Author: Gourab Giri, Postdoctoral researcher, University of Pretoria

There is a supermassive black hole at the centre of nearly every big galaxy – including ours, the Milky Way (it’s called Sagittarius A*). Supermassive black holes are the densest objects in the universe, with masses reaching billions of times that of the Sun. Sometimes a galaxy’s supermassive black hole “wakes up” due to a sudden influx of gas and dust, most likely supplied from a neighbouring galaxy. It begins eating up lots of nearby gas and dust. This isn’t a calm, slow or passive process. As the black hole pulls in material, the material gets superheated on a scale…