dark matter



  • Material in the universe which cannot be observed directly. The rotational velocity of stars around the centres of galaxies reveals that they contain more material than can be observed directly. Many types of material, including small planet-sized objects of normal matter as well as concentrations of exotic ‘non-baryonic’ material unknown on Earth, have been proposed as possible solutions to the missing mass problem, whose solution is vital to such large problems as working out whether the universe will continue to expand indefinitely.