What Is an Open Cluster?
Open clusters are loosely bound groups of a few tens to a few hundred stars. They are found in spiral and irregular galaxies.
Open clusters are significantly smaller and less densely populated than globular clusters. Open clusters may contain anything from a few dozen stars up to a few hundred stars. Open clusters have been observed with a range of ages — they may be made up of young stars or older stars.
Owing to their open and diffuse structure, they are not particularly stable, and their constituent stars might disperse after a few million years. For this reason, open clusters are found in spiral and irregular galaxies, where new stars are being formed, but not in elliptical galaxies, which are not forming stars and in which any open clusters would have long since broken up.
Within the
Open clusters are loosely bound groups of a few tens to a few hundred stars. They are found in spiral and irregular galaxies. Credit: globular but is much younger, and, like many open clusters, has bluer stars. Such intermediate clusters are common in the Large Magellanic Cloud.
Hubble has also targeted a spectacular section of the well-known Eagle Nebula known as NGC 6611, an open star cluster that formed about 5.5 million years ago and is found approximately 6500 light-years from Earth. It is a very young cluster, containing many hot, blue stars, whose fierce ultraviolet glow makes the surrounding Eagle Nebula glow brightly.