Monte Carlo Simulations of Star Clusters - V. The globular cluster M4

TL;DR

This paper presents detailed Monte Carlo simulations of the globular cluster M4, modeling its dynamical evolution over 12 billion years to match observed properties and analyze its core, binary populations, and stellar remnants.

Contribution

It introduces a comprehensive Monte Carlo model including multiple stellar interactions and evolution, providing new insights into M4's post-collapse state and binary dynamics.

Findings

M4 is a post-collapse cluster with a core sustained by binary burning.

The model successfully reproduces observed surface brightness and velocity dispersion profiles.

Binary and stellar remnant populations are characterized in detail.

Abstract

We describe Monte Carlo models for the dynamical evolution of the nearby globular cluster M4. The code includes treatments of two-body relaxation, three- and four-body interactions involving primordial binaries and those formed dynamically, the Galactic tide, and the internal evolution of both single and binary stars. We arrive at a set of initial parameters for the cluster which, after 12Gyr of evolution, gives a model with a satisfactory match to the surface brightness profile, the velocity dispersion profile, and the luminosity function in two fields. We describe in particular the evolution of the core, and find that M4 (which has a classic King profile) is actually a post-collapse cluster, its core radius being sustained by binary burning. We also consider the distribution of its binaries, including those which would be observed as photometric binaries and as radial-velocity binaries. We also consider the populations of white dwarfs, neutron stars, black holes and blue stragglers, though not all channels for blue straggler formation are represented yet in our simulations.