Missing Matter

Hi Hoof,Dark matter is a catchall term for matter that cannot be seen. It might be argued that a brick orbitting Alpha Centauri at 10AU is dark matter since it does not emit light and the amount of light it reflects is below the level of detection. Bricks are unlikely, but difficult to detect Brown Dwarfs or massive compact halo objects or neutrinos.
Theory suggests that these can only account for some of the dark matter.There are large amounts of 'exotic' matter that does not interact (or only weakly interacts) in an electromagnetic fashion, but still interacts gravitationally. Examples are the theoretical particle the sterile neutrino, the axion or Weakly Interacting Massive Particles (WIMPs). Different cosmology models predict the existence of different types of candidate exotic dark matter. LHC may well discover which flavour of dark matter can actually exist, providing some evidence in support of one model or another.Enough of these particles of non-zero mass travelling at relativistic speeds (or perhaps just very 'hot') can generate significant gravitational fields which in turn can affect the structure of galaxies etc.Edited by Modulous, : No reason given.