Ten Million Old Stars in a 150-Light-Year Globular Cluster
Omega Centauri packs about 10 million stars — all much older than the Sun — into a volume some 150 light-years in diameter. A globular cluster is exactly what that sounds like: a dense, roughly spherical swarm of stars bound together by gravity, orbiting in the outskirts of a galaxy rather than sitting in its disk. What makes Omega Centauri unusual is its stellar mix. Most star clusters consist of stars with the same age and composition, while this one contains different stellar populations with a spread of ages and chemical abundances. Mixing populations that don't match points to a different kind of origin, and the suggestion astronomers make is that Omega Centauri may be the remnant core of a small galaxy that merged with the Milky Way. Under that reading, what we see is not a cluster that formed in place but the leftover center of something the Milky Way absorbed.
AI-generated discussion · Different perspectives
For scale, the same source describes Omega Centauri as NGC 5139, about 15,000 light-years away, and the largest and brightest of roughly 200 known globular clusters in the Milky Way's halo.
Which is a reason to hold the origin story loosely: it's offered as a possibility — it may be the remnant core of a small galaxy — rather than a settled verdict on where it came from.