Evolution and structure of galaxies. The structure and evolution of the galaxy Three pillars on which the theory of galaxy evolution stands
The formation and structure of galaxies is the next important question about the origin of the Universe. It is studied not only by cosmology as the science of the Universe, but also cosmogony (Greek. “Goneya” means birth) is a field of science that studies the origin and development of cosmic bodies and their systems (planetary, stellar, galactic cosmogony is distinguished). Cosmology bases its conclusions on the laws of physics, chemistry and geology.
Galaxy are giant clusters of stars and their systems (up to about 10 13 stars), having their own center (core) and different shapes (spherical, spiral, elliptical, oblate or even irregular). The cores of galaxies produce hydrogen, the basic substance of the Universe. The sizes of galaxies range from several tens of light years to 18 million light years. In the part of the Universe visible to us - the Metagalaxy - there are billions of galaxies and in each of them there are billions of stars. All galaxies are moving away from each other, and the speed of this “expansion” increases as the galaxies move away. Galaxies are far from static structures: they change shape and outline, collide and absorb each other. Our Galaxy is currently engulfing the Sagittarius Dwarf Galaxy. In about 5 billion years, a “collision of worlds” will occur. The neighboring galaxies the Milky Way and the Andromeda Nebula are slowly but inevitably moving towards each other at a speed of 500 thousand km/h.
Our galaxy is called the Milky Way and consists of 150 billion stars. We see this cluster of stars on clear nights as a strip of the Milky Way. It consists of a core and several spiral branches. Its dimensions are 100 thousand light years. The age of the Galaxy is about 15 billion years. The closest galaxy to the Milky Way (which a light beam reaches in 2 million years) is the Andromeda Nebula. Most of the stars in our galaxy are concentrated in a giant “disk” in the form of a biconvex lens about 1500 light years thick. Stars and nebulae within the Galaxy move in very complex orbits. First of all, they participate in the rotation of the Galaxy around its axis at a speed of approximately 250 km/s. The Sun is located at a distance of about 30 thousand light years from the center of the galaxy. During its existence, the Sun made approximately 25 revolutions around its axis of rotation.
The process of galaxy formation—as opposed to the formation of stars and the synthesis of elements within them—is not yet well understood. In 1963, at the border of the observable Universe, they discovered quasars(quasi-stellar radio sources) are the most powerful sources of radio emission in the Universe with a luminosity hundreds of times greater than the luminosity of galaxies and sizes tens of times smaller than them. It was assumed that quasars represent the nuclei of new galaxies and, therefore, the process of galaxy formation continues to this day.
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Non-state educational institution
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ABSTRACT
according to the concept of modern natural science
on the topic: “Evolution and structure of the Galaxy”
Moscow 2013
Introduction
1. Evolution of galaxies
2. Structure of galaxies
3. The structure of our galaxy (Milky Way)
Conclusion
Bibliography
Introduction
At the moment, there is no satisfactory theory of the origin and evolution of galaxies. There are several competing hypotheses to explain this phenomenon, but each has its own serious problems. According to the inflation hypothesis, after the appearance of the first stars in the Universe, the process of their gravitational unification into clusters and then into galaxies began. Recently, this theory has been called into question. Modern telescopes are able to “look” so far that they see objects that existed approximately 400 thousand years after the Big Bang. It was discovered that fully formed galaxies already existed at that time. It is assumed that too little time passed between the emergence of the first stars and the above-mentioned period of development of the Universe, and according to the Big Bang theory, galaxies simply would not have had time to form.
Another common hypothesis is that quantum vibrations constantly occur in a vacuum. They also occurred at the very beginning of the existence of the Universe, when the process of inflationary expansion of the Universe, expansion at superluminal speed, was underway. This means that the quantum fluctuations themselves expanded (from the Latin fluctuatio - oscillation), and to sizes that were perhaps many, many times larger than their initial size. Those of them that existed at the moment of the cessation of inflation remained “inflated” and thus turned out to be the first gravitating inhomogeneities in the Universe. It turns out that matter had about 400 thousand years to undergo gravitational compression around these irregularities and form gas nebulae. And then the process of the emergence of stars and the transformation of nebulae into galaxies began.
1. Evolution of galaxies
The formation of galaxies is considered as a natural stage in the evolution of the Universe, occurring under the influence of gravitational forces. Apparently, about 14 billion years ago, the separation of protoclusters began in the primary substance (proto from Greek - first). In protoclusters, groups of galaxies were separated in the course of various dynamic processes. The variety of galaxy shapes is associated with the variety of initial conditions for the formation of galaxies. The contraction of the galaxy lasts about 3 billion years. During this time, the gas cloud transforms into a star system. Stars are formed by the gravitational compression of clouds of gas. When the center of the compressed cloud reaches densities and temperatures sufficient for thermonuclear reactions to occur effectively, a star is born. In the depths of massive stars, thermonuclear fusion of chemical elements heavier than helium occurs. These elements enter the primary hydrogen-helium environment during stellar explosions or during the quiet outflow of matter with stars. Elements heavier than iron are formed during enormous supernova explosions. Thus, first-generation stars enrich the primary gas with chemical elements heavier than helium. These stars are the oldest and consist of hydrogen, helium and very small amounts of heavy elements. In second-generation stars, the admixture of heavy elements is more noticeable, since they are formed from a primary gas already enriched with heavy elements. The process of star birth occurs with the ongoing compression of the galaxy, so the formation of stars occurs closer and closer to the center of the system, and the closer to the center, the more heavy elements there should be in the stars. This conclusion agrees well with data on the abundance of chemical elements in stars in the halo of our Galaxy and elliptical galaxies. In a rotating galaxy, the stars of the future halo form at an earlier stage of contraction, when the rotation has not yet affected the overall shape of the galaxy.
Evidence of this era in our Galaxy are globular star clusters. When the compression of the protogalaxy stops, the kinetic energy of the resulting disk stars is equal to the energy of the collective gravitational interaction. At this time, conditions are created for the formation of a spiral structure, and the birth of stars occurs in the spiral branches, in which the gas is quite dense. These are third generation stars. These include our Sun. The reserves of interstellar gas are gradually depleted, and the birth of stars becomes less intense. In a few billion years, when all gas reserves are exhausted, the spiral galaxy will turn into a lenticular galaxy, consisting of faint red stars. Elliptical galaxies are already at this stage: all the gas in them was consumed 10-15 billion years ago. The age of galaxies is approximately the age of the Universe. One of the secrets of astronomy remains the question of what the nuclei of galaxies are. A very important discovery was that some galactic nuclei are active. This discovery was unexpected. Previously, it was believed that the galactic core was nothing more than a cluster of hundreds of millions of stars. It turned out that both the optical and radio emission of some galactic nuclei can change over several months. This means that within a short time, a huge amount of energy is released from the nuclei, hundreds of times greater than that released during a supernova explosion. Such nuclei are called “active”, and the processes occurring in them are called “activity”. In 1963, objects of a new type were discovered located beyond the boundaries of our galaxy. These objects have a star-shaped appearance. Over time, they found out that their luminosity is many tens of times greater than the luminosity of galaxies! The most amazing thing is that their brightness changes. The power of their radiation is thousands of times greater than the power of active nuclei. These objects were called quasars. It is now believed that the nuclei of some galaxies are quasars.
Scientists began to take a serious approach to the problem of galaxy evolution in the mid-1940s. These years were marked by a number of important discoveries in stellar astronomy. It was possible to find out that among star clusters, open and globular, there are young and old, and scientists were even able to estimate their age. It was necessary to carry out a kind of population census in galaxies of different types and compare the results. In which galaxies (elliptical or spiral), in which classes of galaxies are younger or older stars predominant. Such a study would give a clear indication of the direction of evolution of galaxies and would make it possible to clarify the evolutionary meaning of the Hubble classification of galaxies. But first, astronomers needed to figure out the numerical relationship between different types of galaxies. Direct study of photographs taken at the Mount Wilson Observatory allowed Hubble to obtain the following results: elliptical galaxies - 23%, spiral galaxies - 59%, barred spirals - 15%, irregular - 3%.
Astrophysicist Edwin Powell Hubble proposed an interesting classification of galaxies in 1926 and improved it in 1936. This classification is called the “Hubble Tuning Fork.” Until his death in 1953. Hubble improved his system, and after his death, this was done by the American astronomer Allan Rex Samndige, who in 1961 introduced significant innovations to the Hubble system. star dark matter galaxy milky way
However, in 1948, astronomer Yuri Nikolaevich Efremov processed data from the galaxy catalog of the American astronomer Harlow Shapley and the NASA Research Center. Ames and came to the following conclusions: elliptical galaxies are on average 4 magnitudes fainter than spiral galaxies in absolute magnitude. Among them there are many dwarf galaxies. If we take this circumstance into account and recalculate the number of galaxies per unit volume, it turns out that there are approximately 100 times more elliptical galaxies than spiral ones. Most spiral galaxies are giant galaxies, most elliptical galaxies are dwarf galaxies. Of course, among both there is a certain spread in size; there are elliptical giant galaxies and spiral dwarfs, but there are very few of both. In 1947, H. Shapley drew attention to the fact that the number of bright supergiants gradually decreases as we move from irregular galaxies to spiral ones, and then to elliptical ones. It turned out that it was precisely the irregular galaxies and galaxies with highly branched branches that were young. H. Shapley then expressed the idea that the transition of galaxies from one class to another does not necessarily occur. It is possible that the galaxies were all formed as we see them, and then only slowly evolved in the direction of smoothing and rounding their shapes. There is probably no unidirectional change in galaxies. H. Shapley drew attention to another important circumstance. Double galaxies are not the result of one galaxy colliding and being captured by another. Spiral galaxies often coexist in such pairs with elliptical ones. Such galactic pairs, in all likelihood, arose together. In this case, it is impossible to assume that they have gone through a significantly different development path. In 1949, Soviet astronomer Boris Vasilyevich Kukarkin drew attention to the existence of not only paired galaxies, but also clusters of galaxies. Meanwhile, the age of a galaxy cluster, judging by celestial mechanics data, cannot exceed 10-12 billion years. Thus, it turned out that galaxies of different shapes formed almost simultaneously in the Metagalaxy. This means that the transition of each galaxy during its existence from one type to another is completely unnecessary.
2. Structure of galaxies
The galamctic (ancient Greek GblboYabt - Milky Way) is a gravitationally bound system of stars, interstellar gas, dust and dark matter. All objects within galaxies participate in motion relative to a common center of mass. Galaxies are extremely distant objects; the distance to the nearest ones is usually measured in megaparsecs, and to distant ones - in units of redshift z. It is precisely because of their distance that only three of them can be distinguished in the sky with the naked eye: the Andromeda nebula (visible in the northern hemisphere), the Large and Small Magellanic Clouds (visible in the southern hemisphere). It was not possible to resolve images of galaxies down to individual stars until the beginning of the 20th century. By the early 1990s, there were no more than 30 galaxies in which individual stars could be seen, and all of them were part of the Local Group. After the launch of the Hubble Space Telescope and the commissioning of 10-meter ground-based telescopes, the number of galaxies in which it was possible to distinguish individual stars increased sharply. One of the unsolved problems in the structure of galaxies is dark matter, which manifests itself only in gravitational interaction. It can make up up to 90% of the total mass of the galaxy, or it can be completely absent, as in dwarf galaxies.
The galaxy consists of a disk, a halo and a corona.
1. Halo (spherical component of the Galaxy). Its stars are concentrated towards the center of the galaxy, and the density of matter, high in the center of the galaxy, falls quite quickly with distance from it.
2. The bulge is the central, densest part of the halo within several thousand light years from the center of the Galaxy.
3. Stellar disk (flat component of the Galaxy). It looks like two plates folded at the edges. The concentration of stars in the disk is much greater than in the halo. The stars inside the disk move in circular trajectories around the center of the Galaxy. The Sun is located in the stellar disk between the spiral arms.
The central, most compact region of the Galaxy is called the core. The core has a high concentration of stars, with thousands of stars in every cubic parsec. At the center of almost every galaxy there is a very massive body - a black hole - with such powerful gravity that its density is equal to or greater than the density of atomic nuclei. In fact, each black hole is a small in space, but in terms of mass it is simply a monstrous, furiously rotating core. The name “black hole” is clearly unfortunate, since it is not a hole at all, but a very dense body with powerful gravity - such that even light photons cannot escape from it. And when a black hole accumulates too much mass and kinetic energy of rotation, the balance of mass and kinetic energy is disturbed in it, and then it expels fragments from itself, which (the most massive) become small black holes of the second order, smaller fragments become future stars, when they gather large hydrogen atmospheres from galactic clouds, and small fragments become planets, when the collected hydrogen is not enough to start thermonuclear fusion. I think that galaxies are formed from massive black holes; moreover, the cosmic circulation of matter and energy takes place in galaxies. First, the black hole absorbs matter scattered in the Metagalaxy: at this time, thanks to its gravity, it acts as a “dust and gas sucker.” Hydrogen scattered in the Metagalaxy is concentrated around the black hole, and a spherical accumulation of gas and dust is formed. The rotation of the black hole entrains gas and dust, causing the spherical cloud to flatten, forming a central core and arms. Having accumulated a critical mass, the black hole in the center of the gas and dust cloud begins to eject fragments (fragmentoids), which break away from it with high acceleration, sufficient to be thrown into a circular orbit around the central black hole. In orbit, interacting with gas and dust clouds, these fragmentoids gravitationally capture gas and dust. Large fragmentoids become stars. Black holes, with their gravity, pull in cosmic dust and gas, which, falling onto such holes, become very hot and emit X-rays. When the amount of matter around a black hole becomes scarce, its glow decreases sharply. This is why some galaxies have a bright glow at their center, while others do not. Black holes are like cosmic “killers”: their gravity attracts even photons and radio waves, which is why the black hole itself does not emit and looks like a completely black body. But, probably, periodically the gravitational balance inside black holes is disrupted, and they begin to eject clumps of superdense matter with strong gravity, under the influence of which these clumps take on a spherical shape and begin to attract dust and gas from the surrounding space. From the captured substance, solid, liquid and gaseous shells are formed on these bodies. The more massive the clot of superdense matter (fragmentoid) ejected by the black hole was, the more dust and gas it will collect from the surrounding space (if, of course, this substance is present in the surrounding space). Almost all the molecular matter of the interstellar medium is concentrated in the annular region of the galactic disk (3-7 kpc). The visible radiation from the central regions of the Galaxy is completely hidden from us by thick layers of absorbing matter.
There are three types of galaxies: spiral, elliptical and irregular. Spiral galaxies have a well-defined disk, arms, and halos. At the center is a dense cluster of stars and interstellar matter, and at the very center is a black hole. The arms in spiral galaxies extend from their center and twist to the right or left depending on the rotation of the core and the black hole (more precisely, a superdense body) at its center. At the center of the galactic disk is a spherical condensation called a bulge. The number of branches (arms) can be different: 1, 2, 3,... but most often there are galaxies with only two branches. In galaxies, the halo includes stars and very rarefied gaseous matter that is not included in the spirals or disk. We live in a spiral galaxy called the Milky Way, and on clear days our Galaxy is clearly visible in the night sky as a wide, whitish stripe across the sky. Our Galaxy is visible to us in profile. Globular clusters in the center of galaxies are practically independent of the position of the galactic disk. The arms of galaxies contain a relatively small part of all stars, but almost all hot stars of high luminosity are concentrated in them. Stars of this type are considered young by astronomers, so the spiral arms of galaxies can be considered the place of star formation. Elliptical galaxies are often found in dense clusters of spiral galaxies. They have the shape of an ellipsoid or a ball, and spherical ones are usually larger than ellipsoidal ones. The rotation speed of ellipsoidal galaxies is less than that of spiral galaxies, which is why their disk is not formed. Such galaxies are usually saturated with globular clusters of stars. Elliptical galaxies, astronomers believe, consist of old stars and are almost completely devoid of gas. Irregular galaxies typically have low mass and volume and contain few stars. As a rule, they are satellites of spiral galaxies. They usually have very few globular clusters of stars. Examples of such galaxies are the satellites of the Milky Way - the Large and Small Magellanic clouds. But among the irregular galaxies there are also small elliptical galaxies.
3. The structure of our galaxy (Milky Way)
Milky Way - from lat. via lactea "milk road"
In the Soviet astronomical school, the Milky Way was simply called “our Galaxy” or “the Milky Way system”; The phrase "Milky Way" was used to refer to the visible stars that optically constitute the Milky Way to an observer.
The diameter of the Galaxy is about 30 thousand parsecs (about 100,000 light years, 1 quintillion kilometers) with an estimated average thickness of about 1000 light years. The galaxy contains, according to the lowest estimate, about 200 billion stars (modern estimates range from 200 to 400 billion). The bulk of stars are located in the shape of a flat disk. As of January 2009, the mass of the Galaxy is estimated at 3·10 12 solar masses, or 6·10 42 kg. Most of the Galaxy's mass is contained not in stars and interstellar gas, but in a non-luminous halo of dark matter. It wasn't until the 1980s that astronomers suggested that the Milky Way was a barred spiral galaxy rather than a regular spiral galaxy. This assumption was confirmed in 2005 by the Lyman Spitzer Space Telescope, which showed that the central bar of our galaxy is larger than previously thought. Young stars and star clusters, whose age does not exceed several billion years, are concentrated near the plane of the disk. They form the so-called flat component. Among them are many bright and hot stars. The gas in the Galaxy's disk is also concentrated mainly near its plane. It is distributed unevenly, forming numerous gas clouds - from giant clouds of heterogeneous structure, extending over several thousand light years, to small clouds no more than a parsec in size. In the middle part of the Galaxy there is a thickening called a bulge, which is about 8 thousand parsecs in diameter. The center of the galactic core is located in the constellation Sagittarius. The distance from the Sun to the center of the Galaxy is 8.5 kiloparsecs (2.62·10 17 km, or 27,700 light years). In the center of the Galaxy, apparently, there is a supermassive black hole around which, presumably, a black hole of average mass and an orbital period of about 100 years and several thousand relatively small ones rotate. Their combined gravitational effect on neighboring stars causes the latter to move along unusual trajectories. There is an assumption that most galaxies have supermassive black holes at their core. The central regions of the Galaxy are characterized by a strong concentration of stars: each cubic parsec near the center contains many thousands of them. The distances between stars are tens and hundreds of times smaller than in the vicinity of the Sun. Like most other galaxies, the distribution of mass in the Milky Way is such that the orbital speed of most stars in this Galaxy does not depend significantly on their distance from the center. Further from the central bridge to the outer circle, the usual speed of rotation of stars is 210-240 km/s. Thus, such a distribution of speed, not observed in the solar system, where different orbits have different speeds of rotation, is one of the prerequisites for the existence of dark matter. The length of the galactic bar is believed to be about 27,000 light years. This bar passes through the center of the galaxy at an angle of 44 ± 10 degrees to the line between our Sun and the center of the galaxy. It consists primarily of red stars, which are considered very old. The jumper is surrounded by a ring called the "Five Kiloparsec Ring". This ring contains most of the Galaxy's molecular hydrogen and is an active star-forming region in our Galaxy. If observed from the Andromeda Galaxy, the galactic bar of the Milky Way would be a bright part of it.
Our galaxy belongs to the class of spiral galaxies, which means that the Galaxy has spiral arms located in the plane of the disk. The disk is immersed in a spherical halo, and around it is a spherical corona. The solar system is located at a distance of 8.5 thousand parsecs from the galactic center, near the plane of the Galaxy (the offset to the North Pole of the Galaxy is only 10 parsecs), on the inner edge of the arm called the Orion arm. This arrangement does not make it possible to observe the shape of the sleeves visually. New data from observations of molecular gas (CO) suggest that our Galaxy has two arms, starting at a bar in the inner part of the Galaxy. In addition, there are a couple more sleeves in the inner part. These arms then transform into a four-arm structure observed in the neutral hydrogen line in the outer parts of the Galaxy. Most celestial bodies are combined into various rotating systems. Thus, the Moon revolves around the Earth, the satellites of the giant planets form their own systems, rich in bodies. At a higher level, the Earth and the rest of the planets revolve around the Sun. A natural question arose: is the Sun also part of an even larger system? The first systematic study of this issue was carried out in the 18th century by the English astronomer William Herschel. He counted the number of stars in different areas of the sky and discovered that there was a large circle in the sky (later it was called the galactic equator), which divides the sky into two equal parts and on which the number of stars is greatest. In addition, the closer the part of the sky is to this circle, the more stars there are. Finally it was discovered that it was on this circle that the Milky Way was located. Thanks to this, Herschel guessed that all the stars we observed form a giant star system, which is flattened towards the galactic equator. At first it was assumed that all objects in the Universe are parts of our Galaxy, although Kant also suggested that some nebulae could be galaxies similar to the Milky Way. As early as 1920, the question of the existence of extragalactic objects caused debate (for example, the famous Great Debate between Harlow Shapley and Heber Curtis; the former defended the uniqueness of our Galaxy). Kant's hypothesis was finally proven only in the 1920s, when Edwin Hubble was able to measure the distance to some spiral nebulae and show that, due to their distance, they cannot be part of the Galaxy.
Conclusion
There is a cycle of matter in the Universe, the essence of which is the scattering of matter by supermassive black holes, explosions of novae and supernovae, and then the collection of scattered matter by planets, stars and black holes using their gravity. There was no Big Bang, as a result of which our Universe (Metagalaxy) was born from a singularity. Explosions (and very powerful ones) happen and have happened in the Metagalaxy periodically here and there. The Universe does not pulsate, it simply boils, it is infinite, and we know very little about it and understand even less about it. There is no final theory that explains the Universe and the processes occurring in it, and there never will be. Theories and hypotheses correspond to the level of development of our technology, our science, and the experience that humanity has accumulated at the moment. Therefore, we must treat the accumulated experience as carefully as possible and always put fact above theory. As soon as some science does the opposite, it immediately ceases to be an open information system and turns into a new religion. In science the main thing is doubt, and in religion it is faith.
Bibliography:
1. Wikipedia. Access address: http://ru.wikipedia.org/wiki/
2. Agekyan T.A. Stars, Galaxies, Metagalaxy. - M.: Nauka, 1981.
3. Vaucouleurs J. Classification and morphology of galaxies // Structure of stellar systems. Per. with him. - M., 1962.
4. Zeldovich Ya.B. Novikov I.D. The structure and evolution of the Universe, - M.: Nauka, 1975.
5. Levchenko I.V. The many-sided Universe // Discoveries and hypotheses, LLC "Intelligence Media". - September 9 (67), 2007.
6. Novikov I. D., Frolov V. P. Black holes in the Universe // Advances in Physical Sciences. - 2001. - T. 131. No. 3.
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The poet asked: “Listen! After all, if the stars light up, that means someone needs it?” We know that stars are needed to shine, and our Sun provides the energy necessary for our existence. Why are galaxies needed? It turns out that galaxies are also needed, and the Sun not only provides us with energy. Astronomical observations show that there is a continuous outflow of hydrogen from the nuclei of galaxies. Thus, the nuclei of galaxies are factories for the production of the main building material of the Universe - hydrogen.
Hydrogen, the atom of which consists of one proton in the nucleus and one electron in its orbit, is the simplest “building block” from which more complex atoms are formed in the depths of stars in the process of atomic reactions. Moreover, it turns out that it is no coincidence that stars have different sizes. The greater the mass of a star, the more complex atoms are synthesized in its depths.
Our Sun, like an ordinary star, produces only helium from hydrogen (which is produced by the cores of galaxies); very massive stars produce carbon - the main “building block” of living matter. That's what galaxies and stars are for. What is the Earth for? It produces all the necessary substances for the existence of human life. Why does man exist? Science can't answer this question, but it can make us think about it again.
If someone needs the “ignition” of the stars, then maybe someone needs a person too? Scientific data helps us formulate an idea of our purpose, the meaning of our lives. When answering these questions, turning to the evolution of the Universe means thinking cosmically. Natural science teaches us to think cosmically, while at the same time not breaking away from the reality of our existence.
The question of the formation and structure of galaxies is the next important question of the origin of the Universe. It is studied not only by cosmology as the science of the Universe - a single whole, but also by cosmogony (Greek “gonea” means birth) - a field of science that studies the origin and development of cosmic bodies and their systems (planetary, stellar, galactic cosmogony is distinguished) .
A galaxy is a giant cluster of stars and their systems that have their own center (core) and a different, not only spherical, but often spiral, elliptical, oblate or generally irregular shape. There are billions of galaxies, and each of them contains billions of stars.
Our galaxy is called the Milky Way and consists of 150 billion stars. It consists of a core and several spiral branches. Its dimensions are 100 thousand light years. Most of the stars in our galaxy are concentrated in a giant “disk” about 1,500 light-years thick. The Sun is located at a distance of about 30 thousand light years from the center of the galaxy.
The closest galaxy to ours (to which the light ray travels 2 million years) is the “Andromeda nebula”. It is named so because it was in the constellation Andromeda that the first extragalactic object was discovered in 1917. Its belonging to another galaxy was proven in 1923 by E. Hubble, who found stars in this object through spectral analysis. Later, stars were discovered in other nebulae.
And in 1963, quasars (quasi-stellar radio sources) were discovered - the most powerful sources of radio emission in the Universe with a luminosity hundreds of times greater than the luminosity of galaxies and sizes tens of times smaller than them. It was assumed that quasars represent the nuclei of new galaxies and, therefore, the process of galaxy formation continues to this day.
Astronomy and space exploration
Stars are studied by astronomy (from the Greek “astron” - star and “nomos” - law) - the science of the structure and development of cosmic bodies and their systems. This classical science is experiencing its second youth in the 20th century due to the rapid development of observation technology - its main method of research: reflecting telescopes, radiation receivers (antennas), etc. In the USSR, in 1974, a reflector with The mirror is 6 m in diameter, collecting light millions of times more than the human eye.
Astronomy studies radio waves, light, infrared, ultraviolet, x-rays and gamma rays. Astronomy is divided into celestial mechanics, radio astronomy, astrophysics and other disciplines.
Astrophysics, a part of astronomy that studies physical and chemical phenomena occurring in celestial bodies, their systems and in outer space, is currently acquiring particular importance. Unlike physics, which is based on experiment, astrophysics is based primarily on observations. But in many cases, the conditions in which matter is found in celestial bodies and systems differ from those available to modern laboratories (ultra-high and ultra-low densities, high temperatures, etc.). Thanks to this, astrophysical research leads to the discovery of new physical laws.
The intrinsic significance of astrophysics is determined by the fact that currently the main attention in relativistic cosmology is transferred to the physics of the Universe - the state of matter and physical processes occurring at different stages of the expansion of the Universe, including the earliest stages.
One of the main methods of astrophysics is spectral analysis. If you pass a beam of white sunlight through a narrow slit and then through a glass triangular prism, it breaks down into its component colors, and a rainbow color stripe appears on the screen with a gradual transition from red to violet - a continuous spectrum. The red end of the spectrum is formed by the rays that are the least deflected when passing through a prism, the violet end is the most deflected. Each chemical element corresponds to well-defined spectral lines, which makes it possible to use this method for studying substances.
Unfortunately, short-wave radiation - ultraviolet, x-rays and gamma rays - do not pass through the Earth’s atmosphere, and here science comes to the aid of astronomers, which until recently was considered primarily technical - astronautics (from the Greek “nautika” - the art of navigation) , providing space exploration for the needs of mankind using aircraft.
Cosmonautics studies problems: theories of space flight - calculations of trajectories, etc.; scientific and technical - design of space rockets, engines, on-board control systems, launch facilities, automatic stations and manned spacecraft, scientific instruments, ground-based flight control systems, trajectory measurement services, telemetry, organization and supply of orbital stations, etc.; medical and biological - the creation of on-board life support systems, compensation for adverse phenomena in the human body associated with overload, weightlessness, radiation, etc.
The history of astronautics begins with theoretical calculations of man's exit into unearthly space, which were given by K. E. Tsiolkovsky in his work “Exploration of world spaces with jet instruments” (1903). Work in the field of rocket technology began in the USSR in 1921. The first launches of liquid fuel rockets were carried out in the United States in 1926.
The main milestones in the history of astronautics were the launch of the first artificial Earth satellite on October 4, 1957, the first human flight into space on April 12, 1961, the lunar expedition in 1969, the creation of manned orbital stations in low-Earth orbit, and the launch of a reusable spacecraft.
The work was carried out in parallel in the USSR and the USA, but in recent years there has been a unification of efforts in the field of space exploration. In 1995, the joint Mir-Shuttle project was carried out, in which American Shuttle ships were used to deliver astronauts to the Russian orbital station Mir.
The ability to study cosmic radiation at orbital stations, which is delayed by the Earth's atmosphere, contributes to significant progress in the field of astrophysics.
Topic 5
Structure and evolution of stars and planets
The structure and evolution of stars. Solar system and its origin. Structure and evolution of the Earth
The structure and evolution of stars
There are two main concepts of the origin of celestial bodies. The first is based on the nebular model of the formation of the solar system, put forward by the French physicist and mathematician Pierre Laplace and developed by the German philosopher Immanuel Kant. In accordance with it, stars and planets were formed from scattered diffuse matter (cosmic dust) through the gradual compression of the original nebula.
The acceptance of the Big Bang model and the expanding Universe significantly influenced the models of the formation of celestial bodies and led to Victor Ambartsumyan’s hypothesis about the emergence of galaxies, stars and planetary systems from superdense (consisting of the heaviest elementary particles - hyperons) prestellar matter located in the nuclei of galaxies, by fragmenting it.
The interpretation of celestial bodies is determined by which of the two hypotheses is considered true. V. Ambartsumyan's discovery of stellar associations consisting of very young stars trying to escape from each other was understood by him as confirmation of the hypothesis of the formation of stars from the original superdense matter. Which of the two concepts is closer to the truth will decide the subsequent development of natural science.
The expanding universe model encountered several difficulties that contributed to the progress of astronomy. Scattering after the Big Bang from a point with an infinitely high density, the clumps of matter should slightly slow down each other by forces of mutual attraction, and their speed should fall. But the entire mass of the Universe is not enough to decelerate. From this objection, a hypothesis was born in 1939 about the presence in the Universe of so-called “black holes”, which cannot be seen, but which store 9/10 of the mass of the Universe (i.e., as much as is missing).
What are "black holes"? If a certain mass of a substance ends up in a relatively small volume, critical for a given mass, then under the influence of its own gravity such a substance begins to compress uncontrollably. Gravitational collapse occurs. As a result of compression, the concentration of mass increases and a moment comes when the gravitational force on the surface becomes so great that to overcome it it would be necessary to develop a speed greater than the speed of light. Therefore, the “black hole” does not let anything out or reflect anything, and therefore it cannot be detected. In a “black hole,” space bends and time slows down. If the compression continues further, then at some stage undamped nuclear reactions begin. The compression stops, and then an anti-collapse explosion occurs, and the “black hole” turns into a “white hole”. It is assumed that “black holes” are located in the cores of galaxies, being a super-powerful source of energy.
All celestial bodies can be divided into those emitting energy - stars, and those not emitting energy - planets, comets, meteorites, cosmic dust. The energy of stars is generated in their depths by nuclear processes at temperatures reaching tens of millions of degrees, which is accompanied by the release of special particles of enormous penetrating power - neutrinos.
Stars are factories for the production of chemical elements and sources of light and life. This solves several problems at once. Stars move around the center of the galaxy in complex orbits. There may be stars whose brightness and spectrum change - variable stars (Tau Ceti) and non-stationary (young) stars, as well as stellar associations whose age does not exceed 10 million years. Perhaps supernovae are formed from them, during the outbursts of which a huge amount of energy of non-thermal origin is released and nebulae (clusters of gases) are formed.
There are very large stars - red giants and supergiants, and neutron stars, whose mass is close to the mass of the Sun, but the radius is 1/50000 of the solar one (10-20 km); they are called that because they consist of a huge bunch of neutrons).
In 1967, pulsars were discovered - cosmic sources of radio, optical, x-ray and gamma radiation that come to Earth in the form of periodically repeating bursts. Radio pulsars (rapidly rotating neutron stars) have pulse periods of 0.03-4 seconds; X-ray pulsars (double stars where matter from a second, ordinary star flows to the neutron star) have periods of several seconds or more.
Interesting celestial bodies that have often been attributed supernatural significance include comets. Under the influence of solar radiation, gases are released from the comet's nucleus, forming the extensive head of the comet. Exposure to solar radiation and solar wind causes the formation of a tail, sometimes reaching millions of kilometers in length. The released gases escape into outer space, as a result of which the comet loses a significant part of its mass each time it approaches the Sun. In this regard, comets live relatively short lives (millennia and centuries).
The sky only seems calm. Catastrophes constantly occur in it and new and supernova stars are born, during the outbreaks of which the luminosity of the star increases hundreds of thousands of times. These explosions characterize the galactic pulse.
At the end of the evolutionary cycle, when all the hydrogen fuel is used up, the star contracts to infinite density (the mass remains the same). An ordinary star turns into a “white dwarf” - a star with a relatively high surface temperature (from 7000 to 30000 ° C) and low luminosity, many times less than the luminosity of the Sun.
It is assumed that one of the stages in the evolution of neutron stars is the formation of a nova and supernova, when it increases in volume, sheds its gas envelope and releases energy within a few days, shining like billions of suns. Then, having exhausted its resources, the star dims, and a gas nebula remains in the place of the flare.
If the star had super-large dimensions, then at the end of its evolution the particles and rays, having barely left the surface, immediately fall back due to gravitational forces, i.e. a “black hole” is formed, which then turns into a “white hole”.
The process of evolution of stars is presented in the diagram.
On a clear night, you can watch the Milky Way streak in the sky. For thousands of years, astronomers have looked at it in awe, slowly coming to the realization that our Sun is just one of billions of stars in the Galaxy. Over time, our tools and techniques have improved, and we have come to understand that the Milky Way itself is just one of the billions of galaxies that make up the Universe.
Thanks to the theory of relativity and the discovery of the speed of light, we also realized that when we look through space, we are looking back in time. By seeing an object one billion light years away, we know that this is what it looked like a billion years ago. The time machine effect has allowed astronomers to study the evolution of galaxies.
The process of formation and development of galaxies remains the subject of intense attention and still hides its share of mysteries.
Formation of galaxies
The current scientific consensus is that all matter in the universe was created approximately 13.8 billion years ago during an event known as the Big Bang. Initially, all matter was compressed into a very small ball of infinite density and enormous temperature, called a singularity. Suddenly the singularity began to expand. This is how the Universe began.
After rapid expansion and cooling, all matter was almost uniformly distributed. Over the course of several billion years, denser regions of the Universe began to gravitationally attract each other. Therefore, they became denser, forming gas clouds and large clumps of matter.
The spiral galaxy Messier 74, located 32 million light-years away, contains about 100 billion stars. Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration
Clouds of hydrogen gas inside protogalaxies underwent gravitational collapse to become the first stars. Some of these early objects were tiny dwarf galaxies, while others took on the familiar spiral shape, like our Milky Way.
Galactic mergers
Once formed, these galaxies evolved into larger galactic structures called groups, clusters, and superclusters. Over time, the galaxies were attracted to each other by gravity and united. The outcome of these mergers depended on the mass of the colliding galaxies.
Small galaxies are absorbed by large neighbors, increasing their mass. So the Milky Way recently gobbled up several dwarf galaxies, turning them into streams of stars that orbit the galactic core. But galaxies of similar size combine to become giant elliptical galaxies.
When this happens, the fine spiral structures disappear. Elliptical galaxies are among the largest stellar associations. Another consequence of these mergers is that the supermassive black holes at their centers become even larger.
A collision of two spiral galaxies, which, if it does not create one huge elliptical galaxy, will certainly change their slender structures. Credit: ESA/Hubble & NASA, Acknowledgment: Luca Limatola
Although not all mergers result in elliptical structures, they all significantly change the structure of the merged galaxy.
During mergers, actual collisions between star systems are unlikely, given the vast distances between the stars. However, the merger can lead to gravitational shock waves that can trigger the formation of new stars. This is what is predicted to happen when the Milky Way merges with the Andromeda Galaxy in 4 billion years.
Death of galaxies
Eventually, galaxies stop forming stars when their supply of cold gas and dust is depleted. Star formation slows down over billions of years until it stops completely. However, ongoing mergers ensure that more and more stars, gas and dust settle into old galaxies, thereby extending their lives.
It is currently believed that our Galaxy has almost a full supply of hydrogen, and star formation will continue as it depletes. Stars like the Sun can last about 10 billion years, but the smallest red dwarfs can live for several trillions of years. Thanks to the presence of dwarf galaxies and the upcoming merger with Andromeda, the Milky Way could exist even longer.
As a result, all galaxies in the Universe eventually become gravitationally bound to each other and unite into giant elliptical galaxies. Astronomers have encountered similar "fossils", a good example of which is Messier 49, a supermassive elliptical galaxy.
Elliptical Galaxy Messier 49. Credit: Siggi Kohlert
These galaxies have already used up all their gas reserves for star formation, and all they have left are small, long-lived stars. Eventually, the stars will go out one by one.
After our Galaxy merges with Andromeda, it will continue on its path to merge with all other nearby galaxies in the Local Group. We can expect this supergalaxy to suffer the same fate. Thus, the evolution of galaxies occurs over billions of years and will continue into the foreseeable future.
Galaxies– giant gravitationally bound systems of stars and star clusters, interstellar gas and dust, and dark matter. In space, galaxies are distributed unevenly: in one area you can detect a whole group of nearby galaxies, or you may not detect a single galaxy, even the smallest one. The exact number of galaxies in the observable universe is unknown, but it is likely to be on the order of one hundred billion.
The first condition The appearance of galaxies in the Universe was the appearance of random clusters and concentrations of matter in a homogeneous Universe. For the first time such an idea was expressed by I. Newton, who argued that if matter were uniformly scattered throughout infinite space, it would never have gathered into a single mass.
Second condition the appearance of galaxies - the presence of small disturbances, fluctuations of matter leading to a deviation from the homogeneity and isotropy of space. It was precisely the fluctuations that became the “seeds” that led to the appearance of larger compactions of matter. These processes can be represented by analogy with the processes of cloud formation in the Earth's atmosphere.
GENERAL CHARACTERISTICS OF GALAXIES(SIZE, LUMINITY, MASS, COMPOSITION)
Size. The concept of size is not strictly defined, because... galaxies do not have sharp boundaries; their brightness gradually decreases with distance from the center outward. The apparent size of galaxies depends on the telescope's ability to highlight their low-brightness outer regions against the glow of the night sky, which is never completely black. The peripheral parts of galaxies “drown” in its weak light. To objectively estimate the size of galaxies, a certain level of surface brightness, or, as they say, a certain isophote (this is the name of the line along which the surface brightness has a constant value) is conventionally taken as their boundary.
Luminosity of galaxies(i.e., the total radiation power) varies within even greater limits than their size - from several million solar luminosities (Lc) for the smallest galaxies to several hundred billion Lc for giant galaxies. This value roughly corresponds to the total number of stars in the galaxy, or its total mass.
Galaxy masses, as well as their luminosities, can also differ by several orders of magnitude - from a million solar masses to a thousand billion solar masses in some elliptical galaxies.
Composition and structure. The components of the Galaxy are stars, rarefied gas, dust (this is the interstellar medium) and cosmic rays. Galaxies are, first of all, star systems. Spatially, the stars form two main structural components of the galaxy, as if nested one inside the other: rapidly rotating star disk, And slowly rotating spherical (or spheroidal) component. The inner, brightest part of the spherodal component is called bulge(from the English bulge - swelling), and the outer part of low brightness - star halo. At the center of most galaxies there is a bright region called core. In the central part of massive galaxies, a small and rapidly rotating perinuclear disk which also consists of stars and gas. A large number of stars, closely interconnected by gravity, revolve around the galactic center as a satellite - this is - globular star cluster. In addition to globular star clusters distinguish open star clusters. Unlike open star clusters, which are located in the galactic disk, globular clusters are located in the halo; they are much older, contain many more stars, have a symmetrical spherical shape and are characterized by an increase in the concentration of stars towards the center of the cluster. Observations of globular clusters indicate that they occur primarily in regions with efficient star formation, that is, where the interstellar medium is denser than normal star-forming regions.
Stars in open clusters are bound together by relatively weak gravitational forces, so as they orbit the galactic center, the clusters can be destroyed by passing close to other clusters or clouds of gas, in which case the stars that form them become part of the normal population of the galaxy. Open star clusters are found only in spiral and irregular galaxies, where active star formation processes occur.
In addition to stars with different masses, chemical compositions and ages, each galaxy contains a rarefied and slightly magnetized interstellar medium (gas and dust), penetrated by high-energy particles (cosmic rays). The relative mass attributable to the interstellar medium is also one of the most important observable characteristics of galaxies. The total mass of interstellar matter varies greatly from one galaxy to another and usually ranges from a few tenths of a percent to 50% of the total mass of stars (in rare cases, the gas can even predominate in mass over the stars). Content gas in a galaxy - this is a very important characteristic, on which the activity of processes occurring in galaxies and, above all, the process of star formation largely depends. Interstellar gas consists mainly of hydrogen and helium with a small admixture of heavier elements. These heavy elements are formed in stars and, together with the gas lost by the stars, end up in interstellar space.
The gaseous environment of interstellar space also contains a finely dispersed solid component - interstellar dust. She manifests herself in two ways. First, dust absorbs visible and ultraviolet light, causing an overall dimming and reddening of the galaxy. The most opaque (due to dust) areas of the galaxy are visible as dark areas against a light, bright background. There are especially many opaque regions near the plane of the stellar disk - this is where the cold interstellar medium is concentrated. Secondly, the dust itself radiates, releasing the accumulated light energy in the form of far infrared radiation. The total mass of the dust is relatively small: it is several hundred times less than the total mass of interstellar gas.
Galaxies are very diverse: among them one can distinguish spherical elliptical galaxies, disk spiral galaxies, barred galaxies, lenticular, dwarf, irregular, etc. The variety of observed shapes of galaxies has caused astronomers to want to combine similar objects and divide galaxies into series classes by their appearance (by morphology). The most commonly used morphological classification of galaxies is based on the scheme proposed by E. Hubble in 1925 and developed by him in 1936. Galaxies are divided into several main classes: elliptical (E), spiral (S), lenticular (S0) and irregular (Irr).
Elliptical E-galaxies They look like elliptical or oval spots, not too elongated, the brightness inside of which gradually decreases with distance from the center. There is usually no internal structure (there is no noticeable disk in them, although precise photometric measurements in some cases allow one to suspect its existence. Traces of dust or gas are also rarely found in them)
Spiral galaxies (S) is the most common type (about half of them). Typical representatives are our Galaxy and the Andromeda nebula. Unlike elliptical galaxies, they exhibit a structure in the form of characteristic spiral branches. Despite the variety of shapes, spiral galaxies have a similar structure. Three main components are observed in them: a stellar disk, a spheroidal component, a bright inner region called the bulge, and a flat component, which is several times smaller in thickness than the disk. The flat component includes interstellar gas, dust, young stars, and spiral arms. Our Galaxy has a similar structure.
Between types E and S there is a type lenticular galaxies (S0). Like S galaxies, they have a stellar disk and bulge, but they do not have spiral arms. It is believed that these are galaxies that in the distant past were spiral, but have now almost completely “lost” or used up interstellar gas, and with it the ability to form bright spiral branches. Any spiral galaxy, if stripped of its gas and young stars, will be classified as lenticular.
Irregular Irr galaxies do not have an ordered structure, they do not have spiral branches, although they contain bright regions of various sizes (as a rule, these are regions of intense star formation). The bulge in these galaxies is very small or completely absent. These galaxies tend to be high in interstellar gas and young stars.
Some galaxies have an unusually bright nucleus. Galaxies with active nuclei are usually divided into several types. There are Seyfert galaxies, radio galaxies, quasars C Heifert galaxies are named in honor of the American astronomer Carl Seyfert, who first noticed them in 1943. In some cases, the nuclei of Seyfert galaxies are 100 billion times brighter than the Sun. S.g. - these are, as a rule, spiral galaxies. The most likely hypothesis to explain the activity of the nuclei assumes the presence of a black hole (with a mass of tens or hundreds of millions of solar masses) in the center of the galaxy.
The most unusual of all are objects called quasars. The English term quasar literally means “star-like radio source”) - a powerful and distant active galactic nucleus. They emit from an area with a diameter of less than 1 light. years, the same amount of energy as would be emitted by hundreds of normal galaxies. Despite their unusual nature, quasars are not visually impressive, so they were noticed only after 1963.
Today, the most common point of view is that a quasar is a supermassive black hole that sucks in surrounding matter. As charged particles approach a black hole, they accelerate and collide, resulting in intense light emission. According to another point of view, quasars are the first young galaxies, and we are simply observing the process of their birth. However, there is also an intermediate, although it would be more accurate to say a “united” version of the hypothesis, according to which a quasar is a black hole that absorbs the matter of a forming galaxy.
A radio galaxy is a type of galaxy that has much greater radio emission compared to other galaxies. Radiation sources of radio galaxies usually consist of several components (core, halo, radio emissions). Radio galaxies usually have the shape of ellipses and are gigantic in size.
Several percent of the observed galaxies do not fit into the described classification scheme; they are called Peculiar. Typically these are galaxies whose shape is distorted by strong interactions with neighboring galaxies (such galaxies are called interacting. There is no clear definition for this term, and the assignment of galaxies to this type may be disputed. Sometimes the classification of a galaxy as a peculiar type was disputed. So, for example, B.A. Vorontsov-Velyaminov believed that interacting galaxies are not peculiar, since visible changes in their shape are caused by disturbances of close neighbors. However, among interacting systems there are objects of such bizarre shapes that it is difficult not to call them peculiar.
A classic example of a peculiar galaxy is the radio galaxy Centaurus A (NGC 5128).
In a separate group are allocated dwarf galaxies- small in size, the luminosity of which is thousands of times less than that of galaxies such as ours or the Andromeda nebula. They are the most numerous class of galaxies, but their low luminosity makes them difficult to detect at great distances. Among them there are also elliptical dE, spiral dS (very rare), and irregular (dIrr). The letter d (from the English dwarf - dwarf) denotes membership in dwarf systems.
Evolution of galaxies
The observed diversity of galaxies is a consequence of the different conditions in which they arose. Analysis of the spectra and stellar composition of galaxies showed that the vast majority of them are very old and were formed 10-15 billion years ago. According to modern concepts, the formation of galaxies began in the early era of the expansion of the Universe, when the average density of matter in the Universe was hundreds of times greater than at present. Galaxies arose from hydrogen-helium gas clouds collapsing under the influence of their own gravity. At a certain stage of compression, intense star formation began in protogalaxies. Massive stars, rapidly evolving and exploding as supernovae, ejected gas enriched with various chemical elements resulting from the explosion into the surrounding space.
The formation of a disk in galaxies is associated with dissipation(Energy dissipation is the transition of part of the energy of ordered processes (kinetic energy of a moving body, electric current energy, etc.) into the energy of disordered processes, ultimately into heat.) gas energy in a contracting protogalaxy. Possessing a certain torque, the gas, losing its mechanical energy, was compressed into a disk, which, as a result of the formation of stars from the gas, gradually became a stellar disk.
A major role in the evolution of galaxies was played by the absorption of smaller systems by large galaxies, which were destroyed by tidal forces and replenished the mass of the forming galaxies.
CLUSTERS AND SUPERCLUSTERS
The photographs of galaxies show that there are few truly lonely galaxies. About 95% of galaxies form groups of galaxies.. They are often dominated by one massive elliptical or spiral galaxy, which, due to tidal forces, destroys satellite galaxies over time and increases its mass, consuming them.
Cluster of galaxies are called associations of several hundred galaxies, which can contain both individual galaxies and groups of galaxies. Typically, when observed at this scale, several very bright supermassive elliptical galaxies can be identified. Such galaxies should directly influence the process of formation and formation of the cluster structure.
Supercluster- the largest type of galaxy association, includes thousands of galaxies. At the scale of superclusters, galaxies arrange themselves into bands and filaments surrounding vast, tenuous voids. The shape of such clusters can vary: from a chain, such as the Markarian chain, to walls, like the great wall of Sloan.
Local group of galaxies. Milky way galaxy
The Local Group of galaxies is a collection of nearby galaxies, the distances to which do not exceed approximately 1 million pc (about 3 million light years). It consists of two large groups and dwarf galaxies scattered among them - about 30 members in total. One of the groups is dominated by our Galaxy with its nearby Magellanic Clouds in size, mass and light intensity. In another group, the main place is occupied by a spiral galaxy (Andromeda nebula), which is even more powerful. It is adjacent to a smaller spiral galaxy - M 33 in the Triangulum, two small elliptical galaxies and several dwarf galaxies. The galaxies included in the M. g. g., due to their proximity to us, are accessible to the most detailed study.
Members of the Local Group move relative to each other, but are connected by mutual gravity and therefore occupy a limited space of about 6 million light years for a long time and exist separately from other similar groups of galaxies. All members of the Local Group are believed to have a common origin and have been coevolving for about 13 billion years.
Our Galaxy - the Milky Way - has the shape of a disk with a bulge in the center - the core, from which spiral arms extend. Its thickness is 1.5 thousand light years, and its diameter is 100 thousand light years. The age of our Galaxy is about 15 billion years. It rotates in a rather complex way: a significant part of its galactic matter rotates differentially, like planets rotate around the Sun, without paying attention to the orbits in which other, fairly distant cosmic bodies move, and the speed of rotation of these bodies decreases with increasing their distance from the center. Another part of the disk of our Galaxy rotates solidly, like a music disk spinning on a record player. Our Sun is located in a region of the Galaxy in which the velocities of solid-state and differential rotation are equal. Such a place is called a corotation circle. It creates special, calm and stationary conditions for star formation processes.
Our Galaxy has two small satellite galaxies called the Magellanic Clouds. There are Large and Small Magellanic Clouds. These are rich areas for observation with instruments of all sizes and are visible to the naked eye in the Southern Hemisphere. The Magellanic Clouds were familiar to sailors in the southern hemisphere and were called the "Cape Clouds" in the 15th century. Ferdinand Magellan used them for navigation, as an alternative to the North Star, during his trip around the world in 1519-1521. When, after the death of Magellan, his ship returned to Europe, Antonio Pigafetta (Magellan's companion and official chronicler of the trip) proposed calling the Cape Clouds Magellan's Clouds as a kind of perpetuation of his memory
Both Clouds were previously considered irregular galaxies, but subsequently discovered structural features of barred spiral galaxies. They are located relatively close to each other and form a gravitationally bound (double) system. Both Magellanic Clouds are immersed in a common shell of neutral hydrogen. In addition, they are connected to each other by a hydrogen bridge
There are a lot of star clusters in the Magellanic Clouds. Scientists have recorded 1,100 open clusters in the Large Cloud and more than 100 in the Small Cloud. 35 globular clusters have been discovered in the Large Cloud, and 5 in the Small Cloud. Globular clusters have been discovered in the Magellanic Clouds, which are not found in our Galaxy. They contain many blue and white giants. That's why they are white. Ordinary globular clusters consist of red giants, so their color is yellow-orange.
1). A star as an object of study in astrophysics.
2). Classifications of stars.
3). The birth and evolution of stars.
