Galactic centre. Coloured Chandra X-ray telescope image of the centre of our galaxy, the Milky Way. The bright white/yellow patch in the centre of the image is an X-ray flare released by material falling towards the Sagittarius A* radio source. Sagittarius A* is believed to be a supermassive black hole, a star that has collapsed under its own gravity. It is thought to have a mass of around 2.6 million times that of the Sun. Matter falling towards Sagittarius A* is thought to fuel energetic activity at the galactic centre.