  Fluid and ultralight bosonic dark matter can interact through gravity to form
stable fermion-boson stars, which are static and regular mixed solutions of the
Einstein-Euler-(complex, massive) Klein-Gordon system. In this work we study
the dynamical formation via gravitational cooling of a spherical mixed
white-dwarf--boson star, whose properties depend on the boson particle mass and
the mass of the boson star. Due to the accretion of bosonic dark matter, the
white dwarf migrates to a denser and more compact object with a boson star
core, thus modifying its gravitational redshift and altering the
electromagnetic radiation emitted from the photosphere. We discuss the
implications of the changes in the gravitational redshift that in principle
could be produced by any type of dark matter and that might lead to small
discrepancies in the estimation of masses and radii derived from white dwarf
observations.
