Strings in Kerr-Newman black holes

We study the evolution of strings in the equatorial plane of a Kerr-Newman black hole. Writing the equations of motion and the constraints resulting from Hamilton's principle, three classes of exact solutions are presented, for a closed string, encircling the black hole. They all depend on two arbitrary integration functions and two constants. A process for extracting energy is examined for the case of one of the three families of solutions. This is the analogue of the Penrose process for the case of a particle.