Star Clusters

Star clusters are groups of stars that formed roughly at the same time, from the same molecular cloud, and are held together by their mutual gravitational attraction. Open star clusters consist of a few dozen to a few thousand stars, are loosely grouped, and are located in the gas-rich spiral arms of a galaxy, such as our Milky Way. Globular star clusters contain hundreds of thousands to over a million stars, are extremely densely packed, and are found in a spherical halo around the center of a galaxy. They are among the oldest objects in the universe.