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 color.

The secret of the multi-colored stars has become an important tool for astronomers - the color of the stars helped them to find out the temperature of the surface of stars. The remarkable a natural phenomenon- the ratio 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 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, had 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 color 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 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.

Characteristics

Due to their large masses, blue supergiants have a rather short lifespan and are observed only in young cosmic structures, such as open clusters, arms spiral galaxies and in 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 Big 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 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, the mass of which varies between eight and 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.

Because 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 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 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 +1.79), the left and most nearby 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 Big Dog. 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 given 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.

Multicolored stars in the sky. Shot with enhanced colors

The color palette of stars is wide. Blue, yellow and red - shades are visible even through the atmosphere, which usually distorts the outlines of cosmic bodies. But where does the color of a star come from?

The origin of the color of the stars

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

You have probably already made your own observations on this subject. 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 a star on its color is very small - the temperature can hide individual elements, ionizing them.

But it is 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 that pass through the substance. A hot medium shortens the waves, while a cold medium, on the contrary, lengthens them. And the visible color of a light beam is precisely determined by the wavelength of light: short waves are responsible for blue hues, and long ones are responsible for red ones. White color is obtained as a result of the imposition of multispectral rays.

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 hue, 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 path". For example, Rigel, one of the two main luminaries of the constellation Orion, bluish-white.

yellow stars

Center of our planetary system - Sun- has a surface temperature exceeding 6000 Kelvin. From space, it and similar luminaries look dazzling white, although from Earth they seem rather 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 overflow 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 tint 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.

With a telescope, you can observe 2 billion stars up to 21 magnitudes. There is a Harvard spectral classification of stars. In it, the spectral types are arranged in order of decreasing stellar temperature. Classes are designated by letters of the Latin alphabet. There are seven of them: O - B - A - P - O - K - M.

A good indicator of the temperature of a star's outer layers is its color. Hot stars of spectral types O and B are blue; stars similar to our Sun (whose spectral type is 02) appear yellow, while stars of spectral classes K and M are red.

Brightness and color of stars

All stars have a color. There are blue, white, yellow, yellowish, orange and red stars. For example, Betelgeuse is a red star, Castor is white, Capella is yellow. By brightness, they are divided into stars 1st, 2nd, ... nth star values ​​(n max = 25). The term "magnitude" has nothing to do with true dimensions. The magnitude characterizes the light flux coming to Earth from a star. Stellar magnitudes can be both fractional and negative. The magnitude scale is based on the perception of light by the eye. The division of stars into stellar magnitudes according to apparent brightness was carried out by the ancient Greek astronomer Hipparchus (180 - 110 BC). Hipparchus attributed the first magnitude to the brightest stars; he considered the next in brightness gradation (i.e., about 2.5 times weaker) to be stars of the second magnitude; stars weaker than stars of the second magnitude by 2.5 times were called stars of the third magnitude, etc.; stars at the limit of visibility to the naked eye were assigned a sixth magnitude.

With such a gradation of the brightness of the stars, it turned out that the stars of the sixth magnitude are weaker than the stars of the first magnitude by 2.55 times. Therefore, in 1856, the English astronomer N. K. Pogsoi (1829-1891) proposed to consider as stars of the sixth magnitude those that are exactly 100 times weaker than the stars of the first magnitude. All stars are located at different distances from the Earth. It would be easier to compare magnitudes if the distances were equal.

The magnitude that a star would have at a distance of 10 parsecs is called absolute magnitude. The absolute stellar magnitude is indicated - M, and the apparent stellar magnitude - m.

The chemical composition of the outer layers of stars, from which their radiation comes, is characterized by the complete predominance of hydrogen. In second place is helium, and the content of other elements is quite small.

Temperature and mass of stars

Knowing the spectral type or color of a star immediately gives the temperature of its surface. Since stars radiate approximately like absolutely black bodies of the corresponding temperature, the power radiated by a unit of their surface per unit of time is determined from the Stefan-Boltzmann law.

The division of stars based on a comparison of the luminosity of stars with their temperature and color and absolute magnitude (Hertzsprung-Russell diagram):

1. the main sequence (in the center of it is the Sun - a yellow dwarf)
2. supergiants (large in size and high luminosity: Antares, Betelgeuse)
3. red giant sequence
4. dwarfs (white - Sirius)
5. subdwarfs
6. white-blue sequence

This division is also based on the age of the star.

The following stars are distinguished:

1. ordinary (Sun);
2. double (Mizar, Albkor) are divided into:

• a) visual double, if their duality is noticed when observing through a telescope;
• b) multiples - this is a system of stars with a number greater than 2, but less than 10;
• c) optical-double - these are stars that their proximity is the result of a random projection onto the sky, and in space they are far away;
• d) physical binaries are stars that form single system and circulate under the action of forces of mutual attraction around a common center of mass;
• e) spectroscopic binaries are stars that, when mutually revolving, come close to each other and their duality can be determined from the spectrum;
• e) eclipsing binary - these are stars "which, when mutually revolving, block each other;

new stars- these are stars that existed for a long time, but suddenly flared up. Their brightness increased in a short time by 10,000 times (the amplitude of the change in brightness from 7 to 14 magnitudes).

supernovae- these are stars that were invisible in the sky, but suddenly flashed and increased in brightness 1000 times relative to ordinary new stars.

Pulsar- a neutron star that occurs during a supernova explosion.

Data about total number pulsars and their lifetimes indicate that, on average, 2-3 pulsars are born per century, which approximately coincides with the frequency of supernova explosions in the Galaxy.

Star evolution

Like all bodies in nature, stars do not remain unchanged, they are born, evolve, and finally die. Astronomers used to think that it took millions of years for a star to form from interstellar gas and dust. But in last years photographs were taken of a region of the sky that is part of the Great Nebula of Orion, where a small cluster of stars has appeared over the course of several years. In the photographs of 1947, a group of three star-like objects was recorded in this place. By 1954 some of them had become oblong, and by 1959 these oblong formations had disintegrated into individual stars. For the first time in the history of mankind, people observed the birth of stars literally before our eyes.

In many parts of the sky, there are conditions necessary for the appearance of stars. When studying photographs of foggy areas Milky Way found small black spots irregular shape, or globules, which are massive accumulations of dust and gas. These gas and dust clouds contain dust particles that very strongly absorb the light coming from the stars behind them. The size of the globules is huge - up to several light years in diameter. Despite the fact that the matter in these clusters is very rarefied, their total volume is so large that it is quite enough to form small clusters of stars close in mass to the Sun.

In a black globule, under the influence of radiation pressure emitted by surrounding stars, the matter is compressed and compacted. Such compression proceeds for some time, depending on the sources of radiation surrounding the globule and the intensity of the latter. The gravitational forces arising from the concentration of mass in the center of the globule also tend to compress the globule, causing matter to fall towards its center. Falling, particles of matter acquire kinetic energy and heat up the gas and cloud.

The fall of matter can last hundreds of years. At first, it happens slowly, unhurriedly, because gravitational forces, which attract particles to the center, are still very weak. After some time, when the globule becomes smaller and the gravitational field increases, the fall begins to occur faster. But the globule is huge, no less than a light year in diameter. This means that the distance from its outer border to the center can exceed 10 trillion kilometers. If a particle from the edge of the globule starts to fall towards the center at a speed slightly less than 2 km/s, then it will reach the center only after 200,000 years.

The lifespan of a star depends on its mass. Stars With a mass less than that of the Sun use their nuclear fuel very sparingly and can shine for tens of billions of years. The outer layers of stars like our Sun, with masses no greater than 1.2 solar masses, gradually expand and, in the end, completely leave the core of the star. In place of the giant remains a small and hot white dwarf.

Stars are giant agglomerations of hot gas. They consist mainly of two types of gas - hydrogen and helium. Due to the fusion of hydrogen and helium, an energy release occurs, due to which the stars are so bright and hot and, probably, that is why they appear white to us. And what about the most famous star -? It no longer seems so white to us, and looks more like yellow. And there are red, brown, blue stars.

In order to understand why stars come in different colors, it is necessary to trace the entire life path of a star from the moment it appears to its complete extinction.

Photo by Nigel Howe

Now you understand that each star goes through different paths of its development and constantly changes its size, color, brightness, temperature. Hence, there are so many varieties of stars. The smallest stars are red. Medium stars are yellow in color, such as our Sun. Bigger stars are blue, they are the most bright stars. brown dwarfs have very low energy and are not able to compensate for the energy loss to radiation. White dwarfs are gradually cooling stars that soon become invisible and dark.

Our only star solar system, the Sun, belongs to the type of "yellow dwarfs". The North Star, which points the way for sailors, is a blue supergiant. Proxima Centauri, the closest star to the Sun, is a red dwarf. Most of the stars in the universe are also red dwarfs. And we see all the stars as white, why? It turns out that the reason for this is the dimness of the stars and our vision. It is not sharp enough to catch the different colors of such stars. But the color of the most bright stars we can still discern.

Now you know that stars are not only white and you can easily cope with the task.

Exercise:

1. Draw a sky full of colorful stars. This is exactly the kind of sky that we would see if we had a sharper vision.