Areas of the Event Horizon and Stationary Limit Surface for a Kerr Black Hole

The notions of an event horizon, (EH), and stationary limit surface, (SLS), are important concepts in black hole physics. The former requires no comment, while the latter is less well-known. The SLS geometrically bounds a region outside the EH known as an ergosphere. Inside the ergosphere a test particle cannot travel along the orbit of a timelike Killing vector and remain at rest, and the red shift is infinite on the SLS. While surface area of an EH has been related to the entropy of a black hole, that of the SLS has not been given a physical interpretation. In this note our approximate evaluation of the area of a SLS suggests a reinterpretation of the area of an EH.