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.

It was through the study of globular clusters that the sun's position in the Milky Way galaxy is know. Until the 1930s, it was thought that the sun was near the middle of the galaxy because the distribution of stars in the observable Milky War appeared uniform. However, the distribution of globular clusters was strongly asymmetric. In looking at the distances to the clusters, it became clear that the observable Milky Way was only a small part of the total galaxy, most of which was obscured by gas and dust. Because globular clusters lie outside the plane of the Milky Way, they are not blocked by the gas and dust of the galactic disk.

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