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K. Nandra (Universities Space Research Association)
Most candidate black holes are at the centers of active galaxies. The holes themselves are inherently dark, but a copious amount of radiation is generated when they accrete surrounding matter. Close to the event horizon, X-rays are produced in the accreting material that escape the gravitational pull. In the process, the black holes leave observable imprints on the spectrum. X-ray observations show evidence for matter orbiting with extremely high velocities, and the characteristic red-shift expected due to time dilation in the intense gravitational field. Current and future data can be used to help determine both the properties of the black holes, and the processes fueling galaxy activity.
The author(s) of this abstract have provided an email address for comments about the abstract: nandra@milkyway.gsfc.nasa.gov