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Interstellar medium astronomy presentation. Presentation on the theme "galaxy". Star formation in galaxies

26.02.2024

Interstellar medium astronomy presentation. Presentation on the topic

Composition of the interstellar medium

The main component of the ISM is hydrogen (~ 70% of the total mass), which is present there in various forms: neutral atomic

hydrogen, molecular hydrogen (H2), ionized hydrogen.

About 28% of the mass is helium and ~2% is the share of other elements.

In addition to gas, the ISM contains solid particles (dust). The ratio of dust mass to gas mass is ~0.01.

Two-phase model of the interstellar medium

In the simplest two-phase model, in a certain pressure range, the neutral ISM breaks up into two stable phases (being in pressure equilibrium): a dense cold phase (“clouds”), T ~ 100 K,

n ~ 10 cm-3, and rarefied hot (“intercloud medium”), T ~ 104 K, n ~ 0.1 cm-3.

Main components of the MZS

Phase

Coronal gas

Low Density HII Zones

Cross-cloud environment

Warm areas HI

Clouds HI

dark clouds

Areas HII

Giant molecular clouds

Maser

condensation

T(K)	n(cm-3)	M (Msun)	L (pc)
~ 5·105
~104
~104
~103

	~103			~ 10-5
	~104			~ 3·10-9
~104				~ 10-4
		~ 3·105		~ 3·10-4
	~ 1010		~ 10-5

Heating and cooling mechanisms

Basic heating mechanisms

Ultraviolet radiation from stars (photoionization).

Heating by shock waves.

Volumetric heating of gas by penetrating radiation and cosmic rays

Volumetric heating of gas by hard electromagnetic radiation (X-ray and gamma quanta).

Basic cooling mechanisms

Free-free(bremsstrahlung) radiation

Recombination radiation

Emission in spectral lines

Dust radiation

Electron impact ionization

Cosmic rays

The cosmic ray flux in the vicinity of the Solar System is ~ 1 particle/cm 2·s. Hence the average concentration of fast protons in the interstellar medium is ~ 10-10 –10-11 cm-3.

Cosmic rays contain the most protons (~ 90% by number of particles). Helium nuclei make up about 7% by number of particles. A feature of the CR is the relatively large abundance of lithium, beryllium, boron nuclei (~ 0.14%), while in the interstellar There are very few of them in the gas-dust environment (~ 10-6%).

The CR energy spectrum has a power-law character, although the spectrum index can vary in different regions. The average CR energy density is close to 10-12 erg/cm3.

Most likely, cosmic rays are accelerated during supernova explosions and (or) in pulsars.

Differential spectrum of cosmic rays in interplanetary space near the Earth's orbit: 1 - protons; 2 - particles of galactic cosmic rays; 3 - protons from solar flares.

Shown for comparison

spectra of protons and -particles

Origin of cosmic rays

Dependence of the gamma ray flux on galactic longitude l according to observational data (vertical lines) in comparison with the calculation results (solid curve) based on the hypothesis of supernova remnants as the main source of cosmic rays.

CL acceleration mechanisms

Fermi mechanism.

Interaction between a particle and interstellar clouds that move along with frozen magnetic fields

(magnetic bottle). Traffic jams approach at speed U<< V . За одно столкновение частица приобретает скорость 2U , число столкновений в единицу времени V /2L .

			V dL

Statistical acceleration mechanism (during chaotic motion of a particle between clouds). During oncoming collisions with clouds, the energy of the particle increases, and during overtaking collisions, it decreases. The relative speed during oncoming collisions is higher, and therefore the number of such collisions is greater. The gas of heavy clouds is in equilibrium with the gas of particles. The direction of the process should lead to the establishment of equidistribution of energy between clouds and particles. The role of the magnetic field is reduced to reflecting particles from clouds.

Interstellar gas and dust.

The interstellar medium is the matter and fields that fill interstellar space inside galaxies. Composition: interstellar gas, dust (1% of gas mass), interstellar magnetic fields, cosmic rays, and dark matter. The entire interstellar medium is permeated by magnetic fields, cosmic rays and electromagnetic radiation.

Interstellar gas is the main component of the interstellar medium. Interstellar gas is transparent. The total mass of interstellar gas in the Galaxy exceeds 10 billion solar masses or several 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. Its bulk is contained near the plane of the Galaxy in a layer several hundred parsecs thick. The average gas density is about 10 −21 kg/m³. The chemical composition is approximately the same as that of most stars: it consists of hydrogen and helium (90% and 10% by number of atoms, respectively) with a small admixture of heavier elements (O, C, N, Ne, Si, etc.).

Depending on temperature and density, interstellar gas is in molecular, atomic or ionized states.

The main data on 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. It turned out that atomic hydrogen having a temperature of 100 K forms a layer 200-300 pc thick in the galactic disk at a distance of 15- 20 kpc from its center. By receiving and analyzing this radiation, scientists learn about the density, temperature and movement of interstellar gas in space.

About half of the interstellar gas is contained in giant molecular clouds with an average mass of 10^5 solar masses and a diameter of about 40 pc. Due to the low temperature (about 10 K) and increased density (up to 10^3 particles per 1 cm^3), hydrogen and other elements in these clouds are combined into molecules.

There are about 4000 such molecular clouds in the Galaxy.

Regions of ionized hydrogen with a temperature of 8000-10000 K manifest themselves in the optical range as light diffuse nebulae.

Ultraviolet rays, unlike visible light rays, are absorbed by gas and give it their energy. Thanks to this, hot stars heat the surrounding gas with their ultraviolet radiation to a temperature of approximately 10,000 K. The heated gas begins to emit light itself, and we observe it as a light gas nebula.

It is these nebulae that are indicators of places of star formation currently occurring.

Thus, in the Great Orion Nebula, protostars surrounded by protoplanetary disks were discovered using the Hubble Space Telescope.

The Great Orion Nebula is the brightest gas nebula. It is visible through binoculars or a small telescope

A special type of nebula is planetary nebulae, which appear as faintly luminous disks or rings resembling the disks of planets. They were discovered in 1783 by W. Herschel, and now there are more than 1200 of them. In the center of such a nebula is the remnant of a dead red giant - a hot white dwarf or neutron star. Under the influence of internal gas pressure, the planetary nebula expands at a speed of approximately 20-40 km/s, while the gas density decreases.

(Planetary Hourglass Nebula picture)

Interstellar dust is solid microscopic particles, along with interstellar gas, filling the space between stars. It is currently believed that dust grains have a refractory core surrounded by organic matter or an icy shell. The chemical composition of the core is determined by the atmosphere of which stars they condensed in. For example, in the case of carbon stars, they will consist of graphite and silicon carbide.

The typical size of interstellar dust particles 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 to several tens of Kelvin, making interstellar dust a source of long-wave infrared radiation.

Because of the dust, the densest gas formations - molecular clouds - are almost opaque and appear in the sky as dark areas, almost devoid of stars. Such formations are called dark diffuse nebulae. (picture)

Dust also affects chemical processes occurring in the interstellar medium: dust granules contain heavy elements that are used as catalysts in various chemical processes. Dust granules also participate in the formation of hydrogen molecules, which increases the rate of star formation in metal-poor clouds.

Tools for studying interstellar dust

Distance learning.
Research of micrometeorites for the presence of inclusions of interstellar dust.
Study of ocean sediments for the presence of cosmic dust particles.
Study of cosmic dust particles present at high altitudes in the Earth's atmosphere.
Launching spacecraft to collect, study and deliver interstellar dust particles to Earth.

Interesting

Over the course of a year, over 3 million tons of cosmic dust fall onto the earth's surface, as well as from 350 thousand to 10 million tons of meteorites - stone or metal bodies that fly into the atmosphere from outer space.
Over the last 500 years alone, the mass of our planet has increased by a billion tons due to cosmic matter, which is only 1.7·10 -16% of the Earth's mass. However, it apparently influences the annual and daily motion of our planet.

Initially, nebulae in astronomy were any stationary extended (diffuse) luminous astronomical objects, including star clusters or galaxies outside the Milky Way, which could not be resolved into stars. Some examples of such use still exist today. For example, the Andromeda Galaxy is sometimes called the "Andromeda Nebula." Thus, Charles Messier, who was intensively searching for comets, compiled in 1787 a catalog of stationary diffuse objects similar to comets. The Messier catalog includes both nebulae themselves and galaxies (for example, the above-mentioned Andromeda galaxy M31) and globular star clusters (M13 Hercules cluster). As astronomy and the resolution of telescopes developed, the concept of “nebula” became more and more refined: some of the “nebulae” were identified as star clusters, dark (absorbing) gas-dust nebulae were discovered, and, finally, in the 1920s. first Lundmark, and then Hubble, managed to resolve the peripheral regions of a number of galaxies into stars and thereby establish their nature. Since that time, the term “nebula” has been used in the above sense.

The primary feature used in the classification of nebulae is the absorption or emission (scattering) of light by them, that is, according to this criterion, nebulae are divided into dark and light. The former are observed due to the absorption of radiation from sources located behind them, the latter due to their own radiation or reflection (scattering) of light from nearby stars. The nature of the radiation of light nebulae, the energy sources that excite their radiation, depend on their origin and can be of a diverse nature; Often several radiation mechanisms operate in one nebula. The division of nebulae into gas and dust is largely arbitrary: all nebulae contain both dust and gas. This division is historically determined by various methods of observation and radiation mechanisms: the presence of dust is most clearly observed when radiation is absorbed by dark nebulae of sources located behind them and when radiation from nearby stars or in the nebula itself is reflected, scattered, or re-emitted by dust contained in the nebula; The intrinsic emission of the gas component of the nebula is observed when it is ionized by ultraviolet radiation from a hot star located in the nebula (emission regions of H II ionized hydrogen around stellar associations or planetary nebulae) or when the interstellar medium is heated by a shock wave due to a supernova explosion or the influence of a powerful stellar wind of Wolf-Rayet type stars.

Dark nebulae are dense (usually molecular) clouds of interstellar gas and interstellar dust that are opaque due to interstellar absorption of light by the dust. They are usually visible against the background of bright nebulae. Less often, dark nebulae are visible directly against the background of the Milky Way. These are the Coalsack Nebula and many smaller ones called giant globules. Horsehead Nebula as seen by Hubble

Interstellar absorption of light A v in dark nebulae varies widely, from 110 m to m in the densest nebulae. The structure of nebulae with large A v can only be studied by methods of radio astronomy and submillimeter astronomy, mainly from observations of molecular radio lines and infrared radiation from dust. Often, within dark nebulae, individual densities from A v to m are found in which stars apparently form. In those parts of nebulae that are translucent in the optical range, the fibrous structure is clearly visible. The filaments and general elongation of nebulae are associated with the presence of magnetic fields in them, which impede the movement of matter across the lines of force and lead to the development of a number of types of magnetohydrodynamic instabilities. The dust component of nebula matter is associated with magnetic fields due to the fact that dust grains are electrically charged.

Reflection nebulae are clouds of gas and dust illuminated by stars. If the star(s) are in or near an interstellar cloud, but are not hot enough to ionize a significant amount of interstellar hydrogen around it, then the main source of optical radiation from the nebula is starlight scattered by interstellar dust. An example of such nebulae are the nebulae around bright stars in the Pleiades cluster. The Angel reflection nebula is located at an altitude of 300 pc above the galactic plane

Most reflection nebulae are located near the plane of the Milky Way. In a number of cases, reflection nebulae are observed at high galactic latitudes. These are gas-dust (often molecular) clouds of various sizes, shapes, densities and masses, illuminated by the combined radiation of the stars in the Milky Way disk. They are difficult to study because of their very low surface brightness (usually much fainter than the sky background). Sometimes, projected on images of galaxies, they lead to the appearance in photographs of galaxies of non-existent details of tails, bridges, etc. Some reflection nebulae have a comet-like appearance and are called cometary. In the “head” of such a nebula there is usually a variable star of the T Tauri type, which illuminates the nebula. Such nebulae often have variable brightness, tracking (with a delay during the propagation of light) the variability of the radiation of the stars illuminating them. The sizes of cometary nebulae are usually small in hundredths of a parsec.

A rare type of reflection nebula is the so-called light echo, observed after the 1901 Novaya explosion in the constellation Perseus. The bright flare of the new star illuminated the dust, and for several years a faint nebula was observed, spreading in all directions at the speed of light. In addition to the light echo, after the outbursts of new stars, gaseous nebulae are formed, similar to the remnants of supernova explosions. Merope Reflection Nebula

Many reflection nebulae have a fine-fibrous structure, a system of almost parallel filaments several hundredths or thousandths of a parsec thick. The origin of the filaments is associated with flute or permutation instability in a nebula penetrated by a magnetic field. Fibers of gas and dust push apart the magnetic field lines and penetrate between them, forming thin filaments. Studying the distribution of brightness and polarization of light over the surface of reflection nebulae, as well as measuring the dependence of these parameters on wavelength, makes it possible to establish such properties of interstellar dust as albedo, scattering indicatrix, size, shape and orientation of dust grains.

Radiation-ionized nebulae are areas of interstellar gas that have been highly ionized by radiation from stars or other sources of ionizing radiation. The brightest and most widespread, as well as the most studied representatives of such nebulae are regions of ionized hydrogen (H II zones). In H II zones, the matter is almost completely ionized and heated to a temperature of ~10 4 K by ultraviolet radiation from the stars located inside them. Inside the HII zones, all the star's radiation in the Lyman continuum is processed into radiation in the lines of subordinate series, in accordance with Rosseland's theorem. Therefore, in the spectrum of diffuse nebulae there are very bright lines of the Balmer series, as well as the Lyman-alpha line. Only rarefied low-density H II zones are ionized by stellar radiation, in the so-called. coronal gas.

Radiation-ionized nebulae also occur around powerful X-ray sources in the Milky Way and other galaxies (including active galactic nuclei and quasars). They are often characterized by higher temperatures than in H II zones and a higher degree of ionization of heavy elements. Giant star forming region NGC 604.

A type of emission nebula is planetary nebula, formed by the upper outflowing layers of stellar atmospheres; usually this is a shell ejected by a giant star. The nebula expands and glows in the optical range. The first planetary nebulae were discovered by W. Herschel around 1783 and were named so for their external resemblance to the disks of planets. However, not all planetary nebulae are disk-shaped: many are ring-shaped or symmetrically elongated along a certain direction (bipolar nebulae). A fine structure in the form of jets, spirals, and small globules is noticeable inside them. The expansion rate of planetary nebulae is km/s, diameter is 0.010.1 pc, typical mass is about 0.1 solar masses, lifetime is about 10 thousand years. Planetary Cat's Eye Nebula.

The variety and multiplicity of sources of supersonic motion of matter in the interstellar medium lead to a large number and variety of nebulae created by shock waves. Typically, such nebulae are short-lived, since they disappear after the kinetic energy of the moving gas is exhausted. The main sources of strong shock waves in the interstellar medium are stellar explosions, ejections of shells during explosions of supernovae and novae, as well as stellar wind. In all these cases, there is a point source of ejection of matter (a star). The nebulae created in this way have the appearance of an expanding shell, close to spherical in shape. The ejected substance has speeds of the order of hundreds and thousands of km/s, so the temperature of the gas behind the shock wave front can reach many millions and even billions of degrees.

Gas heated to a temperature of several million degrees emits mainly in the X-ray range, both in the continuous spectrum and in spectral lines. In optical spectral lines it glows very weakly. When the shock wave encounters inhomogeneities in the interstellar medium, it bends around the densities. A slower shock wave propagates inside the seals, causing radiation in the spectral lines of the optical range. The result is bright fibers that are clearly visible in photographs. The main shock front, compressing a clump of interstellar gas, sets it in motion in the direction of its propagation, but at a speed lower than that of the shock wave. Pencil Nebula - Supernova shock wave

The brightest nebulae created by shock waves are caused by supernova explosions and are called supernova remnants. They play a very important role in shaping the structure of interstellar gas. Along with the described features, they are characterized by non-thermal radio emission with a power-law spectrum, caused by relativistic electrons accelerated both during the supernova explosion and later by the pulsar that usually remains after the explosion. Nebulae associated with nova explosions are small, weak and short-lived Crab Nebula remnant of a supernova explosion 1054 g

Another type of nebula created by shock waves is associated with stellar wind from Wolf Rayet stars. These stars are characterized by a very powerful stellar wind with a mass flux per year and an outflow velocity of (1 3)×10 3 km/s. They create nebulae several parsecs in size with bright filaments. Unlike the remnants of supernova explosions, the radio emission of these nebulae is of a thermal nature. The lifetime of such nebulae is limited by the duration of the stars' stay in the Wolf-Rayet star stage and is close to 10 5 years. Thor's Helmet nebula around the Wolf Rayet star

Shock waves of lower speeds arise in regions of the interstellar medium in which star formation occurs. They lead to heating of gas to hundreds and thousands of degrees, excitation of molecular levels, partial destruction of molecules, heating of dust. Such shock waves are visible in the form of elongated nebulae that glow primarily in the infrared. A number of such nebulae have been discovered, for example, in the star formation center associated with the Orion Nebula. The Orion Nebula A giant star-forming region

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MUNICIPAL BUDGETARY EDUCATIONAL INSTITUTION LYCEUM No. 11 OF THE CITY OF CHELYABINSK

Essay

nand the topic:

"Gas and dust complexes. Interstellar medium»

Performed:

11th grade student

Kiseleva Polina Olegovna

Checked:

Lykasova Alevtina Pavlovna

Chelyabinsk 2015

ABOUTTOPICAL

Introduction

1. History of ISM research

2. Main components of the MLS

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 (light) nebula

4.2 Dark nebula

5. Radiation

6. Evolution of the interstellar medium

Conclusion

List of sources

INTRODUCTION

The universe is, at its core, almost empty space. Only relatively recently has it been 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 filling 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 I tried to use scientific methods to find irrefutable evidence that space is not empty, and that the light of distant stars is absorbed in it, but to no avail. interstellar medium cloud gas

Later German astrophysicist F. Hartmann conducted a study of the spectrum of Delta Orionis and studied the orbital motion of the companions of the Delta Orionis system and the light coming from the star. Having realized that some light was absorbed on its way to Earth, Hartmann wrote that “the calcium absorption line is very weak,” and that “it was somewhat of a surprise that the calcium lines at 393.4 nanometers did not move in a periodic line divergence.” spectrum, which is present in spectroscopic binary stars." The stationary nature of these lines led Hartmann to suggest that the gas responsible for the absorption was not present in the atmosphere of Delta Orionis, but, on the contrary, was located outside the star and located between the star and the observer. This study marked 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 absorption medium, which has been shown Kaptein, absorbs only at some wavelengths, may indicate the presence of gas and gaseous molecules that are emitted by the Sun and stars.”

In the same year 1912 IN.Hess discovered cosmic rays, energetic charged particles that bombard the Earth from space. This allowed some researchers to declare that they also fill the interstellar medium.

After Hartmann's research, in 1919, Eger While studying absorption lines at waves of 589.0 and 589.6 nanometers in the Delta Orionis and Beta Scorpii systems, he discovered sodium in the interstellar medium.

The presence of an absorbing rarefied medium was convincingly demonstrated less than a hundred years ago, in the first half of the 20th century, by comparing the observed properties of distant star clusters at various distances from us. This was done independently by an American astronomer Robert Trumpler(1896-1956) and Soviet astronomer B.A.Vorontsov-Velyaminov(1904-1994). More precisely, 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 of the Milky Way. The presence of dust meant that both the apparent brightness and the observed color of distant stars were distorted, and to know their true values required a rather complex accounting of extinction. Dust was thus perceived by astronomers as an annoying nuisance that interfered 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 are destroyed, 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 using its radio emission. As a result of targeted searches, radiation from neutral hydrogen atoms in interstellar space was discovered at a frequency of 1420 MHz (corresponding to a wavelength of 21 cm). Radiation at this frequency (or, as they say, in a radio link) was predicted by a Dutch astronomer Hendrik van de Hulst in 1944 on the basis of quantum mechanics, and it was discovered in 1951 after calculating its expected intensity by a Soviet astrophysicist I.S. Shklovsky. Shklovsky also pointed out the possibility of observing the radiation of 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 greater than the mass of rarefied dust. But the gas is completely transparent to visible light, so it could not be detected using the same methods that dust was discovered.

With the advent of X-ray telescopes installed on space observatories, another, 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 from optical observations or from observations in radio links - 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 capabilities, has made it possible to study in detail the physical processes in the interstellar medium. Entire scientific directions have emerged - space gas dynamics And space electrodynamics, studying the properties of rarefied space media. Astronomers have learned to determine distances to gas clouds, measure the temperature, density and pressure of gas, its chemical composition, and estimate the speed of movement of matter. In the second half of the 20th century. A complex picture of the spatial distribution of the interstellar medium and its interaction with stars emerged. It turned out that the possibility of the birth of stars depends on the density and amount of interstellar gas and dust, and stars (primarily the most massive of them), in turn, change the properties of the surrounding interstellar medium - they heat it, support the constant movement of gas, and replenish the medium with their matter , change its chemical composition.

2. MAIN COMPONENTS OF MZS

The interstellar medium includes interstellar gas, dust (1% of the gas mass), interstellar magnetic fields, interstellar clouds, 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 several 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 gas density 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 gas and give it their energy. Thanks to this, hot stars heat the surrounding gas with their ultraviolet radiation to a temperature of approximately 10,000 K. The heated gas begins to emit light itself, and we observe it as a light gas nebula. Cooler, “invisible” gas is observed using radio astronomy methods. Hydrogen atoms in a rarefied environment emit radio waves at a wavelength of about 21 cm. Therefore, streams of radio waves continuously propagate from regions of interstellar gas. By receiving and analyzing this radiation, scientists learn about the density, temperature and movement of interstellar gas in space.

2 .2 Interstellar dust

Interstellar dust is solid microscopic particles that, along with interstellar gas, fill the space between stars. Currently, it is believed that dust grains have a refractory core surrounded by organic matter or an icy shell. The chemical composition of the core is determined by the atmosphere of which stars they condensed in. For example, in the case of carbon stars, they will consist of graphite and silicon carbide.

The typical size of interstellar dust particles 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 to several tens of K, making interstellar dust a source of long-wave infrared radiation.

2 .3 interstellar cloud

An interstellar cloud is a general name for accumulations of gas, plasma and dust in our and other galaxies. In other words, the interstellar cloud has a higher density than the average density of the 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, it is possible to determine the chemical composition of the cloud.

Typically, about 70% of the mass of an interstellar cloud is hydrogen, the remainder being mainly helium. The 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. Their main (but not the only) source is supernova explosions.

Extragalactic and galactic rays are usually called primary. Secondary flows of particles passing and transforming in the Earth’s atmosphere are usually called secondary.

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% protons, and 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 approximately one hundred thousand times less than that of the Earth's magnetic field. The interstellar magnetic field, acting on charged particles with a force depending on their energy, “confuses” the trajectories of the particles, and they continuously change the direction of their movement in the Galaxy. Charged particles flying in an interstellar magnetic field are deviated from straight trajectories under the influence of the Lorentz force. Their trajectories seem to be “wound” on the lines of magnetic induction.

3. PHYSICAL FEATURES OF MZS

· Lack of local thermodynamic equilibrium(LTR)- With state of a system in which the macroscopic quantities of this system (temperature, pressure, volume, entropy) remain unchanged over time under conditions of isolation from the environment.

· Thermal instability

The thermal equilibrium condition may not be satisfied at all. There is a magnetic field that prevents compression unless it occurs along field lines. Secondly, the interstellar medium is in continuous motion and its local properties are constantly changing, new energy sources appear in it and old ones disappear. Thirdly, in addition to thermodynamic instability, there are gravitational and magnetohydrodynamic instability. And this does not take into account any kind of cataclysms in the form of supernova explosions, tidal influences passing through neighboring galaxies, or the passage of the gas itself through the spiral branches of the Galaxy.

· Prohibited lines and 21 cm line

A distinctive feature of an optically thin medium is radiation in prohibited lines. Forbidden lines are those that are prohibited by selection rules, that is, they originate from metastable levels (quasi-stable equilibrium). The characteristic lifetime 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 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 a metastable state. If there is no LTE, then the population of energy levels should be calculated from the balance of elementary processes of excitation and deactivation.

The most important prohibited line of the MZS is atomic hydrogen radio link 21cm. This line appears 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 have 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.

· Frozen magnetic field.

Freezing-in of a magnetic field means the conservation of magnetic flux through any closed conductive circuit during its deformation. Under laboratory conditions, magnetic flux can be considered to be conserved in environments 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 field lines, and thus excite an electric field, but, on the contrary, should carry along the magnetic field lines; the magnetic field appears to be frozen into the conductor.

Real space plasma is far from ideal, and freezing-in should be understood in the sense that it takes a very long time to change the flow through the circuit. In practice, this means that we can consider the field constant while the cloud is compressed, rotated, etc.

4. NEBULA

Nebula- a section of the interstellar medium that stands out due to its radiation or absorption of radiation against the general background of the sky. Nebulae are composed 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 gas and dust is largely arbitrary: all nebulae contain both dust and gas. This division is historically determined by various methods of observation and radiation mechanisms: the presence of dust is most clearly observed when dark nebulae absorb radiation from sources located behind them and when radiation from nearby stars or in the nebula itself is reflected, scattered, or re-emitted by dust contained in the nebula; the intrinsic radiation of the gas component of a nebula is observed when it is ionized by ultraviolet radiation from a hot star located in the nebula (emission regions of H II ionized hydrogen around stellar associations or planetary nebulae) or when the interstellar medium is heated by a shock wave due to a supernova explosion or the influence of a powerful stellar wind of Wolf-type stars -- Rayet.

4 .1 Diffuse(light)nebula

Diffuse (light) nebula is a general term in astronomy used to refer to nebulae that emit light. The three types of diffuse nebulae are reflection nebula, emission nebula (of which protoplanetary, planetary, and H II regions are varieties), and 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 to ionize a significant amount of interstellar hydrogen around itself, then the main source of optical radiation from the nebula is starlight scattered by interstellar dust.

The spectrum of a reflection nebula is the same as that of the star illuminating it. The microscopic particles responsible for scattering light include carbon particles (sometimes called diamond dust), as well as iron and nickel particles. 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 blue light is scattered more efficiently than red light (this, in part, explains the blue color of the sky).

Currently, about 500 reflection nebulae are known, the most famous of which are around the Pleiades (star cluster). The giant red (spectral class M1) star Antares is surrounded by a large red reflection nebula. Reflection nebulae are also common in star formation sites.

In 1922, Hubble published the results of studies of some bright nebulae. In this work, Hubble derived the luminosity law for reflection nebula, which establishes the relationship between the angular size of the nebula ( R) and the apparent magnitude of the 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 a nearby hot star. There are several types of emission nebulae. Among them are the H II regions, in which new stars are formed, and the sources of ionizing photons are young, massive stars, as well as planetary nebulae, in which a dying star has thrown off its upper layers, and the exposed hot core ionizes them.

Planetmdark fogmness-- an astronomical object consisting of an ionized shell of gas and a central star, a 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 shed 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, with the lifespan of the ancestor star being several billion years. Currently, about 1,500 planetary nebulae are known in our galaxy.

The process of formation of planetary nebulae, along with supernova explosions, plays an important role in the chemical evolution of galaxies, ejecting into interstellar space material enriched in heavy elements - products of stellar nucleosynthesis (in astronomy, all elements are considered heavy, with the exception of the products of the primary nucleosynthesis of the Big Bang - hydrogen and helium, such as carbon, nitrogen, oxygen and calcium).

In recent years, with the help of images obtained by the Hubble Space Telescope, it has been possible to find out that many planetary nebulae have a very complex and unique structure. Although about a fifth of them are circumspherical, the majority do not have any spherical symmetry. The mechanisms that make it possible to form such a variety of forms remain not fully understood to date. It is believed that the interaction of the stellar wind and binary stars, the magnetic field and the interstellar medium may play a large role in this.

Planetary nebulae are mostly faint objects and are usually not visible to the naked eye. The first planetary nebula discovered was dumbbell nebula in the constellation Chanterelle.

The unusual nature of planetary nebulae was discovered in the middle of the 19th century, with the beginning of the use of spectroscopy in observations. William Huggins became the first astronomer to obtain spectra of planetary nebulae - objects that stood out for their unusualness. When Huggins studied the spectra of nebulae N.G.C.6543 (Cat's Eye), M27 (Dumbbell), M57 (Lyra ring nebula) and a number of others, it turned out that their spectrum was extremely different from the spectra of stars: all the spectra of stars obtained by that time were absorption spectra (a continuous spectrum with a large number of 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 was fundamentally different from the nature of stars.

Planetary nebulae represent the final stage of evolution for many stars. A typical planetary nebula has an average extent 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 about 10-100 times greater than the density of interplanetary space at the distance of the Earth's orbit from the Sun. Young planetary nebulae have the highest density, sometimes reaching 10 6 particles per cm3. As nebulae age, their expansion causes their density to decrease. 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 exists briefly between the time an intermediate-mass star (1-8 solar masses) leaves the asymptotic giant branch (AGB) and the subsequent planetary nebula (PN) phase. A protoplanetary nebula shines primarily in the infrared and is a subtype of reflection nebula.

RegionHII- This is a cloud of hot gas and plasma, reaching several hundred light years in diameter, which is an area of active star formation. In this region, young, hot, bluish-white stars are born, which abundantly emit ultraviolet light, thereby ionizing the surrounding nebula.

H II regions can give birth to thousands of stars in just a few million years. Eventually, supernova explosions and powerful stellar winds from the most massive stars in the resulting star cluster disperse the region's gases, and it becomes a group like the Pleiades.

These regions got their name because of the large amount of ionized atomic hydrogen, designated by astronomers as H II (the HI region is the zone of neutral hydrogen, and H 2 stands for molecular hydrogen). They can be seen at considerable distances throughout the Universe, and studying 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, Tarantula Nebula,N.G.C. 604 , Orion's trapezoid, 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 enormous speed, which forms supernova remnant. The remnant consists of stellar material ejected by the explosion and interstellar matter absorbed by the shock wave.

Probably the most beautiful and best studied young supernova remnant S.N. 1987 A in the Large Magellanic Cloud, which exploded in 1987. Other well-known supernova remnants are Crab Nebula, remnant of a relatively recent explosion (1054), supernova remnant Quiet (S.N. 1572) , named after Tycho Brahe, who observed and recorded its initial brightness immediately after the flare in 1572, as well as the remainder Kepler supernova (S.N. 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 coming from emission or reflection nebulae (such as , Horsehead Nebula) or stars (for example, Coalsack Nebula) located behind her.

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 (GMCs). 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 twisted, serpentine shapes. The largest dark nebulae are visible to the naked eye, appearing like pieces of blackness against the bright Milky Way.

Active processes often occur in the interiors of dark nebulae, such as star birth or maser emission.

5. RADIATION

Stellar wind-- the process of outflow of matter from stars into interstellar space.

The matter that stars are made of can, under certain conditions, overcome their gravity and be ejected into interstellar space. This occurs when a particle in the atmosphere of a star accelerates to a speed exceeding the second escape velocity for a given star. In fact, the speeds of the particles that make up the stellar wind are hundreds of kilometers per second.

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.

Stellar wind can play an important role in stellar evolution: since this process results in a decrease in the mass of the star, the lifespan of the star depends on its intensity.

Stellar wind is a means of transporting matter over significant distances in space. In addition to the fact that it itself consists of matter flowing from stars, it can influence the surrounding interstellar matter, transferring part of its kinetic energy to it. Thus, the “Bubble” shape of the emission nebula NGC 7635 was formed as a result of such an impact.

In the case of an outflow of matter from several nearby stars, supplemented by the influence of radiation from these stars, condensation of interstellar matter is possible, followed by star formation.

With an active stellar wind, the amount of ejected material may be sufficient to form a planetary nebula.

6. EVOLUTION OF THE INTERSTELLAR MEDIUM

The evolution of the interstellar medium, or more precisely 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 during primordial nucleosynthesis hydrogen, helium, deuterium, lithium and other light nuclei were formed, which split apart at the Hayashi track or protostar stage. In other words, we should observe long-lived G dwarfs with zero metallicity. But none of them have been found in the Galaxy; moreover, most of them have almost solar metallicity. Based on indirect evidence, it can be judged that something similar is happening in other galaxies. At the moment, the issue remains open and awaits a solution.

There was no dust in the primordial interstellar gas. As is now believed, dust grains form on the surface of old, cold stars and leave it along with the outflowing matter.

CONCLUSION

The study of such a complex system as “stars - interstellar medium” turned out to be a very difficult astrophysical task, 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 stellar system, lasting billions of years, is reflected in the interstellar medium.

LIST OF SOURCES

1) Materials taken from the site www.wikipedia.org

2) Materials taken from the site www.krugosvet.ru

3) Materials taken from the site www.bse.sci-lib.com

4) Materials taken from the site www.dic.academic.ru

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