Formation of ultralight dark matter solar halos

This short contribution summarizes some recent results on the formation of ultra-light dark matter halos around the Sun and other massive astrophysical objects. These halos, resembling gravitational atoms, are formed quite generically via the capture of light scalar dark matter, mediated by its (weak) self-interactions. The capture process is effective whenever the dark matter waves in the galactic halo are gravitationally focused by an external gravitational potential. One of our most striking results is that for a dark matter boson with mass of order 10⁻¹⁴ eV, a halo around the Sun can form on a timescale comparable to the lifetime of the Solar System, with a density at the position of the Earth O(10⁴) times larger than that predicted in the standard galactic halo model. If the self-interactions are attractive, the halo collapses when its density is large, and this is likely to be associated with the emission of relativistic bosons, a `Bosenova'.