Dynamical Evolution of Boson Stars II: Excited States and Self-Interacting Fields

TL;DR

This paper investigates the dynamical evolution of boson stars, including excited states and self-interacting fields, revealing their stability properties, oscillation frequencies, and decay processes, with implications for their astrophysical relevance.

Contribution

It extends previous work on non-interacting boson stars to include excited states and self-interactions, analyzing their stability, oscillations, and decay mechanisms.

Findings

Self-interactions significantly increase boson star sizes and masses.

Both stable and unstable branches of excited states are identified and characterized.

Highly excited states decay through cascades similar to atomic transitions.

Abstract

The dynamical evolution of self-gravitating scalar field configurations in numerical relativity is studied. The previous analysis on ground state boson stars of non-interacting fields is extended to excited states and to fields with self couplings. Self couplings can significantly change the physical dimensions of boson stars, making them much more astrophysically interesting (e.g., having mass of order 0.1 solar mass). The stable ($S$) and unstable ($U$) branches of equilibrium configurations of boson stars of self-interacting fields are studied; their behavior under perturbations and their quasi-normal oscillation frequencies are determined and compared to the non-interacting case. Excited states of boson stars with and without self-couplings are studied and compared. Excited states also have equilibrium configurations with $S$ and $U$ branch structures; both branches are intrinsically unstable under a generic perturbation but have very different instability time scales. We carried out a detailed study of the instability time scales of these configurations. It is found that highly excited states spontaneously decay through a cascade of intermediate states similar to atomic transitions.