The mystery of the Milky Way haunted people for many centuries. In the myths and legends of many peoples of the world, it was called the Road of the Gods, the mysterious Star Bridge leading to the heavenly groves, the magical Heavenly River filled with divine milk. It is believed that it was he who meant when old Russian fairy tales spoke of a milk river with jelly banks. And the inhabitants of ancient Hellas called him Galaxias kuklos, which means "milk circle". This is where the word Galaxy, familiar today, comes from.
But in any case, the Milky Way, like everything that can be seen in the sky, was considered sacred. He was worshiped, temples were built in his honor. By the way, few people know that the tree that we decorate for the New Year is nothing but an echo of those ancient cults when the Milky Way seemed to our ancestors the axis of the Universe, the World Tree, on the invisible branches of which the fruits of the stars ripen. It is on New Year's Eve that the Milky Way "stands" vertically, like a trunk rising from the horizon. That is why, in imitation of the heavenly tree, eternally bearing fruit, the earthly tree was dressed up at the beginning of the new annual cycle. They believed that this gave hope for a future harvest and the favor of the gods.
What is the Milky Way, why does it glow, and it glows non-uniformly, then it flows along a wide channel, then suddenly it splits into two arms?
The scientific history of this issue can be counted at least 2,000 years. So, Plato called the Milky Way a seam connecting the celestial hemispheres, Democritus and Anaxagoras said that it was illuminated by the stars, and Aristotle explained it by luminous pairs located under the Moon. There was another suggestion, made by the Roman poet Marcus Manilius: perhaps the Milky Way is the merging glow of small stars. How close he was from the truth. But it was impossible to confirm it by observing the stars with the naked eye.
The mystery of the Milky Way was revealed only in 1610, when the famous Galileo Galilei pointed his first telescope at it, through which he saw "an immense cluster of stars" merging into a solid white stripe for the naked eye. Galileo was amazed, he realized that the heterogeneity, even the tattered structure of the white stripe is explained by the fact that it consists of many star clusters and dark clouds. Their combination creates a unique image of the Milky Way. However, why dim stars are concentrated in a narrow band, it was impossible to understand at that time.
In the motion of stars in the Galaxy, scientists distinguish whole stellar streams. The stars in them are connected to each other. Do not confuse stellar streams with constellations, the outlines of which can often be a simple game of nature and represent a connected group only when observed from the solar system. In fact, it happens that in the same constellation there are stars belonging to different streams. For example, in the well-known Ursa Major bucket (the most noticeable figure of this constellation), only five stars from the middle of the bucket belong to one stream, the first and last in a characteristic figure from another stream. And at the same time, in the same stream with the five middle stars, there is the famous Sirius - the brightest star in our sky, belonging to a completely different constellation.
Another explorer of the Milky Way was William Herschel in the 18th century. As a musician and composer, he was involved in the science of stars and telescope making. The last of them weighed a ton, had a mirror diameter of 147 centimeters and a pipe length of 12 meters. However, most of his discoveries, which became a natural reward for diligence, Herschel made with a telescope half the size of this giant.
One of the most important discoveries, as Herschel himself called it, was the Great Plan of the Universe. The method he applied turned out to be a simple count of the stars in the telescope's field of view. And naturally, different numbers of stars were found in different parts of the sky. (There were more than a thousand parts of the sky where the stars were counted.) Based on these observations, Herschel concluded that the shape of the Milky Way was already a stellar island in the Universe, to which the Sun also belongs. He even drew a schematic drawing, which shows that our star system has an irregular elongated shape and resembles a giant millstone. Well, since this millstone surrounds our world with a ring, then, consequently, the Sun is inside it and is located somewhere near the central part. This is how Herschel painted,and this idea survived in the minds of scientists almost until the middle of the last century.
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Based on the conclusions of Herschel and his followers, it turned out that the Sun has a special central position in the Galaxy called the Milky Way. This structure was somewhat similar to the geocentric system of the world, adopted before the Copernican era, with the only difference that earlier the Earth was considered the center of the Universe, and now the Sun is.
And yet, it remained unclear whether there are other stars outside the star island, otherwise our Galaxy? Herschel's telescopes made it possible to get closer to solving this mystery. The scientist discovered many faint foggy spots in the sky and investigated the brightest of them. Seeing that some of the sunspots disintegrate into stars, Herschel made the bold conclusion that these are nothing more than other stellar islands, like our Milky Way, only very distant. It was then that he suggested, in order to avoid confusion, to write the name of our World with a capital letter, and the rest - with a lowercase letter. The same thing happened with the word Galaxy. When we write it with a capital letter, we mean our Milky Way, when with a lowercase - all other galaxies. Today, astronomers call the Milky Way the "milk river" visible in the night sky, and our entire Galaxy,consisting of hundreds of billions of stars. Thus, this term is used in two senses: in one - when talking about the stars in the Earth's sky, in the other - when discussing the structure of the Universe.
Scientists explain the presence of spiral branches in the Galaxy by giant waves of compression and rarefaction of interstellar gas moving along the galactic disk. Due to the fact that the orbital speed of the Sun almost coincided with the speed of the compression waves, it has remained ahead of the wave front for several billion years. This circumstance was of great importance for the emergence of life on Earth.
The spiral arms contain many stars of high luminosity and mass. And if the mass of a star is large, about ten times the mass of the Sun, an unenviable fate awaits it, ending in a grandiose cosmic catastrophe - an explosion called a supernova explosion. In this case, the flare is so strong that this star shines like all the stars of the Galaxy combined. Astronomers often record such catastrophes in other galaxies, but this has not happened in ours for the past several hundred years. When a supernova explodes, a powerful wave of hard radiation is generated that can destroy all life on the way. Perhaps it is precisely because of the unique position in the Galaxy that our civilization managed to develop to such an extent that its representatives are trying to learn about their star island. It turns outthat possible brothers in mind can be sought only in quiet galactic “nooks” like ours.
Studies of the Andromeda nebula played an important role in understanding the structure of the "own" Galaxy. Fog spots in the sky have been known for a long time, but they were considered either patches that broke away from the Milky Way, or merging into a solid mass by distant stars. But one of these spots, known as the Andromeda nebula, was the brightest and most attention-grabbing. It was compared to both a luminous cloud and a candle flame, and one astronomer even believed that in this place the crystal dome of the heavens is thinner than in others, and the light of the Kingdom of God pours through it to Earth.
The Andromeda Nebula is truly a spectacular sight. If our eyes were more sensitive to light, it would appear to us not as a small elongated foggy speck, somewhere in the quarter of the lunar disk (this is its central part), but as a formation seven times larger than the full moon. But that's not all. Modern telescopes see the Andromeda nebula in such a way that up to 70 full moons fit in its area. It was possible to understand the structure of the Andromeda nebula only in the 20s of the last century. This was done using a telescope with a mirror diameter of 2.5 m by the American astrophysicist Edwin Hubble. He received pictures in which he flaunted, now there was no doubt, a giant star island, consisting of billions of stars - another galaxy. And the observation of individual stars in the Andromeda nebula allowed us to solve another problem - to calculate the distance to it. The fact is that in the Universe there are the so-called Cepheids - variable stars, pulsating due to internal physical processes that change their brightness. These changes occur with a certain period: the longer the period, the higher the luminosity of the Cepheid - the energy released by the star per unit of time. And from it you can determine the distance to the star. For example, the Cepheids found in the Andromeda nebula made it possible to determine the distance to it. It turned out to be huge - 2 million light years. However, this is only one of the galaxies closest to us, of which, as it turned out, there are a great many in the Universe.the higher the luminosity of the Cepheid - the energy released by the star per unit time. And from it you can determine the distance to the star. For example, the Cepheids found in the Andromeda nebula made it possible to determine the distance to it. It turned out to be huge - 2 million light years. However, this is only one of the galaxies closest to us, of which, as it turned out, there are a great many in the Universe.the higher the luminosity of the Cepheid - the energy released by the star per unit time. And from it you can determine the distance to the star. For example, the Cepheids found in the Andromeda nebula made it possible to determine the distance to it. It turned out to be huge - 2 million light years. However, this is only one of the galaxies closest to us, of which, as it turned out, there are a great many in the Universe.
The more powerful the telescopes became, the clearer the options for the structure of the galaxies observed by astronomers, which turned out to be very unusual, were outlined. Among them there are the so-called irregular ones, which do not have a symmetrical structure, there are elliptical, and there are spiral ones. Here they seem to be the most interesting and mysterious. Imagine a brightly shining core from which gigantic glowing spiral branches emerge. There are galaxies in which the core is more pronounced, while the branches dominate in others. There are also galaxies where branches do not come out of the core, but from a special bridge - the bar.
So what type of our Milky Way belongs to? After all, being inside the Galaxy, it is much more difficult to understand its structure than observing from the side. Nature itself helped to answer this question: galaxies in relation to us are "scattered" in various positions. Some we can see from the edge, others “flat”, and still others from different angles.
For a long time, it was believed that the nearest galaxy to us is the Large Magellanic Cloud. Today it is known that this is not so. In 1994, cosmic distances were measured more accurately, and a dwarf galaxy in the constellation Sagittarius took the lead. However, quite recently this statement also had to be revised. An even closer neighbor of our Galaxy was discovered in the constellation Canis Major. It is only 42 thousand light years from the center of the Milky Way.
In total, 25 galaxies are known that make up the so-called Local System, that is, a community of galaxies that are directly connected to each other by gravitational forces. The Local System of Galaxies is about three million light years across. In addition to our Milky Way and its satellites, the Local System also includes the Andromeda Nebula, the nearest giant galaxy with its satellites, and another spiral galaxy in the constellation Triangulum. She is turned to us "flat". Dominates the Local System, of course, the Andromeda Nebula. It is one and a half times more massive than the Milky Way.
If the Cepheids of the Andromeda nebula made it possible to understand that it is far beyond our Galaxy, then the study of closer Cepheids made it possible to determine the position of the Sun inside the Galaxy. The pioneer here was the American astrophysicist Harlow Shapley. One of the objects of his interest were globular star clusters, so dense that their core merges into a solid glow. The region richest in globular clusters is located in the direction of the zodiacal constellation Sagittarius. They are also known in other galaxies, and these clusters are always concentrated near galactic nuclei. If we assume that the laws for the Universe are the same, we can conclude that our Galaxy should be arranged in a similar way. Shapley found Cepheids in its globular clusters and measured the distance to them. It turned outthat the Sun is not located at all in the center of the Milky Way, but on its outskirts, one might say, in a stellar province, at a distance of 25 thousand light years from the center. So, for the second time after Copernicus, the idea of our special privileged position in the Universe was debunked.
Realizing that we are on the periphery of the Galaxy, scientists became interested in its center. Like other stellar islands, it was expected to have a core from which spiral branches emerge. We see them as the bright strip of the Milky Way, but - we see from the inside, from the edge. These spiral branches, projecting onto each other, do not allow us to understand how many there are and how they are arranged. Moreover, the nuclei of other galaxies shine brightly. But why is this radiance not visible in our Galaxy, is it possible that it does not have a core? The solution came again thanks to observations of others. Scientists have noticed that in spiral nebulae, to the type of which our Galaxy was also attributed, a dark layer is clearly visible. This is nothing more than an accumulation of interstellar gas and dust. It was they who allowed to answer the question - why do not we see our own kernel:our solar system is located exactly at such a point in the galaxy that giant dark clouds block the core for an observer on Earth. Now we can answer the question: why does the Milky Way bifurcate into two arms? As it turned out, its central part is obscured by powerful dust clouds. In fact, there are billions of stars behind the dust, including the center of our galaxy.
Studies have also shown that if the dust cloud did not bother us, earthlings would observe a grand spectacle: a giant shining ellipsoid of the core with countless stars would occupy an area of more than a hundred moons in the sky.
Telescopes operating in such ranges of the spectrum of electromagnetic radiation that the dust shield does not interfere with helped to see the galactic core behind this dust cloud. But most of these emissions are trapped by the Earth's atmosphere, therefore, at the present stage, astronautics and radio astronomy play an essential role in the knowledge of the Galaxy. It turned out that the center of the Milky Way glows well in the radio range. Scientists were especially interested in the so-called radio source Sagittarius A * - an object in the Galaxy that actively emits radio waves and X-rays. Today it can be considered actually proven that in the constellation Sagittarius there is a mysterious space object - a supermassive black hole. It is estimated that its mass may be equal to the mass of 3 million suns. This object of monstrous density has such a powerful gravitational field,that even light cannot escape from it.
Naturally, the black hole itself does not glow in any range, but the matter falling on it emits X-rays and allows you to locate the space "monster". True, the radiation of Sagittarius A * is weaker than that found in the nuclei of other galaxies. Perhaps this is due to the fact that the fall of matter is carried out not intensively, but when it occurs, a flash of X-ray radiation is recorded. Once the brightness of the object Sagittarius A * increased literally in minutes - this is impossible for a large formation. Hence, this object is compact and it can only be a black hole. By the way, to turn the Earth into a black hole, it needs to be compressed to the size of a matchbox.
In general, many variable X-ray sources have been discovered in the center of our Galaxy, which are possibly smaller black holes grouping around the central supermassive one. They are being watched by the American space X-ray observatory "Chandra".
Another confirmation of the presence of a supermassive black hole in the center of the core of our Galaxy was provided by the study of the motion of stars located in the immediate vicinity of the core. So, in the infrared range, astronomers managed to observe the motion of a star that slipped from the center of the nucleus at a negligible distance on a galactic scale: only three times the radius of Pluto's orbit. The parameters of the orbit of the motion of this star indicate that it is located near a compact invisible object with a monstrous gravitational field. This can only be a black hole, and a supermassive one. Her research is ongoing.
There is surprisingly little information about the structure of the spiral arms of our Galaxy. By the appearance of the Milky Way, one can only judge that the Galaxy has the shape of a disk. And only with the help of observations of the radiation of interstellar hydrogen - the most abundant element in the Universe - was it possible to reconstruct to some extent the picture of the arms of the Milky Way. This became possible again thanks to an analogy: in other galaxies, hydrogen is concentrated just along the spiral arms. There are also regions of star formation - many young stars, clusters of dust and gas - gas and dust nebulae.
In the 50s of the last century, scientists managed to draw up a picture of the distribution of clouds of ionized hydrogen in the galactic vicinity of the Sun. It turned out that there are at least three areas that could be identified with the spiral arms of the Milky Way. One of them, the closest to us, scientists called the Orion-Cygnus arm. The one farther from us and, accordingly, close to the center of the Galaxy is called the Sagittarius-Carina arm, and the peripheral one, the Perseus arm. But the explored galactic neighborhood is limited: interstellar dust absorbs the light of distant stars and hydrogen, so that it becomes impossible to understand the further drawing of the spiral branches.
However, where optical astronomy cannot help, radio telescopes come to the rescue. It is known that hydrogen atoms emit at a wavelength of 21 cm. It was this radiation that the Dutch astrophysicist Jan Oort began to catch. The picture he received in 1954 was impressive. The spiral arms of the Milky Way could now be traced over great distances. There was no more doubt: the Milky Way is a spiral star system similar to the Andromeda nebula. However, we do not yet have a detailed picture of the spiral pattern of the Milky Way: its branches merge with one another and it is very difficult to determine the distance to them.
Today it is known that our Galaxy is a giant stellar system, which includes hundreds of billions of stars. All the stars that we see overhead on a clear night belong to our Galaxy. If we could move in space and look at the Milky Way from the side, our gaze would appear a star city in the form of a huge flying saucer 100 thousand light years across. In its center, we would see a noticeable thickening - a bar - 20 thousand light years in diameter, from which gigantic spiral branches go into space.
Despite the fact that the Galaxy's appearance suggests a flat system, this is not entirely true. The so-called halo, a cloud of rarefied matter, stretches around it. Its radius reaches 150 thousand light years. Around the central bulge and core are many globular star clusters of old, cool red stars. Harlow Shapley called them the "skeleton of the body" of our Galaxy. Cool stars make up the so-called spherical subsystem of the Milky Way, and its flat subsystem, in other words, spiral arms, is "stellar youth." There are many bright, prominent stars of high luminosity.
Young stars in the galactic plane appear due to the presence of a huge amount of dust and gas there. It is known that stars are born due to the compression of matter in gas and dust clouds. Then, over millions of years, newborn stars “inflate” these clouds and become visible. The Earth and the Sun are not the geometric center of the World - they are located in one of the quiet corners of our Galaxy. And, apparently, this particular location is ideal for the emergence and development of life.
For ten years now, scientists have been able to detect large planets - the size of Jupiter - in other stars. Today they are known about one and a half hundred. This means that such planetary systems are widespread in the Galaxy. Armed with more powerful telescopes, you can find such small planets as Earth, and on them, perhaps, brothers in mind.
All stars in the Galaxy move in their orbits around its core. The sun has its own orbit. To make a complete revolution, the Sun needs no less than 250 million years, which is a galactic year (the speed of the Sun is 220 km / s). The Earth has already circled the center of the Galaxy 25-30 times. It means that it is exactly that many galactic years.
It is very difficult to trace the path of the Sun through the Milky Way. But modern telescopes can detect this movement too. In particular, to determine how the appearance of the starry sky changes when the Sun moves relative to the nearest stars. The point towards which the solar system moves is called the apex and is located in the constellation Hercules, on the border with the constellation Lyra.
