Introduction to physics dark matter:
In cosmology and astronomy, matter that exist due to background radiation and gravitational effects on visible matter incidentally is referred as dark matter and are undetectable by emitted electromagnetic radiation. By the observations of structures larger than galaxies and Big bang cosmology, it is observed that the observable universe’s 23% mass-energy density is reported by dark matter. However, only 4.6% is the other ordinary matter and remaining is the dark energy. According to these, 80% of universe is constituted of dark matter. Fritz Zwicky was the first to assume dark matter in 1934 to report for evidence of missing mass in galaxies’ orbital velocity in clusters. In galaxy evolution and state-of-the-art formation, dark matter plays an important role. Dark matter’s largest part, which is non-intractable by electromagnetic radiation, is not only dark but also transparent.
Image on dark matter in physics
Image on dark matter in physics
Composition of Dark Matter
All dark matter behaves like and is modeled like a perfect fluid. This is an important property of dark matter meaning that there is no internal resistance or viscosity, i.e. without bumping or colliding they move past each other. According to the travelling speed of these particles they are categorize into three categories.
Cold dark matter
Dark matter travelling at classical speed is termed as Cold Dark Matter. This is less than 0.1c. As hot and warm dark matter theories are not viable for galaxy and their cluster formation, cold dark matter area is of greatest interest for research. By the requirement of concordance model, invoking of cold dark matter is necessary to explain the structure of universe. They can be RAMBOs or MACHOs type large objects or WIMPs, axions like particles.
Warm dark matter
Particles travelling at relativistic speed but less than ultra relativistic particles and more than cold dark matter are often termed as warm dark matter. They are less than 0.95c but more than 0.1c.Formation of galaxies from big bang can neither be explained by hot dark matter nor by warm dark matter. That’s because they move too quickly to stay together and form a large scale structures.
Hot dark matter
Particles travelling at ultra-relativistic are termed as hot dark matter. These are velocity approximately over 0.95c. An already existing and known example of hot dark matter is ‘the neutrino’.
Detection of Dark Matter
Currently, there are many experiments running or planned for searching WIMPs to test the theory of dark matter. These experiments are categorized into direct detection and indirect detection experiments.
Direct detection experiments
These experiments are operated in deep underground laboratories so that the background from cosmic rays could be reduced. These experiments use either cryogenic detectors, which operates below 100mk temperature or noble liquid detectors.
Indirect detection experiments
These experiments detect WIMP annihilation. They detect signal containing gamma rays, anti protons or positrons. Even detection of such signal is not enough to conclude evidence of dark matter.
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* Lars Hernquist, Mallinckrodt Professor of Astrophysics at Harvard, gives Carnegie Mellon’s Bennett-McWilliams Lecture in Cosmology. The lecture was held March 15, 2016. www.cmu.edu/cosmology
Bennett-McWilliams Lecture in Cosmology: Next Generation Cosmological Simulations