X-ray sources in Galactic globular clusters and old open clusters

TL;DR

This paper reviews the properties and origins of X-ray sources in Galactic globular and old open clusters, emphasizing how cluster characteristics influence X-ray source populations and recent observational insights from XMM-Newton and Chandra.

Contribution

It provides a comprehensive review of the current understanding of X-ray sources in old star clusters, highlighting recent observational findings and their implications.

Findings

X-ray source populations depend on cluster properties like age, mass, and encounter rate.

Recent X-ray observations have improved understanding of individual sources and cluster dynamics.

Comparison of X-ray emissivities reveals differences between globular and open clusters.

Abstract

The features and make up of the population of X-ray sources in Galactic star clusters reflect the properties of the underlying stellar environment. Cluster age, mass, stellar encounter rate, binary frequency, metallicity, and maybe other properties as well, determine to what extent we can expect a contribution to the cluster X-ray emission from low-mass X-ray binaries, millisecond pulsars, cataclysmic variables, and magnetically active binaries. Sensitive X-ray observations with XMM-Newton and certainly Chandra have yielded new insights into the nature of individual sources and the effects of dynamical encounters. They have also provided a new perspective on the collective X-ray properties of clusters, in which the X-ray emissivities of globular clusters and old open clusters can be compared to each other and to those of other environments. I will review our current understanding of cluster X-ray sources, focusing on star clusters older than about 1 Gyr, illustrated with recent results.