Young Massive Clusters

TL;DR

Recent advances have significantly expanded our knowledge of young massive stellar clusters in the Galaxy, revealing multiple clusters with masses over 10^4 solar masses through infrared observations, and promising larger samples for future study.

Contribution

This paper reviews the recent progress in identifying and characterizing young massive clusters in the Galaxy, highlighting the increase in known examples and the methods used.

Findings

At least a half dozen clusters with masses >10^4 solar masses are now known.

Infrared observations are crucial for determining cluster masses.

The sample of young massive clusters is rapidly growing.

Abstract

Over the past ten years, there has been a revolution in our understanding of massive young stellar clusters in the Galaxy. Initially, there were no known examples having masses $>10^4$, yet we now know that there are at least a half dozen such clusters in the Galaxy. In all but one case, the masses have been determined through infrared observations. Several had been identified as clusters long ago, but their massive natures were only recently determined. Presumably, we are just scratching the surface, and we might look forward to having statistically significant samples of coeval massive stars at all important stages of stellar evolution in the near future. I review the efforts that have led to this dramatic turn of events and the growing sample of young massive clusters in the Galaxy.