Tomorrow morning, I'll be giving a public lecture entitled Observational Evidence for Black Holes. This is part of a regular series of talks sponsored by MICA, Saturday mornings at 10:00 AM pacific time (1:00 PM Eastern, 18:00 UT). They're open to anybody.
These talks are in Second Life. A basic Second Life account— everything you need to attend the talk— is free. Go to the Second Life page I just linked in order to sign up. Once you've downloaded the Second Life viewer, and have created an account and logged in to Second Life, you can follow the link on our Upcoming Public Events page to find the talk.
Here's my blurb for tomorrow's talk:
Black holes are a theoretical prediction of Einstein's Relativity. But do they really exist? The answer is a nuanced "yes." We have observational evidence for two sorts of black holes. In our Galaxy, we observe black holes that are several times the mass of the Sun. At the core of almost every big Galaxy, we find a supermassive black hole that's a million or more times the mass of the Sun. In this talk, I'll give an overview of the evidence that these objects are in fact black holes. I'll also point out that the observational definition of "black hole", meaning those things that we know exist, isn't exactly the same as the definition of the objects predicted by Relativity, although most astronomers suspect and assume that what we observe are in fact the things that Relativity predicts.