Speedy black hole holds galaxy’s history

A rapidly rotating supermassive black hole has been found in the heart of a spiral galaxy by ESA's XMM-Newton and NASA's NuSTAR space observatories, opening a new window into how galaxies grow. Supermassive black holes are thought to lurk in the centre of almost all large galaxies, and scientists believe that the evolution of a galaxy is inextricably linked with the evolution of its black hole. How fast a black hole spins is thought to reflect the history of its formation. In this picture, a black hole that grows steadily, fed by a uniform flow of matter spiralling in, should end up spinning rapidly. Rapid rotation could also be the result of two smaller black holes merging. On the other hand, a black hole buffeted by small clumps of material hitting from all directions will end up rotating relatively slowly. These scenarios mirror the formation of the galaxy itself, since a fraction of all the matter drawn into the galaxy finds its way into the black hole.