Boson stars in massless and massive scalar-tensor gravity

TL;DR

This paper investigates the properties and stability of boson stars within massless and massive scalar-tensor gravity theories, focusing on spontaneous scalarization effects and how they influence star structure and energetics.

Contribution

It provides the first systematic numerical analysis of boson stars in scalar-tensor gravity, highlighting the impact of scalarization on their structure and stability.

Findings

Scalarization can produce larger, more massive boson stars.

Boson stars are less prone to scalarization than neutron stars.

Scalarized solutions are energetically favored over non-scalarized ones.

Abstract

We study phenomenological features and stability of boson stars in massless and massive scalar-tensor theory of gravity with Damour-Esposito-Farese coupling. This coupling between the tensor and scalar sectors of the theory leads to a phenomenon called spontaneous scalarization, the onset of which we investigate by numerically computing families of boson-star models using shooting and relaxation algorithms. We systematically explore the effects of the theory's coupling, the mass of the gravitational scalar and the choice of the bosonic potential on the structure of weakly and strongly scalarized solutions. Scalarized boson-star models share many common features with neutron stars in the same scalar-tensor theory of gravity. In particular, scalarization can result in boson stars with significantly larger radii and masses, which tend to be energetically favored over their weakly or non-scalarized counterparts. Overall, we find that boson stars are not quite as susceptible to scalarization as neutron stars.