The biggest globular star cluster in the Milky Way Galaxy may not be a child of the Milky Way. Instead, it may be a sort of orphan — the surviving core of a smaller galaxy that was captured by the Milky Way.

Omega Centauri contains perhaps 10 million stars, all packed into a dense ball about 150 light-years across. In the cluster’s middle, the stars are packed so tightly that they’re only about a tenth of a light-year apart. Compare that to our part of the galaxy, where the nearest neighbor star is more than four light-years away.

The cluster appears to be about 12 billion years old — one of the older clusters in the entire galaxy. But the composition of its stars, and the way it orbits the center of the Milky Way, suggest that Omega Centauri wasn’t born here. Instead, it appears to be one of many dwarf galaxies captured by the Milky Way. Over time, the stars in the smaller galaxy’s outer regions were pulled away. So over the eons, that left only Omega Centauri’s core — a possible “orphan” adopted by the Milky Way.

Omega Centauri is about 16,000 light-years away, in the constellation Centaurus, which is quite low in the south at nightfall. If you live south of about Dallas, and you have dark skies, you might just make out the cluster as a hazy patch of light about as wide as the Moon.

We’ll talk about one of the possible escapees from Omega Centauri tomorrow.

Script by Damond Benningfield