Black holes are huge chunks of matter that were dead stars. Nothing can escape from them, not even light. They are made from stars that die. The first black hole to be discovered was Cygnus X-1.
Black holes have been of a long time debate, due to the fact that if light can't escape, then it must be a solid, liquid, or gas. The possibility of our sun becoming a black hole is very low, due to the fact that it is a somewhat small star. Black holes smear matter through the time-space continum. Inside a black hole, the speed of rotation is possibly faster than the speed of light, which is technically the cosmic speed limit. Inside of a black hole, time is at a standstill. When something is going near the speed of light, two minutes for them is 1 million years for a normal person.