Chemically Homogeneous Evolution: A rapid population synthesis approach

TL;DR

This paper introduces a rapid population synthesis method to study chemically homogeneous evolution as a formation channel for massive binary black holes, predicting its significant contribution to gravitational-wave detections.

Contribution

It develops the first integrated approach to include CHE in population synthesis, comparing it with conventional binary evolution under consistent assumptions.

Findings

CHE could account for up to 70% of BBH merger detections.

The mass distribution of BBHs aligns with current gravitational-wave observations.

The method enables simultaneous predictions for different formation channels.

Abstract

We explore chemically homogeneous evolution (CHE) as a formation channel for massive merging binary black holes (BBHs). We develop methods to include CHE in a rapid binary population synthesis code, Compact Object Mergers: Population Astrophysics and Statistics (COMPAS), which combines realistic models of binary evolution with cosmological models of the star-formation history of the Universe. For the first time, we simultaneously explore conventional isolated binary star evolution under the same set of assumptions. This approach allows us to constrain population properties and make simultaneous predictions about the gravitational-wave detection rates of BBH mergers for the CHE and conventional formation channels. The overall mass distribution of detectable BBHs is consistent with existing gravitational-wave observations. We find that the CHE channel may yield up to ~70% of all gravitational-wave detections of BBH mergers coming from isolated binary evolution.