Supergiant stars - the cosmic fate of these colossal luminaries destined them to burst into a supernova at a certain time.

All stars are born in the same way. A giant cloud of molecular hydrogen begins to shrink into a ball under the influence of gravity until the internal temperature triggers nuclear fusion. Throughout their existence, the luminaries are in a state of struggle with themselves, outer layer crushes by gravity, and the core - by the force of a heated substance, which tends to expand. In the process of existence, hydrogen and helium gradually burn out in the center and ordinary luminaries with a significant mass become supergiants. There are such objects in young formations, such as irregular galaxies or open clusters.

Properties and Options

Mass plays a decisive role in the formation of stars - more energy is synthesized in a large core, which increases the temperature of the star and its activity. Approaching the final segment of existence, objects with a weight exceeding the sun by 10-70 times, pass into the category of supergiants. In the Hertzsprung-Russell diagram, which characterizes the relationship of magnitude, luminosity, temperature and spectral type, such luminaries are located on top, indicating a high (from +5 to +12) apparent magnitude of objects. They are shorter than those of other stars, because they reach their state at the end of the evolutionary process, when the reserves of nuclear fuel are running out. In hot objects, helium and hydrogen run out, and combustion continues due to oxygen and carbon and further up to iron.

Classification of supergiant stars

According to the Yerkes classification, which reflects the subordination of the luminosity spectrum, supergiants belong to class I. They were divided into two groups:

• Ia - bright supergiants or hypergiants;
• Ib are less luminous supergiants.

According to their spectral type in the Harvard classification, these stars occupy the interval from O to M. Blue supergiants are represented by classes O, B, A, red - K, M, intermediate and poorly studied yellow - F, G.

Red supergiants

Large stars leave the main sequence when carbon and oxygen start burning in their core - they become red supergiants. Their gas envelope grows to enormous sizes, spreading over millions of kilometers. Chemical processes that take place with the penetration of convection from the shell into the core lead to the synthesis heavy elements iron peak, which, after the explosion, scatter in space. It is the red supergiants that usually end up life path luminaries and explode in a supernova. The gas envelope of the star gives rise to a new nebula, and the degenerate core turns into a white dwarf. And - largest objects from among the dying red luminaries.

Blue supergiants

Unlike red, long-living giants, these are young and hot stars, exceeding the mass of the sun by 10-50 times, and by a radius of 20-25 times. Their temperature is impressive - it is 20-50 thousand degrees. The surface of blue supergiants is rapidly decreasing due to compression, while the radiation of internal energy is constantly growing and increasing the temperature of the star. The result of this process is the transformation of red supergiants into blue ones. Astronomers have noticed that stars go through various stages in their development, at intermediate stages they turn yellow or white. Orion's brightest star is a great example of a blue supergiant. Its impressive mass is 20 times greater than the Sun, its luminosity is 130 thousand times higher.

Supergiants are among the most massive stars. Masses of supergiants vary from 10 to 70 solar masses, luminosities - from 30,000 up to hundreds of thousands of solar masses. The radii can vary greatly - from 30 to 500, and sometimes exceed 1000 solar, then they can still be called hypergiants. It follows from the Stefan-Boltzmann law that the relatively cold surfaces of red supergiants emit much less energy per unit area than hot blue supergiants. Therefore, at the same luminosity, a red supergiant will always be larger than a blue one.

In the Hertzsprung-Russell diagram, which characterizes the relationship of magnitude, luminosity, temperature and spectral type, such luminaries are located on top, indicating a high (from +5 to +12) apparent magnitude of objects. Their life cycle is shorter than that of other stars, because they reach their state at the end of the evolutionary process, when the stocks of nuclear fuel are running out. In hot objects, helium and hydrogen run out, and combustion continues due to oxygen and carbon and further up to iron.

Large stars leave the main sequence when carbon and oxygen start burning in their core - they become red supergiants. Their gas envelope grows to enormous sizes, spreading over millions of kilometers. Chemical processes that take place with the penetration of convection from the shell into the core lead to the synthesis of heavy elements of the iron peak, which, after the explosion, scatter in space. It is red supergiants that usually end the life of a star and explode in a supernova. The gas envelope of the star gives rise to a new nebula, and the degenerate core turns into a white dwarf. Antares and Betelgeuse are the largest of the dying red stars.

Fig.74. The disk of the star Betelgeuse. Image from the Hubble telescope.

Unlike red, long-living giants, blue giants are young and hot stars, exceeding the mass of the sun by 10-50 times, and by a radius of 20-25 times. Their temperature is impressive - it is 20-50 thousand degrees. The surface of blue supergiants is rapidly decreasing due to compression, while the radiation of internal energy is constantly growing and increasing the temperature of the star. The brightest star in the Orion constellation, Rigel, is an excellent example of a blue supergiant. Its impressive mass is 20 times greater than the Sun, the luminosity is 130 thousand times higher.

Fig.75. Constellation of Orion.

In the constellation Cygnus, the star Deneb is observed - another representative of this rare class. This is a bright supergiant. In the sky, in its luminosity, this distant star can only be compared with Rigel. The intensity of its radiation is comparable to 196 thousand Suns, the radius of the object exceeds our star by 200 times, and its mass is 19 times. Deneb is rapidly losing its mass, a stellar wind of incredible strength carries its substance throughout the Universe. The star has already entered a period of instability. So far, its brilliance varies in small amplitude, but over time it will become pulsating. After exhausting the supply of heavy elements that keep the core stable, Deneb, like other blue supergiants, will burst into a supernova, and its massive core will become a black hole.

Hypergiants slightly exceed supergiants in size, but at the same time they prevail in mass by tens of times, and their brightness reaches from 500 thousand to 5 million solar luminosities. These stars have the most short life, sometimes hundreds of thousands of years old. About 10 such bright and powerful objects have been found in our Galaxy.

Fig.76. Deneb.

The brightest star to date (and the most massive) is the luminary R136a1. Its opening was announced in 2010. It is a Wolf-Rayet star with a luminosity of about 8,700,000 solar luminosities and a mass 265 times greater than our own star. Once its mass was 320 solar. R136a1 is actually part of a dense cluster of stars called R136 located in the Large Magellanic Cloud. According to Paul Crowther, one of the discoverers, “Planets take longer to form than such a star has to live and die. Even if there were planets, there would be no astronomers on them, because the night sky was as bright as the daytime sky.”

Fig.77. Computer processing of a photograph of the star R136a1.

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. Relatively brief evolution 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 the outer layers of gas, thereby forming planetary nebulae, and the core collapses into a small, dense white dwarf.

The red giant is big star reddish or orange color. 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 relatively low temperature surface, 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 a prime example 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 not sized more earth, 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).

Impossible in red dwarfs thermonuclear reactions with the participation of helium, 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 ideas, 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 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 understand that before astronomers double star succeeds 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 larger than in the case new star. So 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 gravitational forces. The density of such stars is extremely high, it is commensurate, and according to some estimates, it can be several times higher than the average density atomic nucleus. One cubic centimeter NZ matter will 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 coming to Earth in the form of periodic bursts (pulses).

According to the dominant astrophysical model, pulsars are rotating neutron stars from magnetic field, which 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 description, of course, does not exhaust the entire possible variety of stars in the Universe.

The results of determining the stellar diameters turned out to be truly amazing. did not suspect before that there could be such giant stars. The first star whose true size could be determined (in 1920) was the bright star of the constellation Orion, bearing the Arabic name Betelgeuse. Its diameter turned out to be greater than the diameter of the orbit of Mars! Another giant star is Antares, the brightest star in the constellation Scorpius: its diameter is about one and a half times the diameter of the earth's orbit. Among the stellar giants discovered so far, one should also put the so-called Marvelous "Mira", a star in the constellation Cetus, the diameter of which is 330 times greater than the diameter of our Sun. Usually giant stars have radii from 10 to 100 solar radii and luminosities from 10 to 1000 solar luminosities. Stars with a luminosity greater than that of giants are called supergiants and hypergiants.

Giant stars have an interesting physical structure. The calculation shows that such stars, despite their monstrous sizes, contain disproportionately little matter. They are only a few times heavier than our Sun; and since the volume of Betelgeuse, for example, more sun 40,000,000 times, then the density of this star must be negligible. And if the matter of the Sun, on average, approaches in density, then the matter of giant stars in this respect is like rarefied air. Giant stars, in the words of one astronomer, "resemble a huge balloon of low density, much less than the density of air."

A star becomes a giant after all the hydrogen available for reaction in the star's core has been used up. A star whose initial mass does not exceed about 0.4 solar masses, will not become a giant star. This is because the matter inside such stars is highly mixed by convection, and so the hydrogen continues to react until it has used up all of the star's mass, at which point it becomes a white dwarf made up mostly of helium. If the star is more massive than this lower limit, then when it consumes all the hydrogen available in the core for the reaction, the core will begin to shrink. Now the hydrogen reacts with helium in a shell around the helium-rich core, and the part of the star outside the shell expands and cools. In this place of its evolution, the luminosity of the star remains approximately constant and the temperature of its surface decreases. The star begins to become a red giant. At this point, already, as a rule, a red giant will remain approximately constant, while its luminosity and radius will increase significantly, and the core will continue to shrink, increasing its temperature.

If the star's mass was below about 0.5 solar masses, it is believed that it will never reach the central temperatures needed to fuse helium. Therefore, it will remain a red giant star with hydrogen fusion until it begins to turn into a helium white dwarf.

The birth of any star occurs in approximately the same way - as a result of compression and compaction under the influence of its own gravity of a cloud, which consists mainly of interstellar gas and dust. According to scientists, it is this compression process that contributes to the formation of new stars. At present, thanks to modern equipment, scientists can see this process. In a telescope, it looks like certain zones that look like dark spots on a bright background. They are referred to as "giant molecular cloud complexes". These zones got such a name due to the fact that they contain hydrogen in the form of molecules. These complexes or systems, together with globular star clusters, are the largest structures in the Galaxy with a diameter of up to 1300 light years.

Simultaneously with the process of compression of the nebula, dense, dark, round-shaped clouds of gas and dust are also formed, which are called the Bok Globules. It was the American astronomer Bock who first described these globules, thanks to which they are now called that way. Initially, the mass of the globule is 200 times the mass of the Sun. However, gradually the globules continue to thicken, gaining mass and attracting matter from neighboring regions due to their gravity. It is worth paying attention to the fact that inner part globule thickens many times faster than the outer one. In turn, this leads to heating and rotation of the globule. This process continues for several hundred thousand years, after which a protostar is formed.

As the mass of the star increases, more and more matter is attracted. There is also a release of energy from the gas that contracts inside, which leads to the formation of heat. In this regard, the pressure and temperature of the star increase, which leads to its glow with a dark red light. The protostar is characterized by its fairly large-scale dimensions. Despite the fact that heat is evenly distributed over its entire surface, it is still considered relatively cold. At the core, the temperature continues to rise. In addition, its rotation occurs and it acquires a somewhat flat shape. This process takes several million years.

Young stars are very difficult to see, especially with the naked eye. They can only be seen with special equipment. This is due to the fact that due to the dark dust cloud that surrounds the stars, the glow of young stars is almost invisible.

Thus, stars are born, evolve and die. At each stage of their development, stars have their own specific mass, temperature, and brightness. In this regard, all stars are usually classified into:

Main sequence stars;

Stars are dwarfs;

Giant stars.

What stars are giants

So, giant stars speak for themselves and, accordingly, have a significantly larger radius and high luminosity, in contrast to those main sequence stars that have the same surface temperature. Giant stars typically range in radius from 10 to 100 solar radii, and have luminosities between 10 and 1000 solar luminosities. The temperature of giant stars is relatively low due to the mass of the star, since it is distributed over the entire stellar surface, and reaches about 5000 degrees.

However, there are also stars that have many times greater luminosity than giant stars. Such stars are called supergiants and hypergiants.

A supergiant star is considered one of the most massive stars. Stars of this type occupy upper part Hertzsprung-Russell diagrams. These stars have a mass that ranges from 10 to 70 solar masses. Their luminosity is 30,000 solar luminosities or more. But the radii of supergiant stars can vary significantly - ranging from 30 to 500 solar radii. But there are also stars that have a radius exceeding 1000 solar. However, these supergiants are already moving into the category of hypergiants.

Due to the fact that these stars have very huge masses, their life expectancy is extremely short and ranges from 30 to several hundred million years. Supergiants can be observed, as a rule, in regions of active star formation - open star clusters, arms spiral galaxies, as well as in irregular galaxies.

red giant

A red giant is a star of late spectral classes, which has a high luminosity and extended envelopes. The most famous red giants are Arcturus, Aldebaran, Gacrux, Mira.

Red giants belong to the spectral classes K and M. They also have a relatively low temperature of the radiating surface, which is about 3000 - 5000 degrees Kelvin. In turn, this indicates that the energy flux per unit radiating area is 2-10 times less than that of the Sun. The radius of red giants is in the range from 100 to 800 solar radii.

The spectra of red giants are characterized by the presence of molecular absorption bands, since some molecules are stable in their relatively cold photosphere. The maximum radiation falls on the red and infrared regions of the spectrum.

In addition to red giants, there are also white giants. A white giant is a main sequence star that is quite hot and bright. Sometimes a white giant star can combine with a red dwarf. Such a combination of stars is called a double or multiple and, as a rule, consists of stars of various types.