Dark Compact Planets

TL;DR

This paper explores the theoretical existence of dark matter-admixed compact objects, called dark compact planets, which could have Earth-like or Jupiter-like masses and very small radii, and discusses their formation, detection, and implications for dark matter in neutron stars.

Contribution

The study introduces the concept of dark compact planets formed by non-self annihilating dark matter with an interacting Fermi gas equation-of-state, expanding the types of stable compact objects.

Findings

Dark compact planets with Earth-like masses and meter-scale radii are possible.

Strongly interacting dark matter can form planets with Jupiter-like masses and kilometer-scale radii.

Constraints on dark matter inside neutron stars are set by observed 2 solar mass pulsars.

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, $10^{-5}{\rm M}_\odot$.