Black Holes in Astrophysics

This article reviews the current status of black hole astrophysics, focusing on topics of interest to a physics audience. Astronomers have discovered dozens of compact objects with masses greater than 3M⊙, the likely maximum mass of a neutron star. These objects are identified as black hole candidates. Some of the candidates have masses ∼ 5− 20M⊙ and are found in X-ray binaries, while the rest have masses ∼ 10 − 10M⊙ and are found in galactic nuclei. A variety of methods are being tried to estimate the spin parameters of the candidate black holes. There is strong circumstantial evidence that many of the objects have event horizons, so there is good reason to believe that the candidates are true black holes. Recent MHD simulations of magnetized plasma accreting on rotating black holes seem to hint that relativistic jets may be produced by a magnetic analog of the Penrose process. Subject headings: accretion, accretion disks — active galactic nuclei — black hole physics — X-rays: binaries