Dark matter admixed relativistic stars: Structural properties and tidal Love numbers

TL;DR

This paper investigates how bosonic dark matter influences the structure and tidal deformability of relativistic stars, revealing that dark matter presence leads to more compact stars with lower maximum masses and reduced tidal deformability.

Contribution

It introduces a two-fluid formalism to model dark matter effects on relativistic stars, analyzing their structural properties and tidal Love numbers with a specific dark matter EoS.

Findings

Dark matter reduces maximum stellar mass.

Dark matter leads to smaller, more compact stars.

Tidal deformability remains below the upper bound of 800.

Abstract

We study the impact of bosonic, self-interacting dark matter on structural properties and tidal deformabilities of compact stars. As far as the gravitational theory is concerned, we assume Einstein's gravity in four dimensions with a vanishing cosmological constant. Regarding matter content, we consider a state-of-matter to a linear form of equation-of-state (EoS), while for dark matter we assume a quartic scalar potential, which implies a certain non-linear EoS obtained long time ago. Adopting the two-fluid formalism we integrate the structure equations as well as the Riccati equation for the metric even perturbations imposing appropriate initial conditions at the center of the stars and matching conditions at their surface. We compute the stellar mass and radius, factor of compactness and dimensionless deformability varying several free parameters of the model studied here. Tidal deformability and the corresponding tidal Love number determine the imprint of the underlying EoS within the signals emitted during binary coalescences, and it is expected to be altered due to the presence of dark matter inside the objects. We find that in all cases considered here, the dimensionless deformability of the canonical stellar mass remains lower than the upper bound, $\Lambda_{1.4} < 800$. We also look at the stability of these stars based on the Harrison-Zeldovich-Novikov criterion under various conditions. It is observed that the presence of dark matter implies significantly lower highest stellar mass, and also smaller and more compact stars for a given stellar mass.