This incredible image of the open star cluster IC 4651 was captured using the Wide Field Imager on the MPG/ESO 2.2-m telescope at ESO’s La Silla Observatory, Chile.
This image shows an open star cluster known as IC 4651. Image credit: ESO.
IC 4651, also known as Melotte 169, was discovered by the American astronomer Solon Irving Bailey, and catalogued in 1896 by the Danish-Irish astronomer John Louis Emil Dreyer.
The cluster lies in the constellation Ara and is about 2,900 light-years away from Earth. It is around 1.7 billion years old, making it middle-aged by open cluster standards.
The stars in the cluster all formed around the same time out of the same gas cloud. These sibling stars are only bound together very loosely by their attraction to one another and also by the gas between them.
Recent observations of the cluster showed that it contains a mass of 630 solar masses and yet it is thought that it initially contained at least 8,300 stars, with a total mass of 5,300 solar masses.
As IC 4651 is relatively old, a part of this lost mass will be due to the most massive stars in the cluster having already reached the ends of their lives and exploded as supernovae. However, the majority of the stars that have been lost will not have died, but merely moved on.
These stars will have been stripped from the cluster as it passed by a giant gas cloud or had a close encounter with a neighboring cluster, or even simply drifted away.
A fraction of these lost stars may still be gravitationally bound to the cluster and surround it at a great distance.
The remaining lost stars will have migrated away from the cluster to join others, or have settled elsewhere in the busy Milky Way.
Scientists suggest that our Sun was once part of a cluster like IC 4651, until it and all its siblings were gradually separated and spread across the Galaxy.
