Galaxy (alias "Han Yin", "Tianhe, Yinhe, Xinghe, Tianhan", etc. ) "is a rod-shaped galaxy where the solar system is located, including1000 ~ 400 billion stars, a large number of star clusters, nebulae and various types of interstellar gas and dust. Seen from the earth, the Milky Way is a silver ring around the sky. The total mass is about 265.438+000 billion times that of the sun [654.38+0], belonging to this galaxy group. The nearest extragalactic galaxy is Andromeda, which is 2.54 million light years away from the Milky Way.

The Milky Way is a oblate sphere with a huge disk structure, consisting of a bright and dense core, two main spiral arms and two unformed spiral arms, which are 4,500 light years apart. The sun is located on the arm of Orion, an arm of the Milky Way, and the distance to the center of the Milky Way is about 26,000 light years.

At the center of the Milky Way is a supermassive black hole (Sagittarius A), which consists of a silver core, a silver core, a silver disk, a silver halo and a silver crown from the inside out. Most of the central regions of the Milky Way are old stars (mainly white dwarfs [2]), and most of the peripheral regions are new young stars. There are more than a dozen satellite galaxies around hundreds of thousands of light years, of which large magellanic cloud and small magellanic cloud are the largest. The Milky Way keeps growing by slowly devouring dwarf galaxies around it. In March 20 15, scientists found that the size of the Milky Way is 50% larger than previously thought.

Chinese name

Galaxy system

Foreign name

Galactic System

shape

Elliptical disc

type

barred spiral galaxy

definition

The galaxy where the earth and the sun are located.

Applied discipline

Astronomy, astrophysics

diameter

10~ 12 million light years [1]

quality

4. 177 1× 10^4 1kg

Center thickness

65438+200,000 light years

span

65438+600,000 light years [3]

Applied discipline

Astronomy; The stars and the milky way

catalogue

1 overview of celestial bodies

2 celestial structure

3 structural research

? Discovery process

? Galaxy disk

? galactic center

? galactic halo

? Galactic corona

? solar system

? Galaxy wave

4 Galaxy Age

? Speculative method

? Speculation conclusion

Panorama of galaxy 5

? Major constellations

? All-sky 88 constellation

? Full map of galaxies

Six companion galaxies

? companion galaxy

? nubeculae

7 Origin and evolution

? Cosmic origin

? Mass reduction

Eight important events

? Observation partner

? Strange stars

? The birth of life

? cosmic expansion

? Real map

? Observation characteristics

9 study history

10 research chronology

1 1 background knowledge

? Travel through space

? fourth cosmic velocity

? Future situation

12 common data

13 Galaxy Panorama

14 galactic mass

Overview of celestial bodies

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The night sky in Shenzhen presents a clear picture of the Milky Way.

The Milky Way is the star system where the solar system is located, including150-400 billion stars, a large number of star clusters and nebulae, and various types of interstellar gas, interstellar dust and black holes. Its total visible mass is 2 1000 billion times that of the sun. [3]

Most 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 larger spherical area outside the silver disk, where there are few stars and low density, which is called "silver halo" with a diameter of 70 thousand light years.

In the past, the Milky Way was thought to be a spiral galaxy similar to Andromeda, but the latest research shows that the Milky Way should be a rod spiral galaxy.

90% of the matter in the Milky Way is stars. There are many kinds of stars. According to physical properties, chemical composition, spatial distribution and motion characteristics, stars can be divided into five star groups. 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. Gas and dust are unevenly distributed, and some of them gather into nebulae.

The Milky Way (10) is scattered in interstellar space. [4]

Since 1960s, a large number of interstellar molecules, such as carbon monoxide and water, have been discovered.

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 radiation, infrared radiation, X-ray radiation and gamma-ray radiation, and its properties are still unclear. There may be a giant black hole, whose mass is estimated to be 2.5 million times that of the sun.

sagittarius a

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 central region of the Milky Way should be a black hole, and predicted that if their hypothesis was correct, a small-scale radio emitting source could be observed in the central region of the Milky Way, and the nature of this radiation. Three years later, such a radiation source was discovered, which is Sagittarius A.

Sagittarius A is very small, only equivalent to the size of an ordinary star. The emitted radio emission intensity 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. As we all know, all the activities of star-level celestial bodies cannot explain the strange 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, of which about 1 000 billion stars, and the sun is a typical one. The Milky Way is a fairly large rod-like galaxy, which consists of three parts, including a silver disk with spiral arms, a silver center protruding from the center and a halo part.

The spiral galaxy M83 is very similar to our Milky Way in size and shape. Outside the silver disk is a sphere composed of sparse stars and interstellar matter, called halo, with a diameter of about 654.38+ million light years.

The Milky Way also rotates. The solar system rotates around the center of the Milky Way at a speed of 250 km/s, and the rotation period is about 220 million years. The Milky Way has two companion galaxies: large magellanic cloud and small magellanic cloud.

Astronomer Maria g.

Schematic diagram of the position of the sun in the galaxy

Mann believes that through the study of the disk of the galactic cluster, it shows that the inner cluster of the Milky Way is older, while the outer stars are younger. It can be inferred that the formation of the Milky Way started from the inside, and then gradually evolved to a diameter of more than 654.38+ million light years. Scientists said that the survey also found new evidence that the Milky Way also annexed many small galaxies during its growth, and celestial bodies from other galaxies also merged into the Milky Way. [4] Stephen Hawking once claimed that his observations showed that the center of the Milky Way was a huge black hole.

June 20 13, NASA released the clearest galaxy map, with 654.38+600 million pixels and a capacity of 457MB.

Celestial structure

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The main part of galactic matter consists of a thin disk called a silver disk. The approximately spherical part of the center of the silver disk is called the nuclear sphere, where the stars are highly concentrated. There is a small dense area in the center of the nuclear sphere, which is called the silver nucleus. Outside the silver disk is a larger, nearly spherical area, in which the density of matter is much lower than that in the silver disk, which is called silver halo. There is also a silver corona outside the silver halo, and its material distribution is also roughly spherical.

Observed galactic spiral arm structure

In 2005, the structure of the spiral arms of the Milky Way was observed. According to Hubble's classification, the Milky Way should be a huge rod-spinning galaxy SBc (loose-arm rod-spinning galaxy), with a total mass of 0.6 trillion to 3 trillion times that of the sun and about/kloc-0.00 billion stars.

Since 1980s, astronomers have always suspected that the Milky Way is a rod-shaped spiral galaxy rather than an ordinary spiral galaxy. In 2005, the Spitzer Space Telescope confirmed this suspicion, and also confirmed that the rod-like structure in the galactic core was larger than expected.

The disk diameter of the Milky Way is estimated to be 98,000 light years, and the distance from the sun to the center of the Milky Way is about 26,000 light years. The center of the disc protrudes outward.

The center of the Milky Way has a huge mass and a dense structure, so it is suspected that there are supermassive black holes in it, because many galaxies are considered to have supermassive black holes in their cores.

Like many typical galaxies, the speed of celestial bodies orbiting the center of the Milky Way is not determined by the distance from the center and the distribution of the mass of the Milky Way. After leaving the core bulge or at the periphery, the typical velocity of a star is between 2 10 and 240 km/s. So the period of these stars orbiting the Milky Way is only related to the length of their orbits. This is different from the solar system. Different distances have different orbital speeds.

The rod-like structure of the Milky Way is about 27,000 light years long and spans between the sun and the center of the Milky Way at an angle of 4410. Mainly composed of red stars, mostly elderly stars.

Each spiral arm of the inferred and observed spiral arm structure of galaxies is given a corresponding number (just like the spiral arms of all spiral galaxies), which can be divided into 100 segments. There are four main spiral arms originating from the core of the Milky Way, including:

Schematic diagram of galaxy cantilever

2 and 8-3000 parsec arms and Perseus spiral arms.

3 and 7- Rectangular spiral arms and cygnus spiral arms (extended by the recently discovered -6).

4 and 10- southern cross and shield arm.

5 and 9- Carina and Sagittarius.

There are also two small branches, including:

1 1- Orion spiral arms (including the sun and solar system-12).

The latest research found that the Milky Way may only have two main spiral arms-Sagittarius spiral arm and rectangular spiral arm, most of which are gas, and only a few stars are dotted among them.

The Gude Belt (this cluster) is a bright star cluster extending from one end of Orion's arm. Its main members are B2 ~ B5 stars, but there are also some O stars, diffuse nebulae and several star complexes. The nearest OB star association is Scorpio Centauri, which is about 400 light years away from the sun.

Basically

Galaxy system

On the outer side of the spiral arm is the outer ring or unicorn ring, which was proposed by astronomers Brian Yanni and Heidi Joe newberg. It is a ring of stars around the periphery of the Milky Way, including stars and gases produced by interaction with other galaxies billions of years ago.

The disk of the Milky Way is surrounded by a spherical silver halo with a diameter of 250,000 ~ 400,000 light years. Because the gas and dust on the disk will absorb electromagnetic waves of some wavelengths, the composition and structure of the silver halo are still unclear. The disk (especially the spiral arm) is the active area where stars are born, but the silver halo does not. The open clusters mainly appear on the disk.

It is generally believed that the stars in the Milky Way are mostly binary or multi-star. In 2006, it was found that two-thirds of the main sequence stars in the Milky Way are single stars. Most of the matter in the Milky Way is dark matter, and the dark silver halo is 0.6 trillion to 3 trillion solar masses, centered on the silver core.

The new discovery has increased our understanding of the structure and dimensions of galaxies, which is more than what was previously obtained from the disk of Andromeda galaxy (M3 1). The newly discovered evidence confirms that the outer ring extends from the spiral arm of Cygnus, which obviously supports the possibility that the silver plate extends outward. The discovery of Sagittarius dwarf ellipsoid galaxy and the debris in its orbit around the silver pole show that it was torn by the interaction with the galaxy. Similarly, the Canis Canis dwarf galaxy also makes debris surround the Milky Way on the disk because of its interaction with the Milky Way.

65438+200610.9, some people in mario juric and Princeton University announced that a huge cloud structure (spanning about 5000 full moons) was found in the sky in the northern hemisphere by Si Long's digital survey, but it doesn't seem to be suitable for all current galaxy models. He concentrated some stars on the vertical line perpendicular to the disk where the spiral arm is located, which may be explained by the merger of Pettigrew and the Milky Way. This structure is located in the direction of Virgo, about 30 thousand light years away from us, and is temporarily called Virgo Star Jet.

On May 9th, 2006, Daniel Zucker and Vasily Belokurov announced that two dwarf galaxies, Canis and Capricorn, had been discovered by Si Long's digital survey.

Structural research

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Discovery process

The English name of the Milky Way is "milky white" because it is a dim luminous belt across the night sky. The name "galaxy" is translated from Latin via lactea, and it comes from Greek γ α λ α ξ? α? κ? κλο? (galaxí as k？ Close, "nipple ring"). Galileo analyzed for the first time that the ring belt was composed of stars with a telescope in 16 10.

1785, F.W. Herschel was the first to study the structure of the Milky Way. He concluded by counting the stars that the distribution of the stars in the Milky Way is flat and the sun is located in the center of the disk.

19 18, H. shapley studied the spatial distribution of globular clusters and established a lenticular model of the Milky Way, in which the sun is not in the center.

In the 1920s, shapley model was recognized. However, the shapley model is not accurate because it does not include interstellar extinction. Traditionally, optical methods are used to study the structure of the Milky Way, but there are some limitations. The radio method and infrared technology developed in recent decades have become powerful tools to study the structure of the Milky Way. On the basis of shapley model, we have a deeper understanding of the structure of the Milky Way.

Galaxy disk

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 protruding nuclear sphere. The silver plate itself is only 2000 light years thick and nearly 1000 light years in diameter. Generally speaking, silver plates are very thin.

Except that the silver core in the range of 1 thousand parsec rotates around the silver core with a rigid axis, the other parts of the silver disk rotate around the silver core in a poor way, that is, the farther away from the silver core, the slower the rotation speed. 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 galaxy) in the 1940s, the main types of spiral arm celestial bodies were obtained, and then these kinds of celestial bodies were surveyed in the Milky Way, and three parallel spiral arms near the sun were found. 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.

The silver disk is mainly composed of star group I celestial bodies, such as G ~ K main sequence star, giant star, nova, planetary nebula, RR variable star in Lyra, long-period variable star, semi-regular variable star and so on.

galactic center

The center of the Milky Way, that is, the intersection of the axis of rotation of the Milky Way and the galactic plane. At the center of the galaxy, the prominent part is a bright sphere with a diameter of about 20,000 light years and a thickness of 6,543.8+0,000 light years. The region is composed of high-density stars, mainly red stars with an age of about 654.38+000 billion years. Evidence shows that there is a huge black hole in the central region, and the activity of galactic nuclei is very intense.

The orbits of several stars around Sagittarius A.

The center of the Milky Way is in the direction of Sagittarius, and the coordinates of 1950 are: right ascension17 42' 29 "and declination-28 59'18".

Besides being a geometric point, the galactic center also means the central region of the Milky Way. The sun is about10,000 parsec from Yin Xin and 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 silver center in the band of 2 microns to 73 cm through interstellar dust. The observation of neutral hydrogen spectrum at 2 1 cm reveals that there is a hydrogen flow expansion arm, the so-called "3000 parsec arm", at a distance of 4000 parsec from Yin Xin (at first, the distance was wrongly set at 3000 parsec, and later it was revised to 4000 parsec, but the old name is still used). About 1 10 million neutral hydrogens with solar mass rushed to the solar system at a speed of 53km/ s, and on the other side of the silver nucleus, there was a neutral hydrogen expansion arm with roughly the same mass, which left the silver nucleus at a speed of 135km/ s, and they should have arrived at10000 to/kloc-0. 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/s, and 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 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 ten astronomical units, 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. There is a huge dense nucleus in the center of the Milky Way, which may be a black hole. Relativistic electrons flowing into the compact core accretion disk are accelerated in a strong magnetic field, resulting in synchrotron radiation.

The latest observation of the center of the Milky Way shows that the core of the Milky Way is basically composed of white dwarfs, the number of which is at least 654.38+ million. The core of harmony consists of about 70 large white dwarfs. As for how to observe more contents, scientists say that this needs to be done by the next generation of observation equipment, such as the james webb Telescope being built by NASA. [2]

galactic 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 65,438+000 kiloparsec or 320,000 light years from the silver center.

Typical globular clusters: M 13 globular clusters