Astronomers have discovered many potential black holes in X-ray binaries andgalactic nuclei. These black holes are usually identified by the fact that theyare too massive to be neutron stars. Until recently, however, there was noconvincing evidence that the objects identified as black hole candidatesactually have event horizons. This has changed with extensive applications of aclass of accretion models for describing the flow of gas onto compact objects;for these solutions, called advection-dominated accretion flows (ADAFs), theblack hole nature of the accreting star, specifically its event horizon, playsan important role. We review the evidence that, at low luminosities, accretingblack holes in both X-ray binaries and galactic nuclei contain ADAFs ratherthan the standard thin accretion disk.
展开▼
