This illustration shows the evolution of two populations of stars in the ancient globular cluster 47 Tucanae.
The first panel shows a grouping of red stars, an older population containing fewer chemical elements heavier than helium and hydrogen. These stars move in random, circular orbits. As the most massive of these stars die, they return chemically enhanced material back into the cluster. This material helps form another generation of stars, shown as the blue stars in the second panel. The blue stars are more chemically enriched and are concentrated towards the cluster's center, traveling in elliptical orbits. Slowly, over time, the blue stars have been moving outward, putting them on more radial orbits, as seen in the third panel.