Among objects that are ever weaker in brilliance, the number of G. is rapidly increasing. So, G. brighter than the 12th magnitude is known approx. 250, 15th - already approx. 50 thousand, and the number of G., which can be photographed with a 6-meter telescope at the limit of its capabilities, is many billions. It indicates means. the remoteness of most

Extragalactic astronomy studies the dimensions of stellar systems, their masses, structure, and optical, infrared, and x-ray properties. and radio emission. The study of the spatial distribution of geometries reveals the large-scale structure of the Universe (it can be said that the part of the Universe accessible to observation is the world of geometries). In the study of the spatial distribution of G. and the ways of their evolution extragalactic. astronomy merges with cosmology - the science of the universe as a whole.

One of the most important extragalactic astronomy remains the problem of determining the distance to G. Due to the fact that in the nearest G. found, as well as the brightest stars of constant brilliance (supergiants), it was possible to establish the distances to these galaxies. To even more distant girders, in which it is impossible to distinguish even supergiant stars, the distances are estimated in other ways (see).

In 1912, Amer. astronomer V. Slifer discovered a remarkable property of gyros: in the spectra of distant gyros, the whole spectrum. the lines turned out to be shifted to the long-wavelength (red) end in comparison with the same lines in the spectra of sources that are stationary relative to the observer (the so-called lines). In 1929, Amer. astronomer E. Hubble, comparing the distances to G. and their redshifts, found that the latter grow on average in direct proportion to the distances (see). This law gave into the hands of astronomers effective method determining distances to G. by their redshift. The redshifts of thousands of G. and hundreds have been measured.

Determining the distances to galaxies and their positions in the sky made it possible to establish that there are single and double gyros, groups of gyros, large clusters of them, and even clouds of clusters (superclusters). Wed distances between G. in groups and clusters are several. hundreds of kpc; this is about 10-20 times the size of the largest G. Cf. the distances between groups of galaxies, single gyros, and multiple systems are 1–2 Mpc, and the distances between clusters are tens of Mpc. Thus, stars fill space with a higher relative density than intragalactic stars. space (distances between stars are on average 20 million times greater than their diameters).

According to the radiation power, G. can be divided into several. luminosity classes. The widest range of luminosities is observed in ellipticals. G., in the central regions of certain accumulations of G., so-called. cD-galaxies, which are record-breaking in luminosity (abs. magnitude - 24 m, luminosity ~ 10 45 erg / s) and mass (). And in our Local G. group, ellipticals were found. G. low luminosity (abs. values ​​from -14 to -6 m, i.e. luminosity ~10 41 -10 38 erg / s) and mass (10 8 -10 5 ). At spiral G. an interval abs. stellar magnitudes range from -22 to -14 m , luminosities - from 10 44 to 10 41 erg / s, mass interval 10 12 -10 8 . Wrong G. by abs. weaker values ​​- 18 m , their luminosity 10 43 erg/s, masses .

The formation of young stars is still going on in the central region of the Galaxy. A gas that has no rotational momentum falls towards the center of the Galaxy. Here, the stars of the 2nd generation of spherical are born. subsystems that make up the core of the Galaxy. But there are no favorable conditions for the formation of supergiant stars in the core, since the gas breaks up into small clumps. In the same rare cases where the gas transmits torque environment and shrinks into a massive body - with a mass of hundreds and thousands of solar masses, this process does not end successfully: gas compression does not lead to the formation of a stable star, it can occur and arise. The collapse is accompanied by the ejection of part of the matter from the galactic region. kernels (see).

The more massive the spiral gyroscope, the stronger gravity compresses the spiral arms; therefore, the arms of massive galaxies are thinner, they contain more stars and less gas (more stars are formed). For example, in the giant nebula M81, thin spiral arms are visible, while in the nebula M33, which is a medium-sized spiral, the arms are much wider.

Depending on the type, spiral galaxies also have different rates of star formation. The Sc type has the highest speed (about 5 per year), the Sa has the lowest speed (about 1 per year). The high rate of star formation in the former is also apparently associated with the flow of gas from galaxies. coron.

At the elliptical star systems, the evolutionary path should be simpler. The substance in them from the very beginning did not have significant torque and magnetic. field. Therefore, compression in the process of evolution did not lead such systems to a noticeable rotation and strengthening of the magnetic field. fields. All the gas in these systems from the very beginning turned into spherical stars. subsystems. In the course of subsequent evolution, the stars ejected gas, which descended to the center of the system and went to the formation of new generation stars of the same spherical. subsystems. Star formation rate in elliptic. G. should be equal to speed the flow of gas from evolved stars, mainly supernovae, since the outflow of matter from stars in an elliptical. G. slightly. Annual loss of gas by stars in elliptic. G. according to calculations is ~0.1 per galaxy with a mass of 10 11 . It also follows from the calculations that the central parts of the elliptic G. due to the presence of young stars should be bluer than the peripheral regions of G. However, this is not observed. It's about what it means. part of the resulting gas in an elliptical. G. is blown out by the hot wind that occurs during outbursts of supernovae, and in G. clusters it is also blown out by rather dense hot intergalactic matter. gas, discovered recently by its X-ray. radiation.

Comparing the number of stars of different generations in a large number similar G., it is possible to establish possible ways of their evolution. In older galaxies, there is a depletion of interstellar gas reserves and, as a result, a decrease in the rate of formation and in the total number of stars of new generations. But they have a lot - superdense stars of small sizes, representing one of the last stages of the evolution of stars. This is precisely the aging of galaxies. It should be noted that, at the beginning of their evolution, galaxies apparently had a higher luminosity, since they contained more massive young stars. It is possible, in principle, to reveal the evolutionary change in the luminosity of galaxies by comparing the luminosities of nearby and very distant galaxies, from which light comes for many billions of years.

Extragalactic astronomy has not yet given a definitive answer to questions related to the origin of gyratory clusters, in particular, why in spherical clusters are dominated by elliptic. and lenticular systems. Apparently, from relatively small clouds of gas that did not have a rotational moment, spherical ones were formed. clusters with a predominance of elliptic. and lenticular systems, also having a small torque. And from large clouds of gas, which possessed a significant rotational moment, clusters of gyros arose, similar to the Supercluster in Virgo. Here there were more variants of the distribution of the rotational moment among the individual clumps of gas, from which galaxies were formed, and therefore spiral systems are more common in such clusters.

G.'s evolution in clusters and groups has a number of features. Calculations have shown that during collisions of galaxies, their extended gaseous coronas must be “stripped off” and dispersed over the entire volume of the group or cluster. This intergalactic gas was detected by high-temperature X-ray. In addition, the massive members of the clusters, moving among the rest, create "dynamic friction": by their gravity they drag the neighboring hydrometeors, but in turn experience deceleration. Apparently, this is how the Magellanic Stream was formed in the Local Group G. Sometimes massive G. located in the center of the cluster not only "tear off" the gaseous coronas of the G. passing through them, but also capture the "visitor" stars. It is assumed, in particular, that cD galaxies with massive halos formed them in such a "cannibalistic" way.

According to existing calculations, in 3 billion years our Galaxy will also become a "cannibal": it will absorb the Large Magellanic Cloud approaching it.

Uniform distribution of matter on the scales of the Metagalaxy determines the identity of St-in matter and space in all parts of the Metagalaxy (homogeneity) and their identity in all directions (isotropy). These important Holy Islands of the Metagalaxy are characteristic, apparently, for the modern. states of the Metagalaxy, however, in the past, at the very beginning of the expansion, anisotropy and inhomogeneity of matter and space could exist. The search for traces of anisotropy and inhomogeneity of the Metagalaxy in the past is a complex and urgent task of extragalactic astronomy, which astronomers are only just beginning to solve.

The most striking feature of the spatial distribution of globular clusters in the Galaxy is a strong concentration towards its center. On fig. 8-8 shows the distribution of globular clusters over the entire celestial sphere, here the center of the Galaxy is in the center of the figure, the north pole of the Galaxy is at the top. There is no visible zone of avoidance along the plane of the Galaxy, so interstellar extinction in the disk does not hide a significant number of clusters from us.

On fig. 8-9 shows the distribution of globular clusters along the distance from the center of the Galaxy. There is a strong concentration towards the center - most globular clusters are located in a sphere with a radius of ≈ 10 kpc. It is within this radius that almost all globular clusters formed from matter are located. single protogalactic cloud and formed subsystems of the thick disk (clusters with > -1.0) and halo proper (less metallic clusters with extreme blue horizontal branches). Metal-poor clusters with horizontal branches anomalously red for their metallicity form a spheroidal subsystem accreted halo radius ≈ 20 kpc. About a dozen more distant clusters belong to the same subsystem (see Fig. 8-9), among which there are several objects with anomalously high metal contents.

Clusters of the accreted halo are believed to be selected by the gravitational field of the Galaxy from satellite galaxies. On fig. 8-10 schematically shows this structure according to Borkova and Marsakov from the South federal university. Here, the letter C denotes the center of the Galaxy, S is the approximate position of the Sun. At the same time, accumulations with a high content of metals belong to the oblate subsystem. We will dwell on a more detailed substantiation of the division of globular clusters into subsystems in § 11.3 and § 14.3.

Globular clusters are also common in other galaxies, and their spatial distribution in spiral galaxies resembles the distribution in our Galaxy. Noticeably different from the Galactic clusters of the Magellanic Clouds. The main difference is that along with old objects, the same as in our Galaxy, young clusters are also observed in the Magellanic Clouds - the so-called blue globular clusters. Probably, in the Magellanic Clouds, the epoch of the formation of globular clusters either continues or ended relatively recently. It seems that there are no young globular clusters in our Galaxy similar to the blue clusters of the Magellanic Clouds, so the era of the formation of globular clusters in our Galaxy ended a very long time ago.

Globular clusters are evolving objects that gradually lose stars in the process. dynamic evolution . Thus, all clusters for which it was possible to obtain a high-quality optical image showed traces of tidal interaction with the Galaxy in the form of extended deformations (tidal tails). Currently, such lost stars are also observed in the form of increases in stellar density along the galactic orbits of clusters. Some clusters that orbit near the galactic center are destroyed by its tidal action. At the same time, the galactic orbits of clusters also evolve due to dynamic friction.

On fig. 8-11 is a dependency diagram masses of globular clusters from their galactocentric positions. Dashed lines mark the region of slow evolution of globular clusters. The upper line corresponds to the critical value of the mass that is stable for effects of dynamic friction , leading to a slowdown of a massive star cluster and its fall to the center of the Galaxy, and the lower one - for dissipation effects taking into account tidal clusters during the flight through the galactic plane. The reason for dynamic friction is external: a massive globular cluster moving through the stars of the field attracts the stars it meets on its way and forces them to fly around itself behind along a hyperbolic trajectory, due to which an increased density of stars is formed behind it, creating a decelerating acceleration. As a result, the cluster slows down and begins to approach the galactic center along a spiral trajectory until it falls on it in a finite time. The greater the mass of the cluster, the shorter this time. Dissipation (evaporation) of globular clusters occurs due to the internal mechanism of stellar-stellar relaxation that is constantly operating in the cluster, distributing stars according to velocities according to Maxwell's law. As a result, the stars that have received the largest increments of speed leave the system. This process is significantly accelerated by the passage of the cluster near the galactic core and through the galactic disk. Thus, with a high probability we can say that the clusters lying on the diagram outside the area bounded by these two lines are already ending their life path.

It's interesting that accreted globular clusters discover the dependence of their masses on their position in the Galaxy. The solid lines in the figure represent direct regressions for genetically related (black dots) and accreted (open circles) globular clusters. It can be seen that genetically related clusters show no change in the average mass with increasing distance from the galactic center. On the other hand, there is a clear anticorrelation for accreted clusters. Thus, the question that needs to be answered arises, why is there an increasing deficit of massive globular clusters in the outer halo with increasing galactocentric distance (almost empty upper right corner in the diagram)?

Usually galaxies are found in small groups containing ten members, often combined into vast clusters of hundreds and thousands of galaxies. Our Galaxy is part of the so-called Local Group, which includes three giant spiral galaxies (our Galaxy, the Andromeda nebula and the nebula in the constellation Triangulum), as well as more than 15 dwarf elliptical and irregular galaxies, the largest of which are the Magellanic Clouds. The average size of galaxy clusters is about 3 Mpc. In some cases, their diameter can exceed 10–20 Mpc. They are divided into scattered (irregular) and spherical (regular) clusters. Open clusters do not have a regular shape and have blurred outlines. The galaxies in them are very weakly concentrated towards the center. An example of a giant open cluster is the closest cluster of galaxies to us in the constellation Virgo (241). In the sky, it occupies about 120 square meters. degrees and contains several thousand predominantly spiral galaxies. The distance to the center of this cluster is about 11 Mpc. Spherical clusters of galaxies are more compact than open ones and have spherical symmetry. Their members are noticeably concentrated towards the center. An example of a spherical cluster is the cluster of galaxies in the constellation Coma Berenices, which contains a large number of elliptical and lenticular galaxies (242). Its diameter is almost 12 degrees. It contains about 30,000 galaxies brighter than 19 photographic magnitude. The distance to the center of the cluster is about 70 Mpc. Many rich clusters of galaxies are associated with powerful extended sources of X-rays, the nature of which is most likely associated with the presence of hot intergalactic gas, similar to the coronas of individual galaxies. There is reason to believe that clusters of galaxies, in turn, are also unevenly distributed. According to some studies, the clusters and groups of galaxies surrounding us form a grandiose system - the Supergalaxy. In this case, individual galaxies apparently concentrate towards a certain plane, which can be called the equatorial plane of the Supergalaxy. The cluster of galaxies just discussed in the constellation Virgo is at the center of such a gigantic system. The mass of our Supergalaxy should be about 1015 solar masses, and its diameter should be about 50 Mpc. However, the reality of the existence of such clusters of second-order galaxies currently remains controversial. If they exist, then only as a weakly expressed inhomogeneity of the distribution of galaxies in the Universe, since the distances between them can slightly exceed their sizes.

Usually galaxies are found in small groups containing ten members, often combined into vast clusters of hundreds and thousands of galaxies. Our Galaxy is part of the so-called Local Group, which includes three giant spiral galaxies (our Galaxy, the Andromeda nebula and the nebula in the constellation Triangulum), as well as more than 15 dwarf elliptical and irregular galaxies, the largest of which are the Magellanic Clouds. The average size of galaxy clusters is about 3 Mpc. In some cases, their diameter can exceed 10–20 Mps. They are divided into scattered (irregular) and spherical (regular) clusters. Open clusters do not have a regular shape and have blurred outlines. The galaxies in them are very weakly concentrated towards the center. An example of a giant open cluster is the nearest cluster of galaxies in the constellation Virgo. In the sky, it occupies about 120 square meters. degrees and contains several thousand predominantly spiral galaxies. The distance to the center of this cluster is about 11 Mpc. Spherical clusters of galaxies are more compact than open ones and have spherical symmetry. Their members are noticeably concentrated towards the center. An example of a spherical cluster is the cluster of galaxies in the constellation Coma Berenices, which contains a lot of elliptical and lenticular galaxies (Fig. 242). Its diameter is almost 12 degrees. It contains about 30,000 galaxies brighter than 19 photographic magnitude. The distance to the center of the cluster is about 70 Mpc. Many rich clusters of galaxies are associated with powerful extended sources of X-rays, the nature of which is most likely associated with the presence of hot intergalactic gas, similar to the coronas of individual galaxies.

There is reason to believe that clusters of galaxies, in turn, are also unevenly distributed. According to some studies, the clusters and groups of galaxies surrounding us form a grandiose system - the Supergalaxy. In this case, individual galaxies apparently concentrate towards a certain plane, which can be called the equatorial plane of the Supergalaxy. The cluster of galaxies just discussed in the constellation Virgo is at the center of such a gigantic system. The mass of our Supergalaxy should be about 1015 solar masses, and its diameter is about 50 Mpc. However, the reality of the existence of such clusters of second-order galaxies currently remains controversial. If they exist, then only as a weakly expressed inhomogeneity of the distribution of galaxies in the Universe, since the distances between them can slightly exceed their sizes. On the evolution of galaxies The ratio of the total amount of stellar and interstellar matter in the Galaxy changes with time, since stars form from interstellar diffuse matter, and at the end of their evolutionary path they return only part of the matter to interstellar space; some of it remains in white dwarfs. Thus, the amount of interstellar matter in our Galaxy should decrease with time. The same should happen in other galaxies. Being processed in the stellar interior, the substance of the Galaxy gradually changes chemical composition enriched with helium and heavy elements. It is assumed that the Galaxy was formed from a gas cloud, which consisted mainly of hydrogen. It is even possible that, apart from hydrogen, it did not contain any other elements. Helium and heavy elements were formed in this case as a result of thermonuclear reactions inside stars. The formation of heavy elements begins with the triple helium reaction 3He4 ® C 12, then C 12 combines with a-particles, protons and neutrons, the products of these reactions undergo further transformations, and thus more and more complex nuclei appear. However, the formation of the heaviest nuclei, such as uranium and thorium, cannot be explained by gradual growth. In this case, one would inevitably have to go through the stage of unstable radioactive isotopes, which would decay faster than they could capture the next nucleon. Therefore, it is assumed that the heaviest elements at the end of the periodic table are formed during supernova explosions. A supernova explosion is the result of a star collapsing rapidly. At the same time, the temperature rises catastrophically, chain thermonuclear reactions take place in the contracting atmosphere and powerful neutron fluxes arise. The intensity of neutron fluxes can be so high that intermediate unstable nuclei do not have time to collapse. Before that happens, they capture new neutrons and become stable. As already mentioned, the abundance of heavy elements in the stars of the spherical component is much less than in the stars of the flat subsystem. This is apparently explained by the fact that the stars of the spherical component were formed at the very initial stage of the evolution of the Galaxy, when the interstellar gas was still poor in heavy elements. At that time, the interstellar gas was an almost spherical cloud, the concentration of which increased towards the center. The stars of the spherical component that formed in this epoch also retained the same distribution. As a result of collisions of clouds of interstellar gas, their speed gradually decreased, kinetic energy turned into thermal energy, and the general shape and size of the gas cloud changed. Calculations show that in the case of rapid rotation, such a cloud should have taken the form of an oblate disk, which is what we observe in our Galaxy. Stars formed at a later time therefore form a flat subsystem. By the time the interstellar gas formed into a flat disk, it had been processed in the stellar interior, the abundance of heavy elements had increased significantly and the stars of the flat component were therefore also rich in heavy elements. Often the stars of the flat component are called second generation stars, and the stars of the spherical component are called first generation stars, to emphasize the fact that the stars of the flat component were formed from matter that had already been in the stellar interior. The evolution of other spiral galaxies probably proceeds in a similar way. The shape of the spiral arms, in which the interstellar gas is concentrated, is apparently determined by the direction of the field lines of the general galactic magnetic field. The elasticity of the magnetic field, to which the interstellar gas is "glued", limits the flattening of the gaseous disk. If only gravity acted on the interstellar gas, its compression would continue indefinitely. In this case, due to its high density, it would quickly condense into stars and practically disappear. There is reason to believe that the rate of star formation is approximately proportional to the square of the density of the interstellar gas.

If the galaxy rotates slowly, then the interstellar gas is collected by gravity in the center. Apparently, in such galaxies the magnetic field is weaker and hinders the compression of the interstellar gas less than in rapidly rotating ones. The high density of interstellar gas in the central region leads to the fact that it is quickly consumed, turning into stars. As a result, slowly rotating galaxies should have an approximately spherical shape with a sharp increase in stellar density in the center. We know that elliptical galaxies have just such characteristics. Apparently, the reason for their difference from the spiral ones lies in the slower rotation. From what has been said above, it is also clear why there are few stars of early classes and little interstellar gas in elliptical galaxies.

Thus, the evolution of galaxies can be traced from the stage of a gaseous cloud of approximately spherical shape. The cloud consists of hydrogen, it is not uniform. Separate clumps of gas, moving, collide with each other - the loss of kinetic energy leads to cloud compression. If it rotates quickly, it turns out spiral galaxy, if slowly - elliptical. It is natural to ask why the matter in the Universe broke up into separate gas clouds, which later became galaxies, why we observe the expansion of these galaxies, in what form was the matter in the Universe before the formation of galaxies.

65. Distribution of stars in the Galaxy. Clusters. General structure Galaxies.

end of form beginning of form Knowing the distances to the stars allows us to approach the study of their distribution in space, and hence the structure of the Galaxy. In order to characterize the number of stars in different parts of the Galaxy, the concept of stellar density is introduced, which is analogous to the concept of the concentration of molecules. Stellar density is the number of stars in a unit volume of space. The unit of volume is usually taken to be 1 cubic parsec. In the vicinity of the Sun, the stellar density is about 0.12 stars per cubic parsec, in other words, each star has an average volume of over 8 ps3; the average distance between the stars is about 2 ps. To find out how the stellar density changes in different directions, the number of stars per unit area (for example, 1 square degree) in different parts of the sky is counted.

The first thing that catches your eye in such calculations is an unusually strong increase in the concentration of stars as you approach the Milky Way band, the middle line of which forms a large circle in the sky. On the contrary, as we approach the pole of this circle, the concentration of stars decreases rapidly. This fact is already at the end of the 18th century. allowed V. Herschel to draw the correct conclusion that our star system has an oblate shape, and the Sun should be close to the plane of symmetry of this formation. spherical sector, the radius of which is determined by the formula

lg r m =1 + 0.2 (m * M)

end of form beginning of form To characterize how many stars of different luminosities are contained in a given region of space, the luminosity function j (M) is introduced, which shows what proportion of the total number of stars has a given value of absolute stellar magnitude, say, from M to M + 1.

end of form beginning of form Clusters of galaxies are gravitationally bound systems galaxies, one of the largest structures in universe. The sizes of clusters of galaxies can reach 10 8 light years.

Accumulations are conditionally divided into two types:

regular - clusters of a regular spherical shape, in which elliptical and lenticular galaxies, with a clearly defined central part. At the centers of such clusters are giant elliptical galaxies. An example of a regular cluster - Cluster of Veronica's Hair.

irregular - clusters without a definite shape, inferior to regular ones in the number of galaxies. Clusters of this species are dominated by spiral galaxies. Example - Virgo Cluster.

Cluster masses vary from 10 13 to 10 15 solar masses.

The structure of the galaxy

The distribution of stars in the Galaxy has two pronounced features: firstly, a very high concentration of stars in the galactic plane, and secondly, a large concentration in the center of the Galaxy. So, if in the vicinity of the Sun, in the disk, one star falls on 16 cubic parsecs, then in the center of the Galaxy there are 10,000 stars in one cubic parsec. In the plane of the Galaxy, in addition to an increased concentration of stars, there is also an increased concentration of dust and gas.

Dimensions of the Galaxy: - the diameter of the disk of the Galaxy is about 30 kpc (100,000 light years), - the thickness is about 1000 light years.

The Sun is located very far from the nucleus of the Galaxy - at a distance of 8 kpc (about 26,000 light years).

The center of the Galaxy is located in the constellation Sagittarius in the direction of? = 17h46.1m, ? = –28°51′.

The galaxy consists of a disk, a halo and a corona. The central, most compact region of the Galaxy is called the nucleus. There is a high concentration of stars in the core: there are thousands of stars in every cubic parsec. If we lived on a planet near a star located near the core of the Galaxy, then dozens of stars would be visible in the sky, comparable in brightness to the Moon. A massive black hole is assumed to exist at the center of the Galaxy. Almost all molecular matter of the interstellar medium is concentrated in the annular region of the galactic disk (3–7 kpc); there is the largest number of pulsars, supernova remnants and sources of infrared radiation. The visible radiation of the central regions of the Galaxy is completely hidden from us by powerful layers of absorbing matter.

The galaxy contains two main subsystems (two components), nested one into the other and gravitationally bound to each other. The first is called spherical - a halo, its stars are concentrated towards the center of the galaxy, and the density of matter, which is high in the center of the galaxy, decreases rather quickly with distance from it. The central, densest part of the halo within a few thousand light-years of the center of the Galaxy is called the bulge. The second subsystem is a massive stellar disk. It looks like two plates folded at the edges. The concentration of stars in the disk is much greater than in the halo. The stars inside the disk move in circular paths around the center of the Galaxy. The Sun is located in the stellar disk between the spiral arms.

The stars of the galactic disk were called population type I, the stars of the halo - population type II. The disk, the flat component of the Galaxy, includes stars of the early spectral classes O and B, stars in open clusters, and dark dusty nebulae. Halos, on the contrary, are made up of objects that arose in the early stages of the evolution of the Galaxy: stars of globular clusters, stars of the RR Lyrae type. The stars of the flat component, compared with the stars of the spherical component, are distinguished by a high abundance of heavy elements. The age of the population of the spherical component exceeds 12 billion years. It is usually taken as the age of the Galaxy itself.

Compared to the halo, the disk rotates noticeably faster. The disk rotation speed is not the same at different distances from the center. The mass of the disk is estimated at 150 billion M. There are spiral branches (sleeves) in the disk. Young stars and star formation centers are located mainly along the arms.

The disk and the halo surrounding it are immersed in the corona. It is currently believed that the size of the corona of the Galaxy is 10 times larger than the size of the disk.