How supernova feedback turns dark matter cusps into cores

We propose and successfully test against new cosmological simulations a novel analytical description of the physical processes associated with the origin of cored dark matter density profiles. In the simulations, the potential in the central kiloparsec changes on sub-dynamical timescales over the redshift interval 4> z> 2 as repeated, energetic feedback generates large underdense bubbles of expanding gas from centrally-concentrated bursts of star formation. The model demonstrates how fluctuations in the central potential irreversibly transfer energy into collisionless particles, thus generating a dark matter core. A supply of gas undergoing collapse and rapid expansion is therefore the essential ingredient. The framework, based on a novel impulsive approximation, breaks with the reliance on adiabatic approximations which are inappropriate in the rapidly-changing limit. It shows that both outflows and galactic foun-tains can give rise to cusp-flattening, even when only a few per cent of the baryons form stars. Dwarf galaxies maintain their core to the present time. The model suggests that constant den-sity dark matter cores will be generated in systems of a wide mass range if central starbursts or AGN phases are sufficiently frequent and energetic. 1

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