Gravitational-wave extraction from neutron-star oscillations: Comparing linear and nonlinear techniques
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, nonrotating, 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 via three methods: the gauge-invariant curvature-perturbation theory based on the Newman-Penrose scalar ${\ensuremath{\psi}}_{4}$; the gauge-invariant Regge-Wheeler-Zerilli-Moncrief metric-perturbation theory of a Schwarzschild space-time; some generalization of the quadrupole emission formula.