According to the standard model of cosmology, most galaxies contain a great amount of dark matter. Astrophysicists of the Charles University in Prague postulated that both galaxies dominated by dark matter and galaxies lacking dark matter have to exist. An international team of scientists, also including Charles University, now verified this so-called dual dwarf galaxy theorem with one of the most modern galaxy evolution simulations. The results are in disagreement with observations and challenge the standard model of cosmology. The study will appear in the Journal Astronomy & Astrophysics and is already available online.