Eccentric binary black hole mergers in globular clusters hosting intermediate-mass black holes

Giacomo Fragione*, Omer Bromberg

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Globular clusters (GCs) may harbour intermediate-mass black holes (IMBHs) at their centres. In these dynamically active environments, stellar-mass black holes (SBHs) sink to the centre soon after formation, due to dynamical friction and start interacting among themselves and with the central IMBH. Likely, some of the SBHs will form bound systems with the IMBH. A fraction of those will be triple systems composed of binary SBHs and the IMBH acting as a third distant perturber. If the SBH binary orbit is sufficiently inclined, it can develop Lidov–Kozai (LK) oscillations, which can drive the system to high eccentricities and eventually to a merger due to gravitational wave (GW) emission on short time-scales. In this work, we focus on the dynamics of the IMBH–SBH–SBH triples and illustrate that these systems can be possible sources of GWs. A distinctive signature of this scenario is that a considerable fraction of these mergers are highly eccentric when entering the LIGO band (10 Hz). Assuming that ∼ 20 per cent of GCs host IMBHs and a GC density in the range nGC = 0.32–2.31 Mpc−3, we have estimated a rate ⌈ = 0.06–0.46 Gpc−3 yr−1 of these events. This suggests that dynamically driven binary SBH mergers in this scenario could contribute to the merger events observed by LIGO/VIRGO. Full N-body simulations of GCs harbouring IMBHs are highly desirable to give a more precise constrain on this scenario.

Original languageEnglish (US)
Pages (from-to)4370-4377
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Sep 21 2019


  • Galaxies: star clusters: general
  • Galaxy: centre
  • Galaxy: kinematics and dynamics
  • Stars: black holes
  • Stars: kinematics and dynamics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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