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

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. Darkmatter 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 1.3M ⊙ and radii around 500 km. The increasing compactness leads to changes in the fundamental modes of radial oscillations (∼20% 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.