Dark Matter-admixed Rotating White Dwarfs as Peculiar Compact Objects

Discoveries of anomalous compact objects challenge our understanding of the standard theory of stellar structures and evolution, so they serve as an excellent laboratory for searching for new physics. Earlier studies on spherically symmetric dark matter (DM)–admixed compact stars could explain a handful of anomalies. In this paper, we investigate the observational signatures of DM-admixed rotating white dwarfs, and make connections to observed peculiar compact objects. We compute the equilibrium structures of DM-admixed rotating white dwarfs using a self-consistent, two-fluid method, with the DM component being a nonrotating degenerate Fermi gas. We find that admixing DM to rotating white dwarfs could: (1) account for some peculiar white dwarfs that do not follow their usual mass–radius relation; (2) allow stable rapid-rotating white dwarfs that are free from thermonuclear runaway to exist, which could explain some soft gamma-ray repeaters/anomalous X-ray pulsars; and (3) produce universal I (moment of inertia)–Love (tidal Love number)–Q (quadrupole moment) relations that span bands above those without DM admixture, thus providing an indirect way of searching for DM in white dwarfs through gravitational-wave detection. To conclude, DM-admixed rotating white dwarfs can account for some peculiar compact objects. Our results suggest a systematic approach to accounting for the unusual compact objects that upcoming surveys could discover.