Understanding the Dynamical State of Globular Clusters: Core-Collapsed vs Non Core-Collapsed

TL;DR

This study uses advanced Monte Carlo simulations to explore the evolution of globular clusters, successfully reproducing observed properties and the bimodal distribution of core radii, distinguishing core-collapsed from non core-collapsed clusters.

Contribution

It introduces a comprehensive simulation approach that models the dynamical evolution of globular clusters, explaining the origin of core-collapsed and non core-collapsed states.

Findings

Reproduces the bimodal distribution of core radii in globular clusters.

Core-collapsed clusters are in or near the binary burning phase.

Non core-collapsed clusters are still contracting under gravity.

Abstract

We study the dynamical evolution of globular clusters using our H\'enon-type Monte Carlo code for stellar dynamics including all relevant physics such as two-body relaxation, single and binary stellar evolution, Galactic tidal stripping, and strong interactions such as physical collisions and binary mediated scattering. We compute a large database of several hundred models starting from broad ranges of initial conditions guided by observations of young and massive star clusters. We show that these initial conditions very naturally lead to present day clusters with properties including the central density, core radius, half-light radius, half-mass relaxation time, and cluster mass, that match well with those of the old Galactic globular clusters. In particular, we can naturally reproduce the bimodal distribution in observed core radii separating the "core-collapsed" vs the "non core-collapsed" clusters. We see that the core-collapsed clusters are those that have reached or are about to reach the equilibrium "binary burning" phase. The non core-collapsed clusters are still undergoing gravo-thermal contraction.