Stability and physical properties of spherical excited scalar boson stars

TL;DR

This paper investigates the stability and physical characteristics of excited scalar boson stars with multiple radial nodes, demonstrating their potential stability and implications for astrophysical phenomena like galactic rotation.

Contribution

It shows that excited scalar boson stars with up to 10 radial nodes can be stable for significant timescales, expanding understanding of their properties and potential astrophysical relevance.

Findings

Stars with up to 10 radial nodes can be stable for long timescales.

Compactness is insensitive to the number of nodes at large self-interaction coupling.

These stars are generally not compact enough for stable circular orbits or light rings.

Abstract

We study the time evolution of spherical, excited -- with $n$ radial nodes -- scalar boson stars in General Relativity minimally coupled to a complex massive scalar field with quartic self-interactions. We report that these stars, with up to $n=10$, can be made dynamically stable, up to timescales of $t\sim\frac{10^{4}}{c\mu}$, where $\mu$ is the inverse Compton wavelength of the scalar particle, for sufficiently large values of the self-interactions coupling constant $\lambda$, which depend on $n$. We observe that the compactness of these solutions is rather insensitive to $n$, for large $\lambda$ and fixed frequency. Generically, along the branches where stability was studied, these excited boson stars are not compact enough to allow for innermost stable circular orbits or light rings. Finally, we discuss the angular velocity of particles along timelike circular orbits, suggesting an application, for solutions in the Newtonian limit, to galactic rotation curves.