... GRO J1655 40: Evidence for a Spinning Black Hole . ... Credit Copyright: A. Hobart, CXC Explanation: In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole . Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering at a rate of 450 times a second. ...