2021MNRAS.502.2364B

New data from the Gaia satellite, when combined with accurate photometry from the Pan-STARRS survey, allow us to accurately estimate the properties of the GD-1 stream. Here, we analyse the stellar density variations in the GD-1 stream and show that they cannot be due to known baryonic structures such as giant molecular clouds, globular clusters, or the Milky Way's bar or spiral arms. A joint analysis of the GD-1 and Pal 5 streams instead requires a population of dark substructures with masses ≃10⁷-10⁹\M_☉. We infer a total abundance of dark subhaloes normalized to standard cold dark matter n_sub/n_sub, CDM_ = 0.4 ^+0.3_–0.2 (68 per cent), which corresponds to a mass fraction contained in the subhaloes f_ sub_ = 0.14 ^+0.11_–0.07 per cent, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons.