Wikipedia:Today's featured article/September 23, 2006

The Globular Cluster M80 in the constellation Scorpius

A globular cluster is a spherical collection of stars that orbits a galaxy core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shape, and relatively high stellar density towards their core. Globular clusters contain considerably more stars than the less dense galactic, or open clusters. Globular clusters are fairly numerous; there are about 150 currently known globular clusters in the Milky Way, with perhaps 10–20 more undiscovered. Large galaxies can have more: Andromeda, for instance, may have as many as 500. Some giant elliptical galaxies, such as M87, may have as many as 10,000 globular clusters. These globular clusters orbit the galaxy out to large radii, 40 kiloparsecs or more. Every galaxy of sufficient mass in the local group has an associated group of globular clusters, and almost every large galaxy has been found to possess a system of globular clusters. The Sagittarius Dwarf and Canis Major Dwarf galaxies appear to be in the process of donating their associated globular clusters to the Milky Way, such as Palomar 12. (more...)

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