Darren Croton uses the results of supercomputer simulations to study the universe. Our sun is just one of about 10 billion stars in our galaxy, the Milky Way. At the centre of the Milky Way is a super-massive black hole. It's a million times the mass of our sun. This is determined using the basic laws of physics. But some galaxies appear quiet, almost dead. So what kills a galaxy? One suggestion points the finger at super massive black holes.