The largest galaxy in the local group of galaxies. Local Group of Galaxies: Closest galaxy to the Milky Way

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Local Group of Galaxies

The MW subgroup has a linear size of the order of 140 kpc, and the radial velocity dispersion of galaxies in it is 68 km/s.

• As can be seen from Table 1, dwarf diffuse (spheroidal) galaxies of the Sculptor dSph type make up more than half of the objects in the subgroup of our Galaxy.
• Except for the most distant ones dwarf galaxies NGC 6822 +SagittariusDIG and Tucana (which may be unrelated satellites of the Galaxy) all other galaxies have tidal index> 0, i.e. are gravitationally connected, so that the subgroup occupies a volume in space, the boundaries of which can be represented by an ellipsoid with the axial ratio Z:Y:X=8:3:1. Together with clouds of neutral hydrogen from Magellanic Stream this structure should be called a polar ellipsoid rather than a polar ring.
• The spheroidal dwarf galaxy Leo-I at a distance of 0.27 Mpc (Lee et. al., 1993) has a radial velocity of +176 km/s (Zaritsky et. al., 1989) relative to the Galactic center, which is significantly greater than the parabolic velocity of 118 km /With. According to the scenario described in Byrd et.al. (1994) the Leo-I galaxy was thrown out of the neighborhood M31 when galaxies M31 And Milky Way moved away from each other.
• The distribution of spheroidal and irregular satellites shows no noticeable segregation with distance from our Galaxy.
• Judging by the average radial velocity of the satellites +19±20 km/s, the Milky Way subgroup is not experiencing significant compression or expansion.

Subgroup M31

Subgroups of the Community Group

The Andromeda Nebula galaxy system, visible from the outside, clusters around its main galaxy M31, containing the nearest high surface brightness galaxies M32 and M110, as well as fainter and more distant NGC147 and NGC185, very weak systems And I, And II, And III.
In the summer of 1998, two groups of observers(I.D. Karachentsev and V.E. Karachentseva; T. Armandroff, J. Davies and G. Jacoby) at least 3 more dwarf spheroidal galaxies were discovered - possibly distant members of the subgroup M31(one of these galaxies was discovered independently by both groups): Pegasus DEG (And VI), Cassiopea Dw and And V. The third largest galaxy in the Local Group, M33 (Triangulum), which may or may not be a distant gravitationally bound companion to M31, itself has a dwarf companion LGS 3.

• Satellites of the galaxy Andromeda form a flat system with an axial ratio of 5:2:1. Its semimajor axis and the major (polar) axis of the Milky Way subgroup form an angle of about 57 o.
• Morphological segregation in the subgroup is clearly visible. All seven closest satellites M31 have types E and Sph, while only spiral and irregular galaxies are found on the periphery.
• As noted by Arp (1982), the radial velocity distribution of satellites M31 highly asymmetrical. Using our criterion for galaxy membership the difference in radial velocities decreases compared to Arp to +46±29 km/s. However, if we consider total weight M31 more; let's say To=3.0 instead of 2.5, then into the zone of influence M31 Other galaxies will also be included (WLM, Pegasus and NGC 404), which increase the asymmetry to +70 km/s.
• The asymmetry of radial velocities decreases significantly if we consider the system relative to the center of mass M31+M33. This may provide evidence that main mass of this subgroup is contained in its members, and is not distributed throughout the group.
• Number of satellites located in the North and South of M31 somewhat asymmetrical. If this is due to the absorption of radiation by our Galaxy, then we should expect the discovery of new members of the subgroup near the galaxy IC 10. The validity of this assumption has been shown quite recently.

Galaxies NGC3109, Antlia,Sextans A And Sextans B, apparently form a separate subgroup with V r=+114+-12 km/s, which is located outside the so-called “zero Local Group distance” of 1.7 Mpc from the Local Group centroid (van den Bergh, 1999).

Other members cannot be assigned to any main subgroup and move completely isolated in the gravitational field of the members of giant groups. The substructures in the group are probably not stable. Observations and calculations suggest that the groups are very dynamic and have changed significantly in the past: the galaxies around the large elliptical galaxy Maffei 1 were likely once members of the group of our galaxy.

All of the above shows that the MG is not isolated, but is in gravitational interaction and exchange of members with the nearest surrounding groups of galaxies. Particularly noticeable is the interaction with:

• group IC342/Maffei, which, in addition to the giant elliptical galaxy, also contains the smaller Maffei 2, and interacts with the complex around IC 342. It is strongly absorbed by dust, as it is located near the equatorial plane of the Milky Way.
• group Sculptor"a or South Pole group(with members located around the South Galactic Poles), dominated by galaxy NGC 253
• group M83

Local group of galaxies

The group of galaxies that includes our Milky Way is located on the periphery (at a distance of about 50 million light years from the center) of a giant cluster of galaxies visible in our sky in the constellation Virgo (Virgo Cluster) and consisting of more than 2000 star systems . It is formed at the intersection of two universal fibers dark matter. It should be noted that this cluster is one of the great many superclusters of star islands that make up the fibrous megastructure of the part of the Universe observed today.

Hypothetical inhabitants of a highly developed civilization located in the center of the Virgo cluster, using powerful telescopes could observe a close pair of spiral galaxies, indicated by faint foggy lines in the starry sky - this is how our Local Group is visible from there, the light from which would travel to these imaginary observers for 50 million years. About fifty smaller galaxies included in our group are difficult to register from such a huge distance, and conversely, the number of star systems included, according to modern calculations, in the Virgo Cluster does not include a huge number of dwarf galaxies. tick within this supercluster.

The concept of a Local Group used by astronomers can be interpreted as a small town on the outskirts of the country, on the streets of which its own laws apply. Its inhabitants actively interact, determining the present and future of each other, the stronger members of the community organize and subordinate to their will the movement of the weaker ones, and ultimately absorb them (scientists like to call these processes in the life of galaxies cannibalism), exciting in your expanding womb active processes the birth of new generations of stars, planetary systems and, perhaps, new organic life.

Similar scenarios describe the birth and development of our Galaxy and the Andromeda Galaxy (M31). The merger of this couple after several billion years is very likely from the point of view of modern science.

With a diameter of about 6 million light years, our Local Group represents the Universe in miniature. Its structure and composition allows us to study in detail the processes of birth, development and structure of all currently known types of galaxies. By studying the stars that form the galaxies in our immediate environment, using the most powerful ground-based and space telescopes, we obtain information about the age of the objects from which they consist. For the most ancient of them, it is 13 billion years old, which is almost equal to the age of the Universe. These are representatives dwarf stars, nuclear combustion in which occurs extremely slowly. Oxygen, nitrogen, carbon, as well as heavier chemical elements(astrophysicists generally call them “metals”) were formed only during nuclear reactions in the depths of the stars. By shedding their shells or flaring up as Supernovae, the stars enriched the surrounding space with the products of their vital activity. Representatives of luminaries of later generations are much richer in heavy elements, and the younger the star, the greater its metallicity, the more later generation she belongs. Thus, determining the composition of the stellar population of members of the Local Group of galaxies allows us to draw a conclusion about the age of its members.

Astronomers have received a huge amount of statistical and factual material as a result of the implementation of the GOODS program (Great Observatori-es Origins Deep Survey, which in one of the literary translations sounds like this: “Deep study of the origin of objects of the Universe at the largest observatories”). At present, the most substantiated theory is that the first stars formed from cold dark matter, which makes up 90% of the baryonic matter of the Universe, or more precisely, from giant hydrogen clouds. star clusters and dwarf galaxies, which themselves had a very stormy, bright and explosive youth. Subsequently, from these dwarf galaxies, through their merger and mutual absorption by larger smaller ones, the spiral, elliptical, irregular galaxies that we observe today were formed.

Astronomers believe that our Local Group formed from a cloud of dark matter when the Universe cooled to a temperature of 2000 K, about 13 billion years ago. If we extrapolate the linear dimensions into the past, taking into account changes in the scale of the expanding Universe, then at that time the diameter of the group was 600,000 light years (a quarter of the current distance between the Milky Way and the Andromeda Nebula). Moreover, the sizes of the two largest galaxies should have been smaller, and the members of the Local Group should have been more numerous.

Local scale

In order to understand the scale relationships in our Local Group, Ray Willard, an employee of the Space Telescope Science Institute in Baltimore, proposed the following comparison in his article in the journal Astronomy. Let's imagine our Galaxy as a compact disc (diameter 12 cm), in the center of which a tennis ball is placed. Now imagine the same design, but 1.5 times larger. This will be the Andro-meda Nebula. By placing these two disks at a distance of 3 m, we obtain a model of a galactic pair, and all dwarf galaxies - satellites of our galaxies and more distant members of the group - will fit into a sphere with a radius of 4.5 m.

The oldest globular star clusters and dwarf galaxies collided and merged, forming the core of our Galaxy. In the process of further evolution, a disk with spiral arms was formed. The turbulent past has left behind traces that appear in the form of huge arc-shaped gas and stellar flows that exist in the galactic halo - a very rarefied stellar environment. The size of the Milky Way halo in the scale model adopted above would occupy the volume of a volleyball (according to other estimates, the diameter of a spherical halo is approximately equal to the diameter of the galactic disk).

Only a few of the relict globular clusters have survived to today. Within the Milky Way, they resemble the ruins of ancient castles. The ability to survive depended on their masses and trajectories relative to the disk of the “host” galaxy. Modern observations allow us to conclude that our Galaxy has absorbed, is absorbing and will continue to absorb smaller stellar communities. We wrote about the M12 cluster, which is in the process of destruction due to interaction with the galactic disk as it passes through its plane. Like the face of a child engrossed in eating jam, the face of our Galaxy bears many traces of large-scale meals. The galactic halo contains the remains of swallowed star systems, the disk of the Milky Way is deformed by the passages of satellites - dwarf galaxies. Streams of stars located along the previous trajectories of dwarf satellites around the center of our Galaxy literally rain stars onto the galactic disk.

According to some assumptions, the huge star cloud in the Milky Way, which can be observed in the constellation Sagittarius, represents the “population” of a dwarf galaxy that merged with our stellar island in the distant past. According to Steve Majewski, an employee of the University of Virginia, this is the largest satellite of our Galaxy that ended up in its womb.

The most impressive trace of the Galaxy's turbulent past is the huge flows of cold hydrogen forming arcs spanning 100 arc degrees around the south galactic pole. At the head of these flows are the Large and Small Magellan clouds - largest satellites Milky Way.

Mysteries of the Magellanic Clouds

The most recent studies of the movement of Magellanic clouds, carried out by astronomers Nithya Kallivavalil, Charles Alcock from the Harvard-Smithsonian Center for Astrophysics ( Nitya Kallivayalil, Charles Alcock, Harvard-Smithsonian Center for Astrophysics ) and Roland Van der Marel from the Space Telescope Science Institute ( Roeland van der Marel, Space Telescope Science Institute ), made it possible to clarify the dynamics of the movement of these dwarf galaxies. This dynamics was revised on the basis of refined values ​​of the spatial velocity components of the Small and Large Magellanic clouds.

The greatest difficulty was calculating the velocity component perpendicular to the line of sight. This required several years of meticulous observations (using the Hubble Space Telescope) and calculations. As a result, the authors presented surprising findings at the 209th Conference of the American Astronomical Society. It turned out that the LMC, relative to our Galaxy, has a speed of 378 km/s, while the MMC has a speed of 302 km/s. In both cases, the speeds “turned out to be significantly greater than previously expected. There can be two explanations for this fact:

The mass of the Milky Way is greater than previously thought. Magellanic clouds are not in orbit around the Galaxy and will overcome its gravitational forces in the future.

The difference in cloud speeds (i.e., the speed of their relative movement) is also surprisingly high. This suggests that they are not gravitationally connected to each other. In addition, this explains the fact that they have not merged with each other in the more than ten billion history of the Local Group. Detailed studies of hydrogen flows trailing in trails behind the Magellanic clouds are planned for the future. This will make it possible to clarify the trajectories of their movements relative to each other and relative to our Galaxy.

Laboratory in the backyard

The theory of the development and formation of galaxy clusters unsatisfactorily explains the possibility of the formation of an isolated pair of large galaxies on the periphery of a giant cluster in the constellation Virgo. Scientists consider it a gift from Fate to have such a wonderful representative of spiral galaxies in our immediate surroundings, which is M31, or the Andromeda Nebula. Moreover, nature has decreed that the plane of its disk is at an optimal angle to the direction towards the observer located on Earth (and on any planet located in our Galaxy). It is this angle of view that allows us to study with maximum care all the components - the core, spiral arms and halo of a huge stellar island.

Like our Galaxy, M31 contains many globular clusters. Some of them are located outside the spiral arms, but move around galactic centers without leaving the halo. Space telescope Hubble received an image of the globular star cluster G1 orbiting the center of M31 in an orbit with a radius of 130 thousand light years (the radius of the disk of the Andromeda Nebula is 70 thousand light years). G1, also designated Mayall II, is the brightest globular cluster in the Local Group: it consists of at least 300 thousand old stars. Analysis of this detailed image, obtained in the near infrared in July 1994, allows us to conclude that the cluster contains stars in which helium nuclear burning processes occur, and the temperature and brightness of these stars suggests that it is the same age as our Milky Way and the Local Group as a whole. G1 is unique in that it contains a 10,000 solar mass black hole at its center.

A real miracle is the MZZ, a spiral galaxy in the Triangulum (NGC 598, or Trian-gulum Pinwheel Galaxy). It is half the diameter of the Milky Way and three times the size of the Andromeda Nebula. According to astronomers, over billions of years of close coexistence with M31, it should have collided with it long ago. But for some still unclear reasons this did not happen.

The study of the Local Group - the Universe in miniature - allows scientists to penetrate into many of the secrets of the Universe.

There are black holes of various masses in our environment: in the center of our own Galaxy, in the center of the Andromeda Nebula and the globular clusters M15 and G1. The assumption that the mass of the central black hole should be one ten-thousandth of the mass of the entire galaxy is confirmed by the examples of the mentioned clusters. This makes it possible to identify some fundamental patterns connecting the parameters of black holes and their “mother” galaxies.

Of particular interest is the discovery of hypothetical compact massive non-luminous (invisible) baryonic halo objects that concentrate the light of more distant stars due to the effect of gravitational lensing.

Modern cosmological models, based on long-term observations of the starry sky and on the huge amount of factual material obtained, admit that planets similar to our Earth began to form more than ten billion years ago. Thus the Universe evolved sufficient quantity time for the emergence of conditions that ensure the formation of high-molecular organic compounds and life, and also, given the colossal number of galaxies and stars, for the emergence of intelligence. No matter how improbable it may be, let us still assume that in our local group there is, besides us, only one highly developed civilization. It is natural to assume that its representatives are interested in the world around them. We can hope that their scientists, having more than long history, observed the evolution of our group of galaxies, and terrestrial science will eventually be able to obtain this knowledge. Our civilization happened to exist in a relatively calm period of galactic history, which will end in about 2-3 billion years with a grandiose cataclysm - the collision of the Milky Way and the Andromeda Nebula.

True, one important circumstance should be taken into account here. Our Galaxy and M31 are approaching at a speed of 120 km/s, or 3.8 billion km per year, or 400 light years in one billion years (as the distances between their centers decrease, this speed will increase). The radial velocity can be determined quite accurately from the shift of the spectral lines. However, does the velocity vector have relative motion tangential component? If it does, and it is large enough, then the collision will not occur at all, at least within the next tens of billions of years. Galaxies will pass each other at enormous speeds, stir up their “hairs” by mutual gravitational influences and continue traveling along elliptical trajectories, closing the colossal arcs of their orbits around general center wt.

It is still possible that the Milky Way and the Andromeda Nebula are on collision courses. It was this assumption that Thomas Cox and Avi Loeb from the Harvard-Smithsonian Center for Astrophysics (TJ. Cox, Avi Loeb, Harvard Smithsonian Center for Astrophysics) based their model on. Having performed scrupulous calculations, entering into the equations all currently known parameters and initial conditions, scientists have concluded that our star will live until the time when galaxies begin to merge. According to researchers, the first "contact"will take place in 2 billion years. Terrestrial astronomers will observe increasing deformations of the spiral structures of our Galaxy under the influence of gravity of the approaching “stellar monster”. As a result of several oscillatory movements, indicated by the nuclei of galaxies, the population of their stellar disks will increasingly mix, gradually forming a relatively homogeneous body of a giant elliptical galaxy. According to the assumptions of Cox and Loeb, our star, in its extreme old age, will still reach the period of formation of the “final” structure and, if this can console anyone living today, will end up on the periphery of the newly formed stellar island at a distance of 100 thousand light years from its center. Whether this area will be a “life zone” of a new galaxy, in which dynamic and energy parameters will provide conditions favorable for the existence of life on the planets around the stars inhabiting it, is, of course, impossible to say today. Let's hope for the best, for the benefit of our descendants.

As Avi Loeb joked, observing all these enchanting and grandiose changes in the starry sky, future scientists may refer to the lines of his report: “This is my first publication that will be quoted 5 billion years later.”

Computer simulation of the merger of galaxies allows us to trace the development of events: at the first stage of the collision, processes similar to those observed today in the “Mouse” galaxy (NGC 4676) will occur. First, the Milky Way and M31 will come into contact with their peripheral regions. In the process of further, deeper mutual absorption, the pattern will resemble the Antennae galaxies (NGC 4038-4039). Then the nuclei will merge, then perhaps the black holes that exist at the center of each will collide. star system. Then jets will appear - ejections of matter into intergalactic space, similar to those observed near the galaxy NGC 5128. The universal catastrophe will most likely end with the formation of one giant elliptical galaxy - an analogue of NGC 1316." Our local group will submit to the gravitational influence of this galaxy, and the appetites of the newly baked monster will be so great that the remaining members of the group will be absorbed by it in a relatively short time (by galactic standards).

Let's not forget that the Local Group, among other things, is moving towards the center of the Virgo cluster at a speed of 3 million light years for every billion years. How would we avoid colliding with something larger (as they say, “don’t hit a pine tree”)... After all, there are clearly more invisible objects hidden from us in the Universe than directly observed! How many years has earthly science been collecting photographic data about the world of galaxies around us? About a hundred? In any case, this is not even a moment, it is just a frozen photograph of the Cosmos. The development of processes within such short periods of time is noticeable only within very small volumes of space. Besides evolution solar system, we can observe the expansion of the shells of novae, supernovae, changes in the interiors of gas and dust clouds under the influence of “hurricane winds” generated by the young stellar inhabitants of these areas of space. To understand the dynamics of such formations as a cluster of galaxies (even “local” and on the “outskirts” of the solid Virgo cluster) requires at least millennia. Of course, over these millennia we plan to inform our readers about current changes in the surrounding Universe. There must be at least something stable in this world!