NASA astronomers have recently found evidence for matter actually falling into a black hole. As random material falls anywhere between us and the black hole, it blocks some of the X-rays in the accretion disk from reaching us. By analyzing the spectra of the iron X-rays that reached us and that were absorbed along the way, the astronomers could determine that the iron was heading straight for the black hole at over 600 million miles an hour. Scientists are now probing the jet phenomenon to understand how this process works. It's not all fireworks, though.
Black holes can also be quiet.
Such objects do not accrete matter, probably because they have long ago used up their fuel supply. They can still be detected by their gravitational influence on their environment. Our own galaxy probably contains a dormant supermassive black hole at its center. Weak X-ray emission emanates from near the galactic center. Our only map is the radiation, often X-ray light, emitted from the vicinity.