Characteristic numerical relativity applied to hydrodynamic studies of neutron stars

TL;DR

This paper introduces a new axisymmetric, fully general relativistic code for simulating neutron stars, demonstrating its stability and ability to track gravitational wave emission accurately.

Contribution

The authors develop and validate a novel numerical relativity code based on the Bondi metric for hydrodynamic studies of neutron stars in axisymmetry.

Findings

Code maintains long-term stability of neutron star models.

Accurately conserves energy and tracks gravitational wave emission.

Demonstrates global energy conservation in perturbed neutron stars.

Abstract

We present tests and results of a new axisymmetric, fully general relativistic code capable of solving the coupled Einstein-matter system for a perfect fluid matter field. Our implementation is based on the Bondi metric, by which the spacetime is foliated with a family of outgoing light cones. We use high-resolution shock-capturing schemes to solve the fluid equations. The code can accurately maintain long-term stability of a spherically symmetric, relativistic, polytropic equilibrium model of a neutron star. In axisymmetry, we demonstrate global energy conservation of a perturbed neutron star in a compactified spacetime, for which the total energy radiated away by gravitational waves corresponds to a significant fraction of the Bondi mass.