Stars - dwarfs of the Galaxy (8 photos). Dwarf galaxy spawns young stars after black eye encounter

The image shows a dwarf galaxy in the constellation Sculptor (Sculptor Dwarf Galaxy). The image was taken with the Wide Field Imager on the 2.2-meter MPG/ESO telescope at the European Southern Observatory at La Silla. This galaxy is one of the neighbors of our Milky Way. But despite this proximity to each other, these two galaxies have completely different history of origin and evolution, we can say that their characters are completely different. The dwarf galaxy in Sculptor is much smaller and older than the Milky Way, making it a very valuable object for studying the processes that led to the birth of new stars and other galaxies in the early Universe. However, due to the fact that it emits very little light, its study is very difficult.

The dwarf galaxy in the constellation Sculptor belongs to a subclass of dwarf spheroidal galaxies and is one of fourteen satellite galaxies that orbit the Milky Way. All of them are located close to each other in the halo region of our Galaxy, which is a spherical region that extends far beyond the boundaries of the spiral arms. As the name suggests, this dwarf galaxy is located in the constellation Sculptor and lies at a distance of 280,000 light-years from Earth. Despite its proximity, it was discovered only in 1937 with the advent of new powerful instruments, since the stars that make it up are very faint and seem to be scattered throughout the sky. Also, do not confuse this galaxy with NGC 253, which is located in the same constellation Sculptor, but looks much brighter and is a barred spiral.

Dwarf galaxy in the constellation Sculptor. Source: ESO

Photo Information

Photo Information

Despite the difficulty of its detection, this dwarf galaxy was among the first faint dwarf objects discovered in the region around the Milky Way. Its strange shape makes astronomers think from the moment of discovery to the present day. But in our time, astronomers have become accustomed to spheroidal galaxies and have realized that such objects allow us to look far into the past of the Universe.

It is believed that the Milky Way, however, like all large galaxies, was formed as a result of mergers with smaller objects during the first years of the existence of the Universe. And if some of these small galaxies still exist today, then they must contain many extremely old stars. That is why the Dwarf Galaxy in the constellation Sculptor meets all the requirements that apply to the original galaxies. Just these ancient stars can be observed in this image.

Astronomers have learned to determine the age of stars in the galaxy by the characteristic signatures that are present in their light flux. This radiation carries very little evidence of the presence of heavy objects in these objects. chemical elements. The point is that such chemical compounds tend to accumulate in galaxies as the generations of stars change. Thus, low concentrations of heavy molecules indicate that average age stars in this spheroidal galaxy is quite high.

A region of the sky around a dwarf galaxy in the constellation Sculptor.

Messier 32, or M32, is an elliptical dwarf galaxy. It is located in the constellation Andromeda. M32 has an apparent magnitude of 8.1 with an angular size of 8 x 6 arc minutes. The galaxy is 2.9 million light years away from our planet. According to Equinox 2000, the following coordinates are derived: right ascension 0 h. 42.8 min.; declination +40°52′. Thanks to this, the galaxy can be seen throughout the autumn.

Messier 32 is one of the two elliptical galaxies of the satellites of the Great Andromeda that can be observed in the images provided. On the lower edge of the M31 object, the M32 galaxy is the closest galaxy, while the M110 object is the most distant galaxy on the upper right edge. M31 is a large Andromeda galaxy, represented by a bright celestial object that can be observed with the naked eye. Messier 31, Messier 32 and Messier 110 belong to the Local Group of galaxies. It also includes the Triangulum galaxy and the Milky Way.

The images provided show uncompressed photographs of all three objects - M31, M32 and M110. All photos were taken with a Takahashi E-180 astrograph. Nearby is a 3x magnification image of the center of the galaxy Messier 32.

The object was included in Messier's catalog, but it was discovered by the French scientist Le Gentil in 1749. Based on the data of advanced researchers in 2010, it is possible to calculate approximate data about this galaxy. The distance from Earth to Messier 32 is 2.57 million light years, the approximate mass varies within 3000000000 solar masses, and the diameter reaches 6500 light years.

Observations

M32 belongs to the small galaxies, but has a bright elliptical shape. When amateurs look at the Andromeda Nebula, this particular object will seem strange to them. Even the most ordinary telescope will show the features of the diffuse nature of the galaxy. It lies half a degree south of the center of the M31 galaxy. If you look at M32 in a medium-quality telescope, you can see a star-shaped core and a compact, smoothly decreasing oval halo in brightness.

Neighboring objects from the Messier catalog

The first neighbor of the M32 galaxy is its physical satellite, the Andromeda Nebula. It is a spiral supergiant galaxy. The second neighboring galaxy is the elliptical M110, and the third is M31, a satellite that lies on the other side of the object Messier 32.

Thanks to the Dwarf Galaxy, you can see the globular cluster G156. It belongs to object M31. The best tool For observation, a telescope with an aperture of 400 mm will serve.

Description Messier 32 in the catalog

August 1764

Below Andromeda's belt, there is a small starless nebula for several minutes. Compared to the belt, this small nebula has a dimmer light. She was discovered by Le Gentil on October 29, 1749, and in 1757 Messier saw her.

Technical details of Messier 32 photo

An object: M32

Other designations: NGC 221

Object type: dwarf elliptical galaxy

Position: Bifrost Astronomical Observatory

Mount: Astro-Physics 1200GTO

Telescope: Hyperbolic astrograph TakahashiEpsilon 180

Camera: Canon EOS 550D (Rebel T2i) (Baader UV/IR filter)

Exposure: 8 x 300s, f/2.8, ISO 800

Original photo size: 3454 × 5179 pixels (17.9 MP); 11.5″ x 17.3″ @ 300dpi

Most galaxies, like our Milky Way, are surrounded by dozens of small satellites that orbit around them. These satellites are extremely dim - of them, only the brightest and closest were seen in the vicinity of our Galaxy and the nearest neighbor, the Andromeda galaxy. But these dwarf satellite galaxies do not fly randomly: they are all located approximately in the same plane, which seems to us to be a straight line.

The coplanarity seems unexpected. Computer models of the evolution of galaxies showed that in each direction of the celestial sphere there should be approximately the same number satellite galaxies. For a long time it was believed that such a spherically symmetric distribution is a natural consequence of the existence of dark matter, a mysterious substance that interacts with ordinary matter only through gravity. Astronomers believe that dark matter dominates the universe and plays a key role in the formation of galaxies and the expansion of space.

However, the mystery of the coplanarity of dwarf galaxies has haunted and led some astronomers, including Krupa, to question whether dark matter even exists. “The dark matter hypothesis has shown itself to be untenable,” he said, interrupting my talk, “because the predictions made on its basis that satellites should be distributed spherically symmetrically around the Milky Way are in direct contradiction to what we observe.”

I presented a different view of the problem, which tries to explain the strange arrangement of galactic satellites by the presence space structures dark matter larger than our Milky Way. While a small number of skeptics like Krupa remain undecided, recent work, including mine, shows how a giant web of dark matter can explain the unique arrangement of satellite galaxies in the sky.

missing matter

The dark matter hypothesis at the center of this controversy was first proposed to explain other mysterious properties of galaxies. In the 1930s the great astronomer Fritz Zwicky wanted to "weigh" the Coma Cluster, a gigantic group of almost a thousand galaxies. He began by measuring the speeds at which galaxies move in this cluster. To his surprise, he found enormous speeds—thousands of kilometers per second—great enough to blow the cluster apart. Why didn't it shatter into pieces? Zwicky suggested that the cluster is filled with some kind of invisible substance that holds the galaxies together by the force of its gravity. This missing substance was later called dark matter.

Since Zwicky first proposed his suggestion 80 years ago, the specter of dark matter has been popping up all over the universe, in almost every galaxy studied. In our own - the Milky Way - astronomers have identified its existence based on the nature of the movement of stars in the outskirts of the galaxy. Like the galaxies in the Coma Cluster, these stars move too fast to be held up by all visible matter. And a dozen dwarf galaxies near the Milky Way appear to be richer in dark matter.

The omnipresence of dark matter has reinforced confidence in its existence. Indeed, most cosmologists believe that dark matter makes up about 84% of all matter, outweighing normal atoms by about five to one.

This abundance of dark matter suggests that it appears to play a pivotal role in the evolution of the universe. One way to study this evolution is to use computer models. Since the 1970s scientists in the field of computational cosmology have attempted to model the history of the universe using computer programs. The technique is simple: set an imaginary rectangular volume; place imaginary point particles there at the nodes of an almost perfect lattice, which in this model imitate clots of dark matter; calculate the gravitational attraction of each particle from all the others and let them move in accordance with the gravitational field acting on them: trace this process over an interval of 13 billion years.

Since the 1970s strategies of this kind have evolved significantly and become much more complex, but at its core this method is still used today. Forty years ago, a program could only work with a few hundred particles. Modern methods computer simulations make it possible to calculate the behavior of billions of particles in a volume approaching the size of the observable universe.

Computer simulation of the universe turned out to be incredible convenient way to explore individual galaxies, but it also gave rise to a number of difficult mysteries. For example, computer models indicate that the dark matter that fills the halo around the Milky Way pulls gas and dust into separate clumps. These clumps should compress under the influence of gravity, forming stars and dwarf galaxies. Around the Milky Way, surrounded by dark matter, there should be thousands of small galaxies. However, when observing the night sky, we see only a few dozen of them. The failure of all attempts to detect them became apparent in the 1990s, and since then it has been called the “missing satellite problem”.

Over the years, astronomers have come up with several possible explanations for this dilemma. The first and most convincing is that not all satellites that appear in computer models strictly correspond to real-life satellite galaxies. The masses of the smallest clumps of dark matter (and their gravitational pull) may not be enough to capture gas and form stars. Continuing this line of reasoning, we can assume that the observed satellite galaxies are only the visible tip of a dark iceberg: perhaps hundreds, if not thousands, of dark satellite galaxies that do not have stars exist nearby. We just don't see them.

Second, even if stars formed in small clumps of dark matter, they may be too dim for us to see with our telescopes. Then, as technology develops and the sensitivity of telescopes increases, astronomers will discover new satellite galaxies. Indeed, over the past few years, the number of known satellite galaxies orbiting the Milky Way has doubled.

In addition, the very disk of our galaxy probably prevents us from seeing some satellites. This disk is essentially a dense, flat collection of stars so bright that it appears to the naked eye as a streak of white liquid (hence the name "Milky Way"). It is very difficult to detect satellites hiding behind the disk, as difficult as it is to see the Moon during the day - the dim light of the satellite galaxy is drowned in the radiance of the Milky Way.

All these arguments taken together solve the problem of missing satellite galaxies and convince most astrophysicists. They rescue the idea of ​​dark matter by protecting it from the most serious observational counterarguments. However, the strange spatial arrangement of satellite galaxies still baffles scientists.

New Dwarf Threat

In several articles published in the late 1970s and early 1980s, Donald Lynclen-Bell. astrophysicist at the University of Cambridge, noted that many of the satellite galaxies orbiting the Milky Way, apparently, are located in the water plane. How to explain such a strange picture? In 2005, Krupa and his group at the University of Bonn convinced the world that this coplanar arrangement could not be accidental. They suggested that dark matter satellites were evenly distributed around the Milky Way, as computer simulations had predicted, and that only one of the hundreds of these dwarfs was large enough to form stars in it and became visible in a telescope. Given these perfectly reasonable assumptions, they wondered: how often can we expect to find a system like the Milky Way, around which the luminous satellites would be lined up? The answer has exploded in cosmology: the probability of this is less than one in a million.

“If dark matter controlled the formation of galaxies,” Krupa argues. - then the satellite galaxies would never line up along the plane. Describing your results in the article. Krupa offered his own solution. “The only way out,” he wrote. - to assume that the satellites of the Milky Way were not formed as a result of the aggregation of dark matter. Dark matter, he argued. does not exist.

being a good theoretician. Krupa offered an alternative. He believes that satellites are fragments of a large progenitor galaxy, which once flew near the Milky Way in the past. Just as an asteroid breaks apart as it passes through Earth's atmosphere, leaving a trail of debris behind it, it is possible that the Milky Way's satellites originated from matter taken from a larger ancestor.

When we look out into the universe, Krupa says, we see long bridges of stellar matter called tidal arms around some of the colliding galaxies. Often, tidal arms contain small satellite galaxies that were formed as a result of the compression of trapped matter. Under suitable conditions, the very process of detachment leads to the fact that the captured matter is collected in the water plane, similar to the satellites of the Milky Way.

Krupa's explanation was elegant, simple, and most importantly, undeniable. It quickly came under a flurry of attacks. For example, the stars in the satellite galaxies of the Milky Way move too fast in the case of ordinary matter alone. Dark matter must hold them together, just as it holds all parts of the Milky Way. (Indeed, observations indicate that the dwarf satellites of the Milky Way are the galaxies with the highest content of dark matter in the Universe.) And the tidal scenario for the formation of dwarf galaxies suggests that they do not have dark matter, leaving open the question of what prevents them from flying apart .

Second, just as one car damages another in a collision, collisions between disk galaxies destroy disks. Almost always, the end result of a collision of galaxies is a shapeless bunch of stars. The Milky Way has a distinct structure and a rather thin disk. We do not see any indication that it has been affected by any collision or merger in the recent past.

dark web

An alternative solution to the puzzle of the unusual alignment of dwarf galaxies requires looking further into the depths of space. Numerical modeling work, which began in the 1970s, is not easy to study the evolution of individual galaxies, they model gigantic volumes of the universe. When we do this on the largest scale, we see that the galaxies are not randomly distributed. On the contrary, they tend to unite in a strictly defined filamentous structure called the cosmic web. We clearly distinguish the predicted structure when we consider distribution maps in the space of real galaxies.

This cosmic web consists of majestic layers filled with millions of galaxies and stretching for hundreds of millions of light years. These layers are connected by cigar-shaped threads. In the gaps between the threads there are voids in which there are no galaxies. Large galaxies, such as ours, are usually located at those points on the web where many threads intersect.

As a graduate student at Durham University in England, I built computer models of these dense regions. One day I brought a printout of the latest results to my supervisor Carlos Frenk's office. The model I was working on traced the formation of the Milky Way and its environs over 13 billion years of the history of the universe - Frank studied the computer drawing for several seconds, and then waved the paper and exclaimed: “Leave everything else! The satellite galaxies that you study, every one of them, lie in that very incredible Krupa plane! Our model did not reproduce the results of previously made computer models - uniform distribution satellite galaxies in the halo of the Milky Way. Instead, the computer predicted the formation of satellites of the water plane - very close to what astronomers observe. We felt that our model would begin to unravel the mystery of how dwarf satellites could be so strangely located in space.

"Why don't you follow the evolution of satellites back in time to see where they came from?" Frank suggested. We had the end result; now it is time to explore the intermediate stages of evolution.

When we studied the course of modeling in reverse direction, we saw that dwarf galaxies did not originate in the regions immediately adjacent to Milky Way. As a rule, they were grouped a little further, inside the threads of the cosmic web. Threads are areas more high density than space voids. This is probably why they attract nearby dust and gas and collect them into nascent galaxies.

Which occupy a border position between dwarf and normal galaxies, the first dwarf galaxies were discovered by H. Shapley in the late 1930s, when surveying the sky in the vicinity of the South Pole of the world for a statistical study of galaxies at the Harvard University Observatory in South Africa. First, Shapley discovered a previously unknown cluster of stars in the constellation Sculptor, containing about 10 thousand stars 18-19.5 m. A similar cluster was soon discovered in the constellation Furnace. After the 2.5 m telescope of the Mount Wilson Observatory was used to study these clusters, Cepheids were found in them and distances were determined. It turned out that both unknown clusters are located outside our galaxy, that is, they are new type galaxies with low surface brightness.

Discoveries of dwarf galaxies became widespread after the Palomar sky survey was made in the 1950s using the 120 cm Schmidt camera at the Mount Palomar Observatory. It turned out that dwarf galaxies are the most common galaxies in the universe.

Formation of dwarf galaxies

local dwarfs

Morphology

There are several main types of dwarf galaxies:

• dwarf elliptical galaxy ( dE) - similar to elliptical galaxies
  • Dwarf spheroidal galaxy ( dSph) - subtype dE, characterized by a particularly low surface brightness
• Dwarf irregular galaxy ( dir) - similar to irregular galaxies, has a ragged structure
• Dwarf blue compact galaxy ( dBCG or BCD) - has signs of active star formation
• Ultra-compact dwarf galaxies ( UCD) is a class of very compact galaxies containing about 10 8 stars with a characteristic transverse size of about 50 pc. Presumably, these galaxies are dense remnants (cores) of dwarf elliptical galaxies that flew through the central parts of rich galaxy clusters. Ultra-compact galaxies have been found in galaxy clusters in Virgo, Furnace, Coma Veronica, Abel 1689, and others.
• Dwarf spiral galaxy - analogue of spiral galaxies, but, unlike normal galaxies, extremely rare

Hobbit Galaxies

The recently coined term Hobbit Galaxies has been adopted to refer to galaxies that are smaller and dimmer than dwarf galaxies.

The shortage of dwarf galaxies

A detailed study of such galaxies, and especially the relative velocities of individual stars in them, allowed astronomers to suggest that the powerful ultraviolet radiation of giant young stars at one time "blew" out of such galaxies. most gas (which is why there are few stars), but left dark matter, which is why it now prevails. Some of these dim dwarf galaxies, overwhelmingly dominated by dark matter astronomers propose to search by indirect observations: along the "wake trail" in the intergalactic gas, i.e. by the attraction of jets of gas to this "invisible" galaxy.

Partial list of dwarf galaxies

see also

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Notes

1. Linda S. Sparke, John S. Gallagher III. Galaxies in the Universe: An Introduction. - 2nd ed. - Cambridge University Press, 2007. - P. 410. - 442 p. - ISBN 978-0-521-85593-8.
2. Zasov, A. V. Dwarf galaxies (New in life, science, technology). - M .: Knowledge, 1984. - 64 p. - (Cosmonautics, astronomy).
3. Shapley, Harlow. Two Stellar Systems of a New Kind // Nature. - 1938. - T. 142. - pp. 715-716.
5. Astronomy: XXI century / Ed.-comp. V.G. Surdin. - 2nd ed. - Fryazino: Century 2, 2008. - S. 373. - ISBN 978-5-85099-181-4.
7. arXiv :astro-ph/0307362 Galaxies and Overmerging: What Does it Take to Destroy a Satellite Galaxy? July 21, 2003
8. arXiv :astro-ph/0406613 Ultra Compact Dwarf galaxies in Abell 1689: a photometric study with the ACS. June 28, 2004
9. SPACE.com
11. Simon, J. D. and Geha, M. (Nov 2007). "The Kinematics of the Ultra-faint Milky Way Satellites: Solving the Missing Satellite Problem". The Astrophysical Journal 670 (1): 313–331. arXiv :0706.0516 . DOI:10.1086/521816. Bibcode :.
12. September 27, 2007.
13. January 17, 2011.

Bound by gravity Not bound by gravity Connected visually

Kinds Structure Active cores Interaction Phenomena and processes Lists

An excerpt characterizing the Dwarf Galaxy

The horses were given.
- Bonjour, messieurs, [Here: goodbye, gentlemen.] - said Dolokhov.
Petya wanted to say bonsoir [good evening] and could not finish the words. The officers whispered something to each other. Dolokhov sat for a long time on a horse that did not stand; then walked out of the gate. Petya rode beside him, wanting and not daring to look back to see whether the French were running or not running after them.
Leaving on the road, Dolokhov did not go back to the field, but along the village. At one point he stopped, listening.
- Do you hear? - he said.
Petya recognized the sounds of Russian voices, saw the dark figures of Russian prisoners by the fires. Going down to the bridge, Petya and Dolokhov passed the sentry, who, without saying a word, walked gloomily along the bridge, and drove out into a hollow where the Cossacks were waiting.
- Well, goodbye now. Tell Denisov that at dawn, at the first shot, - said Dolokhov and wanted to go, but Petya grabbed his hand.
- Not! he yelled, “you are such a hero. Ah, how good! How excellent! How I love you.
“Good, good,” said Dolokhov, but Petya did not let him go, and in the darkness Dolokhov saw that Petya was leaning towards him. He wanted to kiss. Dolokhov kissed him, laughed and, turning his horse, disappeared into the darkness.

X
Returning to the guardhouse, Petya found Denisov in the entryway. Denisov, in agitation, anxiety and annoyance at himself for letting Petya go, was waiting for him.
- God bless! he shouted. - Well, thank God! he repeated, listening to Petya's enthusiastic story. “And why don’t you take me, because of you I didn’t sleep!” Denisov said. “Well, thank God, now go to bed.” Still vzdg "let's eat to utg" a.
“Yes… No,” said Petya. “I don’t feel like sleeping yet. Yes, I know myself, if I fall asleep, it's over. And then I got used to not sleeping before the battle.
Petya sat for some time in the hut, joyfully recalling the details of his trip and vividly imagining what would happen tomorrow. Then, noticing that Denisov had fallen asleep, he got up and went into the yard.
It was still quite dark outside. The rain had passed, but the drops were still falling from the trees. Near the guardroom one could see the black figures of Cossack huts and horses tied together. Behind the hut, two wagons with horses stood black, and a burning fire burned red in the ravine. The Cossacks and hussars were not all asleep: in some places, along with the sound of falling drops and the close sound of horses chewing, soft, as if whispering voices were heard.
Petya came out of the passage, looked around in the darkness, and went up to the wagons. Someone was snoring under the wagons, and saddled horses stood around them, chewing oats. In the darkness, Petya recognized his horse, which he called Karabakh, although it was a Little Russian horse, and went up to her.
“Well, Karabakh, we’ll serve tomorrow,” he said, sniffing her nostrils and kissing her.
- What, sir, do not sleep? - said the Cossack, who was sitting under the wagon.
- Not; and ... Likhachev, it seems to be your name? After all, I just arrived. We went to the French. - And Petya told the Cossack in detail not only his trip, but also why he went and why he thinks that it is better to risk his life than to make Lazarus at random.
“Well, they would have slept,” said the Cossack.
“No, I’m used to it,” Petya answered. - And what, the flints in your pistols are not upholstered? I brought with me. Isn't it necessary? You take it.
The Cossack leaned out from under the truck to take a closer look at Petya.
“Because I’m used to doing everything carefully,” said Petya. - Others, somehow, do not get ready, then they regret it. I don't like that.
“That’s right,” said the Cossack.
“And one more thing, please, my dear, sharpen my saber; blunt ... (but Petya was afraid to lie) she had never been honed. Can it be done?
- Why, maybe.
Likhachev got up and rummaged through his packs, and Petya soon heard the warlike sound of steel on a bar. He climbed onto the wagon and sat on its edge. The Cossack sharpened his saber under the wagon.
- And what, the good fellows sleep? Petya said.
- Who is sleeping, and who is like this.
- Well, what about the boy?
- Is it spring? He was there, in the hallways, collapsed. Sleeping with fear. It was glad.
For a long time after that Petya was silent, listening to the sounds. Footsteps were heard in the darkness and a black figure appeared.
- What are you sharpening? the man asked, approaching the wagon.
- But the master sharpen his saber.
“It’s a good thing,” said the man, who seemed to be a hussar to Petya. - Do you have a cup left?
“At the wheel.
The hussar took the cup.
“It’s probably light soon,” he said, yawning, and went somewhere.
Petya should have known that he was in the forest, in the party of Denisov, a verst from the road, that he was sitting on a wagon recaptured from the French, near which horses were tied, that the Cossack Likhachev was sitting under him and sharpening his saber, which is great black spot to the right - a guardhouse, and a bright red spot below to the left - a dying fire, that the man who came for a cup was a hussar who wanted to drink; but he knew nothing and did not want to know it. He was in a magical realm, in which there was nothing like reality. A big black spot, maybe it was definitely a guardhouse, or maybe there was a cave that led into the very depths of the earth. The red spot may have been fire, or perhaps the eye of a huge monster. Maybe he’s definitely sitting on a wagon now, but it’s very possible that he’s not sitting on a wagon, but on a terribly high tower, from which if you fall, you would fly to the ground all day, a whole month - all fly and you will never reach . It may be that just the Cossack Likhachev is sitting under the wagon, but it may very well be that this is the kindest, bravest, most wonderful, most excellent person in the world, whom no one knows. Perhaps it was the hussar who was passing for water and went into the hollow, or perhaps he had just disappeared from sight and completely disappeared, and he was not there.
Whatever Petya saw now, nothing would surprise him. He was in a magical realm where anything was possible.
He looked up at the sky. And the sky was as magical as the earth. The sky was clearing, and over the tops of the trees clouds quickly ran, as if revealing the stars. Sometimes it seemed that the sky was clearing and showing black, clear sky. Sometimes it seemed that these black spots were clouds. Sometimes it seemed that the sky was high, high above the head; sometimes the sky descended completely, so that you could reach it with your hand.
Petya began to close his eyes and sway.
Drops dripped. There was a quiet conversation. The horses neighed and fought. Someone snored.
“Fire, burn, burn, burn…” whistled the saber being sharpened. And suddenly Petya heard a harmonious chorus of music playing some unknown, solemnly sweet hymn. Petya was musical, just like Natasha, and more than Nikolai, but he never studied music, did not think about music, and therefore the motives that suddenly came to his mind were especially new and attractive to him. The music played louder and louder. The tune grew, passed from one instrument to another. There was what is called a fugue, although Petya had no idea what a fugue was. Each instrument, now resembling a violin, now like trumpets - but better and cleaner than violins and trumpets - each instrument played its own and, without finishing the motive, merged with another, which began almost the same, and with the third, and with the fourth , and they all merged into one and again scattered, and again merged now into a solemn church, now into a brightly shining and victorious one.
“Oh, yes, it’s me in a dream,” Petya said to himself, swaying forward. - It's in my ears. Or maybe it's my music. Well, again. Go ahead my music! Well!.."
He closed his eyes. And with different parties, as if from afar, the sounds began to tremble, they began to harmonize, scatter, merge, and again everything united into the same sweet and solemn hymn. “Ah, what a delight it is! As much as I want and how I want,” Petya said to himself. He tried to lead this huge chorus of instruments.
“Well, hush, hush, freeze now. And the sounds obeyed him. - Well, now it's fuller, more fun. More, even happier. - And from an unknown depth rose increasing, solemn sounds. “Well, voices, pester!” Petya ordered. And first, men's voices were heard from afar, then women's. The voices grew, grew in a steady solemn effort. Petya was terrified and joyful to listen to their extraordinary beauty.

Any star is a huge ball of gas, which consists of helium and hydrogen, as well as traces of other chemical elements. Stars exist great amount and they all differ in their size and temperature, and some of them consist of two or more stars, which are connected together by the force of gravity. From Earth, some stars are visible to the naked eye, while others can only be seen through a telescope. However, even with special equipment, not every star can be viewed the way you want, and even with powerful telescopes, some stars will look like nothing more than just luminous dots.

Thus, a simple person with a fairly good visual acuity in clear weather in the night sky can see about 3000 stars from one earth's hemisphere, however, in fact, there are much more of them in the Galaxy. All stars are classified according to size, color, temperature. Thus, there are dwarfs, giants and supergiants.

Dwarf stars are of the following types:

• yellow dwarf. This type is a small main sequence star of spectral class G. Their mass ranges from 0.8 to 1.2 solar masses.
• orange dwarf. This type includes small stars of the main sequence of the spectral class K. Their mass is 0.5 - 0.8 solar masses. Unlike yellow dwarfs, orange dwarfs have a longer lifespan.
• red dwarf. This type combines small and relatively cold main sequence stars of spectral type M. Their differences from other stars are quite pronounced. They have a diameter and mass that is no more than 1/3 of the Sun's.
• blue dwarf. This type of star is hypothetical. Blue dwarfs evolve from red dwarfs before all hydrogen burns out, after which they presumably evolve into white dwarfs.
• white dwarf. This is the type of already evolved stars. They have a mass that is no more than the mass of Chandrasekhar. White dwarfs are deprived of their own source of thermonuclear energy. They belong to the DA spectral class.
• black dwarf. This type is a cooled white dwarfs, which, accordingly, do not radiate energy, i.e. do not glow, or emit it very, very weakly. They represent the final stage in the evolution of white dwarfs in the absence of accretion. The mass of black dwarfs, as well as white ones, does not exceed the mass of Chandrasekhar.
• brown dwarf. These stars are substellar objects that have a mass of 12.57 to 80.35 Jupiter masses, which, in turn, corresponds to 0.012 - 0.0767 solar masses. Brown dwarfs differ from main sequence stars in that the reaction thermonuclear fusion, as a result of which hydrogen in other stars turns into helium.
• subbrown dwarfs or brown subdwarfs. They are absolutely cold formations, the mass of which is below the limit of brown dwarfs. To a greater extent, they are considered to be planets.

So, it can be noted that the stars belonging to white dwarfs are those stars that are initially small in size and are at their final stage of evolution. The history of the discovery of white dwarfs goes back to the relatively recent year 1844. It was at that time that the German astronomer and mathematician Friedrich Bessel, while observing Sirius, discovered a slight deviation of the star from rectilinear motion. As a result of this, Friedrich suggested that Sirius had an invisible massive companion star. This assumption was confirmed in 1862 by the American astronomer and telescope designer Alvan Graham Clarke during the adjustment of the largest refractor at that time. A dim star was discovered near Sirius, later called Sirius B. This star is characterized by low luminosity, and its gravitational field affects its bright partner quite noticeably. This, in turn, confirms that this star has a very small radius with a significant mass.

What stars are dwarfs

Dwarfs are evolved stars that have a mass that does not exceed the Chandrasekhar limit. The formation of a white dwarf occurs as a result of the burning out of all hydrogen. When the hydrogen burns out, the core of the star is compressed to high densities, while the outer layers expand greatly and are accompanied by a general dimming of the luminosity. Thus, the star first turns into a red giant, which sheds its shell. The ejection of the shell occurs due to the fact that the outer layers of the star have an extremely weak connection with the central hot and very dense core. Subsequently, this shell becomes expanding planetary nebula. It is worth paying attention to the fact that red giants and white dwarfs have a very close relationship.

All white dwarfs are divided into two spectral groups. The first group includes dwarfs with a "hydrogen" spectral type DA, in which there are no helium spectral lines. This type is the most common. The second type of white dwarfs is DB. It is rarer and is called a "helium white dwarf". In the spectrum of stars of this type no hydrogen lines were found.

According to the American astronomer Iko Iben, these types of white dwarfs are formed in completely different ways. This is due to the fact that helium combustion in red giants is unstable and a helium sheet flash develops periodically. Iko Iben also suggested a mechanism by which the shell is ejected at different stages of the development of a helium flash - at its peak and between flashes. Accordingly, its formation is affected by the shell ejection mechanism.