interstellar gas
interstellar gas is a rarefied gaseous medium that fills all the space between stars. Interstellar gas is transparent. The total mass of interstellar gas in the Galaxy exceeds 10 billion solar masses, or a few percent of the total mass of all the stars in our Galaxy. The average concentration of atoms in interstellar gas is less than 1 atom per cm³. Its main mass is contained near the plane of the Galaxy in a layer several hundred parsecs thick. The average density of the gas is about 10 −21 kg/m³. Chemical composition approximately the same as that of most stars: it consists of hydrogen and helium (90% and 10% by the number of atoms, respectively) with a small admixture of heavier elements. Depending on temperature and density, interstellar gas is in molecular, atomic or ionized states. Cold molecular clouds, rarefied intercloud gas, clouds of ionized hydrogen with a temperature of about 10 thousand K. (Orion Nebula), and vast areas of rarefied and very hot gas with a temperature of about a million K are observed. Ultraviolet rays, unlike visible light rays, are absorbed gas and give it their energy. Due to this, hot stars with their ultraviolet radiation heat the surrounding gas to a temperature of about 10,000 K. The heated gas begins to emit light itself, and we observe it as a bright gaseous nebula. The colder, "invisible" gas is observed by radio astronomical methods. Hydrogen atoms in a rarefied medium emit radio waves at a wavelength of about 21 cm. Therefore, streams of radio waves propagate continuously from regions of interstellar gas. By receiving and analyzing this radiation, scientists learn about the density, temperature and movement of interstellar gas in outer space.
| interstellar medium | ||
|---|---|---|
| Components | interstellar gas Interstellar dust Interstellar cloud Cosmic rays Magnetic field |  |
| Nebulae | Diffuse (light) nebula Dark nebula Emission nebula Reflection nebula Supernova remnant Planetary nebula Protoplanetary nebula | |
| Regions of star formation | Molecular cloud Globule Region H II | |
| Circumstellar formations | Accretion disk Protoplanetary disk Polar jet streams Herbig-Haro object | |
| Radiation | Stellar wind CMB | |
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See what "Interstellar gas" is in other dictionaries:
Main component of the interstellar medium, constituting approx. 99% of its weight. M. g. fills almost the entire volume of galaxies. Naib, studied M. g. in the Galaxy. M. is characterized by a wide variety of structures arising in it, physical. conditions and flowing ... ... Physical Encyclopedia
One of the main components of the interstellar medium (See Interstellar medium). Consists mainly of hydrogen and helium; the total mass of other elements is less than 3% ...
Matter that fills the space between stars within galaxies. Matter in the space between galaxies called. intergalactic medium (see Clusters of galaxies. Intergalactic gas). Gas in shells around stars (circumstellar shells) often ... ... Physical Encyclopedia
Interstellar dust is solid microscopic particles that, along with interstellar gas, fill the space between stars. It is currently believed that dust particles have a refractory core surrounded by organic matter or an ice shell. ... ... Wikipedia
Map of the local interstellar cloud The interstellar medium (ISM) is the substance and fields that fill the interstellar space inside galaxies ... Wikipedia
Rarefied matter, interstellar gas and tiny dust particles that fill the space between stars in our and other Galaxies. In structure M. page. include, in addition, cosmic rays, interstellar magnetic fields (See Interstellar ... ... Great Soviet Encyclopedia
Map of the local interstellar cloud The interstellar medium (ISM) is the matter and fields that fill the interstellar space inside galaxies. Composition: interstellar gas, dust (1% of the mass of gas), interstellar magnetic fields, cosmic rays, and also ... ... Wikipedia
Over 200 newly formed stars inside a cloud known as NGC 604 in the Triangulum Galaxy. Stars irradiate gas with high energy ... Wikipedia
Map of interstellar gas in our Galaxy Interstellar gas is a rarefied gaseous medium that fills all the space between stars. Interstellar gas is transparent. The total mass of interstellar gas in the Galaxy exceeds 10 billion solar masses or ... ... Wikipedia
Stellar wind is the process of outflow of matter from stars into interstellar space. Contents 1 Definition 2 Energy sources ... Wikipedia
Even from the above overview one can see how complex the structure of the interstellar medium is. Let's list the components of which it should consist.
Compact regions with Te These characteristics are possessed by clouds, which are studied by their molecular radio lines. They are characterized wide range densities, many of them are associated with regions of recent star formation. In table. 17.2, borrowed from the review, shows the values of the densities, sizes, degree of ionization, and root-mean-square velocity dispersions characteristic of these regions.
Diffuse neutral hydrogen. Most of what is shown in Fig. 17.1 Neutral hydrogen is diffuse, i.e. it does not enter clouds. It is clear that the density varies from point to point, but on average a value can be used with a reasonable degree of accuracy. Some of this gas may be hot, but, of course, non-ionized.
ionized gas. The regions, which are one of the most interesting astronomical objects in the Galaxy, are directly associated with young, bright, hot stars of spectral classes, and certainly not typical of the interstellar medium. Many of the methods described above are used to comprehensive study these objects. As an example, in fig. 17.3 shows the results of observations of the source in different ranges. In general, it is a source of diffuse thermal bremsstrahlung. At higher resolution, isolated areas are visible, some of them have a shell structure, which means that they arose as a result of a recent outbreak.
(click to view scan)
(see scan)
star formation. Even more compact are the areas associated with powerful infrared sources. Finally, smallest dimensions have sources of maser radiation on molecules and The corresponding physical parameters are shown in Figs. 17.3.
There is also an ionized component of diffuse interstellar gas. Its density is best determined from the measures of pulsar dispersion. The values found in this way have a large scatter, which is not surprising, since physical conditions in the interstellar medium vary widely. A reasonable average value for the density of interstellar gas is
Hot phase Te Observations of highly ionized elements, for example, show that a much hotter phase must be present in the interstellar gas. It is noteworthy that its temperature does not differ much from the temperatures of old supernova remnants. As can be shown, a significant portion of the interstellar gas is constantly heated by shock waves arising at the boundaries of old supernova remnants. This provides a rather attractive explanation for the hot phase.
It is clear that the structure of the interstellar medium is very complex. However, it is useful to have a simple model for calculations. The regions are concentrated near the plane of the Galaxy. The half-thickness of the layer of neutral hydrogen (i.e., the distance between the half-density levels) is approximately On the other hand, judging by the rotation measures, bremsstrahlung at low frequencies, and the measures of pulsar dispersion, the half-thickness of the layer is much larger, about The accuracy of these values is low, but they give correct in order of magnitude representation of the distribution of various components of the gaseous disk of the Galaxy. These values refer to the vicinity of the Sun. Closer to the center of the Galaxy, the situation changes significantly, and within a radius from the center, most of the hydrogen is in the molecular state.
Finally, we did not even try to understand the mechanisms of heating and ionization of interstellar gas. Many of them are detailed. Among them: heating and ionization by cosmic rays, i.e., ionization losses, which were discussed in detail in Chap. 2; heating during cloud collisions; heating with hard ultraviolet and soft x-rays; heating during supernova explosions. By virtue of great variety structures in the interstellar medium, it would be surprising if for each of the listed mechanisms there would not be a point in the Galaxy where it prevails.
The mechanism of supernova heating provides an attractive explanation for the existence of a very hot phase c. The original paper by Cox and Smith suggested that further heating could come from collisions of old supernova remnants. According to these authors, the intersection of old shells and their heating during collisions lead to the formation of a network of hot gas penetrating the disk of the Galaxy.
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MUNICIPAL BUDGET GENERAL EDUCATIONAL INSTITUTION LYCEUM №11 OF THE CITY OF CHELYABINSK
abstract
nbut the topic:
"Gas and dust complexes. interstellar medium»
Performed:
11th grade student
Kiseleva Polina Olegovna
Checked:
Lykasova Alevtina Pavlovna
Chelyabinsk 2015
OHEAD
Introduction
1. History of ISM research
2. Main components of the ISM
2.1 Interstellar gas
2.2 Interstellar dust
2.3 Interstellar cloud
2.4 Cosmic rays
2.5 Interstellar magnetic field
3. Physical features of the ISM
4. Nebulae
4.1 Diffuse (bright) nebula
4.2 Dark Nebula
5. Radiation
6. Evolution of the interstellar medium
Conclusion
List of sources
INTRODUCTION
The universe, at its core, is almost empty space. It was only comparatively recently that it was possible to prove that stars do not exist in absolute emptiness and that outer space is not completely transparent. Stars occupy only a small part of the vast universe. The matter and fields that fill the interstellar space inside galaxies are called the interstellar medium (ISM). The nature of the interstellar medium has attracted the attention of astronomers and scientists for centuries. The term "interstellar medium" was first used by F. Bacon in 1626.
1. HISTORY OF RESEARCHMZS
Back in the middle of the 19th century. Russian astronomer V. Struve was trying scientific methods to find indisputable evidence that space is not empty, and light from distant stars is being absorbed in it, but to no avail. interstellar medium cloud gas
Later German astrophysicist F. Hartman conducted a study of the spectrum of Delta Orion and studied the orbital motion of the companions of the Delta Orion system and the light coming from the star. Realizing that some of the light is absorbed on its way to Earth, Hartmann wrote that "the absorption line of calcium is very weak", and also that "it turned out to be somewhat surprising that the calcium lines at a wavelength of 393.4 nanometers do not move in a periodic divergence of lines spectrum, which is present in the spectroscopic double stars Oh". The stationary nature of these lines allowed Hartmann to suggest that the gas responsible for the absorption is not present in the atmosphere of Delta Orion, but, on the contrary, is located outside the star and is located between the star and the observer. This study was the beginning of the study of the interstellar medium.
Intensive studies of interstellar matter have made it possible W. Pickering in 1912 to state that "the interstellar absorbing medium, which, as shown Captain, absorbs only at some wavelengths, may indicate the presence of gas and gaseous molecules that are ejected by the Sun and stars.
In the same year 1912 AT.Hess discovered cosmic rays, energetic charged particles that bombard the Earth from space. This allowed some researchers to state that they also fill the interstellar medium.
After Hartmann's research, in 1919, Eger while studying absorption lines at wavelengths of 589.0 and 589.6 nanometers in the Delta Orion and Beta Scorpio systems, he discovered sodium in the interstellar medium.
The presence of an absorbing rarefied medium was convincingly shown less than a hundred years ago, in the first half of the 20th century, by comparing the observed properties of distant star clusters at different distances from us. It was done independently by an American astronomer Robert Trumpler(1896-1956) and Soviet astronomer B.A.Vorontsov-Velyaminov(1904-1994). Rather, this is how one of the components of the interstellar medium was discovered - fine dust, due to which the interstellar medium is not completely transparent, especially in directions close to the direction to Milky Way. The presence of dust meant that both the apparent brightness and the observed color of distant stars were distorted, and in order to recognize them true values, we need a rather complex absorption accounting. Dust, thus, was perceived by astronomers as an unfortunate hindrance, interfering with the study of distant objects. But at the same time, interest arose in the study of dust as a physical medium - scientists began to find out how dust grains arise and collapse, how dust reacts to radiation, and what role dust plays in the formation of stars.
With the development of radio astronomy in the second half of the 20th century. it became possible to study the interstellar medium by its radio emission. As a result of purposeful searches, radiation of neutral hydrogen atoms was discovered in interstellar space at a frequency of 1420 MHz (which corresponds to a wavelength of 21 cm). Radiation at this frequency (or, as they say, in the radio line) was predicted by the Dutch astronomer Hendrik van de Hulst in 1944 on the basis quantum mechanics, and it was discovered in 1951 after the calculation of its expected intensity by a Soviet astrophysicist I.S. Shklovsky. Shklovsky also pointed out the possibility of observing radiation various molecules in the radio range, which, indeed, was later discovered. The mass of interstellar gas, consisting of neutral atoms and very cold molecular gas, turned out to be about a hundred times larger than the mass of rarefied dust. But the gas is completely transparent to visible light, so it could not be detected by the same methods that dust was discovered.
With the advent of X-ray telescopes mounted on space observatories, another, the hottest component of the interstellar medium, was discovered - a very rarefied gas with a temperature of millions and tens of millions of degrees. It is impossible to “see” this gas either by optical observations or by observations in radio lines - the medium is too rarefied and completely ionized, but, nevertheless, it fills a significant fraction of the volume of our entire Galaxy.
The rapid development of astrophysics, which studies the interaction of matter and radiation in outer space, as well as the emergence of new observational possibilities, made it possible to study in detail physical processes in the interstellar environment. Whole scientific directions - space gas dynamics and space electrodynamics who study the properties of rarefied space media. Astronomers have learned to determine the distance to gas clouds, to measure the temperature, density and pressure of the gas, its chemical composition, to estimate the speed of movement of matter. In the second half of the 20th century revealed a complex picture of the spatial distribution of the interstellar medium and its interaction with stars. It turned out that the possibility of the birth of stars depends on the density and amount of interstellar gas and dust, and the stars (first of all, the most massive of them), in turn, change the properties of the surrounding interstellar medium - they heat it, support the constant movement of gas, replenish the medium with their substance change its chemical composition.
2. MAIN COMPONENTS OF MLT
The interstellar medium includes interstellar gas, dust (1% of the gas mass), interstellar magnetic fields, interstellar cloud, cosmic rays, and dark matter. The chemical composition of the interstellar medium is a product of primary nucleosynthesis and nuclear fusion in stars.
2 .1 Interstellar gas
Interstellar gas is a rarefied gaseous medium that fills all the space between stars. Interstellar gas is transparent. The total mass of interstellar gas in the Galaxy exceeds 10 billion solar masses, or a few percent of the total mass of all the stars in our Galaxy. The average concentration of interstellar gas atoms is less than 1 atom per cm3. The average density of the gas is about 10–21 kg/m3. The chemical composition is about the same as that of most stars: it consists of hydrogen and helium with a small admixture of heavier elements. Depending on temperature and density, interstellar gas is in molecular, atomic or ionized states. Ultraviolet rays, unlike visible light rays, are absorbed by the gas and give it their energy. Due to this, hot stars with their ultraviolet radiation heat the surrounding gas to a temperature of about 10,000 K. The heated gas begins to emit light itself, and we observe it as a bright gaseous nebula. The colder, "invisible" gas is observed by radio astronomical methods. Hydrogen atoms in a rarefied medium emit radio waves at a wavelength of about 21 cm. Therefore, streams of radio waves propagate continuously from regions of interstellar gas. By receiving and analyzing this radiation, scientists learn about the density, temperature and movement of interstellar gas in outer space.
2 .2 Interstellar dust
Interstellar dust is solid microscopic particles that, along with interstellar gas, fill the space between stars. It is currently believed that dust particles have a refractory core surrounded by organic matter or an ice shell. The chemical composition of the nucleus is determined by the atmosphere in which stars they condensed. For example, in the case of carbon stars, they will be composed of graphite and silicon carbide.
The typical particle size of interstellar dust is from 0.01 to 0.2 microns, the total mass of dust is about 1% of the total mass of gas. Starlight heats interstellar dust up to several tens of K, due to which interstellar dust is a source of long-wave infrared radiation.
Dust also affects the chemical processes taking place in the interstellar medium: dust granules contain heavy elements that are used as a catalyst in various chemical processes. Dust granules are also involved in the formation of hydrogen molecules, which increases the rate of star formation in metal-poor clouds.
2 .3 interstellar cloud
The interstellar cloud is the general name for accumulations of gas, plasma and dust in our and other galaxies. In other words, the interstellar cloud has more high density, how average density interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it can be neutral, ionized (that is, in the form of plasma) or molecular. Neutral and ionized clouds are sometimes called diffuse clouds, while molecular clouds are called dense clouds.
Analysis of the composition of interstellar clouds is carried out by studying their electromagnetic radiation using large radio telescopes. By examining the emission spectrum of an interstellar cloud and comparing it with the spectrum of specific chemical elements, one can determine the chemical composition of the cloud.
Usually about 70% of the mass of an interstellar cloud is hydrogen, the rest is mainly helium. Clouds also contain traces of heavy elements: metals such as calcium, neutral or in the form of Ca+ (90%) and Ca++ (9%) cations, and inorganic compounds such as water, carbon monoxide, hydrogen sulfide, ammonia and hydrogen cyanide.
2 .4 Cosmic rays
Cosmic rays are elementary particles and atomic nuclei moving with high energies in outer space. Explosions are their main (but not the only) source. supernovae.
Extragalactic and galactic rays are usually called primary. It is customary to call secondary flows of particles passing and transforming in the Earth's atmosphere.
Cosmic rays are a component of natural radiation (background radiation) on the Earth's surface and in the atmosphere.
The chemical spectrum of cosmic rays in terms of energy per nucleon consists of more than 94% of protons, another 4% of helium nuclei (alpha particles). There are also nuclei of other elements, but their share is much smaller.
By particle number, cosmic rays are 90 percent protons, 7 percent helium nuclei, about 1 percent heavier elements, and about 1 percent electrons.
2 .5 Interstellar magnetic field
The particles move in the weak magnetic field of interstellar space, the induction of which is about a hundred thousand times less than that of the Earth's magnetic field. The interstellar magnetic field, acting on charged particles with a force that depends on their energy, "confuses" the trajectories of particles, and they continuously change the direction of their movement in the Galaxy. Charged particles flying in the interstellar magnetic field deviate from straight trajectories under the influence of the Lorentz force. Their trajectories seem to "wind" on the lines of magnetic induction.
3. PHYSICAL FEATURES OF THE ISM
· Lack of local thermodynamic equilibrium(LTR)- with the state of a system in which the macroscopic quantities of this system (temperature, pressure, volume, entropy) remain unchanged in time under conditions of isolation from the environment.
· Thermal instability
Condition thermal equilibrium may not be performed at all. There is a magnetic field that resists compression unless it occurs along field lines. Secondly, the interstellar medium is in constant motion and its local properties are constantly changing, new sources of energy appear in it and old ones disappear. Thirdly, in addition to thermodynamic instability, there are gravitational and magnetohydrodynamic ones. And this is without taking into account any kind of cataclysms in the form of supernova explosions, tidal influences passing in the neighborhood of galaxies, or the passage of the gas itself through the spiral branches of the Galaxy.
· Forbidden lines and 21cm line
A distinctive feature of an optically thin medium is radiation in forbidden lines. Forbidden lines are called lines that are forbidden by the selection rules, that is, they come from metastable levels (quasi-stable equilibrium). characteristic time the life of an electron at this level is from s to several days. At high concentrations of particles, their collision removes the excitation and the lines are not observed due to extreme weakness. At and low densities, the line intensity does not depend on the transition probability, since the low probability is compensated by a large number of atoms in the metastable state. If there is no LTE, then the population energy levels should be calculated from the balance of elementary processes of excitation and deactivation.
The most important forbidden line of the ISM is radio link atomic hydrogen 21 cm. This line arises during the transition between sublevels of the hyperfine structure of the hydrogen level, associated with the presence of spin in the electron and proton. The probability of this transition (that is, 1 time in 11 million years).
Studies of the 21 cm radio line made it possible to establish that neutral hydrogen in the galaxy is mainly contained in a very thin, 400 pc thick, layer near the plane of the Galaxy.
· Frozenness of the magnetic field.
Frozenness of the magnetic field means the preservation of the magnetic flux through any closed conducting circuit when it is deformed. Under laboratory conditions, the magnetic flux can be considered conserved in media with high electrical conductivity. In the limit of infinite electrical conductivity, an infinitely small electric field would cause the current to increase to an infinite value. Therefore, an ideal conductor should not cross magnetic lines of force, and thus excite the electric field, but on the contrary, it should drag the lines of the magnetic field with it, the magnetic field turns out to be, as it were, frozen into the conductor.
Real space plasma is far from ideal, and freezing-in should be understood in the sense that it requires very big time to change the flow through the loop. In practice, this means that we can consider the field to be constant while the cloud contracts, rotates, etc.
4. Nebulae
Nebula- a section of the interstellar medium, distinguished by its radiation or absorption of radiation on general background sky. Nebulae are made up of dust, gas, and plasma.
The primary feature used in the classification of nebulae is absorption, or emission or scattering of light by them, that is, according to this criterion, nebulae are divided into dark and light.
The division of nebulae into gaseous and dusty ones is largely arbitrary: all nebulae contain both dust and gas. This division is historically different ways observations and emission mechanisms: the presence of dust is most clearly observed when dark nebulae absorb radiation from sources located behind them and when reflection or scattering, or re-emission, contained in the dust of radiation from stars located nearby or in the nebula itself; The intrinsic radiation of the gaseous component of a nebula is observed when it is ionized by ultraviolet radiation from a hot star located in the nebula (H II emission regions of ionized hydrogen around stellar associations or planetary nebulae) or when the interstellar medium is heated shock wave due to a supernova explosion or the impact of a powerful stellar wind of Wolf-Rayet stars.
4 .1 Diffuse(light)nebula
Diffuse (light) nebula -- In astronomy, a general term used to refer to light-emitting nebulae. The three types of diffuse nebulae are the reflection nebula, the emission nebula (of which the protoplanetary, planetary, and H II regions are varieties), and the supernova remnant.
· reflection nebula
Reflection nebulae are clouds of gas and dust illuminated by stars. If the star(s) is in or near an interstellar cloud, but is not hot enough (hot) to ionize a significant amount of interstellar hydrogen around it, then the main source optical radiation The nebula is stellar light scattered by interstellar dust.
The spectrum of the reflection nebula is the same as that of the star that illuminates it. Among the microscopic particles responsible for light scattering are particles of carbon (sometimes called diamond dust), as well as particles of iron and nickel. The last two interact with the galactic magnetic field, and therefore the reflected light is slightly polarized.
Reflection nebulae usually have a blue tint because scattering blue color more effective than red (this, in particular, explains the blue color of the sky).
Currently, about 500 reflection nebulae are known, the most famous of which is around the Pleiades (star cluster). giant red ( spectral type M1) the star Antares is surrounded by a large red reflection nebula. Reflection nebulae are also often found at star-forming sites.
In 1922, Hubble published the results of studies of some bright nebulae. In this work, Hubble derived the luminosity law for a reflection nebula, which establishes the relationship between the angular size of the nebula ( R) and apparent magnitude illuminating star ( m):
where is a constant depending on the sensitivity of the measurement.
· emission nebula
An emission nebula is a cloud of ionized gas (plasma) emitting in the visible color range of the spectrum. Ionization occurs due to high-energy photons emitted by the nearest hot star. There are several types of emission nebulae. Among them are the H II regions, in which the formation of new stars occurs, and the sources of ionizing photons are young, massive stars, as well as planetary nebulae, in which the dying star has discarded its upper layers, and the exposed hot core ionizes them.
Planetmrye fogmness -- astronomical object, consisting of an ionized gas envelope and a central star, white dwarf. Planetary nebulae are formed when the outer layers (shells) of red giants and supergiants with a mass of 2.5–8 solar masses are ejected at the final stage of their evolution. A planetary nebula is a fast-moving (by astronomical standards) phenomenon lasting only a few tens of thousands of years, while the lifespan of the ancestor star is several billion years. Currently, about 1500 planetary nebulae are known in our galaxy.
The process of formation of planetary nebulae, along with supernova explosions, plays important role in the chemical evolution of galaxies, throwing into interstellar space material enriched with heavy elements - products of stellar nucleosynthesis (in astronomy, all elements are considered heavy, with the exception of products of primary nucleosynthesis big bang-- hydrogen and helium, such as carbon, nitrogen, oxygen and calcium).
AT last years With the help of images taken by the Hubble Space Telescope, it was possible to find out that many planetary nebulae have a very complex and peculiar structure. Despite the fact that about a fifth of them have a circumspherical shape, most do not have any kind of spherical symmetry. The mechanisms by which the formation of such a variety of forms is possible remain to date not fully elucidated. It is believed that big role this can be played by the interaction of the stellar wind and binary stars, the magnetic field and the interstellar medium.
Planetary nebulae are mostly dim objects and are generally not visible to the naked eye. The first planetary nebula to be discovered was nebula dumbbell in the constellation Vulpecula.
The unusual nature of planetary nebulae was discovered in the middle of the 19th century, with the beginning of the use of the spectroscopy method in observations. William Huggins became the first astronomer to obtain the spectra of planetary nebulae - objects that stood out for their unusualness. When Huggins studied the spectra of nebulae NGC 6543 (cat's eye) , M27 (Dumbbell), M57 (ring nebula in Lyra) and a number of others, it turned out that their spectrum is extremely different from the spectra of stars: all the spectra of stars obtained by that time were absorption spectra (continuous spectrum with large quantity dark lines), while the spectra of planetary nebulae turned out to be emission spectra with a small number of emission lines, which indicated their nature, which is fundamentally different from the nature of stars.
Planetary nebulae represent the final stage of evolution for many stars. Typical planetary nebula has an average length of one light year and consists of highly rarefied gas with a density of about 1000 particles per cm3, which is negligible in comparison, for example, with the density of the Earth's atmosphere, but approximately 10-100 times greater than the density of interplanetary space at a distance of the orbit Earth from the Sun. Young planetary nebulae have highest density, sometimes reaching 10 6 particles per cm³. As nebulae age, their expansion leads to a decrease in density. Most planetary nebulae are symmetrical and almost spherical in appearance, which does not prevent them from having many very complex shapes. Approximately 10% of planetary nebulae are practically bipolar, and only a small number are asymmetric. Even a rectangular planetary nebula is known.
protoplanetary nebula is an astronomical object that does not exist for long between the time a medium-mass star (1-8 solar masses) has left the asymptotic giant branch (AGB) and the subsequent planetary nebula (PT) phase. The protoplanetary nebula shines primarily in the infrared and is a subtype of reflection nebula.
RegionHII is a cloud of hot gas and plasma, reaching several hundred light-years across, which is an area of active star formation. Young hot bluish-white stars are born in this region, which emit abundant ultraviolet light, thereby ionizing the surrounding nebula.
H II regions can give birth to thousands of stars over a period of just a few million years. Eventually, supernova explosions and powerful stellar winds from the most massive stars in the resulting star cluster scatter the region's gases, and it turns into a Pleiades-like group.
These regions got their name because of the large amount of ionized atomic hydrogen, referred to by astronomers as H II (the H I region is the zone of neutral hydrogen, and H 2 denotes molecular hydrogen). They can be seen at considerable distances throughout the universe, and the study of such regions located in other galaxies is important for determining the distance to the latter, as well as their chemical composition.
Examples are carina nebula, nebula Tarantula,NGC 604 , Trapeze of Orion, Barnard's loop.
· supernova remnant
supernova remnant(English) S uperN ova R emnant, SNR ) is a gas and dust formation, the result of a catastrophic explosion of a star that occurred many tens or hundreds of years ago and its transformation into a supernova. During the explosion, the supernova shell scatters in all directions, forming a shock wave expanding at a tremendous speed, which forms supernova remnant. The rest consists of stellar material ejected by the explosion and interstellar matter absorbed by the shock wave.
Probably the most beautiful and best studied young remnant formed by a supernova SN 1987 A in the Large Magellanic Cloud that erupted in 1987. Other well-known supernova remnants are crab nebula , remnant of a relatively recent explosion (1054), supernova remnant Quiet (SN 1572) , named after Tycho Brahe, who observed and recorded its initial brightness immediately after the outbreak in 1572, as well as the remainder Kepler's supernova (SN 1604) named after Johannes Kepler.
4 .2 Dark Nebula
A dark nebula is a type of interstellar cloud so dense that it absorbs visible light, emanating from emission or reflection nebulae (such as , Horsehead Nebula) or stars (for example, Coal Sack Nebula) behind it.
Light is absorbed by interstellar dust particles located in the coldest and densest parts of molecular clouds. Clusters and large complexes of dark nebulae are associated with giant molecular clouds (GMOs). Isolated dark nebulae are most often Bok globules.
Such clouds have a very irregular shape: they do not have clearly defined boundaries, sometimes they take on swirling snake-like images. The largest dark nebulae are visible to the naked eye, appearing as patches of black against the bright Milky Way.
In the inner parts of dark nebulae, active processes often take place: for example, the birth of stars or maser radiation.
5. RADIATION
Stellar wind- the process of outflow of matter from stars into interstellar space.
The substance of which stars are composed, under certain conditions, can overcome their attraction and be ejected into interstellar space. This happens if a particle in the atmosphere of a star accelerates to a speed exceeding the second cosmic speed for this star. In fact, the speeds of the particles that make up the stellar wind are hundreds of kilometers per second.
The stellar wind can contain both charged particles and neutral ones.
Stellar wind is a constantly occurring process that leads to a decrease in the mass of a star. Quantitatively, this process can be characterized as the amount (mass) of matter that the star loses per unit time.
The stellar wind can play an important role in stellar evolution: since this process results in a decrease in the mass of a star, the lifespan of a star depends on its intensity.
The stellar wind is a way of transporting matter over considerable distances in space. In addition to the fact that it itself consists of matter flowing from stars, it can act on the surrounding interstellar matter, transferring to it part of its kinetic energy. Thus, the shape of the emission nebula NGC 7635 "Bubble" was formed as a result of such an impact.
In the case of the outflow of matter from several closely spaced stars, supplemented by the influence of the radiation of these stars, condensation of interstellar matter is possible with subsequent star formation.
With an active stellar wind, the amount of ejected matter may be sufficient to form a planetary nebula.
6. EVOLUTION OF THE INTERSTELLAR MEDIUM
The evolution of the interstellar medium, or to be more precise, the interstellar gas, is closely related to the chemical evolution of the entire Galaxy. It would seem that everything is simple: stars absorb gas, and then throw it back, enriching it with nuclear combustion products - heavy elements - thus the metallicity should gradually increase.
The Big Bang theory predicts that hydrogen, helium, deuterium, lithium, and other light nuclei were formed during primordial nucleosynthesis, which are still splitting on the Hayashi track or the protostar stage. In other words, we should observe long-lived G-dwarfs with zero metallicity. But none of these have been found in the Galaxy; moreover, most of them have an almost solar metallicity. According to indirect data, it can be judged that something similar exists in other galaxies. On the this moment The question remains open and awaits a decision.
There was also no dust in the primordial interstellar gas. It is now believed that dust grains are formed on the surface of old cold stars and leave it together with the outflowing matter.
CONCLUSION
The study of such complex system as "stars - interstellar medium" turned out to be a very difficult astrophysical problem, especially considering that the total mass of the interstellar medium in the Galaxy and its chemical composition slowly change under the influence of various factors. Therefore, we can say that the entire history of our planet is reflected in the interstellar medium. star system lasting billions of years.
LIST OF SOURCES
1) Materials taken from www.wikipedia.org
2) Materials taken from the site www.krugosvet.ru
3) Materials taken from www.bse.sci-lib.com
4) Materials taken from the site www.dic.academic.ru
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Nebula as a section of the interstellar medium, distinguished by its radiation or absorption of radiation against the general background of the sky, its varieties and forms: emission, supernova remnants. The history of the emergence and development of some nebulae: Eagle, Hourglass.
presentation, added 10/11/2012
Dust, gas and plasma as the main components of the nebula. Classification of nebulae, characteristics of their main types. Features of the structure of diffuse, reflection, emission, dark and planetary nebulae. Formation of a supernova remnant.
presentation, added 12/20/2015
Description of the phenomena of the nebula and solar activity. The study of galactic, solar and cosmic rays, methods of their registration. Properties of the interstellar magnetic field. Features of the spatial distribution of galaxies. Ideas about the expansion of the universe.
summary, added 01/06/2012
The stellar core is the central, compact region of the Galaxy. Basic elements of the structure of the Galaxy. Open and globular type of clusters. Characteristics of interstellar gas. General concept of light gaseous nebulae. Planetary, dark nebulae.
presentation, added 09/28/2011
Cosmogony as a science that studies the origin and development of celestial bodies. The essence of the Jeans hypothesis. Nebula, the birth of the Sun. The main stages of the process of transformation of nebula particles into planets: particle adhesion; warming up; volcanic activity.
abstract, added 06/20/2011
spacecraft research of natural resources of the Earth and control of the environment of the Resurs-F series. Main technical characteristics of spacecraft Resurs-F1 and photographic equipment. Spacecrafts of space medicine and biology spacecraft Bion, materials science Foton.
abstract, added 08/06/2010
Stellar evolution - changes of a star during its life. Thermonuclear fusion and the birth of stars; planetary nebula, protostars. Characteristics of young stars, their maturity, later years, death. neutron stars(pulsars), white dwarfs, black holes.
presentation, added 05/10/2012
Stages of formation solar system. The composition of the medium of the protoplanetary disk of the Sun, the study of its evolution using a numerical two-dimensional gas-dynamic model, which corresponds to the axisymmetric movement of the gaseous medium in a gravitational field.
term paper, added 05/29/2012
Characteristics of the stars. Stars in outer space. A star is a plasma ball. Dynamics of stellar processes. Solar system. Interstellar medium. The concept of stellar evolution. The process of star formation. Star as a dynamic self-regulating system.
abstract, added 10/17/2008
The eighth planet from the Sun. Some parameters of the planet Neptune. Chemical composition, physical conditions, structure, atmosphere. Temperature surface areas. Satellites of Neptune, their sizes, characteristics, history of discoveries. Rings of Neptune, magnetic field.
Component approx. 99% of its mass and approx. 2% of the mass of the Galaxy. Mg is very evenly mixed with interstellar dust, which often makes gas-dust structures observable by its absorption or scattering of light (see ). The range of change of the main. The parameters describing M. g. are very wide. The temperature of M. g. fluctuates from 4-6 K to 10 6 K (in interstellar ionic temperature M. g. sometimes exceeds 10 9 K), the concentration varies from 10 -3 -10 -4 to 10 8 -10 12 particles in 1 cm 3. Mg radiation is characterized by a wide range, from long radio waves to hard gamma radiation.
There are areas where M. g. is predominantly in a molecular state (molecular clouds) - these are the densest and coldest parts of M. g.; there are areas where M. g. consists of Ch. arr. from neutral hydrogen atoms (HI regions), these are less dense and, on average, warmer regions; there are areas of ionized hydrogen (HII zones), to-rymi yavl. bright emission nebulae around hot stars, and areas of rarefied hot gas (coronal gas). Mg, like the substance of stars, consists of Ch. arr. from hydrogen and helium with a small addition of other chem. elements (see). On average, in M., hydrogen atoms make up approx. 90% of the number of all atoms (70% by weight). Helium atoms account for approx. 10% of the number of atoms (approx. 28% by mass). The remaining 2% of the mass are all subsequent chem. elements (the so-called heavy elements). Of these, O, C, N, Ne, S, Ar, and Fe are the most abundant. All of them together amount to approx. 1/1000 of the number of atoms of M. g. However, their role in the processes occurring in M. g. is very large. In comparison with the composition of the Sun, a deficit of a number of heavy elements is observed in Mg, especially Al, Ca, Ti, Fe, Ni, which are tens and hundreds of times less than on the Sun. In different parts of the M. city of the Galaxy, the magnitude of the deficit is not the same. The occurrence of a deficit is related to what it means. some of these elements are included in the composition of dust grains and are almost absent in the gaseous phase.Outside the galaxy disk M. g. very little. In the main part of the Galactic halo, the gas is apparently hot (~ 10 o K) and very rarefied (at a height of 5 kpc above the symmetry plane of the disk). The most noticeable are the densest gaseous formations of the halo - . Apparently not a large number of gas is available in some, the most dense,. In addition, in high galaxies. latitudes discovered hydrogen.
3. Methods for observing interstellar gas
The strong rarefaction of M. and a wide range of temperatures, at which it can be located, determine the variety of methods for its study.
The most accessible for observation are gaseous and gaseous-dust light nebulae. By optical and in lesser degree The infrared emission spectra of the emission nebulae succeeded in establishing the density, temperature, composition, and state of ionization of the matter in the H II zones. Rich information about magnetism in emission nebulae is obtained from hydrogen, helium, and other elements, as well as from continuous radio emission.
The state of magnetism outside nebulae is studied using interstellar optical data. and UV absorption lines in the spectra of stars. Based on them, it was possible to establish that the magnetic field consists of separate clouds, and the matter in them is predominantly in a neutral atomic state. According to the absorption lines in the optical. range were discovered (1938) the first. The absorption lines of most atoms, ions, and molecules lie in the UV region of the spectrum (Fig. 3). Their observations carried out on satellites made it possible to study the abundance of elements and ionization. the state of M. g. and to detect in it a deficiency of a number of heavy elements. The absorption lines of NV (1238 and 1242 ) and OVI (1032 and 1038 ) ions revealed corridors of hot gas. They study the large-scale and fine structure of HI regions in the Galaxy and other galaxies, the density and temperature of interstellar clouds, their structure, movement, and rotation around the centers of galaxies.It is more difficult to study the H2 distribution. For this, they most often use indirect method: investigate the spatial distribution of the CO molecule, the concentration of which is proportional to the concentration of H 2 molecules (H 2 molecules are approximately 10 5 times larger than CO). The radio emission of a CO molecule with = 2.6 mm is practically not absorbed by interstellar dust and makes it possible to study the distribution of CO and H 2 molecules, as well as to study the conditions in the coldest and densest part of the astronomical city - in molecular clouds and gas-dust complexes. H 2 molecules are directly observed only in absorption bands lying in the far UV region of the spectrum ( 1108 ), and in several. cases by IR emission lines (= 2 µm and 4 µm). However, due to interstellar absorption of light by dust, this method does not allow one to study H 2 in dense opaque molecular clouds, where these molecules are mainly concentrated. Separate, densest condensations of molecular gas located near strong sources of excitation (for example, IR stars) are observed in the form of powerful cosmic masers (see ).
High spectrum. the resolution achieved in the radio range makes it possible to study molecules containing various isotopes of atoms, for example. 1 H and 2 D (deuterium), 12 C and 13 C, 14 N and 15 N, 16 O, 17 O, 18 O, etc., i.e. the isotopic composition of M. g. and its variations. Comparison of the isotopic composition of modern. Mg with the isotopic composition of the solar system, formed from the interstellar medium approx. years ago, makes it possible to judge changes in the isotopic composition associated with the evolution of M. g.
By absorption of roentgen. rays in interstellar space, one can judge the total amount of interstellar matter located in the atomic and molecular form, as well as in the form of dust particles. In the future, from the fluorescence of atoms in the X-ray lines of various elements (see), it will be possible to obtain fairly complete information on the abundance of elements in interstellar matter no matter what state it is in. The hottest parts of the magnetic field (supernova remnants and hot gas corridors) radiate in x-rays. range, which allows methods to study their spatial arrangement and physical. sv.
The interstellar medium also radiates in -rays. Energetic -photons (with an energy of 50 MeV) arise in M. g. due to the fact that when protons collide with protons of M. g., - are formed, which decay into 2 -photons. The contribution of 50% gives relativistic electrons cosmic. rays in collisions with the nuclei of atoms M. In addition, during the interaction of particles of space. low-energy rays with atomic nuclei M. g. and dust - lines appear in the range of 1-6 MeV. A strong line, with a photon energy of 0.511 MeV, can be formed during the annihilation of positrons arising from the interaction of space. rays with M. g.
The state of the gas in the immediate the vicinity of the solar system is established by the parameters , determined relative to the interstellar medium.
Observations of scintillations of the radio emission of pulsars at small inhomogeneities of the interstellar plasma turned out to be another subtle method for studying magmatics (see ). With its help, it was possible to establish that the concentration of electrons that in M. g. fluctuates weakly. The average value along the line of sight (here - the deviation of the electron concentration from the average value along the line of sight). The sizes of inhomogeneities can be different, but when observing pulsars, the main. contribution to the scintillation comes from inhomogeneities ~ 10 10 -10 13 cm in size, apparently generated by .
4. Processes that form the state of interstellar gas
Thermal and ionization states of M. g.The sparseness of M. leads to the fact that it is transparent to most types of radiation. Therefore, the conditions in it are very far from. However, the distribution of energy between the particles of M. g. in most cases (with the exception of the main arr.
To determine the equilibrium St. in MG (the degree of ionization, radiation intensity, etc.), the balance of the processes of excitation of ions, atoms, and molecules (collisions, absorption of radiation, etc.) and the processes of removal of excitation (recombinations, emission of photons) occurring in k.-l. allocated volume in a finite time interval.
The zones of HII Mg are heated by the UV radiation of the stars located inside them (hydrogen atoms actively absorb radiation from ). HI regions and molecular clouds are heated by penetrating radiation: cosmic particles. low energy rays (~ 1-10 MeV/nucleon), as well as UV and soft x-rays. radiation. The role of more energetic photons and particles is small, since there are fewer of them, and they interact with M. g. weaker (see). In some places M. g., other mechanisms of heating are also essential, for example. shock waves generated by cloud collisions or supernova explosions.
The cooling of the magnetic field occurs due to radiation in spectral lines more often in IR and optical. regions of the spectrum, less often in UV and X-rays. bands or in the radio band (see). Radiation in the continuous spectrum plays, as a rule, a secondary role. On the whole, the mechanism of cooling in almost all regions of molecular regions is similar to the cooling of HII zones, but radiation in the IR range plays an increased role in cooling in HI regions, and radiation in the radio range plays an increased role in cooling in cold molecular regions.
Mg is ionized by the same types of radiation as it is heated. Ionization equilibrium is achieved when the ionization rate and the rate of ch are equal. arr. radiation recombination. In some cases, eg. for the OH ion in the HI regions, certain role charge exchange reactions (recharge reactions) play with hydrogen and less often with helium.
Formation of the structure of M. g.
Another, even stronger factor influencing the structure of the magnetic field in S-galaxies is yavl. spiral shock waves. They arise during the collision of the magnetism, already accumulated in the spiral arms, with gas, which, during a circular motion around the center of the galaxy, catches up with the spiral arms and enters them at supersonic speed (the spiral arms rotate around the center of the Galaxy in the same direction as gas and stars, but at a slower rate). At the shock wave front, the incoming gas is decelerated and compacted. Due to the increased pressure, almost all of the gas is in a dense phase. This is how gas-dust complexes are formed, observed on the inside. sides of the spiral branches.
Gas-dust complexes can arise not only under the action of spiral shock waves, but also due to the so-called. gas disk of galaxies. As a result of the development of instability, compact (10-30 pc) gas-dust clumps appear, which then become centers of formation star clusters. In S galaxies, the Rayleigh-Taylor instability probably plays a lesser role than spiral shock waves, but in Ir galaxies it seems to be the case. main the reason for the formation of complexes M. g.
Observations show that interstellar clouds, in addition to orderly movement around the center of the Galaxy, are chaotic. speed from cf. value approx. 10 km/s. On average, after 30-100 million years, a cloud collides with another cloud, which leads to dissipation (reduction) of these random movements, partial coalescence of clouds and the formation of a power-law (~ ) spectrum of their masses. Chaotic the motions are maintained by supernova explosions: the shell of the star thrown off during the explosion of the M. G. is decelerated in the M. G. and transfers part of its momentum to the clouds.
From the region of M. g., along which the shock wave caused by the flash passed, almost all the gas is swept out. The resulting region of rarefied gas (a cavern measuring tens of pc s n~ 10 -2 cm -3 and T~ 10 6 K) may exist for ~10 7 years. If during this time another supernova flares up nearby, then a new cavity, having closed with the previous one, can form a vast corridor of hot, rarefied, highly ionized gas. The radiation of hot gas can heat up to 300-5000 K gas clouds located at a distance of many pc from the corridors (the existence of clouds with such a temperature is impossible in the simple two-phase model of M. g. described above).
Outbursts of supernovae that have "drilled through" the gaseous disk of the galaxy through and through cause outflow of gas from the plane of the galaxy into the intergalactic space. environment and heating it there up to 10 7 -10 8 K. As a result, in the intergalactic. gas enriched with heavy elements enters the medium. It is possible that it is thanks to these processes that the intergalactic The gas in galaxy clusters has almost the same iron content as the Sun's atmosphere. Part of the gas, apparently, falls back to the galactic. planes in the form of high-latitude and high-velocity clouds of hydrogen.
5. Processes occurring in gas-dust complexes
The substance in the gas-dust complexes is dense enough not to pass to a great depth of the main. part of the penetrating radiation. Therefore, magma within complexes is colder than in interstellar clouds and exists predominantly in molecular form. Molecules are formed. arr. in ion-molecular reactions, as well as on the surface of dust particles (H 2 molecules and some others, see). The ionization necessary for the occurrence of ion-molecular reactions is supported by the UV radiation of stars (in regions where interstellar absorption of light) and, apparently, cosmic. beams of low energies (4-12 K) bunches. Together with these processes in cold fragments of molecular clouds, they lead to the emergence of self-gravitating clumps of gas-dust matter of stellar mass - protostars, from which stars are subsequently formed.
Thus, molecular clouds should quickly (in ~ 10 6 years) turn into stars. Because they exist much longer, factors that slow down the formation of stars must act (for example, magnetic pressure, turbulence, heating of the gas by the formed stars, see).
6. Evolution of interstellar gas
Mg is constantly exchanging matter with the stars. According to estimates, at present, in the Galaxy, gas passes into stars in an amount per year. At the same time, the stars, ch. arr. on the late stages evolution, lose substance (see) and replenish M. g.
Part of the emitted substance participated in thermonuclear reactions in the depths of stars and enriched there with heavy elements. Therefore, over time, the composition (abundance of elements) in Mg changes. In different galaxies and in different parts of each galaxy, these processes go with various speeds. As a result, in chem. and the isotopic composition of M., inhomogeneities appear, and above all the gradient of the chemical. composition along the galactic radii. Closer to the center of galaxies, the magnetic field is somewhat more enriched in heavy elements.
It is still unknown when and how the primary gas (which had a composition of 75% H and 25% He by mass, see) was enriched with heavy elements: whether it was before the formation of galaxies or at the very beginning of their evolution. But it is clear that in the early stages of the history of galaxies this process was much more active than at present.
In galaxies with large sp. moment of momentum over a time of ~ 109 years after their formation, M. g. settled into the disk, also enriched in heavy elements. Further star formation took place in the disk. In S galaxies, star formation in the disk is stimulated by a spiral shock wave. With each passage through the spiral shock wave, the gas elements slow down, lose energy, and with each revolution approach the center of the galaxy.
Spiral waves did not form in Ir galaxies, and the gas was exhausted slowly. Therefore, at present they are the most rich in gas (cf. the content of atomic hydrogen is 18% of the mass of the galaxy). In lenticular (SO) galaxies, the part of the gas was probably swept into the intergalactic. space during their interaction with other galaxies, and the remaining gas was not enough for active star formation.
Thus, in the process of the evolution of galaxies, a cycle of matter takes place: Mg stars Mg, leading to a gradual increase in the content of heavy elements in Mg and stars and a decrease in the amount of Mg in each of the galaxies. In different types of galaxies, the depletion of magma proceeds at significantly different rates. It is possible that the processes of star formation and gas enrichment with heavy elements proceeded nonmonotonically in the Galaxy, i.e. several Once in the history of the Galaxy, star formation could be delayed by billions of years. This, in principle, should have an effect on the abundance of elements in various types stellar population.
interstellar medium- this is the substance and fields that fill the interstellar space inside the Galaxy. The bulk of the interstellar matter falls on rarefied interstellar gas and dust. The entire interstellar medium is permeated magnetic fields, cosmic rays, electromagnetic radiation.
The main component of the interstellar medium is interstellar gas, which consists of hydrogen (70% mass) and helium (28%). The rest of the interstellar gas mass is made up of heavier chemical elements (O, C, N, Ne, S, Ar, Fe, etc.). The mass of interstellar matter in our Galaxy (excluding the corona) is estimated at 2% of total mass the entire galaxy. Depending on temperature conditions and density, interstellar gas is observed in three states: ionized, atomic and molecular.
Extra-atmospheric observations in the ultraviolet range revealed a very hot gas (hydrogen) with a temperature of 10 6 K, which fills most volume of the galaxy. Such low-density hot gas is produced by supernova explosions and the loss of matter by hot giants in the form of hot stellar winds. The density of such a gas is 1.6 · 10 -3 particles per 1 cm 3 .
The main data on the interstellar gas were obtained by radio astronomical methods after the radio emission of neutral atomic hydrogen at a wavelength of 21 cm was discovered in 1951. The main part of the interstellar gas is concentrated in the spiral arms of the Galaxy. In them, the gas is unevenly distributed: it is collected in ragged formations tens and hundreds of parsecs in size. About half of the mass of interstellar gas is contained in giant molecular clouds co average weight 105 solar masses and about 40 pc in diameter.
interstellar dust - these are small particulate matter irregular shape with a size of 0.01 to 1 micron. They consist of a refractory core and a shell of volatile compounds. Dust plays a significant role and actively participates in the processes occurring in the Universe.
In addition to rarefied gas and dust in interstellar space, a large number of elementary particles and nuclei various atoms(electrons, helium nuclei and more heavy elements). The streams of these particles are called cosmic rays. On an area of 1m 2, on average, about 10 thousand different particles fall every second.
Not all particles that form cosmic rays come to us from the depths of the Universe. Many of them have solar origin- they are born during solar flares. The main sources of cosmic rays in the Galaxy are supernova remnants and pulsars.
Observations show that radio emission also comes to us from regions of interstellar space where there are no supernova remnants. Therefore, a magnetic field also exists in interstellar space.
