Numerical studies of Phi^2-Oscillatons

TL;DR

This paper conducts a detailed numerical analysis of oscillatons, stable and unstable scalar field configurations in general relativity, revealing their stability properties, evolution, and collapse behavior under perturbations.

Contribution

It provides the first comprehensive numerical study of the stability and evolution of Phi^2-oscillatons, including their response to perturbations and collapse mechanisms.

Findings

S-oscillatons are stable under small perturbations.

U-oscillatons are inherently unstable and tend to collapse or migrate.

Gravitational cooling can prevent collapse in diluted oscillatons.

Abstract

We present an exhaustive analysis of the numerical evolution of the Einstein-Klein-Gordon equations for the case of a real scalar field endowed with a quadratic self-interaction potential. The self-gravitating equilibrium configurations are called oscillatons and are close relatives of boson stars, their complex counterparts. Unlike boson stars, for which the oscillations of the two components of the complex scalar field are such that the spacetime geometry remains static, oscillatons give rise to a geometry that is time-dependent and oscillatory in nature. However, they can still be classified into stable (S-branch) and unstable (U-branch) cases. We have found that S-oscillatons are indeed stable configurations under small perturbations and typically migrate to other S-profiles when perturbed strongly. On the other hand, U-oscillatons are intrinsically unstable: they migrate to the S-branch if their mass is decreased and collapse to black holes if their mass is increased even by a small amount. The S-oscillatons can also be made to collapse to black holes if enough mass is added to them, but such collapse can be efficiently prevented by the gravitational cooling mechanism in the case of diluted oscillatons.