Multipole moments of compact objects with NUT charge: Theoretical and observational implications

TL;DR

This paper derives the multipole moments of Kerr-NUT black holes, revealing unique asymmetries and complex structures that significantly impact gravitational wave observations and differ from traditional Kerr black holes.

Contribution

It introduces a method to compute multipole moments for Kerr-NUT spacetimes, highlighting the effects of NUT charge on symmetry and multipolar structure.

Findings

All-order multipole moments are present due to NUT charge.

The multipolar structure differs markedly from Kerr black holes.

Implications for gravitational wave detection are significant.

Abstract

We derive the multipole moments of the Kerr-NUT black hole spacetime using the Geroch-Hansen formalism, even though the spacetime is not asymptotically flat. Intriguingly, in the presence of the NUT charge, the absence of reflection symmetry about the equatorial plane, leads to mass and spin multipole moments of all orders, in stark contrast to Kerr-like spacetimes. This leads to a drastic departure of the multipolar structure of a compact object with NUT charge, whose implications for gravitational wave observations have been explored. Our analysis of multipole moments for the Kerr-NUT spacetime is also in tune with the Thorne's approach.