NASA: X-ray 'Echoes'

X-ray 'Echoes' Probe Monster Black Hole's Habitat

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 disk reflects the emission about half an hour later. The discovery pro