Fundamental equations for the gravitational and electromagnetic   perturbations of a charged black hole
  A pair of wave equations is presented for the gravitational and electromagnetic perturbations of a charged black hole. One of the equations is uncoupled and determines the propagation of the electromagnetic perturbation. The other is for the propagation of the shear of a principal null direction and has a source term given by the solution of the first equation. This result is expected to have important applications in astrophysical models. 
Zolt\'an Perj\'es