Amateur astronomers often debate which globular cluster is the best, or prettiest. I’m not sure I would enter into that debate even if I had an opinion, so I’ll stick to the facts: Omega Centauri, also known as NGC5139, is the largest globular cluster in our galaxy. Or at least the largest one visible from Earth. Since these clusters are generally located outside the disk of the galaxy, they are not hidden behind the dense dust lanes of the disk, so it probably is the largest one.
Located some 15,800 light-years from Earth in the constellation Centaurus, the apparent size of NGC5139 is slightly larger than our Moon (36 arcminutes), while its actual size is roughly 150 light-years. It is estimated to contain about 10 million stars and to have a total mass of about 4 million times that of our Sun.
Omega Centauri is also unusual among globular clusters in that it doesn’t appear to have been formed in the same way as others. It has been suggested that there may be a black hole at the center of this cluster, but that has been disputed. Another idea is that the cluster may be the core of a “disrupted” dwarf galaxy, where the rest of the dwarf galaxy was absorbed into the Milky Way.
This image was captured in Australia, and the cluster is not visible in the northern hemisphere. It is a mere 3 hours of exposure, consisting of 6 sub-exposures of 10 minutes for each color channel (red, green, and blue). Unlike my typical nebula images, the color is fairly accurate, although a bit exaggerated. The processing is relatively simple, so what you see here is pretty close to what it would look like through a modest telescope. It can also be seen naked eye – if you are on the other side of Earth.