Session D3 - The Discovery of Black Holes.
INVITED session, Saturday afternoon, May 01
Plaza E, Adam's Mark Hotel
Cygnus X-1, the first bonafide black hole, was established in 1972. Dynamical optical observations of its massive B0 supergiant companion showed that the compact X-ray source was too massive to be a neutron star and must be a black hole, if one assumes that general relativity is valid in strong gravitational fields. In 1986 a new class of black hole binary was discovered which differs from Cygnus X-1 in two key respects: the optical companion is a low-mass star, and the X-ray source is transient with yearlong outbursts that are followed by decades of quiescence. These systems are often referred to as X-ray novae. Presently, a total of 16 X-ray novae are known to contain a massive compact X-ray source that is almost certainly a black hole. I will discuss the measurement of black hole masses and review our knowledge of these masses, and then I will turn to the importance of these systems as potential sites for tests of general relativity. Topics include the following: the distinct X-ray states exhibited by accreting black holes; relativistically broadened Fe K emission lines; quasi-periodic X-ray oscillations (100-450 Hz); relativistic radio and X-ray jets; and evidence for the existence of the event horizon. The challenge we now face is to prove that these compact objects are the black holes described by general relativity. To do this we must make clean quantitative measurements in the strong fields near these objects. Throughout the talk, I will make a determined effort to avoid jargon and to make these black holes immediate to the nonexpert.