Photograph
The M5 Star Cluster (Messier 5 / NGC 5904)
A globular cluster in the constellation Serpens, located about 25,000 light-years from Earth. More than 100,000 stars are packed into a region roughly 165 light-years across, and most of them formed more than 12 billion years ago.
Beyond the frame
Among the ancient yellow and red stars of M5 are several unusually bright blue stars. They appear much younger than the rest of the cluster, although they probably did not form at a later time. These are known as blue stragglers—stars that gained additional material through an interaction with another star or formed when two stars merged. In this way, the cluster’s crowded environment can temporarily “rejuvenate” some of its oldest inhabitants.