Cosmos in the popular consciousness is represented by the realm of cold and emptiness (remember the song: “Here it is cosmic cold, the color of the sky is different”?). However, from about the middle of the 19th century, researchers began to understand that the space between the stars is at least not empty. A clear sign of the existence of interstellar matter is the so-called dark clouds, shapeless black spots, especially well distinguishable on the bright band of the Milky Way. In the 18th and 19th centuries, it was believed that these were real “holes” in the distribution of stars, but by the 1920s it was believed that the spots betray the presence of colossal clouds of interstellar dust that prevent us from seeing the light of the stars behind them (photo 1).

In the middle of the 19th century, a new era in astronomy began: thanks to the work of Gustav Kirchhoff and Robert Bunsen, spectral analysis appeared, which made it possible to determine chemical composition and physical parameters of gas in astronomical objects. Astronomers were quick to appreciate the new opportunity, and the 1860s saw a boom in stellar spectroscopy. At the same time, largely due to the efforts of the remarkable observer William Heggins, evidence was accumulating for the presence of gas not only in stars, but also in the space between them.

Heggins was a pioneer scientific research non-stellar matter. From 1863 he published the results of a spectroscopic study of certain nebulae, including the Great Nebula of Orion, and demonstrated that the spectra of nebulae in the visible range are very different from the spectra of stars. The radiation of a typical star is a continuous spectrum, on which absorption lines are superimposed, born in the stellar atmosphere. And the spectra of the nebulae obtained by Heggins consisted of several emission lines, with virtually no continuous spectrum. It was a spectrum of hot rarefied gas, the parameters of which are completely different from the parameters of gas in stars. The main conclusion of Heggins: observational confirmation of Herschel's assumption that in space, in addition to stars, there is diffuse matter distributed over significant volumes of space has been obtained.

In order for the proper glow of interstellar gas to be observed in the optical range, it must be not only hot, but also rather dense, and far from all interstellar matter meets these conditions. In 1904, Johannes Hartmann noticed that cooler and/or rarefied interstellar gas betrays its presence by leaving its own absorption lines in stellar spectra, which are not born in the atmosphere of the star, but outside it, on the way from the star to the observer.

The study of the emission and absorption lines of interstellar gas made it possible by the 1930s to study its chemical composition quite well and establish that it consists of the same elements that are found on Earth. Several lines in the spectra for a long time did not lend themselves to identification, and Heggins suggested that this was a new chemical element - nebulium (from lat. nebula- a cloud), but it turned out to be just doubly ionized oxygen.

By the early 1930s, it was believed that all lines in the spectrum of interstellar gas had been identified and assigned to specific atoms and ions. However, in 1934, Paul Merrill reported four unidentified lines in the yellow and red regions of the spectrum. Previously observed interstellar lines had a very small width, as befits atomic lines formed in low-density gas, but these were wider and blurry. Almost immediately, it was suggested that these are absorption lines not of atoms or ions, but of molecules. But what? Both exotic molecules were proposed, such as sodium (Na 2), and the usual diatomic compounds, discovered in cometary tails by the same Heggins back in the 19th century, for example, the CN molecule. The existence of interstellar molecules was finally established in the late 1930s, when several unidentified lines in the blue region of the spectrum were unambiguously associated with the compounds CH, CH + and CN.

A feature of chemical reactions in the interstellar medium is the dominance of two-particle processes: stoichiometric coefficients are always equal to one. At first the only way To the formation of molecules, the reactions of "radiative association" seemed: in order for two atoms, colliding, to unite into a molecule, it is necessary to remove excess energy. If a molecule, having formed in an excited state, has time to emit a photon before decay and pass into an unexcited state, it remains stable. Calculations carried out before the 1950s showed that the observed abundance of these three simple molecules seems to be able to be explained on the assumption that they are formed in radiative association reactions and are destroyed by the interstellar radiation field - the total radiation field of the stars of the Galaxy.

The range of concerns of astrochemistry at that time was not particularly wide, at least in the interstellar medium: three molecules, with a dozen reactions between them and their constituent elements. The situation ceased to be calm in 1951, when David Bates and Lyman Spitzer recalculated the equilibrium abundances of molecules, taking into account new data on the rates of radiative association reactions. It turned out that atoms bind into molecules much more slowly than previously thought, and therefore the simple model misses the prediction of the content of CH and CH + by orders of magnitude. Then they suggested that two of these molecules do not appear as a result of synthesis from atoms, but as a result of the destruction of more complex molecules, specifically methane. Where did methane come from? Well, it could have formed in stellar atmospheres and then entered the interstellar medium as dust grains.

Later, cosmic dust began to be attributed to a more active chemical role than the role of a simple carrier of molecules. For example, if for the effective flow of chemical reactions in the interstellar medium there is not enough third body, which would remove excess energy, why not assume that this is a grain of dust? Atoms and molecules could react with each other on its surface, and then evaporate, replenishing the interstellar gas.

Properties of the interstellar medium

When the first molecules were discovered in the interstellar medium, none of them physical properties nor even the chemical composition were well known. The very discovery of CH and CH+ molecules was considered in the late 1930s to be important evidence for the presence of carbon and hydrogen there. Everything changed in 1951, when the emission of interstellar atomic hydrogen, the famous emission at a wavelength of about 21 cm, was discovered. It became clear that hydrogen was the most abundant in the interstellar medium. According to modern concepts, interstellar matter is hydrogen, helium, and only 2% by mass of heavier elements. A significant part of these heavy elements, especially metals, is found in dust particles. The total mass of interstellar matter in the disk of our Galaxy is several billion solar masses, or 1–2% of the total mass of the disk. And the mass of dust is about a hundred times less than the mass of gas.

The matter is distributed over the interstellar space inhomogeneously. It can be divided into three phases: hot, warm and cold. The hot phase is a very rarefied coronal gas, ionized hydrogen with a temperature of millions of kelvins and a density of about 0.001 cm -3, which occupies about half the volume of the galactic disk. The warm phase, which accounts for another half of the disk volume, has a density of about 0.1 cm–3 and a temperature of 8000–10,000 K. Hydrogen in it can be both ionized and neutral. The cold phase is really cold, its temperature is no more than 100 K, and in the densest areas, frost is down to a few kelvins. Cold neutral gas occupies only about a percent of the volume of the disk, but its mass is about half of the total mass of interstellar matter. This implies a significant density, hundreds of particles per cubic centimeter and above. Significant in terms of interstellar concepts, of course - for electronic devices this is a wonderful vacuum, 10-14 Torr!

Dense cold neutral gas has a ragged cloud structure, the same one that can be traced in clouds of interstellar dust. It is logical to assume that clouds of dust and clouds of gas are the same clouds in which dust and gas are mixed with each other. However, observations have shown that the regions of space in which the absorbing effect of dust is maximum do not coincide with the regions of maximum intensity of atomic hydrogen radiation. In 1955, Bart Bock and co-authors suggested that in the densest parts of interstellar clouds, those that become opaque in the optical range due to a high concentration of dust, hydrogen is not in an atomic, but in a molecular state.

Since hydrogen is the main component of the interstellar medium, the names of the various phases reflect the state of hydrogen itself. An ionized medium is a medium in which hydrogen is ionized, other atoms can remain neutral. A neutral environment is one in which hydrogen is neutral, although other atoms may be ionized. Dense, compact clouds thought to be composed primarily of molecular hydrogen are called molecular clouds. It is in them that the true history of interstellar astrochemistry begins.

Invisible and visible molecules

The first interstellar molecules were discovered due to their absorption lines in the optical range. At first, their set was not too large, and simple models based on radiative association reactions and/or reactions on the surfaces of dust grains were enough to describe them. However, back in 1949, I.S. Shklovsky predicted that the radio range is more convenient for observing interstellar molecules, in which one can observe not only absorption, but also the emission of molecules. To see the absorption lines, you need a background star whose radiation will be absorbed by interstellar molecules. But if you're looking at a molecular cloud, you won't see the background stars, because their radiation will be completely absorbed by the dust that is part of the same cloud! If the molecules themselves radiate, you will see them wherever they are, and not just where they are carefully illuminated from behind.

The radiation of molecules is associated with the presence of additional degrees of freedom in them. A molecule can rotate, vibrate, make more complex movements, each of which is associated with a set of energy levels. Passing from one level to another, a molecule, like an atom, absorbs and emits photons. The energy of these movements is low, so they are easily excited even at low temperatures in molecular clouds. Photons corresponding to transitions between molecular energy levels do not fall into visible range, and in infrared, submillimeter, millimeter, centimeter ... Therefore, studies of the radiation of molecules began when astronomers had instruments for observations in the long wavelength ranges.

True, the first interstellar molecule discovered from observations in the radio range was nevertheless observed in absorption: in 1963 in the radio emission of the supernova remnant Cassiopeia A. This was the absorption line of hydroxyl (OH) - a wavelength of 18 cm, and soon hydroxyl was discovered in radiation. In 1968, an ammonia emission line of 1.25 cm was observed, a few months later water was found - a 1.35 cm line. Very important discovery in the study of the molecular interstellar medium was the discovery in 1970 of the emission of a molecule of carbon monoxide (CO) at a wavelength of 2.6 mm.

Until that time, molecular clouds were, to a certain extent, hypothetical objects. The most common chemical compound in the universe - the hydrogen molecule (H 2) - has no transitions in the long-wavelength region of the spectrum. At low temperatures in a molecular medium, it simply does not glow, that is, it remains invisible, despite all its high content. It is true that the H 2 molecule has absorption lines, but they fall into the ultraviolet range, in which it is impossible to observe from the surface of the Earth; we need telescopes mounted either on high-altitude rockets or on spacecraft, which greatly complicates observations and makes them even more expensive. But even with an extraatmospheric instrument, absorption lines of molecular hydrogen can only be observed in the presence of background stars. If we take into account that there are not so many stars or other astronomical objects emitting in the ultraviolet range, and, moreover, dust absorption reaches a maximum in this range, it becomes clear that the possibilities for studying molecular hydrogen from absorption lines are very limited.

The CO molecule has become a salvation - unlike, for example, ammonia, it begins to glow at low densities. Its two lines, corresponding to transitions from the ground rotational state to the first excited state and from the first to the second excited state, fall into the millimeter range (2.6 mm and 1.3 mm), which is still accessible for observations from the Earth's surface. Shorter wavelength radiation is absorbed by the earth's atmosphere, longer wavelength radiation produces less clear images (for a given objective diameter, the angular resolution of the telescope is the worse, the longer the observed wavelength). And there are a lot of CO molecules, and so many that, apparently, most of all carbon in molecular clouds is in this form. This means that the CO content is determined not so much by the features of the chemical evolution of the medium (unlike CH and CH + molecules), but simply by the number of available C atoms. Therefore, the CO content in a molecular gas can be considered, at least in the first approximation, to be constant.

Therefore, it is the CO molecule that is used as an indicator of the presence of a molecular gas. And if you come across somewhere, for example, a map of the distribution of molecular gas in the Galaxy, it will be a map of the distribution of precisely carbon monoxide, and not molecular hydrogen. The admissibility of such a widespread use of CO has recently been increasingly questioned, but there is nothing to replace it with. So one has to compensate for the possible uncertainty in the interpretation of CO observations with caution in its implementation.

New approaches to astrochemistry

In the early 1970s, the number of known interstellar molecules began to be measured in dozens. And the more they were discovered, the clearer it became that the previous chemical models, which did not explain the content of the first three CH, CH + and CN very confidently, do not work at all with an increased number of molecules. A new view (and still accepted today) of the chemical evolution of molecular clouds was proposed in 1973 by William Watson and independently by Eric Herbst and William Klemperer.

So, we are dealing with a very cold environment and a very rich molecular composition: about one and a half hundred molecules are known today. Radiative association reactions are too slow to provide an observable abundance of even diatomic molecules, let alone more complex compounds. Reactions on the surfaces of dust grains are more efficient, but at 10 K a molecule synthesized on the surface of a grain of dust will in most cases remain frozen to it.

Watson, Herbst and Klemperer suggested that in the formation of the molecular composition of cold interstellar clouds, the decisive role is played not by radiative association reactions, but by ion-molecular reactions, that is, reactions between neutral and ionized components. Their speeds do not depend on temperature, and in some cases even increase at low temperatures.

The point is small: the substance of the cloud needs to be ionized a little. Radiation (the light of stars close to the cloud or the total radiation of all the stars in the Galaxy) does not so much ionize as it dissociates. In addition, due to dust, radiation does not penetrate into molecular clouds, illuminating only their periphery.

But in the Galaxy there is another ionizing factor - cosmic rays: atomic nuclei accelerated by some process to a very high speed. The nature of this process has not yet been finally revealed, although the acceleration of cosmic rays (those that are of interest from the point of view of astrochemistry) most likely occurs in shock waves that accompany supernova explosions. Cosmic rays (like all matter in the Galaxy) consist mainly of fully ionized hydrogen and helium, that is, of protons and alpha particles.

Colliding with the most common H 2 molecule, the particle ionizes it, turning it into an H 2 + ion. He, in turn, enters into an ion-molecular reaction with another H 2 molecule, forming an H 3 + ion. And it is this ion that becomes the main engine of all subsequent chemistry, entering into ion-molecular reactions with oxygen, carbon and nitrogen. Then everything goes according to the general scheme, which for oxygen looks like this:

O + H 3 + → OH + + H 2
OH + + H 2 → H 2 O + + H
H 2 O + + H 2 → H 3 O + + H
H 3 O + + e → H 2 O + H or H 3 O + + e → OH + H 2

The last reaction in this chain, the dissociative recombination of a hydronium ion with a free electron, leads to the formation of a hydrogen-saturated molecule, in this case a water molecule, or to the formation of a hydroxyl. Naturally, dissociative recombination can also occur with intermediate ions. The end result of this sequence for the main heavy elements is the formation of water, methane and ammonia. Another option is possible: the particle ionizes an atom of an impurity element (O, C, N), and this ion reacts with an H 2 molecule, again with the formation of OH + , CH + , NH + ions (further with the same stops). Chains of different elements, of course, do not develop in isolation: their intermediate components react with each other, and as a result of this “cross-pollination”, most of the carbon passes into CO molecules, oxygen, which remains unbound in CO molecules, into water and O molecules. 2, and the N 2 molecule becomes the main reservoir of nitrogen. The same atoms that were not included in these basic components become constituent parts more complex molecules, the largest of which, known today, consists of 13 atoms.

Several molecules do not fit into this scheme, the formation of which in the gas phase turned out to be extremely inefficient. For example, in the same 1970, in addition to CO, a significantly more complex molecule, methanol, was discovered in significant quantities. For a long time, the synthesis of methanol was considered the result of a short chain: the CH 3 + ion reacted with water, forming protonated methanol CH 3 OH 2 + , and then this ion recombined with an electron, splitting into methanol and a hydrogen atom. However, experiments have shown that it is easier for a CH 3 OH 2 + molecule to fall apart in the middle during recombination, so that the gas-phase mechanism of methanol formation does not work.

However, there is a more important example: molecular hydrogen is not formed in the gas phase! The scheme with ion-molecular reactions works only if there are already H 2 molecules in the medium. But where do they come from? There are three ways to form molecular hydrogen in the gas phase, but all of them are extremely slow and cannot work in galactic molecular clouds. The solution to the problem was found in a return to one of the previous mechanisms, namely, reactions on the surfaces of cosmic dust particles.

As before, a grain of dust in this mechanism plays the role of a third body, providing conditions on its surface for the union of atoms that cannot be combined in the gas phase. In a cold environment, free hydrogen atoms freeze to dust particles, but due to thermal fluctuations, they do not sit in one place, but diffuse over their surface. Two hydrogen atoms, having met during these wanderings, can combine into an H 2 molecule, and the energy released during the reaction separates the molecule from the dust grain and transfers it to the gas.

Naturally, if a hydrogen atom meets on the surface not its counterpart, but some other atom or molecule, the result of the reaction will also be different. But are there other components on the dust? There is, and this is indicated by modern observations of the densest parts of molecular clouds, the so-called cores, which (it is possible) will turn into stars surrounded by planetary systems in the future. Chemical differentiation occurs in the nuclei: from the densest part of the nucleus, radiation of nitrogen compounds (ammonia, N 2 H + ion) mainly comes out, and carbon compounds (CO, CS, C 2 S) glow in the shell surrounding the nucleus, therefore, on radio emission maps such the nuclei look like compact spots of emission of nitrogen compounds, surrounded by emission rings of carbon monoxide.

The modern explanation of differentiation is as follows: in the densest and coldest part of the molecular core, carbon compounds, primarily CO, freeze to dust particles, forming ice mantle shells on them. In the gaseous phase, they are preserved only at the periphery of the core, where the radiation from the stars of the Galaxy possibly penetrates, partially evaporating the ice mantles. With nitrogen compounds, the situation is different: the main nitrogen-containing molecule N 2 does not freeze to dust as quickly as CO, and therefore enough nitrogen remains in the gas phase of even the coldest part of the core for much longer to provide the observed amount of ammonia and the N 2 H + ion.

In the icy mantles of dust particles, chemical reactions also take place, mainly associated with the addition of hydrogen atoms to frozen molecules. For example, the successive addition of H atoms to CO molecules in ice shells of dust grains leads to the synthesis of methanol. Slightly more complex reactions, in which other components are involved in addition to hydrogen, lead to the appearance of other polyatomic molecules. When a young star lights up in the depths of the core, its radiation evaporates the mantles of dust particles, and the products of chemical synthesis appear in the gas phase, where they can also be observed.

Successes and challenges

Of course, in addition to ion-molecular and surface reactions, other processes also occur in the interstellar medium: both neutral-neutral reactions (including radiative association reactions), and photoreactions (ionization and dissociation), and the processes of component exchange between the gas phase and dust grains. Modern astrochemical models have to include hundreds of different components interconnected by thousands of reactions. What is important is this: the number of simulated components significantly exceeds the number that is actually observed, since it is not possible to create a working model from the observed molecules alone! In fact, this has been the case since the very beginning of modern astrochemistry: the H 3 + ion, whose existence was postulated in the models of Watson, Herbst, and Klemperer, was observed in observations only in the mid-1990s.

All modern data on chemical reactions in the interstellar and circumstellar medium are collected in specialized databases, of which two are the most popular: UDFA (UMIST Database for Astrochemistry) and KIDA ( Kinetic Database for Astrochemistry).

These databases are essentially lists of reactions with two reactants, several products, and numerical parameters (from one to three) that make it possible to calculate the reaction rate as a function of temperature, radiation field, and cosmic ray flux. The sets of reactions on the surfaces of dust particles are less standardized, however, there are also two or three variants that are used in most astrochemical studies. The reactions included in these sets make it possible to quantitatively explain the results of observations of the molecular composition of objects of different ages and under different physical conditions.

Today, astrochemistry is developing in four directions.

First, the chemistry of isotopomers, primarily the chemistry of deuterium compounds, attracts much attention. In addition to H atoms, the interstellar medium also contains D atoms, in a ratio of approximately 1:100,000, which is comparable to the abundance of other impurity atoms. In addition to H2 molecules, HD molecules are also formed on dust grains. In a cold environment, the reaction
H 3 + + HD → H 2 D + + H 2
is not balanced by the reverse process. The H 2 D + ion plays a role in chemistry similar to that of the H 3 + ion, and through it the deuterium atoms begin to propagate through more complex compounds. The result turns out to be quite interesting: at a total D/H ratio of about 10–5, the ratio of the content of some deuterated molecules to the content of non-deuterated analogs (for example, HDCO to H 2 CO, HDO to H 2 O) reaches percent and even tens of percent. A similar direction for improving models is taking into account differences in the chemistry of carbon and nitrogen isotopes.

Secondly, reactions on the surfaces of dust grains remain one of the main astrochemical trends. Here, a lot of work is being done, for example, on studying the features of reactions depending on the properties of the surface of a dust grain and on its temperature. The details of evaporation from a dust grain of organic molecules synthesized on it are still unclear.

Thirdly, chemical models are gradually penetrating deeper and deeper into the study of the dynamics of the interstellar medium, including studies of the processes of the birth of stars and planets. This penetration is very important, since it makes it possible to correlate directly the numerical description of the motions of matter in the interstellar medium with observations of molecular spectral lines. In addition, this problem also has an astrobiological application related to the possibility of interstellar organic matter getting onto the forming planets.

Fourth, there are more and more observational data on the abundance of various molecules in other galaxies, including galaxies at high redshifts. This means that we can no longer close ourselves within the framework of the Milky Way and must deal with how chemical evolution occurs with a different elemental composition of the medium, with other characteristics of the radiation field, with other properties of dust grains, or what chemical reactions took place in the pre-galactic environment, when all the set of elements was limited to hydrogen, helium and lithium.

At the same time, many mysteries remain next to us. For example, the lines found in 1934 by Merill have not yet been identified. And the origin of the first found interstellar molecule - CH + - remains unclear ...

Infinitely diverse living organisms are composed of a limited set of atoms, the appearance of which we owe to a large extent to the stars. The most powerful event in the life of the Universe - the Big Bang - filled our world with a substance of a very meager chemical composition.
It is believed that the union of nucleons (protons and neutrons) in expanding space did not have time to advance further than helium. Therefore, the pre-galactic Universe was filled almost exclusively with hydrogen nuclei (that is, simply protons) with a small - about a quarter by mass - addition of helium nuclei (alpha particles). There was practically nothing else in it, apart from light electrons. How exactly the primary enrichment of the Universe with nuclei of heavier elements took place, we cannot yet say. To this day, not a single "primordial" star, that is, an object consisting only of hydrogen and helium, has been discovered. There are special programs for searching for stars with a low metal content (we recall that astronomers have agreed to call all elements heavier than helium “metals”), and these programs show that stars of “extremely low metallicity” are extremely rare in our Galaxy. They are, in some record specimens the content, for example, of iron is inferior to that of the sun by tens of thousands of times. However, there are only a few such stars, and it may well turn out that “in their person” we are dealing not with “almost primary” objects, but simply with some kind of anomaly. On the whole, even the oldest stars in the Galaxy contain fair amounts of carbon, nitrogen, oxygen, and heavier atoms. This means that even the most ancient galactic luminaries are in fact not the first: before them, there were already some “factories” in the Universe for the production of chemical elements.

The Herschel European Infrared Space Observatory has detected spectral "fingerprints" of organic molecules in the RTO. In this image, an infrared image of the Orion Nebula taken by NASA's Spitzer Space Telescope is overlaid with its spectrum taken by the Herschel Observatory's HIFI high-resolution spectrograph. It clearly demonstrates its saturation with complex molecules: the lines of water, carbon monoxide and sulfur dioxide, as well as organic compounds - formaldehyde, methanol, dimethyl ether, hydrocyanic acid and their isotopic analogues are easily identified in the spectrum. The unsigned peaks belong to numerous yet unidentified molecules.

Now it is believed that such factories could be supermassive stars of the so-called population of the third (III) type. The fact is that heavy elements are not just a “seasoning” for hydrogen and helium. These are important participants in the process of star formation, which allow a collapsing protostellar gas clump to release heat released during compression. If you deprive it of such a heat sink, it simply cannot shrink - that is, it cannot become a star ... More precisely, it can, but only on condition that its mass is very large - hundreds and thousands of times more than modern stars. Since a star lives less, the greater its mass, the first giants existed for a very short time. They lived short bright lives and exploded, leaving no trace, except for the atoms of heavy elements that had time to be synthesized in their depths or formed directly during explosions.
In the modern Universe, practically the only supplier of heavy elements is stellar evolution. Most likely, the periodic table is "filled" by stars whose mass exceeds the solar mass by more than an order of magnitude. If on the Sun and other similar luminaries, thermonuclear fusion in the core does not go beyond oxygen, then more massive objects in the process of evolution acquire an “onion” structure: their nuclei are surrounded by layers, and the deeper the layer, the heavier nuclei are synthesized in it. Here the chain of thermonuclear transformations ends not with oxygen, but with iron, with the formation of intermediate nuclei - neon, magnesium, silicon, sulfur and others.

The Great Nebula of Orion (LTO) is one of the closest star forming regions containing large amounts of gas, dust and newborn stars. At the same time, this nebula is one of the largest "chemical factories" in our Galaxy, and its true "power", as well as the ways of synthesis of molecules of interstellar matter in it, are not yet entirely clear to astronomers. This image was taken with the Wide Field Imager Camera on the 2.2-meter MPG/ES0 telescope at the La Silla Observatory in Chile.

ORGANIC MOLECULES IN SPACE

To enrich the Universe with this mixture, it is not enough to synthesize atoms - you also need to throw them into interstellar space. This happens during a supernova explosion: when an iron core forms at a star, it loses stability and explodes, scattering some of the fusion products around it. Along the way, in the expanding shell, reactions occur that generate nuclei heavier than iron. Another type of supernova explosions lead to a similar result - thermonuclear explosions on white dwarfs, the mass of which, due to the flow of matter from a satellite star or due to a merger with another white dwarf, becomes greater than the Chandrasekhar limit (1.4 solar masses).
In the enrichment of the Universe with a number of elements - including carbon and nitrogen, necessary for the synthesis of organic molecules - a significant contribution is also made by less massive stars, which end their lives with the formation of a white dwarf and an expanding planetary nebula. At the final stage of evolution, nuclear reactions also begin to occur in their shells, complicating the elemental composition of matter later ejected into outer space.
As a result, the interstellar matter of the Galaxy, to this day consisting mainly of hydrogen and helium, turns out to be polluted (or enriched - that's how you look at it) with atoms of heavier elements.

Buckminsterfullerenes (abbreviated as "fullerenes" or "buckyballs") - tiny spherical structures consisting of an even number (but not less than 60) carbon atoms connected in a similar pattern to a soccer ball - were first detected in the spectra of a planetary nebula in the Small Magellanic Cloud (MMO) , one of the closest star systems to our galaxy. The discovery was made in July 2010. working group the Spitzer Space Telescope (NASA), which conducts observations in the infrared range. The total mass of fullerenes contained in the nebula is only five ra? less than the mass of the earth. Against the background of the MMO image taken by the Spitzer telescope, an enlarged image of the planetary nebula (smaller inset) and the fullerene molecules found in it (large inset), consisting of 60 carbon atoms, is shown. To date, reports have already been received on the registration of characteristic lines of such molecules in the spectra of objects located within the Milky Way.

ORGANIC MOLECULES IN SPACE

These atoms are transported by the general "currents" of galactic gas, together with it they condense into molecular clouds, get into protostellar clumps and protoplanetary disks ... to eventually become part of planetary systems and those creatures that inhabit them. At least one example of such a habitable planet is known to us quite reliably.

Organic from inorganic

Terrestrial life - at least from a scientific point of view - is based on chemistry and is a chain of mutual transformations of molecules. True, not any, but very complex, but still molecules - combinations of carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur atoms (and a couple of dozen less common elements) in various proportions. The complexity of even the most primitive "living" molecules for a long time prevented us from recognizing ordinary chemical compounds in them. There was an idea that the substances that make up living organisms are endowed with a special quality - “life force”, therefore a special branch of science - organic chemistry - should be engaged in their study.
One of the turning points in the history of chemistry is the experiments of Friedrich Wohler, who in 1828 was the first to synthesize urea - an organic substance - from an inorganic one (ammonium cyanate). These experiments were the first step towards the most important concept - the recognition of the possibility of the origin of life from "non-living" ingredients. It was first formulated in specific chemical terms in the early 1920s by the Soviet biologist Alexander Oparin. In his opinion, a mixture of simple molecules (ammonia, water, methane, etc.), now known as the "primordial soup", became the environment for the emergence of life on Earth. In it, under the influence of external “injections” of energy (for example, lightning), the simplest organic molecules were synthesized in a non-biological way, which then “gathered” into highly organized living beings over a very long period of time.

Experimental evidence of the possibility of organic synthesis in the "primordial soup" in the early 1950s was the famous experiments of Harold Urey and Stanley Miller (Harold Urey, Stanley Miller), which consisted in passing electrical discharges through a mixture of the above molecules. After a couple of weeks of the experiment, a rich assortment of organics was found in this mixture, including the simplest amino acids and sugars. This clear demonstration of the simplicity of abiogenesis was related not only to the problem of the origin of terrestrial life, but also to the larger problem of life in the Universe: since no exotic conditions were required for the synthesis of organic matter on the young Earth, it would be logical to assume that such processes took place (or will take place) on other planets.

Looking for signs of life

If, until the middle of the 20th century, only Mars was actually considered as the most likely habitat for "brothers in mind", then after the end of World War II, establishing contacts at interstellar distances began to seem like a matter of the near future. It was at that time that the foundations of a new science, located at the intersection of astronomy and biology, were born. It is called in many ways - exobiology, xenobiology, bioastronomy - but the name "astrobiology" is most often used. And one of the most unexpected astrobiological discoveries in recent decades has been the realization of the fact that the simplest "building blocks" of life did not need to be synthesized on Earth from inanimate matter, in the "primordial soup". They could have reached our planet already in a ready state, because, as it turned out, organic molecules are abundant not only on planets, but also - which was not even suspected at first - in interstellar gas.
The most powerful tool for studying extraterrestrial matter is spectral analysis. It is based on the fact that electrons in an atom are in states - or, as they say, occupy levels - with strictly defined energies, and move from level to level, emitting or absorbing a photon whose energy is equal to the difference between the energies of the initial and final levels. If an atom is located between the observer and some source of light (for example, the photosphere of the Sun), it will “eat out” from the spectrum of this source only photons of certain frequencies that can cause electron transitions between the energy levels of this atom. Dark dips appear in the spectrum at these frequencies - absorption lines. Since the set of levels is individual not only for each atom, but also for each ion (an atom deprived of one or more electrons), it is possible to reliably establish from the set of spectral lines which atoms gave rise to them. For example, from the lines in the spectrum of the Sun and other stars, you can find out what their atmospheres are made of.
In 1904, Johannes Hartmann was the first to establish an important fact: not all lines in the spectra of stars originate in stellar atmospheres. Some of them are generated by atoms that are much closer to the observer - not near the star, but in interstellar space. Thus, signs of the existence of interstellar gas (more precisely, only one of its components - ionized calcium) were discovered for the first time.
Needless to say, this was a shocking discovery. After all, why shouldn't there be ionized calcium in the interstellar medium (ISM)? But the idea that it can contain not only ionized and neutral atoms of various elements, but also molecules, seemed fantastic for a long time. The ISM at that time was considered a place unsuitable for the synthesis of at least some complex compounds: extremely low densities and temperatures should slow down the rates of chemical reactions in it to almost zero. And if suddenly some molecules do appear there, they will immediately disintegrate again into atoms under the influence of starlight.
Therefore, more than 30 years elapsed between the discovery of interstellar gas and the recognition of the existence of interstellar molecules. In the late 1930s, ISM absorption lines were found in the ultraviolet region of the spectrum, which at first could not be attributed to any chemical element. The explanation turned out to be simple and unexpected: these lines do not belong to individual atoms, but to molecules - the simplest diatomic carbon compounds (CH, CN, CH+). Further spectral observations in the optical and ultraviolet ranges made it possible to detect absorption lines from more than a dozen interstellar molecules.

"Hint" of radio astronomy

The real flourishing of research into the interstellar "chemical assortment" began after the advent of radio telescopes. The fact is that the energy levels in an atom - if you do not go into details - are associated only with the movement of electrons around the nucleus, but the molecules that unite several atoms have additional "movements" that are reflected in the spectrum: the molecule can rotate, vibrate, twist. .. And each of these movements is associated with energy, which, like the energy of an electron, can only have a fixed set of values. The various states of molecular rotation or vibration are also called "levels". When moving from level to level, the molecule also emits or absorbs a photon. An important difference is that the energies of the rotational and vibrational levels are relatively close. Therefore, their difference is small, and the photons absorbed or emitted by the molecule during the transition from level to level do not fall into the ultraviolet or even into the visible range, but into the infrared (vibrational transitions) and into the radio range (rotational transitions).

The Soviet astrophysicist Iosif Shklovsky was the first to draw attention to the fact that the spectral emission lines of molecules must be sought in the radio range. Specifically, he wrote about a molecule (more precisely, a free radical) of OH hydroxyl, which under certain conditions becomes a source of radio emission at a wavelength of 18 cm, which is very convenient for observations from the Earth. It was hydroxyl that became the first molecule in the ISM, discovered in 1963 during radio observations and supplementing the list of already known diatomic interstellar molecules.
But then it got more interesting. In 1968, the results of observations of three- and four-atomic molecules - water and ammonia (H 2 0, NH 3) were published. A year later, a message appeared about the discovery at the ISM of the first organic molecule - formaldehyde (H 2 CO). Since then, astronomers have been discovering several new interstellar molecules every year, so that the total number now exceeds two hundred. Of course, this list is dominated by simple compounds containing from two to four atoms, but a significant part (more than a third) are polyatomic molecules.
A good half of the polyatomic interstellar compounds under terrestrial conditions we would unequivocally classify as organic: formaldehyde, dimethyl ether, methyl and ethyl alcohol, ethylene glycol, methyl formate, acetic acid... The longest molecule discovered in the ISM was found in 1997. in one of the dense clumps of the TMS-1 molecular cloud in the constellation Taurus. For the Earth, this is not a very common compound from the cyanopolyin family, which is a chain of 11 carbon atoms, to one end of which a hydrogen atom is "attached", to the other - a nitrogen atom. Other organic molecules were also found in the same clot, but for some reason it is especially rich in cyanopolyin molecules with carbon chains of various lengths (3, 5, 7, 9, 11 atoms), for which it received the name "cyanopolyin peak".
Another well-known object with a rich "organic content" is the molecular cloud Sgr B2(N), located near the center of our Galaxy in the direction of the constellation Sagittarius. It contains a particularly large number of complex molecules. However, it does not have any exclusivity in this respect - rather, the effect of “search under the lantern” is triggered here. Finding new molecules, especially organic ones, is a very difficult task, and observers often prefer to point their telescopes at areas of the sky that are more likely to succeed. Therefore, we know a lot about the concentration of organics in the molecular clouds of Taurus, Orion, Sagittarius, and almost do not have information about the content of complex molecules in many other similar clouds. But this does not mean at all that organics are not there - it's just that "antennas have not yet reached" these objects.

Difficulties in deciphering

Here it is necessary to clarify what "complexity" means in this case. Even an elementary analysis of stellar spectra is a very difficult task. Yes, the set of lines of each atom and ion is strictly individual, but in the spectrum of a star, lines of many dozens of elements overlap each other, and it can be very difficult to “sort” them. In the case of the spectra of organic molecules, the situation becomes more complicated in several directions at once. Most of the numerous emission (absorption) lines of atoms and ions fall within a narrow spectral range accessible for observations from the Earth. Complex molecules also have thousands of lines, but these lines are "scattered" much wider - from the near infrared range (units and tens of micrometers) to the radio range (tens of centimeters).
Let's say we want to prove that there is an acrylonitrile (CH 2 CHCN) molecule in the molecular cloud. For this, it is necessary, first, to know in which lines this molecule radiates. But for many compounds such data are not available! Theoretical methods do not always make it possible to calculate the position of the lines, and in the laboratory the spectrum of a molecule often cannot be measured, for example, because it is difficult to isolate it in its pure form. Second, it is necessary to calculate the relative intensities of these lines. Their brightness depends on the properties of the molecule and on the parameters of the medium (temperature, density, etc.) in which it is located. The theory will make it possible to predict that in the investigated molecular cloud the line at one wavelength should be three times brighter than the line of the same molecule at another wavelength. If lines are found at the required wavelengths, but with the wrong ratio of intensities, this is a weighty reason to doubt the correctness of their identification. Of course, to reliably detect a molecule, it is necessary to observe the cloud in the widest possible spectral range. But a significant part of the electromagnetic radiation from space does not reach the surface of the Earth! This means that one has to either observe the spectrum of the molecule fragmentarily in the "transparency windows" of the earth's atmosphere, which, of course, does not add reliability to the results obtained, or use a space telescope, which is extremely rare. Finally, do not forget that the lines of the desired molecule will have to be distinguished from other molecules, of which there are dozens of varieties, and each has thousands of lines ...
It is not surprising, therefore, that astronomers have been going for years to identify some "representatives" of cosmic organic matter. Indicative in this respect is the history of the discovery of glycine, the simplest amino acid, in the ISM. Although reports of the registration of characteristic features of this molecule in the spectra of molecular clouds have repeatedly appeared, the fact of its presence is still not generally recognized: although many lines, as if belonging to glycine, are actually observed, its other expected lines are absent in the spectra, which gives reason to doubt identification.

Interstellar Fusion Laboratories

But all this is the complexity of observations. In theory, over the past decades, the situation with interstellar organic synthesis has become much clearer, and now we clearly understand that the initial ideas about the chemical inertness of the ISM were wrong. To do this, of course, we had to learn a lot about its composition and physical properties beforehand. A significant proportion of the volume of interstellar space is indeed "sterile". It is filled with very hot and rarefied gas with temperatures ranging from thousands to millions of kelvins and is permeated with hard, high-energy radiation. But there are also individual condensations of interstellar matter in the Galaxy, where the temperature is low (from a few to tens of kelvins), and the density is noticeably higher than the average (hundreds or more particles per cubic centimeter). The gas in these condensations is mixed with dust, which effectively absorbs hard radiation, as a result of which their interior - cold, dense, dark - turns out to be a convenient place for chemical reactions to occur and the accumulation of molecules. Basically, such "space laboratories" are found in the already mentioned molecular clouds. Together they occupy less than a percent of the total volume of the galactic disk, but they contain about half the mass of interstellar matter in the Milky Way.

Polycylic aromatic hydrocarbons (PAHs) are the most complex compounds found in interstellar space. This infrared image of a star-forming region in the constellation Cassiopeia shows the molecular structures of some of them (hydrogen atoms are white, carbon atoms are grey, oxygen atoms are red), as well as several of their characteristic spectral lines. Scientists believe that in the near future PAH spectra will be of particular value for deciphering the chemical composition of the interstellar medium using infrared spectroscopy.

ORGANIC MOLECULES IN SPACE

The elemental composition of molecular clouds resembles the composition of the Sun. Basically, they consist of hydrogen - more precisely, hydrogen molecules H 2 with a small "additive" of helium. The remaining elements are present at the level of minor impurities with a relative content of about 0.1% (for oxygen) and below. Accordingly, the number of molecules containing these impurity atoms is also very small compared to the most common H 2 molecule. But why are these molecules formed at all? On Earth, special facilities are used for chemical synthesis, providing sufficiently high densities and temperatures. How does an interstellar "chemical reactor" work - cold and rarefied?
It must be remembered here that astronomy deals with other time scales. On Earth, we need to get results fast. Nature is in no hurry. Synthesis of interstellar organics takes hundreds of thousands and millions of years. But even these slow reactions require a catalyst. In molecular clouds, its role is played by particles of cosmic rays. The formation of a CH bond can be considered the first step towards the synthesis of complex organic molecules. But if you just take a mixture of hydrogen molecules and carbon atoms, this bond will not form by itself. Another thing is if some of the atoms and molecules are somehow turned into ions. Chemical reactions involving ions proceed much faster. It is this initial ionization that is provided by cosmic rays, initiating a chain of interactions during which atoms of heavy elements (carbon, nitrogen, oxygen) begin to "attach" hydrogen atoms to themselves, forming simple molecules, including those discovered in the ISM in the first place ( CH and CH+).
Further synthesis is even easier. Diatomic molecules attach new hydrogen atoms to themselves, turning into three- and four-atomic (CH 2 +, CH 3 +), polyatomic molecules begin to react with each other, transforming into more complex compounds - acetylene, hydrocyanic acid (HCN), ammonia, formaldehyde, which , in turn, become "building blocks" for the synthesis of complex organics.
After the cosmic rays gave the primary impetus chemical reactions, cosmic dust particles become an important catalyst for interstellar organic synthesis. They not only protect the inner regions of molecular clouds from destructive radiation, but also provide their surface for the efficient "production" of many inorganic and organic molecules. In the totality of reactions, it is not difficult to imagine the formation of not only glycine, but also more complex compounds. In this sense, we can say that the task of discovering the simplest amino acid has more of a sporting meaning: who will be the first to confidently find it in space. Scientists have no doubt that glycine is present in molecular clouds.

How to survive the "molecules of life"

In general, on this moment it can be considered proven that for the synthesis of organic matter, a "primary broth" is not necessary. Nature perfectly copes with this task in outer space. But does interstellar organic matter have anything to do with the emergence of life? Indeed, stars and planetary systems are formed in molecular clouds and, naturally, "absorb" their substance. However, before becoming a planet, this substance passes through rather harsh conditions of the protoplanetary disk and no less harsh conditions of the young Earth. Unfortunately, our ability to study the evolution of organic compounds in protoplanetary disks is very limited. They are very small in size, and it is even more difficult to search for organic molecules in them than in molecular clouds. So far, about a dozen molecules have been found in the forming planetary systems of other stars. Of course, they also include simple organic compounds (in particular, formaldehyde), but we cannot yet describe in more detail the evolution of organics under these conditions.
The research of our own planetary system comes to the rescue. True, it is already more than four and a half billion years old, but part of its primary protoplanetary matter has been preserved to this day in some meteorites. It was in them that the abundance of organic matter turned out to be quite impressive - especially in the so-called carbonaceous chondrites, which make up a few percent of total number"heavenly stones" that fell to Earth. They have a loose clay structure, are rich in bound water, but most importantly, a significant part of their substance is “occupied” by carbon, which is part of many organic compounds. Meteoritic organic matter consists of relatively simple molecules, among which there are amino acids, and nitrogenous bases, and (carboxylic acids, and "insoluble organic matter", which is a product of polymerization (tarring) of simpler compounds. Of course, we cannot now confidently say that this organic matter was “inherited” from the substance of a protosolar molecular bunch, but indirect evidence indicates this - in particular, a clear excess of isotopomers of a number of molecules was found in meteorites.

	Acetaldehyde (left) and its isomers, vinyl alcohol and ethylene oxide, have also been detected in interstellar space.
10 eight-atom		In 1997, radio observations confirmed the presence of acetic acid in space.
9 nine-atom molecules and 17 molecules containing from 10 to 70 atoms		Some of the heaviest (and longest) molecules found in outer space belong to the class of polyins - they contain several triple bonds connected in series "in a chain" by single bonds. They do not occur on earth.
MOLECULES CURRENTLY DISCOVERED IN INTERSTELLAR SPACE

Isotopomers or isotopologues are molecules in which one or more atoms are replaced by a minor (not the most common) isotope of a chemical element. For example, the isotopomer is heavy water, in which the light hydrogen isotope protium is replaced by deuterium. A feature of the chemistry of molecular clouds is that isotopomers are formed in them somewhat more efficiently than "ordinary" molecules. For example, the content of deuterated formaldehyde (HDCO) can be tens of percent of the content of conventional formaldehyde - despite the fact that, in general, deuterium (D) atoms in space are a hundred thousand times less than protium (H) atoms. Interstellar molecules give the same "preference" to the nitrogen isotope 15N over the usual 14N. And the same relative overenrichment is observed in meteorite organic matter.
So far, three important conclusions can be drawn from the available data. First, organic compounds of a very high degree of complexity are very efficiently synthesized in the interstellar medium of our and other galaxies. Secondly, these compounds can be preserved in protoplanetary disks and be part of planetesimals - the "embryos" of planets. And finally, even if the organic matter "did not survive" the very process of the formation of the Earth or another planet, it could well get there later with meteorites (as it happens today).
Naturally, the question arises of how far organic synthesis could go at the pre-planetary stage. But what if not the "building blocks" for the origin of life, but life itself, came to Earth with meteorites? After all, at the beginning of the 20th century it seemed impossible for even simple diatomic molecules to appear in the ISM. Now we are massively finding in molecular clouds substances whose names are difficult to pronounce the first time. The detection of amino acids in the ISM is most likely only a matter of time. What prevents us from taking the next step and assuming that meteorites brought life to Earth "in finished form"?
Indeed, several times in the literature there have been reports that the remains of the simplest extraterrestrial organisms were found in meteorites ... However, so far this information is too unreliable and scattered to be confidently included in the general picture of the origin of life.

While "hot" nuclear processes in space - the plasma state, nucleogenesis (the process of elements) inside stars, etc. - are mainly dealt with by physics. - a new field of knowledge, which received significant development in the 2nd half of the 20th century. mainly due to the success of astronautics. Previously, studies of chemical processes in outer space and the composition of cosmic bodies were carried out mainly by radiation from the Sun, stars, and, to some extent, the outer layers of planets. This method made it possible to discover the element on the Sun even before it was discovered on Earth. The only direct method for studying cosmic bodies was the phase composition of various meteorites that fell to the Earth. Thus, significant material was accumulated, which is of fundamental importance for further development. The development of astronautics, flights of automatic stations to the planets of the solar system - the Moon, Venus, Mars - and, finally, visiting the Moon by man opened up completely new opportunities. First of all, this is a direct exploration of the Moon with the participation of cosmonauts or by taking samples by automatic (mobile and stationary) vehicles and delivering them to Earth for further study in chemical laboratories. In addition, automatic descent vehicles made it possible to study the conditions of its existence in and on the surface of other planets in the solar system, primarily Mars and Venus. One of the most important tasks is to study, on the basis of the composition and distribution of cosmic bodies, the desire to explain chemical basis their origin and history. The greatest attention is paid to the problems of prevalence and distribution. The prevalence in space is determined by nucleogenesis inside stars. The chemical composition of the Sun, terrestrial planets of the solar system and meteorites, apparently, is almost identical. The formation of nuclei is associated with various nuclear processes in stars. Therefore, at different stages of their development, different stars and stellar systems have different chemical compositions. Known stars with particularly strong spectral lines Ba or Mg or Li, etc. The phase distribution in cosmic processes is extremely diverse. The state of aggregation and phase in space at different stages of its transformations are influenced in many ways: 1) a huge range, from stellar to absolute zero; 2) a huge range, from millions in the conditions of planets and stars to space; 3) deeply penetrating galactic and solar radiation different composition and intensity; 4) radiation accompanying the transformation of unstable into stable; 5) magnetic, gravitational and other physical fields. It has been established that all these factors affect the composition of the outer crust of the planets, their gaseous shells, meteoritic, cosmic, etc. At the same time, fractionation processes in space concern not only the atomic, but also the isotopic composition. Determination of isotopes that have arisen under the influence of radiation allows one to penetrate deeply into the history of the processes of formation of planets, asteroids, meteorites and to establish the age of these processes. Due to extreme conditions in outer space, processes take place and states occur that are not characteristic of the Earth: the plasma state of stars (for example, the Sun); condensation of He, Na, CH 4, NH 3 and other volatile in major planets at very low ; the formation of stainless in space at the Moon; chondrite structure of stony meteorites; the formation of complex organics in meteorites and, probably, on the surface of planets (for example, Mars). In interstellar space, they are found in extremely small and many elements, as well as (, etc.) and, finally, there is a synthesis of various complex (arising from the primary solar H, CO, NH 3, O 2, N 2, S and other simple compounds under equilibrium conditions with the participation of radiation). All these organic in meteorites, in interstellar space - are not optically active.

With the development of astrophysics and some other sciences, the possibilities of obtaining information related to . So, searches in the interstellar medium are carried out by means of radio astronomy methods. By the end of 1972, more than 20 species were discovered in interstellar space, including several rather complex organic ones, containing up to 7 species. It is established that their observed values ​​are 10-100 million times less than . These methods also allow, by comparing the radio lines of the isotopic varieties of one (for example, H 2 12 CO and H 2 13 CO), to investigate the isotopic composition of the interstellar and check the correctness of existing theories of origin.

Of exceptional importance for the knowledge of the cosmos is the study of a complex multi-stage low-temperature process, for example, the transition of the solar to the solid planets of the solar system, asteroids, meteorites, accompanied by condensation growth, accretion (increase in mass, "growth" of any by adding particles from the outside, for example from a gas and dust cloud) and agglomeration primary aggregates (phases) with simultaneous loss of volatiles in outer space. In space, at relatively low (5000-10000 ° C), solid phases of different chemical composition (depending on ), characterized by different binding energies, oxidizing potentials, etc., successively precipitate from the cooling one. For example, in chondrites, silicate, metallic, sulfide, chromite, phosphide, carbide, and other phases that agglomerate at some point in their history into a stony meteorite and, probably, in a similar way into terrestrial-type planets.

Further, in the planets, the process of differentiation of the solid takes place, cooling down into shells - a metal core, silicate phases (mantle and crust) and - already as a result of the secondary heating of the planets by the heat of radiogenic origin released during the decay of radioactive, and, possibly, other elements. This melting process is also characteristic of the Moon, Earth, Mars, and Venus during volcanism. It is based on the universal principle of zone separation, separating fusible (for example, crust and) from the refractory mantle of planets. For example, primary solar CaSiO 3 + CO 2 reaches an equilibrium state where it contains 97% CO 2 at 90 atm. The example of the Moon suggests that secondary (volcanic) ones are not held by a celestial body if its mass is small.

Collisions in outer space (either between meteorite particles, or during the impact of meteorites and other particles on the surface of planets) due to the huge cosmic speeds movements can cause thermal, leaving traces in the structure of solid cosmic bodies, and the formation of meteorite craters. It happens between space bodies. For example, according to the minimum estimate, at least 1 × to others, and in the general case - to a change in the isotopic or atomic composition", 1971, c. eleven; Aller L. H., trans. from English, M., 1963; Seaborg G. T., Valens E. G., Elements of the Universe, trans. from English, 2nd ed., M., 1966; Merrill P. W., Space chemistry, Ann Arbor, 1963; Spitzer L., Diffuse matter in space, N. Y., 1968; Snyder L. E., Buhl D., Molecules in the interstellar medium, Sky and Telescope, 1970, v. 40, p. 267, 345.

“The beast and the bird, the stars and the stone — we are all one, all one ...” muttered Cobra, lowering her hood and also swaying. - The snake and the child, the stone and the star - we are all one ...

Pamela Travers. "Mary Poppins"

To establish the prevalence of chemical elements in the Universe, it is necessary to determine the composition of its matter. And it is concentrated not only in large objects - stars, planets and their satellites, asteroids, comets. Nature, as you know, does not tolerate emptiness, and therefore outer space is beyond full of interstellar gas and dust. Unfortunately, only terrestrial matter (and only that which is “under our feet”) and a very small amount of lunar soil and meteorites, fragments of once existing cosmic bodies, are available to us for direct study.

How to determine the chemical composition of objects thousands of light years away from us? It became possible to obtain all the information necessary for this after the development in 1859 by the German scientists Gustav Kirchhoff and Robert Bunsen of the method of spectral analysis. And in 1895, Wilhelm Conrad Roentgen, a professor at the University of Würzburg, accidentally discovered an unknown radiation, which the scientist called X-rays (now they are known as X-rays). Thanks to this discovery, X-ray spectroscopy appeared, which allowsdirectly from the spectrum to determine the ordinal number of the element.

The basis of spectral and X-ray spectral analysis is the ability of the atoms of each chemical element to emit or absorb energy in the form of waves of a strictly defined, characteristic length only for it alone, which is captured by special devices - spectrometers. Atom emits waves visible light during transitions of electrons at external levels, and more “deep” electron layers are responsible for X-ray radiation. By the intensity of certain lines in the spectrum, they find out the content of the element in a particular celestial body.

By the end of XX in. the spectra of many objects in the Universe have been studied, and a vast amount of statistical material has been accumulated. Of course, the data on the chemical composition of cosmic bodies and interstellar matter are not final and are constantly being refined, but thanks to the information already collected, it was possible to establish calculate the average content of elements in space.

All bodies in the Universe consist of atoms of the same chemical elements, but their content in different objects is different. In this case, interesting patterns are observed. The leaders in prevalence are hydrogen (its atoms in space are 88.6%) and helium (11.3%). The remaining elements account for only 1%! Carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, argon, and iron are also common in stars and planets. Thus, light elements predominate. But there are exceptions. Among them are a "failure" in the field of lithium, beryllium and boron and a low content of fluorine and scandium, the cause of which has not yet been established.

The revealed patterns can be presented in the form of a graph. Outwardly, it resembles an old saw, the teeth of which have worn off in different ways, and some have even broken. The tops of the teeth correspond to elements with even serial numbers (that is, those in which the number of protons in the nuclei is even). This pattern is called the Oldo-Harkins rule after the Italian chemist Giuseppe Oddo (1865-1954) and American physicist and chemist William Harkins (1873–1951). According to this rule, the abundance of an element with an even charge is greater than its neighbors with an odd number of protons in the nucleus. If the element has an even number of neutrons, then it occurs even more often and forms more isotopes. There are 165 stable isotopes in the universe that have an even number of neutrons and protons; 56 isotopes with an even number of protons and an odd number of neutrons; 53 isotopes that have an even number of neutrons and an odd number of protons; and only 8 isotopes with an odd number of both neutrons and protons.

It is striking and another maximum attributable to iron - one of the most common elements. On the graph, its prong rises like Everest. This is due to the high binding energy in the core of iron - the highest among all chemical elements.

And here is the broken tooth of our saw - on the graph there is no value for the prevalence of technetium, element No. 43, instead of it there is a gap. It would seem that it is so special? Technetium is located in the middle of the periodic table, the prevalence of its neighbors is subject to general patterns. And here's the thing: this element simply "ended" a long time ago, the half-life of its longest-lived isotope 2.12.10 6 years. Technetium was not even discovered in the traditional sense of the word: it was synthesized artificially in 1937, and then by accident. But here's what's interesting: in 1960, a line of "non-existent" element No. 43 was discovered in the spectrum of the Sun! This is a brilliant confirmation of the fact that the synthesis of chemical elements in the interior of stars continues to this day.

The second broken tooth is the absence of promethium on the graph (No. 61), and it is explained by the same reasons. The half-life of the most stable isotope of this element is very short, only 18 years. And so far, he has not made himself felt anywhere in space.

There are no elements with serial numbers greater than 83 on the graph at all: they are also very unstable, and there are extremely few of them in space.

Bovyka Valentina Evgenievna

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Municipal budgetary educational institution

average comprehensive school No. 20 Krasnodar

Distribution of chemical elements on Earth and in space. The formation of chemical elements in the process of primary nucleosynthesis and in the interiors of stars.

Physics abstract

Done by a student:

10 "B" class MBOU secondary school No. 20 of Krasnodar

Bovyka Valentina

Teacher:

Skryleva Zinaida Vladimirovna

Krasnodar

2016

1. Chemistry of space, which studies the chemistry of space.
2. Some terms.
3. The chemical composition of the planets of the solar system and the moon.
4. The chemical composition of comets, meteorites.
5. primary nucleosynthesis.
6. Other chemical processes in the universe.
7. Stars.
8. interstellar medium
9. List of used resources

Space Chemistry. What does space chemistry study?

The subject of the study of space chemistry is the chemical composition of cosmic bodies (planets, stars, comets, etc.), interstellar space, as well as chemical processes that occur in space.

The chemistry of the cosmos deals mainly with the processes that occur during the atomic-molecular interaction of substances, and physics deals with nucleosynthesis inside stars.

Some terms

For ease of perception of the following material, a glossary of terms is needed.

Stars - luminous gas massive balls, in the bowels of which reactions of synthesis of chemical elements take place.

Planet - celestial bodies that revolve in orbits around stars or their remnants.

Comets - space bodies, which consist of frozen gases, dust.

meteorites - small cosmic bodies falling to Earth from interplanetary space.

Meteors - phenomena in the form of a luminous trail, which is due to the impact of a meteoroid into the Earth's atmosphere.

interstellar medium- rarefied matter, electromagnetic radiation and magnetic field that fill the space between stars.

The main components of interstellar matter: gas, dust, cosmic rays.

Nucleosynthesis - the process of formation of nuclei of chemical elements (heavier than hydrogen) in the course of nuclear fusion reactions.

The chemical composition of the planets of the solar system and the moon

The planets of the solar system are celestial bodies revolving around a star called the Sun.

The solar system consists of 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Let's consider each planet separately.

Mercury

The closest planet to the Sun in the solar system, the smallest planet. The diameter of Mercury is approximately 4870 km.

Chemical composition

The core of the planet is iron, ferromagnetic. Iron content = 58%

The atmosphere, according to one data, consists mostly of nitrogen (N 2 ) mixed with carbon dioxide (CO 2 ), according to others - from helium (He), neon (Ne) and argon (Ar).

Venus

The second planet in the solar system. Diameter ≈ 6000 km.

Chemical composition

The core is iron, the mantle contains silicates, carbonates.

The atmosphere is 97% carbon dioxide (CO 2 ), the rest is nitrogen (N 2 ), water (H 2 O) and oxygen (O 2 ).

Earth

The third planet of the solar system, the only planet in the solar system with the most favorable conditions for life. The diameter is approximately 12,500 km.

Chemical composition

Iron core. The Earth's crust contains oxygen O 2 (49%), silicon Si (26%), aluminum Al (4.5%), as well as other chemical elements. The atmosphere is 78% nitrogen (N 2 ), 21% from oxygen (O 2 ) and 0.03% from carbon dioxide (CO 2 ), the rest is inert gases, water vapor and impurities. The hydrosphere consists mostly of oxygen O 2 (85.82%), hydrogen H 2 (10.75%) and other elements. All living things contain carbon (C).

Mars

Mars is the fourth planet in the solar system. Diameter approximately 7000 km

Chemical composition

Iron core. The planet's crust contains iron oxides and silicates.

Jupiter

Jupiter is the fifth planet from the Sun. The largest planet solar system. Diameter over 140,000 km.

Chemical composition

The core is compressed hydrogen (H 2 ) and helium (He). The atmosphere contains hydrogen (H 2 ), methane (CH 4 ), helium (He), ammonia (NH 3 ).

Saturn

Saturn is the sixth planet from the Sun. It has a diameter of about 120,000 km.

Chemical composition

There are no data on the core and the earth's crust. The atmosphere is made up of the same gases as Jupiter's atmosphere.

Uranus and Neptune

Uranus and Neptune are the seventh and eighth planets respectively. Both planets have an approximate diameter of 50,000 km.

Chemical composition

There are no data on the core and cortex. The atmosphere is formed by methane (CH 4 ), helium (He), hydrogen (H 2 ).

Moon

The moon is a satellite of the Earth, its raw material base. Lunar soil is called regolith, it consists of silicon oxide (IV), aluminum oxide and oxides of other metals, a lot of uranium, no water.

The chemical composition of comets, meteorites

meteorites

Meteorites are iron, iron-stone and stone. Most often, stone meteorites fall to Earth. On average, according to calculations, for every iron meteorite there are 16 stone ones.

The chemical composition of iron meteorites is 90% iron (Fe), 8.5% nickel (Ni), 0.6% cobalt (Co), and 0.01% silicon (Si).

Stony meteorites are mainly composed of oxygen (0 2 ) (41%) and silicon (Si) (21%).

Comets

Comets are solid bodies surrounded by a shell of gas. The core is made up of frozen methane (CH 4) and ammonia (NH 3 ) with mineral impurities. A variety of radicals and ions have been found in gas comets. The most recent observations were made of the Hale-Bopp comet, which included hydrogen sulfide, water, heavy water, sulfur dioxide, formaldehyde, methanol, formic acid, hydrogen cyanide, methane, acetylene, ethane, fosterite, and other compounds.

Primary nucleosynthesis

To consider primary nucleosynthesis, let's turn to the table.

age of the universe	Temperature, K	State and composition of matter
0.01 s	10 11	neutrons, protons, electrons, positrons in thermal equilibrium. The number n and p are the same.
0.1 s	3*10 10	The particles are the same, but the ratio of the number of protons to the number of neutrons is 3:5
	10 10	electrons and positrons annihilate, p:n =3:1
13.8 s	3*10 9	Deuterium D and helium nuclei begin to form 4 No, electrons and positrons disappear, there are free protons and neutrons.
35 min	3*10 8	Sets the number of D and Not in relation to the number p and n 4 He:H + ≈24-25% by weight
7*10 5 years	3*10 3	Chemical energy is sufficient to form stable neutral atoms. The universe is transparent to radiation. Matter dominates radiation.

The essence of primary nucleosynthesis is reduced to the formation of deuterium nuclei from nucleons, from deuterium nuclei and nucleons - helium nuclei with mass number 3 and tritium, and from the nuclei 3 Not, 3 H and nucleons - nuclei 4 Not.

Other chemical processes in the universe

At high temperatures(in circumstellar space the temperature can reach several thousand degrees) chemical substances begin to decompose into components - radicals (CH 3 from 2 , CH, etc.) and atoms (H, O, etc.)

Stars

Stars differ in mass, size, temperature, luminosity.

The outer layers of stars consist mainly of hydrogen, as well as helium, oxygen and other elements (C, P, N, Ar, F, Mg, etc.)

Subdwarf stars are composed of heavier elements: cobalt, scandium, titanium, manganese, nickel, etc.

In the atmosphere of giant stars, not only atoms of chemical elements can be found, but also molecules of refractory oxides (for example, titanium and zirconium), as well as some radicals: CN, CO, C 2

The chemical composition of stars is studied by the spectroscopic method. Thus, iron, hydrogen, calcium and sodium were found on the Sun. Helium was first found on the Sun, and later found in the atmosphere of planet Earth. At present, in the spectra of the Sun and other celestial bodies 72 elements have been found, all of these elements have also been found on Earth.

The energy source of stars is thermonuclear fusion reactions.

At the first stage of a star's life, hydrogen is converted into helium in its interior.

4 1 H → 4 Not

Helium then turns into carbon and oxygen

3 4 He → 12 C

4 4 He → 16 O

At the next stage, carbon and oxygen are fuel, in alpha processes, elements of neon are formed to iron. Further reactions of capturing charged particles are endothermic, so nucleosynthesis stops. Due to the stop of thermonuclear reactions, the balance of the iron core is disturbed, gravitational compression begins, part of the energy of which is spent on the decay of the iron core into α-particles and neutrons. This process is called gravitational collapse and takes about 1 s. As a result of a sharp increase in temperature in the shell of a star, thermonuclear combustion reactions of hydrogen, helium, carbon and oxygen occur. A huge amount of energy is released, which leads to an explosion and expansion of the matter of the star. This phenomenon is called a supernova. During a supernova explosion, energy is released, which gives the particles a large acceleration, neutron fluxes bombard the nuclei of elements that were formed earlier. In the process of neutron captures followed by β-radiation, the nuclei of elements heavier than iron are synthesized. Only the most massive stars reach this stage.

During the collapse, neutrons are formed from protons and electrons according to the scheme:

1 1 p + -1 0 e → 1 0 n + v

Formed neutron star.

The core of a supernova can turn into a pulsar - a core that rotates with a period of a fraction of a second and emits electromagnetic radiation. Its magnetic field reaches colossal proportions.

It is also possible that most of the shell overcomes the force of the explosion and falls onto the core. Receiving additional mass, the neutron star begins to shrink to the formation of a "black hole".

interstellar medium

The interstellar medium consists of gas, dust, magnetic fields and cosmic rays. The absorption of stellar radiation occurs due to gas and dust. The dust of the interstellar medium has a temperature of 100-10 K, the temperature of the interstellar gas can vary from 10 to 10 7 K and depends on the density and heat sources. Interstellar gas can be either neutral or ionized (H 2 0 , H 0 , H + , e - , He 0 ).

First chemical compound in space was discovered in 1937 using spectroscopy. This compound was the CH radical, a few years later the cyanogen CN was found, and in 1963 the hydroxyl OH was discovered.

With the use of radio waves and infrared radiation in spectroscopy, it became possible to study the "cold" regions of outer space. First, inorganic substances were found: water, ammonia, carbon monoxide, hydrogen sulfide, and then organic: formaldehyde, formic acid, acetic acid, acetaldehyde and formic alcohol. Ethyl alcohol was found in space in 1974. Then Japanese scientists discovered methylamine CH 3 -NH 2 .

Streams move in interstellar space atomic nuclei- cosmic rays. About 92% of these nuclei are hydrogen nuclei, 6% are helium, and 1% are nuclei of heavier elements. Cosmic rays are believed to be produced by supernova explosions.

The space between space bodies is filled with interstellar gas. It consists of atoms, ions and radicals, and it also includes dust. The existence of such particles as: CN, CH, OH, CS, H 2 O, CO, COS, SiO, HCN, HCOOH, CH 3OH and others.

The collision of particles of cosmic radiation, solar wind and interstellar gas leads to the formation of various particles, including organic ones.

When protons collide with carbon atoms, hydrocarbons are formed. Hydroxyl OH is formed from silicates, carbonates and various oxides.

Under the action of cosmic rays in the Earth's atmosphere, such isotopes are formed as: carbon with a mass number of 14 14 C, beryllium, whose mass number is 10 10 Be, and chlorine with a mass number of 36 36Cl.

The carbon isotope with a mass number of 14 accumulates in plants, corals, and stalactites. Beryllium isotope with a mass number of 10 - in the bottom sediments of the seas and oceans, polar ice.

The interaction of cosmic radiation with the nuclei of terrestrial atoms provides information about the processes occurring in space. These issues are dealt with modern science– experimental paleoastrophysics.

For example, cosmic ray protons, colliding with nitrogen molecules in the air, break the molecule into atoms, and a nuclear reaction proceeds:

7 14 N + 1 1 H→2 2 4 He + 4 7 Be

As a result of this reaction, radioactive isotope beryllium.

A proton at the moment of collision with atmospheric atoms knocks out neutrons from these atoms, these neutrons interact with nitrogen atoms, which leads to the formation of a hydrogen isotope with a mass number of 3 - tritium:

7 14 N + 0 1 n → 1 3 H + 6 12 C

Tritium, undergoing β-decay, ejects an electron:

1 3 H → -1 0 e + 2 3 He

This is how the light isotope of helium is formed.

A radioactive isotope of carbon is formed during the capture of electrons by nitrogen atoms:

7 14 N + -1 0 e → 6 14 C

The prevalence of chemical elements in space

Consider the abundance of chemical elements in the galaxy Milky Way. Data on the presence of certain elements were obtained by spectroscopy. For visual representation, we use a table.

Core charge	Element	Mass fraction in parts per thousand
	Hydrogen
	Helium
	Oxygen	10,4
	Carbon
	Neon	1,34
	Iron
	Nitrogen	0,96
	Silicon	0,65
	Magnesium	0,58
	Sulfur	0,44

For a more visual representation, let's turn to a pie chart.

As you can see in the diagram, the most abundant element in the universe is hydrogen, the second most abundant is helium, and the third is oxygen. Mass fractions of other elements are much less.

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Slides captions:

The prevalence of chemical elements on Earth and in space. The formation of chemical elements in the process of primary nucleosynthesis and in the interior of stars Completed by a student of 10 "B" class MBOU secondary school No. 20 Bovyka Valentina Supervisor: Skryleva Z.V.

Space chemistry is the science of the chemical composition of cosmic bodies, interstellar space, and chemical processes that flow in space.

Necessary terms Stars are luminous gaseous massive balls, in the depths of which the reactions of synthesis of chemical elements take place. Planet - celestial bodies that revolve in orbits around stars or their remnants. Comets are cosmic bodies that consist of frozen gases and dust. Meteorites are small cosmic bodies that fall to Earth from interplanetary space. Meteors are phenomena in the form of a luminous trail, which is due to the entry of a meteoroid into the Earth's atmosphere. The interstellar medium is rarefied matter, electromagnetic radiation and a magnetic field that fills the space between stars. The main components of interstellar matter: gas, dust, cosmic rays. Nucleosynthesis is the process of formation of nuclei of chemical elements (heavier than hydrogen) in the course of nuclear fusion reactions.

Mercury Venus Earth Mars

Jupiter Saturn Uranus Neptune

The moon is a satellite of the Earth, its raw material base.

Meteorite Comet

Primary nucleosynthesis Age of the universe Temperature, K State and composition of matter 0.01 s 10 11 neutrons, protons, electrons, positrons in thermal equilibrium. The number n and p are the same. 0.1 s 3*10 10 The particles are the same, but the ratio of the number of protons to the number of neutrons is 3:5 1s 10 10 electrons and positrons annihilate, p:n =3:1 13.8 s 3*10 9 Deuterium nuclei begin to form D and helium 4 He, electrons and positrons disappear, there are free protons and neutrons. 35 min 3*10 8 The amount of D and He is set in relation to the number p and n 4 He:H + ≈24-25% by weight 7*10 5 years 3*10 3 Chemical energy is sufficient to form stable neutral atoms. The universe is transparent to radiation. Matter dominates radiation.

The main reactions occurring in the interiors of stars 4 1 H → 4 He 3 4 He → 12 C 4 4 He → 16 O +1 1 p + -1 0 e → 1 0 n + v

The main reactions occurring due to the components of the interstellar medium 7 14 N + 1 1 H →2 2 4 He + 4 7 Be 7 14 N + 0 1 n→ 1 3 H + 6 12 C 1 3 H → -1 0 e + 2 3 He 7 14 N + -1 0 e → 6 14 C

The abundance of chemical elements in the Milky Way galaxy

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