What is dark matter?
Dark matter accounts for about 85% of the total matter in the universe, and about a quarter of its total energy density. The majority of these substances are considered to be non-bionic in nature, possibly composed of some as-yet-unseen sub-atomic particles.
History of dark matter
Dark Matter is a detailed history of the concept of unintentional matter. When Newton’s theory of gravity appeared to the world in the 1600s, some astronomers had begun to speculate about the existence of dark matter.
Research and experiment
Astronomers researched some objects in the universe that emit little or no light, and found that objects that emit little or no light were detected on their shiny objects like stars and planets. It can be known from the gravitational tug. Thus the idea of dark matter was reinforced in the 1700s, when Pierre-Simon Laplace argued that there could be massive stars whose gravity is so great that even light cannot escape from their surface.
In the 1800s, Urbain Le Verrier and John Couch Adams estimated the speed of Uranus and the presence of Neptune using gravity anomalies. Using these same gravity anomalies, astronomers also detected the presence of dark nebula, which could only be seen by the light emanating from bright objects. Thus it was clear that visible light in the universe can only be seen, that is, we can see any Vastu in the universe only when light comes from it.
Lord Kelvin in 1884 estimated the dispersion velocity of stars orbiting around the center of the galaxy by the “velocity dispersion” of the number of dark bodies in the Milky Way. He also estimated the mass of the galaxy using these measurements. Which he also determined that the stars are different from the mass of the observable. In this way, Lord Kelvin concluded that “many of our stars, perhaps most of them, maybe dark bodies”. Then in 1906, Henry Poincaré used the term Dark Matter to discuss Lord Kelvin’s works in “The Milky Way and Theory of Gases”.
And thus, in 1922 Dutch astronomers Jacobus Kapteyn became the first to suggest the existence of dark matter, using stellar velocities. In 1932 Jan Hendrik Oort also envisaged the existence of dark matter. Hendrik Oort By studying the stellar motions, ie stellar motions, in the galaxy near our Milkey Way galaxy, he found that the mass (mass) in the galactic plane should be greater than what was observed, but this measurement was later determined to be incorrect.
Similarly, in 1933, Swiss astrophysicist Fritz Zwicky, who worked at the California Institute of Technology, studied galaxy clusters and made similar hypotheses. Fritz Zwicky obtained evidence of undiscovered mass with the aid of virial theorem in the Coma Cluster, which he called Dark Matter. Fritz Zwicky estimated its mass (mass) based on the speeds of nearby galaxies, and compared their brightness and their numbers based on galaxies. He estimated that the Cluster had about 400 times more mass.
The gravitational effect of visible galaxies was too small for such fast orbits, thus the mass must be hidden from view. Based on these findings, Zwicky hypothesized that some unseen matter provided mass and associated gravitational attraction to hold the clusters together. Zwicky’s estimates were closed by more than an order of magnitude, mainly due to an obsolete value of Hubble constant. The same calculation today shows a smaller fraction, which uses more values for the luminous mass. However, Zwicky correctly concluded from his calculations that the bulk of this substance was dark matter.
Further indications are that there was no similarity between mass and light ratio, which came from measurements of the galaxy’s rotating curves. In 1939 Horace W. Babcock reported the curve of rotation for the Andromeda nebula (now known as the Andromeda Galaxy), suggesting that the mass-to-light ratio increases radially. He attributed this to the light absorption within the galaxy or to the modified dynamics in the outer parts of the spiral and not to the missing matter that he had exposed. Following the 1939 report of an unexpectedly rapid turn around on the outskirts of the Andromeda galaxy and in 1940, Jan Oort discovered and wrote about the large non-visible halo of NGC 3115.
The work of Vera Rubin, Kent Ford, and Ken Freeman in the 1960s and 1970s provided even stronger evidence of Dark Matter, as well as the use of Galaxy rotation curves. Rubin and Ford worked with a new spectrograph to measure the velocity curve of edge spiral galaxies with greater accuracy. This result was confirmed in 1978. An influential paper presented the results of Rubin and Ford in 1980. He showed that most galaxies should be about six times as dark as the visible mass; Thus, the 1980 Dark Matter apparent need was widely recognized as a major unsolved mystery in astronomy.
At the same time as Rubin and Ford were searching for optical rotation curves, radio astronomers were using new radio telescopes to map the 21-cm line of atomic hydrogen in nearby galaxies. The radial distribution of interstellar atomic hydrogen (HI) often extends to much larger galactic radii than those accessible by optical studies, expanding the sample of rotation curves – and thus the total mass distribution – into a new dynamic regime. The initial mapping of Andromeda with a 300-foot telescope at Green Bank and a 250-foot dish at Jodrell Bank already showed that the HI rotation curve did not predict Keplerian degradation.
As more sensitive receivers became available, Morton Roberts and Robert Whitehurst were able to detect rotational velocities of 30 kpc Andromeda, far ahead of optical measurements. Illustrating the advantage of tracing gas discs in large ready, the image in that paper combines 16 optical data (a cluster of points less than 15 kpc with a single point that exceeds 15 kpc) with HI data at 20 And between 30 kpc, exhibiting the flatness of the outer galaxy rotation curve; The solid curve located at the center is the optical surface density, while the second curve shows the cumulative mass, still linearly increasing in the outermost measurement.
In parallel, the use of interferometric arrays for extragalactic HI spectroscopy was being developed. In 1972, David Rosstad and Seth Shostak published the HI rotation curves of five spirals mapped with an Owens Valley interferometer; The rotation curves of all five were very flat, suggesting very large values of mass-to-light ratio in the outer parts of their extended HIX.
A stream of observations in the 1980s supported the presence of dark matter, including gravitational lensing of background objects by galaxy clusters, the temperature distribution of hot gas in galaxies and clusters, and the pattern of anisoties in cosmic microwave backgrounds. According to consensus among cosmologists, dark matter is primarily not yet a characteristic of subatomic particles. The discovery of this Particle by a variety of means is one of the major efforts in particle physics.
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This Article was Published On: 21 July, 2019 And Last Modified On: 11 April, 2021