Dr. Andrea Derdzinski -- How do we see black holes?

A black hole is so dense, its gravitational field prevents anything from escaping, including light. You would think that would make them the "blackest" things in the universe; how in the world do we know they are there? Dr. Andrea Derdzinski tells us about how we detect black holes, either due to the gravitational waves they produce, or due to their interaction with material orbiting around them, which paradoxically can make them some of the brightest objects in the universe.