# Bondi-Hoyle-Lyttleton Accretion onto Star Clusters

## TL;DR

This study uses 3D hydrodynamic simulations to explore how star clusters influence accretion rates onto individual stars, revealing collective effects that can enhance accretion beyond isolated star predictions, especially with efficient cooling.

## Contribution

It provides the first detailed analysis of accretion in star clusters, showing how collective potential and cluster properties modify individual accretion rates compared to classical theory.

## Key findings

- Accretion rates increase when accretion radii overlap.
- Gas is effectively accreted into the cluster's collective potential.
- Cooling enhances the accretion onto individual stars.

## Abstract

An isolated star moving supersonically through a uniform gas accretes material from its gravitationally-induced wake. The rate of accretion is set by the accretion radius of the star and is well-described by classical Bondi-Hoyle-Lyttleton theory. Stars, however, are not born in isolation. They form in clusters where they accrete material that is influenced by all the stars in the cluster. We perform three-dimensional hydrodynamic simulations of clusters of individual accretors embedded in a uniform-density wind in order to study how the accretion rates experienced by individual cluster members are altered by the properties of the ambient gas and the cluster itself. We study accretion as a function of number of cluster members, mean separation between them, and size of their individual accretion radii. We determine the effect of these key parameters on the aggregate and individual accretion rates, which we compare to analytic predictions. We show that when the accretion radii of the individual objects in the cluster substantially overlap, the surrounding gas is effectively accreted into the collective potential of the cluster prior to being accreted onto the individual stars. We find that individual cluster members can accrete drastically more than they would in isolation, in particular when the flow is able to cool efficiently. This effect could potentially modify the luminosity of accreting compact objects in star clusters and could lead to the rejuvenation of young star clusters as well as globular clusters with low-inclination and low-eccentricity.