Evolution of 3D Boson Stars with Waveform Extraction

TL;DR

This paper presents 3D numerical simulations of boson stars under perturbations, analyzing gravitational wave emission, quasinormal modes, and collapse behavior, providing new insights into their stability and gravitational wave signatures.

Contribution

It introduces a comprehensive 3D simulation code for boson stars, enabling detailed analysis of gravitational waves and stability under various perturbations, including collapse to black holes.

Findings

Boson stars emit detectable gravitational waves with characteristic quasinormal modes.

Unstable boson stars can collapse into black holes or migrate to stable states.

Nonspherical perturbations do not significantly alter collapse times.

Abstract

Numerical results from a study of boson stars under nonspherical perturbations using a fully general relativistic 3D code are presented together with the analysis of emitted gravitational radiation. We have constructed a simulation code suitable for the study of scalar fields in space-times of general symmetry by bringing together components for addressing the initial value problem, the full evolution system and the detection and analysis of gravitational waves. Within a series of numerical simulations, we explicitly extract the Zerilli and Newman-Penrose scalar $\Psi_4$ gravitational waveforms when the stars are subjected to different types of perturbations. Boson star systems have rapidly decaying nonradial quasinormal modes and thus the complete gravitational waveform could be extracted for all configurations studied. The gravitational waves emitted from stable, critical, and unstable boson star configurations are analyzed and the numerically observed quasinormal mode frequencies are compared with known linear perturbation results. The superposition of the high frequency nonspherical modes on the lower frequency spherical modes was observed in the metric oscillations when perturbations with radial and nonradial components were applied. The collapse of unstable boson stars to black holes was simulated. The apparent horizons were observed to be slightly nonspherical when initially detected and became spherical as the system evolved. The application of nonradial perturbations proportional to spherical harmonics is observed not to affect the collapse time. An unstable star subjected to a large perturbation was observed to migrate to a stable configuration.