Star cluster

ASTRONOMY

WRITTEN BY:

Eric J. Chaisson, Helen Sawyer Hogg-Priestly, John Donald Fernie

Star cluster, either of two general types of stellar assemblages held together by the mutual gravitational attraction of its members, which are physically related through common origin. The two types are open (formerly called galactic) clusters and globular clusters.

General Description And Classification

Open clusters contain from a dozen to many hundreds of stars, usually in an unsymmetrical arrangement. By contrast, globular clusters are old systems containing thousands to hundreds of thousands of stars closely packed in a symmetrical, roughly spherical form. In addition, groups called associations, made up of a few dozen to hundreds of stars of similar type and common origin whose density in space is less than that of the surrounding field, are also recognized.