On the relationship between the ellipticity of Galactic globular clusters and their X-ray luminosity

TL;DR

This study finds that Milky Way globular clusters with higher X-ray luminosity tend to be more elliptical, revealing a significant relationship between their shape and X-ray brightness.

Contribution

It demonstrates a correlation between ellipticity and X-ray luminosity in globular clusters, using combined optical and X-ray data with modern catalogs.

Findings

Clusters with high X-ray luminosity have higher ellipticity.

Two X-ray luminosity thresholds effectively distinguish ellipticity distributions.

Results differ from earlier optical-only studies, highlighting the role of X-ray data.

Abstract

We examine the dependence of the ellipticity of globular clusters in the Milky Way on their X-ray luminosity using two modern catalogs and combine them with optical and X-ray data from the literature. Kolmogorov-Smirnov tests applied across multiple subsets reveal statistically significant differences in the ellipticity distributions when both $L_{\rm X}$ and optical luminosity are considered. Two X-ray luminosity thresholds, $L_{\rm X}^*(M_{\rm{V}}=-7)=10^{33.05}$ erg/s and $L_{\rm X}^*(M_{\rm{V}}=-7)=10^{32.01}$ erg/s, yield the most reliable distinction. In contrast to earlier findings based solely on optical data, our results demonstrate that globular clusters with the highest X-ray luminosity tend to have higher ellipticity on average.