Modelling individual globular clusters

TL;DR

This paper reviews historical globular cluster models and introduces new Monte Carlo simulations incorporating stellar evolution to better understand cluster dynamics and initial conditions.

Contribution

It presents enhanced Monte Carlo modeling with stellar evolution, applied to the globular cluster M4, and discusses methods to estimate initial conditions for such models.

Findings

Predicted the spatial distribution of binary stars in M4

Analyzed the effects of 12 Gyr of dynamical evolution

Developed an approximate method for initial condition estimation

Abstract

Astronomers have constructed models of globular clusters for over 100 years. These models mainly fall into two categories: (i) static models, such as King's model and its variants, and (ii) evolutionary models. Most attention has been given to static models, which are used to estimate mass-to-light ratios and mass segregation, and to combine data from proper motions and radial velocities. Evolutionary models have been developed for a few objects using the gaseous model, the Fokker-Planck model, Monte Carlo models and N-body models. These models have had a significant role in the search for massive black holes in globular clusters, for example. In this presentation the problems associated with these various techniques will be summarised, and then we shall describe new work with Giersz's Monte Carlo code, which has been enhanced recently to include the stellar evolution of single and binary stars. We describe in particular recent attempts to model the nearby globular cluster M4, including predictions on the spatial distribution of binary stars and their semi-major axis distribution, to illustrate the effects of about 12 Gyr of dynamical evolution. We also discuss work on an approximate way of predicting the "initial" conditions for such modelling.