What are Star Clusters?

About Star Clusters:

• A Star cluster is 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.
• They are particularly useful to astronomers as they provide a way to study and model stellar evolution and ages. 
• The two basic categories of stellar clusters are open clusters, also known as galactic clusters and globular clusters.
• Open (Galactic) Clusters:
  • Open clusters are so named due to the fact that the individual component stars are easily resolved through a telescope.
  • They are sometimes called galactic clusters due to their location on the dusty spiral arms on the plane of spiral galaxies.
  • Stars in an open cluster have a common origin: they formed from the same initial giant molecular cloud.
  • Open clusters contain from a dozen to many hundreds of stars, usually in an unsymmetrical arrangement.
• Globular Clusters:
  • Globular clusters contain several thousand to one million stars in a spherical, gravitationally-bound system. 
  • Located mostly in the halo surrounding the galactic plane, they comprise the oldest stars in the galaxy.
  • There is little free dust or gas found in globular clusters, so no new star formation is taking place in them.
  • Stellar densities within the inner regions of a globular cluster are very high compared with regions such as those around the Sun.
• 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.