Growing black holes through successive mergers in galactic nuclei - I. Methods and first results

Dany Atallah*, Alessandro A. Trani*, Kyle Kremer, Newlin C. Weatherford, Giacomo Fragione, Mario Spera, Frederic A. Rasio*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

We present a novel, few-body computational framework designed to shed light on the likelihood of forming intermediate-mass (IM) and supermassive (SM) black holes (BHs) in nuclear star clusters (NSCs) through successive BH mergers, initiated with a single BH seed. Using observationally motivated NSC profiles, we find that the probability of an BH to grow beyond through successive mergers ranges from in low-density, low-mass clusters to nearly 90 per cent in high-mass, high-density clusters. However, in the most massive NSCs, the growth time-scale can be very long (Gyr); vice versa, while growth is least likely in less massive NSCs, it is faster there, requiring as little as Gyr. The increased gravitational focusing in systems with lower velocity dispersions is the primary contributor to this behaviour. We find that there is a simple '7-strikes-and-you're-in' rule governing the growth of BHs: Our results suggest that if the seed survives 7-10 successive mergers without being ejected (primarily through gravitational wave recoil kicks), the growing BH will most likely remain in the cluster and will then undergo runaway, continuous growth all the way to the formation of an SMBH (under the simplifying assumption adopted here of a fixed background NSC). Furthermore, we find that rapid mergers enforce a dynamically mediated 'mass gap' between about in an NSC.

Original languageEnglish (US)
Pages (from-to)4227-4250
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Volume523
Issue number3
DOIs
StatePublished - Aug 1 2023

Funding

This work was supported by NASA Grant 80NSSC21K1722 and NSF Grant AST-2108624 at Northwestern University. We thank Jeremy Rath for helpful discussions on secular evolution of orbits. This work was supported through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University. Quest is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. This work also used computing resources at CIERA funded by NSF Grant PHY-1726951. AAT is supported by JSPS Grants-in-Aid for Scientific Research 19K03907 and 21K13914. DVA acknowledges support from the NSF Graduate Research Fellowship Program under Grant DGE-1842165. KK is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2001751.

Keywords

  • black hole mergers
  • galaxies: nuclei
  • methods: numerical
  • quasars: supermassive black holes
  • stars: kinematics and dynamics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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