A black hole consists of a few key things. The singularity is the center of the black hole, the point at which the matter is being compressed into a massive density. The event horizon is the point at which not even photons of light can escape the tremendous gravitational pull of the black hole. This makes it hard to discover black holes, since you cannot directly see that they are there. It is believed that black holes emit "Hawking" radiation, also called black hole radiation. This is one way that matter could escape the black hole. Huge jets of gas sometimes come out from either ends of the hole, or gas will spin around the hole, called an accretion disk.