Page "Open cluster" Paragraph 1

An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age.

More than 1, 100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist.

They are loosely bound to each other by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center, resulting in a migration to the main body of the galaxy as well as a loss of cluster members through internal close encounters.

Open clusters generally survive for a few hundred million years.

In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for many billions of years.

Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring.