The Effect of Stellar Metallicity on the Sizes of Star Clusters

TL;DR

This study uses N-body simulations to show that metallicity-dependent stellar evolution influences the early dynamical sizes of star clusters, explaining observed size differences between red and blue globular clusters.

Contribution

It demonstrates that metallicity-driven stellar evolution effects can account for size differences in star clusters, a novel insight into cluster evolution.

Findings

Blue clusters are larger than red clusters regardless of mass segregation.

Size differences are more pronounced in low central concentration models.

Results align with observed size differences in globular clusters.

Abstract

Observations indicate blue globular clusters have half-light radii systematically larger than those of red globular clusters. In this paper, we test whether the different metallicity-dependent stellar evolution timescales and mass-loss rates within the clusters can impact their early dynamical evolution. By means of N-body simulations including stellar evolution recipes we simulate the early evolution of small centrally concentrated clusters with and without primordial mass segregation. Our simulations include accurate metallicity-dependent mass loss from massive stars. We find blue clusters to be larger than red clusters regardless of whether the clusters have been primordially mass segregated. In addition, the size difference is found to be larger and consistent with observations for initial models with a low central concentration. These results indicate that the systematic size difference found between red and blue clusters can, at least in part, be attributed to the dynamical effects of differing stellar evolution histories, driven by metallicity.