Black hole thermodynamics in Caratheodory's approach

We show that, in the framework of Caratheodory's approach to thermodynamics, one can implement black hole thermodynamics by realizing that there exists a quasi-homogeneity symmetry of the Pfaffian form deltaQ(rev) representing the infinitesimal heat exchanged reversibly by a Kerr-Newman black hole; this allow us to calculate readily an integrating factor, and, as a consequence, a foliation of the thermodynamic manifold can be recovered. (C) 2003 Elsevier Science B.V. All rights reserved.