Dwarf galaxy forming one billion years after the Big
Bang. The background image shows the large-scale cosmic
context (the panel is approximately 100,000 light years
across); the inset shows the central 2,000 light years
of the dwarf galaxy where powerful feedback from newly
born star clusters drives bulk motions in the gas. Stars
are shown in yellow; colours from violet to blue to
green to white correspond to gas of increasing density.
(Credit: S. Mashchenko, J. Wadsley, and H. M. P.
The findings, published in Science, solve a longstanding
problem of the widely accepted model -- Cold Dark Matter
cosmology -- which suggests there is much more dark matter
in the central regions of galaxies than actual scientific
"This standard model has been hugely successful on the
largest of scales--those above a few million
light-years--but suffers from several persistent
difficulties in predicting the internal properties of
galaxies," says Sergey Mashchenko, research associate in the
Department of Physics & Astronomy at McMaster University.
"One of the most troublesome issues concerns the mysterious
dark matter that dominates the mass of most galaxies."
Supercomputer cosmological simulations prove that indeed,
this problem can be resolved. Researchers modeled the
formation of a dwarf galaxy to illustrate the very violent
processes galaxies suffer at their births, a process in
which dense gas clouds in the galaxy form massive stars,
which, at the ends of their lives, blow up as supernovae.
"These huge explosions push the interstellar gas clouds back
and forth in the centre of the galaxy," says Mashchenko, the
lead author of the study. "Our high-resolution model did
extremely accurate simulations, showing that this 'sloshing'
effect -- similar to water in a bathtub-- kicks most of the
dark matter out of the centre of the galaxy."
Cosmologists have largely discounted the role interstellar
gas has played in the formation of galaxies and this new
research, says Mashchenko, will force scientists to think in
new terms and could lead to a better understanding of dark
The simulations reported in the research paper were carried
out on the Shared Hierarchical Academic Research Computing