Omega Centauri (ω Cen, NGC 5139, or Caldwell 80) is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677.

[12] Around 150 AD, Greco-Roman writer and astronomer Ptolemy catalogued this object in his Almagest as a star on the centaur's back, "Quae est in principio scapulae".

[17] It was first recognized as a globular cluster by Scottish astronomer James Dunlop in 1826, who described it as a "beautiful globe of stars very gradually and moderately compressed to the centre".

[18][19] At a distance of about 17,000 light-years (5,200 parsecs) from Earth, Omega Centauri is one of the few globular clusters visible to the naked eye—and appears almost as large as the full Moon when seen from a dark, rural area.

[citation needed] A 2008 study presented evidence for an intermediate-mass black hole at the center of Omega Centauri, based on observations made by the Hubble Space Telescope and Gemini Observatory on Cerro Pachón in Chile.

[26][27] Calculations using a revised location for the center found that the velocity of core stars does not vary with distance, as would be expected if an intermediate-mass black hole were present.

A study from July 10, 2024 has examined seven fast-moving stars from the center of Omega Centauri and found that their speeds were consistent with an intermediate-mass black hole of at least 8,200 solar masses.