Computing gravitational waves from slightly nonspherical stellar collapse to black hole: Odd-parity perturbation

TL;DR

This paper models gravitational waves from slightly nonspherical stellar collapse to black holes using linearized Einstein theory, focusing on odd-parity perturbations and analyzing how waveforms depend on stellar properties and initial conditions.

Contribution

It introduces a perturbative approach to simulate gravitational waves from nonspherical stellar collapse, highlighting the dependence of waveforms on stellar type and initial perturbations.

Findings

Waveforms for n_p=1 show black hole quasinormal mode ringing.

Waveforms for n_p=3 depend strongly on initial perturbation profiles.

Collapse of neutron stars and supermassive stars analyzed qualitatively.

Abstract

Nonspherical stellar collapse to a black hole is one of the most promising gravitational wave sources for gravitational wave detectors. We numerically study gravitational waves from a slightly nonspherical stellar collapse to a black hole in linearized Einstein theory. We adopt a spherically collapsing star as the zeroth-order solution and gravitational waves are computed using perturbation theory on the spherical background. In this paper we focus on the perturbation of odd-parity modes. Using the polytropic equations of state with polytropic indices $n_p=1$ and 3, we qualitatively study gravitational waves emitted during the collapse of neutron stars and supermassive stars to black holes from a marginally stable equilibrium configuration. Since the matter perturbation profiles can be chosen arbitrarily, we provide a few types for them. For $n_p=1$, the gravitational waveforms are mainly characterized by a black hole quasinormal mode ringing, irrespective of perturbation profiles given initially. However, for $n_p=3$, the waveforms depend strongly on the initial perturbation profiles. In other words, the gravitational waveforms strongly depend on the stellar configuration and, in turn, on the ad hoc choice of the functional form of the perturbation in the case of supermassive stars.