Multipole Moments of numerical spacetimes

TL;DR

This paper refines methods for accurately determining the multipole moments of numerical spacetimes, impacting the modeling of rotating neutron stars and their exterior gravitational fields.

Contribution

It introduces corrected techniques for identifying relativistic multipole moments and provides explicit formulas for quadrupole and octupole moments based on neutron star properties.

Findings

Corrected multipole moment identification methods.

Expressions for quadrupole and octupole moments as functions of spin.

Relevance for modeling realistic rotating neutron stars.

Abstract

In this article we present some recent results on identifying correctly the relativistic multipole moments of numerically constructed spacetimes, and the consequences that this correction has on searching for appropriate analytic spacetimes that can approximate well the previously mentioned numerical spacetimes. We also present expressions that give the quadrupole and the spin octupole as functions of the spin parameter of a neutron star for various equations of state and in a range of masses for every equation of state used. These results are relevant for describing the exterior spacetime of rotating neutron stars that are made up of matter obeying realistic equations of state.