Comparison of particle properties in Kerr metric and in rotating   coordinates
  Properties of particles in Kerr metric are compared with properties of particles in rotating coordinates in Minkowski space-time. It is shown that particles with negative and zero energies existing in the ergosphere of the rotating black hole also exist in the region out of the static limit in rotating coordinates in Minkowski space-time. Some similarities like the Penrose process and differences in both cases are analyzed. 
A. A. Grib, Yu. V. Pavlov
gr-qc