Accretion onto Black Holes: the Emergent Radiation Spectrum. III. Rotating (kerr) Black Holes

Steady-state, spherically symmetric accretion of matter onto rotating black holes is examined for simple polytropic gases. The total luminosity and frequency spectrum of the radiation emitted by interstellar hydrogen accreting onto a rotating black hole and observed above 1 keY are computed. It is found that for the same interstellar conditions and mass of the central hole, the total luminosity increases as the angular momentum of the black hole increases. Spherical accretion onto a maximally rotating black hole with a = m produces 13.3 percent more energy in the form of hard X-rays and y-rays than accretion onto a nonrotating black hole. Sabject headings: black holes - rotation - X-rays

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