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

Dark matter is a form of matter that neither emits nor absorbs light. Within physics, this behavior is characterized by dark matter not interacting with electromagnetic radiation, hence making it dark and rendering it undetectable via conventional instruments in physics.[1] Data from galaxy rotation curves indicate that approximately 80% of the mass of a galaxy cannot be seen, forcing researchers to innovate ways that indirectly detect it through dark matter's effects on gravitational fluctuations.[2] As we shall see below, it is useful to differentiate dark matter into "hot" (HDM) and "cold" (CDM) types–some even suggesting a middle-ground of "warm" dark matter (WDM). The terminology refers to the mass of the dark matter particles (which dictates the speed at which they travel): HDM travels faster than CDM because the HDM particles are theorized to be of lower mass.[3]

Role in galaxy formation
Artist's impression of dark matter surrounding the Milky Way. Credit: ESO/L. Calçada

In terms of its application, the distribution of hot dark matter could also help explain how clusters and superclusters of galaxies formed after the Big Bang. Theorists claim that there exist two classes of dark matter: 1) those that "congregate around individual members of a cluster of visible galaxies" and 2) those that encompass "the clusters as a whole." Because cold dark matter possesses a lower velocity, it could be the source of "smaller, galaxy-sized lumps," as shown in the image.[4] Hot dark matter, then, should correspond to the formation of larger mass aggregates that surround whole galaxy clusters. However, data from the cosmic microwave background radiation, as measured by the COBE satellite, is highly uniform, and such high-velocity hot dark matter particles cannot form clumps as small as galaxies beginning from such a smooth initial state, highlighting a discrepancy in what dark matter theory and the actual data are saying. Theoretically, in order to explain relatively small-scale structures in the observable Universe, it is necessary to invoke cold dark matter or WDM. In other words, Hot dark matter being the sole substance in explaining cosmic galaxy formation is no longer viable, placing hot dark matter under the larger umbrella of mixed dark matter (MDM) theory.

Neutrinos

An example of a hot dark matter particle is the neutrino.[5] 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 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 – Model of big-bang cosmology
Modified Newtonian dynamics – Hypothesis proposing a modification of Newton's laws

References

McGaugh, Stacy (2007). "Seeing through Dark Matter". Science. 317 (5838): 607–608. doi:10.1126/science.1144534. JSTOR 20037494. PMID 17673645.
Drake, Nadia (2012). "Dark matter, where art thou?". Science News. 181 (10): 5–6. JSTOR 41697649.
Matt Williams (August 31, 2016). "Dark matter—hot or not?". Retrieved June 2, 2017.
Cowen, R. (1996). "Tracing the Architecture of Dark Matter". Science News. 149 (6): 87. Bibcode:1996SciN..149...87C. doi:10.2307/3979991. JSTOR 3979991.

Hannestad, Steen; Mirizzi, Alessandro; Raffelt, Georg G.; Wong, Yvonne Y. Y. (2010-08-02). "Neutrino and axion hot dark matter bounds after WMAP-7". Journal of Cosmology and Astroparticle Physics. 2010 (8): 001. arXiv:1004.0695. Bibcode:2010JCAP...08..001H. doi:10.1088/1475-7516/2010/08/001. ISSN 1475-7516.

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

vte

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 Primordial black holes


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 globular cluster Dark matter halo Dark radiation Dark star Dwarf galaxy problem Halo mass function Mass dimension one fermions Massive compact halo object Mirror matter Navarro–Frenk–White profile Scalar field dark matter

Search
experiments
Direct
detection

ADMX ANAIS ArDM CDEX CDMS CLEAN CoGeNT COSINE COUPP CRESST CUORE D3 DAMA/LIBRA DAMA/NaI DAMIC DarkSide DARWIN DEAP DM-Ice DMTPC DRIFT EDELWEISS EURECA KIMS LUX LZ MACRO MIMAC NAIAD NEWAGE NEWS-G PandaX PICASSO PICO ROSEBUD SABRE SIMPLE TREX-DM UKDMC WARP XENON XMASS ZEPLIN

Indirect
detection

AMS-02 ANTARES ATIC CALET CAST DAMPE Fermi HAWC HESS IceCube MAGIC MOA OGLE PAMELA VERITAS

Other projects

MultiDark PVLAS

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 Imaginary mass Negative mass UniverseMachine

Physics Encyclopedia

World

Index

Hellenica World - Scientific Library

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