An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A spherical aggregate of stars made up of thousands to a few million stars which is an orbiting satellite of a galaxy. There are over 150 globular clusters orbiting our galaxy. Globular clusters are gravitationally → bound systems, highly concentrated to the center (up to a few 10³ stars per cubic → light-years), with a volume ranging from a few dozen up to more than 300 light-years in diameter. They are generally old and → metal-poor and are among the first objects to be formed in a galaxy. There is also strong evidence that they form in major galaxy interactions and → mergers. The stars in a globular cluster are thought to have a common origin and thus a single age and → chemical abundance; with some exceptions such as → Omega Centauri and NGC 2808, which exhibit multiple populations. The presence of various sub-populations within a globular cluster is interpreted as indicating distinct epochs of mass → accretion and/or major → star formation. The Milky Way hosts about 200 globular clusters. They are spherically distributed about the → Galactic Center up to a radius of 350 light-years, with a maximum concentration toward the Galactic center. All but the smallest → dwarf galaxies possess globular clusters. Some galaxies, e.g. M87, contain several thousands of them. There are, however, important differences. While all the globular clusters in our Galaxy and in → M31 are old (ages of about 10 billion years, at least), there are galaxies, such as the two → Magellanic Clouds and → M33, that host much younger globular clusters (ages of a few billion years, or less).

Globular, from → globule + -ar, variant of → -al; → cluster.

Xušé, → cluster; guysân "shaped like a globe," from guy, → globe + -sân "manner, semblance" (variant sun, Mid.Pers. sân "manner, kind," Sogdian šôné "career").