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He estimated the cluster had about 400 times more mass than was visually observable. Zwicky estimated its mass based on the motions of galaxies near its edge and compared that to an estimate based on its brightness and number of galaxies. Zwicky applied the virial theorem to the Coma Cluster and obtained evidence of unseen mass he called Dunkle Materie ('dark matter'). In 1933, Swiss astrophysicist Fritz Zwicky, who studied galaxy clusters while working at the California Institute of Technology, made a similar inference. Oort was studying stellar motions in the local galactic neighborhood and found the mass in the galactic plane must be greater than what was observed, but this measurement was later determined to be erroneous. Fellow Dutchman and radio astronomy pioneer Jan Oort also hypothesized the existence of dark matter in 1932. The first to suggest the existence of dark matter using stellar velocities was Dutch astronomer Jacobus Kapteyn in 1922. In 1906, Henri Poincaré in "The Milky Way and Theory of Gases" used the French term matière obscure ("dark matter") in discussing Kelvin's work. Lord Kelvin thus concluded "many of our stars, perhaps a great majority of them, may be dark bodies". By using these measurements, he estimated the mass of the galaxy, which he determined is different from the mass of visible stars. In a talk given in 1884, Lord Kelvin estimated the number of dark bodies in the Milky Way from the observed velocity dispersion of the stars orbiting around the center of the galaxy. The hypothesis of dark matter has an elaborate history. 4.1.3 Dark matter aggregation and dense dark matter objects.3.9 Sky surveys and baryon acoustic oscillations.3.8 Type Ia supernova distance measurements.These models attempt to account for all observations without invoking supplemental non-baryonic matter. Current models favor a cold dark matter scenario, in which structures emerge by the gradual accumulation of particles.Īlthough the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations which are not well-explained by standard dark matter, argue for various modifications of the standard laws of general relativity, such as modified Newtonian dynamics, tensor–vector–scalar gravity, or entropic gravity.
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Dark matter is classified as "cold", "warm", or "hot" according to its velocity (more precisely, its free streaming length). Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded. The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, in particular, weakly interacting massive particles (WIMPs). Most dark matter is thought to be non-baryonic in nature it may be composed of some as-yet-undiscovered subatomic particles. īecause dark matter has not yet been observed directly, if it exists, it must barely interact with ordinary baryonic matter and radiation, except through gravity.
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Thus, dark matter constitutes 85% of total mass/energy, while dark energy plus dark matter constitute 95% of total mass–energy content. In the standard Lambda-CDM model of cosmology, the total mass–energy of the universe contains 5% ordinary matter and energy, 27% dark matter and 68% of a form of energy known as dark energy. Other lines of evidence include observations in gravitational lensing and in the cosmic microwave background, along with astronomical observations of the observable universe's current structure, the formation and evolution of galaxies, mass location during galactic collisions, and the motion of galaxies within galaxy clusters. Primary evidence for dark matter comes from calculations showing that many galaxies would fly apart, or that they would not have formed or would not move as they do, if they did not contain a large amount of unseen matter.
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Dark matter is called dark because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect or emit electromagnetic radiation, and is therefore difficult to detect. For this reason, most experts think that dark matter is abundant in the universe and that it has had a strong influence on its structure and evolution. Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.