Brans-Dicke Boson Stars: Configurations and Stability through Cosmic History

Abstract

We make a detailed study of boson star configurations in Jordan--Brans--Dicke theory, studying both equilibrium properties and stability, and considering boson stars existing at different cosmic epochs. We show that boson stars can be stable at any time of cosmic history and that equilibrium stars are denser in the past. We analyze three different proposed mass functions for boson star systems, and obtain results independently of the definition adopted. We study how the configurations depend on the value of the Jordan--Brans--Dicke coupling constant, and the properties of the stars under extreme values of the gravitational asymptotic constant. This last point allows us to extract conclusions about the stability behaviour concerning the scalar field. Finally, other dynamical variables of interest, like the radius, are also calculated. In this regard, it is shown that the radius corresponding to the maximal boson star mass remains roughly the same during cosmological evolution.