Black Hole Mergers in Galactic Nuclei Induced by the Eccentric Kozai-Lidov Effect

Bao Minh Hoang, Smadar Naoz, Bence Kocsis, Frederic A. Rasio, Fani Dosopoulou

Research output: Contribution to journalArticlepeer-review

210 Scopus citations


Nuclear star clusters around a central massive black hole (MBH) are expected to be abundant in stellar black hole (BH) remnants and BH-BH binaries. These binaries form a hierarchical triple system with the central MBH, and gravitational perturbations from the MBH can cause high-eccentricity excitation in the BH-BH binary orbit. During this process, the eccentricity may approach unity, and the pericenter distance may become sufficiently small so that gravitational-wave emission drives the BH-BH binary to merge. In this work, we construct a simple proofof-concept model for this process, and specifically, we study the eccentric Kozai-Lidov mechanism in unequalmass, soft BH-BH binaries. Our model is based on a set of Monte Carlo simulations for BH-BH binaries in galactic nuclei, taking into account quadrupole- and octupole-level secular perturbations, general relativistic precession, and gravitational-wave emission. For a typical steady-state number of BH-BH binaries, our model predicts a total merger rate of ∼1-3 Gpc-3 yr-1, depending on the assumed density profile in the nucleus. Thus, our mechanism could potentially compete with other dynamical formation processes for merging BH-BH binaries, such as the interactions of stellar BHs in globular clusters or in nuclear star clusters without an MBH.

Original languageEnglish (US)
Article number140
JournalAstrophysical Journal
Issue number2
StatePublished - Apr 1 2018


  • black hole physics
  • galaxies: star clusters: general
  • gravitational waves
  • stars: kinematics and dynamics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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