GW170817A as a Hierarchical Black Hole Merger. (arXiv:1911.11142v1 [astro-ph.HE])
<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:+Bartos_I/0/1/0/all/0/1">I. Bartos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haiman_Z/0/1/0/all/0/1">Z. Haiman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Klimenko_S/0/1/0/all/0/1">S. Klimenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kocsis_B/0/1/0/all/0/1">B. Kocsis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marka_S/0/1/0/all/0/1">S. Marka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_Y/0/1/0/all/0/1">Y. Yang</a>
Despite the rapidly growing number of stellar-mass binary black hole mergers
discovered through gravitational waves, the origin of these binaries is still
not known. In galactic centers, black holes can be brought to each others’
proximity by dynamical processes, resulting in mergers. It is also possible
that black holes formed in previous mergers encounter new black holes,
resulting in so-called hierarchical mergers. Hierarchical events carry
signatures such as higher-than usual black hole mass and spin. Here we show
that the recently reported gravitational-wave candidate, GW170817A, could be
the result of such a hierarchical merger. In particular, its chirp mass
$sim40$ M$_odot$ and effective spin of $chi_{rm eff}sim0.5$ are the
typically expected values from hierarchical mergers within the disks of active
galactic nuclei. While we cannot rule out an isolated-binary origin, our
results are suggestive (albeit not definitive, with a Bayes factor of
$sim10$), especially together with the binary merger GW170729, that some
gravitational-wave observations may come from hierarchical mergers.
Despite the rapidly growing number of stellar-mass binary black hole mergers
discovered through gravitational waves, the origin of these binaries is still
not known. In galactic centers, black holes can be brought to each others’
proximity by dynamical processes, resulting in mergers. It is also possible
that black holes formed in previous mergers encounter new black holes,
resulting in so-called hierarchical mergers. Hierarchical events carry
signatures such as higher-than usual black hole mass and spin. Here we show
that the recently reported gravitational-wave candidate, GW170817A, could be
the result of such a hierarchical merger. In particular, its chirp mass
$sim40$ M$_odot$ and effective spin of $chi_{rm eff}sim0.5$ are the
typically expected values from hierarchical mergers within the disks of active
galactic nuclei. While we cannot rule out an isolated-binary origin, our
results are suggestive (albeit not definitive, with a Bayes factor of
$sim10$), especially together with the binary merger GW170729, that some
gravitational-wave observations may come from hierarchical mergers.
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