Constraining accretion efficiency in massive binary stars with LIGO-Virgo black holes

TL;DR

This study uses gravitational wave data to constrain the mass accretion efficiency in massive binary star evolution, finding that accretion efficiencies below 0.6 are unlikely based on observed black hole mergers.

Contribution

It provides the first observational constraint on accretion efficiency in massive binary evolution using LIGO-Virgo data.

Findings

Lower accretion efficiency reduces merger rates and BH masses.

Data favors accretion efficiency above 0.6.

Constraints are robust across different common-envelope efficiencies.

Abstract

The growing sample of LIGO--Virgo black holes (BHs) opens new perspectives for the study of massive binary evolution. Here, we study the impact of mass accretion efficiency and common envelope on the properties of binary BH (BBH) mergers, by means of population synthesis simulations. We model mass accretion efficiency with the parameter $f_{\rm MT}\in[0.05,1]$, which represents the fraction of mass lost from the donor which is effectively accreted by the companion. Lower values of $f_{\rm MT}$ result in lower BBH merger rate densities and produce mass spectra skewed towards lower BH masses. Our hierarchical Bayesian analysis, applied to BBH mergers in the first and second gravitational wave transient catalogue, yields zero support for values of $f_{\rm MT}\lesssim{}0.6$, with a lower boundary of the 99\% credible intervals equal to $f_{\rm MT}= 0.59$. This result holds for all the values of the common-envelope efficiency parameter we considered in this study $\alpha_{\rm CE} \in [1,10]$. This confirms that gravitational-wave data can be used to put constraints on several uncertain binary evolution processes.