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16-01-2018

To you, astrobiology lovers. At the end of 2017 in Chile (in Santiago and Coyhaique), the IAU Commission 3 (Astrobiology) held an astrobiology school and conference “Astrobiology 2017”. School and conference materials are now available for viewing. Watch and enjoy: school program with links to videos, conference program with links to videos.

04-01-2017

In the astrobiological context, the mechanisms of synthesis of organic molecules of various types in protostellar shells and other objects associated with star formation regions are of particular interest. The work of J. Lindberg et al. presents estimates of the radial concentrations of C4H and methanol in the direction of 40 protostars. Of these protostars, sixteen objects in molecular clouds from the constellations Ophiuchus and Corona Southernis have been observed

23-10-2016

The closest molecular cloud complex to us is in the constellation Taurus, at a distance of approximately 140 pc. Due to their proximity, these clouds are quite well studied, including from the point of view of their molecular composition, which in recent decades has become, if not a standard, then at least a “reference point” for testing astrochemical models. Meanwhile, even

03-08-2016

The number of planets discovered by the Kepler space telescope is in the thousands. Among them, of particular interest are terrestrial (presumably) type planets located within the so-called habitable zone, that is, in the range of distances from the central star where the existence of liquid water on the surface of the planet is possible. Determining the relative share of such planets in their total number is considered one of the main

02-08-2016

The molecular nucleus L1544 in Taurus is one of the “standard” prestellar nuclei, and therefore a very large number of studies are devoted to it. In particular, the L1544 core is considered a typical example of an object with so-called chemical differentiation, that is, specific differences in the distribution of carbon and nitrogen compounds. In nuclei with chemical differentiation, nitrogen compounds (NH3, N2H+) are concentrated in the center, then

13-07-2016

The international conference “Search for life: from early Earth to exoplanets” will be held from June 12 to 16, 2016 in Vietnam. Conference website - http://rencontresduvietnam.org/conferences/2016/search-for-life. The conference program covers four main topics: education, evolution and habitability of planetary systems; early Earth; from pre-biological chemistry to first life; life in the universe - impact on society and ethical issues.

11-06-2016

Manara et al. report in the journal Astronomy & Astrophysics that they discovered a correlation between the rate of accretion in a protoplanetary disk and the mass of this disk. This correlation follows from theoretical ideas about the evolution of protoplanetary disks, but so far it has not been possible to detect it. The authors of the new work examined an almost complete sample of young stars in the star-forming region Lupus (Wolf).

14-05-2016

There is such a concept - “oxygen catastrophe”. This scary term refers to a stage in the evolution of the earth’s atmosphere, which for us today was rather favorable. It is assumed that during the oxygen catastrophe approximately 2.4 billion years ago, a significant enrichment of the earth's atmosphere with molecular oxygen occurred. Until this time, the air envelope of our planet contained virtually no oxygen. Most scientists believe that

One of the most important ideological tasks of astronomy is to find an answer to the question of whether we are alone in the Universe. In the absence of direct contact with extraterrestrial intelligence, we have to be content with indirect arguments.

We do not know, of course, how wide the range of physical conditions is in which the origin of life is possible, but we can say with certainty that at least on one specific planet, near one specific star in one specific galaxy, the emergence of life and intelligence turned out to be possible. If we prove that such planets, stars and galaxies are common in the Universe, there will be hope that the final outcome of their evolution, similar to that on Earth, is not uncommon.

Until recently, it seemed that in this regard, things were going well with all three components - planet, star, galaxy. At least not bad. True, we cannot yet judge with confidence how typical the Earth is - like a planet that has fallen into the habitable zone of its star. But there is no reason to believe that she is atypical. Such reasons may, of course, appear in the future (who knows?). However, the information available today about planetary systems suggests that their formation is a completely routine process.

The sun is also not exotic. In many popular books, and even in textbooks, he is often called the most ordinary, unremarkable star. This seemingly derogatory characteristic is very important from the point of view of the evolution of life: for four and a half billion years, the Earth has been warmed by a calmly humming stove, which all this time has been transmitting to us exactly as much energy as we need, without sharp declines or powerful outbreaks. Any feature, “unusuality,” would make the Sun a very interesting object for an outside researcher, but for us, who live nearby, boring stability is better than exciting changeability. And there are still many such stars “without any special features”, similar to our central luminary, in the Galaxy.

Our entire Galaxy (Milky Way) turns out to be just as cozy and “boring”. That is, ten billion years ago, very violent events took place in it: it was then, as a result of the compression of the rotating protogalactic cloud, that a giant star-gas disk arose, in which we now live, and the projection of which onto the sky is called the Milky Way itself. But after the formation of the disk, nothing “interesting” happened to our Galaxy. No, of course, there are still places in it where it is better not for a small star with habitable planets to go. The surroundings of hot massive stars are filled with hard radiation, strong shock waves scatter from supernova explosions... But there are few such dangerous places, and the chances that, for example, our Sun will fly into one of them are very small.

This calmness is due to the fact that star formation processes in the Milky Way have long since assumed a “sluggish” character. A comparison of the number of stars of different ages shows that the average rate of star formation in our Galaxy over the past 10 billion years has remained almost the same, at the level of several stars being born per year. And this constancy may turn out to be not exactly out of the ordinary, but at least a rather unusual property of our star island.

From the point of view of appearance, the Galaxy is a very thin disk (with a “thickness-to-diameter” ratio comparable, for example, to compact disks), crossed by several (two or four) spiral arms. This disk is immersed in a rarefied spherical star cloud - a halo. If you focus only on appearance, then there are not just many such systems in the Universe - they are the majority. According to modern data, about 70 percent of all galaxies belong to such spiral disk systems. This is nice for two reasons. Firstly, the typical nature of the Galaxy makes it unlikely that we will be alone in the Universe. Secondly, we can easily extend the results of studying the Galaxy to most of the rest of the Universe. But that's not all. A favorable fate placed another similar galaxy right next to us - the Andromeda Nebula (aka M31, NGC 224), which was, and is still sometimes considered, almost a twin of the Milky Way. What more could you want? If we want details, we look at our Galaxy, if we want the big picture, we look at the Andromeda Nebula - and 70 percent of the Universe is in our pocket!

Research in recent years shows, alas, that this joy is premature. The more we learn about the Andromeda Nebula, the less it seems to be a twin of the Milky Way. No, there is, of course, a general similarity; M31 is much more similar to the Milky Way than, say, the dwarf galaxy Large Magellanic Cloud. But there are some important discrepancies in particulars. Although the Galaxy and the Andromeda Nebula most likely formed almost simultaneously, M31 looks more... how should I say... shabby. Now there is less gas left in it than in our Galaxy; Accordingly, the birth of stars is happening less actively, but this is only now! The disk and halo of the Andromeda Nebula show traces of numerous powerful bursts of star formation, the most recent of which occurred perhaps only 200 million years ago (a small time compared to the full age of the galaxy). Observations of stellar systems show that the cause of such bursts is almost always galactic collisions. This means that the history of the Andromeda Nebula is significantly richer in large and small cataclysms than the history of the Milky Way.

Given this dissimilarity, it becomes unclear which of the two galaxies should be taken as a standard. The problem is that we cannot study any other spiral galaxy with a similar degree of detail. (More precisely, we have another spiral neighbor - M33, but it is much smaller than M31 and the Milky Way.) In 2007, Francois Hammer (Paris Observatory) and his colleagues decided to check what parameters we would get for the Milky Way and M31 , if they were observed from a great distance, and compare these parameters with the properties of other distant spiral galaxies. It turned out that the more typical system is not the Milky Way! Of all the nearby spiral galaxies, no more than 7 percent are close in parameters to it. The rest are more reminiscent of the Andromeda Nebula: they are poor in gas, richer in stars and have a higher specific angular momentum than the Milky Way, that is, simply put, they rotate faster. For the Andromeda Nebula, all these properties, as well as the peculiarities of the distribution of stars around the disk, can be explained by a major collision that occurred several billion years ago with a star system whose mass was at least a billion solar masses (about a few percent of the mass of the galaxy itself). M31's similarity to other spiral galaxies indicates that similar megacollisions have occurred with almost all of them - with the exception of a small group to which the Milky Way belongs.

Here it is appropriate to recall another oddity of our Galaxy - its two satellites, the Magellanic Clouds. They bear little resemblance to typical satellites of a spiral galaxy. Typically these satellites are small and dim elliptical or spheroidal galaxies. Companions like the Magellanic Clouds, massive, bright, with their own turbulent history of star formation, are also observed in only a few percent of spiral galaxies. A possible explanation for this oddity is that the Magellanic Clouds may not be satellites of the Milky Way. Measuring the speed of their movement using the Space Telescope named after. Hubble showed that for satellites, that is, bodies gravitationally attached to the Galaxy, they fly too fast. The idea arose that the Clouds might just be flying past the Milky Way.

There is, of course, a temptation to connect all these facts into a single picture. In December 2010, Y. Yang and F. Hammer suggested that the Magellanic Clouds flew to the Milky Way from the Andromeda Nebula, escaping from it as a result of that same mega-collision. It must be said that the trajectory of the Clouds is still poorly known, but what is known about it does not contradict the hypothesis of their “Andromedan” origin.

In general, the picture may look like this. Of the two main galaxies of the Local Group (the boring name for the Milky Way, M31 and their surrounding satellites), only one survived a major collision. Two smaller galaxies were formed from the material torn out of M31 as a result of this cataclysm. They are now flying past the Galaxy and, perhaps, will be captured by it, so that in a few billion years they will merge with the Milky Way, allowing it to finally survive the catastrophe that happened much earlier in the lives of other similar systems.

One way or another, recent studies indicate that so far the evolution of the Milky Way has turned out to be significantly more inconspicuous than the evolution of most disk galaxies, which has given earthly life several billion years of silence for quiet development.

The dark beckons and fascinates. Darkness is the friend of youth. We are darkness, and darkness, and darkness. In the movies, the cynical, witty Dark Ones are often more likable than the proper, boring Light Ones. Despite the numerous astrophysical mysteries associated with luminous matter, the imagination is more exciting about dark matter. Analyzing inconsistencies with radiation seems to be nothing more than clarifying already known details, while darkness promises to open the door to new physics.

It is not surprising that a huge number of articles published in the professional literature are devoted to the study of dark matter (DM). (By the way, in Russian it is probably more correct to say “dark matter”, but Google gives an order of magnitude more links for the query “dark matter”, which is a tracing-paper from the English “dark matter”.) How can you study something that does not glow? if the only source of information in astronomy is electromagnetic radiation? Yes, just like many other things - based on indirect evidence.

Let me briefly remind you of the essence of the problem. The main factor moving objects on large scales in our Universe is gravity. By observing the movement of bodies, one can draw conclusions about the gravitational field in which they move and the mass that generates this field. So, in a number of cases, the gravitational field seems to exist, but its source cannot be seen. In particular, the movement of stars in galaxies and galaxies in clusters occurs at speeds that strongly do not correspond to the distribution of “light” matter, which can be observed directly. Hence the assumption arises about the presence of “dark” matter, which itself does not glow, but manifests itself through the gravitational effect on luminous bodies.

The existence of dark matter is indicated by several different pieces of evidence that are consistent with each other. Therefore, to reject the assumption of dark matter, it is not enough to find another explanation, for example, only the movement of stars in galaxies. Nevertheless, attempts to “close” dark matter do not stop. Just in the last ten days, two major studies have appeared, one way or another “digging” under TM.

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In February 2003, American scientists presented to the scientific community a “baby photo” of our Universe - a map of cosmic microwave background radiation, which allows us to look into the pre-galactic era that immediately followed the Big Bang. With its help, astronomers tried to answer with the greatest possible accuracy the question of what the Cosmos is made of. The answer turned out to be disappointing: only 4% of the mass of the Universe comes from the “ordinary” matter we understand, consisting of atoms. The remaining 96% consists of substances with simple but sonorous names - dark matter (23%) and dark energy (73%). What, besides their names, is known about them today?

Over the past hundreds of years, science has dealt several tangible blows to human self-awareness. First, the “cradle of humanity” the Earth was removed from the center of the Universe, then the Sun. Then it turned out that our Galaxy is not the only one in Space, and not even the largest, but just one of many billions of star islands, located either on the outskirts of a large cluster of galaxies, or even beyond its borders - a kind of remote universal province, full of consciousness of self-importance, but hopelessly far from the metropolis.

But if on Earth a provincial can always find solace in dreams of a capital, in the Universe we, as it turns out, are deprived of even this opportunity. Not only cities and countries, large and small, poor and rich, but the entire Earth, the Sun, the Milky Way, and all the galaxies suddenly turned out to be just a shiny coating, a thin gilding on a mysterious, impenetrably black base. The rise and fall of civilizations, the formation and destruction of planets, the explosions of stars and the collisions of galaxies, as well as all the other events that seem to us to fill the Universe, in fact, have the same relation to its life as a narrow strip of surf has to the life of the World. Ocean.

Interstellar space is not empty

Just looking at the starry sky, it is quite difficult to imagine that there is anything else in the Universe besides stars and planets. However, a little closer examination proves that this is not the case. Apparently, one of the first astronomers to encroach on emptiness was the Russian scientist V.Ya. Struve, the founder of the Pulkovo Observatory. In the middle of the 19th century, he discovered that the number of stars per unit volume decreases with distance from the Sun. The scientist associated this decrease with the fact that on the way to the observer, the light of stars weakens in proportion to the distance traveled as a result of interaction with some substance. At first, this absorbing substance was called dark.

The adjective "dark" in astronomy is used according to its direct meaning - "non-luminous". Since the only source of information about deep space for us is light, at the same time another meaning of the word “dark” turns out to be very appropriate - unclear, incomprehensible. Nowadays, the nature of the interstellar absorbing substance is no longer in doubt - it is just dust, microscopic particles consisting of carbon and silicon compounds. Dust is scattered unevenly in space. It is collected in dense clouds that almost completely block the light of the stars located behind them. Against the background of a scattering of stars, such clouds are visible as black starless holes. For old times' sake, astronomers still call such clouds dark, although this is unfair. Dust not only absorbs the radiation of stars, but also glows itself, although not in the visible, but in the infrared, submillimeter and radio ranges. But registering this radiation does not cause any fundamental difficulties for modern astronomers.

With the advent of radio telescopes, it became clear that dust is not the main “filler” of the space between stars. For every gram of dust in interstellar space, there are 100 grams of gas, which is mainly a mixture of hydrogen and helium. And if only a few percent of the mass is concentrated in interstellar gas inside galaxies (the rest is collected in stars), then in the space between galaxies there is much more gas. In clusters, the mass of intergalactic gas is several times greater than the total mass of the “stellar islands” themselves. It may seem that it would be more correct to call galactic swarms not clusters of galaxies, but giant clouds of gas with a small stellar-galactic “admixture”. But even such a derogatory formulation does not reflect the true state of affairs!

Dark matter

Our world is the kingdom of gravity. Of all the fundamental forces, it alone has a long-range action sufficient to overcome cosmic distances. Therefore, the main characteristic of any astronomical object is its mass. It can be estimated both from observations of the object itself (for example, the mass of a star can be approximated by the shape of the lines in its spectrum) and from the gravitational effect it has on other objects. If the estimates obtained by these two methods approximately coincide, then everything is in order with our theoretical ideas about the nature of the object. Their discrepancy indicates that we do not understand something or are missing something. A strong discrepancy in the two mass estimates is a likely sign of some very large misconceptions.

But what difficulties might there be with ideas about the structure of, say, galaxy clusters? Here they are - galaxies, visible even with a small telescope. Here it is - hot gas filling the space between them. True, you cannot see it with a regular telescope, but with the help of X-ray telescopes this gas has been observed several times. We find the total mass of all galaxies, add the gas mass to it and get the total mass of the cluster. For a typical cluster of galaxies, say the cluster in the constellation Virgo, this mass is equal to several tens of trillions of solar masses.

The mass of a galaxy cluster can be determined in another way. The only force that binds the cluster into a single whole is gravity. For a cluster of galaxies, as for the Earth, there is a second escape velocity. If the speed of the galaxy exceeds the “second cosmic speed” for a given cluster, the galaxy is able to escape from its gravitational embrace and go into free flight. The magnitude of the speed depends on the mass of the cluster: the more massive the cluster, the faster the galaxy must move to leave it.

Back in the 30s of the 20th century, American astronomer Fritz Zwicky drew attention to the fact that galaxies in clusters move faster than escape velocity! Clusters with such rapidly moving members simply cannot exist. But they exist, which means we are mistaken in some way. But how can we make a mistake if the entire cluster lies before us in full view? Or not all?

Zwicky's result meant that the entire visible mass of a typical cluster is not enough to keep its constituent galaxies from flying away. This means, Zwicky decided, that in galaxy clusters there is also invisible matter, which does not manifest itself in any way in radiation, but makes a significant, or rather, decisive contribution to the gravitational field of the cluster. To explain the high galactic speeds, we have to assume that there is ten times more “dark” matter in galaxy clusters than “luminous” matter of all types. So it turns out that a cluster of galaxies is actually a cluster of not galaxies or gas, but a condensation of something unknown with a small admixture of gas and galaxies. The problem of clarifying the nature of this mysterious entity has since been known in astronomy as the problem of hidden mass, and this entity itself is called dark matter or dark matter.

It was later discovered that not only galaxy clusters, but also the galaxies themselves contain hidden mass. As is known, our Galaxy (more precisely, its visible part!) is a flat rotating gas-stellar disk. The Sun is 25,000-30,000 light years away from the center of the Galaxy and makes a full revolution in about 200 million years, moving along its galactic orbit at a speed of about 220 km/s. The luminous matter in the disk is highly concentrated towards the galactic core. The gravitational force that controls the orbital motion of stars is known to decrease inversely with the square of the distance, so it is logical to assume that stars on the periphery of the disk, far from the main mass of the Galaxy, will move more slowly than stars close to the core.

Alas, in the 70s of the 20th century it became clear that neither in ours nor in other similar galaxies this apparently logical assumption is fulfilled. Even stars and gas clouds very far from the center rush through their orbits at high speeds, as if not wanting to know that where they are, the galaxy is almost over. Where is the source of this gravity in a space that seems almost empty? The answer was found quickly. If there is hidden mass in galaxy clusters, why shouldn't there be hidden mass in the galaxies themselves? The required amount of dark matter is approximately the same as in clusters. For example, to describe the motion of stars on the outskirts of our Galaxy, we must assume that it is surrounded by an extensive “dark halo”, the size and mass of which is at least several times greater than the size and mass of the visible disk.

At first, to many scientists, the assumption of the existence of dark matter seemed too artificial. However, to date, so much observational data has been accumulated about it that, apparently, it will still not be possible to dismiss the hidden mass. All that remains is to find out what she is. Fortunately, the theory does not stand still, and currently several candidates have already been considered for the role of dark matter.

Of course, from the point of view of simplicity, I would like to assume that dark matter consists of objects familiar to astrophysicists, which have mass, but either do not emit at all, or emit so weakly that with modern astronomical instruments they are visible only on a very small scale (on galactic scales). ) distance. Scientists know many such objects: brown and white dwarfs, neutron stars, black holes, planets, compact gas clouds. Since they all consist or in the past consisted of ordinary protons and neutrons, which in physics are collectively called baryons, the dark matter formed from these objects is called baryonic.

Unfortunately, it is very difficult to explain where a large number of such objects could come from around the Galaxy. Each of them does not arise out of nowhere and, before turning into dark matter, leaves one or another trace in the evolution of the galaxy. Let's say, for example, that the dark halo consists of neutron stars. They are the remains of massive stars that end their life path with a grandiose explosion - a supernova. It is unlikely that the explosion of billions of supernovae around the Galaxy could pass without a trace for it.

Therefore, the hypothesis of non-baryonic dark matter, consisting of special, as yet unknown, elementary particles that have a specific set of properties, in particular, almost do not interact with “ordinary” matter and therefore still evade detection, is now considered preferable. At one time it was believed that dark matter could be neutrinos, but the results of recent experiments and observations at neutrino telescopes prove that the mass of neutrinos, although not equal to zero, is still too small to attribute all the “missing” matter to it.

Neutralino is your reliable super partner!

Most likely, we are talking about particles of a new type. It should be noted that physicists not only do not deny the existence of such particles, but on the contrary, they welcome them in every possible way, since they are consistent with recently refined ideas about the structure of matter, in particular, about the two main types of elementary particles - fermions and bosons. In our relatively cold world, matter itself is made up of fermions (such as protons and neutrons), and bosons (such as photons) carry the force between them. But at a very high temperature, compared with which even the temperature in the interior of stars pales, the difference between matter particles and carrier particles is erased, and they begin to behave the same. The theory of the identity of fermions and bosons at high temperatures is called the theory of supersymmetry. Physicists can still only dream about the energies required to test it experimentally, but they are confident that proof of supersymmetry remains to be seen for several years. Much work in this direction is being carried out in many laboratories around the world, in particular at the Russian neutrino observatories in Baksan (North Caucasus) and on Lake Baikal.

Meanwhile, in Nature, an experiment to obtain elementary particles of ultra-high energies has already been carried out! True, it ended quite a long time ago, more than 10 billion years ago, but traces of its implementation surround us on all sides, and we ourselves are nothing more than the result of this grandiose experiment, called by scientists the Big Bang! The theory of supersymmetry predicts that in the first fractions of a second after the birth of the Universe, all its particles were equal and identical, but then the Universe expanded, cooled, and there was no equality in it... It is interesting that, along with protons, neutrons, electrons, photons, neutrinos and other known elementary “building blocks”, the theory of supersymmetry predicts the birth of a whole zoo of unknown particles. However, we should rather talk not about a zoo, but about an ark - these unknown particles form pairs with known particles: each fermion has a boson paired with it and vice versa. To emphasize the supersymmetry of this community, such pairs are called superpartners.

All hypothetical particles - superpartners of known particles - have a common property: they interact very weakly with ordinary matter, significantly surpassing even penetrating neutrinos in this regard. In scientific jargon, they are sometimes called "WIMPs", from the English abbreviation WIMP - "weakly interacting massive particles", that is, weakly interacting massive particles. It is very difficult to see WIMPs, but you can “feel” them - like everything with mass, they create a gravitational field around themselves. After the Big Bang, a huge number of such particles should have remained, and their combined gravitational influence could well be felt by entire galaxies. So much for dark matter! This fact is very significant, because it clearly demonstrates how the properties of giant galaxy clusters and the macrocosm in general can be related to the properties of the microcosm.

The most likely candidate for the role of dark matter is considered to be the lightest supersymmetric neutralino particle, whose mass exceeds the mass of a proton by a hundred times. Competing with it and other WIMPs is another invisible particle - the axion - whose existence is predicted by another modern physical theory - quantum chromodynamics.

Our Galaxy and other star systems are immersed in clouds of neutralinos, axions and other invisible particles. These clouds, as is now believed, in the pre-galactic era served as gravitational “seeds” onto which ordinary matter was drawn, which became the building material for the first generations of stars. In scientific language, these seeds are called primary density fluctuations. And although much water has passed under the bridge since their inception, the properties of these fluctuations are forever captured in the form of spatial variations in the intensity of the cosmic microwave background radiation. It was by studying these variations that scientists found that only 4% of the mass of the Universe comes from ordinary atomic matter. Another 23% is occupied by nonbaryonic dark matter (neutralinos, axions, etc.). What is the remaining 73%? We can consider ourselves shareholders of Universe OJSC, who at the next meeting discovered that they even approximately do not know who owns the controlling stake!

Einstein's biggest mistake

One of the predictions of Einstein's theory of relativity was that the universe cannot exist forever. Indeed, if we recognize it as the kingdom of gravity alone, that is, attraction, we must also agree that over time all the matter in the Universe should be pulled together to one point. Einstein himself did not like this prospect so much that he forcibly introduced the so-called lambda term into his equations - a hypothetical “universal repulsion”, which was supposed to counteract universal gravitation. However, in 1929 it turned out that the Universe is expanding. This meant that the mutual attraction of galaxies was counteracted by their recession generated by the Big Bang, and the need for mutual repulsion seemed to disappear. Einstein's confession to the Soviet-American astrophysicist Georgi Gamow that he considered the invention of the lambda term his greatest mistake is widely known. But time passed, and this error ceased to be so obvious: as the same Gamow writes, the cosmological constant “continues to raise its ugly head.” True, now it has many other names - antigravity, quintessence, vacuum energy and, of course, dark energy.

The discovery of the non-stationary nature of the Universe forced scientists (and not only them) to think about how its expansion would end. It is convenient to characterize the further fate of our world by comparing the average density of matter in the Universe with a certain critical value. If the density is greater than critical, gravitational forces will sooner or later stop the expansion of galaxies, and it will be replaced by a general compression, which will again pull the Universe to a point. If the density is less than critical, the expansion of the Universe will continue indefinitely... Today, the observed properties of the Cosmos are best described by the so-called inflationary theory, in the development of which Soviet and Russian physicists played a major role. According to it, in the first fractions of a second of its existence, the Universe experienced a catastrophic “inflation” (this is how the word “inflation” is translated from English), during which its size increased 10 50 times. All the inhomogeneities and curvatures that were present in the Universe before were smoothed out during the inflation process - that is why it turned out that we live in such a homogeneous and flat (in the geometric sense!) world.

Inflationary theory, among other things, predicts that the average density of matter in the Universe should be exactly equal to the critical density. As a matter of fact, it is in relation to the critical density that all the percentages that have already been repeatedly mentioned in this article are calculated. The problem is obvious - after scraping out all the bottom ends in outer space, it was possible to collect substances only at 27% of the critical density. Where can I get the remaining 73%?

Well, there is no substance left in space, but space itself remains. Why should we assume that it weighs nothing? Just as in geodesy all heights are counted from a certain zero level (in Russia - from the zero of the Kronstadt foot rod), in physics we can assume that all energies are counted from zero energy - the energy of the vacuum, which does not have to be equal to zero. The missing density may be hidden in this initial energy. Since astronomers had previously called invisible matter dark matter, it seemed logical to apply the same adjective to invisible energy.

Acceleration of the Universe

It may seem that the concept of dark energy is, as they say, “far-fetched”: instead of honestly admitting the failure of the inflationary theory, and indeed the entire cosmology of the Big Bang, scientists attribute energy to the void! To avoid such accusations, it is necessary to find out what properties dark energy should have and try to detect these properties in the results of astronomical observations. And such results were obtained! In 1998, a group of American astronomers led by Adam Rees reported a significant fact - the Universe is not just expanding, it is expanding at an accelerating rate. Scientists came to this conclusion by observing supernova explosions in distant galaxies.

Most methods of measuring distance in astronomy are based on comparing the apparent brightness of an object with its true brightness, which, of course, must be known. Sources with known true brightness are called "standard candles". Type Ia supernovae, believed to be associated with thermonuclear explosions on white dwarfs, are visible at very large distances and have an enviable consistency of brightness, making them an indispensable tool for measuring cosmological distances.

On the other hand, in the close (on cosmological scales) vicinities of our Galaxy, Hubble's law applies - the distance to the galaxy is directly proportional to the speed of its movement along the line of sight. Radial velocity is easy to determine from the spectrum - the Doppler effect shifts the lines to the red part of the spectrum if the source is moving away from us, and to the blue part if the source is approaching. Since the magnitude of the shift is proportional to the speed, Hubble's law makes it possible to estimate the distance to distant objects from spectral observations - provided that far from the Milky Way the expansion of the Universe obeys the same laws - or to identify deviations from these laws.

It was this method that Rees and his colleagues resorted to. Based on the apparent brightness of several supernovae, they determined the distance to them - it turned out to be very significant, several billion light years. Then, using Hubble's law, they calculated the speed at which these supernovae would have to move away from us if the expansion of the Universe several billion years ago had occurred at the same speed as now. The actual speed of supernovae turned out to be significantly lower than the value predicted by Hubble's law - now the Universe is expanding faster than several billion years ago!

Scientists would easily accept the opposite result - in a Universe that obeys the law of gravity, it is logical to expect that expansion will slow down over time. But acceleration means that in addition to attraction, there really is a repulsive force in the Universe, or simply antigravity, and at present it clearly exceeds gravity at cosmological distances. Given the sensational nature of this conclusion, many scientists, including the authors of this discovery themselves, tried to find an error in the results of the Rees group, but so far these attempts have not been crowned with success. We have to admit that dark energy really exists! Moreover, its amount, calculated from observations of supernovae, coincided with what was estimated from observations of fluctuations in the intensity of cosmic microwave background radiation - about 70%.

New ways for scientists to compare theoretical predictions of cosmology with observational data have emerged thanks to data accumulated in recent years on the coordinates of hundreds of thousands of galaxies. In February 2002, scientists from the UK estimated the values ​​of all the main cosmological parameters by combining data on the cosmic microwave background radiation with characteristics of the large-scale distribution of 250 thousand galaxies, the distances to which were determined during the 2dF survey on the Anglo-Australian Telescope. The calculated values ​​are in excellent agreement with data from other studies. And in this work it turned out to be impossible to do without dark energy! Quite independently of the results of Rees's group, George Efstathiou and his colleagues estimated that its contribution to the total density of the Universe is 65-85%.

Dark water in the clouds

Cosmology has long ceased to be a “pure science”. Modern ideas about the structure and evolution of the Universe are based on a significant amount of observational and experimental data. This should be remembered by those who consider themselves ready to create their own Theory of the Universe. We often hear that “official” science is intolerant of new ideas and stubbornly rejects everything that does not fit into the existing system of knowledge. The history of the formation of cosmology is a direct refutation of this thesis. At its various stages, such strange hypotheses as the variability of fundamental constants - the gravitational constant, say, or even the speed of light - were quietly discussed and are still being discussed. Some of these hypotheses have sunk into oblivion, others continue to exist, acquiring experimental evidence and new supporters.

What fate awaits dark matter and dark energy? Will a more successful physical concept appear in ten years, which will include both the oddities in the movement of galaxies and the properties of the cosmic microwave background radiation? So far, only the dark matter hypothesis has a more or less real alternative. This is the so-called MOND theory - Modified Newtonian Dynamics, developed in the mid-1980s by the Israeli physicist M. Milgrom. According to this theory, the usual notation of the law of universal gravitation - with inverse proportion to the square of the distance - is valid only up to a certain limit. If the acceleration of the body caused by the force of gravity turns out to be less than approximately 10 -10 m/s 2, an amendment must be made to the law of universal gravitation, which explains the strange movement of stars on the outskirts of spiral galaxies. Unfortunately, the MOND theory does not have a relativistic extension, so it is unable to explain phenomena that go beyond simple dynamic problems.

Overall, it must be recognized that dark matter and dark energy, which were initially just hypothetical concepts introduced into theory to reconcile it with observations, fit very well into the modern picture of the world. It is important that with their help scientists managed to connect the two poles of physics - cosmology and elementary particle physics. However, direct experimental detection of these two entities remains a matter for the future. Until this happens, we will be prepared for any unexpected turns!

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But there are such people - they hear perfectly,
How a star speaks to a star.
- Y. Kim

The sight of the night sky strewn with stars has long instilled awe and delight in the human soul. Therefore, even with a slight decline in general interest in science, astronomical news sometimes leaks into the media to shake up the imagination of the reader (or listener) with a message about a mysterious quasar on the very outskirts of the Universe, about an exploded star, or about a black hole hidden in the depths of a distant galaxy. It is quite natural that sooner or later an interested person will have a legitimate question: “Come on, aren’t they leading me by the nose?” Indeed, many books have been written on astronomy, popular science films are being made, conferences are being held, the circulation and volume of professional astronomical magazines are constantly growing, and all this is a product of simply looking at the sky?

This image shows the shell ejected during the second nova T Compass (T Pyxidis) outburst. The bright point in the center of the shell is a double star, consisting of an ordinary star and a stellar remnant (white dwarf). The star's matter flows onto the white dwarf, gradually accumulating on its surface. When the mass of accumulated matter exceeds a certain critical limit, an explosion occurs in the system. For some reason (perhaps as a result of interaction with the remnants of previous explosions), the ejected shell disintegrates into thousands of tiny glowing nodules. In addition to spectroscopic examination of these nodules, by observing them over several years, one can directly see how they fly away from the system. © Shara, Williams, Gilmozzi, and NASA. Image from hubblesite.org

Take, for example, physics, chemistry or biology. Everything is clear there. The subject of research of these sciences can be “touched” - if not directly held in hands, then at least subjected to comprehensive research in experimental settings. But how can astronomers assert with the same confidence, for example: “In a binary system, 6 thousand light years away from us, matter is torn from a red star, twists into a thin disk and accumulates on the surface of a white dwarf,” presenting a photograph as evidence , on which neither a red star, nor a dwarf, much less a disk is visible, but there is only a bright point surrounded by several more similar ones, perhaps not so bright? This confidence is not a consequence of inflated self-esteem. It stems from the ability to connect myriads of disparate observational facts into a single, interconnected, internally consistent picture of the Universe, while successfully predicting the discovery of new phenomena.

The basis of our knowledge of the Universe is the conviction that all of it (or at least all of its visible part) is governed by the same physical laws that we discovered on Earth. This idea did not arise out of nowhere. It cannot even be said that physical laws were first discovered on Earth and then found confirmation in Space. Physicists have never considered our planet in isolation from the rest of the Universe. The law of universal gravitation was derived by Newton from observations of the Moon, and his first “triumph” was the calculation of the orbit of Halley’s Comet. Helium was discovered first on the Sun and only then on Earth.

From radio waves to gamma rays

The idea of ​​the unity of physical laws allows us to make a very important assumption. Let us not, for example, penetrate into the bowels of a star or into the core of a galaxy in order to directly see the processes occurring there. But we can logically deduce these processes by observing the result they produce. The result in the overwhelming majority of cases is light, or rather electromagnetic radiation in a very wide frequency range, which we directly register. Everything else - besides radiation - is a product of the theoretical interpretation of observations, the essence of which is contained for astronomers in the simple formula “O - C”, that is, “observable” ( o bserved) minus "calculated" ( c amputated). To understand the nature of an object, you need to construct it model, that is, a physical and mathematical description of the processes occurring in it, and then, using this model, calculate what kind of radiation should be generated in this object. Next, it remains to compare the model’s predictions with the observational results and, if the comparison turns out to be not entirely convincing, then either change the parameters of the existing model or come up with a new, more successful one.

There is something to compare with, because light carries a colossal amount of information. Even a quick glance at the stars is enough to notice that they differ in color. This is already very important information, since color depends on temperature. In other words, simply by looking at the stars with the naked eye and assuming that they are subject to the laws of radiation known to us (say, Wien's law of displacement), we can already say that the surfaces of stars have different temperatures - from two to three thousand degrees (red stars) up to tens of thousands of degrees (white and blue stars).

Color and temperature The simplest type of radiation is thermal- that is, radiation associated with body temperature. Thermal radiation warms the frozen palms of a tired traveler who has built a small fire on the side of the road; incandescent light bulbs illuminate our homes with thermal radiation; It is thermal radiation that carries solar energy to Earth for billions of years. Formally, a heated body emits over the entire range of wavelengths (or frequencies), but there is a certain wavelength at which the maximum emitted energy occurs. For a radiation source with the simplest possible properties, which in physics is called a black body, this wavelength is inversely proportional to the temperature: λ = 0.29/T, where the wavelength is expressed in centimeters and the temperature in Kelvin. This ratio is called Wien's displacement law. Visually, it is this wavelength (of course, in combination with the spectral sensitivity curve of the eye) that determines the visible color of the heated body. In the spectra of stars, the distribution of radiation energy over wavelengths is somewhat different from the “blackbody” one, but the connection between “color” and temperature remains the same. The word “color” is put in quotation marks here, because instead of a subjective description (red, yellow, blue, etc.), astronomy uses less picturesque, but much clearer numerical characteristics - the so-called color indices.

Of course, in reality everything is more complicated, since the radiation of a body is not always associated with the fact that it has a certain temperature. In other words, it may have non-thermal nature, such as synchrotron or maser. However, this can be easily established by determining not only the “color,” that is, the frequency at which the maximum radiation occurs, but also the entire shape of the spectrum, that is, the distribution of emitted energy across frequencies. Modern equipment makes it possible to record radiation in a huge frequency range - from gamma to radio waves.

Although the general shape of the spectrum of a star or other object already speaks volumes (for example, about the nature of the radiation - whether it is thermal or not, and if thermal, then what temperature it corresponds to), the spectrum also contains a much more capacious carrier of information - lines. Under certain conditions, a substance emits (if it emits itself) or absorbs (if it is illuminated by another source) light only at certain frequencies. A specific set of frequencies depends on the individual distribution of energy levels of atoms, ions or molecules of a substance, which means that based on the presence of a particular spectral line, it can be concluded that these atoms and molecules are present in the emitting or absorbing substance. By the intensity of the line, by its shape, polarization, as well as by the ratio of the intensities of different lines of the same atom or molecule, one can determine the content of a given element in the star’s atmosphere, the degree of ionization, the density of the substance, its temperature, the magnetic field strength, and the acceleration of gravity. .. If a substance moves, its spectrum, including lines, shifts as a whole due to the Doppler effect: to the blue side of the spectrum if the substance is approaching us, to the red side if the substance is moving away. This means that from the displacement of the lines relative to the “laboratory position” we can draw conclusions, for example, about the movement of both the star as a whole, if the entire spectrum is shifted, and individual layers of its atmosphere, if the lines formed at different depths are shifted differently .

The first map of the solar spectrum was built at the beginning of the 19th century by the famous optician Joseph Fraunhofer. He assigned letter designations to the most noticeable dark lines in the spectrum of the Sun, some of which are still used by astronomers today ( top picture). In the second half of the 19th century, it became clear that the position of absorption lines ( dark) in the spectrum of the Sun coincides with the position of the emission lines ( light) in laboratory spectra of various chemical elements. From a comparison of the spectra presented here, it can be seen that the Fraunhofer lines h, G", F and C belong to hydrogen, and the double line D belongs to sodium. Fig. from optics.ifmo.ru

In the spectrum of a star like the Sun, the number of spectral lines (in this case, absorption lines) is measured in many thousands, so it can be said without exaggeration that we know almost everything about stellar atmospheres (where the matter is located that manifests itself in the form of lines). Almost - because the theory of spectra formation itself is imperfect, although it continues to be continuously improved. In any case, the radiation of stars carries a huge amount of information that you just need to be able to decipher. It is not for nothing that popular texts like to compare spectra to fingerprints.

Burn, burn, my star

But the atmosphere is only a small fraction of the star's matter. What can we say about its depths? After all, you can look there only theoretically - armed with physical laws. (However, now astronomers are actively mastering the methods of seismology, using the “jitter” of spectral lines to study the features of the propagation of sound waves in the bowels of stars and thus restoring their internal structure.) Knowing the temperature and density on the surface of a star (for example, the Sun), and also assuming that its own gravity is balanced by thermal and light pressure (otherwise the star would expand or contract), you can calculate the change in temperature and density with depth, reaching the very center of the star, and at the same time try to answer the question of what exactly makes the Sun and other stars glow.

Convective movements in the near-surface regions of the Sun generate sound waves that go deep into the star, pierce through it, are reflected from the surface and again plunge into the interior (see figure on the left). This process is repeated many times, as a result of which each section of the solar surface seems to “breathe” or vibrate. The figure on the right shows one of the modes of seismological oscillations of the solar surface (blue areas rise, red areas fall). According to measurements from the SOHO space solar observatory, the oscillation frequency in this mode is approximately 3 millihertz. © GONG (Global Oscillation Network Group). Images from gong.nso.edu

A study of the history of the Earth has shown that the energy output of the Sun has remained almost unchanged for several billion years. This means that the proposed source of solar (stellar) energy must be very “long-lasting.” Currently, only one suitable option is known - this is a chain of thermonuclear reactions, starting with the reaction of converting hydrogen into helium. Assuming that it is this that forms the basis of stellar energy, it is possible to construct theoretical models of the evolution of stars of various masses - evolutionary tracks that make it possible to describe changes in the external parameters of a star (its luminosity and surface temperature) depending on the processes occurring in its interior. Of course, we are deprived of the opportunity to observe a star throughout its entire life. But in star clusters we can observe what stars of different masses look like, but of approximately the same age.

Distances and ages Determining distances in astronomy is, as a rule, a multi-step procedure, therefore the system of astronomical “length standards” is sometimes figuratively called the “distance ladder”. It is based on determinations of distances in the Solar System, the accuracy of which, thanks to radar methods, in some cases has already reached millimeter values. From these measurements the value of the main astronomical standard of length is derived, which without any special frills is called “ astronomical unit" One astronomical unit is the average distance from the Earth to the Sun and is approximately 149.6 million km. The next step in the “distance ladder” is the method of trigonometric parallaxes. The Earth's orbital movement means that over the course of a year we find ourselves on one side of the Sun, then on the other, and as a result we look at the stars from slightly different angles. In the earth's sky, this looks like oscillations of a star around a certain average position - the so-called annual parallax. The farther the star is, the smaller the range of these oscillations. Having determined how much the apparent position of a star changes due to its annual motion, you can determine its distance using ordinary geometric formulas. In other words, the distance determined by parallax is not burdened with any additional assumptions, and its accuracy is limited only by the accuracy of the parallax angle measurement. Another unit of measurement of astronomical distances is associated with the parallax method: parsec. One parsec is the distance from which the radius of the Earth's orbit is visible at an angle of one second. The trouble is that even for the nearest stars the parallactic angle is very small. For example, for α Centauri it is equal to only three quarters of an arc second. Therefore, with the help of even the most modern goniometric instruments, it is possible to determine the distances to stars that are no more than a few hundred parsecs distant from us. For comparison, the distance to the center of the Galaxy is 8–10 thousand parsecs. On the next rung of the ladder are “photometric” distances, which are distances based on measuring the amount of light coming from a radiation source. The further away it is from us, the dimmer it becomes. Therefore, if we somehow If it is possible to determine its true brightness, then, by comparing it with the apparent brightness, we will estimate the distance to the object. At relatively short distances, they have remained out of competition since the beginning of the 20th century. Cepheids- a special type of variable stars whose true brightness is related by a simple ratio to their period. At greater distances, supernovae of the type Ia. Observations indicate that at maximum brightness their true brightness is always approximately the same. Finally, at the greatest distances the only indication of the distance to the object is so far Hubble's law- a direct proportionality between the distance and the shift of lines to the red region of the spectrum, discovered by an American astronomer. It is important to note that outside the solar system the only direct The method for determining distances is the parallax method. All other methods rely to one degree or another on various assumptions. With age the situation is much less certain. So much less that it is not always clear what exactly to call age. Within the Solar System, in addition to conventional geological methods, to estimate the age of the surfaces of celestial bodies, for example, the degree of their coverage with meteorite craters is used (provided that the average frequency of meteorite impacts is known). The color of an asteroid's surface gradually changes under the influence of cosmic rays (a phenomenon called "cosmic erosion"), so its age can be roughly estimated by color. The age of cooling cosmic objects deprived of energy sources - brown and white dwarfs - is estimated by their temperature. Estimates of the ages of pulsars are based on the rate at which their periods slow down. It is possible to approximately determine the age of the expanding shell of a supernova if it is possible to measure its size and expansion rate. Things are better with the ages of the stars. True, it spends most of the star’s life at the stage of central hydrogen combustion, when very few external changes occur to it. Therefore, looking, for example, at a star like the Sun, it is difficult to say whether it was formed 1 billion years ago or 5 billion years ago. The situation becomes simpler if we manage to observe a group of stars of approximately the same age, but of different masses. Star clusters provide us with this opportunity. (The stars in them, of course, do not form exactly at the same time, but in most cases the spread of ages of individual stars is less than the average age of the cluster.) The theory of stellar evolution predicts that stars of different masses evolve differently - the more massive the star, the faster it ends its life. Star Trek". Therefore, the older the cluster, the lower the bar for the maximum mass of the stars inhabiting it falls. For example, in the very young Arches star cluster, located near the center of the Galaxy, there are stars with masses of tens of solar masses. Such stars live no more than a few million years, which means that this is the maximum age of this cluster. But in globular clusters the heaviest stars have a mass of no more than 2 solar masses. This suggests that the ages of globular clusters are measured in billions of years.

Theoretical models of stellar evolution predict that stars of different masses structure their lives differently: massive stars quickly burn through their large reserves of fuel, living brightly but briefly. Low-mass stars, on the contrary, use themselves very sparingly, stretching out their modest amount of hydrogen over billions of years. In other words, the theory predicts that the older a star cluster, the fewer massive stars it will contain. This is exactly the picture our observations give us. In young star clusters (with ages of the order of several million years), sometimes stars with masses of several tens of solar masses are found; in middle-aged clusters (tens and hundreds of millions of years), the upper limit of stellar masses drops to ten solar masses; finally, in the oldest clusters we practically do not see stars more massive than the Sun.

Of course, one can object to this that we use to confirm the theory of stellar evolution the ages of star clusters determined using this very theory. But the correctness of determining the ages of the clusters is confirmed by other facts. For example, clusters that appear to be the youngest from the point of view of stellar evolution theory are almost always surrounded by remnants of the molecular cloud from which they formed. The oldest clusters - globular ones - are old not only from the point of view of the theory of stellar evolution, they are also very poor in heavy elements (compared to the Sun), which is quite consistent with their venerable age. In that distant era when they were born, heavy elements in the Galaxy had not yet had time to be synthesized in large quantities.

Star clusters that inhabit the galactic disk are called open by astronomers. The stars included in them (usually no more than several hundred) are quite scattered in space, so that sometimes it is even difficult to distinguish a real cluster from a random grouping of stars in the sky. These clusters are mostly very young. Sometimes you can still observe remnants of the material from which the stars in the cluster were formed. Pictured on the left shows one of the most famous open clusters- NGC 346 in the satellite of our Galaxy, the Small Magellanic Cloud (210,000 light years away from us) in the constellation Tucana. The image was taken using the Space Telescope. Hubble in July 2004 (© NASA, ESA, and A.Nota, STScI/ESA). On right we see a completely different star family - globular cluster M15 in the constellation Pegasus, 40,000 light-years from Earth (© NASA and STScI/AURA). The stars of globular clusters are very old (see the “Distances and Ages” sidebar) and have low mass, but they are very numerous. If a typical open cluster includes hundreds of stars, then in a globular cluster their number can go into the millions - and this is with comparable sizes! The habitat of globular clusters is not limited to the disk - they form a kind of spherically symmetric cloud around our Galaxy with a radius of tens of thousands of parsecs. (Images from hubblesite.org)

True, the synthesis of heavy elements is also a prediction of the theory of stellar evolution! But it is also confirmed by independent observations: using spectroscopy, we have accumulated a lot of data on the chemical composition of stars, and the theory of stellar evolution perfectly explains these data not only from the point of view of the content of specific elements, but also from the point of view of their isotopic composition.

In general, we can probably end the conversation about the theory of stellar evolution like this. It is unlikely to find any one specific prediction that would confirm any one aspect of the theory. Rather, we have at our disposal a complex theoretical picture of the life of stars of various masses and chemical compositions, starting from the early evolutionary stages, when thermonuclear reactions in the star just ignited, to the last stages of evolution, when massive stars explode as supernovae, and low-mass stars shed their shells, exposing compact hot cores. It has made it possible to make innumerable theoretical predictions that are in excellent agreement with a very complex observational picture containing data on temperatures, masses, luminosities, chemical compositions, and spatial distributions of billions of stars of various types - from bright blue giants to white dwarfs.

Birth of stars and planets

The theory of stellar evolution has reached such impressive heights for a reason. Stars are bright, compact, numerous, and therefore easy to observe. Unfortunately, the Universe does not share information as willingly in everything. The picture of the Universe becomes significantly more vague and fragmented when we move, for example, from stars to the interstellar medium - the gas and dust that fills most of the space in disk galaxies like the Milky Way. The emission from interstellar matter is very weak, because the matter is either very rarefied or very cold. Observing it is much more difficult than the radiation of stars, but, nevertheless, it is also very informative. It’s just that instruments that allow astronomers to study the interstellar medium in detail have only recently appeared at the disposal of astronomers, literally in the last 10-20 years, so it is not surprising that there are still many “blank spots” in this area.

One of the most significant “spots” is connected, oddly enough, also with stars - we still don’t really know where they come from. More precisely, we have a general idea of ​​star formation, but not nearly as clear as the subsequent evolution of stars. We can say with confidence that stars are formed in molecular clouds as a result of compression of gas-dust condensations. From observations we know that, firstly, young stars are always in molecular gas, and secondly, next to “ready-made” young stars, so-called prestellar cores - dense gas-dust clumps, the spectra of which clearly indicate that these clumps are compressed. However, we cannot yet say how these clots appear and why they begin to shrink. More precisely, there are two main versions of star formation. According to one of them, molecular clouds are kept from being compressed by a magnetic field (there is indeed a magnetic field in molecular clouds), and prestellar cores appear where the support of the magnetic field weakens for some reason. According to another version, the driving force behind star formation is the turbulence observed in clouds: prestellar cores form where chaotic flows of matter randomly collide. However, the volume of observational data is still too small to confidently give preference to one of these mechanisms (or propose a third, fourth...).

Things are a little better with the theory of planet formation: according to modern ideas, they are formed in gas-dust disks of young stars. Again, no one has directly seen the formation of planets in them, but these disks themselves have been observed in large numbers. Thanks to this, indirect evidence was obtained that dust grains in young disks at a certain evolutionary stage begin to stick together, gradually increasing in size - at this stage the shape of the spectrum in the infrared range of the disks changes. Some "protoplanetary" disks have anomalous structural details - bends and "holes" - that can be caused by the gravity of the planets already formed in them.

This image of the disk of the young star β Pictoris was taken using the NASA Space Telescope. Hubble in 2003. It shows that in addition to the main disk, the system also has a secondary one, tilted relative to the main one by 4–5°. Astronomers consider this secondary disk to be indirect evidence that there is a planet in the β Pictoris system, the gravity of which disrupted the normal flow of matter in the main disk and led to its “bifurcation.” © NASA, ESA, ACS Science Team, D. Golimowski (Johns Hopkins University), D. Ardila (IPAC), J. Krist (JPL), M. Clampin (GSFC), H. Ford (JHU), and G. Illingworth (UCO/Lick)

Other worlds and lands

One of the hottest topics in astronomy today is extrasolar planets, the first of which was discovered in 1995. The main method for detecting them - the radial velocity method - is based on the Doppler effect: the planet, by its gravity, forces the star to describe a small ellipse around the center of mass of the system. If the planet's orbit is not strictly perpendicular to the line of sight, for half of its period the star approaches the observer, and for half of the period it moves away from him. As a result, the lines in the star’s spectrum “move” slightly, either to the right or to the left, from the average position. Strictly speaking, such fluctuations indicate the presence of a satellite, but do not allow us to confidently state that this is a planet, and not a brown dwarf or a very low-mass star (if it were a “normal” star, it would simply be visible). The “curse of sine” hangs over such observations. i", Where i- the angle between the plane of the planet’s orbit and the plane of the sky. From the amplitude of spectral line oscillations, it is not the mass that is determined, but its product by sin i. The meaning of this multiplication is simple: if the orbit lies exactly in the plane of the sky, we will not see any fluctuations in the spectrum, even if the star’s satellite is very massive. Therefore, doubts are still expressed about the radial velocity method. Firstly, the body discovered with its help may not be a planet, and secondly, fluctuations in radial velocities, generally speaking, can be associated with movements in the atmosphere of the star...

In the overwhelming majority of cases, the only evidence for the existence of a planet is regular fluctuations in the radial velocity of the “parent” star. In several cases, they are supplemented by regular and synchronized with fluctuations in the radial velocity of the decrease in the brightness of the star - eclipses. Only in a couple of unconfirmed cases has the planet been observed as a luminous point next to a star. Therefore, keep in mind - if in an astronomical news you come across a colorful image of a planet near another star, this is always the artist’s imagination... (The figure shows a gas giant ( big blue top picture), orbiting the white dwarf and millisecond pulsar B1620-26 ( two bright dots at the bottom of the picture) in the globular cluster M4. Astronomers suspect it is a planet because its mass is too low for a star or brown dwarf.) Graphic: NASA and G.Bacon (STScI)

It’s another matter if the plane of the planet’s orbit is almost perpendicular to the plane of the sky, that is, almost parallel to the line of sight. In this case, we can expect to see the planet eclipsing the star. And, since 1999, such eclipses have actually been observed! So far, however, only a few examples of extrasolar planets are known, the parameters of which were simultaneously determined both by eclipses and by the radial velocity method. Eclipses in these systems occur exactly when the radial velocity method predicts them, giving hope that in most cases, “planetary” line fluctuations in the spectra of stars are indeed associated with planets.

By the way, since in such an eclipsing system the angle i approximately equal to 90°, and sin i, accordingly, is close to unity, then the minimum mass of the planet determined by the radial velocity method is close to its true mass. Therefore, in this case, we can confidently distinguish the planet from a brown dwarf.

See the invisible

Speaking about the invisible, it is impossible, of course, not to talk about the most intriguing astronomical objects. The concept of black holes - objects with such powerful gravity that even light cannot escape from them - appeared in science back in the 18th century thanks to the Englishman John Michell and the Frenchman Pierre Laplace. At the beginning of the 20th century, the German scientist Karl Schwarzschild gave this idea mathematical validity, deducing black holes as a consequence of the general theory of relativity. In other words, black holes were predicted theoretically long before it was even possible to think of finding evidence of their actual existence in nature. And how can we talk about the discovery of objects that are impossible to see not simply because of the temporary imperfection of the equipment, but by definition? It is quite natural that the main argument in favor of calling a certain massive object a black hole was its invisibility. The first black hole candidate in the early 1970s was the invisible companion of the binary system Cygnus X-1. It has a mass of more than 5 solar masses, but all attempts to detect its own radiation have been unsuccessful. Its presence is indicated only by the gravitational effect that it has on the matter of the visible component. As it turns out, it's very difficult to come up with another a physical entity that would have such a large mass and yet remain invisible.

Even more convincing evidence of the reality of black holes has been obtained in recent years for the core of our Galaxy. Moreover, it does not stem from some complex theories, no, but from ordinary celestial mechanics, which describes the motion of the satellite around the main body. Over the past decade, scientists have been tracking the motion of several stars in the immediate vicinity of the geometric center of the Galaxy. The orbit of one of these stars is drawn almost completely - it revolves around the center in an elongated ellipse as if it were in the gravitational field of an object with a mass of several million solar masses. The radius of the object does not exceed several tens of astronomical units - this is the size of the orbit of this star. Naturally, any gravitating object can only be smaller than the orbit of its satellite. Imagine: millions of solar masses of matter packed into the size of the solar system and yet remain invisible! Here we need to remember another great scientific principle - the so-called Occam's razor: there is no need to multiply entities unnecessarily, giving preference to the simplest of all explanations. The black hole, no matter how exotic it may seem, remains today the simplest solution to this riddle. Although this, of course, does not guarantee that an even simpler solution will not be found in the future.

Orbits of stars in the core of our Galaxy. The length of the double-pointed arrow in the upper right corner is approximately 1600 astronomical units. This map was built by Andrea Ghez and her colleagues from the University of California at Los Angeles based on long-term observations at the Telescope. Keck). The asterisk marks the place where the body should be located, the gravity of which causes the stars to move along these trajectories. The laws of celestial mechanics make it possible to determine that the mass of this body is several million solar masses. Particularly interesting are the orbits of the stars S0-2 and S0-16, which approach the invisible body at a distance of only a few tens of astronomical units, thereby imposing a very serious limitation on its size. Rice. from www.astro.ucla.edu

In principle, the above also applies to quasars - unusually bright and very compact sources of radiation, the incredibly high luminosity of which is explained by the release of energy during the accretion (fall) of matter onto a black hole. Matter does not fall directly onto the hole, but swirls around it, forming a thin accretion disk. This is due to the fact that in a rotating system, gravity (of the central object or the entire system) in the direction perpendicular to the axis of rotation is balanced by centrifugal force, so compression occurs only parallel to the axis of rotation, “flattening” the system into a flat pancake.

The movement of gas in a disk is described by Kepler's laws (therefore, such disks are sometimes called “Keplerian”). Although Kepler's name is usually associated with the conjecture that the planets of the solar system revolve around the Sun in ellipses, Kepler's laws are equally applicable to motion in a circle (which is a special case of an ellipse).

One of the manifestations of Kepler's laws in relation to disks is that layers at different distances from the center move at different speeds and, as a result, “rub” against each other, converting the kinetic energy of orbital motion into thermal energy and then into radiation energy. This explanation may not be the only one, but today it is the simplest. In the end, if we ignore the scale of the phenomenon, the source of heating (and glow) of matter in the accretion model is friction - how much simpler? The monstrous energy of quasars requires that the object on which the matter “falls” be very massive and geometrically small (the smaller the inner radius of the disk, the more energy is released in it). In the core of the active galaxy NGC 4258, it was possible to observe the “Keplerian” disk directly, that is, not just to discern a very flat gas structure, but to measure the speed of movement of matter in it and demonstrate that this is precisely the disk rotating “according to Kepler.” Quasars are located in the centers of galaxies, that is, exactly where objects very similar to black holes have been discovered in our and other galaxies... It is logical to assume that massive compact objects in quasars are also black holes.

Another cosmic invisible thing is dark matter, that is, matter that manifests itself in gravity, but not in radiation. The idea of ​​its existence was expressed by astronomer Fritz Zwicky. He drew attention to the fact that the speeds of galaxies in clusters are too high to be explained by the gravity of visible matter alone. In galaxy clusters there should be something else, invisible, but possessing a gravitational field. Later, similar anomalies were discovered in the motion of stars inside galaxies. The dark matter hypothesis is criticized on the grounds that it seems to violate the same Ockham rule: having discovered ambiguities in the movements of stars and galaxies, astronomers did not explain them from the standpoint of existing theories, but immediately introduced a new entity - dark matter. But this criticism, in my opinion, is unfair. First, “dark matter” is not an entity in itself. This is simply a statement of the fact that the motion of stars in galaxies and galaxies in clusters is not described only by the gravity of visible matter. Secondly, it is not so easy to explain this gravitation by existing entities.

In general, any massive invisible (with the help of modern means of observation) objects are suitable for the role of dark matter. For example, space-filling brown dwarfs or so-called “black” dwarfs, that is, cooled, cold and therefore invisible white dwarfs, could easily pass for dark matter. However, these objects have a major drawback: they can be used to describe dark matter, but they cannot be painlessly fit into the modern picture of the Universe. A white dwarf is not only a few tenths of the solar mass of invisible matter, but also a fair amount of carbon and nitrogen synthesized by the star that was the predecessor of this white dwarf. If we assume that space is filled with cooled white dwarfs, we will answer the question about the nature of dark matter, but we will be forced to engage in a difficult search for an answer to another question - where did the C and N atoms ejected by these dwarfs go, which should have appeared in the chemical composition of the stars of the next generations? In addition, both white and brown dwarfs have another common disadvantage: they do not form on their own. Together with them, more massive stars should have formed in fair quantities. These stars, exploding at the end of their life as supernovae, would simply scatter the galaxy throughout the surrounding space. This is how it turns out that elementary particles unknown to science turn out to be not exotic, but the most easily explained candidate for the role of dark matter. However, attempts to explain the anomalous movement of stars by invisible “ordinary” objects continue.

The "materiality" of dark matter is also disputed. Quite a lot of work is now being published on the theory of MOND - modified Newtonian dynamics. According to it, during movements with very low accelerations, corrections must be introduced into the formulas for Newtonian gravity. Failure to take these corrections into account leads to the illusion of additional mass.

Touch with your hands

The statement that astronomers cannot touch the objects they study is not always true. At least within the Solar System, we can not only photograph something in detail, but also “touch” it (at least through automatic machines). It is not surprising, therefore, that its structure is known to us quite well. It is unlikely that anyone will dispute the fact that the Earth revolves around the Sun and that along with it a great many different bodies also revolve around the Sun. We understand the forces under which these bodies move, and we are able to predict their movement. Actually, it was the study of the movement of celestial bodies that led to the emergence of the most precise branch of astronomy - celestial mechanics.

Let us at least recall the history of the discovery of the first asteroid - Ceres. The Italian astronomer G. Piazzi discovered it on the first night of the 19th century and immediately lost it. However, knowledge of the trajectory along which must The movement of Ceres (if our ideas about the structure of the solar system are correct) allowed the German mathematician K. Gauss to predict its position on future dates, and a year after its discovery, Ceres was found again, and exactly where it should have been.

Here we can also recall the textbook story of the discovery of Neptune “at the tip of a pen,” but a much better proof of understanding the celestial-mechanical structure of the Solar System is its practical use. Nowadays, it is a rare flight of an interplanetary spacecraft without the so-called gravitational maneuver - the flight path is laid out in such a cunning way that in different parts of it the device is accelerated by the attraction of large planets. Thanks to this, it is possible to save a lot of fuel.

In short, we have a very good (though not perfect) understanding of movement bodies of the solar system. The situation is worse when it comes to understanding their individual nature. You don't have to look far for examples. Martian canals - what a wonderful illusion it was! Observational astronomers drew maps of the Martian reclamation network, astrobotanists put forward bold hypotheses about the life cycle of Martian plants, science fiction writers inspired by them painted pictures of contact with Martians (for some reason, one is more terrible than the other)... The first photographs of the Red Planet obtained by spacecraft dispelled these fantasies do not even turn into dust - into smoke. It would be nice if the channels turned out to be something other than what they were taken for. No, they were simply absent! The obsessive desire to see something “like that” on Mars played a cruel joke on observers. Upon closer inspection, the Red Planet appeared completely dead.

Our understanding of Mars now is radically different from what it was just some 50 years ago. Many probes have flown to Mars, landers have visited it, including rovers, which have traveled a significant number of kilometers on its surface. Detailed maps of relief, temperatures, mineral composition, and magnetic field of the surface of Mars were constructed. We can safely say that at least we know almost everything about the surface and atmosphere of Mars. Does this mean that there is no room for guesswork in Martian exploration? Oh no!

The trouble is that the active phase of Mars’ life has long ended. Despite the proximity of the Red Planet, we still see only the result, but are deprived of the opportunity to observe the process. We have to resort to analogies. After all, Earth and Mars aren't that different from each other. Why not assume that similar landforms on both planets were formed by similar processes? The very first photographs of the Martian surface brought earthlings not only the sad news about the absence of channels. They also found something interesting - dry river beds. There may be no water on modern Mars, but it was there in the distant past! For what, other than flowing water, can leave such traces? Add to this the layering of the rocks of Mars, which is very similar to the structure of terrestrial sedimentary rocks, and the presence of minerals that on Earth are formed only in a liquid medium... In a word, the entire body of data on Mars suggests that once, most likely a very long time ago and for a very short time, there were reservoirs on it. But all this data is, of course, indirect evidence. And this is where the line lies beyond which the reader or listener of astronomical news should keep his or her ears open. For from the result of an observation to the conclusion from it there runs a chain of logical conclusions and additional assumptions, which does not always end up in the text of popular news (this, however, is true not only of astronomy, but also of other sciences).

This slope of one of the craters on Mars was photographed several times by the American space probe Mars Global Surveyor. The image, taken in September 2005, clearly shows a fresh trail of... what? Outwardly, it looks as if it was left by groundwater that broke through to the surface and immediately froze. But is this the only possible explanation? © NASA

Another clear example is Europa, one of the Galilean satellites of Jupiter. Spectral analysis shows that the surface of this satellite consists of water ice. But the average density of Europa’s substance (3 g cm–3) is three times higher than the density of water, which means that most of the satellite consists of a rocky core surrounded by a less dense water shell. The differentiation of the structure of Europa, that is, the division into a more refractory core and a low-melting shell, suggests that the interior of this satellite has been and may be subject to significant heating. The source of this heating is most likely tidal interaction with Jupiter and other satellites of the giant planet.

Jupiter's moon Europa, unlike most bodies in the Solar System, is quite smooth and almost completely devoid of meteorite craters. Its surface, consisting of water ice, is constantly smoothed out, retaining only a dense network of shallow cracks from the relief details. The mobility of Europa's crust suggests that some less solid material is hidden underneath it, but this may not be water, but just a loose, wet mass, similar to melted snow. The image was obtained using the Galileo Interplanetary Station (it is composed of a low-resolution image taken on July 28, 1996, during the first Galileo flyby of Jupiter, and a high-resolution image taken on May 31, 1998, during the 15th flyby). © NASA/JPL/University of Arizona/University of Colorado; photo from photojournal.jpl.nasa.gov

The interesting thing about the situation is that tidal heat is enough to keep part of Europa's watery shell in a liquid state. In other words, an ocean may be hidden under Europa’s ice crust... The structure of the satellite’s surface is consistent with this. It is constantly “rejuvenating”, as evidenced by the almost complete absence of meteorite craters, and an extensive network of faults and cracks indicates tectonic activity, which may be associated with the mobility of solid ice on a liquid substrate. Liquid water, a constant source of heat (tidal deformations), the availability of carbon compounds (they are found almost everywhere in the Solar System) - what else is needed for the origin of life? And now a bright headline is ready: “There are living beings on the satellite of Jupiter!” However, it is obvious that until the flight of the research probe to Europa, the presence of an under-ice ocean will remain a hypothesis, and the possible existence of centers of life in it will be a complete fantasy.

The end of the era of anthropocentrism This may seem strange to some, but there is convincing evidence that the solar system is located Not in the center of the Universe were obtained only at the beginning of the 20th century. American astronomer Harlow Shapley obtained them while studying the spatial distribution of globular star clusters (GCs). At that time, it was already known that globular clusters were scattered unevenly across the sky, concentrated mainly in only one half of the sky. But only Shapley was able to reveal the actual scale of this unevenness. Having determined the distances to globular clusters from observations of Cepheids in them (see the sidebar “Distances and ages”), he established that the clusters are distributed in space spherically symmetrically, and the center of this distribution not only does not coincide with the Sun, but is tens of miles away from it thousand light years! Shapley guessed that the center of the SHZ system coincides with the true center of our Galaxy, but for many years he refused to admit that other “stellar islands” could exist in the Universe besides it. The gigantic size of the Galaxy shocked Shapley himself so much that he simply could not imagine that there was room for anything else in the Universe. Meanwhile, in 1924, the American astronomer Edwin Hubble, using the then largest 2.5-meter telescope of the Palomar Observatory, for the first time, as astronomers say, “resolved the stars” of the Andromeda Nebula. In other words, he proved that its hazy glow is in fact generated by myriads of individual stars collected into a single system similar to the Milky Way. Thus, it was proven that the Sun is not located in the center of the Galaxy, but on its outskirts, and the Galaxy itself is only one of many hundreds of billions of star systems.

Can all this be believed?

Alas, the remoteness of most astronomical objects and the significant duration of most astronomical processes lead to the fact that evidence in astronomy is, as a rule, indirect. Moreover, the further we move away from the Earth in space and time, the more indirect the evidence. It would seem that there is every reason to be suspicious of astronomers’ statements! But the strength of these statements lies not in the “reinforced concreteness” of the evidence, but in the fact that this evidence adds up to a single picture. Modern astronomy is not a collection of isolated facts, but a system of knowledge in which each element is connected to others, just as individual pieces of a puzzle are connected to each other. The number of supernovae depends on the total number of stars born per year, which means that the rate of star formation must be consistent with the rate of supernova explosions. This rate, in turn, is consistent with the observed amount of the radioactive isotope of aluminum synthesized during flares. Moreover, many of these connections were first predicted and then discovered in observations. The cosmic microwave background radiation was first predicted and then discovered, neutron stars were first predicted and then discovered... The shape of protoplanetary disks and the presence of various molecules in molecular clouds were predicted...

Each of the elements of this mosaic, taken separately, is of little significance, but together they form a very solid picture, which is closely linked to the successes of “terrestrial” physics. How much can you trust this picture? Of course, some pieces of the puzzle are better grounded than others. On the one hand, modern ideas about the nature of dark matter may be subject to revision. But it is unlikely that it will be possible to select an adequate replacement, for example, for the thermonuclear mechanism of energy production in the bowels of stars. Even at the beginning of the 20th century, there was some room for imagination in this area, but now the thermonuclear mechanism is consistent with a very large amount of observational data. If someone now wants to come up with their own mechanism, they will have to explain at least all of the same data without losing consistency with the adjacent pieces of the puzzle.

Astronomers' mistakes Alas, even an old woman can get into trouble. The remoteness of astronomical objects and the complexity of their study sometimes lead to the fact that the interpretation of observations is either ambiguous or completely incorrect. When there is a detailed spectrum of an object over a wide range, it is relatively easy to explain the observations. But what to do if only a piece of the spectrum was measured, and even that one was of low quality? This is exactly what often happens with distant and therefore very dim objects. For example, in 1999, the galaxy STIS 123627+621755 claimed the title of the most distant known galaxy in the Universe. A fragment of its spectrum measured using the Space Telescope. Hubble, corresponded to a huge redshift of 6.68 (see Spectroscopic identification of a galaxy at a probable redshift of z = 6.68 // Nature. 15 April 1999. V. 398. P. 586-588). At that time, this was a record, and therefore it was decided to continue research into the STIS 123627+621755 galaxy. However, going beyond the spectral range studied by Hubble, astronomers discovered that there was no longer any resemblance to a galaxy on the outskirts of the Universe. The full spectrum of the object turned out to be not only not similar to the spectrum of the galaxy at redshift 6.68, but also not similar to the spectrum of the galaxy at all! (See Evidence against a redshift z > 6 for the galaxy STIS123627+621755 // Nature. 30 November 2000. V. 408. P. 560-562.) In another example, an error in the interpretation of observational results turned out to be more serious. We were talking about observations of the phenomenon of “microlensing” - if any massive body appears on the line of sight between a distant star and the observer, its gravitational field acts like a lens, bends the path of the rays of the background star and leads to a short-term increase in its brightness. In 2001, astronomers from the Space Telescope Institute (USA) reported that during observations of the globular cluster M22, they noticed six such sudden increases in the brightness of the cluster stars (see Gravitational microlensing by low-mass objects in the globular cluster M22 // Nature. 28 June 2001. V. 411. P. 1022-1024). The brevity of the bursts indicated that the mass of the gravitational microlenses was very small - less than the mass of Jupiter. These observations prompted the announcement that free-flying planets had been discovered in the globular cluster M22. However, a detailed study of the images of M22 showed that the brightness jumps have nothing to do with the background stars. An imaginary increase in brightness occurred when a particle of cosmic rays fell directly into the image of the star during shooting (see A Re-examination of the "Planetary" Lensing Events in M22 // astro-ph/0112264, 12 Dec 2001). There are so many stars in a globular cluster, and they are located so densely, that a precise hit by cosmic rays on a star turned out to be not such an unlikely event.

I would say this: the foundations of the modern astronomical picture of the World can only be completely incorrect. That is, we can make mistakes not in individual fragments, but in all of physics at once. For example, if it turns out that the stars are not stars after all, but holes in the crystal sky, into which some joker releases radiation of different spectral composition...

A sign of the reliability of an element of an astronomical picture can, of course, be its longevity. And in this regard, astronomy seems to be a completely prosperous science: its basic concepts have not changed for many decades (it must be taken into account that modern astrophysics is only one and a half hundred years old). The theory of thermonuclear fusion was developed in the 1930s, the recession of galaxies was discovered in the 1920s, the theory of star formation is now rapidly evolving, but the key concept in it remains, for example, gravitational instability, the basic principles of which were formulated by J. Jeans at the very beginning of the 20th century ... We can probably say that conceptually nothing has changed in astronomy since Harlow Shapley proved that the Sun is not at the center of the Galaxy, and Hubble proved that the Andromeda Nebula is an extragalactic object. Of course, our ideas about the planets changed greatly with the advent of the Space Age, but early fantasies about Mars and Venus were born more of scientific romanticism than scientific foresight.

How to read astronomical news

Unfortunately, the presentation of this wonderful picture in the media leaves much to be desired. Therefore, one should be very careful when reading astronomical news in the press. As a rule, they are based on press releases, which in many cases are translated into Russian or retold in it rather poorly. Moreover, the general credibility of the publication publishing the news also does not guarantee anything. Therefore, if something in the news seemed vague, far-fetched, exaggerated, or illogical to you, do not rush to blame the scientists mentioned in it! If the message really interests you, try to at least find the original press release.

If the message captivates you so much that you want to conduct a critical analysis of it, do not consider it difficult to read the original work! Fortunately, most astronomical articles can be found on the Internet completely free of charge. True, to read them, you need to know English.

Dmitry Vibe,
Doctor of Physical and Mathematical Sciences,
Leading Researcher at the Institute of Astronomy of the Russian Academy of Sciences