Globular clusters are among the oldest stellar systems in the universe, created more than ten billion years ago by the gravitational collapse of dense clouds of primordial hydrogen and helium.
The most massive stars in a globular cluster quickly burn through their fuel supply and explode as supernovae, leaving behind black holes, neutron stars, or white dwarfs. The gas they expel halts further star formation, and over billions of years gravitational interactions drive lighter stars to the outer edges and denser stars toward the core, resulting in a dramatic increase in the density of the core.
Globular clusters are spherical and densely packed, containing mostly old red and yellow stars. They’re typically found in a halo around a galaxy’s core and provide astronomers with crucial insights into the formation and evolution of galaxies. The study of globulars complements the information gleaned from open clusters, which are much newer, loosely-bound groups embedded in galactic disks, containing young, hot, blue stars alongside more massive short-lived stars.
