Stable mass transfer in massive binaries leading to merging black holes

TL;DR

This paper models stable mass transfer in massive binaries with detailed evolution including rotation and mass transfer, showing it can produce black hole mergers consistent with gravitational wave observations.

Contribution

It provides detailed binary evolution models for the stable mass transfer channel, incorporating internal differential rotation and mass transfer, to explain observed black hole mergers.

Findings

Black hole spins and mass ratios match observed gravitational wave sources.

The stable mass transfer channel likely contributes significantly to the population of merging black holes.

Models reproduce the properties of black hole binaries in the 10-25 solar mass range.

Abstract

The vast majority of massive binary systems in the universe is evidently unsuited to produce merging binary black holes. However, several narrow evolutionary paths of isolated massive binaries towards this goal have recently been identified. Due to the high degree of simplification and assumptions applied in previous modelling of these paths, conclusions remained vague so far. For one of these paths, the stable mass transfer channel, we now construct detailed binary evolution models which include internal differential rotation as well as mass and angular momentum transfer between the stars, all the way from the zero-age main sequence to the formation of the black holes, only skipping the rapid late burning stages. This allows us to follow the mass and chemical structure evolution of the mass accreting component, which turns out to have a key influence on the phase of reverse mass transfer, that allows the obtained black hole spins and mass ratios to naturally fall into the regime observed for the gravitational-wave source in the 10--25$M_\odot$ primary black hole mass range. As for this channel, also a large number of progenitor binaries are known, we conclude that it likely contributes to the observed population of gravitational wave sources.