Seeds don't sink: Even massive black hole 'seeds' cannot migrate to galaxy centres efficiently

Linhao Ma*, Philip F. Hopkins, Xiangcheng Ma, Daniel Anglés-Alcázar, Claude André Faucher-Giguère, Luke Zoltan Kelley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Possible formation scenarios of supermassive black holes (BHs) in the early universe include rapid growth from less massive seed BHs via super-Eddington accretion or runaway mergers, yet both of these scenarios would require seed BHs to efficiently sink to and be trapped in the Galactic Centre via dynamical friction. This may not be true for their complicated dynamics in clumpy high-z galaxies. In this work, we study this 'sinking problem' with state-of-the-art high-resolution cosmological simulations, combined with both direct N-body integration of seed BH trajectories and post-processing of randomly generated test particles with a newly developed dynamical friction estimator. We find that seed BHs less massive than 108 M⊙ (i.e. all but the already-supermassive seeds) cannot efficiently sink in typical high-z galaxies. We also discuss two possible solutions: dramatically increasing the number of seeds such that one seed can end up trapped in the Galactic Centre by chance, or seed BHs being embedded in dense structures (e.g. star clusters) with effective masses above the mass threshold. We discuss the limitations of both solutions.

Original languageEnglish (US)
Pages (from-to)1973-1985
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume508
Issue number2
DOIs
StatePublished - Dec 1 2021

Keywords

  • black hole physics
  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift
  • galaxies: kinematics and dynamics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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