Gravitomagnetism and pulsar beam precession near a Kerr black hole

ABSTRACT A rotating black hole causes the spin axis of a nearby pulsar to precess due to geodetic and gravitomagnetic frame-dragging effects. The aim of our theoretical work here is to explore how this spin precession can modify the rate at which pulses are received on Earth. Towards this end, we obtain the complete evolution of the beam vectors of pulsars moving on equatorial circular orbits in the Kerr space–time, relative to asymptotic fixed observers. We proceed to establish that such spin precession effects can significantly modify observed pulse frequencies and, in specific, we find that the observed pulse frequency rises sharply as the orbit shrinks, potentially providing a new way to locate horizons of Kerr black holes, even if observed for a very short time period. We also discuss implications for detections of sub-millisecond pulsars, pulsar nulling, quasi-periodic oscillations, multiply peaked pulsar Fourier profiles, and how Kerr black holes can potentially be distinguished from naked singularities.