Discovered in 1968, Terzan 5 is a globular star cluster located in the constellation of Sagittarius. It is one of the most massive and densely packed globular clusters known, containing over half a million stars. The central region of the cluster is so dense that it has been nicknamed “the core collapse cluster”.
Terzan 5 is thought to be around 12 billion years old, making it one of the oldest known globular clusters. Its stars are metal-poor, which is typical for globular clusters of its age. The metallicity (a measure of the abundance of elements heavier than hydrogen and helium) of Terzan 5’s stars is only about 1/200th that of our Sun.
The high density of Terzan 5 makes it an ideal laboratory for studying stellar evolution in extreme conditions. In particular, the cluster’s massive stars are thought to be undergoing a process called “gravitational mass loss”, where they are losing mass due to the strong gravitational forces at work in the dense environment. This mass loss could have important implications for our understanding of how these types of stars evolve and die.
Terzan 5 is also home to several unusual types of stars, including blue stragglers (stars that appear to be much younger than their surroundings) and millisecond pulsars (rapidly rotating neutron stars). These unusual objects can help us to understand more about the strange and exotic environments found within globular clusters.