A Caltech Library Service

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

Kimball, Chase and Talbot, Colm and Berry, Christopher P. L. and Zevin, Michael and Thrane, Eric and Kalogera, Vicky and Buscicchio, Riccardo and Carney, Matthew and Dent, Thomas and Middleton, Hannah and Payne, Ethan and Veitch, John and Williams, Daniel (2021) Evidence for Hierarchical Black Hole Mergers in the Second LIGO–Virgo Gravitational Wave Catalog. Astrophysical Journal Letters, 915 (2). Art. No. L35. ISSN 2041-8205. doi:10.3847/2041-8213/ac0aef.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
Creative Commons Attribution.


Use this Persistent URL to link to this item:


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 over an alternative model with no hierarchical mergers (Bayes factor B >1400) and that GW190521 is favored to contain two second-generation black holes with odds O > 700, and GW190519, GW190602, GW190620, and GW190706 are mixed-generation binaries with O > 10. However, our results depend strongly on the cluster escape velocity, with more modest evidence for hierarchical mergers when the escape velocity is ≾100 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 O > 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:Article
Related URLs:
URLURL TypeDescription Paper
Kimball, Chase0000-0001-9879-6884
Talbot, Colm0000-0003-2053-5582
Berry, Christopher P. L.0000-0003-3870-7215
Zevin, Michael0000-0002-0147-0835
Thrane, Eric0000-0002-4418-3895
Kalogera, Vicky0000-0001-9236-5469
Buscicchio, Riccardo0000-0002-7387-6754
Carney, Matthew0000-0003-4957-6679
Dent, Thomas0000-0003-1354-7809
Middleton, Hannah0000-0001-5532-3622
Payne, Ethan0000-0003-4507-8373
Veitch, John0000-0002-6508-0713
Williams, Daniel0000-0003-3772-198X
Additional Information:© 2021. The American Astronomical Society. Received 2021 May 7; revised 2021 June 9; accepted 2021 June 11; published 2021 July 14. 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 María de Maeztu Unit of Excellence MDM-2016-0692, by Xunta de Galicia under project ED431C 2017/07, by Consellería de Educacíon, Universidade e Formacíon Profesional as Centros de Investigacíon 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.
Funding AgencyGrant Number
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Istituto Nazionale di Fisica Nucleare (INFN)UNSPECIFIED
Australian Research CouncilCE170100004
NSF Graduate Research FellowshipDGE-1450006
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)UNSPECIFIED
NASA Hubble FellowshipHST-HF2-51474.001-A
Australian Research CouncilFT150100281
Australian Research CouncilCE170100004
Ministerio de Ciencia, Innovación y Universidades (MCIU)MDM-2016-0692
Xunta de GaliciaED431C 2017/07
Consellería de Educacíon, Universidade e Formacíon Profesional as Centros de Investigacíon do Sistema universitario de GaliciaED431G 2019/05
Fondo Europeo de Desarrollo Regional (FEDER)UNSPECIFIED
Subject Keywords:Gravitational wave sources; Gravitational wave astronomy; Astrophysical black holes; Hierarchical models
Other Numbering System:
Other Numbering System NameOther Numbering System ID
LIGO DocumentP2000466
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Gravitational wave sources (677); Gravitational wave astronomy (675); Astrophysical black holes (98); Hierarchical models (1925)
Record Number:CaltechAUTHORS:20210722-175356302
Persistent URL:
Official Citation:Chase Kimball et al 2021 ApJL 915 L35
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109981
Deposited By: Tony Diaz
Deposited On:26 Jul 2021 22:32
Last Modified:26 Jul 2021 22:32

Repository Staff Only: item control page