Black hole microstates in string theory and massless probes

One of the open problems in Quantum Gravity is the black hole information paradox. A possibile solution within String Theory is given by the fuzzball proposal, where the microstates of the black hole are described by solutions with non-trivial horizon-scale structures. In this thesis we review a method, consisting in the null gauging of an appropriate Wess-Zumino-Witten model, that gives an exact description of some of these microstates in worldsheet String Theory. We then focus on studying dynamical aspects of such solutions. In particular we study the motion of massless probes in the background sourced by brane configurations known as supertubes, that provide the simplest example of fuzzballs, and we discuss how these objects trap light by computing, for different kind of solutions, the impact parameters that lead to a circular orbit of a given critical radius.