Exotic Cores with and without Dark-Matter Admixtures in Compact Stars

Abstract

We parameterize the core of compact spherical star configurations by a mass (mx) and a radius (rx) and study the resulting admissible areas in the total-mass–total-radius plane. The employed fiducial equation-of-state models of the corona at radii r>rx and pressures p≤px with p(r=rx)=px are that of constant sound velocity and a proxy of DYΔ DD-ME2 provided by Buchdahl’s exactly solvable ansatz. The core (r<rx) may contain any type of material, e.g., Standard-Model matter with unspecified equation of state or/and an unspecified Dark-Matter admixture. Employing a toy model for the cool equation of state with first-order phase transition, we also discuss the mass-radius relation of compact stars with an admixture of Dark Matter in a Mirror-World scenario.