In the past, the existence of black holes was inferred by observing orbiting stars and clouds of gas. The mass of the central object can be estimated from the rotation velocity of the orbiting matter. The new results, presented at the American Astronomical Society meeting in San Diego earlier this year, track the ultraviolet emission from hot clumps of gas circling the known black hole candidate Cygnus XR-1. The light dims as it is stretched by gravity to ever-longer wavelengths in the approach to the black hole. The discovery was made during a new analysis of observations dating from 1992.
Work continues to find more such events and eliminate the possibility of errors.
Observations using the Chandra X-ray satellite, also presented at the San Diego meeting, confirm this picture. Picture of the month Article 10 of 20.