The concept of black holes consistently grips the human imagination. Many strange and frightening creatures and objects have been invented in mythology and fiction, and modern scientists have revealed a number of equally bizarre and disquieting things in the natural world. But none of these quite compares to the idea of the black hole-an object whose gravitational pull is so great that even light cannot escape it, and a place where most of the nor- mal laws of nature break down. In the words of noted physicist Kip Thorne, one of the world's leading experts on black holes:

Of all the conceptions of the human mind, from unicorns to gargoyles to the hydrogen bomb, the most fantastic, perhaps, is the black hole: a hole in space with a definite edge into which anything can fall and out of which nothing...