Written by: Sakshyam Karna - 26013, Grade IX
Posted on: 01 March, 2023
Unlike other substances in our universe, dark matter is detected by its gravitational pull rather than its luminosity. The universe's matter-energy ratio is made up of 30.1 percent dark matter, 69.4 percent dark energy, and "regular" visible matter (0.5%). The existence of dark matter, also referred to as the "missing mass," was first suggested by Swiss - American astronomer Fritz Zwicky, who found that the mass of all the stars in the Coma cluster of galaxies only made up about 1% of the mass required to prevent the galaxies from escaping the cluster's gravitational pull in 1933. The existence of this missing mass was disputed for many years, but in the 1970s, American astronomers Vera Rubin and W. Kent Ford observed a similar phenomenon that proved its reality: the mass of the visible stars in a typical galaxy is only 10% of the mass necessary to keep those stars orbiting the galaxy's center.In general, the orbital velocity of stars around the galactic center is independent of the distance between them and the galactic center; in fact, orbital velocity either remains constant or slightly rises with distance instead of decreasing as would be predicted. The mass of the galaxy within the orbit of the stars must rise linearly with the stars' separation from the galaxy's center in order to explain this. However, this interior material emits no visible light, hence the term "dark matter."
Since the discovery of dark matter, gravitational lensing—matter acting as a lens by warping space and distorting the passage of background light—has allowed scientists to determine that dark matter predominates in galaxies and clusters of galaxies. The speed and heat of the gas that produces the observed X-rays have also been used to infer the presence of this missing matter in the galaxies and clusters of galaxies' centers. For instance, the drag caused by one galaxy cluster moving through the other has been observed by the Chandra X-ray Observatory in the Bullet cluster, which is made up of two merging galaxy clusters. However, the mass of the clusters is unaffected, proving that dark matter makes up the majority of the mass.
The ratio of matter to energy in the cosmos is 30.6 percent. Just 0.5% of the universe's mass is made up of stars, and only 0.3% of that mass is made up of elements heavier than hydrogen. Dark matter is what remains. There have been proven to be two different types of dark matter. The first type, which makes up around 4.5 percent of the universe, is composed of the well-known baryons (protons, neutrons, and atomic nuclei), which are also responsible for the creation of bright stars and galaxies. It is anticipated that the majority of this baryonic dark matter will be found as gas between and between galaxies. By measuring the number of elements heavier than hydrogen that were formed in the initial few minutes after the big bang happened 13.8 billion years ago, it has been possible to identify this baryonic, or ordinary, component of dark matter.
The remaining 26.1 percent of the universe's mass, known as dark matter, is in an unidentified, non baryonic form. The speed at which galaxies and massive structures made of galaxies coalesced from density fluctuations in the early universe suggests that the non baryonic dark matter is relatively "cold," or "nonrelativistic," meaning that the cores of galaxies and clusters of galaxies are composed of heavy, slow-moving particles. These particles are electromagnetically neutral since there is no light coming from them. Weakly interacting large particles is the name given to the particles as a result of these characteristics (WIMPs). These particles' particular makeup is currently unknown, and the conventional model of particle physics does not predict them. But other potential extensions to the standard model, such supersymmetric theories, predict fictitious elementary particles like axions or neutralinos that might be the undiscovered WIMPs.
Unusual attempts are being made to find and gauge the characteristics of these invisible WIMPs, either by watching their impact in a lab detector or by watching their annihilations after colliding with one another. There is also some expectation that their presence and mass may be inferred from experiments at new particle accelerators such as the large hadron collider.
Source:
https://brainly.com/question/24489670
