1. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada

Correspondence to: Sergey Mashchenko¹ Correspondence and requests for materials should be addressed to S.M. (syam@physics.mcmaster.ca).

Abstract

The standard cosmological model, now strongly constrained by direct observations of the Universe at early epochs, is very successful in describing the evolution of structure on large and intermediate scales¹. Unfortunately, serious contradictions remain on smaller, galactic scales^{1, 2}. Among the main small-scale problems is a significant and persistent discrepancy between observations of nearby galaxies, which imply that galactic dark matter haloes have a density profile with a flat core^{3, 4, 5, 6}, and the cosmological model, which predicts that the haloes should have divergent density (a cusp) at the centre^{7, 8}. Here we report numerical simulations that show that random bulk motions of gas in small primordial galaxies, of the magnitude expected in these systems, will result in a flattening of the central dark matter cusp on relatively short timescales (10⁸ years). Gas bulk motions in early galaxies are driven by supernova explosions that result from ongoing star formation. Our mechanism is general, and would have operated in all star-forming galaxies at redshifts z 10. Once removed, the cusp cannot be reintroduced during the subsequent mergers involved in the build-up of larger galaxies^{9, 10}. As a consequence, in the present Universe both small and large galaxies would have flat dark matter core density profiles, in agreement with observations.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.