Omega Centauri (NGC 5139). Composite infrared and optical image of the Omega Centauri globular cluster. Globular clusters are spherical groups of very old stars, about 12 billion years old, that are tightly bound by gravity and orbit a dense central core. This is the largest globular cluster found in our galaxy (the Milky Way) and is much larger than most others. It spans 150 light years across and contains as many as 10 million stars. Omega Centauri lies about 18,000 light years from Earth, in the constellation Centaurus. Infrared image taken by the Spitzer Space Telescope, optical image taken by the four metre Victor M Blanco telescope at the Cerro Tololo Inter-American University, Chile.