Hot dark matter

Hot dark matter (HDM) is a theoretical form of dark matter which consists of particles that travel with ultrarelativistic velocities.

Dark matter is matter that does not interact with, and therefore 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 cosmic microwave background radiation as measured by the COBE satellite is very smooth and fast moving particles cannot form clumps as small as galaxies beginning from such a smooth initial state. Due to theory,^[1] in order to explain small scale structure in the Universe, it is necessary to invoke cold dark matter (CDM) or warm dark matter (WDM). Hot dark matter as the sole explanation of dark matter is no longer viable,^[1] therefore, it is nowadays considered only as part of a mixed dark matter (MDM) theory.

Neutrinos

An example of a hot dark matter particle 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 theoretically 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.

See also

• Lambda-CDM model
• Modified Newtonian Dynamics

References

Further reading

• Bertone, Gianfranco (2010). Particle Dark Matter: Observations, Models and Searches. Cambridge University Press. p. 762. ISBN 978-0-521-76368-4. 

External links

• Hot dark matter by Berkeley
• Dark Matter

Dark matter
Forms of dark matter	Baryonic dark matter Cold dark matter Hot dark matter Light dark matter Mixed dark matter Warm dark matter Self-interacting dark matter Scalar field dark matter
Hypothetical particles	Axino Axion Dark photon Holeum LSP Minicharged particle Neutralino Sterile neutrino SIMP WIMP
Theories and objects	Cuspy halo problem Dark fluid Dark galaxy Dark matter halo Dark radiation Dark star Dwarf galaxy problem ELKO field Halo mass function Massive compact halo object Mirror matter Navarro–Frenk–White profile Scalar field dark matter
Search experiments	Direct detection ANAIS ArDM ADMX CDEX CDMS CoGeNT COUPP CRESST DAMA/LIBRA DAMA/NaI DarkSide DEAP DMTPC DRIFT EDELWEISS EURECA KIMS LUX LZ PandaX PICO SIMPLE UKDMC WARP XENON ZEPLIN-III Indirect detection AMS-02 ATIC CALET CAST DAMPE IceCube MOA OGLE PAMELA Other projects MultiDark PVLAS SNOLAB
Potential dark galaxies	HE0450-2958 HVC 127-41-330 Smith's Cloud VIRGOHI21
Related	Antimatter Dark energy Exotic matter Galaxy formation and evolution Illustris project