Globular cluster

A globular cluster is a cluster of stars that is spherical in shape and extremely dense towards its core. They are distributed around a galaxy, but not within it, orbiting in the region known as the galactic halo. They are comprised of old stars, similar to the bulge of a spiral galaxy. Omega Centauri is quite an obvious globular, visible to the naked eye as a third magnitude object, a "fuzzy patch" similar to most other deep sky objects. It's also a very massive globular cluster, it's mass being more than the mass of some small galaxies and containing upwards of a billion stars. It's probable that it is the former nucleus of a galaxy that was once orbiting the Milky Way but is now totally engulfed with only the dense nucleus remaining as a globular cluster. The slightly more massive G1, associated with M31, is also probably of this origin.

Globulars are very old, they formed along with the host galaxy.