White dwarfs as a probe of dark energy

TL;DR

This paper explores how dark energy could influence white dwarf structures by analyzing their mass-radius relation and constrains dark energy properties based on observational consistency with known white dwarf characteristics.

Contribution

It introduces a model to study the impact of dark energy with a barotropic equation of state on white dwarf structure and derives constraints on dark energy parameters from astrophysical observations.

Findings

Dark energy affects white dwarf mass-radius relation.

Lower limit on dark energy sound speed: c_s^2  10^{-4}.

No observational evidence for unusual white dwarf structures.

Abstract

We investigate the radial density distribution of the dynamical dark energy inside the white dwarfs (WDs) and its possible impact on their intrinsic structure. The minimally-coupled dark energy with barotropic equation of state which has three free parameters (density, equation of state and effective sound speed) is used. We analyse how such dark energy affects the mass-radius relation for the WDs because of its contribution to the joint gravitational potential of the system. For this we use Chandrasekhar model of the WDs, where model parameters are the parameter of the chemical composition and the relativistic parameter. To evaluate the dark energy distribution inside a WD we solve the conservation equation in the spherical static metric. Obtained distribution is used to find the parameters of dark energy for which the deviation from the Chandrasekhar model mass-radius relation become non-negligible. We conclude also, that the absence of observational evidence for existence of WDs with untypical intrinsic structure (mass-radius relation) gives us lower limit for the value of effective sound speed of dark energy $c_s^2 \gtrsim 10^{-4}$ (in units of speed of light).