Effect of the Quadrupole Moment of a Rotating Massive Object on the Gravitational Faraday Rotation

We study the rotation of the polarization plane for a ray of
electromagnetic radiation propagating in the gravitoelectromagnetic field caused by a rotating massive object with the quadrupole moment. The effect of the quadrupole moment on the gravitational Faraday rotation is investigated. It is found that the gravitational Faraday effect of the quadrupole moment is negligible for Kerr black holes, but this effect is important for rapidly rotating neutron stars.