Effects of light-mass fermionic dark matter on the equilibrium and stability of white dwarfs

Abstract: White dwarfs (WDs) can be used as laboratories to test strong gravity and high-density regimes, once their equation of state is not so uncertain as the one of neutron stars. This makes them also a useful tool to constrain dark-matter models. In this work, we study dark matter white dwarfs (DMWD) composed of white dwarf matter admixed with fermionic dark matter in a two-fluid general relativistic framework. Dark matter particles are considered to have masses between $0.1-10$ GeV. The equilibrium configurations and stability are derived, showing that the DMWD can be more compact, with masses around 1.3 $M\odot$ and radii around 500 km. The increasing compactness leads to changes in the fundamental modes of radial oscillations ($\sim20\%$ for 0.1 GeV DM), which produce detectable shifts in GW frequencies. The interplay between dark matter and normal matter thus provides a compelling avenue for interpreting deviations in observed WD properties and for placing constraints on DM characteristics through astrophysical observations.