Black hole and neutron star mergers in galactic nuclei: The role of triples

Giacomo Fragione*, Nathan W.C. Leigh, Rosalba Perna

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Nuclear star clusters that surround supermassive black holes (SMBHs) in galactic nuclei are thought to contain large numbers of black holes (BHs) and neutron stars (NSs), a fraction of which form binaries and could merge by Kozai–Lidov oscillations (KL). Triple compact objects are likely to be present, given what is known about the multiplicity of massive stars, whose life ends either as an NS or a BH. In this paper, we present a new possible scenario for merging BHs and NSs in galactic nuclei. We study the evolution of a triple black hole (BH) or neutron star (NS) system orbiting an SMBH in a galactic nucleus by means of direct high-precision N-body simulations, including post-Newtonian terms. We find that the four-body dynamical interactions can increase the KL angle window for mergers compared to the binary case and make BH and NS binaries merge on shorter time-scales. We show that the merger fraction can be up to ~5–8 times higher for triples than for binaries. Therefore, even if the triple fraction is only ~10–20 per cent of the binary fraction, they could contribute to the merger events observed by LIGO/VIRGO in comparable numbers.

Original languageEnglish (US)
Pages (from-to)2825-2835
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
StatePublished - Sep 11 2019


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

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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