Putting a New Spin on Black Holes
- According to Einstein's General Relativity (GR), a spinning black hole twists up the nearby space-time. Studying these effects in real black hole systems provides, in principle, a powerful way to test GR. The spin-down of black holes can also be an important source of energy; for example, the fast and powerful jets from some galactic cores may well be powered by black hole spin-down. I will discuss recent measurements of black hole spin from X-ray spectroscopy, focusing on results for the supermassive black holes in the centers of galaxies. Progress over the past few years has been remarkable ; we now have reliable constraints on the spin of over 20 supermassive black holes, and are beginning to probe fundamental issues related to the powering of jets and the history of the black hole population. I shall conclude with a discussion of future prospects by proposed/planned NASA, JAXA and ESA missions.