Monte Carlo Simulations of Star Clusters - VII. The globular cluster 47 Tuc

TL;DR

This paper presents Monte Carlo models of the globular cluster 47 Tuc, successfully matching observed profiles after 12 billion years, and provides insights into its initial mass function, current mass, and dynamical evolution.

Contribution

The study introduces detailed Monte Carlo simulations of 47 Tuc, incorporating complex stellar interactions and Galactic effects, to accurately model its long-term dynamical evolution.

Findings

Current mass estimated at 0.9 million solar masses.

Primordial binaries are becoming the main dynamical driver of the core.

Core collapse is predicted to occur in over 20 billion years.

Abstract

We describe Monte Carlo models for the dynamical evolution of the massive globular cluster 47 Tuc (NGC 104). The code includes treatments of two-body relaxation, most kinds of 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 fairly satisfactory match to surface brightness and density profiles, the velocity dispersion profile, the luminosity function in two fields, and the acceleration of pulsars. Our models appear to require a relatively steep initial mass function for stars above about turnoff, with an index of about 2.8 (where the Salpeter mass function has an index of 2.35), and a relatively flat initial mass function (index about 0.4) for the lower main sequence. According to the model, the current mass is estimated at 0.9 million solar masses, of which about 34% consists of remnants. We find that primordial binaries are gradually taking over from mass loss by stellar evolution as the main dynamical driver of the core. Despite the high concentration of the cluster, core collapse will take at least another 20Gyr.