Black holes and thermal Green functions

This paper concerns itself with the possibility of thermal equilibrium between a black hole and a heat bath implied by Hawking's discovery of black hole emission. It is argued that in an isolated box of radiation, for sufficiently high energy density a black hole will condense out. Thermal Green functions are introduced to discuss this equilibrium and the original arguments, that the equilibrium is possibly based on fields interacting solely with the external gravitational field, are extended to the case when mutual and self interactions are included. (author)