Enigmatic Globular Cluster Ruprecht 106

While the constituent stars of globular clusters all form at approximately the same location and time, it turns out that almost all globular clusters still contain groups of stars with distinct chemical compositions. These distinct chemical fingerprints are left by groups of stars with very slightly different ages or compositions from the rest of the cluster. A tiny handful of globular clusters do not possess these multiple populations of stars, and Ruprecht 106, captured here by the Hubble Space Telescope, is a member of this enigmatic group.