cold dark matter

Cold dark matter (CDM) is a hypothetical form of dark matter (DM) and is an element of the Lambda-CDM model. Dark matter is theorized to explain the dynamics of galaxies and galaxy clusters which appear to have more gravity than would be explained by the visible stars and gas. Theories that posit dark matter to be some kind of particle can be classified as cold, warm, or hot, based on the speed of the theorized particles, which affects the distances they would travel unimpeded in the early universe, and would be affected by their mass, i.e., lighter for faster speeds. Cold dark matter is dark matter that is slow-moving, such that a (typical) particle travel-distance less than the diameter of a protogalaxy. Warm dark matter (WDM) and hot dark matter (HDM) are alternate types of theory that posit the particles generally traveling longer distances.