Measuring a Distant Black Hole's Spin

Black holes are defined by just two simple characteristics: mass and spin. Data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton is helping address the spin question. By a lucky alignment, the light from a quasar some six billion light years away (RX J1131-1231) has ultimately given researchers information about how fast the supermassive black hole at the center of the quasar is spinning. This will help astronomers understand just how black holes grow over time across the universe. (NASA/CXC/A. Hobart)