  Recent applications of Operator Algebras to Quantum Field Theory on a Curved
Spacetime show that the incremental entropy associated with a quantum black
hole, due the addition of a short range charge, is quantized proportionally to
the logarithm of an integer. This talk first reviews the case of a Rindler
black hole and then sketches the case of a spacetime with bifurcate Killing
horizon and charges localizable on the horizon. An important tool is the
construction of the conformal symmetries on the horizon.
