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:
“Coming about its own business
Till, with a sudden sharp hot stink of fox
It enters the dark hole of the head.
The window is starless still; the clock ticks,
The page is printed.”
—Ted Hughes (b. 1930)
“Of a truth, Knowledge is power, but it is a power reined by scruple, having a conscience of what must be and what may be; whereas Ignorance is a blind giant who, let him but wax unbound, would make it a sport to seize the pillars that hold up the long- wrought fabric of human good, and turn all the places of joy as dark as a buried Babylon.”
—George Eliot [Mary Ann (or Marian)
“Of all human events, perhaps, the publication of a first volume of verses is the most insignificant; but though a matter of no moment to the world, it is still of some concern to the author.”
—Herman Melville (1819–1891)