BLACK DOG OBSERVATORY

CDD Images of Globular (Star) Clusters

Star Clusters are collections of stars that formed from the same gas cloud and are gravitationally bound to each other. A star is a sun, a large sphere of gas that makes and emits its own radiation - they form from dust and gas in space. Stars are enourmous nuclear reactors and they shine because of nuclear fusion.

There are two main types of star clusters.

1. Globular Clusters

   • These clusters are found in the halos of galaxies and could contain between tens of thousands to millions of ancient stars (suns) that are seen as a spherical group. Globulars are spherically symmetrical groups of old stars that share a common source. They can have tens of thousands to millions of stars and are tightly bound by gravity. The Milky Way has about 150 globulars.

2. Open Clusters

   • These are found in the disks of galaxies and could contain up to hundreds of young stars (suns) in a loosely bound (spread out) configuration.