Termodin\'amica de agujeros negros y campos escalares

Since the descovery by Stephen Hawking that black holes emit radiation in the context of the semiclassical approach to gravity, the black hole thermodynamics has become an active field of research in theoretical physics. In this thesis, the influence of scalar fields on the black hole thermodynamics in $D=4$ dimensions is studied. On one hand, the role played by scalar fields in the first law of black hole thermodynamics is elucidated, by using the quasilocal formalism of Brown and York, which is based on a correct variational principle, and some concrete examples are provided. On the other, the thermodynamic stability of asymptotically flat charged hairy black hole exact solutions is analysed. The solutions considered have a non-trivial scalar field potential and they can be embebbed in supergravity theories. It is explicitly shown that these solutions contain thermodynamically stable black holes.