Astronomers using data from the European Space Agency's XMM-Newton satellite have found a long-sought X-ray signal from NGC 4151, a galaxy that contains a supermassive black hole. When the black hole's X-ray source flares, its accretion disc reflects the emission about half an hour later. The discovery promises a new way to unravel what's happening in the neighbourhood of these powerful objects.
X-ray echo's probe black hole habitat
This animation shows the flare sequence happening twice.