Omega Centauri

The globular cluster Omega Centauri is one of the finest jewels of the southern night sky, located roughly 17,000 light-years from Earth in the constellation of Centaurus (the Centaur). Spanning about 150 light-years across, it is the most massive of all the Milky Way's globular clusters. It is thought to contain some ten million stars and is around 12 billion years old.

Sparkling at magnitude 3.7 and appearing nearly as large as the full Moon, Omega Centauri is easily visible with the unaided eye from a clear, dark observing site, providing both professional and amateur astronomers with an incredible view.

Recent research into this intriguing celestial giant suggests that there is a medium-size black hole sitting at its centre. Observations made with the Hubble Space Telescope and the Gemini Observatory show that stars at the cluster's centre are moving at an unusual rate — the cause, astronomers conclude, is the gravitational effect of a black hole with a mass of roughly 40,000 times that of the Sun.

The presence of this black hole and the existence of several generations of stars have made astronomers suspicious about Omega Centauri’s origins. Some believe that it is in fact the heart of a dwarf galaxy that was largely destroyed in an encounter with the Milky Way.

Omega Centauri has been observed throughout history. Both the great ancient astronomer Ptolemy and the 17th century German celestial cartographer Johann Bayer catalogued the cluster as a star. It was not until much later, in the early 19th century that the English astronomer John Herschel (son of the discoverer of Uranus) realised that Omega Centauri was in fact a globular cluster.