Dark Compact Planets

Abstract

We investigate compact objects formed by dark matter admixed with ordinary matter made of neutron star matter and white dwarf material. We consider non-self annihilating dark matter with an equation-of-state given by an interacting Fermi gas. We find new stable solutions, dark compact planets, with Earth-like masses or lower and radii about one meter for weakly interacting dark matter. For the strongly interacting dark matter case, we obtain dark compact planets with Jupiter-like masses or lower and radii of a kilometer. These objects could be formed primordially and accrete white dwarf material subsequently. They could be detected by observing exoplanets with unusually small radii. Moreover, we find that the recently observed 2 ${\rm M}_{\odot}$ pulsars set limits on the amount of dark matter inside neutron stars which is, at most, $10^{-5}{\rm M}_\odot$.