Gravitational-Wave Extraction from Neutron Star Oscillations: comparing linear and nonlinear techniques

TL;DR

This study compares gravitational waveforms from nonlinear and linear simulations of oscillating neutron stars using three different wave-extraction techniques to evaluate their accuracy and consistency.

Contribution

It provides a systematic comparison of waveform extraction methods applied to both nonlinear and linear neutron star models.

Findings

Waveforms from different methods show good agreement in certain regimes.

Linear perturbation techniques are computationally less intensive.

Nonlinear simulations capture more complex oscillation features.

Abstract

The main aim of this study is the comparison of gravitational waveforms obtained from numerical simulations which employ different numerical evolution approaches and different wave-extraction techniques. For this purpose, we evolve an oscillating, non-rotating polytropic neutron-star model with two different approaches: a full nonlinear relativistic simulation (in three dimensions) and a linear simulation based on perturbation theory. The extraction of the gravitational-wave signal is performed with three methods: The gauge-invariant curvature-perturbation theory based on the Newman-Penrose scalar $\psi_4$; The gauge-invariant Regge-Wheeler-Zerilli-Moncrief metric-perturbation theory of a Schwarzschild space-time; Some generalization of the quadrupole emission formula.