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Populating the Upper Black Hole Mass Gap through Stellar Collisions in Young Star Clusters

Kremer, Kyle and Spera, Mario and Becker, Devin and Chatterjee, Sourav and Di Carlo, Ugo N. and Fragione, Giacomo and Rodriguez, Carl L. and Ye, Claire S. and Rasio, Frederic A. (2020) Populating the Upper Black Hole Mass Gap through Stellar Collisions in Young Star Clusters. Astrophysical Journal, 903 (1). Art. No. 45. ISSN 1538-4357.

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Theoretical modeling of massive stars predicts a gap in the black hole (BH) mass function above ~40–50 M_⊙ for BHs formed through single star evolution, arising from (pulsational) pair-instability supernovae (PISNe). However, in dense star clusters, dynamical channels may exist that allow construction of BHs with masses in excess of those allowed from single star evolution. The detection of BHs in this so-called "upper-mass gap" would provide strong evidence for the dynamical processing of BHs prior to their eventual merger. Here, we explore in detail the formation of BHs with masses within or above the pair-instability gap through collisions of young massive stars in dense star clusters. We run a suite of 68 independent cluster simulations, exploring a variety of physical assumptions pertaining to growth through stellar collisions, including primordial cluster mass segregation and the efficiency of envelope stripping during collisions. We find that as many as ~20% of all BH progenitors undergo one or more collisions prior to stellar collapse and up to ~1% of all BHs reside within or above the pair-instability gap through the effects of these collisions. We show that these BHs readily go on to merge with other BHs in the cluster, creating a population of massive BH mergers at a rate that may compete with the "multiple-generation" merger channel described in other analyses. This has clear relevance for the formation of very massive BH binaries as recently detected by the Laser Interferometer Gravitational-Wave Observatory/Virgo in GW190521. Finally, we describe how stellar collisions in clusters may provide a unique pathway to PISNe and briefly discuss the expected rate of these events and other electromagnetic transients.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kremer, Kyle0000-0002-4086-3180
Spera, Mario0000-0003-0930-6930
Chatterjee, Sourav0000-0002-3680-2684
Di Carlo, Ugo N.0000-0003-2654-5239
Fragione, Giacomo0000-0002-7330-027X
Rodriguez, Carl L.0000-0003-4175-8881
Ye, Claire S.0000-0001-9582-881X
Rasio, Frederic A.0000-0002-7132-418X
Additional Information:© 2020 The American Astronomical Society. Received 2020 June 17; revised 2020 September 10; accepted 2020 September 15; published 2020 October 30. This work was supported in part by NSF Grant AST-1716762 at Northwestern University. K.K. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001751. M.S. acknowledges funding from the European Union's Horizon 2020 research and innovation program under the Marie-Skłodowska-Curie grant agreement No. 794393. S.C. acknowledges support of the Department of Atomic Energy, Government of India, under project no. 12-R&D-TFR-5.02-0200. G.F. acknowledges support from a CIERA Fellowship at Northwestern University. C.R. was supported by an ITC Postdoctoral Fellowship from Harvard University. This work used computing resources at CIERA funded by NSF PHY-1726951. Software: CMC (Joshi et al. 2000, 2001; Fregeau et al. 2003; Fregeau & Rasio 2007; Chatterjee et al. 2010, 2013; Umbreit et al. 2012; Morscher et al. 2013; Rodriguez et al. 2018a; Kremer et al. 2020), Fewbody (Fregeau et al. 2004), COSMIC (Breivik et al. 2020).
Funding AgencyGrant Number
NSF Astronomy and Astrophysics FellowshipAST-2001751
Marie Curie Fellowship794393
Department of Atomic Energy (India)12-R&D-TFR-5.02-0200
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA)UNSPECIFIED
Harvard UniversityUNSPECIFIED
Subject Keywords:Stellar mass black holes ; Gravitational waves ; Globular star clusters
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Stellar mass black holes (1611); Gravitational waves (678); Globular star clusters (656)
Record Number:CaltechAUTHORS:20201102-100002278
Persistent URL:
Official Citation:Kyle Kremer et al 2020 ApJ 903 45
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106380
Deposited By: Tony Diaz
Deposited On:04 Nov 2020 18:32
Last Modified:04 Nov 2020 18:32

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