Abstract
The Milky Way's massive black hole is called Sagittarius A* and weighs 4 million times the mass of the Sun. Most galaxies have their own massive black hole, with a mass ~ 1 000 times smaller than the mass of the galaxy. We believe that these black holes formed in the first galaxies and have grown in size over time. Their evolution over the first billion years of the Universe set the stage for the following 13 billion years, but some of these black holes developed spectacularly in a short space of time, defying our understanding.
