Do black holes exist? What is a black hole? How do you find black holes? Can you see a black hole?
Astronomers and theoretical physicists discuss their work and whether or not the observations to date support our current understanding of the underlying physics.
Early in the video there are some nice animations to explain general relativity.
Note the use of Kepler's 3rd law to determine the mass of a supermassive black hole during the final section of this video.