Black holes in astrophysics

This paper reviews the current status of black hole (BH) 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 BH candidates. Some of the candidates have masses similar to 5M(.)- 20M(.) and are found in x-ray binaries, while the rest have masses similar to 10(6)M(.) - 10(9.5)M(.) and are found in galactic nuclei. A variety of methods are being tried to estimate the spin parameters of the candidate BHs. 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 BHs. Recent MHD simulations of magnetized plasma accreting on rotating BHs seem to hint that relativistic jets may be produced by a magnetic analogue of the Penrose process.