Non-Existence of Time-Periodic Solutions of the Dirac Equation in a   Reissner-Nordstrom Black Hole Background
  It is shown analytically that the Dirac equation has no normalizable, time-periodic solutions in a Reissner-Nordstrom black hole background; in particular, there are no static solutions of the Dirac equation in such a background field. The physical interpretation is that Dirac particles can either disappear into the black hole or escape to infinity, but they cannot stay on a periodic orbit around the black hole. 
Felix Finster, Joel Smoller, and Shing-Tung Yau