A globular cluster is a gravitationally bound spherical collection of stars that orbits a galactic core, as part of a galaxy. Globular clusters are very old, with an age of around 10 billion years, and are thought to be some of the first generations of stars in the Milky Way. Around 150 globular clusters have been discovered in our galaxy, with sizes ranging from 10,000 to 30 million stars. The most massive known globular cluster is Omega Centauri, which contains over 10 million stars.
Globular clusters are important to astronomers because they can be used to study the evolution of galaxies and stellar populations. By studying the properties of globular clusters, we can learn about the conditions in which these ancient stars formed, and how galaxies have evolved over time. Additionally, because globular clusters contain many older stars, they can be used to study stellar evolution; by observing the different types of stars present in a cluster, we can learn about how stars change as they age.
There are two main types of globular cluster: halo clusters and disk clusters. Halo clusters are found in the outskirts of galaxies, whereas disk clusters are located near the galactic plane. Most known globular clusters belong to the halo population; however, it is thought that there may be more disk clusters yet to be discovered.
The vast majority of globular clusterstars are low-mass red giants or white dwarfstars. However, due to their high densities (up to 1 million times that of Earth’s atmosphere), globulars also contain a significant population of neutron starst and black holecandidates. These exotic objects provide us with an opportunity to study some of the most extreme physical conditions in our Universe.
GlobularyClusters were long thought to be relicsof an earlier epochin Galaxy formationand evolution when Galaxies were much smaller than they currently appear today1 . It was reasonedthat as Galaxies grew larger through continued mergersand accretionof gas clouds , their surrounding halosof GlobularyClusters would dispersebecause individual Clusterstars would become unboundby Galactic tidal forces2 . This so-called”disruption scenario” for GlobularyCluster evolutionsuggested that present-dayGalaxies should not host any primordialglobularyclusters—or at least very few—and that all known GlobularyClusters must have been accretedfrom satellite DwarfGalaxies3 .