An extended halo around an ancient dwarf galaxy

The Milky Way is surrounded by dozens of ultrafaint ( 107 M☉, consistent with a generalized Navarro–Frenk–White density profile. The extended nature of Tucana II suggests that it may have undergone strong bursty feedback or been the product of an early galactic merger10,11. We demonstrate that spatially extended stellar populations in ultrafaint dwarf galaxies13,14 are observable, opening up the possibility for detailed studies of the stellar halos of relic galaxies. Stars in the Tucana II ultrafaint dwarf galaxy observed out to nine half-light radii reveal the presence of an extended dark matter halo with a total mass of >107 solar masses, consistent with a generalized Navarro–Frenk–White density profile and suggestive of past strong bursty feedback or an early galactic merger.