Self-screening Hawking atmosphere in the presence of a bulk viscosity - art. no. 124017

The recent theory of 't Hooft [Nucl. Phys. B (Proc. Suppl.) 68, 174 (1998)] models the black hole as a system endowed with an envelope of matter that obeys an equation of state in the form p = (gamma - 1) rho, and acts as a s ource in Einstein's equations. The present paper generalizes the 't Hooft t heory so as to take into account a bulk viscosity zeta in the fluid. It is shown that even a slight positive value of zeta will suffice to yield compl ete agreement with the Hawking formula for the entropy of the black hole, i f the value of the constant gamma takes a value that: is slightly less than 4/3. The value gamma = 4/3 corresponds to a radiation fluid.