Mysteries of dark matter. Almanac "Day after day": Science. Culture. Education Mysteries of dark matter
Since cosmology is based on the theory of relativity, then all experiments to test its truth contribute to the justification of cosmology. However, having the theory of relativity as its basis, cosmology cannot be reduced to it and, thus, has its own observational base.
Until the beginning of the 1990s, the observational base of cosmology developed within the framework traditional for all astronomy. More and more large telescopes were put into operation, the wave range of observations expanded. For a long time, only galaxies and related phenomena, such as quasars, remained the subject of research. A qualitatively new era in the development of cosmology began in 1992 with the discovery of the so-called relic radiation (appeared, as is assumed at the time of the "big bang"), which contains information about many parameters and processes in the Universe. The value of the data obtained in the study of the CMB is also of great importance because it carries information about a very early stage of the expansion of the Universe, when no galaxies yet existed.
Classical cosmology, as it existed at the time of Einstein and Friedmann, allowed for any value of the density of the universe, both above and below the critical value. It is not by chance that the density value is called critical. Only at this (critical) value, the spatial curvature of the Universe is equal to zero and its main parameter - the baryon, that is, what the substance consists of, turns out to be independent of time. The achievements in the study of the Universe of the last decade include, first of all, a change in ideas about the density of the Universe: data have been obtained that the total density of the Universe is equal to a critical value with a high accuracy.
This did not come as a surprise - most theorists have considered it as the most probable since the early 1980s, when the now generally accepted concept of cosmological inflation was proposed - a model for a very rapid expansion of the Universe at an early stage of its evolution.
Everyone has experienced inflation in the economy, and few can say that this is a positive phenomenon. With cosmological inflation, everything is the opposite - it successfully solved almost all problems of classical cosmology and significantly reduced the relevance of the remaining two or three.
The fact that ordinary matter has practically no effect on the dynamics of the expansion of the Universe is a long and firmly established fact. Back in the mid-1970s, the study of processes in the expanding Universe - mainly the processes of formation of nuclei of deuterium, lithium, helium isotopes with atomic weights of 3 and 4 - showed that the number of nuclei formed depends on the total number of baryons.
Thus, the final point in solving the problem of dark matter interacting with baryons only gravitationally was put by recent studies of cosmic microwave background radiation, which determined the density of dark matter with high accuracy. However, the question of its physical nature still remains open, since not a single type of such particles has been experimentally registered so far.
The second problem is the very physical nature of the cosmological constant: is it equivalent to the one introduced by Einstein, or is it something else. The dominance of the cosmological constant in the Universe radically affects its evolution - such a Universe expands with acceleration and has a greater age (with all the ensuing consequences) than the Universe in which this constant is equal to zero.
From a theoretical point of view, the presence of a cosmological constant does not yet have serious or, at least, generally accepted justifications. Rather, it can be called an "extra" value, but our ideas about the Universe would not change dramatically if it turned out that in fact the cosmological constant is equal to zero (or so small that it cannot be determined with the current level of technology). However, cosmology, like all natural sciences, is built on the foundation of observational data, and these data testify in favor of its significant size.
We live in a world whose expansion dynamics is controlled by an unknown form of matter. The only thing we know for certain about it is the fact of its existence and the equation of its state of a vacuum-like type. We do not know if the equation of state for dark energy changes with time, and if so, how. This means that all arguments about the future of the Universe are essentially speculative and based on the aesthetic views of their authors.
According to the materials of the journal "Science and Life"
The original article is on the site NewsInfo
to the magazine "Man Without Borders"
Sooner or later our world will cease to exist. Just as it once appeared from a single particle smaller than an atom. Scientists have no doubts about this for a long time. However, if earlier the theory was dominant, according to which the death of the Universe will occur as a result of its rapidly accelerating expansion and, as a result, inevitable “thermal death”, then with the discovery of dark matter this opinion has changed.
DARK FORCES OF THE UNIVERSE
Experts say that the entire vast space can die as a result of its collapse, being sucked into some kind of giant black hole, which is part of the mysterious "dark matter".
In the cold depths of space, two irreconcilable forces have been at war since the creation of the world - dark energy and dark matter. If the first ensures the expansion of the Universe, then the second, on the contrary, seeks to draw it into itself, to compress it to non-existence. This confrontation is going on with varying success. The victory of one of the forces over the other, the violation of the cosmic balance is equally disastrous for all that exists.
Even Einstein suggested that there is much more matter in space than we can see. In the history of science, there were situations when the motion of celestial bodies did not obey the laws of celestial mechanics. As a rule, this mysterious deviation from the trajectory was explained by the existence of an unknown material body (or several bodies). This is how the planet Neptune and the star Sirius B were discovered.
SPACE STRIPS
In 1922, astronomers James Jime and Jacobus Kaptein investigated the movement of stars in our Galaxy and concluded that most of the matter in the Galaxy is invisible; in these works, the term “dark matter” (eng. dark matter) first appeared, but it does not quite correspond to the current meaning of this concept.
Astronomers have long known the phenomenon of the accelerating expansion of the universe. Observing the removal of galaxies from each other, they found that this speed is increasing. The energy that pushes the cosmos in all directions, like air in a balloon, has been called "dark". This energy pushes the galaxies apart, it acts against the force of gravity.
But, as it turned out, her powers are not unlimited. There is also a kind of cosmic "glue" that keeps galaxies from spreading. And the mass of this "glue" significantly exceeds the mass of the visible Universe. This huge force of unknown origin has been called dark matter. Despite the threatening name, the latter is not an absolute evil. It's all about the delicate balance of cosmic forces on which the existence of our seemingly unshakable world rests.
The conclusion about the existence of mysterious matter, which is not visible, is not recorded by any of the devices, but whose existence can be considered proven, was made on the basis of a violation of the gravitational laws of the Universe. At least as we know them. It has been observed that stars in spiral galaxies like ours have a fairly high rotation speed and by all laws, with such a fast movement, they should simply fly out into intergalactic space under the action of centrifugal force, but they do not. They are held by some strong gravitational force, which is not registered or captured by any means known to modern science. This got scientists thinking.
ETERNAL FIGHT
If it were not for these elusive, but exceeding the strength of gravity of all visible space objects, dark "bonds", then after some long time the rate of expansion of the Universe under the influence of dark energy would approach the limit at which the space-time continuum would break. Space will annihilate and the universe will cease to exist. However, this is not happening yet.
Astrophysicists have found that about 7 billion years ago, gravity (of which dark matter is the predominant part) and dark energy were in balance. But the Universe expanded, the density decreased, the strength of dark energy increased. Since then, it has dominated our universe. Now scientists are trying to figure out if this process will ever end.
To date, it is already known that the Universe consists of only 4.9% of ordinary matter - baryonic matter, of which our world consists. Most (74%) of the entire universe is the mysterious dark energy, and 26.8% of the mass in the universe is defying physical laws, hard to detect particles called dark matter.
So far, in the irreconcilable eternal struggle between dark matter and dark energy, the latter is winning. They look like two wrestlers in different weight classes. But that doesn't mean the fight is over. The galaxies will continue to scatter. But how long will this process take? According to the latest hypothesis, dark matter is just one of the manifestations of black hole physics.
BLACK HOLES ARE CLOUDS OF DARK MATTER?
Black holes are the most massive and powerful objects in the universe known to us. They bend space-time so strongly that even light cannot leave their limits. Therefore, just like dark matter, we cannot see them. Black holes are a kind of centers of attraction for vast expanses of space. It can be assumed that this is a structured dark matter. A prime example of this is the supermassive black holes that live in the center of galaxies. Looking at the center of, for example, our Galaxy, we see how the stars around it are accelerating.
Ann Martin of Cornell University notes that the only thing that can explain this acceleration is a supermassive black hole. We can judge the existence of dark matter, as well as black holes, only on the basis of their interaction with surrounding objects. Therefore, we observe its effects in the movement of galaxies and stars, but we do not see it directly; it does not emit or absorb light. It is logical to assume that black holes are just clumps of dark matter.
Can one of the giant black holes, which will eventually swallow not only the surrounding space, but also its less powerful "perforated" relatives, swallow the entire Universe? The question about this remains open. According to scientists, if this happens, then not earlier than in 22 billion years. So enough for our lifetime. In the meantime, the surrounding world continues its voyage between Scylla of dark energy and Charybdis of dark matter. The fate of the universe will depend on the outcome of the struggle between these two dominant forces in space.
TESLA'S PROPHECY
There is, however, an alternative view of the problem of dark matter. Certain parallels can be found between the mysterious substance and Nikola Tesla's theory of the universal ether. According to Einstein, the ether is not a real category, but exists as a result of erroneous scientific views. For Tesla, the ether is reality.
A few years ago, at a street sale in New York City, an antique lover bought himself a worn fire helmet. Inside it, under the lining, lay an old notebook. The notebook was thin, with a burnt cover and smelled of mildew. The sheets, yellowed by time, were covered in time-faded ink. As it turned out, the manuscript belonged to the famous inventor Nikola Tesla, who lived and worked in the United States. The entry explains the theory of the aether, in which one can find undoubted indications of the elusive dark matter discovered decades after his death.
“What is aether, and why is it so difficult to detect? - the inventor writes in the manuscript. - I thought about this question for a long time and here are the conclusions I came to. It is known that the denser the substance, the higher the speed of propagation of waves in it. Comparing the speed of sound in air with the speed of light, I came to the conclusion that the density of the ether is several thousand times greater than the density of air. But the ether is electrically neutral and therefore it interacts very weakly with our material world, moreover, the density of the matter of the material world is negligible compared to the density of the ether.”
According to the scientist, it is not the ether that is incorporeal - it is our material world that is incorporeal for the ether. Thus, he offers a much more positive view of dark matter, seeing in it some kind of primary substance, the cradle of the universe. But not only. According to Tesla, with a skillful approach, it is possible to obtain inexhaustible sources of energy from the dark matter of the ether, penetrate into parallel worlds, and even establish contacts with intelligent inhabitants of other galaxies. “I think that stars, planets and our entire world arose from the ether, when, for some reason, part of it became less dense. Compressing our world from all sides, the ether tries to return to its original state, and the internal electric charge in the substance of the material world prevents this. Over time, having lost the internal electric charge, our world will be compressed by ether and turn into ether. The ether has come out of the ether and will leave,” Tesla said.
Maria Saprykina
MYSTERY OF DARK MATTER
Invisible matter, i.e. not emitting or absorbing light, astrophysicists call it dark and detect it by the gravity it creates. It is present everywhere - from galactic scales to superclusters of galaxies. By mass, it is much larger than visible matter, but what it actually is is a mystery. Probably, these are still undiscovered elementary particles or low-mass black holes and hypothetical wormholes. This was told in his English article by a member of the Astrospace Center of the Physical Institute. P.N. Lebedev Russian Academy of Sciences (Moscow) and the International Academy. Niels Bora (Copenhagen, Denmark), Corresponding Member of the Russian Academy of Sciences Igor Novikov. The translation was made by RAS Corresponding Member Viktor Abalakin and published in the Earth and Universe journal.
So, the nature of dark matter is one of the main mysteries of modern cosmology. The discovery and study of this phenomenon has a rather long history. For over 85 years, experts have been passionate about this topic. Now this problem is the main one in all astrophysics.
Even 30 and even 20 years ago, astronomers believed that the mass of dark matter that prevails in the Universe determines its dynamics and the curvature of three-dimensional space. But today we know much more. Observation, within the limits of temperature measurements, of anisotropy in the cosmic microwave background radiation (and it appeared immediately after the birth of the Universe and carries important information about its evolution), data on the degree of distribution of helium and other light elements and the formation of the structure of the Universe indicate: ordinary matter (baryonic - baryonic (heavy) elementary particles with a mass no less than that of protons participate in all fundamental interactions)) is responsible for approximately 4% of the material content of the cosmos. It turns out that stars, planets, gas, dust and we ourselves consist of it, and the remaining 96% is the “dark” sector with approximately 23% dark matter and approximately 73% dark energy. It is known that the matter under consideration causes the effect of gravitational attraction, like ordinary matter, and dark energy, on the contrary, causes gravitational repulsion. The latter really prevails in the Universe, although specialists do not yet know anything about its physical nature.
Dark matter exerts a gravitational influence on the propagation of light from distant sources (the so-called gravitational lensing). An important part of the information also comes from the analysis of the cosmic microwave background radiation and the process of formation of the structure of the Universe from small initial inhomogeneities. But it is precisely the gravitational force of dark matter that interests us is necessary for the formation of galactic clusters and galaxies. Most cosmologists, Novikov states, are developing the idea of a type of dark matter called cold. Many of them are convinced that it consists of particles formed in the early, hot period of the evolution of the Universe, but still existing in our time. The list of elements that can be included in them is very extensive: these are mainly hypothetical particles - say, axions or supersymmetric relics. Experiments have now been launched on their direct and indirect search. As a result, it is quite possible to find dark matter directly, but, according to the author of the article, its physical nature remains a mystery.
Meanwhile, in addition to particles that are still unknown to science and of interest to physicists, there are other objects that dark matter can consist of. Some of them are amazing in themselves - and, by the way, are no less important for the development of science: these are relativistic dark bodies (primordial black holes and wormholes).
The hypothesis of the existence of primordial black holes also has a very long history. Thanks to the research conducted by Russian scientists Academician Yakov Zeldovich and Igor Novikov in 1961, and in 1971 by the English theoretical physicist Stephen Hawking, we can conclude that in the early stages in the Universe (about 13 billion years ago) there were tiny black holes, their masses could be less than those of stars. Calculations show that those whose initial masses were less than a billion tons have by now completely lost their energy due to quantum radiation; heavier ones have survived to this day.
The main question is whether it is possible to detect them by astronomical means, if they really exist in the Universe? To find small black holes, it is necessary to know the radiation of their hard quanta. Observation of the latter would significantly contribute to the identification of primordial black holes, but to date, none of them has been discovered. Only the following has been established: the number of black holes with a mass of about a billion tons does not exceed one thousand per cubic light year. If there were more of them, then it would be possible to calculate their total radiation. The quantum radiation of massive primordial black holes is insignificant, so they can be included among the objects that make up dark matter. In 1994, Russian astrophysicists Pavel Ivanov, Pavel Naselsky, and Igor Novikov, who worked at the Danish Center for Theoretical Astrophysics, pointed to this perspective. At the same time, a message appeared that microlensing of stars in the Large Magellanic Cloud was discovered by massive compact halo objects in our Galaxy. Among others, the following idea was put forward: black holes could be such objects. The new discovery adds to the case for the theory that cold dark matter is composed of primordial black holes.
However, the author of the article emphasizes, one should not forget about primary wormholes. According to the general theory of relativity, this is a strongly curved space in the form of a tunnel connecting two entrances to it. Matter or radiation, falling into one of the holes, is scattered over the entire volume of the tunnel and, accordingly, goes out from the other hole. Or vice versa. According to one hypothesis, these primordial holes most likely existed at the beginning of the expansion of the Universe. And they could keep going. Note that quantum evaporation (the so-called Hawking evaporation) does not affect such objects, so they persist for cosmological time intervals, unless they are subjected to other instabilities. Based on this, it cannot be ruled out that some part of the cold dark matter also consists of wormholes.
So, Novikov concludes, dark objects - primordial dark holes and wormholes - can solve the mystery of dark matter. But how successful (or unsuccessful) the proposed concepts are, it will become clear only when the results of observations on the study of cold dark matter with the help, first of all, of the Planck space observatory, launched on May 14, 2009 as part of the Horizon European Space Agency, become known. -2000 and named after the outstanding German physicist Max Planck (1858-1947).
Novikov I. Dark objects and dark matter. - Journal "Earth and Universe", 2009, No. 5
Illustrations by the editors of the Earth and the Universe magazine
The material was prepared by Maria SAPRYKINA
"Science in Russia", No. 1, 2010
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Mysteries of dark matter
(The Mystery of Dark Matter)
at the rental c: 01.01.2012
Mysteries of dark matter
(The Mystery of Dark Matter)
at the rental c: 01.01.2012
We were all taught in school that the universe is made up of atoms. In fact, atoms make up only 5% of the matter in the universe, the rest is still a mystery to us. There is something else in space, another reality that we are just beginning to discover. We know that they are not atoms, but we do not know what they are. Why are astrophysicists convinced of the existence of this mysterious invisible matter? Because without dark matter, galaxies would not rotate - there would not be enough gravitational forces for the stars of galaxies to rotate at the speed with which they rotate today. There are some anomalies in the behavior and movement of galaxies, in order to understand them, scientists assume the existence of invisible matter involved in the movement of galaxies.
I think I'm here to express the mood of a whole generation of people who have been looking for dark matter particles ever since they were still graduate students. If the LHC brings bad news, it is unlikely that any of us will remain in this field of science.
One of the urgent questions that the LHC may be able to answer is far from theoretical and has very much to do with us. For several decades now, astronomy has been trying to solve a difficult riddle. If we calculate all the mass and energy in space, it turns out that the lion's share of matter is hidden from our eyes. According to modern estimates, the luminous substance is only 4% of the total amount of matter in the universe. This pitiful fraction includes everything that is made of atoms: from gaseous hydrogen to the iron cores of planets like the Earth. Approximately 22% is dark matter, a component of matter that does not emit electromagnetic waves and makes itself felt only through its gravitational field. Finally, current data says that 74% is in the form of dark energy, matter of an unknown nature, causing the Universe to expand at an accelerated rate. In a word, the Universe is an unassembled mosaic. Maybe the missing pieces will help find the LHC?
Hypotheses about hidden matter began to be expressed long before this problem was recognized by the general scientific community. In 1932, the Dutch astronomer Jan Oort calculated that the stars in the outer regions of galaxies move as if they were under a much greater gravitational pull than the observed matter. matter. The Milky Way is essentially like a giant carousel with horses. The stars revolve around the galactic center, some a little closer and others a little further from the disk of the Galaxy. Oort measured their speeds and found what the gravitational force of the Milky Way must be to keep the stars close to the galactic plane and prevent the Galaxy from crumbling. Knowing this force, Oort estimated the total mass of our star system (this value is known today as the Oort limit). The result was unexpected: it was twice the observed mass of light-emitting stars.
The following year, Caltech-based Bulgarian-born physicist Fritz Zwicky independently explored how much gravitational "glue" it takes to hold together a rich cluster of galaxies in the constellation Coma Berenices. The distances between the galaxies in the group are large, which is why Zwicky obtained a large value for the gravitational force. It could be used to calculate the amount of matter needed to create such a force. Zwicky was amazed to see that it was hundreds of times greater than the mass of visible matter. It seemed that this voluminous structure stood on camouflaged props, which alone could keep it stable.
In the 30s. 20th century scientists knew little about the universe, except for the expansion discovered by Hubble. Even the concept of other galaxies as "island universes" like the Milky Way was in its infancy. It is not surprising that, given the infancy of physical cosmology, almost no one paid attention to the extraordinary discoveries of Oort and Zwicky. Years passed before astronomers realized their significance.
We owe our current interest in dark matter to the courage of the young Vera Cooper Rubin, who, contrary to all the prejudices of the time (women astronomers were looked askance at that time), decided to take up astronomy. Rubin was born in Washington, D.C. and has been stargazing at the stars from her bedroom window ever since she was a child. She loved to read books on astronomy, especially the biography of Maria Mitchell, who received international recognition due to the discovery of the comet. Vera Rubin's path to her dream cannot be called easy: the astronomical community in those years resembled a closed club with a bright sign on the door "No entry for women."
Rubin later recalled: “When I was in school, they told me that I couldn’t get a place as an astronomer anywhere and that I should do something else. But I didn't listen to anyone. If you really want something, you need to take it and do it and, probably, have the courage to change something in this area” 86 .
After receiving a bachelor's degree in astronomy from Vassar College, where Mitchell once taught, and a master's degree in astronomy from Cornell University, Rubin returned to her hometown to continue studying astronomy at Georgetown University. Georgy Gamov became the supervisor of her thesis for the degree of Doctor of Philosophy. Although he was not listed among the university teachers, he was also interested in the evolution of galaxies, and he was allowed to work with Rubin. Under his leadership, she defended herself in 1954.
Caring for four children born in marriage to mathematician Robert Rubin, it was not easy for her to find a permanent job that would allow her to combine family and science. Eventually, in 1965, the Department of Terrestrial Magnetism at the Carnegie Institution in Washington named her a Fellow. There Rubin entered into a creative alliance with her colleague Kent Ford. He had a telescope he built with his own hands, and together they began to actively observe the outer regions of galaxies.
First of all, astronomers aimed a telescope at the nearest spiral neighbor of the Milky Way, a galaxy in the constellation Andromeda. With the help of a spectrograph, they began to collect data on the Doppler shift in the spectra of stars located on the galactic periphery. Doppler shift is an increase (decrease) in the frequency of radiation from an object moving towards the observer (from the observer). The magnitude of this displacement depends on the relative velocity of the body. The Doppler effect is inherent in any wave process, including light and sound. For example, whenever we hear a fire siren sounding higher as it approaches and lowers its tone as it moves away, we are dealing with this effect. If we talk about light, then with the approach of the source, its radiation shifts to the violet region of the spectrum (violet shift), and with the removal - to the red (redshift). Redshifts of galaxies provided Hubble with proof that distant galaxies are flying away from us. The Doppler effect in electromagnetic spectra is still one of the indispensable tools of astronomy.
By taking the spectra of stars in the outer parts of Andromeda and measuring the magnitude of the displacement, Rubin and Ford were able to calculate the speed of the stellar matter. They determined how fast the stars in the galactic outskirts move around the center of gravity. Then scientists from the Carnegie Institution built a graph: they plotted the orbital velocities vertically, and the distance from the center horizontally. This relationship, called the rotation curve of the galaxy, clearly showed how Andromeda's most extreme parts are spinning on the carousel.
As Kepler established several centuries ago, in astronomical objects in which the bulk of the mass is concentrated in the center (for example, the solar system), the farther the body is from the middle, the lower its speed. The outer planets move in their orbits much more slowly than the inner ones. Mercury flickers around the Sun at a speed of about 50 km / s, while Neptune is barely crawling - about 5.5 km / s. The reason is simple: the solar attraction quickly decreases with radius, and there is no mass that could affect the speeds of the planets in the outer parts of the solar system.
It used to be thought that in spiral galaxies, like the Milky Way, matter is distributed just as compactly. The observations show that the most densely the stars inhabit the central part of galaxies and form a spherical structure (astronomers say "bulge"). Spiral arms and a halo enveloping the galactic disk, on the contrary, look rarefied and ephemeral. But first impressions are deceiving.
In constructing the rotation curve of Andromeda, Rubin and Ford were firmly convinced that, as in the solar system, velocities would drop over large distances. But instead, the graph went to a straight line, which scientists were pretty puzzled. Instead of a mountain slope, there was a flat plateau. The flat shape of the velocity profile meant that the mass actually extends far beyond the observable structure. Something hidden from our eyes has a tangible effect on those areas where gravity, according to our ideas, should be vanishingly small.
To see if this speed behavior in Andromeda is the exception or the rule, Rubin and Ford, together with their Carnegie Institution colleagues Norbert Tonnard and David Burstein, decided to test another 60 spiral galaxies. Although spiral galaxies are not the only type of galaxy - there are elliptical galaxies, there are irregularly shaped galaxies - astronomers have chosen the "vortex" for its simplicity. Unlike other types of galaxies, the stars in spiral arms all rotate in the same direction. Therefore, their speeds are easier to plot on a graph, and therefore easier to analyze.
A team of scientists made observations at the Kitt Peak observatories in Arizona and Cerro Tololo in Chile and plotted rotation curves for all 60 galaxies. Surprisingly, each graph had the same flat area as Andromeda. From this, Rubin and her co-authors concluded that the main part of the matter in spiral galaxies is collected in extended invisible formations, which, except for the gravitational field, do not manifest themselves in any way. The problem that tormented Oort and Zwicky rose to its full height!
Who is behind the mask? Maybe dark matter consists of ordinary matter, but it is hard to see? Maybe our telescopes are just too weak to see all the objects in space?
At one time, celestial bodies were proposed for the role of dark matter, whose name reflected the gravitational power attributed to them: macho objects (MASHO, an acronym for the English. Massive Compact Halo Objects -"massive compact halo objects"). These are massive celestial bodies in the halo of galaxies that emit little light. These include, in particular, giant planets (the size of Jupiter and more), brown dwarfs (stars with a very short stage of thermonuclear burning), red dwarfs (weakly luminous stars), neutron stars (stellar cores that have experienced catastrophic compression (collapse) and consisting of nucleon matter) and black holes. They all consist of baryonic matter, which includes the matter of atomic nuclei and its closest relatives, such as hydrogen gas.
To hunt for macho objects and other dim sources of gravitational pull, astronomers have developed a clever technique called gravitational microlensing. A gravitational lens is a massive body that, like a prism, deflects light. According to Einstein's general theory of relativity, heavy bodies bend space-time around themselves, due to which the trajectory of a beam passing by is curved. In 1919, the lensing effect was observed during a solar eclipse: at this moment it is possible to see the stars near the disk of the Sun, which deflects their light.
Since macho objects passing between the Earth and distant stars must distort the image, microlensing provides a way to "weigh" them. If a macho object suddenly appears on the line of sight in the direction of the observed star (for example, one of the stars of a nearby galaxy), it will become brighter for a moment due to gravitational focusing. And when the "macho" passes by, the star will dim and take on its former form. From this light curve, astronomers can calculate the mass of an object.
In the 90s. As part of the MACNO project, an international team of astronomers from Mount Stromlo Observatory in Australia compiled a catalog of about 15 “suspicious” events. Section by section, looking through the halo of the Galaxy and using the Large Magellanic Cloud (a satellite of the Milky Way) as a stellar background, scientists came across characteristic light curves. From these observational data, astronomers have estimated that about 20% of all matter in the galactic halo is macho objects with a mass of 15 to 90% of the mass of the Sun. These results indicated that the outskirts of the Milky Way are inhabited by dim and relatively light stars, which, although they hardly shine, create an attractive force. That is, it was partially clear which celestial bodies are found on the periphery of the Galaxy, but it was still not clear how to explain the remaining fraction of the hidden mass.
There are other reasons to believe that macho objects cannot provide a definitive answer to the mystery of dark matter. In astrophysical models of nucleosynthesis (the formation of chemical elements), knowing how much of one or another element is present in space today, it is possible to calculate how many protons the Universe contained in the first moments after the Big Bang. And this makes it possible to estimate the share of baryonic matter in the Universe. Unfortunately, calculations show that only part of the dark matter has a baryonic nature, the rest is in some other form. Since the macho objects, consisting of familiar baryons, did not fit the role of a panacea, scientists turned their eyes to other candidates.
It is no coincidence that macho objects were awarded such a brutal name: in this way they wanted to oppose another class of bodies proposed to explain dark matter - the elusive "wimps" (WIMP - a word derived from the English. Weakly Interacting Massive Particles- “weakly interacting massive particles”). Unlike "machos", "wimps" are not celestial bodies, but a new type of massive particles that participate only in weak and gravitational interactions. Because they are heavy, WIMPs must have low velocities, making them an excellent gravitational "glue" to keep giant structures seen in space, such as galaxies and clusters of galaxies, from falling apart.
Neutrinos could not be discounted if they were heavier and more assiduous. After all, they, as befits leptons, bypass strong processes, and, like all neutral particles, they are not afraid of electromagnetism. However, the negligible mass and restlessness of neutrinos force us to exclude them from consideration. For their agility, neutrinos can be likened to a superficial politician who now and then makes forays into different districts, trying to win over the electorate before elections to the city council. Do people want to unite around a person who is not able to settle down in one place and win firm support? Similarly, neutrinos, which do not linger anywhere for a long time and have little effect on anything, are hardly suitable for the role of a unifying rod.
Neutrino-like particles - too light and fast to form structures - are called hot dark matter. Although the hidden mass in the Universe may be composed of them to some extent, they cannot explain why the stars in the outer regions of galaxies cling so tightly to their home "island" and why the galaxies themselves gather into clusters. Heavier matter, characterized by a measured pace, including "macho" and "wimps", belong to the class of cold dark matter. If we could scrape it together enough, we'd know what space props are made of.
But if not neutrinos, then what neutral particles of non-hadron origin have significant mass and can fly so slowly as to influence stars and galaxies? Regrettably, but in the Standard Model such are in short supply. In addition to neutrinos, "machos" and "wimps", the axion claims the role of dark matter, and, as some theorists believe, not unreasonably. This massive particle is introduced in quantum chromodynamics (the theory of strong interactions), but has not yet been experimentally detected. At the moment, the search for hidden mass in the universe has come to a standstill.
It's time to ask for help from the LHC. Perhaps, in the fragments of collisions at the accelerator, the key to the mystery of cold dark matter will be hidden. The first on the list of contenders are the lightest supersymmetric partners: neutralinos, charginos, gluinos, photinos, squarks, sliptons and some others. If their mass (in energy units) does not differ much from the tera-electronvolt, they will not be difficult to notice from the characteristic decays that appear in calorimeters and tracking systems.
But if dark matter were the only mystery in the universe, physicists would bite their tongues, cross their fingers, and sit quietly and wait for the LHC or some other instrument to come up with the right results. It's like posting a job ad and calmly waiting for a qualified specialist to come for an interview. On the horizon, however, a tougher nut appeared, which had already caused trouble for scientists. It's about dark energy. Not only do they not know what exactly is hidden from them, they do not even know where to look.
For the first time, the scientific community came face to face with dark energy in 1998. Then two groups of astronomers - a research team from the National Laboratory. Lawrence at Berkeley under Saul Perlmutter and Mt Stromlo observatory observers (including Adam Riess, Robert Kirshner and Brian Schmidt) announced the amazing news about the expansion of the universe. To track how the cosmos has expanded in the past, researchers measured the distances to supernovae in distant galaxies. By plotting these distances on a single graph as a function of the velocities of the galaxies, found from the Doppler shift of the spectral lines, astronomers were able to determine how the Hubble parameter, which characterizes the receding rate, changed over billions of years.
The stars used in the observations, the so-called supernovae of type 1a, have a remarkable property: certain regularities can be traced in the intensity of the energy emitted by them during the explosion. Thanks to such predictable behavior, the mentioned groups were able to calculate the distances to stars by comparing the observed brightness with a known value. In other words, astronomers got a kind of roulette, with which you can "get" to the stars that are billions of light years away from us, that is, exploded long ago in the past.
An astronomical object with a known absolute luminosity is called a standard candle. When we drive at night and look at roadside lights, we can estimate the distance to one or another street lamp by whether it seems to us bright or dim. Assuming, of course, that they all produce the same power. If it happened that during a night walk a bright flash hit your eyes, you would most likely decide that its source was near you. And about the barely distinguishable light, you involuntarily think that it is somewhere far away. In short, we often judge distance by the apparent brightness of a light source. Similarly, astronomers, having taken some object, for example, a supernova of type 1a, for a standard candle, have at their disposal almost the only tool for measuring large distances.
Perlmutger's research team, which implemented the SCP project (Supernova Cosmology), is directly related to particle physics. To begin with, this program, like the CMB research on the COBE satellite that brought George Smoot the Nobel Prize, continues the tradition of the Lawrence Laboratory. Such a broad view of things is entirely in the spirit of the head of the Red Lab, who looked everywhere for interconnections and tried to apply the methods of one field of science to another. In addition, one of the initiators of the SCP project, Gerson Goldhaber, who was widely recognized at the Cavendish Laboratory during the time of Rutherford and Chadwick, and then for many years served as director of the Brookhaven National Laboratory. It can be said that cosmology and elementary particle physics - the sciences of the largest and smallest - have long become related.
When the SCP program started, its participants hoped, by taking supernovae for standard candles, to make sure slowdown Universe. The force of gravity, it would seem, by its very nature tends to delay the runaway of any system of massive bodies moving away from each other. Simply put, what is thrown up falls down, or at least slows down. Cosmologists therefore envisioned three possible paths for cosmic evolution. Depending on the ratio between the average and critical density of the Universe, it either slows down quite quickly, and the expansion is replaced by contraction, or slows down not very much, and the breakpoint is not reached, or, if the two densities are equal, it remains in the boundary state and also expands indefinitely.
All three scenarios start with the usual Big Bang. If the universe is dense enough, it gradually slows down, and finally, after billions of years, the expansion is replaced by contraction. Everything that exists, as a result, is ground in the Great Meat Grinder. If the density is below the critical value, the expansion of the Universe continues, slowing down, for an infinitely long time - the cosmos overcomes the distance through force, like an exhausted runner. Although the expansion of galaxies is becoming more and more sluggish, they will never have the courage to run towards each other. This alternative is sometimes referred to as the Big Moan. The third possibility is that the average density is exactly equal to the critical one. In this case, the Universe slows down and, just look, is about to begin to contract, but this does not happen. She, like an experienced tightrope walker, easily keeps her balance.
Perlmutter and his staff expected to see one of these three options. However, observations of supernovae contradicted the known schemes. From the graphs of velocity versus distance, it appeared that the expansion was not slowing down at all. Moreover, it is accelerating. It was as if something had caused gravity to confuse the brake pedal with the gas. But none of the known substances could be suspected in these intrigues. Theorist Michael Turner of the University of Chicago dubbed the unusual component dark energy.
Although dark energy is no less mysterious than dark matter, there is little in common between their properties. Dark matter causes the same attractive force as ordinary matter, but dark energy is a kind of "anti-gravity", causing bodies to fly apart with acceleration. If dark matter were at a party, it would introduce the guests to each other and involve them in the general fun. Dark energy, on the contrary, likes to work in special forces, suppressing street riots. Indeed, if the cosmos were too richly flavored with dark energy, the Universe would embark on a fatal path ending in a Big Rip - it would simply be blown to smithereens.
In connection with dark energy, physicists have started talking about returning to the general theory of relativity the cosmological constant, which was once abandoned by Einstein. Although the term describing antigravity (lambda term) solves the problem with little bloodshed, it would be nice to justify it from a physical point of view. Physicists are very reluctant to add new terms to coherent theories if there are no fundamental prerequisites for this. In other words, the cosmological constant would have to find a place in field theory. However, modern field theories give an unthinkable amount of vacuum energy. In order to get a realistic value from it, it must be reduced to almost zero (that's almost, not exactly). The discovered and experimentally measured cosmic acceleration has given scientists a difficult puzzle.
Moreover, if dark energy remains constant in time and space, its influence never wanes. As gravity loses ground over time to dark energy, the universe is getting closer to the Big Rip. Before resigning themselves to such a gloomy end, most theorists prefer to think and come up with something better.
Princeton theorist Paul Steinhardt, as well as Robert Caldwell and Rahul Dave, have proposed an ingenious way to model dark energy. They introduced a new kind of matter called quintessence. Quintessence is a hypothetical substance that, instead of causing bodies to clump (like ordinary matter that serves as a source of gravity), pushes them apart (like the mighty Samson of the columns of the Philistine temple). The term for this substance is taken from ancient philosophy, in which the quintessence ("fifth essence") continued the series of four elements of Empedocles. The difference between the cosmological constant and the quintessence is this: while the first stands still as if rooted to the spot, the second is like malleable plasticine - it can change from place to place and from era to era.
CMB observations on the WMAP satellite suggest that space is filled with a mixture of dark energy, dark matter, and visible matter (in that order). But the probe images so far, however, are silent about what ingredients the double dark cocktail is made of.
Physicists hope that the LHC will help lift the veil of mystery over the nature of dark energy and dark matter. If, for example, quintessence were discovered at the largest collider, this would mean a revolution in cosmology and would radically change our ideas about matter, energy and the Universe. Judge for yourself, thanks to this discovery, we would know what the future holds for all things.
The addition of a lambda term and the introduction of an unusual substance are not limited to hypotheses. According to some theorists, it is time to reconsider the theory of gravity itself. Maybe the gravitational forces manifest themselves differently on different scales: within planetary systems they behave in this way, but in the galactic expanses - in a different way? Can it happen that Einstein's general theory of relativity, which, according to our understanding, seems to be correct, will have to be replaced by another theory at the most grandiose distances? As Rubin once said, "It looks like until we know what gravity is, we won't know what dark matter is" 87 .
In innovative theories of gravity, it is proposed to radically change the mechanism and scope of its action. Some of its properties, adherents of these theories argue, receive a natural explanation if we assume that the force of gravity penetrates into hidden additional dimensions, where access to other forms of matter and energy is prohibited. Then the dark sector of the Universe can be a shadow of higher spheres.
It is noteworthy that individual exotic theories of this type, no matter how strange they may seem, can be tested on the LHC. The hot furnace of high-energy transformations can not only bring to life unprecedented particles, but also find new dimensions. Who knows from what ancient secrets of nature the unprecedented power of the LHC will tear the covers off ...
