The terms dark energy and dark matter are not entirely successful and represent a literal, but not semantic translation from English. In the physical sense, these terms mean only that these substances do not interact with photons, and they could just as well be called invisible or transparent matter and energy.
Dark matter in astronomy and cosmology, as well as in theoretical physics, is a hypothetical form of matter that does not emit or interact with electromagnetic radiation. This property of this form of matter makes its direct observation impossible.
The conclusion about the existence of dark matter is made on the basis of numerous, consistent with each other, but indirect signs of the behavior of astrophysical objects and the gravitational effects they create. Discovery of the nature of dark matter will help solve the problem of hidden mass, which, in particular, lies in the abnormally high speed of rotation of the outer regions of galaxies.
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Dark matter and dark energy are not visible to the eye, but their presence has been proven through observations of the universe. Billions of years ago, our universe was born after a catastrophic Big Bang. As the early universe slowly cooled, life began to develop in it. As a result, stars, galaxies and other visible parts of it were formed. The size of our universe is simply staggering. For example, one Sun is enough to illuminate and heat a million planets like Earth. In this case, the Sun is a medium-sized star, and our galaxy alone consists of 100 billion stars. This number exceeds the number of grains of sand on a small beach. However, this is not all.
As you know, the Universe consists of several billion galaxies, where a variety of matter exists. Is it possible that any of these matters were invisible to the eye. Most likely, since the results of recent studies have shown that we can see only a tenth of the universe. This means that more than 90% of matter is simply not able to be examined by a person even with the use of special equipment. Astronomers call this matter dark.
It is known that dark matter interacts with "luminous" (baryonic), at least in a gravitational manner, and is a medium with an average cosmological density several times higher than the density of baryons. The latter are captured in the gravitational pits of dark matter concentrations. Therefore, although dark matter particles do not interact with light, light is emitted from where there is dark matter. This remarkable property of gravitational instability made it possible to study the amount, state, and distribution of dark matter from observational data from the radio range to X-rays.
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Published in 2012, a study of the motion of more than 400 stars located at distances up to 13,000 light years from the Sun found no evidence of the presence of dark matter in a large volume of space around the Sun. According to the predictions of theories, the average amount of dark matter in the vicinity of the Sun should have been about 0.5 kg in the volume of the Earth. However, measurements gave a value of 0.00 ± 0.06 kg of dark matter in this volume. This means that attempts to register dark matter on Earth, for example, with rare interactions of dark matter particles with "ordinary" matter, can hardly be successful.
According to the observations of the Planck Space Observatory published in March 2013, interpreted taking into account the standard cosmological Lambda-CDM model, the total mass-energy of the observed Universe is 4.9% of ordinary (baryonic) matter, 26.8% of dark matter and 68.3% from dark energy. Thus, the universe is 95.1% composed of dark matter and dark energy.
The proof of the existence of dark matter is its heaviness - the force of gravity, which, like glue, maintains the integrity of the Universe. All parts of the universe are mutually attracted to each other. Thanks to this, scientists were able to calculate the total mass of the visible Universe, as well as indicators of gravitational forces. In the course of calculations, a significant imbalance in these parameters was revealed, which gave reason to believe that there is some invisible matter that has a certain mass and is also subject to gravity.
The study of dark matter In addition, evidence of the existence of dark matter was its gravitational influence on other objects, including the trajectory of motion of stars and galaxies. Many galaxies have been found to rotate faster than expected. According to A. Einstein's theory of gravity, they should fly in different directions. However, something invisible seems to hold them together.
Also, dark matter can affect the path of light propagation. The phenomenon of gravitational lensing was investigated, which consists in the fact that dense objects are able to reflect the light of distant objects, changing the trajectory of light fluxes. This leads to distortion of the image and the appearance of mirages of stars and galaxies. Scientists record these bends of light, but cannot name the nature of this phenomenon.
Dark matter in our universe can exist in the form of massive astronomical halo objects (MAGOs). These include planets, moons, brown and white dwarfs, dust clouds, neutron stars, and black holes. As a rule, they are too small for their light to be detected by humans, however, their existence can be calculated through the gravitational effect on light fluxes. In recent years, astronomers have discovered several types of MAGO objects. They can consist of both ordinary baryonic particles and axins, neutrins, wimpils and supersymmetric dark matter.
Research on dark matter and dark energy
As interest in dark matter continues to grow, new tools are emerging to help gain broader insights into this mysterious phenomenon. For example, the Hubble Space Telescope has provided very valuable information about the size and mass of the visible universe. These data were the first and very important step towards the study of the true amount of dark matter in the universe.
It is important to understand that the structure of the Universe is not random, and with the help of Hubble, you can represent its structure in detail. It is known for certain that galaxies are located in clusters, and these clusters are in super clusters. Superclusters of cosmic bodies are located in a spongy structure with extensive voids. Obviously, the formation of such a structure is due to very specific reasons. X-ray telescopes at the Chandra Observatory are helping to study the huge clouds of hot gas in these clusters. Scientists have found that dark matter must also be present in these areas, otherwise gas will escape from the cluster. In addition, new tools are currently being developed that, in the end, will help to discern this dark side of the universe.
Approaches and methods for studying dark matter particles
At the moment, scientists around the world are trying in every possible way to discover or artificially obtain particles of dark matter in terrestrial conditions, using specially designed super-technological equipment and many different scientific research methods, but so far all works have not been crowned with success.
What the universe is made of
One of the methods involves conducting experiments on high-energy accelerators, commonly known as colliders. Scientists, believing that dark matter particles are 100-1000 times heavier than a proton, assume that they will have to be generated when ordinary particles collide, accelerated to high energies by a collider. The essence of another method is to register dark matter particles that are all around us. The main difficulty in registering these particles is that they exhibit a very weak interaction with ordinary particles, which are inherently transparent for them. And yet, dark matter particles very rarely, but collide with atomic nuclei, and there is a certain hope, sooner or later, to register this phenomenon.
There are other approaches and methods for studying dark matter particles, and which of them will lead to success first, only time will tell, but in any case, the discovery of these new particles will be a major scientific achievement.
Anti-gravity substance
Dark energy is an even more unusual substance than the same dark matter. It does not have the ability to gather into clumps, as a result of which it is evenly distributed absolutely throughout the entire Universe. But its most unusual property at the moment is anti-gravity.
Thanks to modern astronomical methods, it is possible to determine the rate of expansion of the Universe at the present time and to simulate the process of its change earlier in time. As a result, information was obtained that at the moment, as well as in the recent past, our Universe is expanding, while the rate of this process is constantly increasing. That is why the hypothesis about the antigravity of dark energy appeared, since the usual gravitational attraction would have a slowing effect on the process of "recession of galaxies", restraining the expansion rate of the Universe. This phenomenon does not contradict the general theory of relativity, but at the same time, dark energy must have negative pressure - a property that none of the currently known substances possesses.
Candidates for the role of "Dark Energy"
The mass of galaxies in the Abel 2744 cluster is less than 5 percent of its total mass. This gas is so hot that it only glows in the X-ray range (red in this image). The distribution of invisible dark matter (making up about 75 percent of the mass of this cluster) is colored blue.
One of the supposed candidates for the role of dark energy is vacuum, the energy density of which remains unchanged during the expansion of the Universe and thereby confirms the negative pressure of the vacuum. Another putative candidate is "quintessence" - a previously unexplored superweak field that supposedly passes through the entire universe. There are also other possible candidates, but not one of them at the moment has contributed to obtaining an accurate answer to the question: what is dark energy? But it is already clear that dark energy is something completely supernatural, remaining the main mystery of fundamental physics of the 21st century.