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Globular Star Cluster NGC 5139
Featured in this sharp telescopic image, globular star cluster Omega Centauri (NGC 5139) is some 15,000 light-years away. Some 150 light-years in diameter, the cluster is packed with about 10 million stars—all much older than the Sun. "Omega Cen" is the largest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way.