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

Abstract

We explore the masses, merger rates, eccentricities, and spins for field binary black holes (BHs) driven to merger by a third companion through the Lidov–Kozai mechanism. Using a population synthesis approach, we model the creation of stellar-mass BH 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 BH natal kicks and reduced stellar mass loss. These triples naturally yield heavy binary BHs 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 BH 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.