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 small particles of solid matter found anywhere in the Universe, including meteorite dust and interstellar matter that can absorb starlight and form 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 and destruction of small solid bodies, 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. A star cluster like the Pleiades is completely immersed in a dust cloud. The brightest stars 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 of the school remember the rules.
2. Essay. Disappearance of cosmic dust.
3. Pictures.
Cosmic dust, its composition and properties are little known to people not involved in the study of extraterrestrial space. However, such a phenomenon leaves its traces on our planet! Let's take a closer look at where it comes from and how it affects life on Earth.
Cosmic dust concept
Space dust on Earth is most often found in certain layers of the ocean floor, ice sheets of the planet's polar regions, peat deposits, hard-to-reach desert areas and meteorite craters. The size of this substance is less than 200 nm, which makes its study problematic.
Typically, the concept of cosmic dust includes a distinction between interstellar and interplanetary varieties. However, all this is very conditional. The most convenient option for studying such a phenomenon is considered to be the study of dust from space on the borders of the Solar system or beyond.
The reason for this problematic approach to studying the object is that the properties of extraterrestrial dust change dramatically when it is near a star such as the Sun.
Theories of the origin of cosmic dust
Streams of cosmic dust constantly attack the Earth's surface. The question arises where this substance comes from. Its origins give rise to much debate among experts in the field.
The following theories of the formation of cosmic dust are distinguished:
- Decay of celestial bodies. Some scientists believe that cosmic dust is nothing more than the result of the destruction of asteroids, comets and meteorites.
- Remnants of a protoplanetary type cloud. There is a version according to which cosmic dust is classified as microparticles of a protoplanetary cloud. However, this assumption raises some doubts due to the fragility of the finely dispersed substance.
- The result of an explosion on the stars. As a result of this process, according to some experts, a powerful release of energy and gas occurs, which leads to the formation of cosmic dust.
- Residual phenomena after the formation of new planets. The so-called construction “garbage” has become the basis for the emergence of dust.
The main types of cosmic dust
There is currently no specific classification of cosmic dust types. Subspecies can be distinguished by visual characteristics and location of these microparticles.
Let's consider seven groups of cosmic dust in the atmosphere, different in external indicators:
- Gray fragments of irregular shape. These are residual phenomena after the collision of meteorites, comets and asteroids no larger than 100-200 nm in size.
- Particles of slag-like and ash-like formation. Such objects are difficult to identify solely by external signs, because they have undergone changes after passing through the Earth's atmosphere.
- The grains are round in shape, with parameters similar to black sand. Outwardly, they resemble magnetite powder (magnetic iron ore).
- Small black circles with a characteristic shine. Their diameter does not exceed 20 nm, which makes studying them a painstaking task.
- Larger balls of the same color with a rough surface. Their size reaches 100 nm and makes it possible to study their composition in detail.
- Balls of a certain color with a predominance of black and white tones with inclusions of gas. These microparticles of cosmic origin consist of a silicate base.
- Balls of heterogeneous structure made of glass and metal. Such elements are characterized by microscopic sizes within 20 nm.
- Dust found in intergalactic space. This type can distort the dimensions of distances during certain calculations and is capable of changing the color of space objects.
- Formations within the Galaxy. The space within these limits is always filled with dust from the destruction of cosmic bodies.
- Matter concentrated between stars. It is most interesting due to the presence of a shell and a core of solid consistency.
- Dust located near a certain planet. It is usually located in the ring system of a celestial body.
- Clouds of dust around the stars. They circle along the orbital path of the star itself, reflecting its light and creating a nebula.
- Metal band. Representatives of this subspecies have a specific gravity of more than five grams per cubic centimeter, and their base consists mainly of iron.
- Silicate-based group. The base is transparent glass with a specific gravity of approximately three grams per cubic centimeter.
- Mixed group. The very name of this association indicates the presence of both glass and iron microparticles in the structure. The base also includes magnetic elements.
- Spherules with hollow filling. This species is often found in meteorite crash sites.
- Spherules of metallic formation. This subspecies has a core of cobalt and nickel, as well as a shell that has oxidized.
- Balls of homogeneous build. Such grains have an oxidized shell.
- Balls with a silicate base. The presence of gas inclusions gives them the appearance of ordinary slag, and sometimes foam.
It should be remembered that these classifications are very arbitrary, but serve as a certain guideline for designating the types of dust from space.
Composition and characteristics of cosmic dust components
Let's take a closer look at what cosmic dust consists of. There is a certain problem in determining the composition of these microparticles. Unlike gaseous substances, solids have a continuous spectrum with relatively few bands that are blurred. As a result, the identification of cosmic dust grains becomes difficult.
The composition of cosmic dust can be considered using the example of the main models of this substance. These include the following subspecies:
- Ice particles whose structure includes a core with a refractory characteristic. The shell of such a model consists of light elements. Large particles contain atoms with magnetic elements.
- The MRN model, the composition of which is determined by the presence of silicate and graphite inclusions.
- Oxide cosmic dust, which is based on diatomic oxides of magnesium, iron, calcium and silicon.
- Balls with metallic nature of formation. The composition of such microparticles includes an element such as nickel.
- Metal balls with the presence of iron and the absence of nickel.
- Silicone based circles.
- Iron-nickel balls of irregular shape.
The soils are fertile for the presence of cosmic material. A particularly large number of spherules were found in places where meteorites fell. The basis for them was nickel and iron, as well as various minerals such as troilite, cohenite, steatite and other components.
Glaciers also melt aliens from outer space in the form of dust in their blocks. Silicate, iron and nickel serve as the basis for the spherules found. All mined particles were classified into 10 clearly defined groups.
Difficulties in determining the composition of the object under study and differentiating it from impurities of terrestrial origin leave this issue open for further research.
The influence of cosmic dust on life processes
The influence of this substance has not been fully studied by specialists, which provides great opportunities for further activities in this direction. At a certain altitude, with the help of rockets, they discovered a specific belt consisting of cosmic dust. This gives grounds to assert that such extraterrestrial matter affects some processes occurring on planet Earth.
The influence of cosmic dust on the upper atmosphere
Recent studies indicate that the amount of cosmic dust can influence changes in the upper atmosphere. This process is very significant because it leads to certain fluctuations in the climatic characteristics of planet Earth.
A huge amount of dust resulting from asteroid collisions fills the space around our planet. Its quantity reaches almost 200 tons per day, which, according to scientists, cannot but leave its consequences.
The northern hemisphere, whose climate is prone to cold temperatures and dampness, is most susceptible to this attack, according to the same experts.
The impact of cosmic dust on cloud formation and climate change has not yet been sufficiently studied. New research in this area raises more and more questions, the answers to which have not yet been obtained.
The influence of dust from space on the transformation of oceanic silt
Irradiation of cosmic dust by the solar wind causes these particles to fall to Earth. Statistics show that the lightest of the three isotopes of helium enters ocean silt in huge quantities through dust grains from space.
The absorption of elements from outer space by minerals of ferromanganese origin served as the basis for the formation of unique ore formations on the ocean floor.
At the moment, the amount of manganese in areas that are close to the Arctic Circle is limited. All this is due to the fact that cosmic dust does not enter the World Ocean in those areas due to ice sheets.
The influence of cosmic dust on the composition of the water of the World Ocean
If we look at the glaciers of Antarctica, they are striking in the number of meteorite remains found in them and the presence of cosmic dust, which is a hundred times higher than the normal background.
The excessively increased concentration of the same helium-3, valuable metals in the form of cobalt, platinum and nickel allows us to confidently assert the fact of the interference of cosmic dust in the composition of the ice sheet. At the same time, the substance of extraterrestrial origin remains in its original form and not diluted by ocean waters, which in itself is a unique phenomenon.
According to some scientists, the amount of cosmic dust in such peculiar ice sheets over the last million years is on the order of several hundred trillion formations of meteorite origin. During the warming period, these covers melt and carry elements of cosmic dust into the World Ocean.
Watch a video about cosmic dust:
This cosmic neoplasm and its influence on some factors of life on our planet have not yet been studied enough. It is important to remember that the substance can influence climate change, the structure of the ocean floor and the concentration of certain substances in the waters of the World Ocean. Photos of cosmic dust indicate how many more mysteries these microparticles conceal. All this makes studying this interesting and relevant!
Many people admire with delight the beautiful spectacle of the starry sky, one of nature's greatest creations. In the clear autumn sky, it is clearly visible how a faintly luminous strip, called the Milky Way, runs across the entire sky, having irregular outlines with different widths and brightness. If we examine the Milky Way, which forms our Galaxy, through a telescope, it will turn out that this bright strip breaks up into many faintly luminous stars, which for 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 amount 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
Cosmic X-ray background
Oscillations and waves: Characteristics of various oscillatory systems (oscillators).
Rupture of the Universe
Dust circumplanetary complexes: fig4
Properties of cosmic dust
| S. V. Bozhokin St. Petersburg State Technical University | Content |
Introduction
Many people admire with delight the beautiful spectacle of the starry sky, one of nature's greatest creations. In the clear autumn sky, it is clearly visible how a faintly luminous strip, called the Milky Way, runs across the entire sky, having irregular outlines with different widths and brightness. If we examine the Milky Way, which forms our Galaxy, through a telescope, it will turn out that this bright strip breaks up into many faintly luminous stars, which for 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.
Huge interstellar clouds of luminous rarefied gases got the name gaseous diffuse nebulae. One of the most famous is the nebula in Orion constellation, 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 cold light, re-emitting the light of neighboring hot stars. The composition of gaseous diffuse nebulae consists mainly 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 dust nebulae are also observed. These clouds are made up of tiny solid grains of dust. If there is a bright star near the dust nebula, then its light is scattered by this nebula and the dust nebula becomes directly observable(Fig. 1). Gas and dust nebulae can generally absorb the light of the stars behind them, so in sky photographs they are often visible as black, gaping holes against the background of the Milky Way. Such nebulae are called dark nebulae. There is one very large dark nebula in the sky of the southern hemisphere, which navigators nicknamed the Coal Sack. There is no clear boundary between gas and dust nebulae, so they are often observed together as gas and dust 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 gas in them. Indeed, over a long distance, even such rarefied gas can absorb the radiation of stars. Emergence and rapid development radio astronomy made it possible to detect this invisible gas by the radio waves it emits. The huge, dark clouds of interstellar gas are composed mainly of hydrogen, which, even at low temperatures, emits radio waves at a length of 21 cm. These radio waves travel unimpeded through gas and dust. It was radio astronomy that helped us study 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, emerging from the center of the Galaxy, wrap around its middle, creating something similar to a cuttlefish with long tentacles caught in a whirlpool.
Currently, 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. Due to 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 of all optical spectrum of a star Blue rays are absorbed more strongly and photons corresponding to red are absorbed more weakly. This effect leads to the phenomenon of reddening of the light of stars passing through the interstellar medium.
For astrophysicists, it is of great importance to study the properties of cosmic dust and determine the influence that this dust has when studying physical characteristics of astrophysical objects. Interstellar absorption and interstellar polarization of light, infrared radiation of neutral hydrogen regions, deficiency chemical elements in the interstellar medium, issues 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 discussed 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 violent ejections of gas from the cores of galaxies. Other sources of cosmic dust formation are planetary and protostellar nebulae , stellar atmospheres and interstellar clouds. In all processes of formation of cosmic dust grains, the gas temperature drops as the gas moves outward and at some point passes through the dew point, at which condensation of vapors of substances, forming the nuclei of dust grains. The centers of formation of a new phase are usually clusters. Clusters are small groups of atoms or molecules that form a stable quasi-molecule. When colliding with an already formed dust grain nucleus, atoms and molecules can join it, either entering into chemical reactions with the dust grain atoms (chemisorption) or completing the formation of the emerging cluster. In the densest regions of the interstellar medium, the concentration of particles in which is cm -3, the growth of dust grains can be associated with coagulation processes, in which dust grains can stick together without being destroyed. Coagulation processes, depending on the surface properties of dust grains and their temperatures, occur only when collisions between dust grains occur at low relative collision velocities.
In Fig. Figure 2 shows the process of growth of cosmic dust clusters using the addition of monomers. The resulting amorphous cosmic dust particle may be a cluster of atoms with fractal properties. Fractals are called geometric objects: lines, surfaces, spatial bodies that have a highly rugged shape and have the property of self-similarity. Self-similarity means the unchanged basic geometric characteristics fractal object when changing the scale. For example, images of many fractal objects turn out to be very similar when the resolution in a microscope increases. Fractal clusters are highly branched porous structures formed under highly nonequilibrium conditions when solid particles of similar sizes combine into one whole. Under terrestrial conditions, fractal aggregates are obtained when vapor relaxation metals in nonequilibrium conditions, during the formation of gels in solutions, during the coagulation of particles in smoke. The model of a fractal cosmic dust particle is shown in Fig. 3. Note that the processes of coagulation of dust grains occurring in protostellar clouds and gas and dust disks, are significantly enhanced by turbulent motion interstellar matter.
The nuclei of cosmic dust grains, consisting of refractory elements, hundreds of microns in size, are formed in the shells of cold stars during the smooth outflow of gas or during explosive processes. Such dust grain nuclei are resistant to many external influences.
In interstellar and interplanetary space there are small particles of solid bodies - what we call dust in everyday life. We call the accumulation of these particles cosmic dust to distinguish it from dust in the terrestrial sense, although their physical structure is similar. These are particles ranging in size from 0.000001 centimeter to 0.001 centimeter, the chemical composition of which is generally still unknown.
These particles often form clouds, which are detected in different ways. For example, in our planetary system, the presence of cosmic dust was discovered due to the fact that sunlight scattering on it causes a phenomenon that has long been known as “zodiacal light.” We observe the zodiacal light on exceptionally clear nights in the form of a faintly luminous strip stretching in the sky along the Zodiac; it gradually weakens as we move away from the Sun (which is at this time below the horizon). Measurements of the intensity of zodiacal light and studies of its spectrum show that it comes from the scattering of sunlight on particles forming a cloud of cosmic dust surrounding the Sun and reaching the orbit of Mars (the Earth is thus located inside the cloud of cosmic dust).
The presence of clouds of cosmic dust in interstellar space is detected in the same way.
If any cloud of dust finds itself close to a relatively bright star, then the light from this star will be scattered on the cloud. We then detect this cloud of dust in the form of a bright speck called an “irregular nebula” (diffuse nebula).
Sometimes a cloud of cosmic dust becomes visible because it obscures the stars behind it. Then we distinguish it as a relatively dark spot against the background of a celestial space dotted with stars.
The third way to detect cosmic dust is by changing the color of stars. Stars that lie behind a cloud of cosmic dust are generally more intensely red. Cosmic dust, just like terrestrial dust, causes “reddening” of the light that passes through it. We can often observe this phenomenon on Earth. On foggy nights, we see that the lanterns located far away from us are more red in color than the nearby lanterns, the light of which remains practically unchanged. We must, however, make a reservation: only dust consisting of small particles causes discoloration. And it is precisely this kind of dust that is most often found in interstellar and interplanetary spaces. And from the fact that this dust causes a “reddening” of the light of the stars lying behind it, we conclude that the size of its particles is small, about 0.00001 cm.
We don't know exactly where cosmic dust comes from. Most likely, it arises from those gases that are constantly ejected by stars, especially young ones. Gas freezes at low temperatures and turns into a solid - into particles of cosmic dust. And, conversely, part of this dust, finding itself in a relatively high temperature, for example, near some hot star, or during the collision of two clouds of cosmic dust, which, generally speaking, is a common phenomenon in our region of the Universe, turns back into gas.