Areas of the Event Horizon and Stationary Limit Surface for a Kerr Black   Hole
  We present an elementary evaluation of the surface areas of the event horizon and stationary limit surface for an uncharged Kerr black hole. The latter appears not to have been previously given in the literature, and permits us to suggest new geometrical / physical interpretations of these areas. 
C. A. Pickett, J. D. Zund (Departments of Mathematics and Physics, New   Mexico State University, Las Cruces, New Mexico, USA)