Once everyone thought that the center of the World was the Earth. Over time, this opinion was recognized as erroneous and began to be considered the center of the entire Sun. But then it turned out that the luminary, which gives life to all life on the blue planet, is by no means the center of outer space, but only a tiny grain of sand in the endless ocean of stars. The ocean itself is not as huge as it seems from the Earth, but represents only a small part of the Universe, which is infinite. But she, apparently, is a small fraction of some even more huge and greatest formation, which is beyond reason and imagination.
The Cosmos visible to the human eye includes myriads of stars. All of them are combined into a huge star system, which is called very beautifully and intriguingly - the Milky Way. From Earth, this heavenly splendor is observed in the form of a wide whitish strip, dimly glowing on the celestial sphere.
It stretches across the entire northern hemisphere and crosses the constellations Gemini, Charioteer, Cassiopeia, Chanterelle, Cygnus, Taurus, Eagle, Arrow, Cepheus. It encircles the southern hemisphere and passes through the constellations of the Unicorn, Southern Cross, Southern Triangle, Scorpio, Sagittarius, Sails, Compass.
If you arm yourself with a telescope and look through it at the night sky, the picture will be different. The wide whitish stripe will turn into countless glowing stars. Their weak, distant, alluring light will tell without words about the greatness and endless expanses of the Cosmos, make you hold your breath and realize all the insignificance and worthlessness of momentary human problems.
The Milky Way is called the Galaxy or giant star system. According to the most conservative estimates, there are at least 200 billion stars in it. Currently, more and more leaning towards the figure of 400 billion stars. All these stars move in closed orbits. They are bound to each other by gravity, and most of them have planets. The stars together with the planets form star systems. Such systems are with one star (solar system), double (Sirius - two stars), triple (alpha Centauri). There are four, five stars, or even seven.
The Milky Way is disk-shaped.
All this countless variety of star systems that make up the Milky Way are not scattered throughout space at random, but combined into a colossal formation in the form of a disk with a thickening in the middle. The diameter of the disk is 100,000 light years (one light year corresponds to the distance that light travels in a year, which is approximately 10¹³ km) or 30,659 parsecs (one parsec is 3.2616 light years). The disk is several thousand light-years thick, and its mass is 3 × 10¹² times the mass of the Sun.
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The mass of the Milky Way is made up of the mass of stars, interstellar gas, dust clouds, and a halo shaped like a huge sphere of rarefied hot gas, stars and dark matter. Dark matter is represented by a set of hypothetical space objects, of which 95% of the entire Universe consists of masses. These mysterious objects are invisible and do not react in any way to modern technical means of detection.
The presence of dark matter can be guessed only by its gravitational effect on visible clusters of suns. There are not so many of those available for observation. The human eye, even amplified by the most powerful telescope, can only behold two billion stars. The rest of space is hidden by huge impenetrable clouds of interstellar dust and gas.
The thickening (bulge) in the central part of the Milky Way disk is called the Galactic Center or core. In it, billions of old stars move in very elongated orbits. Their mass is very large and is estimated at 10 billion solar masses. The dimensions of the core are not that impressive. It is 8,000 parsecs across.
The Galactic Core is a brightly shining ball. If earthlings could observe it in the sky, then their eyes would see a gigantic luminous ellipsoid, which in its size would be a hundred times larger than the Moon. Unfortunately, this beautiful and magnificent sight is inaccessible to people because of the powerful gas and dust clouds that block the galactic center from planet Earth.
At a distance of 3000 parsecs from the center of the Galaxy, there is a gas ring, which has a width of 1500 parsecs and has a mass of 100 million solar masses. This is where the central region of new star formation is supposed to be. Gas arms about 4 thousand parsecs long run away from it. At the very center of the nucleus there is a black hole with a mass of more than three million suns.
Arms of the Milky Way.
The galactic disk is heterogeneous in structure. It has separate high-density zones, which are spiral arms. The continuous process of the formation of new stars continues in them, and the arms themselves stretch along the core and, as it were, bend around it in a semicircle. Currently, there are five of them. These are the Swan Sleeve, the Perseus Sleeve, the Centaurus Sleeve and the Sagittarius Sleeve. The fifth arm - the Orion arm - is the solar system.
It is 28,000 light years distant from the galactic core. Around the center of the Galaxy, the Sun with its planets rushes at a speed of 220 km / s, and makes a full revolution in 220 million years. True, there is another figure - 250 million years.
The solar system is located just below the galactic equator, and in its orbit moves not evenly and calmly, but as if bouncing. Once every 33 million years, it crosses the galactic equator and rises above it at a distance of 230 light years. Then it descends back to repeat its takeoff after another interval of 33 million years.
The galactic disk rotates, but it does not rotate as a single body. The core rotates faster, the spiral arms in the plane of the disk are slower. Naturally, a natural question arises: why the spiral arms do not twist around the center of the Galaxy, but always remain the same shape and configuration for 12 billion years (this figure is the age of the Milky Way).
There is a theory that explains this phenomenon quite plausibly. She considers the spiral arms not as material objects, but as waves of density of matter arising against the galactic background. This is caused by star formation and the birth of high luminosity stars. In other words, the rotation of the spiral arms has nothing to do with the movement of stars in their galactic orbits.
The latter, only, pass through the arms either ahead of them in speed, if they are closer to the Galactic center, or lagging behind, if they are located in the peripheral regions of the Milky Way. The outlines of these spiral waves are given by the brightest stars, which have a very short life and manage to live it without leaving the sleeve.
As can be seen from all of the above, the Milky Way is a complex space formation, but it is not limited by the surface of the disk. There is a huge spherical cloud (halo) around. It includes: rarefied hot gases, individual stars, globular star clusters, dwarf galaxies and dark matter. Dense clouds of gas are present on the outskirts of the Milky Way. Their length is several thousand light years, the temperature reaches 10,000 degrees, and the mass is equal to at least ten million suns.
Andromeda's nebula.
In the vast space, the Milky Way is far from alone. At a distance of 772 thousand parsecs from it there is an even more huge star system. It is called the Andromeda Galaxy (it can be more romantic - the Andromeda Nebula). It has been known since ancient times as "a small heavenly cloud, easily distinguishable in a dark night." Even at the beginning of the 17th century, religiously minded astronomers believed that "in this place the crystal firmament is thinner than usual, and through it the light of the kingdom of heaven is poured out."
The Andromeda Nebula is the only galaxy that can be seen in the sky with the naked eye. It is seen as a small oval glowing spot. The light is unevenly distributed in it: the central part is brighter. If you strengthen the eye with a telescope, then the speck will turn into a giant star system, the diameter of which is 150 thousand light years. This is 1.5 times the diameter of the Milky Way.
But Andromeda differs from the galaxy in which the solar system exists not in size. Back in 1991, the planetary camera of the space telescope. Hubble recorded two cores in it. Moreover, one of them is smaller in size and revolves around the other, larger and brighter, gradually collapsing under the influence of the tidal forces of the latter. This slow agony of one of the nuclei suggests that it is the remnant of some other galaxy swallowed by Andromeda.
For many, it will be an unpleasant surprise to learn that the Andromeda Nebula is moving towards the Milky Way, and, therefore, towards the solar system. The approach speed is about 140 km / s. Accordingly, the meeting of the two stellar giants will take place somewhere in 2.5-3 billion years. It will not be a meeting on the Elbe, but it will not be a global catastrophe of cosmic proportions. Two Galaxies will simply merge into one. But which one will dominate - here the scales are tilted in favor of Andromeda. It has a greater mass, moreover, it already has experience in absorbing other galactic systems.
As for the solar system, then the forecasts are different. The most pessimistic one indicates that the Sun with all the planets will simply be thrown into intergalactic space, that is, there will be no place for it in the new formation.
But maybe it's for the best. After all, it is clear that the Andromeda Galaxy is a kind of bloodthirsty monster that devours its own kind. Having absorbed the Milky Way and destroying its core, the Nebula will turn into a huge Nebula and continue its way through the vastness of the Universe, eating more and more galaxies. The end result of this journey will be the collapse, incredibly swollen, above the giant star system.
The Andromeda nebula will disintegrate into countless small stellar formations, exactly repeating the fate of the huge empires of human civilization, which at first grew to unprecedented sizes, and then collapsed with a roar, unable to withstand the burden of their own greed, self-interest and lust for power.
But do not bother with the events of the coming tragedies. It is better to consider another galaxy, which is called the Triangle Galaxy. It spreads in the vastness of the Universe at a distance of 730 thousand parsecs from the Milky Way and is two times smaller in size than the latter, and at least seven times smaller in mass. That is, this is an ordinary mediocre galaxy, of which there are a great many in Space.
All these three star systems, coupled with several dozen more dwarf galaxies, are part of the so-called Local Group, which is part of the Virgo Supercluster - a huge star formation, which is 200 million light years across.
The Milky Way, the Andromeda Nebula, and the Triangulum Galaxy share many similarities. All of them belong to the so-called spiral galaxies. Their disks are flat and consist of young stars, open star clusters and interstellar matter. There is a bulge in the center of each disc. The main feature, of course, is the presence of bright spiral arms containing many young and hot stars.
The nuclei of these galaxies also resemble the clusters of old stars and gas rings in which new stars are being born. An invariable attribute of the central part of each nucleus is the presence of a black hole with a very large mass. It has already been mentioned that the mass of a black hole in the Milky Way corresponds to more than three million solar masses.
Black holes are one of the most impenetrable mysteries of the universe. Of course they are being watched and studied, but these mysterious formations are in no hurry to reveal their secrets. It is known that black holes have a very high density, and their gravitational field is so powerful that even light cannot escape from them. But any cosmic body that finds itself in the zone of influence of one of them (the threshold of events) will be immediately "swallowed" by this terrible universal monster. What will be the further fate of the "unfortunate" - is unknown. In short, it is easy to get into a black hole, but it is impossible to get out of there.
Black hole.
Many black holes are scattered across the vastness of the Cosmos, some of them have a mass many times greater than the mass of a black hole in the center of the Milky Way. But this does not mean that the monster "native" to the solar system is more harmless than its larger colleagues. It is also insatiable and bloodthirsty and is a compact (12.5 light-hours in diameter) and powerful X-ray source.
The name of this mysterious object Sagittarius A. Its mass has already been called - more than 3 million masses of the Suns, and the gravitational trap (threshold of events) of the baby is measured in 68 astronomical units (1 AU equals the average distance of the Earth from the Sun). It is within these limits that the border of his bloodlust and deceit in relation to various cosmic bodies lies, which, for a number of reasons, lightly cross it.
Someone probably naively thinks that the baby is content with random victims - nothing like that: he has a constant source of food. This is the S2 star. It revolves around the black hole in a very compact orbit - a full revolution is only 15.6 years. The maximum distance of S2 from the scary monster is within 5 light days, and the minimum is only 17 light hours.
Under the influence of the tidal forces of the black hole, a part of its substance is torn off from the star doomed to slaughter and with great speed flies towards this terrible cosmic monster. As it approaches, the substance passes into a state of incandescent plasma and, emitting a farewell bright glow, disappears forever in an insatiable invisible abyss.
But that's not all: the deviousness of a black hole has no boundaries. There is another, less massive and dense black hole next to it. Its task is to adjust the stars, planets, interstellar dust and gas clouds to its more powerful counterpart. All of this also turns into plasma, emits bright light and disappears into nowhere.
However, not all scientists, despite such an evidential bloody interpretation of events, are of the opinion that black holes exist. Some argue that this is an unknown mass, driven under a cold dense shell. It has a tremendous density and expands from the inside the surface compressing it with incredible strength. This formation is called gravastar - a gravitational star.
They are trying to fit the entire Universe under this model, thus explaining its expansion. Supporters of this concept argue that outer space is a giant bubble inflated by an unknown force. That is, the entire Cosmos is a huge gravastor, in which smaller models of gravastors coexist, periodically absorbing individual stars and other formations.
The absorbed bodies seem to be thrown into other cosmic spaces, which are essentially invisible, since they do not release light from under an absolutely black shell. Maybe gravastors, these are other dimensions or parallel worlds? A concrete answer to this question will not be found for a very, very long time.
But not only the presence or absence of black holes occupies the minds of space explorers. Much more interesting and exciting are reflections on the existence of intelligent life in other star systems of the Universe.
The Sun that gives life to earthlings revolves among many other suns of the Milky Way. Its disk is visible from Earth in the form of a pale shining strip encircling the celestial sphere. These are distant billions and billions of stars, many of which have their own planetary systems. Is there really not at least one among the innumerable number of these planets, on which intelligent beings live - brothers in reason?
The most reasonable assumption is that life-like life on Earth could arise on a planet orbiting a star of the same class as the Sun. There is such a star in the sky, moreover, it is located in the star system closest to the Earth's luminary. This is Alpha Centauri A, located in the constellation Centaurus. From the ground, it is visible to the naked eye, and its distance to the Sun is 4.36 light years.
It would certainly be nice to have reasonable neighbors right next door. But the desired does not always coincide with the reality. Finding signs of an extraterrestrial civilization, even at a distance of some 4-6 light years, is a rather difficult task with the current advances in technology. Therefore, it is premature to talk about the existence of any intelligence in the constellation Centaurus.
These days, it is only possible to send radio signals into space, hoping that someone unknown will respond to the call of the human intellect. Since the first half of the 20th century, the most powerful radio stations in the world have been persistently and non-stop in this activity. As a result, the level of radio emission from the Earth has increased significantly. The blue planet began to dramatically differ in its radiation background from all other planets of the solar system.
Signals from Earth cover outer space with a radius of at least 90 light years. On the scale of the Universe, this is a drop in the ocean, but as you know, this little wears away the stone. If somewhere far, far away in the Cosmos there is a highly developed intelligent life, then, in any case, it should someday turn its attention to the increased background radiation in the depths of the Milky Way, and to the radio signals coming from there. Such an interesting phenomenon cannot leave indifferent the inquisitive minds of aliens.
Accordingly, an active search for signals from Space has been established. But the dark abyss is silent, which indicates that within the Milky Way there are most likely no intelligent creatures ready to come into contact with the inhabitants of the planet Earth, or else their technical development is at a very primitive level. True, another thought suggests itself, which says that a highly developed civilization, or civilization, exists, but sends some other signals into the vastness of the Galaxy that cannot be captured by terrestrial technical means.
Progress on the blue planet is steadily evolving and improving. Scientists are developing new, completely different, methods of transmitting information over long distances. All this can have a positive effect. But we must not forget that the vastness of the Universe is limitless. There are stars, the light from which reaches the Earth in billions of years. In fact, a person sees a picture of the distant past when he observes such a space object through a telescope.
It may happen that the signal from Space, received by earthlings, will be the voice of a long-vanished extraterrestrial civilization that lived in a time when neither the Solar System nor the Milky Way existed yet. The response message from the Earth will go to the aliens, which were not even in the project at the time when it was sent.
Well, we must take into account the laws of harsh reality. In any case, the search for intelligence in distant galactic worlds cannot be stopped. The present generations will be unlucky, the future generations will be lucky. Hope in this case will never die, and persistence and persistence will undoubtedly pay off handsomely.
But the exploration of galactic space is seen as quite real and close. Already in the next century, fast and graceful spaceships will fly to the nearest constellations. Astronauts on board will observe through the windows not the planet Earth, but the entire solar system. They will see it as a distant, bright star. But it will not be the cold soulless shine of one of the countless suns of the Galaxy, but the native radiance of the Sun, near which Mother Earth will revolve as an invisible, soul-warming dust particle.
Very soon, the dreams of science fiction writers, reflected in their works, will become a common everyday reality, and a walk along the Milky Way will be a rather boring and tedious activity, like, for example, a trip in a subway car from one end of Moscow to another.
Sources: "Astrophysical Journal"