ABSTRACT
This chapter presents a brief introduction to black hole thermodynamics. It shows that it is possible to associate an entropy to a black hole, and that — when quantum mechanics is taken into account — a black hole is not totally black, but rather emits radiation as a black body. The black hole is stationary both before and after the capture. The entropy of a thermo-dynamical system in equilibrium measures the fact that we cannot distinguish between different microstates corresponding to the same macroscopic state. The entropy of the object disappears when it crosses the horizon, because the information on its structure becomes inaccessible; since the final black hole is characterized by mass and angular momentum only, the total entropy of the universe would then decrease, violating the second law of thermodynamics.
