Omega Centauri: A Bright Old Star Cluster

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Explanation: Globular star cluster Omega Centauri contains about 10 million stars that are much older than the Sun, confined within a sphere roughly 150 light-years across. Also known as NGC 5139, it lies about 15,000 light-years away and is the largest and brightest among roughly 200 globular clusters that drift in the halo of the Milky Way. Although most star clusters contain stars all sharing the same age and composition, the enigmatic Omega Cen shows multiple stellar populations with a range of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy that merged with the Milky Way. Its yellowish hue makes the red giant stars easy to spot in this sharp telescope view. A twodecadelong campaign using the Hubble Space Telescope has revealed evidence for a massive black hole near the center of Omega Centauri.

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