Interrupted Binary Mass Transfer in Star Clusters

TL;DR

This study investigates how often binary star systems undergoing mass transfer in star clusters are disrupted by encounters with other stars, revealing that disruption likelihood varies significantly with cluster mass.

Contribution

The paper introduces a method to estimate the probability of binary mass transfer interruption due to stellar encounters, incorporating analytical calculations and numerical scattering experiments.

Findings

A few to tens of percent of binaries in low-mass clusters are interrupted.

Less than 1% of binaries in massive globular clusters are interrupted.

Perturbative fly-bys roughly double the interruption probability.

Abstract

Binary mass transfer is at the forefront of some of the most exciting puzzles of modern astrophysics, including Type Ia supernovae, gamma-ray bursts, and the formation of most observed exotic stellar populations. Typically, the evolution is assumed to proceed in isolation, even in dense stellar environments such as star clusters. In this paper, we test the validity of this assumption via the analysis of a large grid of binary evolution models simulated with the SeBa code. For every binary, we calculate analytically the mean time until another single or binary star comes within the mean separation of the mass-transferring binary, and compare this time-scale to the mean time for stable mass transfer to occur. We then derive the probability for each respective binary to experience a direct dynamical interruption. The resulting probability distribution can be integrated to give an estimate for the fraction of binaries undergoing mass transfer that are expected to be disrupted as a function of the host cluster properties. We find that for lower-mass clusters ($\lesssim 10^4$ M$_{\odot}$), on the order of a few to a few tens of percent of binaries undergoing mass-transfer are expected to be interrupted by an interloping single, or more often binary, star, over the course of the cluster lifetime, whereas in more massive globular clusters we expect $\ll$ 1% to be interrupted. Furthermore, using numerical scattering experiments performed with the FEWBODY code, we show that the probability of interruption increases if perturbative fly-bys are considered as well, by a factor $\sim 2$.