Stellar Encounter Rate in Galactic Globular Clusters

TL;DR

This study estimates stellar encounter rates in 124 Galactic globular clusters using observational data and Monte Carlo simulations, revealing correlations with observed binary systems and gamma-ray luminosity, enhancing understanding of cluster dynamics.

Contribution

It introduces a new method for calculating encounter rates from observational data, avoiding assumptions of King-model profiles, and provides the first catalog with error estimates for these rates.

Findings

Encounter rates correlate with X-ray binaries and millisecond pulsars.

Results differ from previous models assuming King profiles.

The catalog includes error estimates for encounter rates.

Abstract

The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates (Gamma) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed "King-model" profiles for all clusters. By deprojecting cluster surface brightness profiles to estimate luminosity density profiles, we treat "King-model" and "core-collapsed" clusters in the same way. In addition, we use Monte-Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on Gamma, producing the first catalog of GC stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and gamma-ray luminosity) we find both clear correlations and some differences with published results.