On the relation of the mass, spin and charge parameters with the red and blue shifts of photons emitted by particles orbiting a Kerr–Newman black hole

Abstract We found the mass M and rotation a parameters of the Kerr–Newman black hole in terms of the charge Q parameter as well as the red z r and blue z b shifts of light emitted by geodesic particles traveling in circular orbits around it for both cases: corotating and counterrotating directions. These shifts z r and z b cannot acquire arbitrary values; bounds of these shifts are found as functions of the parameters a and Q .