Omega Centauri is the largest globular cluster of the Milky Way, a dense ball of ancient stars that may be the stripped core of a swallowed galaxy.
At a glance
| type | globular cluster |
|---|---|
| distance from the Sun | 17,000 light-years (5.2 kpc) |
| its light left it | 17,000 years ago |
| size in the piece | about 140 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About Omega Centauri
A globular cluster is a tight, round swarm of very old stars orbiting the Galaxy in its halo. Omega Centauri is the biggest of them, holding a vast number of stars packed so closely near its centre that they are far nearer to one another than the Sun is to its neighbours. It is plain to the naked eye in the southern sky as a fuzzy star, which is how it came to be catalogued with a Greek letter, like a star, before it was recognised as a cluster.
Most globular clusters are made of stars of a single age and composition. Omega Centauri is not: its stars span a range of ages and of heavy-element content, more like a small galaxy than a cluster. Its retrograde orbit and this mixture are why many astronomers think it is the nucleus of a dwarf galaxy whose outer stars the Milky Way stripped away long ago.
What you see in the piece
Its stars are old and cool, so the cluster shows a warm yellow-white; fly into it and the crowding toward the centre becomes obvious.
Measured or modelled
That it is the core of a disrupted dwarf galaxy is a leading interpretation, not a settled fact. Fast-moving stars near its centre have been read as the sign of an intermediate-mass black hole, a claim still being tested.
Questions
How far away is Omega Centauri?
Omega Centauri is about 17,000 light-years (5.2 kpc) from the Sun, in the halo of the Milky Way.
Why is Omega Centauri named like a star?
To the naked eye it looks like a single fuzzy star, so it was given a star’s Greek-letter name in Centaurus before telescopes showed it to be a cluster.