Distinguishing between Kerr and rotating JNW space-times via frame dragging and tidal effects

TL;DR

This paper compares frame dragging and tidal effects in Kerr black holes and rotating JNW naked singularities, revealing distinct observational signatures that could help differentiate these space-times.

Contribution

It provides a detailed analysis of gyroscope precession and tidal forces in both Kerr and rotating JNW space-times, highlighting potential observational differences.

Findings

Gyroscope precession frequency can vanish near the ergoregion in Kerr black holes.

Enhanced Lense-Thirring precession observed in naked singularity backgrounds.

Significant deviations in tidal disruption characteristics between Kerr and JNW space-times.

Abstract

In this paper, we first investigate some aspects of frame dragging in strong gravity. The computations are carried out for the Kerr black hole and for the rotating Janis-Newman-Winicour solution, that is known to have a naked singularity on a surface at a finite radius. For the Kerr metric, a few interesting possibilities of gyroscope precession frequency, as measured by a Copernican observer outside the ergoregion, are pointed out. It is shown that for certain angular velocities of a stationary observer, this frequency might vanish exactly, close to the ergoregion. Similar computations are repeated for static observers in the naked singularity background, and strong enhancement of the Lense-Thirring precession frequency compared to the black hole case is established. Then, we study the nature of tidal forces in the rotating naked singularity background, in Fermi normal coordinates. Here, physical quantities characterizing tidal disruptions of celestial objects in equatorial circular orbits are computed numerically. Our results here indicate that there might be significant deviations from corresponding Kerr black hole calculations, up to the level of approximation that we consider.