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2019-08-17


Dark Matter
 
A
The existence of invisible matter in the universe was first suggested by Dutch astronomer Jan Hendrik Oort in 1932 when he observed that the stars at the outer edge of the galaxy were moving at a speed that was much faster than he had earlier predicted. Since gravitational pull is stronger at the center of a galaxy, the stars at the center should move faster. 

Oork concluded that a material with the gravitational power to cause stars to move at increased velocity was present. The only problem was that it could not be seen. He called this invisible material “dark matter”.  Swiss astronomer Fritz Zwicky made a similar observation just one year later, claiming that hidden masses lay among visible ones, and like Oort, gave this material the name “dark matter”. However, these theories were not accepted by the scientific community because a substance with mass was characterized as being visible.
 
B

In the 1950s and 60s, some astronomers discovered through the use of more advanced technology that the stars at the edge of a galaxy had the same velocity as the stars at its center. A few astronomers believed it was an instance of Newton’s law of universal gravitation being broken. Although Newton’s law was superseded by Einstein’s general theory of relativity, it was still considered an excellent means for approximating the effects of gravity. The scientists then surmised, as did Oort and Zwicky before them, that something invisible was responsible for the gravitational effects they were seeing in the motion of the stars.

With the technological means available to them, they were able to predict just how much hidden matter there was and where it existed. The images produced by the computer were of galaxies that appeared to be caught in a web stretching from one end of the universe to the other. It was a gossamer web of invisible material interwoven with visible matter.
 
C

The scientists set about learning as much as they could about dark matter, which is believed to have formed as the universe cooled after the Big Bang. As the universe began to expand, filaments of dark matter formed a network that cut across the entire universe. The cosmos was not a mere sprinkling of galaxies across vast amounts of empty space; dark matter was apparently a major constituent. Computer-generated models suggest that dark matter makes up approximately 85% of the total mass in the universe.
 
D

Scientists have been trying to map the actual location of this material. The mapping of dark matter is not easy even though scientists are convinced that it exists. Only when sufficient light shines at the right angle can its location be pinpointed—not by sight, but by the distortion of space. Even if the material does not emit or reflect light, it is capable of bending or distorting it. Scientists use a lens that measures the displacement of light due to the warping of space, to produce maps of dark matter.  

A team in Munich, Germany accidentally discovered light traveling toward earth from distant background galaxies. They used it to detect the shape of a dark matter component in a filament located in a supercluster of galaxies about 2.7 billion light years from the earth.
 
E

What was particularly noteworthy is that the filament formed part of an enormous network that connects clusters of galaxies together. In other words, dark matter was like connective tissue binding the bigger structures of the universe together. It may even be the glue that allows the universe to maintain its order. If dark matter did not exist, neither would gravity, and gravity is what holds these structures together. Moreover, galaxies would break up and float away to different parts of the universe, considering the speed at which they move.
 
F
But just what is the composition of dark matter? Is it a type of matter as yet unknown to scientists? Many cosmologists agree that it may be composed of a type of subatomic particle that has not yet been identified. Some astronomers consider massive compact halo objects or MACHOs a possibility. MACHOs are supposed to reside in the halos of galaxies but are virtually undetectable because of their low luminosities. However, there are not enough of these MACHOs to account for the dark matter that exists in just one galaxy, let alone a cluster of galaxies. 

Other astronomers think that WIMPs, or weakly interacting massive particles, are a possibility. WIMPs are a non-standard variety of particle that decays and releases UV photons. The idea of WIMPs would seem to account for the excessive ultraviolet light in the universe, the visible sources of which do not seem to be adequate in producing UV light. The hunt for these unusual particles is an aggressive one. The Large Hadron Collider, which lies underground and crosses the French-Swiss border, is being used to produce WIMPs or other particles that can decay into dark matter. 

The particle has not been found, but scientists are optimistic, considering the elusive Higgs-Boson particle, an elementary particle that appears to explain why some fundamental particles have mass even when the physical system controlling them requires that they have no mass, was discovered in a similar experiment in 2013.