A classical instability of Reissner-Nordström solutions and the fate of magnetically charged black holes

Working in the context of spontaneously broken gauge theories, we show that the magnetically charged Reissner-Nordstr\"om solution develops a classical instability if the horizon is sufficiently small. This instability has significant implications for the evolution of a magnetically charged black hole. In particular, it leads to the possibility that such a hole could evaporate completely, leaving in its place a nonsingular magnetic monopole.