A globular cluster is a spherical collection of stars (like our Sun) 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.
Here is one of those globular clusters:
Messier 9, seen here in a recent image from the Hubble Space Telescope, is twice as old as our Sun, and made up of stars that are among the oldest in our galaxy.
About 8 Billion years old, the more than 250,000 stars of Messier 9 are enriched with far fewer heavier elements than the Sun. Elements crucial to life on Earth, like oxygen and carbon, and the iron at Earth’s core are rare in Messier 9.
via C|Net
Thx to Dave Shroeder