Hot dark matter is a hypothetical form of dark matter which consists of particles that travel with ultrarelativistic velocities. The best candidate for the identity of hot dark matter is the neutrino. Neutrinos have very small masses, and do not take part in two of the four fundamental forces, the electromagnetic interaction and the strong interaction. They do interact by the weak interaction, and gravity, but due to the feeble strength of these forces, they are difficult to detect. A number of projects, such as the Super-Kamiokande neutrino observatory, in Gifu, Japan are currently studying these neutrinos.
Dark matter is matter that cannot be detected by electromagnetic radiation, hence dark. It is postulated to exist to explain how clusters and superclusters of galaxies formed after the big bang. Data from galaxy rotation curves indicate that around 90% of the mass of a galaxy cannot be seen. It can only be detected by its gravitational effect.
Hot dark matter cannot explain how individual galaxies formed from the big bang. The microwave background radiation as measured by the COBE satellite is very smooth and fast moving particles cannot clump together on this small scale from such a smooth initial clumping. To explain small scale structure in the Universe it is necessary to invoke cold or warm dark matter. Hot dark matter therefore is nowadays always discussed as part of a mixed dark matter theory.
Famous quotes containing the words hot, dark and/or matter:
“As a bathtub lined with white porcelain,
When the hot water gives out or goes tepid,
So is the slow cooling of our chivalrous passion,
O my much praised but-not-altogether-satisfactory lady.”
—Ezra Pound (1885–1972)
“Why are a lady’s thighs always cool? That is, said the monk, due to three causes for which a place is always naturally cool: primo, because water runs all the way down it; secondo, because it is in a shady, dark and obscure place, where the sun never shines; and thirdly, because it is continually fanned by the winds from the breezy hole.”
—François Rabelais (1494–1553)
“It is not so much that women have a different point of view in politics as that they give a different emphasis. And this is vastly important, for politics is so largely a matter of emphasis.”
—Crystal Eastman (1881–1928)