Kimball, C. et al. (2021) Evidence for hierarchical black hole mergers in the second LIGO–Virgo gravitational wave catalog. Astrophysical Journal Letters, 915(2), L35. (doi: 10.3847/2041-8213/ac0aef)
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Abstract
We study the population properties of merging binary black holes in the second LIGO–Virgo Gravitational-Wave Transient Catalog assuming they were all formed dynamically in gravitationally bound clusters. Using a phenomenological population model, we infer the mass and spin distribution of first-generation black holes, while self-consistently accounting for hierarchical mergers. Considering a range of cluster masses, we see compelling evidence for hierarchical mergers in clusters with escape velocities gsim100 km s−1. For our most probable cluster mass, we find that the catalog contains at least one second-generation merger with 99% credibility. We find that the hierarchical model is preferred over an alternative model with no hierarchical mergers (Bayes factor ${ \mathcal B }\gt 1400$) and that GW190521 is favored to contain two second-generation black holes with odds ${ \mathcal O }\gt 700$, and GW190519, GW190602, GW190620, and GW190706 are mixed-generation binaries with ${ \mathcal O }\gt 10$. However, our results depend strongly on the cluster escape velocity, with more modest evidence for hierarchical mergers when the escape velocity is lesssim100 km s−1. Assuming that all binary black holes are formed dynamically in globular clusters with escape velocities on the order of tens of km s−1, GW190519 and GW190521 are favored to include a second-generation black hole with odds ${ \mathcal O }\gt 1$. In this case, we find that 99% of black holes from the inferred total population have masses that are less than 49M⊙, and that this constraint is robust to our choice of prior on the maximum black hole mass.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Williams, Dr Daniel and Veitch, Dr John and Berry, Dr Christopher |
Authors: | Kimball, C., Talbot, C., Berry, C. P.L., Zevin, M., Thrane, E., Kalogera, V., Buscicchio, R., Carney, M., Dent, T., Middleton, H., Payne, E., Veitch, J., and Williams, D. |
College/School: | College of Science and Engineering > School of Physics and Astronomy |
Research Centre: | College of Science and Engineering > School of Physics and Astronomy > Institute for Gravitational Research |
Journal Name: | Astrophysical Journal Letters |
Publisher: | American Astronomical Society |
ISSN: | 2041-8205 |
ISSN (Online): | 2041-8213 |
Published Online: | 14 July 2021 |
Copyright Holders: | Copyright © 2021 The American Astronomical Society |
First Published: | First published in Astrophysical Journal Letters 915(2): L35 |
Publisher Policy: | Reproduced in accordance with the publisher copyright policy |
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