The impact of binaries on the evolution of star clusters from turbulent molecular clouds

TL;DR

This study uses N-body simulations to explore how binary stars influence the early evolution of star clusters formed from turbulent molecular clouds, revealing self-regulating binary populations and cluster expansion dynamics.

Contribution

It introduces a method to generate realistic initial binary conditions from hydrodynamical simulations and compares different cluster models to understand binary and cluster evolution.

Findings

Cluster expansion is initially balanced by sub-clump motion and accelerates after reaching a monolithic shape.

Clusters develop a hot core of massive stars due to initial mass segregation.

Binary populations self-regulate and show a mass-dependent binary fraction similar to observations.

Abstract

Most of massive stars form in binary or higher-order systems in clumpy, sub-structured clusters. In the very first phases of their life, these stars are expected to interact with the surrounding environment, before being released to the field when the cluster is tidally disrupted by the host galaxy. We present a set of N-body simulations to describe the evolution of young stellar clusters and their binary content in the first phases of their life. To do this, we have developed a method that generates realistic initial conditions for binary stars in star clusters from hydrodynamical simulations. We considered different evolutionary cases to quantify the impact of binary and stellar evolution. Also, we compared their evolution to that of King and fractal models with different length scales. Our results indicate that the global expansion of the cluster from hydrodynamical simulations is initially balanced by the sub-clump motion and accelerates when a monolithic shape is reached, as in a post-core collapse evolution. Compared to the spherical initial conditions, the ratio of the 50% to 10% Lagrangian radius shows a very distinctive trend, explained by the formation of a hot core of massive stars triggered by the high initial degree of mass segregation. As for its binary population, each cluster shows a self-regulating behaviour by creating interacting binaries with binding energies of the order of its energy scales. Also, in absence of original binaries, the dynamically formed binaries present a mass dependent binary fraction, that mimics the trend of the observed one.