Extreme general relativity to one side, what does this mean for black hole studies?
"Where did the black hole get its spin? It could have some spin when it was born, but most of it, particularly at these fast rates, must be accumulated as the black hole grows," said Harrison. "It can accumulate because the accretion disk -- as the matter swirls onto the black hole it can add spin. And also the process by which black holes merge – when two galaxies merge, their black holes also merge – this can add, or subtract, spin from the black hole.
"If we can measure the spins of a large number of black holes, we can begin to say things very concrete about how they grew."
This research isn't restricted to NGC 1365, however.
"(NGC 1365's) properties are pretty "normal", so we expect to find similar line broadening in other (maybe most) supermassive black holes," said Risaliti.
"Actually, it is even better than this: we already have measurement of line broadening for many (~20-30) supermassive black holes. Until now however we could not be sure about the uniqueness of the interpretation. So our result for one black hole also validates previous studies on many others."