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Properties of the instantaneous ergo surface of a Kerr black hole
Classical and quantum gravity
This paper explores properties of the instantaneous ergo surface of a Kerr black hole. The surface area is evaluated in closed form. In terms of the mass (m) and angular velocity (a), to second order in a, the area of the ergo surface is given by 16 π m^2 + 4 π a^2 (compared to the familiar 16 π m^2 - 4 π a^2 for the event horizon). Whereas the total curvature of the instantaneous event horizon is 4 π, on the ergo surface it ranges from 4 π (for a=0) to 0 (for a=m) due to conical singularitiesdoi:10.1088/0264-9381/18/7/314 fatcat:x2g3nhnxffaqxiipz5jqo7fg2e