Effects of Hardness of Primordial Binaries on Evolution of Star Clusters

TL;DR

This study uses N-body simulations to explore how the initial hardness of primordial binaries influences star cluster evolution, revealing different core collapse behaviors depending on binary binding energies.

Contribution

It introduces a new simulation code, GORILLA, and systematically examines the impact of binary hardness on star cluster dynamics across a range of energies.

Findings

Soft and hard binaries lead to deep core collapse.

Intermediate hardness binaries halt collapse halfway due to energy release.

Core radii at halts are explained by binary energy contributions.

Abstract

We investigate effects of hardness of primordial binaries on whole evolution of star clusters by means of N-body simulations. Using newly developed code, GORILLA, we simulated eleven N=16384 clusters with primordial binaries whose binding energies are equal in each cluster in range of 1-300kT_0, where 1.5kT_0 is average stellar kinetic energy at the initial time. We found that, in both soft (< 3kT_0) and hard (> 300kT_0) limits, clusters experience deep core collapse. In the intermediate hardness (10-100kT_0), the core collapses halt halfway due to an energy releases of the primordial binaries. The core radii at the halt can be explained by their energy