What is mysterious dark matter? The dark matter of the universe is “losing weight,” Russian physicists say.

MOSCOW, December 12 - RIA Novosti. The amount of dark matter in the Universe has decreased by about 2-5%, which may explain discrepancies in the values of some important cosmological parameters during the Big Bang and today, Russian cosmologists say in a paper published in the journal Physical Review D.

“Let’s imagine that dark matter consists of several components, like ordinary matter. And one component consists of unstable particles, whose lifetime is quite long: in the era of hydrogen formation, hundreds of thousands of years after big bang, they still exist in the Universe, but today they have already disappeared, decaying into neutrinos or hypothetical relativistic particles. Then the amount of dark matter in the past and today will be different,” said Dmitry Gorbunov from the Moscow Phystech, whose words are quoted by the university’s press service.

Dark matter is a hypothetical substance that manifests itself exclusively through gravitational interaction with galaxies, introducing distortions into their motion. Dark matter particles do not interact with any species electromagnetic radiation, and therefore cannot be recorded during direct observations. Dark matter accounts for about 26% of the universe's mass, while "ordinary" matter makes up only about 4.8% of its mass—the rest is the equally mysterious dark energy.

Hubble helped scientists uncover the unexpectedly rapid expansion of the UniverseIt turned out that the Universe is now expanding even faster than calculations based on observations of the “echo” of the Big Bang showed. This indicates the existence of a third mysterious “dark” substance - dark radiation or the incompleteness of the theory of relativity.

Observations of the distribution of dark matter in the nearest and farthest corners of the universe, carried out using ground-based telescopes and the Planck probe, recently revealed a strange thing - it turned out that the expansion rate of the Universe, and some properties of the “echo” of the Big Bang in the distant past and today noticeably different. For example, today galaxies are flying apart from each other much faster than it follows from the results of the analysis of the cosmic microwave background radiation.

Gorbunov and his colleagues found possible reason this.

A year ago, one of the authors of the article, academician Igor Tkachev from the Institute nuclear physics RAS in Moscow, formulated the theory of so-called decaying dark matter (DDM), in which, unlike the generally accepted theory of “cold dark matter” (CDM), some or all of its particles are unstable. These particles, as suggested by Tkachev and his associates, should decay quite rarely, but in noticeable quantities, in order to give rise to deviations between the young and modern Universe.

In his new job Tkachev, Gorbunov and their colleague Anton Chudaykin tried to calculate how much dark matter must have decayed, using data collected by Planck and other observatories that studied the cosmic microwave background radiation and the first galaxies of the Universe.

As their calculations showed, the decay of dark matter may indeed explain why the results of observations of this substance using Planck do not correspond to observations of galaxy clusters closest to us.

Interestingly, this requires decay relatively small quantity dark matter - from 2.5 to 5% of it total mass, whose quantity almost does not depend on what fundamental properties the Universe should have. Now, as scientists explain, all this matter has decayed, and the rest of the dark matter, stable in nature, behaves as described by the CDM theory. On the other hand, it is also possible that it continues to decay.

“This means that in today’s Universe there is 5% less dark matter than there was in the era of the formation of the first molecules of hydrogen and helium after the birth of the Universe. We cannot now say how quickly this unstable part decayed, it is possible that dark matter continues to decay and now, although this is a different, much more complex model,” concludes Tkachev.

Dark matter- this is another of the discoveries of humanity made “at the tip of the pen.” No one has ever felt it, it does not radiate electromagnetic waves and does not interact with them. For more than half a century, there has been no experimental evidence of the existence of dark matter; only experimental calculations are provided that supposedly confirm its existence. But on at the moment- this is just a hypothesis of astrophysicists. However, it should be noted that this is one of the most intriguing and very reasonable scientific hypotheses.

It all started at the beginning of the last century: astronomers noticed that the picture of the world that they observed does not fit into the theory of gravity. Theoretically, galaxies, having the calculated mass, rotate faster than they should.

This means that they (galaxies) have a much greater mass than calculations from the observations made suggest. But since they still rotate, then either the theory of gravity is not correct, or this theory does not “work” on objects such as galaxies. Or there is more matter in the Universe than modern instruments can detect. This theory became more popular among scientists, and this intangible hypothetical substance was called dark matter.
From calculations it turns out that the dark matter in galaxies is approximately 10 times more than usual and different matters interact with each other only at the gravitational level, that is, dark matter manifests itself exclusively in the form of mass.
Some scientists suggest that some dark matter- This is an ordinary substance, but it does not emit electromagnetic radiation. Such objects include dark galactic halos, neutron stars and brown dwarfs, as well as other still hypothetical space objects.

If you believe the conclusions of scientists, then ordinary matter (mainly contained in galaxies) is collected
around areas with the densest concentrations of dark matter. On the resulting space
On the map, dark matter is an uneven network of giant filaments, over time
increasing and decreasing in places of galactic clusters.

Dark matter is divided into several classes: hot, warm and cold (this depends on the speed of the particles of which it is composed). This is how hot, warm and cold dark matter is distinguished. It is cold dark matter that is of greatest interest to astronomers, since it can form stable objects, for example, entire dark galaxies.
The dark matter theory also fits into the Big Bang theory. Therefore, scientists assume that 300 thousand years after the explosion, particles of dark matter first began to cluster in huge quantities, and after that, particles of ordinary matter gathered on them by the force of gravity and galaxies were formed.
These surprising findings mean that the mass of ordinary matter is only a few percent of the total mass of the Universe!!!

That is, the world visible to us is only a small part of what the Universe actually consists of. And we can’t even imagine what this huge “something” is.

It is known that dark matter interacts with “luminous” (baryonic) matter, at least in a gravitational manner, and represents a medium with an average cosmological density several times higher than the density of baryons. The latter are captured in gravitational holes of dark matter concentrations. Therefore, although dark matter particles do not interact with light, light is emitted from where the dark matter is. This remarkable property of gravitational instability has made it possible to study the amount, state and distribution of dark matter using observational data from radio to X-rays.

Direct study of the distribution of dark matter in galaxy clusters became possible after highly detailed images were obtained in the 1990s. In this case, images of more distant galaxies projected onto the cluster turn out to be distorted or even split due to the effect of gravitational lensing. Based on the nature of these distortions, it becomes possible to reconstruct the distribution and magnitude of mass within the cluster, regardless of observations of the galaxies in the cluster itself. Thus, the presence of hidden mass and dark matter in galaxy clusters is confirmed by a direct method.

A study published in 2012 of the motions of more than 400 stars located at distances of up to 13,000 light-years from the Sun found no evidence of dark matter in the large volume of space around the Sun. According to theoretical predictions, the average amount of dark matter in the vicinity of the Sun should have been approximately 0.5 kg in volume globe. However, measurements gave a value of 0.00±0.06 kg of dark matter in this volume. This means that attempts to detect dark matter on Earth, for example through rare interactions of dark matter particles with “ordinary” matter, are unlikely to be successful.

Dark matter candidates

Baryonic dark matter

The most natural assumption seems to be that dark matter consists of ordinary, baryonic matter, which for some reason weakly interacts electromagnetically and is therefore undetectable when studying, for example, emission and absorption lines. The composition of dark matter may include many already discovered cosmic objects, such as: dark galactic halos, brown dwarfs and massive planets, compact objects in the final stages of evolution: white dwarfs, neutron stars, black holes. In addition, hypothetical objects such as quark stars, Q stars and preon stars may also be part of baryonic dark matter.

The problems with this approach are manifested in Big Bang cosmology: if all dark matter is represented by baryons, then the ratio of concentrations of light elements after primary nucleosynthesis, observed in the oldest astronomical objects, should be different, sharply different from what is observed. In addition, experiments to search for gravitational lensing of the light of stars in our Galaxy show that a sufficient concentration of large gravitating objects such as planets or black holes is not observed to explain the mass of the halo of our Galaxy, and small objects of sufficient concentration should absorb star light too strongly.

Nonbaryonic dark matter

Theoretical models provide large selection possible candidates for the role of nonbaryonic invisible matter. Let's list some of them.

Light neutrinos

Unlike other candidates, neutrinos have a clear advantage: they are known to exist. Since the number of neutrinos in the Universe is comparable to the number of photons, then, even having a small mass, neutrinos may well determine the dynamics of the Universe. To achieve , where is the so-called critical density, neutrino masses of the order of eV are required, where denotes the number of types of light neutrinos. Experiments carried out to date provide estimates of neutrino masses on the order of eV. Thus, light neutrinos are practically excluded as a candidate for the dominant fraction of dark matter.

Heavy neutrinos

From the data on the Z-boson decay width it follows that the number of generations of weakly interacting particles (including neutrinos) is equal to 3. Thus, heavy neutrinos (at least with a mass less than 45 GeV) are necessarily the so-called. “sterile”, that is, particles that do not interact weakly. Theoretical models predict mass over a very wide range of values (depending on the nature of that neutrino). From the phenomenology for follows a mass range of approximately eV, sterile neutrinos may well constitute a significant part of dark matter.

Supersymmetric particles

Under supersymmetric (SUSY) theories, there is at least one stable particle that is a new candidate for dark matter. It is assumed that this particle (LSP) does not participate in electromagnetic and strong interactions. LSP particles can be photino, gravitino, higgsino (superpartners of the photon, graviton and Higgs boson, respectively), as well as sneutrino, wine, and zino. In most theories, an LSP particle is a combination of the above SUSY particles with a mass of the order of 10 GeV.

Cosmions

Cosmions were introduced into physics to solve the problem of solar neutrinos, which consists in a significant difference in the neutrino flux detected on Earth from the value predicted by the standard model of the Sun. However, this problem has been resolved within the framework of the theory of neutrino oscillations and the Mikheev-Smirnov-Wolfenstein effect, so cosmions are apparently excluded from candidates for the role of dark matter.

Topological defects of space-time

According to modern cosmological concepts, the vacuum energy is determined by a certain locally homogeneous and isotropic scalar field. This field is necessary to describe the so-called phase transitions of the vacuum during the expansion of the Universe, during which a consistent violation of symmetry occurred, leading to the separation of fundamental interactions. A phase transition is a jump in the energy of a vacuum field tending to its ground state (the state with minimum energy at a given temperature). Different regions of space could experience such a transition independently, resulting in the formation of regions with a certain “alignment” of the scalar field, which, expanding, could come into contact with each other. At the meeting points of regions with different orientations, stable topological defects of various configurations could form: point-like particles (in particular, magnetic monopoles), linear extended objects (cosmic strings), two-dimensional membranes (domain walls), three-dimensional defects (textures). All these objects, as a rule, have colossal mass and could make a dominant contribution to dark matter. At the moment (2012), such objects have not been discovered in the Universe.

Classification of dark matter

Depending on the speeds of the particles that presumably make up dark matter, it can be divided into several classes.

Hot dark matter

Composed of particles moving at close to the speed of light - probably neutrinos. These particles have a very small mass, but still not zero, and given the huge number of neutrinos in the Universe (300 particles per 1 cm³), this gives a huge mass. In some models, neutrinos account for 10% of dark matter.

Due to its enormous speed, this matter cannot form stable structures, but it can influence ordinary matter and other types of dark matter.

Warm dark matter

Matter moving at relativistic speeds, but lower than hot dark matter, is called “warm.” The speeds of its particles can range from 0.1c to 0.95c. Some data, in particular temperature fluctuations background microwave radiation give reason to believe that such a form of matter may exist.

There are no candidates yet for the role of components of warm dark matter, but it is possible that sterile neutrinos, which should move slower than the usual three flavors of neutrinos, could be one of them.

Cold dark matter

Dark matter that moves at classical speeds is called “cold.” This type of matter is of the greatest interest, since, unlike warm and hot dark matter, cold matter can form stable formations, and even entire dark galaxies.

While particles suitable for the role components cold dark matter has not been detected. Candidates for the role of cold dark matter are weakly interacting massive particles - WIMPs, such as axions and supersymmetric fermion partners of light bosons - photinos, gravitinos and others.

Mixed dark matter

In popular culture

In the Mass Effect series, dark matter and dark energy in the form of so-called "Element Zero" are necessary for movement at superluminal speeds. Some people, biotics, using dark energy, can control mass effect fields.
In the animated series Futurama, dark matter is used as fuel for spaceship Interplanetary Express company. Matter is born in the form of feces of the alien race “Zubastilons” and is extremely dense in density.

Notes

Literature

Modern Cosmology website, which also contains a selection of materials on dark matter.
G.W.Klapdor-Kleingrothaus, A.Staudt Non-accelerator physics elementary particles. M.: Nauka, Fizmatlit, 1997.

Links

S. M. Bilenky, Neutrino masses, mixing and oscillations, UFN 173 1171-1186 (2003)
V. N. Lukash, E. V. Mikheeva, Dark matter: from initial conditions to the formation of the structure of the Universe, UFN 177 1023-1028 (2007)
DI. Kazakov "Dark Matter", from a series of lectures in the PostScience project (video)
Anatoly Cherepashchuk. “New forms of matter in the Universe, part 1” - Dark mass and dark energy, from the lecture series “ACADEMIA” (video)

Wikimedia Foundation. 2010.

See what “Dark Matter” is in other dictionaries:

DARK MATTER- (TM) unusual matter of our Universe, consisting not of (see), i.e. not of protons, neutrons, mesons, etc., and discovered by the strongest gravitational effect on cosmic objects of ordinary baryonic nature (stars, galaxies, black … …

Dark Matter The Outer Limits: Dark Matters Genre science fiction ... Wikipedia

This term has other meanings, see Dark Star. A dark star is a theoretically predicted type of star that could have existed early in the formation of the Universe, even before... ... Wikipedia

MATTER- objective reality that exists outside and independently of human consciousness and is reflected by it (for example, living and non-living M.). The unity of the world is in its materiality. In physics M. all types of existence (see), which can be in different... ... Big Polytechnic Encyclopedia

To date, the mystery of where the dark matter came from has not been solved. There are theories that suggest that it consists of low-temperature interstellar gas. In this case, the substance cannot produce any radiation. However, there are theories against this idea. They say that the gas is able to heat up, which leads to the fact that they become ordinary “baryonic” substances. This theory is supported by the fact that the mass of gas in a cold state cannot eliminate the deficit that arises.

There are so many questions about dark matter theories that it's worth looking into it a little more.

What is dark matter?

The question of what dark matter is arose about 80 years ago. Back at the beginning of the 20th century. At that time, the Swiss astronomer F. Zwicky came up with the idea that the mass of all galaxies in reality is greater than the mass of all those objects that can be seen with their own gases in a telescope. All the numerous clues hinted that there was something unknown in space that had an impressive mass. It was decided to give the name “dark substance” to this inexplicable substance.

This invisible substance occupies at least a quarter of the entire Universe. The peculiarity of this substance is that its particles interact poorly with each other and with ordinary other substances. This interaction is so weak that scientists cannot even detect it. In fact, there are only signs of influence from particles.

The study of this issue is being carried out by the greatest minds around the world, so even the biggest skeptics in the world believe that it will be possible to catch particles of the substance. The most desirable goal is to do this in a laboratory setting. In the mines on great depth work is underway, such conditions for experiments are necessary to eliminate interference caused by particles of rays from space.

There is a possibility that a lot new information will be possible to obtain thanks to modern accelerators, in particular, with the help of the Large Hadron Collider.

Particles of dark matter have one strange feature - mutual destruction. As a result of such processes, gamma radiation, antiparticles and particles (such as electron and positron) appear. Therefore, astrophysicists are trying to find traces of gamma radiation or antiparticles. For this, various ground and space installations are used.

Evidence for the existence of dark matter

The very first doubts about the correctness of calculations of the mass of the Universe, as already mentioned, were shared by the astronomer from Switzerland F. Zwicky. To begin with, he decided to measure the speed of galaxies from the Coma cluster moving around the center. And the result of his work puzzled him somewhat, because the speed of movement of these galaxies turned out to be higher than he had expected. In addition, he pre-calculated this value. But the results were not the same.

The conclusion was obvious: the real mass of the cluster was much greater than the apparent one. This could be explained by the fact that most of the matter that is in this part of the Universe cannot be seen, and it is also impossible to observe it. This substance exhibits its properties only in the form of mass.

A number of gravitational experiments have confirmed the presence of invisible mass in galaxy clusters. The theory of relativity has some interpretation of this phenomenon. If you follow it, then each mass is capable of deforming space, in addition, like a lens, it bends the direct flow of light rays. The galaxy cluster causes distortion, its influence is so strong that it becomes noticeable. The view of the galaxy that is located directly behind the cluster is most distorted. This distortion is used to calculate how the matter is distributed in this cluster. This is how real mass is measured. It invariably turns out to be several times larger than the mass of visible matter.

Four decades after the work of the pioneer in this area, F. Zwicky, the American astronomer V. Rubin took up this issue. She studied the speed at which matter, which is located at the edges of galaxies, rotates around the center of the galaxy. If we follow Kepler's laws concerning the laws of gravity, then there is a certain relationship between the speed of rotation of galaxies and the distance to the center.

But in reality, measurements showed that the rotation speed did not change with increasing distance to the center. Such data could be explained only in one way - the matter of the galaxy has the same density both in the center and at the edges. But the visible substance had a much greater density in the center and was characterized by sparseness at the edges, and the lack of density could only be explained by the presence of some substance that was not visible to the eye.

To explain the phenomenon, it is necessary that there is almost 10 times more of this invisible matter in galaxies than the matter that we can see. This unknown substance is called “dark matter” or “dark matter”. To date, this phenomenon remains the most interesting mystery for astrophysicists.

There is another argument in favor of evidence of the existence of dark matter. It follows from calculations that describe the process of how galaxies formed. It is believed that this began approximately 300,000 years after the Big Bang occurred. The calculation results say that the attraction between the fragments of matter that appeared during the explosion could not compensate kinetic energy from scattering. That is, the matter could not concentrate in galaxies, but we can see it today.

This inexplicable fact called the galaxy paradox, it was cited as an argument that destroys the Big Bang theory. But you can look at it from the other side. After all, particles of the most ordinary matter could be mixed with particles of dark matter. Then the calculations become correct, and how galaxies were formed in which a lot of dark matter had accumulated, and particles of ordinary matter had already joined them due to gravity. After all, ordinary matter makes up a small fraction of the total mass of the Universe.

Visible matter has a relatively low density compared to dark substance, because it is 20 times denser. Therefore, those 95% of the mass of the Universe that are missing according to scientists’ calculations are dark matter.

However, this led to the conclusion that all visible world, which has been studied far and wide, so familiar and understandable, is only a small addition to what actually makes up.

All galaxies, planets and stars are just a small piece of something that we have no idea about. This is what is exposed, but the real is hidden from us.

A theoretical construct in physics called the Standard Model describes the interactions of all known to science elementary particles. But this is only 5% of the matter existing in the Universe, the remaining 95% has absolutely unknown nature. What is this hypothetical dark matter and how are scientists trying to detect it? Hayk Hakobyan, a MIPT student and employee of the Department of Physics and Astrophysics, talks about this as part of a special project.

The Standard Model of elementary particles, finally confirmed after the discovery of the Higgs boson, describes the fundamental interactions (electroweak and strong) of the ordinary particles we know: leptons, quarks and force carriers (bosons and gluons). However, it turns out that this whole huge complex theory describes only about 5-6% of all matter, while the rest does not fit into this model. Observations of the earliest moments of our Universe show us that approximately 95% of the matter that surrounds us is of a completely unknown nature. In other words, we indirectly see the presence of this hidden matter due to its gravitational influence, but we have not yet been able to capture it directly. This hidden mass phenomenon is codenamed “dark matter.”

Modern science, especially cosmology, works according to the deductive method of Sherlock Holmes

Now the main candidate from the WISP group is the axion, which arises in the theory of the strong interaction and has a very small mass. Such a particle is capable of transforming into a photon-photon pair in high magnetic fields, which gives hints on how one might try to detect it. The ADMX experiment uses large chambers that create a magnetic field of 80,000 gauss (that's 100,000 times more magnetic field Earth). In theory, such a field should stimulate the decay of an axion into a photon-photon pair, which detectors should catch. Despite numerous attempts, it has not yet been possible to detect WIMPs, axions or sterile neutrinos.

Thus, we have traveled through a huge number of different hypotheses seeking to explain the strange presence of the hidden mass, and, having rejected all the impossibilities with the help of observations, we have arrived at several possible hypotheses with which we can already work.

A negative result in science is also a result, since it gives restrictions on various parameters of particles, for example, it eliminates the range of possible masses. From year to year, more and more new observations and experiments in accelerators provide new, more stringent restrictions on the mass and other parameters of dark matter particles. Thus, by throwing out all the impossible options and narrowing the circle of searches, day by day we are becoming closer to understanding what 95% of the matter in our Universe consists of.