Impact of dynamical dark energy on the neutron star equilibrium

TL;DR

This paper investigates how dynamical dark energy modeled as a scalar field affects neutron star structure and mass limits, providing constraints on dark energy parameters based on observed neutron star masses.

Contribution

It introduces a model of dark energy inside neutron stars using hydrodynamical representation and derives constraints on dark energy's effective sound speed from neutron star observations.

Findings

Dark energy density distribution depends on its parameters.

Presence of dark energy influences neutron star mass and structure.

Effective sound speed of dark energy cannot be smaller than ~10^{-2}.

Abstract

We study the density distribution of the minimally-coupled scalar field dark energy inside a neutron star. The dark energy is considered in the hydrodynamical representation as a perfect fluid with three parameters (background density, equation of state, and effective sound speed). The neutron star matter is modeled with three unified equations of state, developed by the Brussels-Montreal group. With the calculated density distribution of the dark energy inside a neutron star (and its dependence on the dark energy parameters) we investigate how its presence impacts the macroscopic characteristics and the value of the mass limit for neutron stars. From this impact we derive the possible constrains on the effective speed of sound of dark energy with the help of maximal known masses of observed neutron stars. In this approach, we have found, that the squared effective speed of sound can not be smaller than $\sim 10^{-2}$ in units of squared speed of light.