globular cluster

cluster of up to a million stars that are held together in a spherical form by the force of gravity (Astronomy)

A globular cluster is a spherical collection of stars that orbits a galactic core  as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk.
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A spherical collection of old stars found within galactic halos of spiral galaxies and, more commonly, around elliptical galaxies. The globular clusters formed at the same time as the host galaxy. All the stars are deficient in the metals, hence they are of stellar population II, the same as those in the galactic nucleus of spiral galaxies. As they orbit the galactic nucleus, they periodically pass through the galactic disc.