Dark matter explained in Tamil.
Roughly 80 percent of the mass of the universe is made up of material that scientists cannot directly observe. Known as dark matter, this bizarre ingredient does not emit light or energy. So why do scientists think it dominates?

Studies of other galaxies in the 1950s first indicated that the universe contained more matter than seen by the naked eye. Support for dark matter has grown, and although no solid direct evidence of dark matter has been detected, there have been strong possibilities in recent years.

"Motions of the stars tell you how much matter there is," Pieter van Dokkum, a researcher at Yale University, said in a statement. "They don't care what form the matter is, they just tell you that it's there." Van Dokkum led a team that identified the galaxy Dragonfly 44, which is composed almost entirely of dark matter.

The familiar material of the universe, known as baryonic matter, is composed of protons, neutrons, and electrons. Dark matter may be made of baryonic or non-baryonic matter. To hold the elements of the universe together, dark matter must make up approximately 80 percent of its matter. [Image Gallery: Dark Matter Across the Universe]

The missing matter could simply be more challenging to detect, made up of regular, baryonic matter. Potential candidates include dim brown dwarfs, white dwarfs, and neutrino stars. Supermassive black holes could also be part of the difference. But these hard-to-spot objects would have to play a more dominant role than scientists have observed to make up the missing mass, while other elements suggest that dark matter is more exotic.

Most scientists think that dark matter is composed of non-baryonic matter. The lead candidate, WIMPS (weakly interacting massive particles), have ten to a hundred times the mass of a proton, but their weak interactions with "normal" matter make them difficult to detect. Neutralinos, massive hypothetical particles heavier and slower than neutrinos, are the foremost candidate, though they have yet to be spotted.

Sterile neutrinos are another candidate. Neutrinos are particles that don't make up regular matter. A river of neutrinos streams from the sun, but because they rarely interact with normal matter, they pass through the Earth and its inhabitants. There are three known types of neutrinos; a fourth, the sterile neutrino, is proposed as a dark matter candidate. The sterile neutrino would only interact with regular matter through gravity.

"One of the outstanding questions is whether there is a pattern to the fractions that go into each neutrino species," Tyce DeYoung, an associate professor of physics and astronomy at Michigan State University and a collaborator on the IceCube experiment, told Space.com.

The smaller neutral axion and the uncharged photinos are also potential placeholders for dark matter.

According to a statement by the Gran Sasso National Laboratory in Italy (LNGS), "Several astronomical measurements have corroborated the existence of dark matter, leading to a worldwide effort to observe directly dark matter particle interactions with ordinary matter in extremely sensitive detectors, which would confirm its existence and shed light on its properties. However, these interactions are so feeble that they have escaped direct detection up to this point, forcing scientists to build detectors that are more and more sensitive."

A third possibility exists — that the laws of gravity that have thus far successfully described the motion of objects within the solar system require revision.

Source Links:

1. https://home.cern/science/physics/dar...
2. http://blogs.discovermagazine.com/out...
3. http://chandra.harvard.edu/xray_astro...
4. https://phys.org/news/2019-06-heart-l...
5. https://www.eso.org/public/images/eso...
6. http://mentalfloss.com/article/68083/...

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