Cosmic dust. Cosmic dust and strange balls in ancient earth layers The reason for the creation of cosmic dust

There are billions of stars and planets in the universe. And if a star is a flaming sphere of gas, then 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 not only can dust grains form in giant supernova explosions, they can also survive the subsequent shock waves of various explosions that impact the dust.

Computer generated image of how cosmic dust is formed in supernova explosions. Source: ESO/M. Kornmesser

How cosmic dust was formed has long been a mystery to astronomers. The dust elements themselves are formed in the glowing hydrogen gas in stars. Hydrogen atoms combine with each other to form heavier and 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 into outer 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 that die in a giant explosion. But how single elements stick together to form cosmic dust has remained a mystery.

“The problem was that even if dust were formed along with the elements in supernova explosions, the event itself is so strong that these small grains simply should not have survived. But cosmic dust exists, and its particles can be of completely different sizes. Our study sheds light on this problem,” says Professor Jens Hjort, head of the Center for Dark Cosmology at the Niels Bohr Institute.

Hubble telescope image of an unusual dwarf galaxy in which the bright supernova SN 2010jl originated. The image was taken before its appearance, so the arrow shows its progenitor star. The exploding star was very massive, about 40 solar masses. Source: ESO

In cosmic dust studies, scientists observe supernovae using the X-shooter astronomical instrument at the Very Large Telescope (VLT) complex in Chile. It has amazing sensitivity, and the three spectrographs included in it. can observe the entire light spectrum at once, from ultraviolet and visible to infrared. Hjort explains that at first they were expecting a "proper" supernova explosion. And that's when it happened, the surveillance campaign began. The observed star was extraordinarily bright, 10 times brighter than a typical average supernova, and its mass was 40 times that of the sun. In total, the observation of 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. In the results, we found something really exciting,” Christa Gol.

The first step in the formation of space 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 of these flashes and the shell becomes denser. Finally, the star explodes, and a dense gas cloud completely envelops its core.

“When a star explodes, the shock wave hits the 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 down 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 a very large value for these elements. At that size, they should 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.

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

Night street lighting makes life more comfortable and safer, but, unfortunately, deprives the citizens of the starry sky. The brightest stars from the city can still be seen, but the Milky Way is already completely inaccessible to many residents of the 21st century. But our ancestors had no problem admiring not only the Milky Way itself, but also the intricacies of its pattern. In particular, back in the 15th century, sailors sailing in the southern seas distinguished a distinct dark spot on the bright strip of the Milky Way. In those days, when the sky was not yet hopelessly spoiled by widespread illumination, a noticeable gap in the constellation of the Southern Cross was awarded its own name - it was called the Coal Sack.

Space dust captures the history of the solar systemComets contain the primordial dust from which our solar system was formed, and since these particles have remained very far from the Sun throughout their existence, they create the effect of deep freezing, thus preserving dust that is billions of years old.

However, this did not mean that the stain was formed by some substance. Rather, on the contrary: in fact, until the beginning of the 20th century, these and other dark spots on the starry background were considered simply places where there were no stars. Legend has it that the greatest astronomer-observer William Herschel, seeing one of these spots through a telescope, shouted to his sister Caroline, his faithful assistant: “My God, there is a hole in the sky!”

The idea of ​​voids in the distribution of stars has receded largely due to the painstaking work of Edward Barnard, who compiled a large-scale photographic atlas of the Milky Way. At first, in the descriptions of his photographs, he called dark spots “vacancies” or even “black holes” (not in the current sense of these words), but over time he came to the conclusion that in this case we are dealing with clouds of absorbing matter, which covers us some of the stars in the Milky Way.

Convincing evidence that the absorption of light in the Galaxy occurs not only in dark clouds, but generally everywhere, was first (in 1930) collected by another American, Robert Trumpler. He noted the following important facts. First, the light from a star is absorbed the stronger, the farther away from us the star is. Secondly, light passing through interstellar space is not only absorbed, but also turns red (like the Sun near the horizon), because blue rays are absorbed more than red ones. And the degree of this reddening also increases with the distance to the star. Trumpler concluded from this that absorbing matter is represented by particles (dust grains) scattered throughout the Galaxy with a size somewhat smaller than the wavelength of visible light. Dark clouds are particularly dense concentrations of these particles.

Initially, it was assumed that interstellar particles consist of ice - in the broad sense of the word, including not only water ice, but also other frozen gases (ammonia, carbon dioxide, etc.) - and condense in the same place where they are observed, that is, directly between the stars. This assumption seemed quite natural, taking into account the ideas of the middle of the 20th century about the content of atoms in the interstellar medium (ISM). However, already in the 1960s, these ideas had to be abandoned.

Ancient galaxies contain 100 times less dust than scientists expectedIn the past few years, astronomers have been delving deeper into the past of the universe, trying to understand how the first stars and galaxies arose and whether they were different from their modern cousins.

The fact is that the words "blue color is absorbed stronger than red" describe only the general dependence of absorption on the wavelength. Against the general background of an increase in absorption upon transition to shorter wavelengths, this dependence may have additional dips due to the fact that various substances have the ability to absorb light more efficiently in certain spectral ranges. For example, water ice is particularly good at absorbing infrared radiation with a wavelength of about 3 microns (µm). Therefore, if you look at a star through a cloud of ice particles, you can expect a dip near 3 microns in its spectrum. In addition, water ice strongly absorbs ultraviolet radiation with a wavelength shorter than 160 nm, which means that a dip in the ultraviolet (UV) range should also appear in the spectrum of the same star.

Both IR and UV observations require additional, sometimes very significant, efforts. As long as only the visible range was available to observers, the ice particle model did not encounter any particular inconsistencies. However, as soon as observations spread in both directions from the visible range, it became clear that traces of water ice are not observed either in the ultraviolet or in the IR, which means that the mixture of frozen gases, if included in the composition of cosmic dust particles, is not the main component . More precisely, a three-micron dip is observed, but only in those cases when the light of the background star passes through dense dust clouds, where water and other molecules can freeze in the form of ice mantles onto dust particles that are not ice themselves.

Planck telescope lifts 'dusty curtain' hiding ancient galaxiesEuropean scientists presented the first results obtained by the Planck space microwave observatory, in particular, data on "cold galaxies" that were not previously visible behind a veil of interstellar dust.

Other characteristics of absorption in the UV and IR ranges became an indication of the "true" composition of cosmic dust grains. It turned out that cosmic dust “steals” photons with wavelengths of about 200 nm and 10 microns from stellar spectra especially effectively. This selectivity reflects some features of the chemical and mineral composition of dust grains. In the late 1960s, absorption at 200 nm was associated with graphite, and absorption at 10 µm (and some other wavelengths) with minerals from the silicate group. On this basis, the idea was formed of interstellar dust as a mixture of graphite (or some other, but also containing carbon) and silicate particles. This idea has been preserved to this day, although, of course, in a repeatedly modified and supplemented form.

The graphite-silicate model is good in that it not only allows one to explain the nature of interstellar extinction, but also sheds some light on the origin of dust grains. Now, most experts believe that it is still impossible to condense stone dust particles in a cold rarefied interstellar gas in a reasonable period of time; you need to look for a place denser and hotter. Such a place turned out to be the extended atmospheres of stars in the last stages of evolution. While a Sun-like star is "in its prime," its atmosphere is too hot for solid matter to exist. However, at the end of a star's life path, its atmosphere swells and cools to such an extent that dust particles can already condense there, much like soot condenses in an insufficiently hot flame. Then the newly formed dust grains, together with the matter of the star, scatter through interstellar space.

For a long time, it was not clear why dust particles can collect into large clouds. However, in the 1960s and 1970s, it became clear that dust was in fact only a minor admixture (about 1% by mass) to the main ingredient in interstellar matter, gas, consisting mainly of hydrogen and helium. To estimate the scale of the gas content in the ISM, observations in the visible part of the spectrum are no longer enough: the gas almost does not absorb starlight, and itself glows only in the radio range. But there is so much of it that it completely entrains the dust with its movements. And the dark dust clouds are actually not even the tip of an iceberg, but just a tiny coating that betrays the presence of much more massive, but invisible clouds of interstellar gas.

This does not mean, of course, that dust can be neglected in the study of the Universe. First, its presence must be taken into account when studying stars, so as not to mistakenly attribute to a star the properties of dust grains that block its radiation. Second, dust plays an important role in the thermoregulation of the interstellar medium, acting as a powerful heat sink. Thirdly, it turns out to be a catalyst in interstellar chemical reactions, allowing the formation of complex organic compounds. Fourthly, cosmic dust particles serve as the raw material for the formation of planets, on one of which - consisting of myriads of cosmic dust particles stuck together - we live. Finally, the carbon that we ourselves are made of could also have been part of interstellar carbon dust grains in the past.

Of course, the question of the role that cosmic dust plays in the emergence of life remains open. But in any case, we have to admit that the coal fantasy of medieval sailors turned out to be surprisingly visionary.

Interstellar dust is a product of various intensity processes occurring in all corners of the Universe, and its invisible particles even reach the surface of the Earth, flying in the atmosphere around us.

A repeatedly confirmed fact - nature does not like emptiness. Interstellar outer space, which seems to us to be vacuum, is actually filled with gas and microscopic dust particles, 0.01-0.2 microns in size. The combination of these invisible elements gives rise to objects of enormous size, a kind of clouds of the Universe, capable of absorbing some types of spectral radiation from stars, sometimes completely hiding them from earthly researchers.

What is interstellar dust made of?

These microscopic particles have a nucleus, which is formed in the gaseous envelope of stars and depends entirely on its composition. For example, graphite dust is formed from grains of carbon luminaries, and silicate dust is formed from oxygen ones. This is an interesting process that lasts for decades: when the stars cool down, they lose their molecules, which, flying into space, combine into groups and become the basis of the core of a dust grain. Further, a shell of hydrogen atoms and more complex molecules is formed. At low temperatures, interstellar dust is in the form of ice crystals. Wandering around the Galaxy, little travelers lose part of the gas when heated, but new molecules take the place of the departed molecules.

Location and properties

The main part of the dust that falls on our Galaxy is concentrated in the region of the Milky Way. It stands out against the background of stars in the form of black stripes and spots. Despite the fact that the weight of dust is negligible compared to the weight of gas and is only 1%, it is able to hide celestial bodies from us. Although the particles are separated from each other by tens of meters, but even in such an amount, the densest regions absorb up to 95% of the light emitted by stars. The sizes of gas and dust clouds in our system are really huge, they are measured in hundreds of light years.

Impact on observations

Thackeray globules obscure the region of the sky behind them

Interstellar dust absorbs most of the radiation from stars, especially in the blue spectrum, it distorts their light and polarity. Short waves from distant sources receive the greatest distortion. Microparticles mixed with gas are visible as dark spots on the Milky Way.

In connection with this factor, the core of our Galaxy is completely hidden and is available for observation only in infrared rays. Clouds with a high concentration of dust become almost opaque, so the particles inside do not lose their icy shell. Modern researchers and scientists believe that it is they who stick together to form the nuclei of new comets.

Science has proven the influence of dust granules on the processes of star formation. These particles contain various substances, including metals, which act as catalysts for numerous chemical processes.

Our planet increases its mass every year due to falling interstellar dust. Of course, these microscopic particles are invisible, and in order to find and study them, they explore the ocean floor and meteorites. The collection and delivery of interstellar dust has become one of the functions of spacecraft and missions.

When entering the Earth's atmosphere, large particles lose their shell, and small ones invisibly circle around us for years. Cosmic dust is ubiquitous and similar in all galaxies, astronomers regularly observe dark lines on the face of distant worlds.

In science, imagination is especially in demand. It is not only mathematics or logic, but something between beauty and poetry.
- Maria Mitchell

Looking at the immensity of the night sky, where there are a few clouds, no moon, at a fairly dark time of the day, you will see not just thousands of tiny white dots illuminating the black canopy of the night.

Although on average stars are white, there is an important reason for this. Our eyes have evolved to see the very narrow part of the spectrum known to us as visible light, from violet at 400nm to red at 700nm.

In fact, these wavelengths are not distinguished by anything special, it just happened. But this happened on the surface of the Earth, which is illuminated by the Sun during the day!

This means that stars burning at temperatures higher than the Sun will appear blue to us, while cooler stars will appear, as they decrease, yellow, orange, and even red. In the southern hemisphere, the view of the Southern Cross and terminal stars demonstrates this contrast.

In both hemispheres, the great winter constellation, Orion (rising at 2 a.m. in September), includes stars ranging from dark orange Betelgeuse to bright blue stars in the belt.

And although these stars in the images are so colorful, this does not explain much.

Long reddish regions can be found in both pictures. These are clearly not cold red stars. The astronomical image of the day image released just before this writing showed a close-up of this reddish nebula region in Orion from the image above.

This remarkable nebula has two of the colors visible to human eyes, of the kind found in dusty regions of space. The blue nebula on the left is in stark contrast to the large red glow on the right.

It turns out that areas of space that glow red are a little more common, but there are also plenty of blue areas. The question you're probably thinking about is why is that? Let's take a closer look at Orion's nearby belt.

Even if a star is not blue, its reflection nebula is usually blue (with a few exceptions), for the same reason the sky is blue: cosmic dust, like Earth's atmosphere, is better at scattering blue than red!

And when light collides with a neutral, non-ionized gas, the red light just passes through, with only a small part of it reflected, and the blue is scattered in all directions, including ours!

Therefore, looking at the huge complex of molecular clouds in the constellation of Orion - hundreds of light years across - you can see that it is filled with both emitting and reflecting nebulae, as well as dark lanes of absorbing dust!

This is how hot stars, hydrogen, heavier elements and light-scattering dust, along with the light coming from all the surrounding stars, work together to illuminate the depths of space with the entire spectrum of visible light!

If you're starting to imagine what you could see if, instead of a tiny part of the visible spectrum, we could see everything from gamma rays to radio waves, congratulations! You have just understood why we need telescopes that are sensitive to such a variety of wavelengths, and why we use false color compositions with all this information.

The wide variety of information visible to our eyes covers only 1/60 of all the wavelengths of the electromagnetic spectrum on a logarithmic scale! So rejoice in what you see and the reasons why it is such a light, but do not believe that only what you see exists. There is a whole universe, and every day science helps us to see it and understand it a little more. Don't forget the importance of looking.

space x-ray background

Oscillations and waves: Characteristics of various oscillatory systems (oscillators).

Breaking the Universe

Dusty circumplanetary complexes: fig4

Space dust properties

S. V. Bozhokin St. Petersburg State Technical University	Content

Introduction

Many people admire with delight the beautiful spectacle of the starry sky, one of the greatest creations of nature. In the clear autumn sky, it is clearly visible how a faintly luminous band called the Milky Way runs through the entire sky, having irregular outlines with different widths and brightness. If we look at the Milky Way, which forms our Galaxy, through a telescope, it turns out that this bright band breaks up into many faintly luminous stars, which, to the naked eye, merge into a continuous radiance. It is now established that the Milky Way consists not only of stars and star clusters, but also of gas and dust clouds.

Huge interstellar clouds from luminous rarefied gases got the name gaseous diffuse nebulae. One of the most famous is the nebula in constellation Orion, which is visible even to the naked eye near the middle of the three stars that form the "sword" of Orion. The gases that form it glow with a cold light, reradiating the light of neighboring hot stars. Gaseous diffuse nebulae are mainly composed of hydrogen, oxygen, helium, and nitrogen. Such gaseous or diffuse nebulae serve as a cradle for young stars, which are born in the same way as ours was once born. solar system. The process of star formation is continuous, and stars continue to form today.

IN interstellar space diffuse dusty nebulae are also observed. These clouds are made up of tiny hard dust particles. If a bright star appears near the dusty nebula, then its light is scattered by this nebula and the dusty nebula becomes directly observable(Fig. 1). Gas and dust nebulae can generally absorb the light of stars lying behind them, so they are often visible in sky shots as gaping black holes against the background of the Milky Way. Such nebulae are called dark nebulae. In the sky of the southern hemisphere there is one very large dark nebula, which the sailors called the Coal Sack. There is no clear boundary between gaseous and dusty nebulae, so they are often observed together as gaseous and dusty nebulae.

Diffuse nebulae are only densifications in that extremely rarefied interstellar matter, which was named interstellar gas. Interstellar gas is detected only when observing the spectra of distant stars, causing additional ones in them. After all, over a long distance, even such a rarefied gas can absorb the radiation of stars. The emergence and rapid development radio astronomy made it possible to detect this invisible gas by the radio waves that it emits. Huge dark clouds of interstellar gas are composed mostly of hydrogen, which even at low temperatures emits radio waves at a length of 21 cm. These radio waves pass unhindered through gas and dust. It was radio astronomy that helped us in studying the shape of the Milky Way. Today we know that gas and dust, mixed with large clusters of stars, form a spiral, the branches of which, leaving the center of the Galaxy, wrap around its middle, creating something similar to a cuttlefish with long tentacles caught in a whirlpool.

At present, a huge amount of matter in our Galaxy is in the form of gas and dust nebulae. Interstellar diffuse matter is concentrated in a relatively thin layer in equatorial plane our star system. Clouds of interstellar gas and dust block the center of the Galaxy from us. Because of the clouds of cosmic dust, tens of thousands of open star clusters remain invisible to us. Fine cosmic dust not only weakens the light of stars, but also distorts them spectral composition. The fact is that when light radiation passes through cosmic dust, it not only weakens, but also changes color. The absorption of light by cosmic dust depends on the wavelength, so from all optical spectrum of a star blue rays are absorbed more strongly and photons corresponding to red color are absorbed weaker. This effect leads to the reddening of the light of stars that have passed through the interstellar medium.

For astrophysicists, the study of the properties of cosmic dust and the elucidation of the influence that this dust has on the study of space is of great importance. physical characteristics of astrophysical objects. Interstellar extinction and interstellar polarization of light, infrared radiation of neutral hydrogen regions, deficit chemical elements in the interstellar medium, questions of the formation of molecules and the birth of stars - in all these problems a huge role belongs to cosmic dust, the properties of which are considered in this article.

Origin of cosmic dust

Cosmic dust grains arise mainly in the slowly expiring atmospheres of stars - red dwarfs, as well as during explosive processes on stars and rapid ejection of gas from the nuclei of galaxies. Other sources of cosmic dust formation are planetary and protostellar nebulae , stellar atmospheres and interstellar clouds. In all processes of the formation of cosmic dust particles, the temperature of the gas drops as the gas moves outward and at some point passes through the dew point, at which vapor condensation that form the nuclei of dust particles. The centers for the formation of a new phase are usually clusters. Clusters are small groups of atoms or molecules that form a stable quasi-molecule. In collisions with an already formed dust grain nucleus, atoms and molecules can join it, either by entering into chemical reactions with dust grain atoms (chemisorption) or completing the forming cluster. In the densest parts of the interstellar medium, the concentration of particles in which is cm -3, the growth of a dust grain can be associated with coagulation processes, in which dust grains can stick together without being destroyed. Coagulation processes, which depend on the properties of the surface of dust grains and their temperatures, occur only when collisions between dust grains occur at low relative collision velocities.

On fig. Figure 2 shows the growth of cosmic dust clusters by adding monomers. The resulting amorphous cosmic dust grain can be a cluster of atoms with fractal properties. fractals called geometric objects: lines, surfaces, spatial bodies that have a strongly indented shape and have the property of self-similarity. self-similarity means the invariance of the main geometric characteristics fractal object when changing the scale. For example, images of many fractal objects turn out to be very similar when the resolution is increased in a microscope. Fractal clusters are highly branched porous structures formed under highly nonequilibrium conditions when solid particles of similar sizes combine into a single whole. Under terrestrial conditions, fractal aggregates are obtained when vapor relaxation metals in non-equilibrium conditions, during the formation of gels in solutions, during the coagulation of particles in fumes. The model of a fractal cosmic dust grain is shown in fig. 3. Note that the processes of dust grain coagulation occurring in protostellar clouds and gas and dust disks, increase significantly with turbulent motion interstellar matter.

The nuclei of cosmic dust particles, consisting of refractory elements, hundredths of a micron in size, are formed in the envelopes of cold stars during a smooth outflow of gas or during explosive processes. Such nuclei of dust grains are resistant to many external influences.