Speaker
Description
Massive young clusters, with stellar populations approaching or exceeding ten thousand solar masses, are formidable laboratories to study stellar properties and evolution. On the one hand, they contain so many stars of any given type that they permit statistically robust tests of stellar properties, with samples of the same age and composition. On the other, their upper main sequences are sufficiently populated to probe short-lived but crucial evolutionary phases and allow the study of the effects of rotation and binary interactions.
Until recently, it was assumed that such clusters were very rare or even absent in the Milky Way. Recent developments, however, have shown that they are much more common, although there are strong reasons to believe that most of them are hidden in the inner regions of the Milky Way, obscured from view by interstellar extinction and, most importantly, extreme contamination by the field.
I will review the properties of known massive young clusters in our Galaxy and summarize the empirical constraints they provide on high-mass stellar evolution. I will then discuss the observational limitations that currently prevent a complete census of these systems. Finally, I will present the reasons why we can be certain that a near-IR Gaia would give us a large population of these objects. Such a sample would allow us to trace their properties as a function of environment and metallicity, offering a powerful tool to understand star formation and massive star evolution along cosmic history.
