Lecture 20: Black Holes

What happens if even Neutron Degeneracy pressure is insufficient to halt the collapse of gravity? In that case, the object simply collapses in upon itself, approaching a state of infinite density. Such an object has such strong gravity that nothing, not even light can escape from it. We call these Black Holes. This lecture describes the basic properties of black holes, takes an imaginary journey through the event horizon, and discusses observational evidence that stellar-mass black holes (the remnants of the evolution of very massive stars) actually exist, and ends with the suggestion that if Steven Hawking and others are right, black holes may not be so black after all. One Erratum: during the lecture while commenting on the fate of Karl Schwarzschild, for whom the Schwarzschild Radius is named, I incorrectly identify Henry Moseley (killed by a sniper during the Galipoli Campaign of WWI) as one of the discoverers of the neutron. Moseley was the person who discovered that "atomic number" corresponded to nuclear charge, and hence the number of protons in the nucleus. The discoverer of the neutron was James Chadwick, who died in 1974. Recorded 2006 February 1 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.