from this channel.
The origins of the stellar-mass black hole mergers discovered by LIGO and
Virgo are still unknown. The masses and spins of merging black holes, which can
be reconstructed from gravitational-wave observations, are characteristic of
the formation mechanism. Here we show that the majority of black hole mergers
within the disks of active galactic nuclei (AGNs) will be hierarchical
mergers—with one of the black holes being the remnant of a previous merger.
This results in black hole properties distinct from other channels. Such black
holes will be significantly heavier than their initial mass distribution, with
30% of AGN binaries expected to include one black hole with mass $gtrsim 50$
M$_odot$, the mass limit from stellar core collapse. As orbital planes are
aligned with the AGN disk, the heavier black hole’s spin in hierarchical
mergers will be aligned or anti-aligned with the binary’s orbital axis. We find
that LIGO’s the heaviest black hole merger so far, GW170729, could have
originated from this channel.
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