Conformal nature of the Hawking radiation

String theory usually represents quantum black holes as systems whosestatistical mechanics reproduces Hawking's thermodynamics in a verysatisfactory way. Complicated brane theoretical models are worked out, asquantum versions of Supergravity solutions. These models are then assumed to bein thermal equilibrium: this is a little cheating, because one is looking foran explanation of the seeming thermodynamical nature of black holes, so theycannot be {\it assumed} to be finite temperature systems! In the modelpresented here, the black body spectrum arises with no statistical hypothesisas an approximation of the unitary evolution of microscopic black holes, whichare always described by a 1+1 conformal field theory, characterized by someVirasoro algebra. At the end, one can state that {\it theHawking-thermodynamics of the system is a by-product of the algebraicVirasoro-symmetric nature of the event horizon}. This is {\it the centralresult} of the present work.Comment: 21 pages, no figure