Astronomy Colloquium

I present the recent discoveries of two Galactic massive young clusters, which together contain 40 Red Supergiants – 20% of all those known in the Galaxy, and as many in the entire Large Magellanic Cloud. From observations and evolutionary synthesis models, we argue that the cluster masses are comparable to the other Galactic ’Super Star Clusters’ such as Westerlund 1 and the Arches Cluster. The two clusters are located at the base of the Scutum-Crux spiral arm, and appear to lie at the tip of the Galactic Bar. Therefore, these objects can be used as a probe to study the star-formation history and evolution of the Galaxy. Further, the distinctly different ages of the clusters, uniform metallicity, and large number of RSGs, mean that these objects now offer an unprecedented opportunity to study the pre-supernova evolution of massive stars.