The Flying Geese Cluster at upper left is a textbook example of an open cluster – a group of several hundred stars that formed more than a billion years ago when a giant molecular cloud gravitationally collapsed to create numerous protostars, which in turn evolved into the stars we see today. Most open clusters are found in the disk of our Milky Way galaxy, which is rich in the gas and dust necessary for star formation.
Because of the cluster’s age, most of its massive stars have already run out of fuel and exploded as supernovae, leaving behind lower-mass stars, red giants, and white dwarfs. Tidal forces from gravitational interactions with other clusters, stars, or passing objects will eventually cause the cluster’s stars to drift apart and integrate into the main stellar population of the Milky Way. Open clusters are generally short-lived on cosmic timescales, lasting just a few hundred million years before dispersing.
The Fireworks Galaxy (NGC 6946) at right is a much larger and much more distant object, known for frequent supernovae and a prodigious rate of star formation.
