Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows

Fighting the galactic bulgeObservations show most dwarf galaxies to be almost 'bulgeless', consisting of a rotating stellar disc embedded in a massive near-constant-density core halo of cold dark matter. This sits uncomfortably with the predictions of models based on the dominance of cold dark matter, which invariably generate galaxies with dense stellar spheroidal bulges and steep central dark-matter profiles, as low-angular-momentum baryons and dark matter sink to the centre of galaxies through accretion and repeated mergers. Governato et al. report hydrodynamical simulations that resolve this paradox. Strong outflows from supernovae remove low-angular-momentum gas, thereby inhibiting the formation of bulges and decreasing dark-matter density around the centre of the galaxy.