Figure 12-42X-Rays Generated by Accretion of Matter Near a Black Hole Stellar-remnant black holes, such as Cygnus X-1, LMC X-3, V404 Cygni, and probably A0620-00, are detected in close binary star systems. This drawing (of the Cygnus X-1 system) shows how gas from the 30 M_⊙ companion star, HDE 226868, transfers to the black hole, which has at least 11 M_⊙. This process creates an accretion disk. As the gas spirals inward, friction and compression heat it so much that the gas emits X-rays, which astronomers can detect.