Gravitomagnetism and Pulsar Beam Precession near a Kerr Black Hole

TL;DR

This paper investigates how the spin-precession of pulsars near Kerr black holes affects observed pulse frequencies, suggesting new methods to detect black hole horizons and distinguish them from naked singularities.

Contribution

It provides a detailed theoretical analysis of pulsar beam evolution in Kerr spacetime and links spin-precession effects to observable pulse frequency modifications.

Findings

Pulse frequency rises sharply as orbit shrinks near the black hole

Spin-precession significantly alters observed pulsar signals

Potential to identify black hole horizons through pulse frequency analysis

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 spacetime, 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.