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 of new information will be obtained thanks to modern accelerators, in particular, with the help of the Large Hadron Collider.
Dark matter particles 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 substance that is in this part of the Universe cannot be visible, 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 for the kinetic energy from the expansion. 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 it really consists of.
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.
Everything we see around us (stars and galaxies) is no more than 4-5% of the total mass in the Universe!
According to modern cosmological theories, our Universe consists of only 5% of ordinary, so-called baryonic matter, which forms all observable objects; 25% dark matter detected due to gravity; and dark energy, making up as much as 70% of the total.
The terms dark energy and dark matter are not entirely successful and represent a literal, but not semantic, translation from English.
In a physical sense, these terms only imply that these substances do not interact with photons, and they could just as easily be called invisible or transparent matter and energy.
Many modern scientists are convinced that research aimed at studying dark energy and matter will likely help answer the global question: what awaits our Universe in the future?
Clumps the size of a galaxy
Dark matter is a substance consisting, most likely, of new particles, still unknown in terrestrial conditions, and possessing properties inherent in ordinary matter itself. For example, it is also capable, like ordinary substances, of gathering into clumps and participating in gravitational interactions. But the size of these so-called clumps can exceed an entire galaxy or even a cluster of galaxies.
Approaches and methods for studying dark matter particles
On this moment Scientists all over the world are trying in every possible way to discover or artificially obtain particles of dark matter under terrestrial conditions, using specially designed ultra-technological equipment and many different research methods, but so far all their efforts have not been crowned with success.
One method involves conducting experiments at 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 in the collision of ordinary particles accelerated to high energies through a collider. The essence of another method is to register dark matter particles found all around us. The main difficulty in registering these particles is that they exhibit very weak interaction with ordinary particles, which are inherently transparent to them. And yet, dark matter particles very rarely collide with atomic nuclei, and there is some hope of registering this phenomenon sooner or later.
There are other approaches and methods for studying dark matter particles, and only time will tell which one will be the first to succeed, but in any case, the discovery of these new particles will be a major scientific achievement.
Substance with anti-gravity
Dark energy is an even more unusual substance than dark matter. It does not have the ability to gather into clumps, as a result of which it is evenly distributed throughout the entire Universe. But its most unusual property at the moment is antigravity.
The nature of dark matter and black holes
Thanks to modern astronomical methods, it is possible to determine the rate of expansion of the Universe at the present time and simulate the process of its change earlier in time. As a result of this, information was obtained that at the moment, as well as in the recent past, our Universe is expanding, and the pace of this process is constantly increasing. That is why the hypothesis about the antigravity of dark energy arose, since ordinary gravitational attraction would have a slowing effect on the process of “galaxy recession”, restraining the expansion rate of the Universe. This phenomenon does not contradict general theory relativity, but dark energy must have negative pressure - a property that no currently known substance has.
Candidates for the role of "Dark Energy"
The mass of the galaxies in the Abel 2744 cluster is less than 5 percent of its total mass. This gas is so hot that it only shines in X-ray range(red color in this image). The distribution of invisible dark matter (which makes up about 75 percent of the cluster's mass) 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 the “quintessence” - a previously unknown ultra-weak field that supposedly passes through the entire Universe. There are also other possible candidates, but not one of them has so far contributed to obtaining an exact 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.
A theoretical construct in physics called 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% is of a completely 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, however, it has not yet been possible to catch her directly. This hidden mass phenomenon is codenamed “dark matter.”
Modern science, especially cosmology, works according to deductive method 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 turning 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.
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 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 suggest that 300 thousand years after the explosion, first in a huge number Particles of dark matter began to cluster together, and after that, by the force of gravity, particles of ordinary matter gathered on them 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.
Plays a decisive role in the development of the Universe. However, little is known about this strange substance yet. Professor Matthias Bartelmann - Heidelberg Institute for Theoretical Astrophysics - explains how dark matter research was carried out, answering a number of questions from journalists.
and how does it arise?
I have no idea! No one yet. It probably consists of heavy elementary particles. But no one knows if these are really particles. In any case, they are very different from everything we knew before.
Is it like discovering a whole new species of animal?
Yes, that's right, that's a good comparison.
Who discovered dark matter and when?
In 1933, Fritz Zwicky considered the motion of galaxies in galaxy clusters, which depends on the total mass of the cluster. The researcher noticed that the galaxies, given their calculated mass, move very quickly. This was the first hint of dark matter. No known matter could explain why stars in galaxies stick together: they must fly apart due to their high speed of rotation.
Gravitational lens Photo: Wissensschreiber
What other evidence is there?
A pretty good proof is the gravitational lens effect. Distant galaxies appear distorted to us because light rays are deflected from matter along their path. It's like looking through fluted glass. And the effect is stronger than it would be if only visible matter existed.
What does dark matter look like?
It cannot be seen, since there is no interaction between dark matter and electromagnetic radiation. This means that it does not reflect light and does not emit any radiation.
How do you study dark matter then? What instruments are needed for research?
We do not study dark matter specifically, but only its manifestations, for example, the gravitational lens effect. I'm a theorist. Actually, I just need my computer, a pen and a piece of paper. But I also use data from large telescopes in Hawaii and Chile.
Is it possible to depict dark matter?
Yes, you can create a kind of map of its distribution. Just like the elevation lines show on geographical map The contours of the mountain can be seen here by the density of the lines, where there is especially a lot of dark matter.
When did she appear?
Dark matter arose either directly from Big Bang, or 10,000-100,000 years later. But we are still studying this.
How much dark matter exists?
No one can say this for sure. But based on latest research, we believe that there is approximately seven to eight times more dark matter in the Universe than visible matter.
Computer modeling shows the spread of dark matter in the form of a web, and we see its accumulation in the brightest areas
Photo: Volker Springel
Is there a relationship between dark energy and dark matter?
Probably not. Dark energy powers the accelerated expansion of the Universe, while dark matter holds galaxies together.
Where did she come from?
Dark matter is probably everywhere, but it is not distributed evenly - just like visible matter, it forms clumps.
What does dark matter mean for us and our worldview?
For Everyday life it doesn't matter. But in astrophysics it is very important, as it plays a decisive role in the development of the Universe.
What is our Universe made of? 4.9% - visible matter, 26.8% dark matter, 68.3% - dark energy Photo: Wissensschreiber
What will it cause in the future?
Probably nothing more. Previously, it was very important for the development of the Universe. Today it only continues to hold individual galaxies together. And as the Universe continues to expand, it becomes increasingly difficult for new dark matter structures to emerge.
Will it be possible in the future to directly image dark matter using instruments?
Yes it is possible. For example, it is possible to measure vibrations that occur when dark matter particles collide with atoms in a crystal. The same thing happens in a particle accelerator: if elementary particles, seemingly for no reason flying in an unexpected direction, then an unknown particle may be to blame. Then this would be further evidence of the existence of dark matter. Imagine: you are standing on a football field and there is a ball in front of you. He suddenly flies away without any apparent reason. Something invisible must have hit him.
What interests you most about your work?
I am attracted by the assumption that visible matter is only a small part of the whole, and we have no idea of the remainder.
Thank you for taking the time. We hope that you will learn even more about dark matter soon!
