The radial infall of a highly relativistic point particle into a Kerr   black hole along the symmetry axis
  In this Letter we consider the radial infall along the symmetry axis of an ultra-relativistic point particle into a rotating Kerr black hole. We use the Sasaki-Nakamura formalism to compute the waveform, energy spectra and total energy radiated during this process. We discuss possible connections between these results and the black hole-black hole collision at the speed of light process. 
Vitor Cardoso, Jose' P. S. Lemos