Gravitational-wave Captures by Intermediate-mass Black Holes in Galactic Nuclei

Giacomo Fragione, Abraham Loeb, Kyle Kremer, Frederic A. Rasio

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Intermediate-mass black holes (IMBHs) have not been detected beyond any reasonable doubt, despite their potential role as massive seeds for quasars and sources of tidal disruption events, ultraluminous X-ray sources, dwarf galaxy feedback, and hypervelocity stars. Gravitational wave (GW) observations can help to find and confirm the existence of IMBHs. Current and upcoming detectors, such as LIGO, Virgo, KAGRA, LISA, ET, and DECIGO promise to identify the full range from stellar-mass to supermassive black holes. In this paper, we address the question of whether IMBHs can produce GWs in galactic nuclei. We consider the possibility that stellar black holes (SBHs) form bound systems and later coalesce with an IMBH through gravitational captures in the dense nucleus. We show that this mechanism is efficient for IMBH masses in the range ∼ 3× 103, M⊙ -2× 104, M⊙. We find that the typical distributions of peak frequencies and merger timescales depend mainly on the IMBH mass. In particular, the typical peak frequency is about 0.2 Hz, 0.1 Hz, 0.09 Hz, and 0.05 Hz for MIMBH=5× 103, M⊙, 8× 103, M⊙, 1× 104, M⊙, and 2× 104, M⊙, respectively. Our results show that, at design sensitivity, both DECIGO and ET should be able to detect these IMBH-SBH mergers. Furthermore, most of the mergers will appear eccentric (e ⪆ 0.1), providing an indication of their dynamical origin.

Original languageEnglish (US)
Article number46
JournalAstrophysical Journal
Issue number1
StatePublished - Jul 1 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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