How supernova feedback turns dark matter cusps into cores
(14 votes over all institutions)
We propose and successfully test a novel physical model explaining the origin of cored dark matter density profiles, motivated by recent numerical simulations of dwarf galaxies. In the simulations, the potential in the central kiloparsec repeatedly fluctuates on sub-dynamical timescales over the redshift interval 4>z>2 because energetic feedback generates large underdense bubbles from recurrent, centrally-concentrated bursts of star formation. These fluctuations are shown to be responsible for generating a core. Analytic models are presented which describe how particles orbiting in such rapidly fluctuating gravitational potentials gain energy. We proceed from first principles, breaking with a historical reliance on adiabatic approximations which are inappropriate in the rapidly-changing limit. In the new picture, outflows and galactic fountains can both give rise to cusp-flattening. Concentrations of baryons undergoing cycles of rapid expansion and recollapse are the essential ingredient. Constant density dark matter cores should therefore be generated in systems of a wide mass range if central starbursts or AGN phases are sufficiently frequent and energetic.
