Numerical Simulations of Oscillating Soliton Stars: Excited States in Spherical Symmetry and Ground State Evolutions in 3D

TL;DR

This paper numerically investigates excited and ground state oscillating soliton stars, revealing their stability properties, evolution pathways, and gravitational wave signatures in spherical symmetry and 3D simulations.

Contribution

First numerical study of excited state soliton stars and their stability, including 3D evolution and gravitational wave analysis.

Findings

Excited state stars are unstable, migrating to ground states or collapsing.

Higher excited states cascade through intermediate states during evolution.

Gravitational waves damp out quickly, allowing complete waveform extraction.

Abstract

Excited state soliton stars are studied numerically for the first time. The stability of spherically symmetric S-branch excited state oscillatons under radial perturbations is investigated using a 1D code. We find that these stars are inherently unstable either migrating to the ground state or collapsing to black holes. Higher excited state configurations are observed to cascade through intermediate excited states during their migration to the ground state. This is similar to excited state boson stars. Ground state oscillatons are then studied in full 3D numerical relativity. Finding the appropriate gauge condition for the dynamic oscillatons is much more challenging than in the case of boson stars. Different slicing conditions are explored, and a customized gauge condition that approximates polar slicing in spherical symmetry is implemented. Comparisons with 1D results and convergence tests are performed. The behavior of these stars under small axisymmetric perturbations is studied and gravitational waveforms are extracted. We find that the gravitational waves damp out on a short timescale, enabling us to obtain the complete waveform. This work is a starting point for the evolution of real scalar field systems with arbitrary symmetries.