A Triple Origin for the Heavy and Low-Spin Binary Black Holes Detected by LIGO/Virgo

TL;DR

This paper investigates how the Lidov-Kozai mechanism in stellar triples can produce heavy, low-spin binary black hole mergers with specific eccentricity and spin signatures, potentially explaining LIGO/Virgo observations.

Contribution

It introduces a population synthesis model showing that triple interactions significantly contribute to heavy, low-spin black hole mergers, especially at low metallicities.

Findings

Triple-mediated mergers are enhanced at low metallicities by ~100 times.

The model predicts a merger rate of 2-25 Gpc^-3 yr^-1, consistent with observations.

Triples produce unique eccentricity and spin distributions that can be tested observationally.

Abstract

We explore the masses, merger rates, eccentricities, and spins for field binary black holes driven to merger by a third companion through the Lidov-Kozai mechanism. Using a population synthesis approach, we model the creation of stellar-mass black hole triples across a range of different initial conditions and stellar metallicities. We find that the production of triple-mediated mergers is enhanced at low metallicities by a factor of ~100 due to the lower black hole natal kicks and reduced stellar mass loss. These triples naturally yield heavy binary black holes with near-zero effective spins, consistent with most of the mergers observed to date. This process produces a merger rate of between 2 and 25 Gpc^-3 yr^-1 in the local universe, suggesting that the Lidov-Kozai mechanism can potentially explain all of the low-spin, heavy black hole mergers observed by Advanced LIGO/Virgo. Finally, we show that triples admit a unique eccentricity and spin distribution that will allow this model to be tested in the near future.