h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

A black hole is a creation of gravitation. A large star cools when fission ceases at its centre, this causes the star to grow. The star collapses when the gravity is greater than the outpressure. A black hole is formed with an event horizon at the gravitational radius. Inside the event horizon the escape velocity is greater than the finite limit of the speed of light. At the centre is a point of infinite mass and gravity, the singularity. The gravitational forces around the outside of the event horizon are so strong that space-time is curved into a 4 dimensional gravitational well.

Even time is not safe. Due to the three arrows of time (diffusion, entropy and universal expansion) time flows in a single direction and can only be tampered with relativistically. However when time becomes incident to the massive gravitational field of the singularity it is broken apart and quantised.

The interesting thing is that black holes can evaporate. This is due to Hawking radiation. Hawking radiation occurs because of pair production. For example: in a massive gravitational field E=mc^2 can produce a neutrino and an antineutrino just on the ouside of the singularity. Since neutrinos travel at the speed of light they can escape from just outside the singularity. In normal space the pair would cancel, conserving the energy, but if one is trapped inside the event horizon the other escapes then the black hole loses a neutrinos worth of energy.