Omega Centauri

Omega Centauri is the Milky Way’s most massive known globular cluster, a dense, ancient stellar system in the constellation Centaurus catalogued as NGC 5139.

Globular cluster: A dense, roughly spherical collection of stars bound together by gravity, usually orbiting a galaxy. Omega Centauri is an unusually massive example of this class of stellar system.
Gravitational binding energy: The energy required to disperse a gravitationally bound system into widely separated parts. It helps describe how Omega Centauri’s immense mass holds its stars together.
Nuclear star cluster: A dense concentration of stars at the center of a galaxy. Omega Centauri may be the surviving nucleus of a disrupted dwarf galaxy.
Multiple stellar populations: Distinct groups of stars within one cluster that differ in chemical composition or formation history. Omega Centauri contains several such groups, unlike a simple single-generation cluster.
47 Tucanae: A massive globular cluster in the Milky Way, located in the constellation Tucana. It is a prominent massive cluster, but lacks Omega Centauri’s comparably broad metallicity spread.
NGC 5139: The New General Catalogue designation for the stellar system commonly called Omega Centauri. This catalogue number identifies the same object in astronomical records.
Virial theorem: A relation between average kinetic and potential energies in a stable bound system. Stellar speeds can be used with this relation to estimate the cluster’s mass.
Dwarf galaxy: A small galaxy containing fewer stars and less mass than a large galaxy. A stripped dwarf-galaxy origin could explain the cluster’s multiple stellar populations.
Main-sequence turnoff: The point where stars in a population begin leaving the main sequence as they exhaust core hydrogen. Its location helps estimate the ages of Omega Centauri’s stellar populations.
M54: A globular cluster near the center of the Sagittarius Dwarf Spheroidal Galaxy. It is another proposed stripped galactic nucleus, making it a useful comparison.

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