Chandra pinpoints edge of accretion disk around black hole

An object known as XTE J1118+480 is a black hole roughly seven times the mass of our Sun. XTE J1118+480 is locked in a close binary orbit with a Sun-like star. Recent observations by a team of scientists led by a researcher from the Harvard-Smithsonian Center for Astrophysics show an “accretion disk” around the black hole, which is matter stripped from a companion star by a black hole can that forms a flat, pancake-like structure. Most astronomers agree that when material is transferred onto the black hole at a high rate, then the accretion disk will reach to within about 25 miles of the event horizon — the surface of “no return” for matter or light falling into a black hole. However, scientists disagree on how close the accretion disk comes when the rate of transfer is much less. The accretion disk for this particular black hole gets no closer to the event horizon than about 600 miles — farther than some theories would predict. The observations therefore help to provide a better understanding of how energy is released when matter spirals into a black hole. The observations were made using four NASA space observatories.