Big and small, hot and cold, charged and uncharged. In this article we will give a classification of the main types of stars.

One of the classifications of stars is spectral classification. According to this classification, stars are assigned to one class or another according to their spectrum. The spectral classification of stars serves many problems in stellar astronomy and astrophysics. A qualitative description of the observed spectrum makes it possible to estimate important astrophysical characteristics of a star, such as its effective surface temperature, luminosity, and, in some cases, features of its chemical composition.

Some stars do not fall into any of the listed spectra. Such stars are called peculiar. Their spectra do not fit into the O–B–A–F–G–K–M temperature sequence. Although often such stars represent certain evolutionary stages of completely normal stars, or represent stars that are not quite characteristic of the immediate vicinity (stars poor in metals, such as stars of globular clusters and halo). In particular, stars with peculiar spectra include stars with different features of the chemical composition, which manifests itself in the strengthening or weakening of the spectral lines of some elements.

Hertzsprung-Russell diagram

A good understanding of the classification of stars allows Hertzsprung-Russell diagram. It shows the relationship between absolute magnitude, luminosity, spectral type, and surface temperature of a star. Unexpected is the fact that the stars in this diagram are not arranged randomly, but form well-defined areas. The diagram was proposed in 1910 independently by the researchers E. Hertzsprung and G. Russell. It is used to classify stars and corresponds to modern ideas about.

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 hydrogen burning stage is ~90% of the time of evolution 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 short evolution of red giants leads, depending on their mass, to the formation of white dwarfs, neutron stars or.

yellow dwarf

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. One such example is our Sun. Sometimes such normal stars are called yellow dwarfs.

The star may be called red giant at the time of star formation and in the later stages of development. At an early stage of development, a star radiates 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 leave the main sequence and move to the region of red giants and supergiants of the Hertzsprung-Russell diagram: this stage lasts ~ 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.

giant stars

giant star has a relatively low surface temperature, about 5000 degrees. A huge radius, reaching 800 solar radii, 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.

dwarf stars are the opposite of giants and include several different subspecies:

• white dwarf- evolved stars with a mass not exceeding 1.4 solar masses, deprived of their own sources of thermonuclear energy. The diameter of such stars can be hundreds of times smaller than the sun, and therefore the density can be 1,000,000 times that of water.
• red dwarf- a small and relatively cold main sequence star with a spectral type M or upper K. They are quite different from other stars. The diameter and 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).
• brown dwarf- substellar objects with masses in the range of 5-75 Jupiter masses (and a diameter approximately equal to the diameter of Jupiter), in the depths of which, unlike main sequence stars, there is no thermonuclear fusion reaction with the conversion of hydrogen into helium.
• Subbrown dwarfs or brown subdwarfs- cold formations, in terms of mass, lying below the limit of brown dwarfs. They are mostly considered.
• black dwarf 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.

In addition to those listed above, there are several other products of stellar evolution:

• neutron star. Star formations with masses on the order of 1.5 solar masses and sizes noticeably smaller than white dwarfs, on the order of 10-20 km in diameter. The density of such stars can reach 1,000,000,000,000 of the densities of water. And the magnetic field is the same number of times greater than the magnetic field of the earth. Such stars consist mainly of neutrons tightly compressed by gravitational forces. Often such stars are.
• 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 is a star ending its evolution in a catastrophic explosive process. The flare in this case can be several orders of magnitude larger 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.
• double star are 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, in

With high luminosity [up to 10 5 -10 6 solar luminosities (Lʘ)] and low effective temperature (3000-5000 K).

According to the Yerkes spectral classification, they belong respectively to spectral classes K and M and luminosity classes III and I (or 0 in the case of the most massive red supergiants - the so-called hypergiants). The radii of red giants reach hundreds of solar radii (Rʘ), and red supergiants reach thousands of Rʘ. Red giants and supergiants emit predominantly in the red and IR regions of the spectrum. A characteristic feature of the spectra of red giants and supergiants is the presence of metal emission lines, Ca II, Ca I H and K lines, and molecular absorption bands. Typical red giants include Aldebaran (luminosity ≈ 160Lʘ, radius ≈ 25Rʘ), red supergiants - Betelgeuse (≈ 7 10 4 Lʘ, ≈ 700Rʘ).

Stars fall into the region of the Hertzsprung-Russell diagram, occupied by red giants and supergiants, as a result of the expansion of their shells after hydrogen burns out in the cores of stars (see Evolution of stars). Stars with masses from ≈ 1 solar mass (Mʘ) to ≈ (8-10)Mʘ become red giants. Stars with masses from ≈ (8-10) Mʘ to ≈ 40 Mʘ turn into red supergiants. Initially, red giants and supergiants have helium cores surrounded by a layer in which hydrogen thermonuclear combustion occurs. When the temperature in the center of the star T c reaches ≈ 2·10 8 K, helium combustion begins. Helium burnout leads to the formation of carbon-oxygen nuclei (Fig.), Surrounded by two unstable combustion layers - helium and hydrogen (the so-called giants of the asymptotic branch). The matter in the cores of red giants is degenerate.

Red giants and supergiants are characterized by an intense outflow of matter (stellar wind), the flow of which can reach 10 -5 -10 -4 Mʘ per year. The stellar wind arises under the action of radiation pressure, pulsation instability, and shock waves in stellar coronas. The loss of matter and its cooling can lead to the formation of huge gas-dust circumstellar shells that completely absorb the visible radiation of stars.

Such objects radiate in the IR range of the spectrum (the so-called OH / IR stars).

The combustion of hydrogen and helium in layered sources leads to an increase in the masses of the stellar cores; the nuclei shrink and T c increases. However, in red giants with initial masses ≤(8-10)Mʘ, the loss of matter leads to the fact that the masses of their degenerate carbon-oxygen cores do not reach a value at which carbon ignition is possible, and they turn into white dwarfs with masses ≤Mʘ, having passed stage of a planetary nebula. In the cores of more massive stars, carbon, oxygen, neon, magnesium, silicon are sequentially burnt out, and the process of nucleosynthesis ends with the formation of iron (56 Fe) nuclei with a mass of ≈ (1.5-2)Mʘ, which collapse with the formation of neutron stars or black holes. Collapsing red supergiants appear as type II supernovae. The time that stars spend in the red giant or red supergiant stage is about 10% of their total lifetime.

Variable stars of various types are observed among red giants and supergiants: Mirids, semi-regular variables, etc., with pulsation periods from tens of days to several years and brightness variations of up to several magnitudes. Pulsations can be either radial or non-radial. Shock waves propagating in the shells of stars can be superimposed on pulsations.

Stars with a chemical composition close to the Sun, with initial masses ≥40 Mʘ, do not reach the stage of a red supergiant during evolution, since already at the stage of hydrogen burning in the core they lose most of the hydrogen shell and move to the region of the Hertzsprung-Russell diagram occupied by hot stars (with effective temperature up to 10 5 K). A star can also leave the region of red giants or supergiants and move to the region of hotter stars if it is part of a close binary system and loses its envelope as a result of the filling of the Roche lobe.

Lit .: Zeldovich Ya. B., Blinnikov S. P., Shakura N. I. Physical foundations of the structure and evolution of stars. M., 1981; Zasov A. V., Postnov K. A. General astrophysics. Fryazino, 2006.

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 begin to burn 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 the 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 shortest life, sometimes hundreds of thousands of years. 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 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.

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, whose diameter 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, is 40,000,000 times larger than the Sun, the density of this star should 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.

Star - VY Canis Majoris is the largest of all known stars in the Milky Way. A mention of her can be found in a star catalog published back in 1801. There she is listed as a star of the seventh magnitude.

The red hypergiant VY Canis Majoris is located at a distance of 4900 light years from Earth. It is 2100 times larger than the Sun. In other words, if we imagine that VY suddenly appeared in the place of our luminary, then it would swallow up all the planets up to Saturn. In order to fly around such a "ball" at a speed of 900 km / h, it will take 1100 years. However, when moving at the speed of light, it will take much less time - only 8 minutes.

Since the middle of the 19th century, VY Canis Majoris has been known to have a crimson hue. It was assumed that it is a multiple. But later it turned out that this is a single star and it does not have a companion. And the raspberry glow spectrum is provided by the surrounding nebula.

3 or more stars that are seen as closely spaced are called a multiple star. If in fact they are just close to the line of sight, then this is an optical multiple star, if they are united by gravity, it is physically multiple.

With such gigantic dimensions, the mass of the star is only 40 times the mass of the Sun. The density of gases inside it is very low - this explains such an impressive size and relatively low weight. The force of gravity is not able to prevent the loss of stellar fuel. It is believed that by now the hypergiant has already lost more than half of its original mass.

Back in the middle of the 19th century, scientists noted that a giant star was losing its brightness. However, this parameter is still very impressive even now - the brightness of the VY glow is 500 times greater than the Sun.

Scientists believe that when the VY fuel runs out, it will explode in a supernova. The explosion will destroy any life for several light years around. But the Earth will not suffer - the distance is too great.

And the smallest

In 2006, it appeared in the press that a group of Canadian scientists led by Dr. Harvey Reicher had discovered the smallest star currently known in our galaxy. It is located in the star cluster NGC 6397 - the second farthest from the Sun. The research was carried out using the Hubble telescope.

The mass of the discovered luminary is close to the theoretically calculated lower limit and is 8.3% of the mass of the Sun. The existence of smaller stellar objects is considered impossible. Their small size simply does not allow nuclear fusion reactions to begin. The brightness of such objects is similar to the glow of a candle lit on the moon.

Seemingly inconspicuous UY Shield

Modern astrophysics in terms of stars seems to be re-experiencing its infancy. Observations of the stars give more questions than answers. Therefore, when asking which star is the largest in the Universe, you need to be immediately ready for answers. Are you asking about the largest star known to science, or about what limits science limits a star to? As is usually the case, in both cases you will not get a definitive answer. The most likely candidate for the largest star quite equally shares the palm with his "neighbors". As for how much it can be less than the real "king of the star" also remains open.

Comparison of the sizes of the Sun and the star UY Scuti. The sun is an almost invisible pixel to the left of UY Shield.

The supergiant UY Scutum, with some reservation, can be called the largest star observed today. Why "with reservation" will be said below. UY Scuti is 9500 light-years away and is seen as a dim variable star visible through a small telescope. According to astronomers, its radius exceeds 1700 radii of the Sun, and during the pulsation period this size can increase to as much as 2000.

It turns out that if such a star were placed in the place of the Sun, the current orbits of a terrestrial planet would be in the depths of a supergiant, and the boundaries of its photosphere would sometimes rest against the orbit. If we imagine our Earth as a grain of buckwheat, and the Sun as a watermelon, then the diameter of the UY Shield will be comparable to the height of the Ostankino TV tower.

To fly around such a star at the speed of light will take as much as 7-8 hours. Recall that the light emitted by the Sun reaches our planet in just 8 minutes. If you fly at the same speed with which it makes one revolution around the Earth in an hour and a half, then the flight around the UY Shield will last almost five years. Now imagine these scales, given that the ISS flies 20 times faster than a bullet and tens of times faster than passenger airliners.

Mass and Luminosity of UY Shield

It is worth noting that such a monstrous size of the UY Shield is completely incomparable with its other parameters. This star is "only" 7-10 times more massive than the Sun. It turns out that the average density of this supergiant is almost a million times lower than the density of the air surrounding us! For comparison, the density of the Sun is one and a half times the density of water, and a grain of matter even “weighs” millions of tons. Roughly speaking, the average matter of such a star is similar in density to the layer of the atmosphere located at an altitude of about one hundred kilometers above sea level. This layer, also called the Karman line, is a conditional boundary between the earth's atmosphere and space. It turns out that the density of the UY Shield is only a little short of the vacuum of space!

Also UY Shield is not the brightest. With its own luminosity of 340,000 solar, it is ten times dimmer than the brightest stars. A good example is the star R136, which, being the most massive star known today (265 solar masses), is almost nine million times brighter than the Sun. At the same time, the star is only 36 times larger than the Sun. It turns out that R136 is 25 times brighter and about the same times more massive than UY Shield, despite the fact that it is 50 times smaller than the giant.

Physical parameters of the UY Shield

In general, UY Scuti is a pulsating variable red supergiant of spectral type M4Ia. That is, on the Hertzsprung-Russell spectrum-luminosity diagram, UY Scutum is located in the upper right corner.

At the moment, the star is approaching the final stages of its evolution. Like all supergiants, she began to actively burn helium and some other heavier elements. According to current models, in a matter of millions of years, UY Scutum will successively transform into a yellow supergiant, then into a bright blue variable or a Wolf-Rayet star. The final stages of its evolution will be a supernova explosion, during which the star will shed its shell, most likely leaving behind a neutron star.

Already now UY Scutum shows its activity in the form of semi-regular variability with an approximate pulsation period of 740 days. Given that a star can change its radius from 1700 to 2000 solar radii, the rate of its expansion and contraction is comparable to the speed of spaceships! Its mass loss is an impressive rate of 58 millionth solar masses per year (or 19 Earth masses per year). This is almost one and a half earth masses per month. So, being on the main sequence millions of years ago, UY Scutum could have had a mass of 25 to 40 solar masses.

Giants among the stars

Returning to the reservation mentioned above, we note that the primacy of UY Shield as the largest known star cannot be called unequivocal. The fact is that astronomers still cannot determine the distance to most stars with a sufficient degree of accuracy, and therefore estimate their size. In addition, large stars tend to be very unstable (recall the UY Scutum pulsation). Similarly, they have a rather blurry structure. They may have a fairly extended atmosphere, opaque gas and dust shells, disks, or a large companion star (an example is VV Cephei, see below). It is impossible to say exactly where the boundary of such stars passes. In the end, the well-established concept of the boundary of stars as the radius of their photosphere is already extremely arbitrary.

Therefore, this number can include about a dozen stars, which include NML Cygnus, VV Cepheus A, VY Canis Major, WOH G64 and some others. All these stars are located in the vicinity of our galaxy (including its satellites) and are in many ways similar to each other. All of them are red supergiants or hypergiants (see below for the difference between super and hyper). Each of them in a matter of millions, or even thousands of years, will turn into a supernova. They are also similar in size, ranging from 1400-2000 solar.

Each of these stars has its own peculiarity. So in UY Shield, this feature is the previously discussed variability. WOH G64 has a toroidal gas and dust envelope. Extremely interesting is the double eclipsing variable star VV Cephei. It is a close system of two stars, consisting of the red hypergiant VV Cephei A and the blue main sequence star VV Cephei B. The centers of these stars are located from each other in some 17-34 . Considering that the VV radius of Cepheus B can reach 9 AU. (1900 solar radii), the stars are located at "arm's length" from each other. Their tandem is so close that whole pieces of the hypergiant flow with great speeds to the “little neighbor”, which is almost 200 times smaller than it.

Looking for a leader

Under such conditions, estimating the size of stars is already problematic. How can one talk about the size of a star if its atmosphere flows into another star, or smoothly passes into a gas and dust disk? This is despite the fact that the star itself consists of a very rarefied gas.

Moreover, all the largest stars are extremely unstable and short-lived. Such stars can live for a few millions, or even hundreds of thousands of years. Therefore, observing a giant star in another galaxy, you can be sure that a neutron star is now pulsating in its place or a black hole is warping space, surrounded by the remnants of a supernova explosion. If such a star is even thousands of light years away from us, one cannot be completely sure that it still exists or has remained the same giant.

Add to this the imperfection of modern methods for determining the distance to stars and a number of unspecified problems. It turns out that even among the ten largest known stars, it is impossible to single out a certain leader and arrange them in ascending order of size. In this case, Shield's UY was cited as the most likely candidate to lead the Big Ten. This does not mean at all that its leadership is undeniable and that, for example, NML Cygnus or VY Canis Major cannot be larger than her. Therefore, different sources can answer the question about the largest known star in different ways. This speaks rather not about their incompetence, but about the fact that science cannot give unambiguous answers even to such direct questions.

The largest in the universe

If science does not undertake to single out the largest among the discovered stars, how can we say which star is the largest in the Universe? According to scientists, the number of stars even within the boundaries of the observable universe is ten times greater than the number of grains of sand on all the beaches of the world. Of course, even the most powerful modern telescopes can see an unimaginably smaller part of them. The fact that the largest stars can be distinguished by their luminosity will not help in the search for a “stellar leader”. Whatever their brightness is, it will fade when observing distant galaxies. Moreover, as noted earlier, the brightest stars are not the largest (example - R136).

Also remember that when observing a large star in a distant galaxy, we will actually see its "ghost". Therefore, it is not easy to find the largest star in the Universe, its searches will be simply meaningless.

Hypergiants

If the largest star is impossible to find practically, maybe it is worth developing it theoretically? That is, to find a certain limit, after which the existence of a star can no longer be a star. Even here, however, modern science faces a problem. The current theoretical model of the evolution and physics of stars does not explain much of what actually exists and is observed in telescopes. An example of this is the hypergiants.

Astronomers have repeatedly had to raise the bar for the limit of stellar mass. This limit was first introduced in 1924 by the English astrophysicist Arthur Eddington. Having obtained the cubic dependence of the luminosity of stars on their mass. Eddington realized that a star cannot accumulate mass indefinitely. The brightness increases faster than the mass, and sooner or later this will lead to a violation of hydrostatic equilibrium. The light pressure of the increasing brightness will literally blow away the outer layers of the star. The limit calculated by Eddington was 65 solar masses. Subsequently, astrophysicists refined his calculations by adding unaccounted components to them and using powerful computers. So the modern theoretical limit for the mass of stars is 150 solar masses. Now remember that the mass of R136a1 is 265 solar masses, which is almost twice the theoretical limit!

R136a1 is the most massive star known today. In addition to it, several more stars have significant masses, the number of which in our galaxy can be counted on the fingers. Such stars are called hypergiants. Note that R136a1 is much smaller than the stars that, it would seem, should be below it in class - for example, the supergiant UY Shield. This is because hypergiants are called not the largest, but the most massive stars. For such stars, a separate class was created on the spectrum-luminosity diagram (O), located above the class of supergiants (Ia). The exact initial bar for the mass of a hypergiant has not been established, but, as a rule, their mass exceeds 100 solar masses. None of the biggest stars of the "Big Ten" falls short of these limits.

Theoretical impasse

Modern science cannot explain the nature of the existence of stars whose mass exceeds 150 solar masses. This raises the question of how a theoretical limit to the size of stars can be determined if the radius of a star, unlike mass, is itself a vague concept.

Let's take into account the fact that it is not known exactly what the stars of the first generation were, and what they will be in the course of the further evolution of the Universe. Changes in the composition, metallicity of stars can lead to radical changes in their structure. Astrophysicists have only to comprehend the surprises that will be presented to them by further observations and theoretical research. It is quite possible that UY Shield may turn out to be a real crumb against the background of a hypothetical "king-star" that shines somewhere or will shine in the farthest corners of our Universe.

In fact, this question is not as simple as it seems. It is very difficult to determine the exact sizes of stars, it is calculated on the basis of a lot of indirect data, because we cannot see their disks directly. Direct observation of the stellar disk has so far been carried out only for some large and nearby supergiants, and there are millions of stars in the sky. Therefore, it is not so easy to determine which is the largest star in the Universe - you have to rely mainly on calculated data.

In addition, for some stars, the boundary between the surface and the huge atmosphere is very blurred, and it is difficult to understand where one ends and the other begins. But this is an error not for some hundreds, but for millions of kilometers.

Many stars do not have a strictly defined diameter, they pulsate, and become either larger or smaller. And they can change their diameter very significantly.

In addition, science does not stand still. More and more accurate measurements are being made, distances and other parameters are being refined, and some stars suddenly turn out to be much more interesting than they seemed. This also applies to sizes. Therefore, we consider several candidates that are among the largest stars in the universe. Note that all of them are located not too far in space terms, and they are also the largest stars in the Galaxy.

A red hypergiant that claims to be the largest star in the universe. Alas, it is not, but very close. It is in third place in terms of size.

VV Cephei - that is, double, and the giant in this system is component A, which will be discussed. The second component is an unremarkable blue star, 8 times the size of the Sun. But the red hypergiant is also a pulsating star, with a period of 150 days. Its dimensions can vary from 1050 to 1900 solar diameters, and at its maximum it shines 575,000 times brighter than our star!

This star is located 5000 light-years away from us, and at the same time it has a brightness of 5.18 m in the sky, that is, with a clear sky and good eyesight, it can be found, and even with binoculars it’s generally easy.

UY Shield

This red hypergiant is also striking in its size. Some sites mention it as the largest star in the universe. Refers to semi-regular variables and pulsates, so the diameter can vary - from 1708 to 1900 solar diameters. Just imagine a star, 1900 times larger than our Sun! If you place it in the center of the solar system, then all the planets, up to Jupiter, will be inside it.

In numbers, the diameter of this one of the largest stars in space is 2.4 billion kilometers, or 15.9 astronomical units. 5 billion suns could fit inside it. It shines 340,000 times stronger than the Sun, although the surface temperature is much lower due to its larger area.

At its peak, UY Scutum is visible as a faint reddish star with a brightness of 11.2 m, which means that it can be seen in a small telescope, but it is not visible to the naked eye. The fact is that the distance to this large star is 9500 light years - we would not see another on it at all. In addition, there are clouds of dust between us - if they were not there, UY Scutum would be one of the brightest stars in our sky, despite the huge distance to it.

UY Scutum is a huge star. It can be compared with the previous candidate - VV Cephei. They are about the same at the maximum, and it is not even clear which one is larger. However, there is definitely an even bigger star!

VY Canis Major

The diameter of VY, however, according to some sources, is estimated at 1800-2100 solar, that is, this is a clear champion among all other red hypergiants. If it were at the center of the solar system, it would swallow up all the planets, along with Saturn. Previous candidates for the title of the largest stars in the universe would also fit into it completely.

It only takes 14.5 seconds for light to circle our Sun completely. To go around VY Canis Major, the light would have to fly 8.5 hours! If you dared to make such a flyby along the surface in a fighter jet, at a speed of 4500 km/h, then such a non-stop journey would take 220 years.

This star still raises a lot of questions, since its exact size is difficult to establish due to the diffuse corona, which has a much lower density than the sun. And the star itself has a density thousands of times less than the density of the air we breathe.

In addition, VY Canis Majoris is losing its substance and has formed a noticeable nebula around itself. This nebula may now contain even more matter than the star itself. In addition, it is unstable, and in the next 100 thousand years it will explode in a hypernova. Fortunately, it is 3900 light years away, and this terrible explosion does not threaten the Earth.

This star can be found in the sky with binoculars or a small telescope - its brightness varies from 6.5 to 9.6 m.

What is the largest star in the universe?

We looked at some of the largest stars in the universe known to scientists today. Their size is amazing. All of them are candidates for this title, but the data is constantly changing - science does not stand still. According to some reports, the UY of the Shield can also "swell" up to 2200 solar diameters, that is, become even larger than VY Canis Major. On the other hand, there is too much controversy about the size of VY Canis Majoris. So these two stars are almost equal candidates for the title of the largest stars in the universe.

Which of them will turn out to be more in fact, will be shown by further research and clarification. While the majority is in favor of UY Shield, and you can safely call this star the largest in the Universe, it will be difficult to refute this statement.

Of course, it is not very correct to speak about the entire Universe. Perhaps this is the largest star in our Milky Way galaxy known to scientists today. But since even larger ones have not yet been discovered, it is still the largest in the Universe.

Stars are large celestial bodies of hot plasma, the dimensions of which can amaze the most inquisitive reader. Ready to evolve?

It should be noted right away that the rating was compiled taking into account those giants that are already known to mankind. It is possible that somewhere in outer space there are stars of even larger dimensions, but it is located at a distance of many light years, and modern equipment is simply not enough to detect and analyze them. It is also worth adding that the largest stars will eventually cease to be such, because they belong to the class of variables. Well, do not forget about the probable errors of astrologers. So...

Top 10 biggest stars in the universe

Opens the rating of the largest stars in the Betelgeuse Galaxy, the size of which exceeds the radius of the sun by 1190 times. It is located approximately 640 light years from Earth. Comparing with other stars, we can say that at a relatively short distance from our planet. The giant red in the next few hundred years may turn into a supernova. In this case, its dimensions will increase significantly. For justified reasons, the star Betelgeuse, ranking last in this ranking, is the most interesting!

RW

An amazing star, attracting with an unusual glow color. Its size exceeds the dimensions of the sun from 1200 to 1600 solar radii. Unfortunately, we cannot say exactly how powerful and bright this star is, because it is located far from our planet. Regarding the history of the emergence and distance of RW, leading astrologers from different countries have been arguing for many years. Everything is due to the fact that in the constellation it regularly changes. Over time, it may disappear altogether. But it is still in the top of the largest celestial bodies.

Next in the ranking of the largest known stars is KW Sagittarius. According to ancient Greek legend, she appeared after the death of Perseus and Andromeda. This suggests that it was possible to detect this constellation long before our appearance. But unlike our ancestors, we know about more reliable data. It is known that the size of the stars exceeds the Sun by 1470 times. However, it is relatively close to our planet. KW is a bright star that changes its temperature over time.

At present, it is known for certain that the size of this large star exceeds the size of the Sun by at least 1430 times, but it is difficult to get an accurate result, because it is located 5 thousand light years from the planet. Even 13 years ago, American scientists cite completely different data. At that time, it was believed that KY Cygnus had a radius that raised the Sun by 2850 times. Now we have more reliable dimensions relative to this celestial body, which, for sure, are more accurate. Based on the name, you understand that the star is located in the constellation Cygnus.

A very large star included in the constellation Cepheus is V354, the size of which exceeds the Sun by 1530 times. At the same time, the celestial body is relatively close to our planet, only 9 thousand light years away. It does not differ in special brightness and temperature against the background of other unique stars. However, it belongs to the number of variable luminaries, therefore, the dimensions may vary. It is likely that Cepheus will not last long at this position in the V354 rating. It will most likely decrease in size over time.

A few years ago, it was believed that this red giant could become a competitor for VY Canis Major. Moreover, some experts conditionally considered WHO G64 the largest known star in our Universe. Today, in an age of rapid development of technology, astrologers have managed to obtain more reliable data. It is now known that the radius of the Dorado is only 1550 times the size of the Sun. That's how huge errors are allowed in the field of astronomy. However, the incident is easily explained by distance. The star is outside the Milky Way. Namely, in a dwarf galaxy called the Huge Magellanic Cloud.

V838

One of the most unusual stars in the universe, located in the constellation of the Unicorn. It is located approximately 20 thousand light years from our planet. Even the fact that our specialists managed to find it is surprising. Luminary V838 is even larger than that of Mu Cephei. It is quite difficult to make accurate calculations regarding the dimensions, due to the huge distance from the Earth. Speaking of approximate size data, they range from 1170 to 1900 solar radii.

There are many amazing stars in the constellation Cepheus, and Mu Cephei is considered a confirmation of this. One of the largest stars exceeds the size of the Sun by 1660 times. The supergiant is considered one of the brightest in the Milky Way. Approximately 37,000 times more powerful than the illumination of the star most known to us, that is, the Sun. Unfortunately, we cannot say unequivocally at what distance from our planet Mu Cephei is located.

People tend to look at the sky, watching millions and millions of stars. We dream of distant worlds and draw images of our brothers in mind. Each world illuminates its own "sun". Research equipment looks deep into space at 9 billion light years.

But even this is not enough to say with accuracy how many stars are in space. At the current stage of the study, about 50 billion are known. This number is steadily growing, as there is constant research, technology is being improved. People learn about new giants and dwarfs in the world of space objects. Which of the stars is the largest in the universe?

Sun Dimensions

Thinking about the dimensions of the stars, understand what to compare with, feel the scale. The size of our Sun is impressive. Its diameter is 1.4 million km. This huge number is hard to imagine. The fact that the mass of the Sun is 99.9% of the mass of all objects in the solar system will help in this. Theoretically, a million planets could fit inside our star.

Using these numbers, astronomers have coined the terms "solar radius" and "solar mass" that are used to compare the sizes and masses of space objects. The radius of the Sun is 690,000 km, and the weight is 2 billion kilograms. Compared to other stars, the Sun is a relatively small cosmic object.

Former All-Star Champion

The stellar mass is constantly "thinning" because of the "stellar wind". Thermonuclear processes, continuously shaking the universal luminaries, lead to the loss of hydrogen - "fuel" for reactions. Accordingly, the mass also decreases. Therefore, it is difficult for scientists to give exact figures regarding the parameters of such large and hot objects. Luminaries age and after a supernova explosion turn into a neutron star or a black hole.

For decades, VY was recognized as the largest star in the constellation Canis Major. Not so long ago, the parameters were specified, and scientists' calculations showed that its radius is 1300-1540 solar radii. The diameter of the giant is 2 billion kilometers, and it is located 5,000 light-years from Earth.

To imagine the dimensions of this object, imagine that it will take 1200 years to fly around it, moving at a speed of 800 km / h. If you suddenly imagine that the Earth was compressed to 1 cm and VY was also reduced, then the giant will be 2.2 km in size.

But the mass of the star is small and exceeds the mass of the Sun only 40 times. This is due to the low density of the substance. The brightness of the light is truly amazing. It emits light 500,000 times brighter than ours. VY was first mentioned in 1801. It was described by the scientist Joseph Jérôme de Lalande. The record says that the luminary belongs to the seventh grade.

Since 1850, observations have shown a gradual loss of brightness. The outer edge of VY began to increase because the forces of gravity no longer hold the mass at a constant level. Soon (by cosmic standards) a supernova explosion of this star is possible. Scientists say it could happen tomorrow or in a million years. Science does not have exact numbers.

Reigning Star Champion

Space exploration continues. In 2010, scientists led by Paul Crowther saw an impressive space object using the Hubble telescope. Exploring the Large Magellanic Cloud, astronomers discovered a new star and gave it the name R136a1. From us to R136a1, the distance is 163,000 light years.

The parameters shocked the scientists. The mass of the giant exceeds the mass of the Sun by 315 times, despite the fact that it was previously stated that there are no stars in space that exceed our Sun in mass by 150 times. Such a phenomenon occurred, according to the hypothesis of scientists, due to the connection of several objects. The brightness of the glow of R136a1 exceeds the brightness of the radiation of our sun by 10 million times.

During the period from discovery to our time, the star has lost one-fifth of its mass, but it is still considered a record holder even among its neighbors. They were also discovered by Crowther's group. These objects also exceeded the milestone of 150 solar masses.

Scientists have calculated that if R136a1 is placed in the solar system, then the brightness of the glow compared to our luminary will be the same as if the brightness of the Sun and the Moon were compared.

This is the largest star known to mankind so far. Surely in the Milky Way galaxy there are dozens, if not hundreds, of larger luminaries, closed from our eyes by gas and dust clouds.

VV Cephei 2. At 2400 light years, VV Cepheus 2 is located, which exceeds the size of the Sun by 1600-1900 times. The radius is 1050 radii of our Sun. In terms of light emission, the star exceeds the landmark from 275 to 575 thousand times. This is a variable pulsar, pulsing with an interval of 150 days. The speed of the cosmic wind directed away from the sun is 25 km/sec.

Studies have proven that VV Cephei 2 is a double star. The eclipse of the second star B occurs regularly every 20 years. VV Cephei B revolves around the main star VV Cephei 2. It is blue and has a rotation period of 20 years. The eclipse lasts 3.6 years. The object surpasses the Sun in mass by 10 times, and by the intensity of the glow - by 100,000 times.

Mu Cephei. Cepheus flaunts a red supergiant, larger than the Sun by 1650 times. Mu Cephei is the brightest star in the Milky Way. The brightness of the glow is 38,000 times higher than the guideline. It is also known as the "garnet star of Herschel". Studying the star in the 1780s, the scientist called it "a delightfully beautiful garnet-colored object."

In the sky of the northern hemisphere, it is observed without a telescope from August to January, it resembles a drop of blood in the sky. After two or three million years, a giant supernova explosion is expected, which will turn the star into a black hole or a pulsar and a gas and dust cloud.

At 20,000 light-years from Earth, the red giant V838 shines in the constellation Monoceros. This cluster of stars, previously unknown to anyone, "became famous" in 2002. At this time, an explosion occurred there, which astronomers first perceived as a supernova explosion. But due to its young age, the star did not approach the cosmic "death".

For a long time they could not even guess what the cause of the cataclysm was. Hypotheses have now been put forward that the object has swallowed up a "companion star" or objects orbiting around it.

The object is credited with dimensions from 1170 to 1970 solar radii. Due to the gigantic distance, scientists do not give exact numbers for the mass of the red variable star.

Until recently, scientists believed that the parameters of WHO 64 are comparable to R136a1 from the constellation Canis Major.

But it was found that the size of this luminary is only 1540 times larger than the sun. It shines from the Large Magellanic Cloud.

V354 Cephei. The red supergiant V354 Cephei, 9,000 light-years from Earth, is invisible without a telescope.

It is located in the Milky Way galaxy. The temperature on the shell is 3650 degrees Kelvin, the radius is 1520 times greater than the solar one and is determined at 1.06 billion km.

KY Swan. It would take 5,000 light years to fly to KY Cygnus. This time is hard to imagine. Such numbers mean that a beam of light flies at hyperluminal speed from a star to the Earth for 5000 years.

If we compare the radius of the object and the Sun, then it will be 1420 solar radii. The mass of the star is only 25 times the mass of the landmark. But KY will quite compete for the title of the brightest star in the part of the Universe open to us. Its luminosity outstrips the solar millions of times.

KW Sagittarius. 10,000 irresistible light years separate us from the KW star in Sagittarius.

It is a red supergiant with a size of 1460 solar radii and a luminosity 360,000 times higher than that of our Sun.

The constellation is visible in the sky of the southern hemisphere. It is easy to find on the surface of the Milky Way. The star cluster was first described by Ptolemy in the second century.

RW Cephei. The dimensions of RW Cepheus are still being debated. Some scientists claim that the dimensions are equal to 1260 radii of the landmark, others are inclined to believe that they are 1650 solar radii. It is the largest variable star.

If it is moved to the place of the Sun in our system, then the supergiant photosphere will be between the trajectories of Saturn and Jupiter. The star is rapidly flying towards the solar system at a speed of 56 km/sec. The end of the star will turn it into a supernova, or the core will collapse into a black hole.

Betelgeuse. The red giant Betelgeuse lies 640 light-years away in Orion. The size of Betelgeuse is 1100 solar radii. Astronomers are confident that in the near future there will be a period of rebirth of a star into a black hole or supernova. Humanity will see this universal show from the "front row".

As we eagerly look up into the sky with all our instruments and explore it with robotic spacecraft and human crewed missions, we are sure to make amazing new discoveries that will take us even further into space.

We are constantly exploring new objects among the trillions of celestial bodies. We will discover more than one new star, which will outshine the already known ones in size. But alas, we will never know about the true scale of the universe.