The Gaussian curvature of the event horizon of a black hole embedded in a magnetic field is examined. It is shown that a zone of negative curvature develops if the magnetic field parameter exceeds a certain limit. This particular limit depends on the radius of the black hole. Further, as the magnetic field increases, the polar circumference increases while the equatorial circumference decreases. Possible ramifications to blackhole physics are discussed.

• Received 17 April 1979

DOI:https://doi.org/10.1103/PhysRevD.21.332