Stars are giant, hot balls of gas that emit enormous amounts of energy. Temperatures of thousands and tens of thousands of degrees dominate on the surface of stars. In their depths, the temperature is even higher, which, in combination with high pressure, leads to the occurrence of nuclear reactions, in the process of which stellar energy is produced. Streams of this energy are emitted by the star into the surrounding space for a long time. If it were not for the gravitational force directed towards the center of the celestial body, these flows could explode the star, but the vast majority of stars have achieved complete equilibrium between these two forces, allowing the star to exist for a long time.

The world of stars is very diverse. Among them there are giants, the transverse size of which is thousands of times greater than the size of the Sun, and dwarfs of negligible size. Some stars emit energy much more intensely than our Sun, while others shine so dimly that if they were in the place of the Sun, the Earth would be plunged into darkness.

Stars often form clusters: they unite in pairs, triplets, and sometimes there are more stars in such a cluster. Giant groups of stars, numbering millions of objects, are called galaxies. The star system to which our Sun belongs is usually called the Galaxy. There are supergiant galaxies containing hundreds of billions of eusidae.

Even in ancient times, observers divided all the stars into groups called constellations. Currently, the sky is divided into 88 constellations, many of which were given names by the ancient Greeks, associating them with various legends and myths: the constellations Cassiopeia, Andromeda, Perseus and others.

Stars are incredibly different not only in size, but also in color. Among them there are huge red cool stars and hot white dwarfs. The density of the matter of large stars is very small, while the density of white dwarfs is so high that a matchbox of their matter can weigh hundreds of tons.

Currently, astronomers using powerful telescopes are observing the vigorous activity of stars experiencing grandiose flares. The discovery of radio nebulae and radio galaxies led to ideas about rapid changes in galaxies on large scales.

The brightest star in the northern hemisphere of the sky is Vega, and the brightest star in the entire sky is Sirius.

So, a giant star system containing billions of stars and forming a picture of the Milky Way in the sky is the Galaxy in which we live. At a distance of 25 thousand light years from the center of our Galaxy, the Sun is located - a star that plays an important role in the life of our planet.

SUN

This is a celestial body located in the center of the Solar system. This is the closest star in the Galaxy to Earth. It has a spherical shape and consists of hot gases. The diameter of the Sun is 1,392,000 km, which is 109 times the diameter of the Earth. On the surface of the Sun the temperature is about 6000°C, and in its central part it reaches 15,000,000°C.

The sun is surrounded by an atmosphere, which consists of layers:

The lower layer is called the photosphere, the thickness of which is 200-300 km. All visible radiation from the Sun comes from these layers. Spots and faculae are observed in the photosphere. The spots consist of a dark core and surrounding penumbra. The spot can reach a diameter of 200,000 km;

Chromosphere. It extends on average 14,000 km above the visible edge of the Sun. The chromosphere is much more transparent than the photosphere;

Solar corona. This is the thinnest part of the solar atmosphere. Its thickness is equal to several radii of the Sun, and it can only be observed during a total solar eclipse.

At the edge of the solar disk, prominences are visible - luminous formations from hot gases. The dimensions of prominences sometimes reach hundreds of thousands of kilometers, their average height is from 30 to 50 thousand km.

The mass of the Sun is 333 thousand times greater than the mass of the Earth, and its volume is 1 million 304 thousand times. It follows that the density of the Sun is less than the density of the Earth. Basically, the Sun consists of the same chemical elements as the Earth, but there is less hydrogen on our planet than on the Sun. The energy emitted by the Sun is enormous. Only a tiny fraction of it reaches the Earth, but it is tens of thousands of times more than all the power plants in the world could produce. Almost all of this energy is emitted by the photosphere.

Observations of the surface of the Sun made it possible to establish that it rotates around its axis and makes a full revolution in 25.4 Earth days. The average distance from the Earth to the Sun is 149.5 million km. The Sun, together with the Earth and the entire solar system, moves in cosmic space towards the constellation Lyra at a speed of 20 km/sec.

Light from the Sun reaches the Earth in 8 minutes 18 seconds. The sun plays a very important role in the life of our planet - it is the source of light and heat on Earth.

9 large planets with their satellites, many small planets and other celestial bodies revolve around the Sun. They all make up a system of celestial bodies called the Solar System. The diameter of this system is about 12 billion km.

PLANETS OF THE SOLAR SYSTEM

Planets are celestial bodies orbiting a star. They, unlike stars, do not emit light and heat, but shine with the reflected light of the star to which they belong. The shape of the planets is close to spherical. Currently, only the planets of the solar system are reliably known, but it is very likely that other stars also have planets.

All planets of the Solar System are divided into two groups: internal, or terrestrial (Mercury, Venus, Earth, Mars) and external, or Jupiterian (Jupiter, Saturn, Uranus, Neptune). The planet Pluto has not yet been explored and cannot be classified into any of the groups.

The planets of the inner group have less mass, smaller sizes, higher density, and they rotate around the Sun more slowly than the planets of the outer group.

The planet closest to the Sun is Mercury. It is 2.5 times closer to the Sun than our Earth. Mercury travels its entire orbit in 88 days. The planet rotates slowly around its axis, completing one revolution every 158.7 Earth days. The diameter of the planet is 4880 km.

From Earth, Mercury is visible to the naked eye in the rays of morning or evening dawn in the form of a luminous point, and through a telescope it can be seen in the shape of a sickle or an incomplete circle. The sun always illuminates only one side of the planet, so it is always day on it and the temperature there reaches +300°C, while on the other side it is always night and the temperature there drops to -70°C. The atmosphere of Mercury is very rarefied and consists of helium with an admixture of argon, neon, and signs of carbon dioxide have been found there. There is no water on Mercury; the interior of the planet contains many heavy elements. Mercury has no satellites.

Venus is the planet closest to Earth in the solar system. Its diameter is 12,400 km, distance from the Sun is 108 million km. It completes a full revolution around the Sun in 243 Earth days. The shortest distance from Earth to Venus is 39 million km.

The atmosphere of Venus consists of carbon dioxide (97%), nitrogen (2%), water vapor, oxygen is contained only in the form of impurities (0.01%), and there are poisonous gases. The dense atmosphere prevents the planet from cooling at night and heating up during the day, so the temperature at different times of the day on Venus is almost the same and amounts to 500°C. The pressure is 100 times higher than the pressure at the surface of the Earth. Scientific studies have shown the absence of a magnetic field and radiation belts on Venus, as well as the absence of satellites.

Earth is the third planet in the solar system. It has a shape close to spherical. The radius of a sphere equal in size to the Earth is 6371 km. The Earth revolves around the Sun and rotates on its axis. There is one natural satellite orbiting the Earth - the Moon. The moon is located at a distance of 384.4 thousand km from the surface of our planet. The periods of its revolution around the Earth and around its own axis coincide, so the Moon only faces the Earth, and the other side is not visible from the Earth. The Moon does not have an atmosphere, so the side facing the Sun has a high temperature, and the opposite, darkened side has a very low temperature. The surface of the Moon is heterogeneous. The plains and mountain ranges on the Moon are intersected by cracks.

Mars is the fourth planet of the solar system - the distance to the Sun is measured in the range from 200 to 250 million km. The planet's orbital period around the Sun is almost twice as long as the Earth's orbital period - 1 year 11 months. Marsoi and Earth have a lot in common. There are warm zones on Mars, and the seasons change. The average temperature of Mars is 30°C. The atmosphere of Mars is very rarefied and contains nitrogen (72%), carbon dioxide (16%), argon (8%). No oxygen was found in it, and very little water vapor. The surface of Mars is flat, with “continents” visible on it. and ";sea";. "Continents" - vast deserts, and there are different opinions regarding the Martian seas: they believe that these are low-lying spaces, but it is possible that these are places where bedrock emerges. Mars has two small moons: Phobos and Deimos, with Phobos orbiting Mars at a faster speed than Deimos and the planet itself.

Jupiter is the largest planet in the solar system. This planet is twice as massive as all the other planets combined. The diameter of Jupiter is 143 thousand km. Jupiter is 1300 times larger than Earth in volume. Jupiter rotates around its axis in 10 hours, and makes a full revolution around the Sun in 12 Earth years. It is still unknown what kind of surface it has - solid or liquid; only the gaseous shell of the planet is observed. Jupiter's atmosphere consists of hydrogen, helium, methane and other gases. It has 14 satellites.

Saturn - the sixth planet of the solar system - is in many ways similar to Jupiter. It is located almost twice as far from the Sun as Jupiter. Saturn also belongs to the giant planets. The diameter of its equator is 120 thousand km. It makes one revolution around the Sun in 29.5 Earth years, and around its axis in 10 hours 14 minutes. Saturn, like other giant planets, consists of hydrogen and helium gases, which are in a solid state due to high pressure. Methane and ammonia have also been discovered in Saturn's atmosphere. The temperature on the planet is low, approximately -145°C. A special feature of Saturn are the flat luminous rings that encircle the planet around the equator, without touching its surface. Saturn has 10 satellites.

Uranus is located in seventh place in the solar system. It is located at a distance from the Sun twice as great as Saturn. The period of complete revolution of Uranus around the Sun is more than 84 Earth years. It differs from other planets in that it moves as if lying on its side: the plane of its equator is perpendicular to the plane of its orbit. Uranus rotates around its axis in 10 hours 49 minutes, but in the opposite direction compared to other planets. Thanks to this "lying" position when orbiting the Sun, the planet has a long polar day and polar night - approximately 42 Earth years each. Only in a narrow strip along the equator does the Sun come out every 10 hours. The temperature on Uranus is low, - 220°C. It has been established that the atmosphere of Uranus includes hydrogen, methane and helium. Uranus has 5 satellites.

Neptune is the eighth planet of the solar system. It is even further away from the Sun. The time of its revolution around the Sun is almost 165 Earth years, and the period of rotation of the planet around its own axis is 15.8 hours. The planet's atmosphere, like that of Neptune's other neighbors, consists of hydrogen, methane and helium. Neptune has two satellites. The distance of this planet from Earth significantly limits the possibility of its exploration.

Pluto is the most distant planet in the solar system. Its distance from the Sun is 5.9 billion km. The period of revolution around the Sun is 250 Earth years, and this planet rotates around its axis about 6.4 Earth days per revolution. The presence of an atmosphere at Pluto has not been proven. In 1978, a satellite of Pluto was discovered, relatively bright, but located very close to the planet. Pluto is still very little studied. It was opened only in 1930.

EARTH MAGNETISM

The Earth has a magnetic field, which is clearly manifested in its effect on the magnetic needle. Freely suspended in space, it is installed anywhere in the direction of magnetic lines of force converging at the magnetic poles.

The Earth's magnetic poles do not coincide with the geographic ones and slowly change their position. Currently, they are located in northern Canada and Antarctica. The lines of force running from one pole to the other are called magnetic meridians. They do not coincide with geographical ones in direction, and the magnetic needle does not strictly indicate the north-south direction. The angle between the magnetic and geographic meridians is called magnetic declination. The angle formed by a magnetic needle with a horizontal plane is called magnetic inclination.

There are constant and alternating magnetic fields of the Earth. The constant field is due to the magnetism of the planet itself. An idea of ​​the state of the Earth’s constant magnetic field is given by magnetic maps, which are compiled once every five years, since the magnetic declination and inclination change very slowly. Phenomena such as magnetic anomalies and magnetic storms occur in the Earth's magnetic field.

The Earth's magnetic field extends upward to an altitude of approximately 90 thousand km. Up to an altitude of 44 thousand km. The strength of the Earth's magnetic field weakens. It either deflects or captures charged particles flying from the Sun or formed when cosmic rays interact with atoms or air molecules. The entire region of near-Earth space in which charged particles are located is called the magnetosphere. The distribution of the magnetic field over the earth's surface is constantly changing. It is slowly moving to the west. The position of the magnetic poles also changes. Now their coordinates are 77° N. and 102°W, 65°S. and 139° E.

Magnetism is of great practical importance. Using a magnetic needle, the direction along the sides of the horizon is determined. The connection of magnetic elements with geological structures serves as the basis for magnetic methods of mineral exploration.

HYPOTHESES OF THE ORIGIN OF THE EARTH AND SOLAR SYSTEM

The answer to the question of the origin of the Earth has always depended on the level of knowledge of people. Initially, there were naive legends about the divine power that created the world, then in the works of scientists the Earth acquired the shape of a ball, which, as was then imagined, was the center of the Universe, around which not only the Moon, but also the Sun and other stars revolved. In the 16th century, in connection with the emergence of the teachings of N. Copernicus, the earth became one of the planets revolving around the Sun. This was the first step towards a scientific solution to the question of the origin of the Earth. Currently, there are several hypotheses that explain the origin of the Universe and the position of the Earth in the solar system.

KANT-LAPLACE HYPOTHESIS

This is the first serious attempt to create a picture of the origin of the solar system from a scientific point of view. It is associated with the names of the French mathematician Pierre Laplace and the German philosopher Immanuel Kant, who worked at the end of the 18th century. They believed that the progenitor of the Solar system was a hot gas-dust nebula, which slowly rotated around a dense core located in the center of this nebula. Under the influence of the forces of mutual attraction, the nebula began to flatten at the poles and turn into a disk, the density of which was not uniform, which contributed to its separation into separate gas rings. Later, each gas ring began to condense and turn into a single gas clump that rotated around its axis, then these clumps cooled and gradually turned into planets, and the rings around them into satellites. The main part of the nebula remained in the center and has not yet cooled down (it became the Sun). In the 19th century, the shortcomings of this theory were discovered, since it could not be used to explain new scientific data, but its value is still great.

HYPOTHESIS OF O.YU.SHMIDT

O.Yu. Schmidt, a geophysicist who worked in the first half of the 20th century, had a different idea of ​​the emergence and development of the Solar system. According to his hypothesis, the Sun, traveling through the Galaxy, passed through a gas-dust cloud and carried part of it along with it. Subsequently, the solid particles of the cloud were crushed and turned into initially cold planets. The heating of these planets occurred later as a result of compression, as well as the influx of solar energy. The heating of the Earth was accompanied by a massive outpouring of lava onto the surface of the planet as a result of active volcanic activity. Thanks to this outpouring, the first solid covers of the Earth were formed. Gases were released from the lavas. They formed a primary atmosphere that did not yet contain oxygen, since there were no plants on the planet. More than half the volume of the primary atmosphere consisted of water vapor, and its temperature exceeded 100°C. With further cooling of the atmosphere, condensation of water vapor occurred, which led to rainfall and the creation of the primary ocean. This happened about 4.5-5 billion years ago. Later, the formation of land began, which is thickened, relatively light parts of the lithospheric plate, rising above ocean level.

F.HOYLE'S HYPOTHESIS

According to the hypothesis of Fred Hoyle, an English astrophysicist who worked in the 20th century, the Sun had a twin star that exploded. Most of the fragments were carried away into outer space, while a smaller part remained in the orbit of the Sun and formed planets.

No matter how different hypotheses interpret the origin of the solar system and the family connections between the Earth and the Sun, they are unanimous in that all the planets were formed from a single clump of matter. Then the fate of each of them was decided in its own way. The Earth had to travel about 5 billion years, experiencing a series of amazing transformations, before taking its modern form.

Occupying a middle position among the planets in size and weight, the Earth at the same time turned out to be unique as a refuge for future life. ";Freed"; from some of the gases due to their supervolatility, it retained them just enough to create an air screen capable of protecting its inhabitants from the destructive influence of cosmic rays and numerous meteorites that constantly burn up in the upper layers of the atmosphere.

Analyzing all the available hypotheses about the origin of the Earth and the Solar System, it is necessary to note that there is not yet a hypothesis that does not have serious shortcomings and answers all questions about the origin of the Earth and other planets of the Solar System. But it can be considered established that the Sun and the planets were formed simultaneously from a single material medium, from a single gas-dust cloud.

SHAPE AND SIZE OF THE EARTH

Geodetic measurements have shown that the shape of the Earth is complex and is not a typical sphere. This can be proven by comparing the equatorial and polar radii. The distance from the center of the planet to its equator is called the semi-major axis and is 6,378,245 m. The distance from the center of the planet to its pole is called the semi-minor axis, it is 6,356,863 meters. It follows from this that the semimajor axis is larger than the minor axis by about 22 km. Consequently, our planet does not have the correct proportions, and its shape is not similar to any of the known geometric figures; it is not a regular ball. Under the influence of centrifugal force arising from the rotation of the Earth around its axis, it is slightly flattened at the poles. Therefore, when constructing maps, the Earth is taken as an ellipsoid of revolution, which is understood as a body formed when the ellipse rotates around a short axis. The true shape of the Earth is considered to be the geoid. A geoid is a body bounded by the surface of a calm ocean, and on land by the same surface, mentally extended under continents and islands. The deviation of this surface from the ellipsoid does not exceed tens of meters. The actual land surface deviates upward by 8848 m (Mount Chomolungma in the Himalayas); the maximum deviation of the ocean floor from its level is 11,022 m (Mariana Trench in the Pacific Ocean). The total surface area of ​​the globe is 510 million square meters. km. The length of the equator is 40,000 km.

A star is a massive ball of gas that emits light and heat as a result of thermonuclear fusion occurring in its depths. For example, a series of reactions occurs on the Sun, which is called a cycle. An important characteristic of any star is such a quantity as luminosity (that is, the power of emitted energy). Other stars also illuminate the Earth, but due to the enormous distance from them, this illumination is negligible compared to the illumination provided by the Sun.

For example, according to measurements, the North Star creates illumination on the Earth's surface equal to 4.28×10–9 W/m2. This is about 370 billion times less than the illumination produced by the Sun. However, it should be noted that Polaris is approximately 132 parsecs away from us. Now let's calculate the luminosity of the North Star in the already known way:

Such measurements have shown that there are stars whose luminosity is tens and hundreds of thousands of times greater or less than the luminosity of the Sun. It was also found that the surface temperature of a star determines its visible light and the presence of spectral absorption lines of certain chemical elements in its spectrum. In this regard, in 1910, Einar Hertzsprung and, independently of him, Henry Russell proposed classifying stars using a special diagram.

As you can see, this diagram breaks stars into several spectral classes with corresponding luminosities and surface temperatures. In this diagram, the luminosity of stars is expressed in solar luminosity units. So, the diagram shows such groups of stars as white dwarfs, the main sequence, red giants and supergiants. Let's start with the main sequence, since the Sun belongs to this group of stars. Main sequence stars include those stars whose energy source is the thermonuclear reaction of helium fusion from hydrogen. In this regard, their temperature and luminosity are determined by mass. The luminosity of a main sequence star can be calculated using the simple formula

Red giants are red stars whose sizes are tens of times larger than the size of the Sun, and whose luminosities can be hundreds and even thousands of times greater than the luminosity of the Sun.

As for supergiants, the luminosity of these stars is hundreds of thousands of times greater than the luminosity of the Sun, and the sizes of supergiants are hundreds of times greater than the size of the Sun.

A distinctive feature of red giants and supergiants is that nuclear reactions no longer occur in the center itself, but in thin layers around a very dense central core. In the outermost layers of the core, where the temperature is comparable to the temperature in the center of the Sun, the same thermonuclear reaction occurs: helium is synthesized from hydrogen. But in deeper layers, increasingly heavier elements are formed. First it is carbon, then oxygen. Eventually, iron can form in very massive stars.

The sizes of white dwarfs are comparable to the size of the Earth, and their luminosity is hundreds of thousands of times less than the luminosity of the Sun. Despite this, white dwarfs have a fairly high density (~ 108 kg/m3). In fact, the name “white dwarfs” does not mean that all stars in this group are white. It’s just that stars of this particular color were discovered much earlier than stars of other colors belonging to the same group.

Let's summarize everything that was said in a general table. There are seven main spectral classes - O, B, A, F, G, K and M. This table shows examples of stars in each class.

For example, the star Bellatrix is ​​located in the constellation Orion and is one of the 26 brightest stars in the sky. In ancient times, Bellatrix was one of the navigation stars. Bellatrix is ​​class O and is blue in color. But Betelgeuse is red in color and belongs to class M. This star is a supergiant (it is about 1000 times larger than the Sun), and its luminosity is approximately 90 thousand times higher than the luminosity of the Sun.

But in addition to all the listed classes and groups of stars, there are other objects, perhaps even more interesting. For example, such objects include neutron stars. A neutron star, according to modern concepts, is formed when the energy inside the star runs out. Due to gravitational compression, the core of a neutron star becomes superdense.

At the same time, some neutron stars rotate around their axis at enormous speed. Such neutron stars are called pulsars. Pulsars emit high-frequency pulses of radio emission that so excited astronomers in the late 1960s. The fact is that due to the enormous rotation speed of pulsars (and at the equator this is about several tens of kilometers per second), the pulses were repeated with high stability, and the periods of these pulses were measured in seconds and sometimes in milliseconds. This made scientists think that they were dealing with some signals that some extraterrestrial civilizations were sending to Earth in order to establish contact. However, in the end, it was possible to prove that the problem is in the rotation of neutron stars. In addition, some neutron stars have a colossal magnetic field (on the order of ten or even one hundred billion tesla, while the Earth's magnetic field is ~ 10 μT). Such neutron stars are called magnetars. Magnetars are still very little studied, but it is known that they are the cause of many powerful bursts of X-ray and g-ray radiation.

All types of neutron stars have a radius that is measured in only a few tens of kilometers, but at the same time they have a colossal density - ~ 1017 kg/m3. Such densities are also characteristic of other rather strange objects in the universe - black holes. The second escape velocity of black holes exceeds the speed of light. Thus, even photons cannot escape the gravitational influence of a black hole, which is why black holes remain invisible. Any black hole is characterized by such a value as its event horizon (sometimes the term “gravitational radius” or “Schwarzchild radius” is used). Once at this distance from the black hole, no body can escape its gravitational influence, and therefore will fall into the black hole.

Black holes, like neutron stars, have a radius measured in tens of kilometers, but their mass is at least three solar masses.

However, black holes can grow by repeatedly absorbing matter. Such black holes have a mass millions and even billions of times greater than the mass of the Sun. These objects, as a rule, are located in the center of galaxies (and according to one hypothesis, they are the cause of the formation of galaxies). For example, at the center of our Milky Way galaxy is a supermassive black hole with a mass of about four billion solar masses. Scientists estimate that the Sun is about 27,000 light years away from this black hole.

Generally speaking, certain classes or groups of stars that were considered belong to certain stages of the star’s evolution.

On a dark, cloudless night, you can see thousands of twinkling stars in the sky. Stars are huge, hot balls of gas, just like our Sun, but they shine much weaker than the Sun because they are located much further from us. Even from the stars closest to us, light travels for years. We look at the stars through a layer of air that is constantly in motion, so the light of the stars is not constant - it seems to us that they are flickering. With the naked eye, without a telescope, about 5,780 stars can be seen. On a cloudless, dark night, about 2,500 stars can be seen simultaneously from any place on Earth. Astronomers use the word "nebula" to describe hazy spots in the sky that are not stars. These glowing clouds of gas and dust either emit their own light or reflect the light of nearby stars. The Pleiades, or Seven Sisters, are one of the easiest star clusters to observe in the night sky. It contains six bright stars, and much more can be seen through a telescope. In 1987, a supernova exploded in a galaxy called the Large Magellanic Cloud. This galaxy is located very close to ours and is visible from the countries of the Southern Hemisphere. In 1997, scientists discovered a new star in our Galaxy, which is larger than all the stars known so far. It is more than 100 thousand times larger than our Sun. If this star was in the center of our solar system, it would have swallowed up all the planets right up to Mars. This star cannot be seen from Earth: it is obscured by gas and dust.

Our Sun is the most ordinary star among millions of other stars. At the center of all stars, particles of hydrogen gas collide with each other and release enormous amounts of nuclear energy. This process is called nuclear fusion. Thanks to him, the stars shine so brightly. Stars rush through outer space at colossal speeds, but they seem motionless to us - this is also a consequence of their incredible distance from us. The groups that stars form in the sky remain unchanged. These groups, forming clear patterns in any part of the sky, are called constellations. Some bright stars appear almost red, while others appear diamond white or bluish. Our Sun is a yellow star. Stars emit different colors of light because some are much hotter than others. The surface temperature of the Sun is about 6000C. Red stars are cooler, while white-blue stars are hotter: their temperatures reach 10,000C or more.

A star is born:

Stars arise constantly. At first they are just clouds of gas and dust in outer space. As soon as such clumps of matter begin to gather together, the resulting force of attraction enhances this process. At the center of such formation, the gas becomes hotter and denser, and eventually its temperature and pressure increase so much that the process of nuclear fusion begins (from the Greek word synthesis, meaning “compound”, “combination”, “composition”). Its beginning marks the birth of a new star. Often many stars appear close to each other, in a giant cloud. Then they form a family of stars, which is called a cluster.

Giants and dwarfs:

Astronomers have calculated that stars vary greatly in size. The largest stars are called giants, and the smallest are called dwarfs. The sun is a small star, but there are even smaller stars. The diameter of the so-called white dwarfs is more than a hundred times smaller than the diameter of our Sun. In contrast to dwarfs, there are stars of truly colossal size, the so-called red giants. They are hundreds of times larger than our Sun. The bright red star Betelgeuse from the constellation Orion is 500 times larger than the Sun.

Double stars:

Sun - single star, but most stars are double. The force of gravity holds them together, and they revolve one after the other, just as the planets revolve around the Sun. Sometimes one of a pair of stars passes directly in front of the other (as seen from Earth), thereby blocking some of the light emitted by both stars, causing the binary star to briefly appear less bright. The brightest star in the sky - Sirius - is double.

Death of a star:

Stars don't live forever. Eventually the hydrogen fuel in their cores runs out. When this happens, the star changes and gradually dies. Old stars swell, turning into red giants. They can disperse some of their gas into space in the form of a large misty ring. Astronomers observe such stars in the centers of shells of hot gas. The age of the Sun is already about 5 billion years. It is estimated that this is approximately the middle of his life's journey. In the distant future, the Sun will turn into a red giant and absorb the planets closest to it. After this, it will begin to shrink and will shrink and become denser until all its matter is compressed into a ball the size of the Earth. Then the Sun will become a white dwarf and quietly fade away.

Stars significantly more massive than the Sun, end their existence in a grand explosion, which is called a supernova or simply supernova. When a supernova occurs, it emits a million times more light than the Sun within a few days. Over the past 1000 years, only three supernovae have been reliably recorded in our Galaxy.

Pulsars:

When a supernova occurs, the inner part of the stellar matter remaining after the explosion turns into a star emitting radio waves, the so-called pulsar. Pulsars emit radio signals in a series of fast, short radio pulses. They were first discovered in 1967 by radio astronomers at the University of Cambridge (England). The most famous pulsar is located in the central part of the Crab Nebula in the constellation Taurus. The Crab Nebula Pulsar emits 30 radio pulses every second.

Stars

The stars are distant suns. Stars are huge, hot suns, but so distant from us compared to the planets of the solar system that, although they shine millions of times brighter, their light appears relatively dim to us.

When looking at the clear night sky, the lines of M.V. come to mind. Lomonosov:

An abyss has opened, full of stars,

The stars have no number, the abyss has no bottom.

About 6,000 stars can be seen in the night sky with naked gas. As the brightness of stars decreases, their number increases, and even simple counting of them becomes difficult. All stars brighter than 11th magnitude were counted “piece by piece” and entered into astronomical catalogs. There are about a million of them. In total, about two billion stars are accessible to our observation. The total number of stars in the Universe is estimated at 10 22.

The sizes of stars, their structure, chemical composition, mass, temperature, luminosity, etc. vary. The largest stars (supergiants) exceed the size of the Sun by tens and hundreds of times. Dwarf stars are the size of Earth or smaller. The maximum mass of stars is approximately 60 solar masses.

The distances to the stars are also very different. The light from the stars of some distant star systems travels hundreds of millions of light years to us. The closest star to us can be considered the first magnitude star α-Centauri, which is not visible from the territory of Russia. It is located 4 light years from Earth. A courier train, traveling non-stop at a speed of 100 km/h, would reach it in 40 million years!

The bulk (98-99%) of visible matter in the part of the Universe known to us is concentrated in stars. Stars are powerful sources of energy. In particular, life on Earth owes its existence to the radiation energy of the Sun. The matter of stars is plasma, i.e. is in a different state than matter in our usual terrestrial conditions. (Plasma is the fourth (along with solid, liquid, gaseous) state of matter, which is an ionized gas in which positive (ions) and negative charges (electrons) neutralize each other on average.) Therefore, strictly speaking, a star is not just a gas ball, but a plasma ball. At the later stages of star development, stellar matter transforms into a state of degenerate gas (in which the quantum-mechanical influence of particles on each other significantly affects its physical properties - pressure, heat capacity, etc.), and sometimes neutron matter (pulsars - neutron stars, bursters - sources of X-ray radiation, etc.).

Stars in outer space are distributed unevenly. They form star systems: multiple stars (double, triple, etc.); star clusters (from several tens of stars to millions); galaxies are grandiose star systems (our Galaxy, for example, contains about 150-200 billion stars).

In our Galaxy, stellar density is also very uneven. It is highest in the region of the galactic core. Here it is 20 thousand times higher than the average stellar density in the vicinity of the Sun.

Most stars are in a stationary state, i.e. no changes in their physical characteristics are observed. This corresponds to a state of equilibrium. However, there are also stars whose properties change in a visible way. They are called variable stars And non-stationary stars. Variability and nonstationarity are manifestations of the instability of the star's equilibrium state. Variable stars of some types change their state in a regular or irregular manner. It should also be noted new stars, in which outbreaks occur continuously or from time to time. During flashes (explosions) supernovas The matter of stars in some cases can be completely scattered in space.

The high luminosity of stars, maintained for a long time, indicates the release of enormous amounts of energy in them. Modern physics points to two possible sources of energy - gravitational compression, leading to the release of gravitational energy, and thermonuclear reactions, as a result of which the nuclei of heavier elements are synthesized from the nuclei of light elements and a large amount of energy is released.

Calculations show that the energy of gravitational compression would be sufficient to maintain the luminosity of the Sun for only 30 million years. But from geological and other data it follows that the Sun's luminosity has remained approximately constant for billions of years. Gravitational compression can serve as a source of energy only for very young stars. On the other hand, thermonuclear reactions proceed at a sufficient speed only at temperatures thousands of times higher than the surface temperature of stars. Thus, for the Sun, the temperature at which thermonuclear reactions can release the required amount of energy is, according to various calculations, from 12 to 15 million K. Such a colossal temperature is achieved as a result of gravitational compression, which “ignites” the thermonuclear reaction. Thus, our Sun is currently a slow-burning hydrogen bomb.

Some (but hardly most) stars are thought to have their own planetary systems, similar to our solar system.

11.4.2. Evolution of stars: stars from their “birth” to “death”

Star formation process. The evolution of stars is the change over time in the physical characteristics, internal structure and chemical composition of stars. The modern theory of stellar evolution is able to explain the general course of stellar development in satisfactory agreement with observational data.

The course of a star's evolution depends on its mass and initial chemical composition, which, in turn, depends on the time when the star was formed and on its position in the Galaxy at the time of formation. The stars of the first generation were formed from matter, the composition of which was determined by cosmological conditions (almost 70% hydrogen, 30% helium and an insignificant admixture of deuterium and lithium). During the evolution of the first generation of stars, heavy elements (following helium on the periodic table) were formed, which were ejected into interstellar space as a result of the outflow of matter from stars or during stellar explosions. Stars of subsequent generations were formed from matter containing 3-4% heavy elements.

The “birth” of a star is the formation of a hydrostatically equilibrium object, the radiation of which is supported by its own energy sources. The “death” of a star is an irreversible imbalance leading to the destruction of the star or its catastrophic compression.

The process of star formation continues continuously and is still happening today.. Stars are formed as a result of gravitational condensation of matter in the interstellar medium. Young stars are those that are still in the stage of initial gravitational compression. The temperature in the center of such stars is insufficient for nuclear reactions to occur, and the glow occurs only due to the conversion of gravitational energy into heat.

Gravitational compression is the first stage in the evolution of stars. It leads to heating of the central zone of the star to the “switching on” temperature of the thermonuclear reaction (approximately 10-15 million K) - the transformation of hydrogen into helium (hydrogen nuclei, i.e. protons, form helium nuclei). This transformation is accompanied by a large release of energy.

Star as a self-regulating system. The energy sources of most stars are hydrogen thermonuclear reactions in the central zone. Hydrogen is the main component of cosmic matter and the most important type of nuclear fuel in stars. Its reserves in stars are so large that nuclear reactions can take place over billions of years. At the same time, until all the hydrogen in the central zone burns out, the properties of the star change little.

In the depths of stars, at temperatures of more than 10 million K and enormous densities, gas has a pressure of billions of atmospheres. Under these conditions, the star can be in a stationary state only due to the fact that in each of its layers the internal gas pressure is balanced by the action of gravitational forces. This state is called hydrostatic equilibrium. Hence, a stationary star is a plasma ball in a state of hydrostatic equilibrium. If the temperature inside the star increases for any reason, then the star should inflate, as the pressure in its depths increases.

The stationary state of the star is also characterized by thermal equilibrium. Thermal equilibrium means that the processes of energy release in the interior of stars, the processes of heat removal of energy from the interior to the surface, and the processes of energy emission from the surface must be balanced. If the heat removal exceeds the heat release, the star will begin to shrink and heat up. This will lead to the acceleration of nuclear reactions, and the thermal balance will be restored again. A star is a finely balanced “organism”; it turns out to be a self-regulating system. Moreover, the larger the star, the faster it exhausts its energy reserve.

After hydrogen burns out, a helium core forms in the central zone of the star. Hydrogen thermonuclear reactions continue to occur, but only in a thin layer near the surface of this core. Nuclear reactions move to the periphery of the star. The burnt-out core begins to shrink, and the outer shell begins to expand. The star takes on a heterogeneous structure. The shell swells to colossal sizes, the external temperature becomes low, and the star enters the stage red giant. From this moment on, the star's life begins to decline.

It is believed that a star like our Sun could grow so large that it would fill the orbit of Mercury. True, our Sun will become a red giant in about 8 billion years. So the inhabitants of the Earth have no particular reason to worry. After all, the Earth itself was formed only 5 billion years ago.

From red giant to white and black dwarfs. The red giant is characterized by low external temperatures, but very high internal temperatures. As it increases, increasingly heavier nuclei are included in thermonuclear reactions. At this stage (at temperatures above 150 million K) during nuclear reactions, synthesis of chemical elements. As a result of increasing pressure, pulsations and other processes, the red giant continuously loses matter, which is ejected into interstellar space. When the internal thermonuclear energy sources are completely depleted, the further fate of the star depends on its mass.

With a mass of less than 1.4 solar masses, the star enters a stationary state with a very high density (hundreds of tons per 1 cm3). Such stars are called white dwarfs. Here the electrons form a degenerate gas (due to strong compression, the atoms are so densely packed that the electron shells begin to penetrate one another), the pressure of which balances the gravitational forces. The star's thermal reserves are gradually depleted, and the star slowly cools, which is accompanied by ejections of the star's envelope. Young white dwarfs surrounded by shell remnants are observed as planetary nebulae. The white dwarf matures inside the red giant and is born when the red giant sheds its surface layers, forming a planetary nebula.

When the star's energy runs out, the star changes color from white to yellow to red; finally, it will stop radiating and begin a continuous journey in the vastness of outer space in the form of a small, dark, lifeless object. This is how a white dwarf slowly turns into black dwarf- a dead, cold star, the size of which is usually smaller than the size of the Earth, and the mass is comparable to the sun. The density of such a star is billions of times higher than the density of water. This is how most stars end their existence.

Supernovae. With a mass of more than 1.4 solar masses, the stationary state of a star without internal energy sources becomes impossible, since the pressure cannot balance the gravitational force. Theoretically, the end result of the evolution of such stars should be gravitational collapse - unlimited fall of matter towards the center. In the case when the repulsion of particles and other reasons still stop the collapse, a powerful explosion occurs - a flash supernova with the ejection of a significant part of the star’s matter into the surrounding space with the formation gas nebulae.

Supernova explosions were recorded in 1054, 1572, 1604. Chinese chroniclers wrote about the event of July 4, 1054 as follows: “In the first year of the Chi-ho period, on the fifth Moon, on the day of Chi-Chu, a guest star appeared southeast of the star Tien-Kuan and disappeared more than a year later " And another chronicle recorded: “She was visible during the day, like Venus, rays of light emanated from her in all directions, and her color was reddish-white. So she was visible for 23 days.” Similar sparse records were made by Arab and Japanese eyewitnesses. Already in our time, it was found that this supernova left behind the Crab Nebula, which is a powerful source of radio emission. As we have already noted (see 6.1), the supernova explosion in 1572 in the constellation Cassiopeia was noted in Europe, studied, and widespread public interest in it played an important role in the expansion of astronomical research and the subsequent establishment of heliocentrism. In 1885, the appearance of a supernova was noted in the Andromeda nebula. Its brilliance exceeded the brilliance of the entire Galaxy and turned out to be 4 billion times more intense than the brilliance of the Sun.

Systematic research made it possible by 1980 to discover over 500 supernova explosions. Since the invention of the telescope, not a single supernova explosion has been observed in our star system - the Galaxy. Astronomers have so far observed them only in other incredibly distant star systems, so distant that even with the most powerful telescope it is impossible to see a star like our Sun in them.

A supernova explosion is a gigantic explosion of an old star caused by the sudden collapse of its core, which is accompanied by the short-term emission of a huge amount of neutrinos. Possessing only a weak force, these neutrinos nevertheless scatter the outer layers of the star into space and form wisps of clouds of expanding gas. During a supernova explosion, monstrous energy is released (about 10 52 erg). Supernova explosions are of fundamental importance for the exchange of matter between stars and the interstellar medium, for the distribution of chemical elements in the Universe, and also for the production of primary cosmic rays.

Astrophysicists have calculated that with a period of 10 million years, supernovae erupt in our Galaxy, in the immediate vicinity of the Sun. Doses of cosmic radiation can exceed normal for the Earth by 7 thousand times! This is fraught with serious mutations of living organisms on our planet. This explains, in particular, the sudden death of dinosaurs.

Neutron stars. Part of the mass of an exploding supernova may remain in the form of a superdense body - neutron star or black hole.

New objects discovered in 1967 - pulsars - are identified with theoretically predicted neutron stars. The density of a neutron star is very high, higher than the density of atomic nuclei - 10 15 g/cm3. The temperature of such a star is about 1 billion degrees. But neutron stars cool very quickly, and their luminosity weakens. But they intensely emit radio waves in a narrow cone in the direction of the magnetic axis. Stars in which the magnetic axis does not coincide with the axis of rotation are characterized by radio emission in the form of repeating pulses. This is why neutron stars are called pulsars. Hundreds of neutron stars have already been discovered. The extreme physical conditions in neutron stars make them unique natural laboratories, providing extensive material for studying the physics of nuclear interactions, elementary particles and the theory of gravity.

Black holes. But if the final mass of the white dwarf exceeds 2-3 solar masses, then gravitational compression directly leads to the formation black hole.

A black hole is a region of space in which the gravitational field is so strong that the second cosmic velocity (parabolic velocity) for bodies located in this region must exceed the speed of light, i.e. Nothing can fly out of a black hole - neither radiation nor particles, because in nature nothing can move at a speed greater than the speed of light. The boundary of the region beyond which light does not escape is called horizon of a black hole.

In order for the gravitational field to be able to “lock in” radiation and matter, the mass of the star creating this field must be compressed to a volume whose radius is less than the gravitational radius r = 2GM/C 2, Where G- gravitational constant; With- speed of light; M- mass of the star. The gravitational radius is extremely small even for large masses (for example, for the Sun, r ≈ 3 km). A star with a mass equal to the mass of the Sun will turn from an ordinary star into a black hole in just a few seconds, and if the mass is equal to the mass of a billion stars, then this process will take several days.

The properties of a black hole are unusual. Of particular interest is the possibility of gravitational capture by a black hole of bodies arriving from infinity. If the speed of a body far from a black hole is much less than light speed and the trajectory of its motion approaches close to a circle with R = 2r, then the body will make many revolutions around the black hole before it flies off into space again. If the body comes close to the indicated circle, then its orbit will wrap around the circle without limit, the body will be gravitationally captured by the black hole and will never fly into space again. If the body flies even closer to the black hole, then after several revolutions, or without even having time to make a single revolution, it will fall into the black hole.

Let's imagine two observers: one on the surface of a collapsing star, and the other far from it. Suppose that an observer on a collapsing star sends (radio or light) signals at regular intervals to a second observer, informing him of what is happening. As the first observer approaches the gravitational radius, the signals he sends at regular intervals will reach the other observer at increasingly longer intervals. If the first observer transmits the last signal just before the star reaches the gravitational radius, then the signal will take an almost infinite time to arrive at the distant observer; if the observer sent a signal after it had reached the gravitational radius, the observer in the distance would never receive it because the signal would never leave the star. When photons or particles go beyond the gravitational radius, they simply disappear. Only in the outer region directly at the gravitational radius can they be visible, and it seems as if they are hiding behind a curtain and no longer appear.

In a black hole, space and time are interconnected in an unusual way. For an observer inside a black hole, the direction in which time increases is the direction in which the radius decreases. Once inside a black hole, the observer cannot return to the surface. He can't even stop in the place where he finds himself. He “falls into a region of infinite density, where time ends” *.

* Hawking S. From the big bang to black holes. A Brief History of Time. M., 1990. P. 79.

The study of the properties of black holes (Ya.B. Zeldovich, S. Hawking, etc.) shows that in some cases they can “evaporate”. This “mechanism” is due to the fact that in the strong gravitational field of a black hole, the vacuum (physical fields in the lowest energy state) is unstable and can give birth to particles (photons, neutrinos, etc.), which, when flying away, carry away the energy of the black hole. As a result, the black hole loses energy and its mass and size decrease.

The strong gravitational field of a black hole can cause violent processes when gas falls into them. When gas falls into the gravitational field of a black hole, it forms a rapidly rotating flattened disk swirling around the latter. In this case, the colossal kinetic energy of particles accelerated by the gravity of a superdense body is partially converted into X-ray radiation, and a black hole can be detected by this radiation. One black hole has probably already been discovered in this way in the X-ray source Cygnus X-1. In general, apparently, black holes and neutron stars in our Galaxy account for about 100 million stars.

So, a black hole bends space so much that it seems to cut itself off from the Universe. She could literally disappear from the universe. The question arises “where”. Mathematical analysis provides several solutions. One of them is especially interesting. According to it, a black hole can move to another part of our Universe or even inside another Universe. Thus, an imaginary space traveler could use a black hole to travel through the space and time of our universe and even enter another universe.

What happens when a black hole moves to another part of the Universe or penetrates into another Universe? The birth of a black hole during gravitational collapse is an important indication that something unusual is happening to the geometry of space-time - its metric and topological characteristics are changing. Theoretically, the collapse should end with the formation of a singularity, i.e. should continue until the black hole reaches zero dimensions and infinite density (although in fact we should not be talking about infinity, but about some very large, but finite values). In any case, the moment of singularity is perhaps the moment of transition from our Universe to other universes or the moment of transition to other points in our Universe.

Many questions also arise around the historical fate of black holes. Black holes evaporate by emitting particles and radiation, not from the black hole itself, but from the space that is in front of the horizon of the black hole. Moreover, the smaller the black hole in size and mass, the higher its temperature and the faster it evaporates. And the sizes of black holes can vary: from the mass of a galaxy (10 44 g) to a grain of sand weighing 10 -5 g. The lifespan of a black hole is proportional to the cube of its radius. A black hole with a mass of ten solar masses will evaporate in 10 69 years. This means that massive black holes that formed in the early stages of the evolution of the Universe still exist, and perhaps even within the Solar System. They are trying to detect them using gamma-ray telescopes.

Thus, most of the matter emitting light is concentrated in stars. Each star is a similarity to our Sun, although the size of the stars, their color, composition and evolution differ significantly. Stars, along with some dust and gas (and other objects), are grouped into giant clusters called galaxies.

11.5. Islands of the Universe: galaxies

Stars: their birth, life and death [Third edition, revised] Shklovsky Joseph Samuilovich

Chapter 6 A star is a ball of gas in a state of equilibrium

Chapter 6 A star is a ball of gas in a state of equilibrium

It seems almost obvious that the vast majority of stars do not change their properties over vast periods of time. This statement is quite obvious over a period of time of at least 60 years, during which astronomers in different countries have done a great deal of work measuring the brightness, color and spectrum of many stars. Note that although some stars change their characteristics (such stars are called variables; see § 1), the changes are either strictly periodic or more or less periodic. Systematic Changes in the brightness, spectrum or color of stars are observed in very rare cases. For example, changes in the periods of pulsating Cepheid stars, although detected, are so small that it takes at least several million years for changes in the pulsation period to become significant. On the other hand, we know (see § 1) that the luminosity of Cepheids changes with a change in period. Therefore, we can conclude that for at least several million years, for such stars, their most important characteristic - the power of emitted energy - changes little. Using this example, we see that although the duration of observations is only a few tens of years (an absolutely insignificant period on a cosmic scale!), we can conclude that the properties of Cepheids are constant over immeasurably large time intervals.

But we have another opportunity to estimate the time during which the radiation power of stars remains almost unchanged. From geological data it follows that over at least the last two to three billion years, the Earth’s temperature has changed, if at all, by no more than a few tens of degrees. This follows from the continuity of the evolution of life on Earth. And if so, then over this huge period of time the Sun has never radiated either three times stronger or three times weaker than it does now. It seems that in such a long history of our star there were periods when its radiation differed significantly (but not very much) from the current level, but such eras were relatively short-lived. We have in mind the ice ages, which will be discussed in § 9. But in average solar radiation power in recent years several billion over the years she was distinguished by amazing constancy.

At the same time, the Sun is a fairly typical star. As we know (see § 1), it is a yellow dwarf of spectral class G2. There are at least several billion such stars in our Galaxy. It is also quite logical to conclude that most other main sequence stars, whose spectral types are different from the solar one, should also be very “long-lived” objects.

So, the vast majority of stars change very little over time. This, of course, does not mean that they can exist in an “unchanged form” for any length of time. On the contrary, we will show below that the age of stars, although very great, is finite. Moreover, this age is very different for different stars and is determined primarily by their mass. But even the most “short-lived” stars still hardly change their characteristics over the course of a million years. What conclusions follow from this?

Even from the simplest analysis of the spectra of stars it follows that their outer layers should be in gaseous condition. Otherwise, obviously, sharp absorption lines characteristic of a substance in a gaseous state would never be observed in these spectra. Further analysis of stellar spectra makes it possible to significantly clarify the properties of the substance of the outer layers of stars (i.e., “stellar atmospheres”), from where their radiation comes to us.

Studying the spectra of stars allows us to conclude with complete certainty that stellar atmospheres are ionized gas heated to temperatures of thousands and tens of thousands of degrees, i.e. plasma. Spectral analysis allows us to determine the chemical composition of stellar atmospheres, which in most cases is approximately the same as that of the Sun. Finally, by studying stellar spectra, one can determine density stellar atmospheres, which for different stars varies within very wide limits. So, the outer layers of stars are gas.

But these layers contain a negligible fraction of the mass of the entire star. Although directly The interiors of stars cannot be observed by optical methods due to their enormous opacity, we can now state with complete certainty that internal layers of stars are also in a gaseous state. This statement is by no means obvious. For example, dividing the mass of the Sun equal to 2

10 33 g, for its volume equal

10 33 cm 3, easy to find average density(or specific gravity) of solar matter, which will be about 1 , 4 g/cm 3, i.e. greater than the density of water. It is clear that in the central regions of the Sun the density should be significantly higher than average. Most dwarf stars have an average density greater than that of the Sun. The question naturally arises: how to reconcile our statement that the interior of the Sun and stars are in a gaseous state with such high densities of matter? The answer to this question is that the temperature of the stellar interior, as we will soon see, is very high (significantly higher than in the surface layers), which excludes the possibility of the existence of a solid or liquid phase of matter there.

So, stars are huge balls of gas. It is very significant that such a gas ball is “cemented” by the force of universal gravity, i.e. gravity. Each element of the star’s volume is subject to the force of gravitational attraction from all other elements of the star. It is this force that prevents various parts of the gas that forms the star from scattering into the surrounding space. If it were not for this force, the gas forming the star would first spread out, forming something like a dense nebula, and then would finally dissipate in the vast interstellar space surrounding the star. Let us make a very rough estimate of how long it would take for such a “spreading out” to increase the size of the star, say, 10 times. Let us assume that the “spreading” occurs at the thermal speed of hydrogen atoms (of which the star is mainly composed) at the temperature of the outer layers of the star, i.e. about 10 000 K. This speed is close to 10 km/s, i.e. 10 6 cm/s. Since the radius of the star can be taken to be close to a million kilometers (i.e. 10 11 cm), then for the “spreading” of interest to us with a tenfold increase in the size of the star, a negligibly short time will be required t = 10

10 11 / 10 6 = 10 6 seconds

10 days!

This means that if it were not for the force of gravitational attraction, the stars would scatter in the surrounding space in a negligible (by astronomical terms) time, calculated in days for dwarf stars or years for giants. This means that without the force of universal gravity there would be no stars. Acting continuously, this force strives bring closer together different elements of the star among themselves. It is very important to emphasize that the force of gravity, by its very nature, tends unlimited bring all the particles of the star closer together, i.e., in the limit, as it were, “gather the entire star into a point.” But if the particles forming the star were acted upon only force of universal gravity, then the star would begin to collapse catastrophically quickly. Let us now estimate the time during which this compression will become significant. If no force opposed gravity, the matter of the star would fall towards its center according to the laws of free fall of bodies. Consider an element of matter inside a star somewhere between its surface and the center at a distance R from the last one. This element is affected by the acceleration of gravity g =

Where G- gravitational constant (see page 15), M- mass lying inside the sphere of radius R. As you fall towards the center as M, so R will change, therefore, will change and g. We will not, however, make a big mistake in our assessment if we assume that M And R remain constant. Applying to the solution of our problem an elementary formula of mechanics that relates the path traveled during free fall R with acceleration value g, we obtain formula (3.6) already derived in § 3 of the first part

Where t- time of fall, and we put R

R

A M M

Thus, if no force were to oppose gravity, the outer layers of the star would literally collapsed if only the star would collapse catastrophically in just a fraction of an hour!

What force, continuously acting throughout the entire volume of the star, counteracts the force of gravity? Note that in every elementary volume stars, the direction of this force should be opposite, and the magnitude should be equal to the force of attraction. Otherwise, local, local imbalances would occur, leading in the very short time we have just estimated to large changes in the structure of the star.

The force opposing gravity is pressure gas[ 16 ]. The latter continuously strives expand star, “scatter” it over as large a volume as possible. Above, we already estimated how quickly the star would “dissipate” if its individual parts were not restrained by the force of gravity. So, from the simple fact that stars - balls of gas in an almost unchanged form (that is, without contracting or expanding) exist for at least millions of years, it follows that every element The substance of the star is in equilibrium under the influence of oppositely directed forces of gravity and gas pressure. This equilibrium is called “hydrostatic”. It is widespread in nature. In particular, the earth's atmosphere is in hydrostatic equilibrium under the influence of the gravitational attraction of the Earth and the pressure of the gases in it. If there were no pressure, the earth's atmosphere would very quickly “fall” to the surface of our planet. It should be emphasized that hydrostatic equilibrium in stellar atmospheres is carried out with great precision. The slightest violation of it immediately leads to the appearance of forces that change the distribution of matter in the star, after which its redistribution occurs in such a way that equilibrium is restored. Here we always talk about ordinary “normal” stars. In exceptional cases, which will be discussed in this book, an imbalance between the force of gravity and gas pressure will lead to very serious, even catastrophic consequences in the life of a star. And now we can only say that the history of the existence of any star is truly a titanic struggle between the force of gravity, which seeks to compress it indefinitely, and the force of gas pressure, which seeks to “spray” it, scatter it in the surrounding interstellar space. This “struggle” has lasted for many millions and billions of years. During these monstrously long periods of time, the forces are equal. But in the end, as we will see later, gravity will win. Such is the drama of the evolution of any star. Below we will dwell in some detail on individual stages of this drama associated with the final stages of the evolution of stars.

In the central part of a “normal” star, the weight of the substance enclosed in a column, the base area of ​​which is equal to one square centimeter, and the height is equal to the radius of the star, will be equal to the gas pressure at the base of the column. On the other hand, the mass of the pillar is equal to the force with which it is attracted to the center of the star.

We will now carry out a very simplified calculation, which, nevertheless, fully reflects the essence of the issue. Namely, let's put the mass of our pillar M 1 =

R, Where

(6.1)

Let us now estimate the value of gas pressure P in the central part of a star such as our Sun. Substituting the numerical value of the quantities on the right side of this equation, we find that P= 10 16 dynes/cm 2, or 10 billion atmospheres! This is an unheard of large value. The highest “stationary” pressure achieved in terrestrial laboratories is of the order of several million atmospheres [17].

From an elementary physics course it is known that the pressure of a gas depends on its density

and temperature T. The formula connecting all these quantities is called the “Clapeyron formula”: P = T. On the other hand, the density in the central regions of “normal” stars is, of course, greater than the average density, but not significantly greater. In this case, it directly follows from Clapeyron’s formula that the high density of stellar interiors alone is not able to provide a sufficiently high gas pressure to satisfy the condition of hydrostatic equilibrium. First of all, the gas temperature must be high enough.

The Clapeyron formula also includes the average molecular weight

The main chemical element in the atmospheres of stars is hydrogen, and there is no reason to believe that in the interiors of at least most stars the chemical composition should differ significantly from that observed in the outer layers. At the same time, since the expected temperature in the central regions of stars should be quite high, hydrogen there should be almost completely ionized, i.e., “split” into protons and electrons. Since the mass of the latter is negligible compared to protons, and the number of protons is equal to the number of electrons, the average molecular weight of this mixture should be close to 1 / 2. Then from equations (6.1) and Clapeyron’s formula it follows that the temperature in the central regions of stars is of the order of magnitude equal to

(6.2)

Magnitude

/ c maybe about 1 / 10. It depends on the structure of the stellar interior (see § 12). From formula (6.2) it follows that the temperature in the central regions of the Sun should be on the order of ten million Kelvin. More accurate calculations differ from the estimate we have now received by only 20-30%. So, the temperature in the central regions of stars is extremely high - about a thousand times higher than on their surface. Now let's discuss what the properties of a substance heated to such a high temperature should be. First of all, such a substance, despite its high density, must be in a gaseous state. This has already been discussed above. But we can now clarify this statement. At such a high temperature, the properties of gas in the interior of stars, despite its high density, will be almost indistinguishable from the properties ideal gas, i.e., a gas in which the interactions between its constituent particles (atoms, electrons, ions) are reduced to collisions. It is for an ideal gas that Clapeyron’s law is valid, which we used to estimate the temperature in the central regions of stars.

At temperatures on the order of ten million Kelvin and at the densities that exist there, all atoms should be ionized. In fact, the average kinetic energy of each gas particle

= kT will be about 10 -9 erg or

This means that every collision of an electron with an atom can lead to ionization of the latter, since the binding energy of electrons in an atom (the so-called “ionization potential”) is usually less thousands of electron volts. Only the “deepest” electron shells of heavy atoms will remain “intact”, that is, they will be retained by their atoms. The state of ionization of intrastellar matter determines its average molecular mass, the value of which, as we have already had the opportunity to see, plays a large role in the interior of stars. If the star's matter consisted only from fully ionized hydrogen (as we stated above), then the average molecular weight

Would be equal to 1 / 2. If there were only fully ionized helium, then

4/ 3 (since the ionization of one helium atom with atomic mass 4 produces three particles - a helium nucleus plus two electrons). Finally, if the substance of the star’s interior consisted only of heavy elements (oxygen, carbon, iron, etc.), then its average molecular weight with complete ionization of all atoms would be close to 2, since for such elements the atomic mass is approximately twice as large as the number of electrons in an atom.

In reality, the substance of stellar interiors is some mixture of hydrogen, helium and heavy elements. The relative abundance of these main components of stellar matter (not by the number of atoms, but by mass) is usually indicated by the letters X, Y And Z, which characterize chemical composition stars. In typical stars, more or less similar to the Sun, X = 0, 73, Y = 0, 25, Z = 0, 02. Attitude Y/X

0, 3 means that for every 10 hydrogen atoms there is approximately one helium atom. The relative amount of heavy elements is very small. For example, there are about a thousand times fewer oxygen atoms than hydrogen atoms. Nevertheless, the role of heavy elements in the structure of the inner regions of stars is quite significant, since they strongly influence opacity stellar matter. We can now determine the average molecular mass of a star using a simple formula:

(6.3)

Role Z in assessment

insignificant. The decisive factor for the average molecular weight is X And Y. For stars of the central part of the main sequence (in particular, for the Sun)

0, 6. Since the value

for most stars varies within very small limits, we can write a simple formula for the central temperatures of various stars, expressing their masses and radii in fractions of the solar mass M

And solar radius R:

(6.4)

Where T

Temperature of the central regions of the Sun. Above, we roughly estimated T

At 10 million kelvins. Accurate calculations give meaning T

14 million kelvins. From formula (6.4) it follows, for example, that the temperature of the interiors of massive hot (on the surface!) stars of the spectral class is 2-3 times higher than the temperature of the solar interior, while red dwarfs have central temperatures 2-3 times lower than solar ones.

It is important that the temperature

10 7 K is typical not only for the very central regions of stars, but also for the large volume surrounding the center of the star. Considering that the density of stellar matter increases towards the center, we can conclude that the bulk of the star's mass has a temperature, in any case, exceeding

5 million kelvins. If we also remember that most of the mass of the Universe is contained in stars, then the conclusion arises that the matter of the Universe is, as a rule, hot and dense. It should be added, however, that we are talking about modern Universe: in the distant past and future, the state of matter in the Universe was and will be completely different. This was discussed in the introduction to this book.

From the book Physical Chemistry: Lecture Notes author Berezovchuk A V

1. The concept of chemical equilibrium. Law of mass action When a chemical reaction occurs, after some time a chemical equilibrium is established. There are two signs of chemical equilibrium: kinetic and thermodynamic. In kinetic – ?pr = ?arr, in

From the book Interesting about cosmogony author Tomilin Anatoly Nikolaevich

5. Calculation of the equilibrium composition of a chemical equilibrium The equilibrium composition can be calculated only for a gas system, the equilibrium concentration. The initial concentration of all components The change in each component by the number of moles (or stoichiometric

From the book Prince from the Land of Clouds author Galfar Christophe

An ordinary star - the Sun “...The Sun is the only star in which all phenomena can be studied in detail,” wrote the American astronomer George Ellery Hale, who received the gold medal of the Royal Astronomical Society for his photography method

From the book NIKOLA TESLA. LECTURES. ARTICLES. by Tesla Nikola

Chapter 6 The prison, with blind walls without a single window, was located deep in the depths of the cloud on which the White Capital was built. Once in the cell, frightened Tristam and Tom sat silently for some time on the bed allotted for them - in fact, it was

From the book How to Understand the Complex Laws of Physics. 100 simple and fun experiments for children and their parents author Dmitriev Alexander Stanislavovich

Chapter 7 Several hours passed. Tristam and Tom lay on hard bunks in a dark, windowless cell, constantly tossing and turning from side to side. As soon as the flute's tune ceased, the old man immediately dozed off, muttering something inaudibly in his sleep. Tom began to shiver again; I understood Tristam

From the book Mechanics from Antiquity to the Present Day author Grigoryan Ashot Tigranovich

Chapter 8 Thick smoke pouring out of the chimneys mixed with the cool and damp dawn air. Snowmen were stationed at all intersections in the center of the White Capital. They looked less like law enforcement officers and more like occupation troops. Tristam and Tom in

From the book Interstellar: the science behind the scenes author Thorne Kip Stephen

Chapter 9 Night fell, there was deep silence outside the windows. Tristam fell asleep. Next to him, with an open book on his stomach, Tom was sleeping, immersed in dreams of the future. In the back of the room, stretched out on a mattress, one of the policemen was snoring. The second was sitting on the ladder, which now stood near

From the author's book

Chapter 10 Tristam watched the shadow carefully. She was heading straight towards the military patrol. “He won’t get through there!” - Tristam was worried. But the man with the backpack probably knew it himself: he climbed up the wall and, like a black cat, jumped from roof to roof in a matter of

From the author's book

Chapter 11 The next morning, as soon as the boys woke up, the police took them down into the underground passage. Fortunately, the narrow tunnel, through which we had to move in single file, was clean and dry. “How much longer?” - Tristam asked when they had walked about ten meters. - Shh! - whispered

From the author's book

Chapter 12 Tristam pushed the door and stopped at the threshold. Directly in front of him was a staircase that went to the second floor; Several steps led down to a bolted cellar door. To the left was the kitchen, to the right was a large living room, flooded with bright morning light. - Come in, Tristam

From the author's book

Chapter 13 When Tom entered the living room, Tristam was sitting on the sofa. He hung his mother's pendant around his neck, tucking the crystal under his sweater, and looked at the portrait of Myrtille, which lay in front of him on the low table. Tristam's eyes sparkled, as if he had just cried. “What a guy!” -

From the author's book

Chapter 14 A thick fog, which seemed to combine all shades of gray, enveloped Tristam, Tom, the lieutenant and his fighters. They ran in single file along a road that wound in a narrow valley between two colossal clouds. Gusts of wind showered them with myriads of tiny sprays,

From the author's book

ATTEMPTS TO GET MORE ENERGY FROM COAL - ELECTRIC DRIVE - GAS ENGINE - COLD COAL BATTERY I remember at one time considering the production of electricity by burning coal in a battery as the greatest achievement for the benefit of civilization, and I was

From the author's book

84 How to distinguish a fake, or About the state of a substance For the experiment we will need: a piece of amber or rosin, a piece of plastic, a needle. There are complex ways to distinguish the composition of a substance, usually this is not even physics, but chemistry. Determining what a substance consists of is often

From the author's book

EQUILIBRIUM FIGURES OF A ROTATING FLUID Let us briefly dwell on the problem of equilibrium figures of a rotating fluid, to the development of which the main contribution was made by A.M. Lyapunov.Newton showed that under the influence of centrifugal forces and the mutual attraction of its particles, a homogeneous

From the author's book

Neutron star in orbit around a black hole The waves came from a neutron star orbiting a black hole. The star weighed 1.5 times the Sun, and the black hole weighed 4.5 times the Sun, while the hole was spinning rapidly. Formed by this rotation