# Is There a Fundamental Upper Limit to the Mass of a Star Cluster?

## TL;DR

This paper investigates whether there is a fundamental upper mass limit to star clusters by analyzing a comprehensive catalog of compact stellar systems and discussing physical mechanisms behind such a limit.

## Contribution

It provides evidence that the maximum mass of ancient star clusters is around 5×10^7 solar masses and explores possible physical and statistical reasons for this limit.

## Key findings

- Maximum star cluster mass is approximately 5×10^7 M☉.
- The true ancient star cluster population likely had a birth mass near 10^8 M☉.
- Physical and statistical mechanisms may explain the upper mass limit.

## Abstract

The discovery around the turn of the millenium of a population of very massive (M$_\star$ > 2$\times$10$^6$ M$_\odot$) compact stellar systems (CSS) with physical properties (radius, velocity dispersion, stellar mass etc.) that are intermediate between those of the classical globular cluster (GC) population and galaxies led to questions about their exact nature. Recently a consensus has emerged that these objects, usually called ultra compact dwarfs (UCDs), are a mass-dependent mixture of high mass star clusters and remnant nuclei of tidally disrupted galaxies. The existence of genuine star clusters with stellar masses >10$^7$ M$_\odot$ naturally leads to questions about the upper mass limit of the star cluster formation process. In this work we compile a comprehensive catalog of compact stellar systems, and reinforce the evidence that the true ancient star cluster population has a maximum mass of M$_\star$ ~ 5$\times$10$^7$ M$_\odot$, corresponding to a stellar mass at birth of close to 10$^8$ M$_\odot$. We then discuss several physical and statistical mechanisms potentially responsible for creating this limiting mass.