The stars are the coldest. Characteristics of stars - O'Five in physics! Being at different stages of their evolutionary development, stars are divided into normal stars, dwarf stars, giant stars

The color of a star depends on the temperature on its surface. Our Sun's surface temperature exceeds 6,000 degrees Kelvin. Even though it appears yellow from Earth, the sun's light from space looks blindingly white. This bright white solar glow is due to this high temperature. If the Sun were colder, then its light would acquire a darker shade, closer to red, and if this star were hotter, it would be blue.

The secret of the multicolored stars has become an important tool for astronomers - the color of the stars helped them to know the temperature of the surface of stars. It was based on a remarkable natural phenomenon - the relationship between the energy of a substance and the color of the light emitted by it.

You have probably already made your own observations on this topic. A filament of low-power 30-watt light bulbs glows orange - and when the mains voltage drops, the filament barely glows red. Stronger bulbs glow yellow or even white. And the welding electrode during operation and the quartz lamp glow blue. However, in no case should you look at them - their energy is so great that it can easily damage the retina of the eye.

Accordingly, the hotter the object, the closer its color of its glow to blue - and the colder, the closer to dark red. The stars are no exception: the same principle applies to them. The influence of the composition of a star on its color is very insignificant - the temperature can hide individual elements, ionizing them.

But it is the analysis of the color spectrum of the radiation of a star that helps to find out its composition. The atoms of each substance have their own unique capacity. Light waves of some colors pass through them without hindrance, when others stop - in fact, scientists determine chemical elements from the blocked ranges of light.

The mechanism of "coloring" stars

What is the physical background of this phenomenon? The temperature is characterized by the speed of movement of the molecules of the substance of the body - the higher it is, the faster they move. This affects the length of light waves that travel through matter. A hot environment shortens the waves, and a cold one, on the contrary, lengthens them. And the visible color of the light beam is just determined by the wavelength of the light: short waves are responsible for the blue hues, and long ones for the red ones. White color is obtained as a result of the imposition of multispectral rays.

The color of a star plays a role in several star ordering systems at once. By itself, it is the main criterion for determining the spectral class of the star. Since color is related to temperature, it is plotted along one of the axes of the Hertzsprung-Russell diagram. The diagram can also be used to determine the luminosity, mass, and age of a star, making it a valuable and visual source of information about stars.

Star classes

There are seven classes of stars in the Galaxy:

• "O" class stars, blue, had the highest temperature. They had the shortest lifespan, less than 1 million years. There were approximately 100 million "O" stars in the Galaxy, the planets around which were habitable. Example: Garnib.

• Class "B" stars blue and white were also very hot. Their average lifespan was approximately 10 million years. There were also approximately 100 million class "B" stars in the Galaxy, around which the planets were habitable. Example: Kessa.
• Class "A" stars, white, were hot enough. They had a lifespan of 400 million to 2 billion years. There were also approximately 100 million "A" stars in the Galaxy, around which the planets were habitable. Example: Cola.

• F class stars, yellow-white in color, had an average temperature. Their average lifespan was about 4 billion years. There were also approximately 100 million class "F" stars in the Galaxy, the planets around which were habitable. Example: Ropagi.
• Stars class "G", yellow, also had an average temperature. Their average lifespan was about 10 billion years. There were approximately 2 billion G-class stars in the Galaxy, around which the planets were habitable. Example: Corell.

• "K" class stars, orange in color, had a temperature low enough for stars. Their average lifespan was about 60 billion years. There were approximately 3.75 billion K-class stars in the Galaxy, around which the planets were habitable. Example: Yavin.
• M class stars, red in color, were cold compared to the rest of the stars. Class "M" stars are also called red dwarfs. Their average lifespan was about 100 trillion years. There were approximately 700 million class "M" stars in the Galaxy, the planets around which were habitable. Example: Drum.

The size of a star also depended on its class. The largest were blue hot stars of the "O" class. The lower the temperature of a star, the smaller it was itself. Accordingly, the red stars of the "M" class were the smallest. In addition, approximately 10 percent of all the stars in the Galaxy did not fall under this gradation, and around 500 million of them planets suitable for life revolved.

blue supergiant

Blue supergiants are among the most massive and luminous stars. In size, they are larger than giants, but inferior to hypergiants. The typical mass of blue supergiants is 15-50 solar masses. In astronomy, they are often referred to as OB-type supergiants. They have luminosity class I and spectral class B9 and higher. They are in the upper left of the Hertzsprung-Russell diagram to the right of the main sequence. Surface temperatures - 10,000-50,000 K, luminosity, 10,000-1,000,000 solar luminosities. The typical lifetime of stars of this type is 5-10 million years.

Specifications

Due to their large masses, blue supergiants have relatively short lifespans and are only observed in young cosmic structures such as open clusters, arms of spiral galaxies, and irregular galaxies. They are almost not observed in the centers of spiral galaxies, elliptical galaxies and globular clusters, which consist mainly of old objects.

Despite their rarity and short life, due to their brightness, many blue supergiants can be seen in the sky. One of the most famous supergiants is Rigel, the brightest star in the constellation of Orion - its mass is almost 20 times the mass of the Sun, and its luminosity is almost 120,000 times greater than the luminosity of the Sun.

Blue supergiants are characterized by a strong stellar wind, and, as a rule, they have emission lines in their spectrum.

The stellar wind from blue supergiants is fast but thin, in contrast to the wind from red supergiants, which is slow but dense. When a red supergiant transitions to a blue supergiant, the faster wind "overtakes" the previously emitted slower one and collides with it, causing the ejected material to condense into a thin shell. The reverse process is also possible - the transformation of a blue supergiant into a red one. In some cases, several concentric weak thin shells can be seen, formed by successive episodes of mass loss due to several cycles of "red<->blue supergiant.

Evolution

As the hydrogen fuel is exhausted, the star cools and expands more and more, passing through the spectral classes O, B, A, F, G, K and M, becoming a white, yellow, orange, and finally, a red supergiant. After the hydrogen in the core runs out, helium will enter into a thermonuclear reaction, then carbon, oxygen, silicon. Nucleosynthesis can proceed up to the formation of the most stable iron-56 isotope (all of the following isotopes can reduce the binding energy per nucleon by decay, and all previous elements, in principle, could reduce the binding energy per nucleon by fusion). The resulting iron core collapses into a neutron star, an object the size of a major city but with a mass of 1.4-3 solar masses, and the outer layers of the star explode as a supernova. In the case of especially massive blue supergiants (with an initial mass of 25-40 solar masses), the core may not stop at the formation of a neutron star, but collapses further, turning into a black hole. Even more massive supergiants cannot expand to the red phase, but end their lives in a hypernova explosion (or without it) with the formation of a black hole.

Interchange of supergiants

Blue supergiants are massive stars that are in a certain phase of the "dying" process. In this phase, the intensity of thermonuclear reactions occurring in the core of the star decreases, which leads to the compression of the star. As a result of a significant decrease in the surface area, the density of the radiated energy increases, and this, in turn, entails heating of the surface. This kind of compression of a massive star leads to the transformation of a red supergiant into a blue one. The reverse process is also possible - the transformation of a blue supergiant into a red one.

While the stellar wind from a red supergiant is dense and slow, the wind from a blue supergiant is fast but thin. If the red supergiant becomes blue as a result of compression, then the faster wind collides with the previously emitted slow wind and causes the ejected material to condense into a thin shell. Almost all observed blue supergiants have a similar envelope, confirming that they were all formerly red supergiants.

As it develops, a star can transform from a red supergiant (slow, dense wind) to a blue supergiant (fast, rarefied wind) and vice versa several times, which creates concentric weak shells around the star. In the intermediate phase, the star may be yellow or white, such as the North Star. As a rule, a massive star ends its life in a supernova explosion, but a very small number of stars, whose masses range from eight to twelve solar masses, do not explode, but continue to evolve and eventually turn into oxygen-neon white dwarfs. It is not yet clear exactly how and why these white dwarfs are formed from stars, which theoretically should end their evolution with a small supernova explosion. Both blue and red supergiants can evolve into a supernova.

Since massive stars are red supergiants a significant portion of the time, we see more red supergiants than blue supergiants, and most supernovae come from red supergiants. Astrophysicists have previously even assumed that all supernovae originate from red supergiants, but supernova SN 1987A formed from a blue supergiant and thus this assumption turned out to be incorrect. This event also led to a revision of some provisions of the theory of stellar evolution.

Examples of blue supergiants

Rigel

The most famous example is Rigel (beta Orionis), the brightest star in the constellation Orion, with a mass of about 20 times the mass of the Sun and its luminosity about 130,000 times that of the Sun, which means it is one of the most powerful stars in the Galaxy (in in any case, the most powerful of the brightest stars in the sky, since Rigel is the closest of the stars with such a huge luminosity). The ancient Egyptians associated Rigel with Sakh, the king of the stars and the patron of the dead, and later with Osiris.

Gamma Sails

Gamma Sails is a multiple star, the brightest in the constellation Sails. It has an apparent magnitude of +1.7m. The distance to the stars of the system is estimated at 800 light years. Gamma Sails (Regor) is a massive blue supergiant. It has a mass 30 times the mass of the Sun. Its diameter is 8 times that of the Sun. The luminosity of Regora is 10,600 solar luminosities. The unusual spectrum of the star, where instead of dark absorption lines there are bright emission lines of radiation, gave the name to the star as the “Spectral Pearl of the Southern Sky”

Alpha Giraffe

The distance to the star is about 7 thousand light years, and yet, the star is visible to the naked eye. It is the third brightest star in the constellation Giraffe, followed by Beta Giraffa and CS Giraffa, respectively.

Zeta Orionis

Zeta Orionis (named Alnitak) is a star in the constellation of Orion, which is the brightest class O star with a visual magnitude of +1.72 (at a maximum of +1.72 and at a minimum of up to +1.79), the left and closest star asterism "Orion's Belt". The distance to the star is about 800 light years, the luminosity is about 35,000 solar.

Tau Canis Major

Spectral binary star in the constellation Canis Major. It is the brightest star in the open star cluster NGC 2362, at a distance of 3200 ly. years from Earth. Tau Canis Majoris is a blue supergiant of spectral class O with an apparent magnitude of +4.37m. The Tau Canis Major star system has at least five components. In the first approximation, Tau Canis Majoris is a triple star in which two stars have an apparent magnitude of +4.4m and +5.3m and are 0.15 arc seconds apart, and the third star has an apparent magnitude of +10m and is from them by 8 arc seconds, revolving with a period of 155 days around the inner pair.

Zeta Korma

Zeta Purmus is the brightest star in the constellation Puppis. The star has its own name Naos. It is a massive blue star with a luminosity of 870,000 times that of the Sun. Zeta Puppis is 59 times more massive than the Sun. It has a spectral type O9.

W everywhere - celestial bodies in which thermonuclear reactions take place. These are the most common objects in the universe. More than 98% of the mass of visible cosmic matter is concentrated in these gas balls, the rest of it is scattered in interstellar space.

With the naked eye, and even more so when observing through binoculars or a telescope, it is easy to notice that the stars differ in color. The color of stars is largely determined by the temperature of their apparent surface.

With good visual acuity, about 6,000 stars are visible in the sky, 3,000 in each hemisphere.

SHINE

The first thing that a person notices when observing the night sky is the different brightness (brilliance) of the stars. The apparent brilliance of stars is estimated in stellar magnitudes (see the article "Magnitudes"). Historically, the system of stellar magnitudes assigned the 1st magnitude to the brightest stars, and the 6th to the weakest, located at the limit of visibility with the naked eye. Subsequently, in order to produce objective quantitative estimates of stellar magnitudes, this scale was improved. It was assumed that a difference of five magnitudes corresponds to a difference in apparent brightness of exactly 100 times. Therefore, a difference of one magnitude means that the star is brighter than the other in approx. 2.512 times. For more accurate measurements, the scale containing only whole numbers turned out to be too coarse, so fractional values ​​had to be entered. Star magnitudes are denoted by the index m (from the Latin magnitude - "magnitude"), which is placed at the top after the numerical value. For example, the brightness of the North Star is 2.3 m.

To appreciate the brilliance of the brightest heavenly bodies, six steps were not enough. Zero and negative stellar magnitudes appeared. So, the full Moon has a brightness of about -11 m (10 thousand times brighter than the brightest star - Sirius), Venus - up to -4 m. With the invention of the telescope, astronomers became acquainted with stars fainter than 6m. Even with binoculars, 10^m stars can be seen, and objects 27-29 m are accessible to the largest telescopes.

Visible gloss is an easily measured, important, but far from exhaustive characteristic. In order to establish the radiation power of a star - the luminosity, you need to know the distance to it.

DISTANCES TO THE STARS

The distance to a distant object can be determined without physically reaching it. It is necessary to measure the directions to this object from the two ends of the known segment (basis), and then calculate the dimensions of the triangle formed by the ends of the segment and the distant object. This can be done because in a triangle one side (basis) and two adjacent angles are known. For measurements on Earth, this method is called triangulation.

annual parallax star is the angle at which the average radius of the earth's orbit, perpendicular to the direction of the star, would be visible from it.

The parallaxes of even the closest stars are extremely small, less than 1". Very precise instruments are required here, therefore it is not surprising that for a long time (until the middle of the 19th century) it was not possible to measure parallaxes. And of course, this was completely impossible in the time of Copernicus, who for the first time proposed the parallax method as a direct consequence of his heliocentric system (there should be no parallax displacements in a geocentric system).

The concept of parallax is associated with the name of one of the basic units of distance in astronomy - parsec (short for "parallax" and "second"). This is the distance to an imaginary star whose annual parallax would be exactly 1"". In other words, the radius of the earth's orbit, equal to one astronomical unit (1 AU), is visible from such a star at an angle of 1 ". The annual parallax of any star is related to the distance to it by a simple formula:

r = 1/n (pi)

where r is the distance in parsecs, n is the annual parallax in seconds.

From the ratios in the parallactic triangle, it is easy to calculate that 1 parsec (pc) is equal to 206,265 AU. e., or about 30 trillion kilometers. This is a very large value, light overcomes such a path in 3.26 years.

Now the parallax method has determined the distances to many thousands of stars. Unfortunately, only for nearest neighbors can this be done with great accuracy. However, there are a number of methods by which the distance to a star can be obtained indirectly, using various astrophysical or statistical relationships. Thus, the luminosity of variable stars, called Cepheids, turned out to be associated with the period of change in their brightness. Knowing the period of a distant variable star and its apparent magnitude, it is easy to find the distance to the star. Methods for studying binary stars also make it possible to calculate the distances to some of them. There are other indirect ways to determine the distances to stars and star systems.

Chemical composition of stars

It is determined by the spectrum (the intensity of the Fraunhofer lines in the spectrum). The variety of the spectra of stars is explained primarily by their different temperatures, in addition, the type of spectrum depends on the pressure and density of the photosphere, the presence of a magnetic field, and the characteristics of the chemical composition. Stars consist mainly of hydrogen and helium (95-98% of the mass) and other ionized atoms, while cold ones have neutral atoms and even molecules in the atmosphere.

LUMINOSITY

When the distances to bright stars were measured, it became obvious that many of them are much more luminous than the Sun. If the luminosity of the Sun is taken as a unit, then, for example, the radiation power of the four brightest stars in the sky, expressed in the luminosities of the Sun, will be:

L © = 4*10 26 W

Sirius 22 L©

Canopus 4700 L©

Arcturus 107L©

Vega 50 L©

This, however, does not mean that the Sun is very "pale" compared to the rest of the stars. Its luminosity in the stellar world is above average. So, out of several dozen stars, the distances to which do not exceed 15 light years, only two - Sirius and Procyon - have a higher luminosity than the Sun, and one more - the centauri alufa - is only slightly inferior to it, while the rest have much lower luminosity. Stars are known that emit light tens of thousands of times less than the Sun. The luminosity interval of the observed stars turned out to be incredibly wide: they can differ by more than a billion times!

COLOR BET AND TEMPERATURE

The hottest stars are always blue and white, the less hot are yellowish, and the coldest are reddish. But even the coldest stars have a temperature of 2-3 thousand Kelvin - hotter than any molten metal.

The human eye is not able to determine the color of a star very accurately. For more accurate estimates, photographic and photoelectric radiation detectors are used, which are sensitive to various parts of the visible (or invisible) spectrum. After all, the color of a star depends on which part of the spectrum has the highest radiation energy. Comparison of stellar magnitudes in different ranges of the spectrum (for example, in blue and yellow) makes it possible to quantitatively characterize the color of a star and estimate its temperature.

SPECTRAL CLASSIFICATION OF STARS

More complete information about the nature of stellar radiation is provided by the spectrum. The spectral apparatus mounted on the telescope, with the help of a special optical device - a diffraction grating - decomposes the star's light into wavelengths into the rainbow band of the spectrum. The shortest wavelength of visible radiation corresponds to violet, and the longest wavelength to red. From the spectrum, it is not difficult to find out what energy comes from a star at different wavelengths, and to estimate its temperature more accurately than by color.

Numerous dark lines crossing the spectral strip are associated with the absorption of light by atoms of various elements in the star's atmosphere. Since each chemical element has its own set of lines, the spectrum allows you to determine what substances the star consists of (it turned out to be the same that are known on Earth, and most of all in the stars of the lightest elements - hydrogen and helium). But even for the same element, the set of lines and the amount of energy absorbed in each of them depends on the temperature and density of the atmosphere. Special physical methods have been developed for determining the characteristics of a star by analyzing its spectrum.

In hot blue stars with temperatures above 10-15 thousand kelvins, most of the atoms are ionized, since they are deprived of electrons. Fully ionized atoms do not give spectral lines, so there are few lines in the spectra of such stars. The most notable belong to helium. Stars with a temperature of 5-10 thousand kelvins (the Sun is one of them) have lines of hydrogen, calcium, iron, magnesium and a number of other metals. Finally, cooler stars are dominated by lines of metals and molecules that can withstand high temperatures (for example, titanium oxide molecules).

Sun G2 Sirius A1 Canopus F0 Arcturus K2 Vega A0 Rigel B8 Deneb A2 Altair A7 Betelgeuse M2
Polar F8

STAR DIMENSIONS

The stars are so far away that even in the largest telescope they look like dots. How to find out the size of a star?

The moon comes to the aid of astronomers. It slowly moves against the background of the stars, in turn "blocking" the light coming from them. Although the angular size of the star is extremely small, the Moon does not obscure it immediately, but over a period of several hundredths or thousandths of a second. The duration of the process of reducing the brightness of a star when it is covered by the Moon determines the angular size of the star. And knowing the distance to the star, it is easy to get its true (linear) dimensions from the angular size.

But only a small part of the stars in the sky is located so well for earthly observers that it can be covered by the Moon. Therefore, other methods for estimating stellar sizes are usually used. The angular diameter of bright and not very distant luminaries can be directly measured with a special device - an optical interferometer. True, such measurements are quite laborious. In most cases, the radius of a star (R) is determined theoretically based on estimates of its total luminosity (L) in the entire optical range and temperature (T). According to the laws of radiation of heated bodies, the luminosity of a star is proportional to the value of R 2 T 4 . Comparing any star with the Sun, we obtain a formula convenient for calculations:

which makes it possible to find the radius of a star from its temperature and luminosity (the values ​​R®, L® and T® = 6000 K are known).

So, according to their size, the stars are divided (the name: dwarfs, giants and supergiants was introduced by Henry Ressel in 1913, and Einar Hertzsprung discovered them in 1905, introducing the name "white dwarf"), introduced since 1953 into:

• Supergiants (I)
• Bright Giants (II)
• Giants (III)
• Subgiants (IV)
• Main sequence dwarfs (V)
• Subdwarfs (VI)
• White dwarfs (VII)

Measurements showed that the smallest stars observed in optical beams - the so-called white dwarfs - have a diameter of several thousand kilometers. The dimensions of the largest - red supergiants - are such that if it were possible to place a similar star in the place of the Sun, most of the planets of the solar system would be inside it.

STAR MASS

The most important characteristic of a star is its mass. The more matter gathered into a star, the higher the pressure and temperature in its center, and this determines almost all other characteristics of the star, as well as the features of its life path.

Direct estimates of mass can only be made on the basis of the law of universal gravitation. Such estimates were obtained for a large number of stars in binary systems by measuring the speed of their movement around a common center of mass. All other methods of calculating mass are considered indirect, since they are not based on the law of analysis of those stellar characteristics that are somehow related to mass. Most often, this is luminosity. For many stars, a simple rule holds true: the higher the luminosity, the greater the mass. This dependence is non-linear: for example, with a doubling of the mass, the luminosity increases by more than 10 times.

The masses of stars range from several tens to approximately 0.1 solar masses. (With a smaller mass, the temperature even in the center of the body will not be high enough to generate thermonuclear energy, such objects will turn out to be too cold, they cannot be classified as stars.) Thus, stars differ in mass by only a few hundred times - much less than in size ( hundreds of thousands of times) or by luminosity (more than a billion times).

Analyzing the most important characteristics of stars, comparing them with each other, scientists were able to establish what is inaccessible to direct observations: how stars are arranged, how they form and change during life, what they turn into, having wasted their energy reserves.

Hertzsprung-Russell diagram.

Class O are blue stars, their temperature is 22,000 °C. Typical stars are Zeta in the constellation Puppis, 15 Unicorn.

Class B are white-blue stars. Their temperature is 14,000 °C. Their temperature is 14,000 °C. Typical stars: Epsilon in the constellation Orion, Rigel, Kolos.

Class A are white stars. Their temperature is 10,000 °C. Typical stars are Sirius, Vega, Altair.

Class F are white-yellow stars. Their surface temperature is 6700 °C. Typical stars Canopus, Procyon, Alpha in the constellation Perseus.

Class G are yellow stars. Temperature 5 500 °С. Typical stars: Sun (spectrum C-2), Capella, Alpha Centauri.

Class K are yellow-orange stars. Temperature 3 800 °C. Typical stars: Arthur, Pollux, Alpha Ursa Major.

Class M -. These are red stars. Temperature 1 800 °C. Typical stars: Betelgeuse, Antares

In addition to main sequence stars, astronomers distinguish the following types of stars:

Brown dwarfs are stars in which nuclear reactions could never compensate for energy losses due to radiation. Their spectral class is M - T and Y. Thermonuclear processes can occur in brown dwarfs, but their mass is still too small to start the reaction of converting hydrogen atoms into helium atoms, which is the main condition for the life of a full-fledged star. Brown dwarfs are rather "dim" objects, if that term can be applied to such bodies, and astronomers study them mainly due to the infrared radiation they give off.

Red giants and supergiants are stars with a rather low effective temperature of 2700-4700 ° C, but with a huge luminosity. Their spectrum is characterized by the presence of molecular absorption bands, and the emission maximum falls on the infrared range.

Wolf-Rayet type stars are a class of stars that are characterized by very high temperature and luminosity. Wolf-Rayet stars differ from other hot stars by the presence in the spectrum of wide emission bands of hydrogen, helium, as well as oxygen, carbon, and nitrogen in different degrees of ionization. The final clarity of the origin of Wolf-Rayet type stars has not been achieved. However, it can be argued that in our Galaxy these are the helium remnants of massive stars that shed a significant part of the mass at some stage of their evolution.

T Tauri stars are a class of variable stars named for their prototype T Tauri (final protostars). They can usually be found close to molecular clouds and identified by their (highly irregular) optical variability and chromospheric activity. They belong to the stars of spectral classes F, G, K, M and have a mass less than two solar. Their surface temperature is the same as that of main sequence stars of the same mass, but they have a slightly higher luminosity because their radius is larger. The main source of their energy is gravitational compression.

Bright Blue Variables, also known as S Doradus Variables, are very bright blue pulsating hypergiants named after the star S Doradus. They are extremely rare. The bright blue variables can shine a million times brighter than the Sun and can be as massive as 150 solar masses, approaching the theoretical mass limit of a star, making them the brightest, hottest, and most powerful stars in the universe.

White dwarfs are a type of dying star. Small stars such as our Sun, which are widely distributed in the Universe, will turn into white dwarfs at the end of their lives - these are small stars (former stellar cores) with a very high density, which is a million times higher than the density of water. The star is deprived of energy sources and gradually cools down, becoming dark and invisible, but the cooling process can last for billions of years.

Neutron stars - a class of stars, like white dwarfs, are formed after the death of a star with a mass of 8-10 solar masses (stars with a larger mass already form black holes). In this case, the nucleus is compressed until most of the particles turn into neutrons. One of the features of neutron stars is a strong magnetic field. Thanks to it and the rapid rotation acquired by the star due to non-spherical collapse, radio and X-ray sources are observed in space, which are called pulsars.

Star evolution

Stars are among the hottest objects in the universe. It was the heat of our Sun that made it possible on Earth. But the reason for such a strong heating of the stars for a long time remained unknown to people.

The key to the secret of a star's high temperature lies within it. This refers not only to the composition of the luminary - in the literal sense, the entire glow of the star comes from within. - this is the hot heart of the star, in which the thermonuclear fusion reaction takes place, the most powerful of nuclear reactions. This process is the source of energy for the entire luminary - heat from the center rises outward, and then into outer space.

Therefore, the temperature of the star varies greatly depending on the location of the measurement. For example, the temperature in the center of our core reaches 15 million degrees Celsius - and already on the surface, in the photosphere, the heat drops to 5 thousand degrees.

Why is the temperature of the star so different?

The primary union of hydrogen atoms is the first step in the process of nuclear fusion

Indeed, the differences in the heating of the core of a star and its surface are surprising. If all the energy of the core of the Sun were distributed evenly throughout the star, the surface temperature of our star would be several million degrees Celsius! No less striking differences in temperature between stars of different spectral classes.

The thing is that the temperature of a star is determined by two main factors: the level of the core and the area of ​​​​the radiating surface. Let's consider them in more detail.

Emission of energy from the nucleus

Although the core heats up to 15 million degrees, not all of this energy is transferred to neighboring layers. Only the heat that was received from the thermonuclear reaction is radiated. Energy, despite its power, remains within the core. Accordingly, the temperature of the upper layers of a star is determined only by the strength of thermonuclear reactions in the core.

The differences here can be qualitative and quantitative. If the core is large enough, more hydrogen will “burn” in it. In this way, young and mature stars of the size of the Sun, as well as blue giants and supergiants, receive energy. Massive stars like red giants spend not only hydrogen, but also helium, or even carbon and oxygen in the nuclear “furnace”.

Fusion processes with nuclei of heavy elements provide much more energy. In a thermonuclear fusion reaction, energy is obtained from the excess mass of the connecting atoms. During the time that occurs inside the Sun, 6 hydrogen nuclei with an atomic mass of 1 combine into one helium nucleus with a mass of 4 - roughly speaking, 2 extra hydrogen nuclei are converted into energy. And when carbon "burns", nuclei with a mass of already 12 collide - accordingly, the energy output is much greater.

Radiating surface area

However, stars not only generate energy, but also spend it. Therefore, the more energy a star gives off, the lower its temperature. And the amount of energy given off primarily determines the area of ​​​​the radiated surface.

The truth of this rule can be checked even in everyday life - linen dries faster if it is hung wider on a rope. And the surface of a star expands its core. The denser it is, the higher its temperature - and when a certain bar is reached, hydrogen is ignited from incandescence outside the stellar core.

The cores are very dense, because there is a lot of helium there. Sometimes he himself is already “lit” by a thermonuclear reaction. Therefore, their surface area exceeds the area of ​​the Sun by tens of thousands, or even a million times! So the photosphere of even the largest red giants is twice as cold as the surface of the Sun.

Differences in surface temperature

Another important point is that some places on the surface of the same star can have different temperatures. The differences reach several thousand degrees Celsius! It all depends on how energy is transferred from the core of the star. Astrophysicists distinguish two main ones - radiative transport and convection:

• During radiative transfer, the energy of nuclear fusion breaks from the center of the star right through - in the form of rays. This path is efficient in terms of energy conservation, but very slow. If the radiative transfer zone is located near the center of the star, like our Sun, the path of the rays will take several tens of thousands of years.
• Convection, on the other hand, is based on the well-known law of nature - warm liquids and gases rise up, and cold ones fall down. And since stars are made of gas, convection is also observed in them. The stellar matter, warming up near the hotter layers of the star, rises to the colder zones of the star with less gas pressure. There, the energy taken from within is given away in the form of .

The location of the radiative transport and convection zones depends on the mass of the star. In stars less than the mass of the sun, only convection prevails. Massive luminaries transfer heat from the core to the outer layers by convection, and to the very surface by radiant transfer.

In contrast, the opposite is true: the energy from the core leaves in the form of rays, and then it is thrown out to the surface by convective flows of stellar plasma. There, in the photosphere, the energy of the Sun is again converted into light - including that visible to the human eye.

And it is thanks to convection that temperature drops occur on the surface of the Sun. The places where this happens are also highlighted visually. The three main types are faculae, spots, and prominences.

• Faculae are hot and bright areas on the Sun. Their temperature is higher than the surrounding surface by 1-2 thousand degrees Celsius.
• Sunspots are cooler, darker areas on a star's photosphere. The heating of their center is less than the usual temperature of the Sun by 2000 °C. There is also a “shadow” around the spots, which is already warmer - they are only 200-500 degrees colder than the photosphere surrounding them.
• are an eruption of stellar matter from the depths that rise above the solar atmosphere. Although they are colder than the corona of the Sun, their temperature is higher than photospheric - up to 15 thousand degrees Celsius.

Like faculae, spots with prominences do not appear due to the star's magnetic fields crossing the photosphere during periods . Torches appear in those places where magnetic lines accelerate the convective flows of gases from the depths of the Sun. Prominences also have a similar origin - but their magnetic field exit zone is much narrower, and the strength of the magnetic lines is greater. In spots, on the contrary, the magnetic field slows down the process of thermal transfer - so they are dimmer and cooler.

By virtue of the Sun towards us, it remains the only star on which such phenomena have been observed. But since the nature of the stars is very similar, astronomers assume the presence of spots and torches on other luminaries.

Stars are very different: small and large, bright and not very bright, old and young, hot and cold, white, blue, yellow, red, etc.

The Hertzsprung-Russell diagram allows you to understand the classification of stars.

It shows the relationship between absolute magnitude, luminosity, spectral type, and surface temperature of a star. The stars in this diagram are not arranged randomly, but form well-defined areas.

Most of the stars are located on the so-called main sequence. The existence of the main sequence is due to the fact that the stage of hydrogen burning is ~90% of the evolutionary time of most stars: the burning of hydrogen in the central regions of the star leads to the formation of an isothermal helium core, the transition to the red giant stage, and the departure of the star from the main sequence. The relatively brief evolution of red giants leads, depending on their mass, to the formation of white dwarfs, neutron stars, or black holes.

Being at different stages of their evolutionary development, stars are divided into normal stars, dwarf stars, giant stars.

Normal stars are the main sequence stars. Our sun is one of them. Sometimes such normal stars as the Sun are called yellow dwarfs.

yellow dwarf

A yellow dwarf is a type of small main sequence star with a mass between 0.8 and 1.2 solar masses and a surface temperature of 5000–6000 K.

The lifetime of a yellow dwarf is on average 10 billion years.

After the entire supply of hydrogen burns out, the star increases many times in size and turns into a red giant. An example of this type of star is Aldebaran.

The red giant ejects its outer layers of gas, forming planetary nebulae, and the core collapses into a small, dense white dwarf.

A red giant is a large reddish or orange star. The formation of such stars is possible both at the stage of star formation and at the later stages of their existence.

At an early stage, the star radiates due to the gravitational energy released during compression, until the compression is stopped by the onset of a thermonuclear reaction.

At the later stages of the evolution of stars, after the hydrogen burns out in their interiors, the stars descend from the main sequence and move to the region of red giants and supergiants of the Hertzsprung-Russell diagram: this stage lasts about 10% of the time of the “active” life of stars, that is, the stages of their evolution , during which nucleosynthesis reactions take place in the stellar interior.

The giant star has a relatively low surface temperature, about 5000 degrees. A huge radius, reaching 800 solar and due to such large sizes, a huge luminosity. The maximum radiation falls on the red and infrared regions of the spectrum, which is why they are called red giants.

The largest of the giants turn into red supergiants. A star called Betelgeuse in the constellation Orion is the most striking example of a red supergiant.

Dwarf stars are the opposite of giants and can be as follows.

A white dwarf is what remains of an ordinary star with a mass not exceeding 1.4 solar masses after it passes through the red giant stage.

Due to the absence of hydrogen, a thermonuclear reaction does not occur in the core of such stars.

White dwarfs are very dense. They are no larger than the Earth in size, but their mass can be compared with the mass of the Sun.

These are incredibly hot stars, reaching temperatures of 100,000 degrees or more. They shine on their remaining energy, but over time, it runs out, and the core cools down, turning into a black dwarf.

Red dwarfs are the most common stellar-type objects in the universe. Estimates of their abundance range from 70 to 90% of the number of all stars in the galaxy. They are quite different from other stars.

The mass of red dwarfs does not exceed a third of the solar mass (the lower mass limit is 0.08 solar, followed by brown dwarfs), the surface temperature reaches 3500 K. Red dwarfs have a spectral type M or late K. Stars of this type emit very little light, sometimes in 10,000 times smaller than the Sun.

Given their low radiation, none of the red dwarfs are visible from Earth to the naked eye. Even the closest red dwarf to the Sun, Proxima Centauri (the closest star in the triple system to the Sun) and the closest single red dwarf, Barnard's Star, have an apparent magnitude of 11.09 and 9.53, respectively. At the same time, a star with a magnitude of up to 7.72 can be observed with the naked eye.

Due to the low rate of hydrogen combustion, red dwarfs have a very long lifespan - from tens of billions to tens of trillions of years (a red dwarf with a mass of 0.1 solar masses will burn for 10 trillion years).

In red dwarfs, thermonuclear reactions involving helium are impossible, so they cannot turn into red giants. Over time, they gradually shrink and heat up more and more until they use up the entire supply of hydrogen fuel.

Gradually, according to theoretical concepts, they turn into blue dwarfs - a hypothetical class of stars, while none of the red dwarfs has yet managed to turn into a blue dwarf, and then into white dwarfs with a helium core.

Brown dwarfs are substellar objects (with masses in the range of about 0.01 to 0.08 solar masses, or, respectively, from 12.57 to 80.35 Jupiter masses and a diameter approximately equal to that of Jupiter), in the depths of which, in contrast from main sequence stars, there is no thermonuclear fusion reaction with the conversion of hydrogen into helium.

The minimum temperature of main sequence stars is about 4000 K, the temperature of brown dwarfs lies in the range from 300 to 3000 K. Brown dwarfs constantly cool down throughout their lives, while the larger the dwarf, the slower it cools.

subbrown dwarfs

Subbrown dwarfs or brown subdwarfs are cold formations that lie below the brown dwarf limit in mass. Their mass is less than about one hundredth of the mass of the Sun or, respectively, 12.57 masses of Jupiter, the lower limit is not defined. They are more commonly considered planets, although the scientific community has not yet come to a final conclusion about what is considered a planet and what is a subbrown dwarf.

black dwarf

Black dwarfs are white dwarfs that have cooled down and therefore do not radiate in the visible range. Represents the final stage in the evolution of white dwarfs. The masses of black dwarfs, like the masses of white dwarfs, are limited from above by 1.4 solar masses.

A binary star is two gravitationally bound stars revolving around a common center of mass.

Sometimes there are systems of three or more stars, in such a general case the system is called a multiple star.

In cases where such a star system is not too far removed from the Earth, individual stars can be distinguished through a telescope. If the distance is significant, then it is possible to understand that a double star is possible before astronomers only by indirect signs - fluctuations in brightness caused by periodic eclipses of one star by another and some others.

New star

Stars that suddenly increase in luminosity by a factor of 10,000. A nova is a binary system consisting of a white dwarf and a main sequence companion star. In such systems, gas from the star gradually flows into the white dwarf and periodically explodes there, causing a burst of luminosity.

Supernova

A supernova is a star that ends its evolution in a catastrophic explosive process. The flare in this case can be several orders of magnitude greater than in the case of a new star. Such a powerful explosion is a consequence of the processes taking place in the star at the last stage of evolution.

neutron star

Neutron stars (NS) are stellar formations with masses of the order of 1.5 solar masses and sizes noticeably smaller than white dwarfs, the typical radius of a neutron star is, presumably, of the order of 10-20 kilometers.

They consist mainly of neutral subatomic particles - neutrons, tightly compressed by gravitational forces. The density of such stars is extremely high, it is commensurate with, and according to some estimates, may be several times higher than the average density of the atomic nucleus. One cubic centimeter of NZ matter would weigh hundreds of millions of tons. The force of gravity on the surface of a neutron star is about 100 billion times greater than on Earth.

In our Galaxy, according to scientists, there can be from 100 million to 1 billion neutron stars, that is, somewhere around one in a thousand ordinary stars.

Pulsars

Pulsars are cosmic sources of electromagnetic radiation that come to Earth in the form of periodic bursts (pulses).

According to the dominant astrophysical model, pulsars are rotating neutron stars with a magnetic field that is tilted to the axis of rotation. When the Earth falls into the cone formed by this radiation, it is possible to record a radiation pulse that repeats at intervals equal to the period of revolution of the star. Some neutron stars make up to 600 revolutions per second.

cepheid

Cepheids are a class of pulsating variable stars with a fairly accurate period-luminosity relationship, named after the star Delta Cephei. One of the most famous Cepheids is the North Star.

The above list of the main types (types) of stars with their brief characteristics, of course, does not exhaust the entire possible variety of stars in the Universe.

On a clear night, if you look closely, you can see a myriad of multi-colored stars in the sky. Have you ever wondered what determines the shade of their flicker, and what are the colors of the heavenly bodies?

The color of a star is determined by its surface temperature.. A scattering of luminaries, like precious stones, has infinitely different shades, like a magic palette of an artist. The hotter the object, the higher the radiation energy from its surface, which means the shorter the length of the emitted waves.

Even a slight difference in wavelength changes the color perceived by the human eye. The longest waves have a red tint, with increasing temperature it changes to orange, yellow, turns into white, and then becomes white-blue.

The gas envelope of the luminaries performs the functions of an ideal emitter. The color of a star can be used to calculate its age and surface temperature. Of course, the shade is determined not “by eye”, but with the help of a special tool - a spectrograph.

The study of the spectrum of stars is the foundation of astrophysics of our time. The colors of the heavenly bodies are most often the only information available to us about them.

blue stars

Blue stars are the most big and hot. The temperature of their outer layers is, on average, 10,000 Kelvin, and can reach 40,000 for individual stellar giants.

In this range, new stars radiate, just starting their "life journey". For instance, Rigel, one of the two main luminaries of the constellation Orion, bluish-white.

yellow stars

Center of our planetary system - The sun- has a surface temperature exceeding 6000 Kelvin. From space, it and similar luminaries look dazzling white, although from Earth they seem more likely to be yellow. Gold stars are of middle age.

Of the other luminaries known to us, a white star is also Sirius, although it is quite difficult to determine its color by eye. This is because it occupies a low position above the horizon, and on the way to us, its radiation is strongly distorted due to multiple refraction. In mid-latitudes, Sirius, often flickering, is able to demonstrate the entire color spectrum in just half a second!

red stars

Dark reddish hue have low temperature stars, for example, red dwarfs, whose mass is less than 7.5% of the weight of the Sun. Their temperature is below 3500 Kelvin, and although their glow is a rich play of many colors and shades, we see it as red.

Giant luminaries whose hydrogen fuel has run out also look red or even brown. In general, the emission of old and cooling stars is in this range of the spectrum.

A distinct red hue has the second of the main stars of the constellation Orion, Betelgeuse, and slightly to the right and above it is located on the sky map Aldebaran, which is orange in color.

The oldest red star in existence - HE 1523-0901 from the constellation Libra - a giant luminary of the second generation, found on the outskirts of our galaxy at a distance of 7500 light years from the Sun. Its possible age is about 13.2 billion years, which is not much less than the estimated age of the universe.