E(7) symmetric area of the black hole horizon.

Extreme black holes with 1/8 of unbroken N = 8 supersymmetry are characterized by the non-vanishing area of the horizon. The central charge matrix has four generic eigenvalues. The area is proportional to the square root of the invariant quartic form of E7(7). It vanishes in all cases when 1/4 or 1/2 of supersymmetry is unbroken. The supergravity non-renormalization theorem for the area of the horizon in N = 8 case protects the unique U-duality invariant. 1 E-mail: [email protected] 2 E-mail: [email protected]