In terms of mass, solid dust particles make up an insignificant part of the Universe, but it is thanks to interstellar dust that stars, planets and people who study space and simply admire the stars arose and continue to appear. What kind of substance is this cosmic dust? What makes people equip expeditions into space costing the annual budget of a small state in the hope, and not in the firm confidence, of extracting and bringing back to Earth at least a tiny handful of interstellar dust?
Between stars and planets
In astronomy, dust is called small, fractions of a micron in size, particulate matter flying in outer space. Cosmic dust is often conventionally divided into interplanetary and interstellar, although, obviously, interstellar entry into interplanetary space is not prohibited. It’s not easy to just find it there, among the “local” dust, the probability is low, and its properties near the Sun can change significantly. Now, if you fly further away, to the borders solar system, there the probability of catching real interstellar dust is very high. Perfect option go beyond the solar system altogether.
Interplanetary dust, at least in comparative proximity to the Earth, is fairly studied matter. Filling the entire space of the Solar System and concentrated in the plane of its equator, it was born largely as a result of random collisions of asteroids and the destruction of comets approaching the Sun. The composition of the dust, in fact, does not differ from the composition of meteorites falling on the Earth: it is very interesting to study it, and there are still many discoveries to be made in this area, but there seems to be no particular intrigue here. But thanks to this particular dust, in good weather in the west immediately after sunset or in the east before sunrise, you can admire a pale cone of light above the horizon. This is the so-called zodiac sunlight, scattered by small cosmic dust particles.
Where dust is more interesting interstellar. Its distinctive feature is the presence hard core and shells. The core appears to be composed mainly of carbon, silicon and metals. And the shell is predominantly made from frozen onto the surface of the kernel gaseous elements, crystallized in the “deep freeze” conditions of interstellar space, and this is about 10 kelvins, hydrogen and oxygen. However, there are impurities of molecules that are more complex. These are ammonia, methane and even polyatomic organic molecules, which stick to a speck of dust or form on its surface during wanderings. Some of these substances, of course, fly away from its surface, for example, under the influence of ultraviolet radiation, but this process is reversible - some fly away, others freeze or are synthesized.
Now in the space between stars or near them, water, oxides of carbon, nitrogen, sulfur and silicon have already been found, of course, not by chemical, but by physical, that is, spectroscopic, methods. hydrogen chloride, ammonia, acetylene, organic acids, such as formic and acetic acid, ethyl and methyl alcohols, benzene, naphthalene. They even found the amino acid glycine!
It would be interesting to catch and study interstellar dust penetrating into the solar system and probably falling to Earth. The problem of “catching” it is not easy, because how to keep your ice “coat” in sun rays, especially in the Earth’s atmosphere, few interstellar dust particles succeed. Large ones get too hot them escape velocity cannot be extinguished quickly, and the dust particles “burn out.” Small ones, however, glide in the atmosphere for years, preserving part of the shell, but here the problem arises of finding them and identifying them.
There is one more, very intriguing detail. It concerns dust whose nuclei are made of carbon. Carbon synthesized in the cores of stars and released into space, for example, from the atmosphere of aging (such as red giants) stars, flying into interstellar space, cools and condenses in much the same way as after a hot day, fog from cooled water vapor collects in the lowlands. Depending on the crystallization conditions, layered structures of graphite, diamond crystals (just imagine whole clouds of tiny diamonds!) and even hollow balls of carbon atoms (fullerenes) can be obtained. And in them, perhaps, like in a safe or container, particles of the atmosphere of a very ancient star are stored. Finding such specks of dust would be a huge success.
Where is cosmic dust found?
It must be said that the very concept of the cosmic vacuum as something completely empty has long remained only a poetic metaphor. In fact, the entire space of the Universe, both between stars and between galaxies, is filled with matter, flows elementary particles, radiation and fields magnetic, electric and gravitational. All that can be touched, relatively speaking, is gas, dust and plasma, the contribution of which to the total mass of the Universe, according to various estimates, is only about 12% at medium density about 10-24 g/cm3. There is most gas in space, almost 99%. This is mainly hydrogen (up to 77.4%) and helium (21%), the rest accounting for less than two percent of the mass. And then there is dust; its mass is almost a hundred times less than gas.
Although sometimes the emptiness in interstellar and intergalactic space is almost ideal: sometimes there is 1 liter of space per atom of matter! There is no such vacuum either in terrestrial laboratories or within the solar system. For comparison, we can give the following example: in 1 cm 3 of the air we breathe, there are approximately 30,000,000,000,000,000,000 molecules.
This matter is distributed in interstellar space very uneven. Most of interstellar gas and dust forms a gas-dust layer near the plane of symmetry of the Galactic disk. Its thickness in our Galaxy is several hundred light years. Most of the gas and dust in its spiral branches (arms) and core are concentrated mainly in giant molecular clouds ranging in size from 5 to 50 parsecs (16 x 160 light years) and weighing tens of thousands and even millions of solar masses. But inside these clouds the matter is also distributed non-uniformly. In the main volume of the cloud, the so-called fur coat, mainly made of molecular hydrogen, the density of particles is about 100 pieces per 1 cm 3. In the densities inside the cloud, it reaches tens of thousands of particles per 1 cm3, and in the cores of these densities, generally millions of particles per 1 cm3. It is this uneven distribution of matter in the Universe that owes the existence of stars, planets and, ultimately, ourselves. Because it is in molecular clouds, dense and relatively cold, that stars are born.
What’s interesting is that the higher the density of the cloud, the more diverse its composition. In this case, there is a correspondence between the density and temperature of the cloud (or its individual parts) and those substances whose molecules are found there. On the one hand, this is convenient for studying clouds: by observing their individual components in different spectral ranges along the characteristic lines of the spectrum, for example CO, OH or NH 3, you can “peek” into one or another part of it. On the other hand, data on the composition of the cloud allows us to learn a lot about the processes occurring in it.
In addition, in interstellar space, judging by the spectra, there are substances whose existence under terrestrial conditions is simply impossible. These are ions and radicals. Their chemical activity so high that on Earth they immediately react. And in the rarefied cold space of space they live for a long time and quite freely.
In general, gas in interstellar space is not only atomic. Where it is colder, no more than 50 kelvins, atoms manage to stay together, forming molecules. However large mass interstellar gas is still in the atomic state. It is mainly hydrogen; its neutral form was discovered relatively recently - in 1951. As is known, it emits radio waves 21 cm long (frequency 1,420 MHz), based on the intensity of which it was determined how much there is in the Galaxy. By the way, it is not uniformly distributed in space between stars. In clouds of atomic hydrogen its concentration reaches several atoms per 1 cm3, but between clouds it is orders of magnitude lower.
Finally, near hot stars, gas exists in the form of ions. Powerful ultraviolet radiation heats and ionizes the gas, causing it to glow. This is why areas with a high concentration of hot gas, with a temperature of about 10,000 K, appear as luminous clouds. They are called light gas nebulae.
And in any nebula, in greater or lesser quantities, there is interstellar dust. Despite the fact that nebulae are conventionally divided into dust and gas nebulae, there is dust in both. And in any case, it is dust that apparently helps stars form in the depths of nebulae.
Foggy objects
Among all cosmic objects, nebulae are perhaps the most beautiful. True, dark nebulae in the visible range simply look like black blots in the sky; they are best observed against the background of the Milky Way. But in other ranges electromagnetic waves, for example, infrared, they are visible very well and the pictures turn out to be very unusual.
Nebulae are those isolated in space, connected by the forces of gravity or external pressure accumulations of gas and dust. Their mass can be from 0.1 to 10,000 solar masses, and their size can be from 1 to 10 parsecs.
At first, nebulae irritated astronomers. Until the middle of the 19th century, discovered nebulae were viewed as an annoying nuisance that prevented the observation of stars and the search for new comets. In 1714, the Englishman Edmond Halley, whose name is famous comet, even compiled a “black list” of six nebulae so that they would not mislead “comet catchers,” and the Frenchman Charles Messier expanded this list to 103 objects. Fortunately, the musician Sir William Herschel, who was in love with astronomy, and his sister and son became interested in the nebulae. Observing the sky with telescopes they built themselves, they left behind a catalog of nebulae and star clusters containing information about 5,079 space objects!
The Herschels practically exhausted the capabilities of optical telescopes of those years. However, the invention of photography and big time exposures made it possible to find very faintly luminous objects. A little bit later spectral methods analysis, observations in various ranges of electromagnetic waves made it possible in the future not only to discover many new nebulae, but also to determine their structure and properties.
An interstellar nebula appears bright in two cases: either it is so hot that its gas itself glows, such nebulae are called emission nebulae; or the nebula itself is cold, but its dust scatters the light of a nearby bright star - it is a reflection nebula.
Dark nebulae are also interstellar accumulations of gas and dust. But unlike light gaseous nebulae, which are sometimes visible even with strong binoculars or a telescope, such as the Orion Nebula, dark nebulae do not emit light, but absorb it. When starlight passes through such nebulae, dust can completely absorb it, converting it into infrared radiation that is invisible to the eye. Therefore, such nebulae look like starless holes in the sky. V. Herschel called them “holes in the sky.” Perhaps the most spectacular of these is the Horsehead Nebula.
However, dust grains may not completely absorb the light of stars, but only partially scatter it, and selectively. The fact is that the size of interstellar dust particles is close to the wavelength of blue light, so it is scattered and absorbed more strongly, and the “red” part of star light reaches us better. By the way, this good way estimate the size of dust grains by how they attenuate light of different wavelengths.
Star from the cloud
The reasons why stars arise have not been precisely established; there are only models that more or less reliably explain experimental data. In addition, the paths of formation, properties and further fate stars are very diverse and depend on many factors. However, there is an established concept, or rather, the most developed hypothesis, the essence of which, in the most general outline, is that stars are formed from interstellar gas in areas with increased density of matter, that is, in the depths of interstellar clouds. Dust as a material could be ignored, but its role in the formation of stars is enormous.
Apparently this happens (in the most primitive version, for a single star). First, a protostellar cloud condenses from the interstellar medium, which may be due to gravitational instability, but the reasons may be different and are not yet completely clear. One way or another, it contracts and attracts matter from the surrounding space. The temperature and pressure at its center increase until the molecules at the center of this collapsing ball of gas begin to break apart into atoms and then into ions. This process cools the gas, and the pressure inside the core drops sharply. The core contracts, and a shock wave propagates inside the cloud, throwing off its outer layers. A protostar is formed, which continues to contract under the influence of gravity until reactions begin in its center thermonuclear fusion conversion of hydrogen into helium. The compression continues for some time until strength gravitational compression will not be balanced by the forces of gas and radiant pressure.
It is clear that the mass of the resulting star is always less than the mass of the nebula that “gave birth” to it. During this process, part of the matter that did not have time to fall onto the core is “swept out” by a shock wave, radiation and particle flows simply into the surrounding space.
The process of formation of stars and stellar systems is influenced by many factors, including the magnetic field, which often contributes to the “tearing” of the protostellar cloud into two, rarely three fragments, each of which is compressed under the influence of gravity into its own protostar. This is how, for example, many double star systems two stars that revolve around general center masses and move in space as a single whole.
As you get older nuclear fuel in the depths of stars gradually burns out, and the faster the more star. In this case, the hydrogen cycle of reactions is replaced by the helium cycle, then, as a result of nuclear fusion reactions, increasingly heavier ones are formed chemical elements, right down to the iron. In the end, the nucleus, which no longer receives energy from thermonuclear reactions, sharply decreases in size, loses its stability, and its substance seems to fall on itself. Happening powerful explosion, during which a substance can heat up to billions of degrees, and interactions between nuclei lead to the formation of new chemical elements, up to the heaviest. The explosion is accompanied by a sharp release of energy and the release of matter. A star explodes, a process called a supernova. Ultimately, the star, depending on its mass, will turn into neutron star or a black hole.
This is probably what actually happens. In any case, there is no doubt that young, that is, hot, stars and their clusters are most numerous in nebulae, that is, in areas with an increased density of gas and dust. This is clearly visible in photographs taken by telescopes in different wavelength ranges.
Of course, this is nothing more than the crudest summary of the sequence of events. For us, two points are fundamentally important. First, what is the role of dust in the process of star formation? And secondly, where does it actually come from?
Universal coolant
IN total mass cosmic matter The dust itself, that is, atoms of carbon, silicon and some other elements combined into solid particles, is so small that, in any case, as construction material for stars, it would seem, can be ignored. However, in fact, their role is great - it is they who cool the hot interstellar gas, turning it into that very cold dense cloud from which stars are then formed.
The fact is that interstellar gas itself cannot cool. Electronic structure hydrogen atom is such that it can give up excess energy, if any, by emitting light in the visible and ultraviolet regions of the spectrum, but not in infrared range. Figuratively speaking, hydrogen cannot radiate heat. To cool down properly, it needs a “refrigerator”, the role of which is played by interstellar dust particles.
During a collision with dust grains at high speed unlike heavier and slower dust grains, gas molecules fly quickly they lose speed and their kinetic energy transmitted to a speck of dust. It also heats up and gives off this excess heat to the surrounding space, including in the form of infrared radiation, while it itself cools down. Thus, by absorbing the heat of interstellar molecules, dust acts as a kind of radiator, cooling the gas cloud. It is not much in mass - about 1% of the mass of the entire cloud matter, but this is enough to remove excess heat over millions of years.
When the temperature of the cloud drops, the pressure also drops, the cloud condenses and stars can be born from it. The remains of the material from which the star was born are, in turn, the starting material for the formation of planets. Now their composition already includes dust particles, and in more. Because, having been born, a star heats up and accelerates all the gas around itself, while dust remains flying nearby. After all, it is capable of cooling and is attracted to the new star much stronger than individual gas molecules. In the end, there is a dust cloud near the newborn star, and dust-rich gas at the periphery.
They are born there gas planets, such as Saturn, Uranus and Neptune. Well, stars appear nearby rocky planets. For us it is Mars, Earth, Venus and Mercury. It turns out a fairly clear division into two zones: gas planets and solid ones. So the Earth turned out to be largely made of interstellar dust grains. Metal dust particles became part of the planet's core, and now the Earth has a huge iron core.
The Mystery of the Young Universe
If a galaxy has formed, then where does the dust come from? In principle, scientists understand. Its most significant sources are novae and supernovae, which lose part of their mass, “dropping” the shell into the surrounding space. In addition, dust is also born in the expanding atmosphere of red giants, from where it is literally swept away by radiation pressure. In their cool, by the standards of stars, atmosphere (about 2.5 3 thousand kelvins) there are quite a lot of relatively complex molecules.
But here is a mystery that has not yet been solved. It has always been believed that dust is a product of the evolution of stars. In other words, stars must be born, exist for some time, grow old and, say, in the latest outbreak supernova produce dust. But what came first - the egg or the chicken? The first dust necessary for the birth of a star, or the first star, which for some reason was born without the help of dust, grew old, exploded, forming the very first dust.
What happened in the beginning? After all, when the Big Bang occurred 14 billion years ago, there were only hydrogen and helium in the Universe, no other elements! It was then that the first galaxies began to emerge from them, huge clouds, and in them the first stars, which had to go through a long journey. life path. Thermonuclear reactions in the cores of stars they had to “cook” more complex chemical elements, turn hydrogen and helium into carbon, nitrogen, oxygen, and so on, and after that the star had to throw it all into space, exploding or gradually throwing off the shell. This mass then had to cool, cool down and finally turn into dust. But already 2 billion years after big bang, in the earliest galaxies, there was dust! Using telescopes, it was discovered in galaxies 12 billion light years away from ours. At the same time, 2 billion years is too short a period for complete life cycle stars: during this time, most stars do not have time to grow old. Where the dust came from in the young Galaxy, if there should be nothing there except hydrogen and helium, is a mystery.
Mote reactor
Not only does interstellar dust act as a kind of universal coolant, but perhaps it is thanks to dust that complex molecules appear in space.
The fact is that the surface of a dust grain can serve both as a reactor in which molecules are formed from atoms and as a catalyst for the reactions of their synthesis. After all, the probability that there are many atoms at once various elements collide at one point, and even interact with each other at a temperature slightly higher absolute zero, unimaginably small. But the probability that a speck of dust will sequentially collide in flight with different atoms or molecules, especially inside a cold dense cloud, is quite large. Actually, this is what happens - this is how a shell of interstellar dust grains is formed from the encountered atoms and molecules frozen onto it.
On a solid surface, the atoms are close together. Migrating along the surface of a dust grain in search of the most energetically favorable position, the atoms meet and, finding themselves in close proximity, get the opportunity to react among themselves. Of course, very slowly in accordance with the temperature of the dust particle. The surface of particles, especially those containing a metal core, can exhibit catalyst properties. Chemists on Earth know well that the most effective catalysts are precisely particles a fraction of a micron in size on which molecules are collected and then react, in normal conditions completely “indifferent” to each other. Apparently, this is how it is formed molecular hydrogen: its atoms “stick” to a speck of dust, and then fly away from it, but in pairs, in the form of molecules.
It may very well be that small interstellar dust particles, having retained a few organic molecules in their shells, including the simplest amino acids, brought the first “seeds of life” to Earth about 4 billion years ago. This, of course, is nothing more than a beautiful hypothesis. But what speaks in its favor is that the amino acid glycine was found in cold gas and dust clouds. Maybe there are others, it’s just that the capabilities of telescopes do not yet allow them to be detected.
Dust Hunt
The properties of interstellar dust can, of course, be studied at a distance using telescopes and other instruments located on Earth or on its satellites. But it is much more tempting to catch interstellar dust particles, and then study them in detail, find out, not theoretically, but practically, what they consist of and how they are structured. There are two options here. You can reach the depths of space, collect interstellar dust there, bring it to Earth and analyze it by everyone possible ways. Or you can try to fly outside the solar system and analyze dust along the way directly on board the spacecraft, sending the resulting data to Earth.
The first attempt to bring samples of interstellar dust, and substances of the interstellar medium in general, was made several years ago by NASA. The spacecraft was equipped with special traps - collectors for collecting interstellar dust and cosmic wind particles. To catch dust particles without losing their shell, the traps were filled with a special substance, the so-called airgel. This very light foamy substance (the composition of which is a trade secret) resembles jelly. Once inside, the dust particles get stuck, and then, as in any trap, the lid slams shut to be opened on Earth.
This project was called Stardust star dust. His program is grandiose. After launching in February 1999, the equipment on board will eventually collect samples of interstellar dust and separately from dust in the immediate vicinity of Comet Wild-2, which flew near Earth last February. Now with containers filled with this valuable cargo, the ship flies home to land on January 15, 2006 in Utah, near Salt Lake City (USA). That’s when astronomers will finally see with their own eyes (with the help of a microscope, of course) those very dust grains whose composition and structure models they have already predicted.
And in August 2001, Genesis flew to collect samples of matter from deep space. This NASA project was aimed mainly at capturing particles solar wind. After spending 1,127 days in outer space, during which it flew about 32 million km, the ship returned and dropped a capsule with the resulting samples - traps with ions and solar wind particles - to Earth. Alas, a misfortune happened - the parachute did not open, and the capsule hit the ground with all its might. And crashed. Of course, the debris was collected and carefully studied. However, in March 2005, at a conference in Houston, program participant Don Barnetti said that four collectors with solar wind particles were not damaged, and their contents, 0.4 mg of captured solar wind, were being actively studied by scientists in Houston.
However, NASA is now preparing a third project, even more ambitious. It will be space mission Interstellar Probe. This time spaceship will move away to a distance of 200 a. e. from the Earth (a.e. distance from the Earth to the Sun). This ship will never return, but it will be “stuffed” with a wide variety of equipment, including for analyzing samples of interstellar dust. If everything works out, interstellar dust grains from deep space will finally be captured, photographed and analyzed automatically, right on board the spacecraft.
Formation of young stars
1. A giant galactic molecular cloud with a size of 100 parsecs, a mass of 100,000 suns, a temperature of 50 K, and a density of 10 2 particles/cm 3 . Inside this cloud there are large-scale condensations - diffuse gas and dust nebulae (1 x 10 pc, 10,000 suns, 20 K, 10 3 particles/cm 3) and small condensations - gas and dust nebulae (up to 1 pc, 100 x 1,000 suns, 20 K, 10 4 particles/cm 3). Inside the latter there are precisely clumps of globules with a size of 0.1 pc, a mass of 1 x 10 suns and a density of 10 x 10 6 particles / cm 3, where new stars are formed
2. The birth of a star inside a cloud of gas and dust
3. The new star, with its radiation and stellar wind, disperses the surrounding gas away from itself
4. A young star emerges into space that is clean and free of gas and dust, pushing aside the nebula that gave birth to it
Stages of “embryonic” development of a star with a mass equal to the Sun
5. The origin of a gravitationally unstable cloud with a size of 2,000,000 suns, with a temperature of about 15 K and an initial density of 10 -19 g/cm 3
6. After several hundred thousand years, this cloud will form a core with a temperature of about 200 K and the size of 100 suns, its mass is still only 0.05 of the solar
7. At this stage, the core with a temperature of up to 2,000 K sharply contracts due to the ionization of hydrogen and simultaneously heats up to 20,000 K, the speed of matter falling onto the growing star reaches 100 km/s
8. A protostar the size of two suns with a temperature at the center of 2x10 5 K, and at the surface 3x10 3 K
9. The last stage of the pre-evolution of a star is slow compression, during which lithium and beryllium isotopes burn out. Only after the temperature rises to 6x10 6 K, thermonuclear reactions of helium synthesis from hydrogen are started in the interior of the star. Total duration The birth cycle of a star like our Sun is 50 million years, after which such a star can burn quietly for billions of years
Olga Maksimenko, Candidate of Chemical Sciences
COSMIC DUST, solid particles with characteristic sizes from about 0.001 microns to about 1 microns (and possibly up to 100 microns or more in the interplanetary medium and protoplanetary disks), found in almost all astronomical objects: from the Solar System to very distant galaxies and quasars. Dust characteristics (particle concentration, chemical composition, particle size, etc.) vary significantly from one object to another, even for objects of the same type. Cosmic dust scatters and absorbs incident radiation. Scattered radiation with the same wavelength as the incident radiation propagates in all directions. Radiation absorbed by a speck of dust is transformed into thermal energy, and the particle usually emits in a longer wavelength region of the spectrum compared to the incident radiation. Both processes contribute to extinction - weakening of radiation celestial bodies dust located on the line of sight between the object and the observer.
Dust objects are studied in almost the entire range of electromagnetic waves - from X-rays to millimeter waves. Electric dipole radiation from rapidly rotating ultrafine particles appears to make some contribution to microwave radiation at frequencies 10-60 GHz. Important role play laboratory experiments, in which refractive indices are measured, as well as absorption spectra and scattering matrices of analogue particles cosmic dust particles, simulate the processes of formation and growth of refractory dust grains in the atmospheres of stars and protoplanetary disks, study the formation of molecules and the evolution of volatile dust components under conditions similar to those existing in dark interstellar clouds.
Cosmic dust located in various physical conditions, are directly studied in the composition of meteorites that fell on the Earth’s surface, in upper layers earth's atmosphere(interplanetary dust and remnants of small comets), during spacecraft flights to planets, asteroids and comets (circumplanetary and cometary dust) and beyond the heliosphere (interstellar dust). Ground-based and space-based remote observations of cosmic dust cover the Solar System (interplanetary, circumplanetary and cometary dust, dust near the Sun), the interstellar medium of our Galaxy (interstellar, circumstellar and nebular dust) and other galaxies (extragalactic dust), as well as very distant objects (cosmological dust).
Cosmic dust particles mainly consist of carbonaceous substances (amorphous carbon, graphite) and magnesium-iron silicates (olivines, pyroxenes). They condense and grow in the atmospheres of stars of late spectral classes and in protoplanetary nebulae, and are then ejected into the interstellar medium by radiation pressure. In interstellar clouds, especially dense ones, refractory particles continue to grow as a result of the accretion of gas atoms, as well as when particles collide and stick together (coagulation). This leads to the appearance of shells of volatile substances (mainly ice) and to the formation of porous aggregate particles. The destruction of dust grains occurs as a result of sputtering in shock waves arising after supernova explosions, or evaporation during the process of star formation that began in the cloud. The remaining dust continues to evolve near the formed star and later manifests itself in the form of an interplanetary dust cloud or cometary nuclei. Paradoxically, around evolved (old) stars the dust is “fresh” (recently formed in their atmosphere), and around young stars the dust is old (evolved as part of the interstellar medium). It is believed that cosmological dust, possibly existing in distant galaxies, was condensed in the ejections of material from the explosions of massive supernovae.
Lit. look at Art. Interstellar dust.
Many people admire with delight the beautiful spectacle of the starry sky, one of nature's greatest creations. In a clear autumn sky, it is clearly visible how a faintly luminous stripe runs across the entire sky, called Milky Way, having irregular outlines with different widths and brightness. If we consider Milky Way, forming our Galaxy, in a telescope, it turns out that this bright strip breaks up into many weak glowing stars, which to the naked eye merge into a continuous glow. It is now established that the Milky Way consists not only of stars and star clusters, but also of gas and dust clouds.
Cosmic dust occurs in many space objects, where a rapid outflow of matter occurs, accompanied by cooling. It manifests itself by infrared radiation hot Wolf-Rayet stars with a very powerful stellar wind, planetary nebulae, shells of supernovae and novae. A large number of dust exists in the cores of many galaxies (for example, M82, NGC253), from which there is an intense outflow of gas. The influence of cosmic dust is most pronounced during the emission of a new star. A few weeks after the maximum brightness of the nova, a strong excess of radiation in the infrared appears in its spectrum, caused by the appearance of dust with a temperature of about K. Further
Hello. In this lecture we will talk to you about dust. But not about the kind that accumulates in your rooms, but about cosmic dust. What is it?
Cosmic dust is Very fine particles solid located in any part of the Universe, including meteorite dust and interstellar matter, capable of absorbing starlight and forming dark nebulae in galaxies. Spherical dust particles about 0.05 mm in diameter are found in some marine sediments; It is believed that these are the remnants of the 5,000 tons of cosmic dust that fall on the globe every year.
Scientists believe that cosmic dust is formed not only from collisions, destruction of small solids, but also due to the condensation of interstellar gas. Cosmic dust is distinguished by its origin: dust can be intergalactic, interstellar, interplanetary and circumplanetary (usually in a ring system).
Cosmic dust grains arise mainly in the slowly expiring atmospheres of stars - red dwarfs, as well as during explosive processes on stars and violent ejections of gas from the cores of galaxies. Other sources of cosmic dust include planetary and protostellar nebulae, stellar atmospheres, and interstellar clouds.
Entire clouds of cosmic dust, which are located in the layer of stars that form the Milky Way, prevent us from observing distant star clusters. This star cluster, like the Pleiades, is completely immersed in a dust cloud. The most bright stars, which are in this cluster, illuminate the dust, like a lantern illuminates fog at night. Cosmic dust can only shine by reflected light.
Blue rays of light passing through cosmic dust are attenuated more than red rays, so the starlight that reaches us appears yellowish or even reddish. Entire regions of world space remain closed to observation precisely because of cosmic dust.
Interplanetary dust, at least in comparative proximity to the Earth, is fairly studied matter. Filling the entire space of the Solar System and concentrated in the plane of its equator, it was born largely as a result of random collisions of asteroids and the destruction of comets approaching the Sun. The composition of the dust, in fact, does not differ from the composition of meteorites falling on the Earth: it is very interesting to study it, and there are still many discoveries to be made in this area, but there seems to be no particular intrigue here. But thanks to this particular dust, in good weather in the west immediately after sunset or in the east before sunrise, you can admire a pale cone of light above the horizon. This is the so-called zodiacal light - sunlight scattered by small cosmic dust particles.
Interstellar dust is much more interesting. Its distinctive feature is the presence of a solid core and shell. The core appears to be composed mainly of carbon, silicon and metals. And the shell is mainly made of gaseous elements frozen onto the surface of the core, crystallized under the conditions of “deep freezing” of interstellar space, and this is about 10 kelvins, hydrogen and oxygen. However, there are impurities of molecules that are more complex. These are ammonia, methane and even polyatomic organic molecules that stick to a speck of dust or form on its surface during wanderings. Some of these substances, of course, fly away from its surface, for example, under the influence of ultraviolet radiation, but this process is reversible - some fly away, others freeze or are synthesized.
If a galaxy has formed, then where the dust comes from in it is, in principle, clear to scientists. Its most significant sources are novae and supernovae, which lose part of their mass, “dumping” the shell into the surrounding space. In addition, dust is also born in the expanding atmosphere of red giants, from where it is literally swept away by radiation pressure. In their cool, by the standards of stars, atmosphere (about 2.5 - 3 thousand kelvins) there are quite a lot of relatively complex molecules.
But here is a mystery that has not yet been solved. It has always been believed that dust is a product of the evolution of stars. In other words, stars must be born, exist for some time, grow old and, say, produce dust in the last supernova explosion. But what came first - the egg or the chicken? The first dust necessary for the birth of a star, or the first star, which for some reason was born without the help of dust, grew old, exploded, forming the very first dust.
What happened in the beginning? After all, when the Big Bang occurred 14 billion years ago, there were only hydrogen and helium in the Universe, no other elements! It was then that the first galaxies began to emerge from them, huge clouds, and in them the first stars, which had to go through a long life path. Thermonuclear reactions in the cores of stars should have “cooked” more complex chemical elements, turning hydrogen and helium into carbon, nitrogen, oxygen, and so on, and after that the star should have thrown it all into space, exploding or gradually shedding its shell. This mass then had to cool, cool down and finally turn into dust. But already 2 billion years after the Big Bang, in the earliest galaxies, there was dust! Using telescopes, it was discovered in galaxies 12 billion light years away from ours. At the same time, 2 billion years is too short a period for the full life cycle of a star: during this time, most stars do not have time to grow old. Where the dust came from in the young Galaxy, if there should be nothing there except hydrogen and helium, is a mystery.
Looking at the time, the professor smiled slightly.
But you will try to solve this mystery at home. Let's write down the task.
Homework.
1. Try to guess what came first, the first star or the dust?
Additional task.
1. Report on any type of dust (interstellar, interplanetary, circumplanetary, intergalactic)
2. Essay. Imagine yourself as a scientist tasked with studying cosmic dust.
3. Pictures.
Homemade assignment for students:
1. Why is dust needed in space?
Additional task.
1. Report on any type of dust. Former students schools remember the rules.
2. Essay. Disappearance of cosmic dust.
3. Pictures.
There are billions of stars and planets in the universe. And while a star is a flaming sphere of gas, planets like Earth are made up of solid elements. Planets form in clouds of dust that swirl around a newly formed star. In turn, the grains of this dust are composed of elements such as carbon, silicon, oxygen, iron and magnesium. But where do cosmic dust particles come from? A new study from the Niels Bohr Institute in Copenhagen shows that dust grains can not only form in giant supernova explosions, they can also survive subsequent ones. shock waves various explosions that affect dust.
A computer image of how cosmic dust is formed during supernova explosions. Source: ESO/M. Kornmesser
How cosmic dust was formed has long been a mystery to astronomers. The dust elements themselves form in flaming hydrogen gas in stars. Hydrogen atoms combine with each other to form increasingly heavier elements. As a result, the star begins to emit radiation in the form of light. When all the hydrogen is exhausted and it is no longer possible to extract energy, the star dies, and its shell flies away into space, which forms various nebulae in which young stars can again be born. Heavy elements are formed primarily in supernovae, the progenitors of which are massive stars, dying in a giant explosion. But how single elements clump together to form cosmic dust remained a mystery.
“The problem was that even if the dust formed along with the elements in supernova explosions, the event itself is so strong that these small grains simply should not survive. But cosmic dust exists, and its particles can be completely different sizes. Our research sheds light on this problem,” Professor Jens Hjort, head of the Center for Dark Cosmology at the Niels Bohr Institute.
Snapshot Hubble telescope unusual dwarf galaxy, which produced the bright supernova SN 2010jl. The image was taken before its appearance, so the arrow shows its progenitor star. The star that exploded was very massive, approximately 40 solar masses. Source: ESO
In cosmic dust studies, scientists observe supernovae using the X-shooter astronomical instrument installed on the Very large telescope(VLT) in Chile. It has amazing sensitivity, and the three spectrographs included in it. can observe the entire range of light at once, from ultraviolet and visible to infrared. Hjorth explains that at first they were waiting for the “right” explosion to appear supernova. And so, when this happened, a campaign to monitor it began. The observed star was unusually bright, 10 times brighter than the average supernova, and its mass was 40 times that of the Sun. In total, observing the star took the researchers two and a half years.
“Dust absorbs light, and using our data we were able to calculate a function that could tell us about the amount of dust, its composition and grain size. We found something truly exciting in the results,” Krista Gaul.
The first step toward the formation of cosmic dust is a mini-explosion in which a star ejects material containing hydrogen, helium and carbon into space. This gas cloud becomes a kind of shell around the star. A few more such flashes and the shell becomes denser. Finally, the star explodes and a dense gas cloud completely envelops its core.
“When a star explodes, the impact blast wave collides with a dense gas cloud like a brick hitting a concrete wall. All this happens in the gas phase at incredible temperatures. But the place where the explosion hit becomes dense and cools to 2000 degrees Celsius. At this temperature and density, the elements can nucleate and form solid particles. We found dust grains as small as one micron, which is very great value for these elements. With such dimensions, they will be able to survive their future journey through the galaxy.”
Thus, scientists believe that they have found the answer to the question of how cosmic dust is formed and lives.