The Milky Way is a huge celestial system, consisting of billions of stars, a lot of gas and dust. Is this correct?

You're right. Let me tell you how the Milky Way is made up:

Galaxy (Galaxy)

The Milky Way is the galaxy to which the earth and the sun belong. It is named because the bright band whose main part is projected on the celestial sphere is called the Milky Way in China.

The Milky Way is a whirlpool, and four spiral arms extend evenly and symmetrically from the center of the Milky Way. The center of the Milky Way and the four spiral arms are places where stars are concentrated. From a distance, the Milky Way looks like a discus for exercise. The diameter of discus is 65.438+million light years, equivalent to 946.08 billion kilometers. The thickest part in the middle is about 3000 ~ 6500 light years. The sun is located on a spiral arm called Orion arm, about 33,000 light years away from the center of the Milky Way.

The discovery of the Milky Way has gone through a long process. After the invention of the telescope, Galileo first observed the Milky Way with a telescope and found that the Milky Way was made up of stars. Then there are T. Wright, I. Kant, J. H. Lambert, etc. It is believed that the Milky Way and all the stars may converge and integrate into a huge star system. /kloc-in the late 8th century, F.W. Herschel started the observation of star counting with a self-made reflecting telescope to determine the structure and size of the star system. He asserted that the star system is flat and the sun is not far from the center of the disk. After his death, his son, J.F. Herschel, followed in his father's footsteps, continued his in-depth research and extended the work of counting satellites to Nantian. At the beginning of the 20th century, astronomers called the star system with the Milky Way as its apparent phenomenon the Milky Way. J.C. Kapteyn used statistical parallax method to measure the average distance of stars, and combined with the counting of stars, a model of the Milky Way was obtained. In this model, the sun is at the center, and the Milky Way is disc-shaped, with a diameter of 8,000 parsec and a thickness of 2,000 parsec. H shapley uses the period-luminosity relationship of Cepheid variable to measure the distance of globular clusters, and studies the structure and size of the Milky Way from the distribution of globular clusters. His model is that the Milky Way is a lenticular star system, and the sun is not in the center. Shapley concluded that the Milky Way has a diameter of 80,000 parsec and the sun is 20,000 parsec from the center of the Milky Way. These values are too large, because shapley did not consider interstellar extinction when calculating the distance. In the 1920s, after the discovery of the rotation of the Milky Way, shapley's model of the Milky Way was recognized.

The Milky Way is a huge spiral galaxy, Sb type, with four spiral arms. Contains 100 billion or 200 billion stars. The overall rotation of the Milky Way is not good. The rotation speed at the sun is about 220 km/s, and the sun revolves around the center of the Milky Way for about 250 million years. The absolute visual magnitude of the Milky Way is -20.5. The total mass of the Milky Way is about 1 trillion times that of our sun, and about 10 times that of all the stars in the Milky Way. This is a strong evidence that dark matter exists in our galaxy, far beyond the bright astrolabe. Regarding the age of the Milky Way, the popular view is that the Milky Way was born shortly after the Big Bang. Calculated by this method, the age of our galaxy is about 65.438+0.45 billion years old, and the upper and lower errors are more than 2 billion years each. The scientific community believes that the "big bang" of the birth of the universe occurred around. ...

The Milky Way is the star system where the solar system is located, including120 billion stars, a large number of star clusters and nebulae, and various types of interstellar gas and dust. Its total mass is 654.38+04 billion times that of the sun. Most of the stars in the Milky Way are concentrated in a oblate sphere, which is shaped like a discus. The protruding part in the middle of the oblate sphere is called the "nuclear sphere" with a radius of about 7000 light years. The center of the core ball is called "silver core" and the periphery is called "silver disk". There is a bigger sphere outside the silver disk, where there are fewer stars and less density. It is called "Silver Halo" with a diameter of 70,000 light years. The Milky Way is a spiral galaxy with a spiral structure, that is, it has a silver center and two spiral arms, which are 4500 light years apart. The rotation speed and period of each part of it are different because the distance from the silver center is different. The sun is about 23,000 light years away from the galactic center, and it orbits the galactic center at a speed of 250 km/s with a period of about 250 million years.

About 90% of galactic matter is concentrated in stars. There are many kinds of stars. Stars can be divided into five star families according to their physical properties, chemical composition, spatial distribution and motion characteristics. The youngest extreme group I stars are mainly distributed on the spiral arms in the silver disk; The oldest extreme group II stars are mainly distributed in silver halos. Stars often gather in clusters. In addition to a large number of binary stars, more than 1000 clusters have been found in the Milky Way. There are also gases and dust in the Milky Way, accounting for about 10% of the total mass of the Milky Way. The distribution of gas and dust is uneven, some gather into nebulae, while others are scattered in interstellar space. Since 1960s, people have discovered a large number of interstellar molecules, such as carbon monoxide and H2O. Molecular clouds are the main places where stars form. The core of the Milky Way, the silver nucleus or silver nucleus, is a very special place. It emits intense radio, infrared, X-ray and gamma-ray radiation. Its nature is not clear, and there may be a giant black hole, and its mass is estimated to be tens of millions of times that of the sun. Little is known about the origin and evolution of the Milky Way.

197 1 year, British astronomers Lyndon Bell and Martin Ness analyzed the infrared observation and other properties of the central region of the Milky Way, pointed out that the energy in the center of the Milky Way should be a black hole, and predicted that if their hypothesis is correct, a small-scale source emitting radio emission should be observed in the center of the Milky Way, and the radiation properties should be similar to those of people. Three years later, such a source was discovered, which is Sagittarius A.

Sagittarius A is very small, only equivalent to the size of an ordinary star. The radio emission intensity of Sagittarius A is 2 *10 (34th power) erg/s, which is located within 0.2 light-years of the dynamic center of the Milky Way. It is surrounded by moving ionized gas with a speed as high as 300 km/s, and there is a strong infrared radiation source. It is known that the activities of all star-level celestial bodies cannot explain the peculiar characteristics of Sagittarius A, so Sagittarius A seems to be the best candidate for massive black holes. However, because there is no conclusive evidence of massive black holes at present, astronomers carefully avoid mentioning massive black holes in conclusive language. Our Milky Way contains about 200 billion stars, including about 1000 billion stars, and the sun is a typical one. The Milky Way is a fairly large spiral galaxy, which has three main components: a silver disk with spiral arms, a silver center protruding from the center and a halo.

The spiral galaxy M83 is very similar to our Milky Way in size and shape.

Silver plate:

Galactic disk: A flat disk of stars, dust and gas in spiral galaxies.

The silver disk is the main component of the Milky Way, and 90% of the detectable substances in the Milky Way are within the scope of the silver disk. The shape of the silver disk is like a thin lens, which is distributed around the silver center in the form of axial symmetry. The thickness of its center is about 65,438+0,000 light years, but this is the thickness of the slightly convex core ball. The silver plate itself is only 2000 light years thick and nearly 1000 light years in diameter. It can be seen that the overall silver plate is very thin.

Except that the silver core rotates around the silver core in the range of 1000 parsec, the other parts of the silver disk rotate around the silver core poorly, that is, the farther away from the silver core, the slower it rotates. The matter in the silver disk mainly exists in the form of stars, and the interstellar matter that accounts for less than 10% of the total mass of the Milky Way is mostly scattered in the silver disk. In interstellar matter, besides ionized hydrogen, molecular hydrogen and various interstellar molecules, there is 10% interstellar dust. These solid particles with a diameter of about 1 micron are the main causes of interstellar extinction, and most of them are concentrated near galactic plane.

Because the sun is located in the silver plate, it is not easy for us to know the original appearance of the silver plate. In order to find out the structure of the silver disk, according to Budd and Mayol's research on the spiral arm of spiral galaxy M3 1 (Andromeda Nebula) in the 1940s, the main types of spiral arm celestial bodies were obtained, and then these celestial bodies were surveyed in the galaxy and three parallel spiral arms were found near the sun. Due to interplanetary extinction, the overall appearance of the silver disk cannot be obtained by optical observation. There is evidence that the spiral arm is the gathering place of interstellar gas, so the detection of interstellar gas can show the structure of the spiral arm. The 2 1 cm radio spectrum of interstellar gas is not blocked by interstellar dust, and it can almost reach the whole galaxy. Optical and radio observations show that the silver disk does have a vortex structure.

Silver heart:

The central bulge of the galaxy is a bright sphere with a diameter of about 20,000 light years and a thickness of 10000 light years. This region consists of high-density stars, mainly red stars over10 billion years old. Many evidences show that there is a huge black hole in the central region, and the activity of galactic nuclei is very intense. The center of the Milky Way, that is, the intersection of the axis of rotation of the Milky Way and the galactic plane.

The center of the Milky Way is in the direction of Sagittarius, and the coordinates of 1950 calendar elements are: right ascension 174229, declination -28 59 18. Besides being a geometric point, the galactic center also means the central region of the Milky Way. The sun is about 100000 parsec from Yin Xin, which is about 8 parsec to the north of galactic plane. There is a lot of interstellar dust between the galactic center and the solar system, so it is difficult to see the galactic center in visible light band with optical telescopes in the northern hemisphere. After the rise of radio astronomy and infrared observation technology, people can detect the information of the center of the Milky Way through interstellar dust in the band of 2 microns to 73 centimeters. The observation of neutral hydrogen 2 1 cm spectral line reveals that there is an expanding arm of hydrogen flow in O, which is 4,000 parsec away from Yin Xin, that is, the so-called "3,000 parsec arm" (the distance was mistakenly set at 3,000 parsec at first, and then revised to 4,000 parsec, but the old name is still used). About 1 0,000,000 neutral hydrogens with solar mass rush towards the solar system at a speed of 53 kilometers per second. On the other side of the silver core, there is a neutral hydrogen expansion arm with roughly the same mass, which leaves the silver core at a speed of 135 km per second. They should have been driven out of the silver heart in an asymmetric way from100000 to150000 years ago. In the sky area 300 parsec away from Yin Xin, there is a hydrogen disk rotating rapidly around Yin Xin, expanding outward at a speed of 70 ~ 140 km per second. There is a hydrogen molecular cloud with an average diameter of 30 parsec in the disk. 70 parsec away from Yin Xin, there is a violently disturbed ionized hydrogen region, which also expands outward at a high speed. It has been known that not only a large amount of gas gushes from the center of the Milky Way, but also there is a strong radio source in the center of the Milky Way, Sagittarius A, which emits strong synchronous radiation. The detection of very long baseline interferometer shows that the central area of the central radio source of the Milky Way is very small, even less than 10 astronomical unit, that is, it does not exceed Jupiter's orbit around the sun. According to the infrared observation data of 12.8 micron, the mass of the silver core with the diameter of 1 parsec is equivalent to millions of solar masses, of which about 1 10,000 solar masses exist in the form of stars. Xing has a title? O There is a massive dense nucleus in the center of the Milky Way galaxy, which may be a black hole. Relativistic electrons flowing into the compact core accretion disk are accelerated in a strong magnetic field, thus generating synchrotron radiation. The motion state of galaxy gas, the strong radio source in the center of the galaxy and the existence of special galaxies with strong core activity (such as seyfert galaxy) make us think that there has been core excitation activity in the evolution history of galaxies, including the Milky Way, and it has not stopped yet.

Silver halo:

The galactic halo is scattered in a spherical area around the silver disk. The diameter of the silver halo is about 98,000 light years. The density of stars here is very low, and there are some globular clusters of old stars. Some people think that there is a huge spherical radio emission area outside the silver halo, called the silver corona, which extends at least 1000 parsec or 320,000 light years from the silver center.

Cosmic sayings:

The real mystery of the world lies not in the intangible, but in the tangible. Oscar Wilde

In the vast and silent starry sky, we cry for the lost sun. John Delaville de Maymon

In the center of the black furnace, there are countless places where the sun is sent out, hiding infinite magic. Arthur Limbaugh

If a person can meditate on the things in the sky, what he says and thinks will be more noble when he faces the things on the earth. -Cicero

Galaxy system

Back to the catalogue of Space Exploration: 2005-12-2014: 49:15.

Our star system, where the earth and the sun are located, is an ordinary galaxy, named after its milky bright band projected on the celestial sphere-the Milky Way. The Milky Way is a lens-shaped system with a diameter of about 25,000 parsec and a thickness of about 1 ~ 2000 parsec. Its main body is called a silver plate. The spiral structure composed of high luminosity stars, galaxy clusters and galactic nebulae is superimposed on the silver disk. At the center of the Milky Way is a massive nuclear sphere with a long axis of 4-5 thousand parsec and a thickness of 4 thousand parsec. The Milky Way galaxy is shrouded in a silver halo about 30,000 parsec in diameter. The brightest member of the silver halo is a globular cluster. The mass of the Milky Way is1.4×101solar mass, of which stars account for about 90%, and interstellar matter composed of gas and dust accounts for about 10%. The galaxy as a whole rotates badly. The sun is about 65,438+00 kilometers away from the galactic center. parsec is about 8 parsec to the north of galactic plane. It orbits the galactic center at a speed of 250 kilometers per second, once every 250 million years. The total density of matter (stars and interstellar matter) near the sun is about 0. 13 solar mass/parsec 3 or 8.8× 10-24 g/cm 3. The Milky Way is an Sb or Sc spiral galaxy with 200 billion stars, and it is the largest giant galaxy except Andromeda. Its apparent absolute magnitude is Mv=-20.5. It evolves on the time scale of 10 10 years.

In the middle of the 8th century, people realized that all the stars in the sky are distant "suns" except planets and satellites in the solar system. Wright, Kant and Lambert first thought that it was likely that all the stars were assembled into a huge system with limited space.

The first person who studied the origin of star system through observation was F.W. Herschel. He used his reflecting telescope to count the stars in several celestial bodies. 1785, according to the statistical study of star counting, he drew a horizontal organization map of the Milky Way with the sun as the center. He observed with telescopes with diameters of 50 cm and 120 cm, and found that when the penetration of the telescope increased, the number of dark stars observed also increased, but the edge of the Milky Way still could not be seen. F.W. Herschel realized that the Milky Way was much bigger than he had originally estimated. After the death of F. W. Herschel, his son J. F. Herschel inherited his father's business and expanded the scope of counting stars to the south for half a day. /kloc-in the middle of the 0/9th century, it began to measure the distance between stars and compile the all-sky star map. 1906, in order to re-study the structure of the star world, Kapteyn put forward the plan of "selecting star regions", which was later called "Kapteyn constituency". 1922, he drew a model similar to that of F.W. Herschel, which is also a flat system with the sun at the center, dense stars and sparse edges. Shapley explored the size and shape of the Milky Way on a completely different basis. He used the period-luminosity relationship of Cepheid variables in Magellanic Cloud discovered by Loewit in1908 ~12 to measure the distance between globular clusters and Cepheid variables. Under the assumption that there is no obvious interstellar extinction, 19 18 establishes a lenticular model of the Milky Way, and the sun is not in the center. By the 1920s, shapley model had been recognized by the astronomical community. Shapley overestimated the Milky Way because he didn't consider the interstellar extinction effect. It was not until 1930 that trumpler confirmed the existence of interstellar matter, and this deviation was corrected.

About 90% of the materials that make up the Milky Way are concentrated in the stars. 1905, hertzsprung discovered that stars can be divided into giant stars and dwarf stars. 19 13 years, after Herotto was published, according to the spectral type and luminosity, besides the main sequence star, there are five branches: Supergiant star, Superstar, subgiant, Sub Dwarf and White Dwarf. During the period of 1944, Budd observed the Andromeda galaxy and determined that stars can be divided into two different star groups: star group ⅰ and star group ⅱ. Xingzu I is a young and gold-rich celestial body, distributed on the spiral arms and related to interstellar matter. Xingzu Ⅱ is an ancient metal-poor celestial body, which has no tendency to gather in galactic plane. 1957, according to the metal content, age, spatial distribution and motion characteristics, these two star groups were further subdivided into intermediate star group ⅰ, spiral arm star group ⅰ, discoid star group ⅱ and halo star group ⅱ.

Stars in pairs, groups and clusters are common phenomena. Within 25 parsec near the sun, less than half of the stars are single stars. So far, 65,438+032 globular clusters, more than 65,438+0,000 galactic clusters and quite a few star complexes have been observed. According to statistics, there should be 18000 galactic clusters and 500 globular clusters. At the beginning of the twentieth century, Barnard discovered a large number of bright and dark nebulae through photographic observation. 1904, the discovery of ionized calcium in the stellar spectrum revealed the existence of interstellar matter. Subsequent spectral and polarization studies have determined the gas and dust components in the nebula. In recent years, through the detection of infrared band, it is found that there are forming stars in the dense area of dark nebula. After the birth of radio astronomy, the vortex structure of the Milky Way was outlined by using the neutral hydrogen 2 1 cm spectral line. According to the description of ionized hydrogen region, it is found that there are three spiral arms near the sun: Sagittarius, Orion and Perseus. The sun is in the arm of Orion. In addition, an arm of 3000 parsec was found in the direction of Yin Xin. The distance between the two arms is about 1.6 thousand parsec. In 1963, the interstellar molecule OH was observed in radio astronomy, which was a major breakthrough since the identification of interstellar molecules ch, CN and CH+ in the optical band during the period of 1937 ~ 194 1. By the end of 1979, more than 50 kinds of interstellar molecules had been discovered.

Structure The overall structure of the Milky Way is: the main part of the Milky Way material consists of a thin disk called a silver disk, and the part near the spherical center of the silver disk is called a nuclear ball. Stars are very dense in the nuclear sphere, and there is a small dense area in its center, which is called the silver core. Outside the silver plate is a larger, nearly spherical distribution system, in which the density of substances is much lower than that inside the silver plate, which is called silver halo. There is also a silver corona outside the silver halo, and its material distribution is also roughly spherical. For details about the Milky Way, please see The Structure of the Milky Way.

Little is known about the origin and evolution of the origin of the Milky Way. This is not only to study the origin and evolution of general galaxies, but also to study cosmology. According to the Big Bang cosmology hypothesis, all the galaxies we observed were protogalaxies and evolved into galaxy clusters including the Milky Way due to the fluctuation of high-density primitive materials caused by density, unstable gravity and continuous expansion/10 10 years ago. The hypothesis of the steady-state universe model is that galaxies are constantly formed in the core region of high-density protogalaxies.

Only in recent years have some achievements been made in the study of the evolution of the Milky Way. The data about the spatial movement of old stars near the sun show that the halo star family was first born in the process of the collapse of the protogalaxy nebula. Their age is over 654.38 billion years, and their chemical composition is about 73% hydrogen and 27% helium. Most of the gaseous substances are concentrated into silver disks, which in turn form disk clusters. In recent years, people have discussed the overall evolution of the Milky Way from the perspectives of the formation and evolution of stars, the changes of element abundance, the activities of silver nuclei and their position in evolution. The density wave theory, developed in the 1960s, well explains the overall structure of the spiral structure of the Milky Way and its long-term maintenance mechanism.