NGC 5272 :: new link
APOD: 2007 April 15 – M3: Inconstant Star Cluster:
Star clusters appear constant because photographs of them are frozen in time. In reality, though, cluster stars swarm the center and frequently fluctuate in brightness. Although the time it takes for stars to cross a cluster is about 100,000 years, the time it takes for a star to fluctuate noticeably can be less than one night. In fact, the above time lapse movie of bright globular cluster M3 was taken over a single night…
“NASA’s Hubble Space Telescope has provided astronomers with the best observational evidence to date that globular clusters sort out stars according to their mass, governed by a gravitational billiard ball game between stars. Heavier stars slow down and sink to the cluster’s core, while lighter stars pick up speed and move across the cluster to its periphery. This process, called “mass segregation,” has long been suspected for globular star clusters, but has never before been directly seen in action. “
HubbleSite – Hubble Yields Direct Proof of Stellar Sorting in a Globular Cluster
Globular Clusters Blog 