Detecting dark matter substructures around the Milky Way with Gaia

Cold dark matter (CDM) theory, a pillar of modern cosmology and astrophysics, predicts the existence of a large number of starless dark matter haloes surrounding the Milky Way (MW). However, clear observational evidence of these 'dark' substructures remains elusive. Here, we present a detection method based on the small, but detectable, velocity changes that an orbiting substructure imposes on the stars in the MW disc. Using high-resolution numerical simulations we estimate that the new space telescope Gaia should detect the kinematic signatures of a few starless substructures provided the CDM paradigm holds. Such a measurement will provide unprecedented constraints on the primordial matter power spectrum at low-mass scales and potentially presents a new avenue to explore the particle physics properties of dark matter.