Black holes are the objects that cannot be directly seen, because their gravitational field is so strong that does not allow even light to escape it. However, we can observe the gravitational energy released by the matter falling onto the black hole, this process is called accretion. A common way the matter accretes onto a black hole is through the hot accretion disk with a temperature up to billions kelvins that emits light. That's why black hole accretion is an engine of the most powerful astrophysical phenomena such as quasars -- an extremely luminous active galactic nucleus, X-ray transients in binary systems, and tidal disruption of stars.
I will speak about the history of black hole concept and briefly review the current problems of black hole theory. Also, the backbone of an accretion disk theory and observational behavior of black hole accretion disks will be discussed.
The seminar will be accessible to non-astronomers.