Journal article

Evidence for Hierarchical Black Hole Mergers in the Second LIGO-Virgo Gravitational Wave Catalog

Chase Kimball, Colm Talbot, Christopher PL Berry, Michael Zevin, Eric Thrane, Vicky Kalogera, Riccardo Buscicchio, Matthew Carney, Thomas Dent, Hannah Middleton, Ethan Payne, John Veitch, Daniel Williams



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 ⪆100 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 o..

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University of Melbourne Researchers


Awarded by NSF

Awarded by Australian Research Council (ARC)

Awarded by National Science Foundation

Awarded by NASA - Space Telescope Science Institute

Awarded by ARC Future Fellowship

Awarded by Maria de Maeztu Unit of Excellence

Awarded by Xunta de Galicia

Awarded by Conselleria de Educacion, Universidade e Formacion Profesional as Centros de Investigacion do Sistema universitario de Galicia

Funding Acknowledgements

The authors thank Kyle Kremer, Carl Rodriguez, Mario Spera, and Zoheyr Doctor for their expert advice in constructing this study, and Isobel Romero-Shaw for comments on a draft manuscript. This research has made use of data obtained from the Gravitational Wave Open Science Center (, a service of LIGO Laboratory, the LIGO Scientific Collaboration and the Virgo Collaboration. LIGO is funded by the US National Science Foundation (NSF). Virgo is funded by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale della Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by Polish and Hungarian institutes. This work is supported by the NSF Grant PHY-1607709 and through the Australian Research Council (ARC) Centre of Excellence CE170100004. C.K. is supported supported by the National Science Foundation under grant DGE-1450006. C.P.L.B. is supported by the CIERA Board of Visitors Research Professorship. M.Z. is supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51474.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. E.T. is supported through ARC Future Fellowship FT150100281 and CE170100004. T.D. acknowledges support from the Maria de Maeztu Unit of Excellence MDM-2016-0692, by Xunta de Galicia under project ED431C 2017/07, by Conselleria de Educacion, Universidade e Formacion Profesional as Centros de Investigacion do Sistema universitario de Galicia (ED431G 2019/05), and by FEDER. This research was supported in part through the computational resources from the Grail computing cluster at Northwestern University-funded through NSF PHY-1726951-and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. The authors are grateful for computational resources provided by the LIGO Laboratory and supported by NSF Grants PHY-0757058 and PHY-0823459. This document has been assigned LIGO document number LIGO-P2000466.