Black hole-neutron star mergers from triples - II. The role of metallicity and spin-orbit misalignment

Giacomo Fragione, Abraham Loeb

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Observations of black hole-neutron star (BH-NS) mergers via gravitational waves (GWs) are of great interest for their electromagnetic counterparts, such as short gamma-ray bursts, and could provide crucial information on the nature of BHs and the NS crust and magnetosphere. While no event has been confirmed, a recent possible detection of a BH-NS merger event by the LIGO-Virgo collaboration has attracted a lot of attention to these sources. In this second paper of the series, we follow-up our study of the dynamical evolution of triples composed of an inner BH-NS binary. In particular, we examine how the progenitor metallicity affects the characteristics of the BH-NS mergers in triples. We determine the distributions of masses, orbital parameters, and merger times, as a function of the progenitor metallicity and initial triple orbital distributions, and show that the typical eccentricity in the LIGO band is ∼10−2-10−1. We derive a merger rate range of ГBH-NS = 1.9 × 10−4-22 Gpc−3 yr−1, consistent the LIGO-Virgo upper limit. Finally, we study the expected spin-orbit misalignments of merging BH-NS binaries from this channel, and find that typically the effective spin distribution is peaked at χeff ∼ 0 with significant tails.

Original languageEnglish (US)
Pages (from-to)4991-5001
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Dec 1 2019


  • Black hole physics
  • Dynamics
  • Galaxies: kinematics
  • Galaxy: kinematics and dynamics
  • Stars: kinematics and dynamics
  • Stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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