Dwarf galaxies are small but impressive. Dwarf galaxy

The scientists' study shows how widespread this type of star actually is in our galaxy and how actively they take part in the formation of new stars.

The figures show that 2 -3 stars of other classes account for at least 1 brown dwarf.

This type of space objects clearly stands out from the rest.

They are too big and hot (in 15 -80 times more massive than our Jupiter) so that they can be classified as planets, but at the same time they are too small to be full-fledged stars - they do not have enough mass to maintain stable hydrogen fusion in the core.

However, brown dwarfs initially form in the same way as normal stars, which is why they are often called failed stars.

More in 2013 year, astronomers began to suspect that brown dwarfs are quite a common occurrence for our galaxy, calculating their approximate number in the area 70 billion

However, new data presented at the National Astronomy conference M eeting, which took place recently in English University Halla, they say that there may be about 100 billion

Considering that the entire Milky Way can contain, according to rough estimates, up to 400 billions of stars, the number of brown dwarfs is both impressive and disappointing.

To clarify the results, astronomers conducted a study of more than a thousand brown dwarfs located within a radius of no more than 1500 light years. Since stars of this class are very dim, observing them at longer distances seems extremely difficult, if not impossible.

Most of the brown dwarfs we know of were found in regions where new stars are forming, known as clusters.

One of these clusters is the object NG C133 , which contains almost as many brown dwarfs as ordinary stars.

This seemed quite strange to Alex Scholz from the University of St Andrews and his colleague Koralka Muzic from the University of Lisbon. For a more detailed understanding of the frequency of brown dwarfs born inside star clusters various densities The researchers decided to look for more distant dwarfs in the denser star cluster R C W 38 .

To be able to view a distant cluster located approximately 5000 light years away, astronomers used the NA camera C O with adaptive optics set to Very large telescope European Southern Observatory.

As in previous observations, this time scientists also discovered that the number of brown dwarfs in this cluster is almost half of the total number stars located in it, which, in turn, suggests that the birth rate of brown dwarfs does not depend at all on the composition of star clusters.

“...We discovered a large number of brown dwarfs in these clusters. It turns out that regardless of the type of cluster, this class of stars is found quite often. And since brown dwarfs form together with other stars in clusters, we can conclude that there really are a lot of them in our galaxy..."

- comments Scholz.

It could be a number in 100 billion However, there may be even more of them.

Let us remember that brown dwarfs are very dim stellar objects, so their even fainter representatives could simply not fall into the field of view of astronomers.

At the time of this writing, the results of Scholz's latest research were awaiting critical review by outside scientists, but the first comments on these observations to Gizmodo came from astronomer John Omira of the College of Saint Miguel, who was not involved in the work, but believes that the figures reflected in it may be are true.

"...They come to the number 100 billions, making a lot of assumptions for this. But in fact, the conclusion about the number of brown dwarfs in a star cluster is based on the so-called initial function mass, which describes the distribution of masses of stars in the cluster. Once you know this function and you know the frequency with which the galaxy forms stars, then you can calculate the number of stars of a certain type. Therefore, if we omit a couple of assumptions, then the figure in 100 billions really seems real..."

- Omira commented.

And by comparing the number of brown dwarfs in two different clusters—one with a dense and one with a less dense distribution of stars—the researchers showed that the environment in which stars appear is not always the same. key factor regulating the frequency of appearance of this type of stellar objects.

“The formation of brown dwarfs is universal and integral part star formation in general", says Omira.

Professor Abel Mendez from the Planetary Habitability Laboratory L aboratory, another astronomer who also did not take part in the study under discussion, says that the numbers in the new work may actually make sense, especially considering the fact that our galaxy contains significantly more compact stellar objects than larger ones.

“...Small red dwarfs, for example, are much more common than all other types of stars. Therefore, I would suggest that the new numbers are more likely even the lower limit..."

says Mendez.

There are, of course, back side such fertility of brown dwarfs. A large number of Failed stars also mean a decrease in habitability potential.

Mendez says brown dwarfs are not stable enough to support an environment called the habitable zone. In addition, not all astronomers like the term itself “failed stars”.

“...Personally, I prefer not to call brown dwarfs “failed stars”, since, in my opinion, they simply do not deserve the title of stars...”

— comments Jacqueline Faherty, astrophysicist at the American Museum of Natural History.

“... I would rather call them “overgrown planets”, or simply “superplanets”, since from the point of view of their masses they are still closer to these astronomical objects than to stars...”

- says the scientist.

Any star is a huge ball of gas, which consists of helium and hydrogen, as well as traces of other chemical elements. There are a huge number of stars and they all differ in size and temperature, and some of them consist of two or more stars that are connected by 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 in powerful telescopes, some stars will look like nothing more than just luminous points.

Thus, an ordinary person with fairly good visual acuity, in clear weather in the night sky, can see about 3000 stars from one earthly 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 star main sequence spectral class G. Their mass ranges from 0.8 to 1.2 solar masses.
• orange dwarf. This type includes small main sequence stars of spectral class K. Their mass is 0.5 - 0.8 solar masses. Unlike yellow dwarfs, orange dwarfs have longer lifespans.
• red dwarf. This type unites small and relatively cool main sequence stars of spectral class M. Their differences from other stars are quite pronounced. They have a diameter and mass that is no more than 1/3 of the Solar one.
• blue dwarf This type of star is hypothetical. Blue dwarfs evolve from red dwarfs before burning out all their hydrogen, after which they presumably evolve into white dwarfs.
• white dwarf. This is a type of already evolved stars. They have a mass that is not more than the mass of Chandrasekhar. White dwarfs do not have their own source of thermonuclear energy. They belong to the spectral class DA.
• black dwarf. This type is a cooled white dwarf, which, accordingly, does not emit energy, i.e. do not glow, or emit it very, very weakly. They represent the final stage of the evolution of white dwarfs in the absence of accretion. The mass of black dwarfs, like white dwarfs, does not exceed the mass of Chandrasekhar.
• brown dwarf. These stars are substellar objects that have a mass from 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 no reaction takes place in their interiors. 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 stars belonging to white dwarfs are those stars that initially have small 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 movement. 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 builder Alvan Graham Clark during the adjustment of the largest refractor at that time. A dim star was discovered near Sirius, which was later named 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.

Which 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 of all hydrogen. When hydrogen burns out, the core of the star contracts to high densities, while at the same time the outer layers expand greatly and are accompanied by a general dimming of luminosity. Thus, the star first turns into a red giant, which sheds its shell. The shedding of the shell occurs due to the fact that the outer layers of the star have extremely weak connection with a central hot and very dense core. Subsequently, this shell becomes an 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 that have a “hydrogen” spectral class DA, which does not spectral lines helium This type is the most common. The second type of white dwarf is DB. It is rarer and is called a helium white dwarf. In the spectrum of stars of this type no hydrogen lines detected.

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

Which occupy border position between dwarf and normal galaxies, the first dwarf galaxies were discovered by H. Shapley in the late 1930s, while conducting a survey of the sky in the vicinity South Pole peace for statistical research galaxies at the Harvard University Observatory 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 Fornax. After using the 2.5 m telescope at Mount Wilson Observatory to study these clusters, it was possible to find Cepheids in them and determine the distances. It turned out that both unknown clusters are located outside our galaxy, that is, they represent new type low surface brightness galaxies.

Discoveries of dwarf galaxies became widespread after the Palomar Sky Survey was carried out in the 1950s using the 120-centimeter Schmidt camera at 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 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
• Ultracompact dwarf galaxies ( UCD) - a class of very compact galaxies containing about 10 8 stars with a characteristic transverse size of about 50 pc. Presumably, these galaxies are the dense remnants (nuclei) of dwarf elliptical galaxies that flew through the central parts of rich galaxy clusters. Ultracompact galaxies have been discovered in the Virgo, Fornax, Coma Berenices, Abel 1689, and other galaxy clusters.
• A dwarf spiral galaxy is an analogue of spiral galaxies, but, unlike normal galaxies, is extremely rare

Hobbit galaxies

The recently coined term Hobbit Galaxies was used to refer to galaxies that are smaller and fainter than dwarf galaxies.

The problem of the shortage of dwarf galaxies

A detailed study of such galaxies and especially relative speeds individual stars in them, allowed astronomers to assume that the powerful ultraviolet radiation of giant young stars at one time “blew out” most of the gas from such galaxies (which is why there are few stars there), but left dark matter, which is why it now predominates. Some of these faint dwarf galaxies with an overwhelming predominance dark matter astronomers propose to search by indirect observations: along the “wake” in the intergalactic gas, i.e. by the attraction of gas jets 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. - P. 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 gravitation Not gravitationally bound Visually connected

Kinds Structure Active cores Interaction Phenomena and processes Lists

Excerpt characterizing the Dwarf Galaxy

The horses were brought in.
“Bonjour, messieurs, [Here: farewell, gentlemen.],” said Dolokhov.
Petya wanted to say bonsoir [ Good evening] and couldn’t finish the words. The officers were whispering something to each other. Dolokhov took a long time to mount the horse, which was not standing; then he 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.
Having reached the road, Dolokhov drove not back into the field, but along the village. At one point he stopped, listening.
- Do you hear? - he said.
Petya recognized the sounds of Russian voices and saw the dark figures of Russian prisoners near 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 the ravine 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 him with his hand.
- No! - he cried, - you are such a hero. Oh, how good! How great! How I love you.
“Okay, okay,” said Dolokhov, but Petya did not let him go, and in the darkness Dolokhov saw that Petya was bending down 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 excitement, 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. “What the hell, I couldn’t sleep because of you!” Denisov said. “Well, thank God, now go to bed.” Still sighing and eating until the end.
“Yes... No,” said Petya. – I don’t want to sleep 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 completely dark outside. The rain had passed, but drops were still falling from the trees. Close to the guardhouse one could see black figures of Cossack huts and horses tied together. Behind the hut were two black wagons with horses standing, and in the ravine the dying fire was red. The Cossacks and hussars were not all asleep: in some places, along with the sound of falling drops and the nearby sound of horses chewing, soft, as if whispering voices were heard.
Petya came out of the entryway, looked around in the darkness and approached 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 approached it.
“Well, Karabakh, we’ll serve tomorrow,” he said, smelling her nostrils and kissing her.
- What, master, aren’t you sleeping? - said the Cossack sitting under the truck.
- No; and... Likhachev, I think your name is? 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 believes that it is better to risk his life than to make Lazar at random.
“Well, they should have slept,” said the Cossack.
“No, I’m used to it,” answered Petya. - What, you don’t have flints in your pistols? I brought it 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. “Some people just don’t get ready, and then they regret it.” I don't like it that way.
“That’s for sure,” said the Cossack.
“And one more thing, please, my dear, sharpen my saber; dull it... (but Petya was afraid to lie) it was never sharpened. Can this be done?
- Why, it’s possible.
Likhachev stood up, rummaged through his packs, and Petya soon heard the warlike sound of steel on a block. He climbed onto the truck and sat on the edge of it. The Cossack was sharpening his saber under the truck.
- Well, are the fellows sleeping? - said Petya.
- Some are sleeping, and some are like this.
- Well, what about the boy?
- Is it spring? He collapsed there in the entryway. He sleeps with fear. I was really glad.
For a long time after this, 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 truck.
- But sharpen the master’s saber.
“Good job,” said the man who seemed to Petya to be a hussar. - Do you still have a cup?
- And over there by the wheel.
The hussar took the cup.
“It’ll probably be light soon,” he said, yawning, and walked off somewhere.
Petya should have known that he was in the forest, in Denisov’s party, a mile from the road, that he was sitting on a wagon captured from the French, around which the horses were tied, that the Cossack Likhachev was sitting under him and sharpening his saber, that there was a big black spot to the right is a guardhouse, and a bright red spot below to the left is a dying fire, that the man who came for a cup is a hussar who was thirsty; but he knew nothing and did not want to know it. He was in a magical kingdom in which there was nothing like reality. A large black spot, perhaps there was definitely a guardhouse, or perhaps there was a cave that led into the very depths of the earth. The red spot might have been fire, or maybe 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 terrible high tower, from which if you fall, you would fly to the ground for a whole day, a whole month - you’d keep flying and never reach it. It may be that just a Cossack Likhachev is sitting under the truck, but it may very well be that this is the kindest, bravest, most wonderful, most ripper in a world that no one knows. Maybe it was just a hussar passing for water and going into the ravine, or maybe he 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 kingdom where everything was possible.
He looked at the sky. And the sky was as magical as the earth. The sky was clearing, and clouds were moving quickly over the tops of the trees, as if revealing the stars. Sometimes it seemed that the sky cleared and a black, clear sky appeared. Sometimes it seemed that these black spots were clouds. Sometimes it seemed as if the sky was rising high, high above your head; sometimes the sky dropped completely, so that you could reach it with your hand.
Petya began to close his eyes and sway.
Drops were dripping. There was a quiet conversation. The horses neighed and fought. Someone was snoring.
“Ozhig, zhig, zhig, zhig...” the saber being sharpened whistled. And suddenly Petya heard a harmonious choir of music playing some unknown, solemnly sweet hymn. Petya was musical, just like Natasha, and more than Nikolai, but he had never studied music, did not think about music, and therefore the motives that unexpectedly came to his mind were especially new and attractive to him. The music played louder and louder. The melody grew, moving from one instrument to another. What was called a fugue was happening, although Petya did not have the slightest idea what a fugue was. Each instrument, sometimes similar to a violin, sometimes like trumpets - but better and cleaner than violins and trumpets - each instrument played its own and, not yet finishing the tune, merged with another, which started almost the same, and with the third, and with the fourth , and they all merged into one and scattered again, and again merged, now into the solemn church, now into the brightly brilliant and victorious.
“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 sides, as if from afar, sounds began to tremble, began to harmonize, scatter, merge, and again everything united into the same sweet and solemn hymn. “Oh, what a delight this is! As much as I want and how I want,” Petya said to himself. He tried to lead this huge choir of instruments.
“Well, hush, hush, freeze now. – And the sounds obeyed him. - Well, now it’s fuller, more fun. More, even more joyful. – And from an unknown depth arose intensifying, solemn sounds. “Well, voices, pester!” - Petya ordered. And first, male voices were heard from afar, then female voices. The voices grew, grew in uniform, solemn effort. Petya was scared and joyful to listen to their extraordinary beauty.

Dwarf galaxy- small, consisting of several billion (which is very small compared, for example, to our galaxy, which has about 200-400 billion stars). Dwarf galaxies include galaxies with luminosity less than 10 9 L ☉ (about 100 times less luminosity), which approximately corresponds to −16 m absolute magnitude. The Large Magellanic Cloud, containing 30 billion stars, is sometimes classified as a dwarf galaxy, while others consider it a full-fledged galaxy orbiting the Milky Way.

Dwarf galaxies vary greatly in surface brightness. If ordinary galaxies have an average surface brightness approximately equal to the brightness of the night sky, then dwarf galaxies differ from each other in their surface brightness by more than 10 m.

Discovery of dwarf galaxies

Apart from the satellite galaxies of the Andromeda Nebula M 32 and NGC 205, which occupy a borderline position between dwarf and normal galaxies, the first dwarf galaxies were discovered by H. Shapley in the late 1930s, while conducting a survey of the sky in the vicinity of the South Pole for statistical galaxy research at the observatory Harvard University 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 Fornax constellation. After using the 2.5 m telescope at Mount Wilson Observatory to study these clusters, it was possible to find Cepheids in them and determine the distances. It turned out that both unknown clusters are located outside our galaxy, that is, they represent a new type of low surface brightness galaxy.

Discoveries of dwarf galaxies became widespread after the Palomar Sky Survey was carried out in the 1950s using the 120-centimeter Schmidt camera at Mount Palomar Observatory. It turned out that dwarf galaxies are the most common galaxies in.

Local dwarfs

IN Local group There are a lot of dwarf galaxies: these are small galaxies that often orbit around large galaxies, such as the Milky Way, Andromeda and the Triangulum Galaxy. 14 dwarf galaxies have been discovered orbiting our Galaxy. It is possible that the Omega Centauri globular cluster is the core of a dwarf galaxy captured in the past.

Morphology

There are several main types of dwarf galaxies:

• Dwarf elliptical galaxy ( dE) - similar to
  • Dwarf spheroidal galaxy ( dSph) - subtype dE characterized by particularly low surface brightness
• Dwarf irregular galaxy ( dIr) - similar, has a clumpy structure
• Dwarf blue compact galaxy ( dBCG or BCD) - has signs of active star formation
• Ultracompact dwarf galaxies ( UCD) - 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 (nuclei) of dwarf elliptical galaxies that flew through the central parts of rich ones. Ultracompact galaxies have been discovered in the Virgo, Fornax, Coma Berenices, Abel 1689, and other galaxy clusters.
• A dwarf spiral galaxy is an analogue, but, unlike normal galaxies, it is extremely rare

Hobbit galaxies

The recently coined term Hobbit Galaxies was used to refer to galaxies that are smaller and fainter than dwarf galaxies.

The problem of the shortage of dwarf galaxies

The dwarf galaxy shortage problem (also known as the “missing dwarf satellite galaxy problem”). Its essence is that the number dwarf galaxies(relative to the number of ordinary galaxies) per whole order less number, which should be according to the modeling of the hierarchical distribution of structures and general cosmology.

There are two possible solutions this problem:

1. dwarf galaxies are destroyed by tidal forces of larger galaxies;
2. dwarf galaxies are simply not visible because their dark matter is unable to attract enough baryonic matter to make them visible.

The second solution is partially confirmed by the recent (2007) discovery by the Keck Observatory of eight ultra-faint dwarf galaxies (hobbit galaxies) - satellites milky way. Six of them are 99.9% dark matter (the mass-to-light ratio is about 1000).

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” most of such galaxies (which is why there are few stars there), but left dark matter, which is why now prevails. Astronomers propose to search for some of these dim dwarf galaxies with an overwhelming predominance of dark matter by indirect observations: along the “wake” in the intergalactic gas, i.e. by the attraction of gas jets to this “invisible” galaxy.



Once again my dream torments me,

That somewhere out there, in another corner of the universe,

The same garden, and the same darkness,

And the same stars in imperishable beauty.

N. Zabolotsky

The study of the nature of astronomical (and not only astronomical) objects of one type or another usually goes through several stages. At first there is no clear understanding; there is a bunch of various mutually exclusive assumptions. Then a generally accepted point of view crystallizes, allowing at least a qualitative explanation of the observed picture in its basic details. The objects under study cease to be incomprehensible; threads of connection stretch from them to previously known objects or phenomena.

And after some time the third stage begins. New observations or theoretical calculations show that everything is not as simple as it seemed. Although the old explanations at their core may remain, the objects of study are again puzzling with their reluctance to fit into simple and clear schemes. We need new ideas, new calculations. Finally, at the next, fourth stage, a consistent and more complex picture arises again than before. Understanding has risen to a new, more high level. In the future, everything can repeat itself again - with the appearance of unexpected observational facts and with a different theoretical approach.

The study of dwarf elliptical galaxies (dE galaxies), which will be discussed in this section, is now in its second stage. Of all the dwarf galaxies, these are the most understandable objects for us. They do not represent any group that stands out sharply in their features, and their properties “continue” the properties of ordinary elliptical galaxies, extrapolating to the region of low luminosity and size.

The closest dE galaxies to us are the four elliptical satellites of the Andromeda Nebula. Two of them, galaxies M 32 and NGC 205, are observed very close to the giant spiral galaxy, and two fainter ones, NGC 185 and NGC 147, are located a few angular degrees to the north of it. The first two appear as bright spots in any photograph of the Andromeda Nebula, projected onto its outer regions; The M 32 galaxy is a compact, almost round formation, while the NGC 205 galaxy in the photograph has a blurrier, noticeably elongated image. Their absolute magnitude is close to -16 m, so these galaxies are on that conditional border, which separates dwarfs from “normal” galaxies.

Capture individual stars in photographs of these dwarf galaxies, i.e., as astronomers say, resolve galaxies into stars, at the cost great effort succeeded in the 40s by V. Baada, who worked on the largest telescope in the world at that time - the 2.5-meter Mount Palomar reflector. It must be said that even now, even with the help best telescopes Resolving the satellites of the Andromeda Nebula into stars is not an easy task.

For a long time, the stellar composition of these small galaxies, as well as the central region of the Andromeda Nebula itself, remained mysterious: the presence of the brightest stars - blue supergiants - was not noticeable in the photographs, although these stars are confidently observed in the spiral branches of the nearby Andromeda Nebula.

Having set himself the task of resolving the central part of the Andromeda Nebula and its elliptical satellites into stars, V. Baade began to seriously prepare for its implementation. These objects were known to be reddish in color, and he assumed (correctly) that this was the color of the brightest stars they contained. Therefore, W. Baade abandoned plates that react to blue rays, usually used in astronomical photography, and chose the most sensitive photographic plates available at that time, which perceive orange and red colors. However, these plates had a significantly lower sensitivity than the “blue” ones, and to increase it, it was necessary to specially treat them with ammonia before using the plates.

But even after this, the sensitivity turned out to be not too high, and in order to have any hope of capturing stars that were inaccessible to “blue” plates, it was necessary to rely on many hours of exposure. The fact is that long-term exposures cannot be made on highly sensitive “blue” plates: after only 1.5 hours, the weak glow of the night sky covered them with a dense veil. According to calculations by V. Baade, this approach should have made it possible to obtain stars of 0.5 on the “red” plates T(1.6 times) weaker than on the “blue” ones.

How else can you increase the penetrating power of a telescope, that is, its ability to detect faint stars?

People familiar with the specifics astronomical observations, are well aware that the capabilities of a telescope as an optical instrument vary greatly from night to night, even if they are equally clear, and sometimes during the same night. It's connected with different condition atmosphere, and for large telescopes - also with the state of a mirror lens, the reflective surface of which is subject to temperature deformations due to temperature differences between in different parts mirrors, and between the mirror and air environment. And only in Lately learned to make large mirrors from a substance that is practically not subject to thermal expansion.

Subsequently, V. Baade wrote about this: “One could not hope to achieve success if one simply inserted a “red” plate into the cassette of a 2.5-meter telescope, made an exposure, developed it and tried to see something. It was quite clear that the stars would be very faint and, in all likelihood, extremely closely located. This is at the limit of the resolving power of a 2.5-meter telescope, and obviously one would have to be very careful not to take the slightest chance.

To keep the resolution as high as possible, it was necessary, firstly, to carry out observations only when obtaining the best images, when the turbulent disk of stars is very small. Secondly, it was worth observing only on those nights when the shape of the mirror was close to ideal, without “collapsing” of the edges, which always leads to an increase in the star’s disk. Thirdly (and this was main problem), something had to be done about the changes in focus that arose due to the fact that the mirror of the 2.5-meter telescope was made of an old brand of glass. Even when the nights were satisfactory in this sense, there were changes in the focal length from 1.5 to 2 mm, and there were also nights when these changes reached 5-6 mm.”

As a result, V. Baade had to invent his own way of continuously checking the correct focus of the image, which made it possible not to interrupt the many-hour exposure.

Preparation for the decisive observations lasted more than a year. Finally, in the fall of 1943, for several nights with exclusively good quality Long-awaited negatives were obtained, in which the satellites of the Andromeda Nebula (as well as its central part, consisting of similar stars) were strewn with tiny points of stars. This is how the brightest stars of dwarf elliptical galaxies looked from a distance of almost 700 thousand pcs. It should be said that one important circumstance contributed to the success of their discovery. They really stood above the observatory dark nights, since the war-related blackout of the giant city of Los Angeles with its bustling suburbs nearby had not yet been lifted.

By this time, astronomers were well acquainted with the most diverse types of stars, but the stars photographed by V. Baade puzzled the scientist. They were too luminous for ordinary red stars. It seemed strange that in the observed stellar neighborhood of the Sun there are almost no such stars, and in dwarf elliptical galaxies they make the main contribution to the radiation of the galaxy.

Only after some time did V. Baade realize that the globular clusters of our Galaxy consist of exactly the same stars. These clusters are rather distant associations of hundreds of thousands of stars (the closest of them is several thousand light years away from us). Their age exceeds 10 billion years, i.e. they are real relics of the stellar world.

Further research confirmed V. Baade’s guess. Brightest stars dwarf elliptical galaxies, like globular clusters, turned out to be red giants of high luminosity - greatly inflated and changed their internal structure stars, since over their long lives the main nuclear fuel (hydrogen) has been largely exhausted in the stellar interior. Characteristic feature The stars of dwarf galaxies are also low in the content of heavy chemical elements in the stellar atmosphere (although not as low as in globular clusters). Looking ahead, we note that this so-called deficiency of heavy elements is typical for dwarf galaxies of all types.

“Normal” elliptical galaxies, which are not classified as dwarf in their luminosity, also consist of old stars, although not as strongly depleted in heavy elements as in dwarf galaxies. Apparently, star formation in “normal” E-galaxies practically ended many billions of years ago. The history of dE galaxies, as it turns out, may be different. This is clearly seen in the example of the same satellites of the Andromeda Nebula.

For example, the pattern of the spectrum of the Andromeda Nebula's satellite M 32 can be explained by suggesting that, although star formation does not appear to be occurring in the galaxy now, it existed there several billion years ago.

In two other satellites of the Andromeda Nebula, NGC 205 and NGC 185, several dozen blue stars high luminosity, hidden among a scattering of old red stars. According to astronomical time scales, such stars have just formed, since the high energy consumption makes them short-lived. Their age is unlikely to exceed 100 million years, which is very little for stars. The sun, for example, exists 50 times longer. Consequently, star formation is still ongoing in these galaxies.

Of course, along with hot stars of high luminosity, low-mass stars can also form there (in much greater numbers), but they cannot be found among the brighter, but older stars of the galaxy. Therefore, star formation centers are determined only by the position of blue stars, which are usually localized in small areas of the galaxy. For example, in the NGC 185 galaxy, all blue stars occupy a region less than 300 pc in size (the size of the entire galaxy is tens of times larger).

The problem of the existence of a small number of young stars in some dE galaxies is of considerable interest. Indeed, in massive elliptical galaxies, the lack of star formation is usually associated with the absence of interstellar gas, i.e., the medium that can give birth to stars when it is strongly compressed and cooled. In all cases, the presence of young blue stars is noticeable only in those galaxies where the interstellar medium is observed. However, so far only in two dE galaxies has it been possible to detect cold interstellar gas by direct observations - in the satellites of the Andromeda Nebula NGC 205, NGC 185 (and even here it is extremely small - approximately 0.01% total weight galaxies).

Nevertheless, observations of nearby dE galaxies have shown that young stars in them are also associated with the interstellar medium. In the galaxies NGC 205 and NGC 185, in which young blue stars are observed “one by one,” dark dust nebulae are noticeable, associated, as we know from the example of our Galaxy, with regions of relatively dense and cold gas. Of course, there is little of it there, but star formation, one might say, is barely glimmering.

Where does this gas come from?

It turns out that even if the galaxy is completely “cleared” of gas, over time it will reappear in small quantities. It is delivered into interstellar space by aging stars. Direct evidence of such a process for nearest galaxies serve as observations planetary nebulae- expanding gas shells, thrown off by stars at a certain stage of their life path. Such nebulae have been found in all nearby dE galaxies. Over time, the gas ejected from the stars fills everything interstellar space. And then, depending on the specific physical conditions in the galaxy, it either leaves the galaxy, going into intergalactic space, or gradually cools down and contracts to turn into stars again,

The fate of gas ejected by stars depends on the mass of the elliptical galaxy. Theoretical calculations have shown that interstellar gas cools and contracts faster in small elliptical galaxies. Qualitatively, this can be explained by the fact that the stars in them move more slowly, and collisions of gas masses ejected by individual stars do not lead to such strong heating of the gas as can be expected in large galaxies. Perhaps this is why in elliptical “normal”, non-dwarf, galaxies, traces of gas and young stars are extremely rare. But who knows, if some giant elliptical galaxy was no further from us than the Andromeda Nebula, perhaps we could find individual blue stars in it?

Although dwarf elliptical galaxies do exhibit weak star formation in some cases, they are generally very quiet and very slowly changing star systems. They do not show any active processes associated with non-stellar energy sources - emissions of matter, non-thermal radio emission, nuclear activity. And in most cases there is no core in the usual sense of the word in dE galaxies, although in the very center of NGC 205 and M 32 a small star-shaped object (“core”) is visible, similar to a massive globular cluster of stars. In more distant galaxies, such formations are no longer accessible to observation.

Of course, dE galaxies are not limited to the satellites of the Andromeda Nebula. Among dwarfs, these are galaxies of relatively high luminosity, which is why they are accessible to observations at distances of several tens of millions of light years. Many dE galaxies have been found, for example, in the nearest large cluster galaxies in the constellation Virgo. But among large number dE galaxies, in only one case can one suspect an object with an active nucleus - a kind of dwarf radio galaxy. It is worth telling about this object in more detail to show what difficulties researchers sometimes encounter in trying to figure out the nature of the observed source.

Radio galaxies, the most powerful sources radio waves in nature are, as a rule, giant elliptical galaxies, the active nucleus of which ejects streams of relativistic (i.e., having a speed very close to the speed of light) protons and electrons. Such galaxies are found by studying photographs of those areas of the sky where one or another radio source is observed.

When in the 60s it was established that the coordinates of a radio source designated ZS 276 coincided with the coordinates of a small elliptical galaxy angular size, this could not come as much of a surprise. It could well have been an ordinary radio galaxy, removed to an enormous distance, from which it looked like an object of 15th magnitude. The spectrum of the galaxy was not known, but it itself was mentioned in two of the most full catalogs galaxies - Vorontsov-Velyaminov and Zwicky catalogs. It turned out to have a slightly bluish inner region of fairly high surface brightness and a more “red” shell measuring about 1′.

A “normal” radio galaxy could look like this from a distance of about 100 Mpc. Since in the world of galaxies the law is well followed, according to which next galaxy, the greater the radial velocity it has (Hubble's law), one could expect that its speed should be approximately equal to 6-8 thousand km/s. Imagine the surprise when its spectrum, photographed shortly after identification with the radio source 3S 276, indicated that its speed was only 30 km/s (moreover, the spectrum did not contain the expected emission lines characteristic of radio galaxies).

In 1970, Canadian astronomer S. van den Berg, working in the USA on a giant 5-meter telescope, obtained a new spectrogram of the galaxy using an electron-optical converter to verify the accuracy of the unexpected estimate. More than eight absorption lines were found exact value its speed of movement (relative to the Sun): 10±8 km/s. This speed is more likely characteristic not of galaxies, but of the stars closest to the Sun.

On this basis, the Soviet astronomer Yu. P. Pskovsky suggested that here we are not dealing with a radio galaxy, but with a weak radio source inside our Galaxy. Could this object be an ordinary remnant of a Crab Nebula-type supernova? This seemed to be supported by the fact that the position of the radio source ZS 276 differed by only 1° from the position of the Supernova observed by Chinese astronomers in the 13th century.

However, new studies of the object have made such an explanation unlikely. High-quality photographs of him obtained using large telescopes, showed that it does not contain the kind of filamentary structure that is typical of supernova remnants, and the observed strong concentration of brightness in it towards the center is very characteristic of elliptical galaxies. Finally, S. van den Berg found that the emission spectrum of the object is completely similar to the spectrum of globular clusters depleted in heavy elements, which, as we know, can be expected if we have a dE galaxy in front of us.

Although the speed of motion of this dE galaxy relative to the Sun is close to zero, the speed relative to the center of our Galaxy, taking into account the orbital motion of the Sun, is approximately 200 km/s. According to Hubble's law, this corresponds to a distance only several times greater than to the Andromeda Nebula. True, for galaxies with such insignificant velocities, the distance is determined unreliably from Hubble's law. It could be clarified if individual stars were observed in the galaxy, but, alas, they could not be detected, despite specially undertaken searches.

The low speed of the object ZS 276 definitely shows that it cannot be very far away. It turns out that this is a close dwarf star system. However, even if the distance to it is 2-3 Mpc, then this is not just a dwarf elliptical galaxy, but an object unique in its low luminosity, which is only 3-10 7 Lc. Among the known dE galaxies, there is not a single one whose luminosity was even close to this value. The radius also turned out to be a record - only 150-200 pcs. And from here it is completely incomprehensible how such a tiny galaxy can have an active nucleus and not be inferior in radio emission power to such a giant galaxy as the Andromeda Nebula.

What kind of explosion led to the release of radio-emitting clouds, which, judging by the distribution of radio emission, now occupy a volume many times greater than the volume of the mysterious object itself?

Having become acquainted with dwarf elliptical galaxies, let us now move on to galaxies that are very similar to them in stellar composition, but much less understood in nature.