Compact Stars with Dark Energy in General Relativity and Modified Gravity

TL;DR

This paper explores how dark energy, modeled as a fluid or scalar field, influences the structure of neutron and strange stars within general relativity and modified gravity frameworks, considering observational constraints and various dark energy models.

Contribution

It introduces realistic models of dark energy in compact stars and examines their effects under both general relativity and modified gravity, including scalar fields and $R^2$ gravity.

Findings

Dark energy can significantly affect star mass and radius.

Constraints from cosmological observations limit deviations from $$-Cold Dark-Matter model.

Modified gravity and scalar field models alter star properties in specific ways.

Abstract

We investigate realistic models of compact objects, focusing on neutron and strange stars, composed by dense matter and dark energy in the form of a simple fluid or scalar field interacting with matter. For the dark energy component, we use equations of state compatible with cosmological observations. This requirement strongly constrains possible deviations from the simple $\Lambda$-Cold Dark-Matter model with EoS $p_{d}=-\rho_{d}$ at least for small densities of the dark component. But we can propose that the density of dark energy interacting with matter can reach large values in relativistic stars and affects the star parameters such as the mass and radius. Simple models of dark energy are considered. Then we investigated possible effects from modified gravity choosing to study the $R^2$ model combined with dark energy. Finally, the case of dark energy as scalar field non-minimally interacting with gravity is considered.