What Is the Black Hole?

Black holes are these strange divots in space, originally predicted by einstin's theory of general relativity. Some of them form when stars collapse at the end of their life cycle and they can no longer resist the pressure of gravity squeezing them down into a dense spot. The keything is the density - you can take almost any amount of mass and make it into a black hole if you squeeze it down to a small enough radius. And a peanut sized earth mass could act form a black hole.