Milky Way (computer model). Barred spiral galaxy. Two of the four branches dominate.
The Milky Way (or Galaxy, with a capital letter) is in which they are located, and all the individual ones visible to the naked eye. Refers to barred spiral galaxies.
The Milky Way, together with the Andromeda Galaxy (M31), the Triangulum Galaxy (M33), and more than 40 dwarf satellite galaxies - its own and Andromeda's - form the Local, which is part of the (Virgo Supercluster).
Etymology
Name Milky Way widespread in Western culture and is a tracing paper from Lat. via lactea“milk road”, which, in turn, is a translation from ancient Greek. ϰύϰλος γαλαξίας “milk circle”. Name Galaxy formed by analogy with ancient Greek. γαλαϰτιϰός “milk”. According to ancient Greek legend, Zeus decided to make his son Hercules, born from a mortal woman, immortal, and for this he planted it on his sleeping wife Hera so that Hercules would drink divine milk. Hera, waking up, saw that she was not feeding her child, and pushed him away from her. The stream of milk that splashed from the goddess’s breast turned into the Milky Way.
In the Soviet astronomical school, the Milky Way galaxy was simply called “our Galaxy” or “the Milky Way system”; The phrase "Milky Way" was used to refer to the visible stars that optically constitute the Milky Way to an observer.
Outside Western culture, there are many other names for the Milky Way. The word “Path” often remains, the word “Milky” is replaced by other epithets.
Galaxy structure
The diameter of the Galaxy is about 30 thousand parsecs (about 100,000 light years, 1 quintillion kilometers) with an estimated average thickness of about 1000 light years. The galaxy contains, according to the lowest estimate, about 200 billion stars (modern estimates range from 200 to 400 billion). The bulk of stars are located in the shape of a flat disk. As of January 2009, the mass of the Galaxy is estimated at 3·10 12 solar masses, or 6·10 42 kg. The new minimum estimate puts the galaxy's mass at just 5·10 11 solar masses. Most of the mass of the Galaxy is contained not in stars and interstellar gas, but in a non-luminous halo of.
Disk
It wasn't until the 1980s that astronomers suggested that the Milky Way was a barred spiral galaxy rather than a regular spiral galaxy. This assumption was confirmed in 2005 by Lyman Spitzer, who showed that the central bar of our galaxy is larger than previously thought.
Scientists estimate that the galactic disk, which protrudes in different directions in the region of the galactic center, has a diameter of about 100,000 light years. Compared to a halo, the disk rotates noticeably faster. The speed of its rotation is not the same at different distances from the center. It rapidly increases from zero at the center to 200-240 km/s at a distance of 2 thousand light years from it, then decreases somewhat, increases again to approximately the same value and then remains almost constant. A study of the rotational features of the disk made it possible to estimate its mass; it turned out that it is 150 billion times greater than M ☉ .
Young stars and star clusters, whose age does not exceed several billion years, are concentrated near the plane of the disk. They form the so-called flat component. There are a lot of bright and hot stars among them. The gas in the Galaxy's disk is also concentrated mainly near its plane. It is distributed unevenly, forming numerous gas clouds - from giant clouds of heterogeneous structure, over several thousand light years in extent, to small clouds no more than a parsec in size.
Core
The galactic center of the Milky Way in infrared.
In the middle part of the Galaxy there is a thickening called bulge (bulge - thickening), which is about 8 thousand parsecs in diameter. The center of the Galaxy's core is located in the constellation Sagittarius (α = 265°, δ = −29°). The distance from the Sun to the center of the Galaxy is 8.5 kiloparsecs (2.62·10 17 km, or 27,700 light years). In the center of the Galaxy, apparently, there is a supermassive (Sagittarius A) (about 4.3 million M ☉) around which a black hole of average mass from 1000 to 10,000 M ☉ and an orbital period of about 100 years and several thousand relatively small. Their combined gravitational effect on neighboring stars causes the latter to move along unusual trajectories. There is an assumption that most galaxies have supermassive black holes in their core.
The central regions of the Galaxy are characterized by a strong concentration of stars: each cubic parsec near the center contains many thousands of them. The distances between stars are tens and hundreds of times smaller than in the vicinity of the Sun. As in most other galaxies, the distribution of mass in the Milky Way is such that the orbital speed of most stars in the Galaxy does not depend significantly on their distance from the center. Further from the central bridge to the outer circle, the usual speed of rotation of stars is 210-240 km/s. Thus, such a distribution of speed, not observed in the solar system, where different orbits have significantly different speeds of rotation, is one of the prerequisites for the existence of dark matter.
The length of the galactic bar is believed to be about 27,000 light years. This bar passes through the center of the galaxy at an angle of 44 ± 10 degrees to the line between our Sun and the center of the galaxy. It consists primarily of red stars, which are considered very old. The jumper is surrounded by a ring called the "Five Kiloparsec Ring". This ring contains most of the Galaxy's molecular hydrogen and is an active star-forming region in our Galaxy. If observed from the Andromeda Galaxy, the galactic bar of the Milky Way would be a bright part of it.
In 2016, Japanese astrophysicists reported the discovery of a second giant black hole in the Galactic center. This black hole is located 200 light years from the center of the Milky Way. The observed astronomical object with a cloud occupies a region of space with a diameter of 0.3 light years, and its mass is 100 thousand solar masses. The nature of this object has not yet been precisely established - it is a black hole or another object.
Sleeves
Galaxy Sleeves
The Galaxy belongs to the class of spiral galaxies, which means that the Galaxy has spiral sleeves, located in the plane of the disk. The disk is immersed in halo spherical in shape, and around it is a spherical crown. The solar system is located at a distance of 8.5 thousand parsecs from the galactic center, near the plane of the Galaxy (the displacement towards the North Pole of the Galaxy is only 10 parsecs), on the inner edge of the arm called Orion's sleeve. This arrangement does not make it possible to observe the shape of the sleeves visually. New data from observations of molecular gas (CO) suggest that our Galaxy has two arms, starting at a bar in the inner part of the Galaxy. In addition, there are a couple more sleeves in the inner part. These arms then transform into a four-arm structure observed in the neutral hydrogen line in the outer parts of the Galaxy.
Halo
The surroundings of the Milky Way and its halo.
The galactic halo has a spherical shape, extending beyond the galaxy by 5-10 thousand light years, and a temperature of about 5 10 5 K. The galactic disk is surrounded by a spheroidal halo consisting of old stars and globular clusters, 90% of which are located at a distance of less than 100,000 light years from the center of the galaxy. However, recently several globular clusters, such as PAL 4 and AM 1, have been found more than 200,000 light years away from the galactic center. The center of symmetry of the Milky Way halo coincides with the center of the galactic disk. The halo consists mainly of very old, dim, low-mass stars. They occur individually and in the form of globular clusters, which can contain up to a million stars. The age of the population of the spherical component of the Galaxy exceeds 12 billion years, it is usually considered to be the age of the Galaxy itself.
While the galactic disk contains gas and dust, which impedes the passage of visible light, the spheroid component does not contain such components. Active star formation occurs in the disk (especially in the spiral arms, which are zones of increased density). In the halo, star formation has completed. Open clusters also occur predominantly in the disk. It is believed that the bulk of the mass of our galaxy is dark matter, which forms a dark matter halo with a mass of approximately 600 - 3000 billion M☉. The dark matter halo is concentrated towards the center of the galaxy.
Stars and halo star clusters move around the center of the Galaxy in very elongated orbits. Since the rotation of individual stars occurs somewhat randomly (that is, the speeds of neighboring stars can have any direction), the halo as a whole rotates very slowly.
History of the discovery of the Galaxy
Most celestial bodies are combined into various rotating systems. So, as it revolves around the Earth, the giant planets form their own systems, rich in bodies. At a higher level, the Earth and the rest revolve around the Sun. A natural question arose: is the Sun also part of an even larger system?
The first systematic study of this issue was carried out in the 18th century by the English astronomer William Herschel. He counted the number of stars in different areas of the sky and discovered that there was a large circle in the sky (later it was called galactic equator), which divides the sky into two equal parts and on which the number of stars is greatest. In addition, the closer the part of the sky is to this circle, the more stars there are. Finally it was discovered that it was on this circle that the Milky Way was located. Thanks to this, Herschel guessed that all the stars we observed form a giant star system, which is flattened towards the galactic equator.
At first it was assumed that all objects were parts of our Galaxy, although Kant also suggested that some nebulae could be galaxies similar to the Milky Way. As early as 1920, the question of the existence of extragalactic objects caused debate (for example, the famous Great Debate between Harlow Shapley and Heber Curtis; the former defended the uniqueness of our Galaxy). Kant's hypothesis was finally proven only in the 1920s, when Ernst Epic and Edwin Hubble managed to measure the distance to some spiral nebulae and show that, due to their distance, they cannot be part of the Galaxy.
Location of the Sun in the Galaxy
According to the latest scientific estimates, the distance from the Sun to the galactic center is 26,000 ± 1,400 light-years, while according to preliminary estimates, our star should be about 35,000 light-years from the bar. This means that the Sun is located closer to the edge of the disk than to its center. Together with other stars, the Sun rotates around the center of the Galaxy at a speed of 220-240 km/s, making one revolution in approximately 200 million years. Thus, during its entire existence, the Earth has flown around the center of the Galaxy no more than 30 times.
In the vicinity of the Sun, it is possible to trace sections of two spiral arms that are approximately 3 thousand light years away from us. Based on the constellations where these areas are observed, they were given the name Sagittarius Arm and Perseus Arm. The sun is located almost in the middle between these spiral branches. But relatively close to us (by galactic standards), in the constellation Orion, there passes another, not very clearly defined arm - the Orion Arm, which is considered a branch of one of the main spiral arms of the Galaxy.
The speed of the Sun's rotation around the center of the Galaxy almost coincides with the speed of the compaction wave forming the spiral arm. This situation is atypical for the Galaxy as a whole: the spiral arms rotate at a constant angular velocity, like spokes in a wheel, and the movement of stars occurs according to a different pattern, so almost the entire stellar population of the disk either falls inside the spiral arms or falls out of them. The only place where the velocities of stars and spiral arms coincide is the so-called corotation circle, and it is on it that the Sun is located.
For the Earth, this circumstance is extremely important, since violent processes occur in the spiral arms, generating powerful radiation that is destructive for all living things. And no atmosphere could protect from it. But our planet exists in a relatively calm place in the Galaxy and has not been affected by these cosmic cataclysms for hundreds of millions (or even billions) of years. Perhaps this is why life was able to be born and survive on Earth.
Evolution and future of the Galaxy
Collisions of our Galaxy with other galaxies are possible, including one as large as the Andromeda Galaxy, but specific predictions are not yet possible due to ignorance of the transverse velocity of extragalactic objects.
Panorama of the Milky Way taken in Death Valley, USA, 2005.
Panorama of the southern sky taken near the Paranal Observatory, Chile, 2009.
MILKY WAY
a hazy glow in the night sky from the billions of stars in our Galaxy. The Milky Way band encircles the sky in a wide ring. The Milky Way is especially visible away from city lights. In the Northern Hemisphere, it is convenient to observe it around midnight in July, at 10 pm in August or at 8 pm in September, when the Northern Cross of the Cygnus constellation is near the zenith. As we follow the Milky Way's shimmering streak north or northeast, we pass the W-shaped constellation Cassiopeia and head toward the bright star Capella. Beyond the Chapel, you can see how the less wide and bright part of the Milky Way passes just east of Orion's Belt and leans towards the horizon not far from Sirius, the brightest star in the sky. The brightest part of the Milky Way is visible to the south or southwest at times when the Northern Cross is overhead. At the same time, two branches of the Milky Way are visible, separated by a dark gap. The Scutum Cloud, which E. Barnard called the “pearl of the Milky Way,” is located halfway to the zenith, and below are the magnificent constellations Sagittarius and Scorpius.
Unfortunately, the brightest parts of the Milky Way are inaccessible to observers in the Northern Hemisphere. To see them, you need to go to the equator, or even better, position yourself between 20 and 40° S. and watch the sky approx. 10 pm in late April or early May. High in the sky is the Southern Cross, and low in the northwest is Sirius. The Milky Way runs between them, dim and narrow, but it becomes much brighter and more interesting 30° west of the Southern Cross, in the constellation Carina. As Sagittarius and Scorpio rise in the east, the brightest and most magnificent parts of the Milky Way appear. Its most remarkable area is visible late in the evening in June-July, when the Sagittarius Cloud is located near the zenith. Against the background of a uniform glow caused by thousands and thousands of distant stars invisible to the eye, one can notice dark clouds and “veins” of cold cosmic dust. Anyone who wants to understand the structure of our Galaxy should take the time to observe the Milky Way - this truly remarkable and most grandiose of celestial phenomena.
To discern the myriad stars that make up the Milky Way, all you need is binoculars or a small telescope. The greatest concentration of stars and the maximum width of the Milky Way are observed in the constellations Sagittarius and Scorpio; It is least populated with stars on the opposite side of the sky - near Orion's Belt and Capella. Accurate astronomical observations confirm the first visual impression: the band of the Milky Way marks the central plane of a giant disk-shaped star system - our Galaxy, often called the "Milky Way Galaxy". One of its stars is our Sun, located very close to the central plane of the Galaxy. However, the Sun is not at the center of the galactic disk, but at a distance of two-thirds from its center to the edge. The stars that make up the Milky Way are located at different distances from the Earth: some are no further than 100 light years. years, and most are removed by 10,000 sv. years and even further. The star cloud in Sagittarius and Scorpio marks the direction of the center of the Galaxy, located at a distance of approximately 30,000 light years from Earth. years. The diameter of the entire Galaxy is at least 100,000 light years. years.
Composition of the Milky Way. The galaxy consists mainly of stars, more or less similar to the Sun. Some of them are several times more massive than the Sun and glow several thousand times brighter, others are several times less massive and glow several thousand times weaker. The Sun is, in many ways, an average star. Depending on the surface temperature, stars have different colors: blue-white stars are the hottest (20,000-40,000 K), and red stars are the coolest (approx. 2500 K). Some stars form groups called star clusters. Some of them are visible to the naked eye, such as the Pleiades. This is a typical open cluster; Typically such clusters contain from 50 to 2000 stars. In addition to open clusters, there are much larger globular clusters containing up to several million stars. These clusters vary significantly in age and stellar composition. Open clusters are relatively young: their typical age is ca. 10 million years, i.e. OK. 1/500th the age of the Earth and the Sun. They contain many massive bright stars. Globular clusters are very old: 10-15 billion years have passed since their formation, i.e. they consist of the oldest stars in the Galaxy, among which only low-mass ones have survived. Open clusters are located near the galactic plane, where there is a lot of interstellar gas from which stars form. Globular clusters fill the galactic halo surrounding the disk and are noticeably concentrated towards the center of the Galaxy.
see also
GALAXIES;
STARS ;
CONSTELLATION. The mass of the Galaxy is at least 2*10 11 solar masses. These are mostly stars, but 5% of its mass is interstellar matter - gas and dust. Interstellar matter fills the space between stars in the galactic disk with a thickness of approx. 600 St. years, and inside the disk it concentrates towards the spiral arms of the Galaxy. A significant part of the interstellar matter is combined into massive cold clouds, in the depths of which stars form.
see also INTERSTELLAR MATTER. The Milky Way Galaxy is one of hundreds of millions of similar star systems discovered in the Universe using large telescopes. It is often called "our star system." It belongs to large galaxies with rapid rotation and clear spiral arms, in which young hot stars and clouds of gas heated by their radiation, called “emission nebulae,” are concentrated. Using optical telescopes, it is not possible to study the entire Galaxy, since light does not penetrate through dense interstellar clouds of gas and dust, which are especially numerous towards the center of the Galaxy. However, for infrared radiation and radio emission, dust is not a hindrance: with the help of appropriate telescopes, it is possible to explore the entire Galaxy and even penetrate to its dense core. Observations have shown that the stars and gas in the galactic disk are moving at a speed of about 250 km/s around the center of the Galaxy. Our Sun, together with the planets, also moves at the same speed, making one revolution around the galactic center in about 200 million years.
Collier's Encyclopedia. - Open Society. 2000 .
Synonyms:See what "MILKY WAY" is in other dictionaries:
Milky Way Galaxy (computer model). Barred spiral galaxy. Two of the four branches dominate. Characteristics Type SBbc (spiral galaxy with bar) Diameter ... Wikipedia
MILKY WAY, a faint band of light visible in the sky on clear, dark nights, running along the line of the galactic equator. It is formed as a result of the glow of a huge number of stars, in some areas covered by clouds of interstellar gas and... ... Scientific and technical encyclopedic dictionary
A wide strip in the sky consisting of countless stars. Wed. The whole sky is strewn with cheerfully twinkling stars, and the Milky Way appears as clearly as if it had been washed and covered with snow before the holiday. A.P. Chekhov. Vanka. See Moiseeva... ... Michelson's Large Explanatory and Phraseological Dictionary (original spelling)
MILKY WAY, 1) a dimly luminous stripe crossing the starry sky. It is a huge number of visually indistinguishable stars, concentrating towards the main plane of the Galaxy. The Sun is located near this plane, so... ... Modern encyclopedia
1) a dimly luminous stripe crossing the starry sky. It is a huge number of visually indistinguishable stars, concentrating towards the main plane of the Galaxy. The Sun is located near this plane, so most stars... ... Big Encyclopedic Dictionary
MILKY, oh, oh Explanatory Dictionary of Ozhegov. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary
1) Galaxy. 2) A light stripe in the night sky is a projection onto the celestial sphere of distant (from the Sun) stars of the Galaxy, close to its plane. Increase The brightness of this band is due to higher concentration of stars in the galactic plane. Physical... ... Physical encyclopedia
Planet Earth, the Solar System, billions of other stars and celestial bodies - all this is our Milky Way galaxy - a huge intergalactic formation, where everything obeys the laws of gravity. Data on the true size of the galaxy are only approximate. And the most interesting thing is that there are hundreds, maybe even thousands, of such formations, larger or smaller, in the Universe.
The Milky Way Galaxy and what surrounds it
All celestial bodies, including the Milky Way planets, satellites, asteroids, comets and stars, are constantly in motion. Born in the cosmic vortex of the Big Bang, all these objects are on the path of their development. Some are older, others are clearly younger.
The gravitational formation rotates around the center, with individual parts of the galaxy rotating at different speeds. If in the center the rotation speed of the galactic disk is quite moderate, then at the periphery this parameter reaches values of 200-250 km/s. The Sun is located in one of these areas, closer to the center of the galactic disk. The distance from it to the center of the galaxy is 25-28 thousand light years. The Sun and the Solar System complete a full revolution around the central axis of the gravitational formation in 225-250 million years. Accordingly, in the entire history of its existence, the Solar System has flown around the center only 30 times.
Place of the galaxy in the Universe
One notable feature should be noted. The position of the Sun and, accordingly, the planet Earth is very convenient. The galactic disk is constantly undergoing a process of compaction. This mechanism is caused by the discrepancy between the speed of rotation of the spiral branches and the movement of stars, which move within the galactic disk according to their own laws. During compaction, violent processes occur, accompanied by powerful ultraviolet radiation. The Sun and the Earth are comfortably located in the corotational circle, where such vigorous activity is absent: between two spiral branches on the border of the Milky Way arms - Sagittarius and Perseus. This explains the calm in which we have been for such a long time. For more than 4.5 billion years, we have not been affected by cosmic disasters.
Structure of the Milky Way galaxy
The galactic disk is not homogeneous in its composition. Like other spiral gravitational systems, the Milky Way has three distinguishable regions:
- a core formed by a dense star cluster containing a billion stars of varying ages;
- the galactic disk itself, formed from clusters of stars, stellar gas and dust;
- corona, spherical halo - the region in which globular clusters, dwarf galaxies, individual groups of stars, cosmic dust and gas are located.
Near the plane of the galactic disk there are young stars collected in clusters. The density of star clusters in the center of the disk is higher. Near the center, the density is 10,000 stars per cubic parsec. In the region where the Solar System is located, the density of stars is already 1-2 stars per 16 cubic parsecs. As a rule, the age of these celestial bodies is no more than several billion years.
Interstellar gas also concentrates around the plane of the disk, subject to centrifugal forces. Despite the constant speed of rotation of the spiral branches, the interstellar gas is distributed unevenly, forming large and small zones of clouds and nebulae. However, the main galactic building material is dark matter. Its mass prevails over the total mass of all celestial bodies that make up the Milky Way galaxy.
If in the diagram the structure of the galaxy is quite clear and transparent, then in reality it is almost impossible to examine the central regions of the galactic disk. Gas and dust clouds and clusters of stellar gas hide from our view the light from the center of the Milky Way, in which lives a real space monster - a supermassive black hole. The mass of this supergiant is approximately 4.3 million M☉. Next to the supergiant is a smaller black hole. This gloomy company is complemented by hundreds of dwarf black holes. The black holes of the Milky Way are not only devourers of stellar matter, but also act as a maternity hospital, throwing huge bunches of protons, neutrons and electrons into space. It is from them that atomic hydrogen is formed - the main fuel of the star tribe.
The jumper bar is located in the region of the galactic core. Its length is 27 thousand light years. Old stars reign here, red giants, whose stellar matter feeds black holes. The bulk of molecular hydrogen is concentrated in this region, which acts as the main building material for the star formation process.
Geometrically, the structure of the galaxy looks quite simple. Each spiral arm, and there are four of them in the Milky Way, originates from a gas ring. The sleeves diverge at an angle of 20⁰. At the outer boundaries of the galactic disk, the main element is atomic hydrogen, which spreads from the center of the galaxy to the periphery. The thickness of the hydrogen layer on the outskirts of the Milky Way is much wider than in the center, while its density is extremely low. The discharge of the hydrogen layer is facilitated by the influence of dwarf galaxies, which have been closely following our galaxy for tens of billions of years.
Theoretical models of our galaxy
Even ancient astronomers tried to prove that the visible stripe in the sky is part of a huge stellar disk rotating around its center. This statement was supported by the mathematical calculations carried out. It was possible to get an idea of our galaxy only thousands of years later, when instrumental methods of space exploration came to the aid of science. A breakthrough in the study of the nature of the Milky Way was the work of the Englishman William Herschel. In 1700, he was able to experimentally prove that our galaxy is disk-shaped.
Already in our time, research has taken a different turn. Scientists relied on comparing the movements of stars between which there were different distances. Using the parallax method, Jacob Kaptein was able to approximately determine the diameter of the galaxy, which, according to his calculations, is 60-70 thousand light years. Accordingly, the place of the Sun was determined. It turned out that it is located relatively far from the raging center of the galaxy and at a considerable distance from the periphery of the Milky Way.
The fundamental theory of the existence of galaxies is that of the American astrophysicist Edwin Hubble. He came up with the idea to classify all gravitational formations, dividing them into elliptical galaxies and spiral-type formations. The latter, spiral galaxies, represent the largest group, which includes formations of various sizes. The largest recently discovered spiral galaxy is NGC 6872, with a diameter of more than 552 thousand light years.
Expected future and forecasts
The Milky Way Galaxy appears to be a compact and orderly gravitational formation. Unlike its neighbors, our intergalactic home is quite calm. Black holes systematically affect the galactic disk, reducing it in size. This process has already lasted tens of billions of years and how much longer it will continue is unknown. The only threat looming over our galaxy comes from its nearest neighbor. The Andromeda Galaxy is rapidly approaching us. Scientists suggest that a collision of two gravitational systems could occur in 4.5 billion years.
Such a meeting-merger will mean the end of the world in which we are accustomed to living. The Milky Way, which is smaller in size, will be absorbed by the larger formation. Instead of two large spiral formations, a new elliptical galaxy will appear in the Universe. Until this time, our galaxy will be able to deal with its satellites. Two dwarf galaxies - the Large and Small Magellanic Clouds - will be absorbed by the Milky Way in 4 billion years.
If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them
On a clear, moonless night, a pale, faintly shining ribbon spreads across the entire sky in a bright arc - Milky Way like a ring encircling the entire sky. Looking at it through a telescope, you are convinced that it is a huge collection of very faint stars.
Since the Milky Way encircles the entire sky, dividing it almost in half, then, obviously, our solar system is located near this plane, near the galactic plane, as it is called.
The farther from the plane of the Milky Way, the fewer faint stars there are and the smaller the distance in these directions the star system stretches. In general, our star system, called Galaxy, occupies a space that resembles a lens from the outside. It is flattened - thickest in the middle and thinner towards the edges. If we could see it “from above” or “from below”, it would have, roughly speaking, the appearance of a circle (not a ring). From the “side” it would look like a spindle. But what are the dimensions of this “spindle”? Is the arrangement of stars in it uniform?
This has become clear in recent years, although the answer to this question is given by a simple examination of the Milky Way, which all consists of a heap of star clouds. Some clouds are brighter and have more stars (such as in the constellations Sagittarius and Cygnus), while others are poorer in stars. The solar system is also located in one of them, called local system.
The Milky Way - how we can see it from Earth
The most powerful clouds of stars are in the direction of the constellation Sagittarius - this is where the core of the galaxy is located, which is where the Milky Way is brightest. Considering that we see the constellation Sagittarius “from the side,” it is logical to conclude that our solar system is far from being in the center of the Milky Way Galaxy, but rather is shifted closer to its edge.
Considering that the diameter of our Galaxy is almost 100 thousand light years, the solar system is located 25 thousand light years from its center, that is, about half its radius.
The solar system revolves around the center of the Galaxy, which lies at a distance of 25 thousand light years from us in the direction of the constellation Sagittarius, at a speed of 250 km/sec. The shape of its orbit is still unknown, but if it is close to a circle, which is likely, then the Sun completes one revolution along it in 200 million years. This period, if you like, can be taken as a “cosmic year” for measuring very large periods of time.
The entire history of mankind in comparison with such a period is only a short moment! If we could see the Sun rushing and turning in its orbit, as we see a train turning at a curve in the track, then we could not follow the revolutions of the planets around the Sun: they would seem to be spinning faster than an electric fan.
When rotating around the center of the Galaxy, not all stars move exactly the same way, and, for example, short-period ones lag behind the Sun by 100 kilometers every second.
The movement of our solar system at a speed of 20 km/sec in the direction of our “neighbor” constellation Lyra is movement within our star cloud, or local system. It is small and does not prevent us, together with the entire local system, from circling around the galactic center.
How bright the center of our Galaxy - the clouds of stars of the Milky Way in the constellation Sagittarius - should have seemed, if they had not been concealed, eclipsed by the absorption of light in the masses filling the space between us and this center!
The mass of our Galaxy, now estimated in various ways, is equal to two hundred billion solar masses, with one thousandth of it contained in interstellar gas and dust. The mass is almost the same, and the mass of the Triangulum galaxy is estimated to be twenty times less.
Looking at the Milky Way and other galaxies from the side, it seems that the stars are so close in it that they literally rub their sides against each other. In reality, everything is completely different.
If we built a model of the Milky Way in which the stars were represented as raindrops, then to give a correct idea of the distribution of stars within a typical galaxy, the mutual distances of the drops would have to be approximately 65 km!
Consequently, for every cubic centimeter of stellar matter there are over 10,000,000,000,000,000,000,000,000 cubic centimeters.
It’s a paradox, but for studying the structure of the Milky Way Galaxy we are at a very disadvantage. We live in it and see it from the inside. It's like trying to imagine the outside of your home while you're in your apartment and looking out the window.
But if our home is the Galaxy, then other houses are other galaxies. Therefore, we can guess about the appearance of our house by studying other houses that we see from the window.
Observing the Milky Way in the sky.
However, no one prevents us from looking at what is visible directly “from the window” in the sky. So what will an observer from Earth see?
The Milky Way passes through the constellations Swan, Cassiopeia And Perseus. The Milky Way is almost invisible. It stretches along the northern side of the sky in a small and low arc from the northwest (where Perseus stands) to the northeast (where Swan stands). The highest point of this arc, at Cassiopeia, is located midway between the horizon and the horizon.
Astronomers say that with the naked eye a person can see about 4.5 thousand stars. And this despite the fact that only a small part of one of the most amazing and unidentified pictures of the world is revealed to our eyes: in the Milky Way Galaxy alone there are more than two hundred billion celestial bodies (scientists have the opportunity to observe only two billion).
The Milky Way is a barred spiral galaxy, representing a huge gravitationally bound star system in space. Together with the neighboring Andromeda and Triangulum galaxies and more than forty dwarf satellite galaxies, it is part of the Virgo Supercluster.
The age of the Milky Way exceeds 13 billion years, and during this time from 200 to 400 billion stars and constellations, more than a thousand huge gas clouds, clusters and nebulae were formed in it. If you look at a map of the Universe, you can see that the Milky Way is presented on it in the form of a disk with a diameter of 30 thousand parsecs (1 parsec is equal to 3.086 * 10 to the 13th power of kilometers) and an average thickness of about a thousand light years (in one light year almost 10 trillion kilometers).
Astronomers find it difficult to answer exactly how much the Galaxy weighs, since most of the weight is not contained in the constellations, as previously thought, but in dark matter, which does not emit or interact with electromagnetic radiation. According to very rough calculations, the weight of the Galaxy ranges from 5*10 11 to 3*10 12 solar masses.
Like all celestial bodies, the Milky Way rotates around its axis and moves around the Universe. It should be taken into account that when moving, galaxies constantly collide with each other in space and the one that has larger sizes absorbs smaller ones, but if their sizes coincide, active star formation begins after the collision.
Thus, astronomers suggest that in 4 billion years the Milky Way in the Universe will collide with the Andromeda Galaxy (they are approaching each other at a speed of 112 km/s), causing the emergence of new constellations in the Universe.
As for the movement around its axis, the Milky Way moves unevenly and even chaotically in space, since each star system, cloud or nebula located in it has its own speed and orbits of different types and shapes.
Galaxy structure
If you look closely at a map of space, you can see that the Milky Way is very compressed in the plane and looks like a “flying saucer” (the Solar system is located almost at the very edge of the star system). The Milky Way Galaxy consists of a core, a bar, a disk, spiral arms and a crown.
Core
The core is located in the constellation Sagittarius, where there is a source of non-thermal radiation, the temperature of which is about ten million degrees - a phenomenon characteristic only of the nuclei of galaxies. In the center of the core there is a condensation - a bulge, consisting of a large number of old stars moving in an elongated orbit, many of which are at the end of their life cycle.
So, some time ago, American astronomers discovered an area here measuring 12 by 12 parsecs, consisting of dead and dying constellations.
At the very center of the core there is a supermassive black hole (an area in outer space that has such powerful gravity that even light is unable to leave it), around which a smaller black hole rotates. Together they exert such a strong gravitational influence on nearby stars and constellations that they move along trajectories unusual for celestial bodies in the Universe.
Also, the center of the Milky Way is characterized by an extremely strong concentration of stars, the distance between which is several hundred times less than at the periphery. The speed of movement of most of them is absolutely independent of how far they are from the core, and therefore the average rotation speed ranges from 210 to 250 km/s.
Jumper
The bridge, 27 thousand light years in size, crosses the central part of the Galaxy at an angle of 44 degrees to the conventional line between the Sun and the core of the Milky Way. It consists mainly of old red stars (about 22 million), and is surrounded by a ring of gas that contains most of the molecular hydrogen, and is therefore the region where stars are formed in the greatest numbers. According to one theory, such active star formation occurs in the bridge due to the fact that it passes gas through itself, from which constellations are born.
Disk
The Milky Way is a disk consisting of constellations, gas nebulae and dust (its diameter is about 100 thousand light years with a thickness of several thousand). The disk rotates much faster than the corona, which is located at the edges of the Galaxy, while the rotation speed at different distances from the core is unequal and chaotic (varies from zero in the core to 250 km/h at a distance of 2 thousand light years from it). Gas clouds, as well as young stars and constellations, are concentrated near the plane of the disk.
On the outer side of the Milky Way there are layers of atomic hydrogen, which extend into space one and a half thousand light years from the outer spirals. Despite the fact that this hydrogen is ten times thicker than in the center of the Galaxy, its density is just as many times lower. On the outskirts of the Milky Way, dense accumulations of gas with a temperature of 10 thousand degrees, the dimensions of which exceed several thousand light years, were discovered.
Spiral sleeves
Immediately behind the gas ring there are five main spiral arms of the Galaxy, the size of which ranges from 3 to 4.5 thousand parsecs: Cygnus, Perseus, Orion, Sagittarius and Centauri (the Sun is located on the inner side of the Orion arm). Molecular gas is located unevenly in the arms and does not always obey the rules of rotation of the Galaxy, introducing errors.
Crown
The Milky Way's corona appears as a spherical halo that extends five to ten light years beyond the Galaxy. The corona consists of globular clusters, constellations, individual stars (mostly old and low-mass), dwarf galaxies, and hot gas. They all move around the core in elongated orbits, while the rotation of some stars is so random that even the speed of nearby stars can differ significantly, so the corona rotates extremely slowly.
According to one hypothesis, the corona arose as a result of the absorption of smaller galaxies by the Milky Way, and is therefore their remnants. According to preliminary data, the age of the halo exceeds twelve billion years and is the same age as the Milky Way, and therefore star formation here has already completed.
star space
If you look at the night starry sky, the Milky Way can be seen from absolutely anywhere on the globe in the form of a strip of lightish color (since our star system is located inside the Orion arm, only part of the Galaxy is accessible for viewing).
The map of the Milky Way shows that our Sun is located almost on the disk of the Galaxy, at its very edge, and its distance to the core is from 26-28 thousand light years. Considering that the Sun moves at a speed of about 240 km/h, to make one revolution, it needs to spend about 200 million years (over the entire period of its existence, our star has not flown around the Galaxy thirty times).
It is interesting that our planet is located in a corotation circle - a place where the speed of rotation of stars coincides with the speed of rotation of the arms, so stars never leave these arms or enter them. This circle is characterized by a high level of radiation, so it is believed that life can only arise on planets near which there are very few stars.
This fact also applies to our Earth. Being on the periphery, it is located in a fairly calm place in the Galaxy, and therefore for several billion years it was almost not subject to global cataclysms, for which the Universe is so rich. Perhaps this is one of the main reasons that life was able to originate and survive on our planet.