Astronomy Picture of the Day

Explanation: Globular star clusterOmega Centauripacks about 10 millionstars much older than the Sun into a volume some 150 light-years in diameter.Also known as NGC 5139, at a distance of 15,000 light-yearsit's the largest and brightest of 200 or so knownglobular clustersthat roam the halo of our Milky Way galaxy.Though most star clusters consist of stars with the same age andcomposition, the enigmatic Omega Cen exhibits the presence ofdifferentstellar populations with a spread of ages and chemical abundances.In fact,Omega Cen may betheremnantcore of a small galaxy merging with the Milky Way.With a yellowish hue,Omega Centauri's red giant stars are easy to pick out in thissharp telescopic view. A two-decade-long exploration of the dense star clusterwith the Hubble Space Telescope has revealed evidencefor a massive black hole near thecenter of Omega Centauri.