This animation (artist’s impression) shows the movement of blue stragglers in a star cluster over time. Blue straggler stars are blue, bright stars, with a higher mass than the average for a cluster, and they are expected to sink towards the centre of a star cluster over time. Those closest to the cluster core are the first to migrate inwards, with more distant blue stragglers progressively moving inwards over time.
More information and download options: http://www.spacetelescope.org/videos/heic1915a/
ESA/Hubble & NASA, L. Calçada