We have discovered supermassive black holes, with masses ranging from millions to billions times the mass of the Sun, at the very centre of massive galaxies. The mass of this central black hole correlates with many of the large scale properties of the host galaxy, for example the total mass of the galaxy is about one thousand times the mass of the black hole. However the direct gravitational influence of the black hole extends to only a minute fraction of the volume of the galaxy (about one billionth of the total volume). So how can such large scale correlations be established? In exploring this question we will discover an unexpected twist in the story of galaxy evolution.