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The stars and dark matter of dwarf galaxies are less concentrated than theories predict.To reconcile cosmological models with observations, Mashchenko et al. used computer simulations to model the effects of expelled material from supernova explosions and stellar winds on the overall properties of dwarf galaxies. Such stellar feedback drives large-scale bulk motions of interstellar gas that change the gravitational potential such that the central matter density of the galaxy is reduced. This effect helps explain many puzzling properties of dwarf galaxies, such as their large dark matter cores, globular cluster distributions, and stellar population gradients. This animation shows the violent and chaotic bulk gas motions (blue) generated by feedback from newly formed star clusters (yellow) near the center of a galaxy (red dot).