SUPERGIANT GALAXIES
Our galaxy, the Milky Way, is big. With a diameter of 100,000 light years, this enormous disc of stars is large for a spiral galaxy. But imagine a galaxy extending to almost 20 times the diameter of the one we call home – so big that if it were to replace our Milky Way, it would not only engulf nearby satellite galaxies such as the Magellanic Clouds, but its outer limits would reach nearly all the way to Andromeda, about 2.5 million light years away.
That’s the staggering scale of IC 1101, an enormous ball of stars more than a billion light years away that is one of the largest measured galaxies in the known universe. It’s an extreme example of a supermassive ‘cD’ galaxy – a class of objects very different from the Milky Way. cD galaxies are closely related to smaller elliptical galaxies – balls of old red and yellow stars that vary in size – from tiny dwarfs to giants with the diameter of the Milky Way – and differ in shape – from perfect spheres to elongated cigars. But they also differ in some other important ways.
“cD galaxies have an extra-large extended and diffuse luminous envelope of stars,” explains Dr Alessia Longobardi
