Ultralight dark matter (ULDM) is known to form self-gravitating bound states through relaxation of the field, through gravity or self-interactions. The canonical example is a boson star, which is self-gravitating and has been studied for decades. In this talk, I will discuss a related but distinct bound state we call a gravitational atom, which is bound by the gravitational potential of some astrophysical body (e.g. a star). Strikingly, the direct capture of ULDM from the background halo to such bound states, boosted by Bose enhancement and gravitational focusing, can be fast enough to give rise to large DM overdensities on astrophysically-relevant timescales. As a result, for strong-enough self-interactions we predict the rapid formation of a solar halo of ULDM around our own Sun in the range of axion masses 10^{-15} eV < m < 10^{-13} eV. This leads to striking modifications of the local density and DM velocity at the position of Earth and near the Sun, including new targets for direct searches on Earth and in space. I will conclude by briefly discussing extensions of these ideas, including gravitational atoms bound to other astrophysical bodies and proposals for signals from other star systems.
Organized by: Catarina Cosme