Bailyn, Charles. ASTR 160: Frontiers and Controversies in Astrophysics, Spring 2007. Yale OpenCourseWare: Astronomy, Accessed 21/9/14 http://oyc.yale.edu/astronomy/astr-160/lecture-8 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license The second half of the course begins, focusing on black holes and relativity. In introducing black holes, Professor Bailyn offers a definition, talks about how their existence is detected, and explains why (unlike in the case with exoplanets where Newtonian physics was applied) Einstein's Theory of Relativity is now required when studying black holes. The concepts of escape and circular velocity are introduced. A number of problems are worked out and students learn how to calculate an object's escape velocity. A historical overview is offered of our understanding and discovery of black holes in the context of stellar evolution.