Omega Centauri is the largest and brightest of the around 160 globular clusters in the Milky Way. Some 10 million stars orbit the centre of the cluster. It it about 12 billion years old, spans 150 light years across, and is located 17,090 light years away in the southern constellation Centaurus. It is easily visible to the naked eye and was initially catalogued as a star by ancient astronomers. Among all the globular clusters in the Local Group of galaxies, only Mayall II in the Andromeda Galaxy is brighter and more massive.

In this image I have focused on bringing out the different colours of the stars in this large globular. The cluster consists mainly of old red giants but with a sprinkling of very conspicuous blue stars. These are 'blue stragglers'; stars that are too hot and massive for the cluster's otherwise old age. Given the ancient origin of the cluster all its stars should have evolved into red giants by now but it has been proposed that the blue stars are the results of mergers and mass transfers in the crowded environment of globular clusters. A main sequence star can exist for billions of years in the cluster and then later gain mass from a close orbiting binary, or as a result of a collision/merger, and thereby become more massive and hotter so that it now appears as a blue giant.

Due to its large mass and somewhat ellipsoid shape, it has been theorised that Omega Centauri is perhaps an ancient remnant core of another galaxy that long ago interacted with our Milky Way. The cluster also contains an unusually large amount of dark matter, further making it stand out among the general globular cluster population.

Despite looking through our Milky Way's densely populated spiral arms, filled with gas and dust, there are still 29 background galaxies visible in this field of view. Can you find them?

Image details:
2x2 mosaic
Date: February - March 2021
Exposure: LRGB: 610:115:105:105 mins, total 16 hours (4 hours per mosaic panel) @ -30C
Telescope: Homebuilt 12.5" f/4 Serrurier Truss Newtonian
Camera: QSI 683wsg with Lodestar guider
Filters: Astrodon LRGB E-Series Gen 2
Taken from my observatory in Auckland, New Zealand