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We use the integrated spectrum of the X-ray background and quasars SpectralEnergy Distribution to derive the contribution of quasars to the energy outputof the Universe. We find a lower limit for the energy from accretion onto blackholes of 6%, of the total luminosity of the Universe and probably more, with15% quite possible. Comparing these values with the masses of black holes inthe center of nearby galaxies we show that the accretion process must be onaverage very efficient: at least 15% of the accreted mass must be transformedinto radiated energy. This further implies that most supermassive black holesare rapidly rotating.Comment: 8 Pages, Astrophysical Journal Letters, in pres

Most Supermassive Black Holes Must Be Rapidly Rotating