Isolated horizons: a generalization of black hole mechanics

A set of boundary conditions defining a non-rotating isolated horizon an given in Einstein-Maxwell theory. A spacetime representing a black hole which itself is in equilibrium but whose exterior contains radiation admits such a horizon. Physically motivated. (quasi-)local definitions of the mass and surface gravity of an isolated horizon are introduced. Although these definitions do not re fer to infinity, the quanti ties assume their standard values in Reissner-Nordstrom solutions. Finally. using these definitions, the zeroth and first laws of black hole mechanics are established for isolated horizons.