Second order variations and the overspinning problem in Kerr-Taub-NUT spacetime

TL;DR

This paper investigates the effect of second order variations on the overspinning of Kerr-Taub-NUT black holes, demonstrating that such variations prevent the formation of naked singularities and uphold cosmic censorship.

Contribution

It extends previous first order analyses by incorporating second order variations, showing they preserve the event horizon and prevent overspinning in Kerr-Taub-NUT black holes.

Findings

Second order variations prevent overspinning of Kerr-Taub-NUT black holes.

The event horizon remains intact, supporting cosmic censorship.

Second order effects drive the black hole away from extremality.

Abstract

Previously, we attempted to over-spin Kerr-Taub-NUT black holes with test fields satisfying the null energy condition. We derived that a non-generic over-spinning could be achieved with strict restrictions on the test field modes and the initial space-time parameters. Here, we incorporate the effect of the second order variations by evaluating the Sorce-Wald condition for Kerr-Taub-NUT black holes. We calculate the second variation of the area for the sub-collection of Kerr-Taub-NUT black holes for which over-spinning is possible due to first order perturbations. We carry out an analysis to second order, avoiding the common order of magnitude problems where the second order variations appear in the form of a product with the square of an additional small parameter. We derive that the contribution of the second order variations fix the final state of the space-time parameters driving the Kerr-Taub-NUT black hole away from extremality. The event horizon is preserved in accord with the cosmic censorship conjecture and the laws of black hole dynamics.