Stars collapse on an almost daily basis. When a massive star collapses, it produces an immense gravitational pull along the way, drawing everything in its path—including light—toward its core, like a giant vacuum cleaner from which there's no escape. While black holes sit at the center of most galaxies, including our own, the real danger comes from a discovery made in the year 2000. "We now have conclusive evidence," physicist Michael Kaku told ABC News, "that there are wandering black holes—nomads, renegades—and right next to us in our own galaxy." How long until one of these nomads bumps into the Earth? No one is sure, and it's a big universe, but everyone agrees that it's going to happen sooner or later.