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Large scale structure of the universe

The distribution characteristics of mass and light in the observable universe

synonym Large-scale structure (Large scale structure) generally refers to the large-scale structure of the universe

Large scale structure of the universe, definition: distribution and motion characteristics of celestial bodies on a larger scale than galaxy clusters^[2] 。

Large scale structure Physical cosmology The middle refers to the distribution characteristics of the mass and light of the observable universe in a large range (the typical scale is one billion light years). The survey of the sky and the investigation and description of various electromagnetic wave radiation wavelengths, especially 21 cm radiation, have obtained many contents and characteristics of the cosmic structure. The structure of the organization seems to follow the hierarchical model to Supercluster (supercluster) and fibrous structures (Cosmic Filaments) are at the top level. No matter how big they are, there seems to be no continuous structure, which means "Great" (end of greatness) phenomenon.

Chinese name: Large scale structure of the universe
Foreign name: large scale structure of the universe^[2]
application area: astronomy

Definition: In physical cosmology, the distribution of mass and light in the observable universe over a wide range
Related disciplines: Astronomy_Galaxies and the Universe^[2]

catalog

one Discipline background
two Cosmic web
three Giant walls, fibrous structures and cavities

eight Endless knowledge

Discipline background

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There is a huge structure formed by countless galaxies in the universe, which is the large-scale structure of the universe.

The large-scale structure of the universe is like countless bubbles closely overlapping. The "membrane" of bubbles is composed of several galaxies, which can be divided into fiber (elongated structure), sheet (flat structure), etc. according to their shapes. Astronomers call the particularly huge structure "great wall". The bubble is empty with almost no galactic matter inside, which is called "void". The part overlapping the adjacent bubbles is densely distributed with a large number of galaxies, and such galaxy clusters are called Galaxy Clusters. Several galaxy clusters together form a supercluster, and several supercluster clusters together form a supercluster compete.

The solar system we live in is located in the Milky Way, which is about 100000 light years in diameter. The diameter of a typical bubble structure is about 100 million light years, which is 1000 times the diameter of the Milky Way. By 2022, although only a few galaxies "the Great Wall" have been discovered, some of them are up to 1 billion light years in diameter. The bubble structure is connected and continuous, and the huge galaxy is just a small point in it.

The bubble structure formed by galaxy aggregation will accumulate in various modes, and there will also be bubble structure in the deep of the "giant hole", and a small number of galaxies will be distributed. It can be said that the large-scale structure is like a sponge, which is full of many holes, large and small.

How is large-scale structure formed? The research believes that the universe at the beginning of its birth is like a fireball, full of hot gas, without stars and galaxies, and its material distribution is very uniform. About 370000 years after its birth, the density of matter in the universe only fluctuates by 0.01%.

This tiny density difference in the early universe has become the "seed" of large-scale structure. As time goes on, the density difference in the universe becomes larger and larger, finally forming galaxies and large-scale structures.

So, how did this density fluctuation of early cosmic matter come into being? Scientists believe that inflation theory is the best answer to this question: the universe was empty at the beginning of its birth, but it was full of huge energy. These energies caused the universe to expand violently in a very short time. In the process of the expansion of the universe, there were extremely small energy differences in some places. After inflation, matter is formed based on energy, so there are extremely small fluctuations in the density of matter^[2] 。

Cosmic web

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The results of galaxy surveys show that our universe seems to show a "bubble network" structure. Almost all galaxies are distributed on narrow "fiber belts", and in the middle of them are huge holes, which are called“ Giant cave ”。 These huge holes are huge in size. Some of them have a diameter of 300 million light years, and almost nothing is in them. But this is not true, because although it seems that there is nothing there, in fact there are many dark substance 。

Giant walls, fibrous structures and cavities

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The organizational dispute over the structure began fixed star Although most of the Cosmologist Seldom in Astrophysics To study this scale. Stars are Galaxy The inner organization and the galaxy are organized into Galaxy cluster And be huge empty Compartmentalized Supercluster 。 Before 1989, the general assumption was that Dexterous Galaxy clusters are the largest structures that exist, and universe The distribution in all directions is more or less uniform. However, based on red shift According to the observed data, Margaret Geller and John Huchra Found in 1989 the Great Wall , 500 million long composed of galaxies Light year The structure is 200 million light years wide and 15 million light years thick. The existence of this structure jumps out of the long-term cognition, because it requires the position of the galaxy in the three spatial dimensions, so it is necessary to add the galaxy distance data from the redshift. In 2003, another large-scale structure - Sloan Great Wall It was also found. However, technically, it is not considered as a structure, because they are not related to each other in gravity, but are all there in the measured distance. One of the largest holes in space is the hole in Capricorn, which is estimated to be 230 million light years in diameter.

In August 2007, a possible supercavity Eridana He was found with WMAP cold spot - a cold region in the microwave sky - consistent, but extremely impossible under the current preferred cosmological model. The cold spots caused by this super hole are beyond imagination and may span a billion light years.

Further study of the universe shows that huge holes like bubbles separate sheet structures and Galactic fibre , and Supercluster It is like a dense node that occasionally appears relatively. This network structure Red shift survey of galaxies in a 2-d field of view It can be clearly seen. The structure of the three-dimensional space map on the inner side of the sky survey shows that the nearby universe shows an impressive structure. Several superclusters show Sloan Great Wall , the largest structure of the universe known so far.

Great

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Great (End of Greatness) is a scale found in observation, roughly 100 million second difference (300 million Light year ）, on this scale universe Block, according to Cosmological principle Roughly Homogeneous And Isotropy Of. Supercluster and Galactic fibre It is obviously evenly distributed in visible areas, but it is Arbitrary 。 Until the 1990s, Redshift Sky Survey The structure of this scale was completely observed only after the survey was completed.

observation

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Another evidence of large-scale structure is Lyman-alpha forest （Lyman alpha forest）。 This is a quasar A group of absorption lines in the spectrum, which is interpreted as many thin but huge gas materials (almost all of them are hydrogen These plates seem to be related to the formation of new star systems.

We must be very careful when describing the structure of the universe, because the facts are not all as they appear. Light distorted by gravity The picture presented by (gravity lens) looks different from the direction of their real source, because the foreground objects (such as galaxies) bend their own space (like General relativity And thus deflects the light passing nearby. Very useful, powerful gravity lenses can sometimes magnify distant galaxies, making them easier to detect; but Weak lens The interference (gravity shear) is very common and subtle, which has changed the observed large-scale structure of the universe. In 2004, the observation of this subtle shear showed that it is worth being a constraint for the test of the universe model.

The large-scale structure of the universe looks different from galaxies that only use redshift to measure distance. For example, the galaxy behind the cluster will be attracted towards it, and will fall towards the cluster, so there is a slight blue shift (compared with the situation without cluster); There will be slight redshift on the side close to. So if only redshift is used to measure distance, the environment of galaxy clusters will appear to be compressed a little. The relative effect will act on the galaxies inside the cluster: the galaxies in the cluster have some irregular movements, and when these irregular movements are converted into redshifts, the cluster looks elongated. This creates the so-called God's finger The illusion that the long chains of galaxies point to the Earth.

Adjacent galaxy

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Adjacent galaxy image

"The panoramic image of the whole near-infrared sky reveals the distribution of galaxies outside the Milky Way. This image is made by 2 micron all day sky survey There are more than 1.5 million galaxies in the diffuse source catalog (XSC), and star points in nearly 50 million galaxies (Galaxy, abbreviated as 湦) derived from the point source catalog (PSC). The color of the galaxy is based on UGC Directory 、 Harvard Center for Astrophysics 、 Tully NBGC、LCRS、 2dFGRS , 6dFGS and SDSS Obtained from patrolling the sky red shift (Various values are passed through NASA / IPAC Of NASA extragalactic database Consolidation), or from K-band (2.2 μ m) given after photoelectric photometry derivation. Blue is the closest (z ＜ 0.01), green is at the ordinary distance (0.01 ＜ z ＜ 0.04), and red is 2MASS The one with the farthest resolution distance (0.04 ＜ z ＜ 0.1). This map is a map of the Milky Way's coordinate system, which is drawn with the same area Aitoff projection method with the Milky Way as the center. "

stay Serpentine supercluster At the center of the Giant source The abnormal gravity of is affecting the movement of galaxies within hundreds of millions of light years. The redshifts of these galaxies are consistent Hubble's law , which means that they and we are regressing each other, but they are red shift The change on the sufficiently shows that there is a mass equivalent to tens of thousands of galaxies concentrated there.

Juyinyuan was discovered in 1986 hydra and Sagittarius In the direction of, the distance is between 150 million and 250 million light years (250 million Light year Is the latest estimate). A large number of old galaxies can be observed near that direction. Many galaxies collide with neighboring galaxies and/or emit a lot of radio waves.

Model

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In an attempt to establish Large-scale structure On the model of, Cosmology There is still much work to be done. use Big bang It is expected that the model and assumption of the type of matter that builds the universe should be able to predict the distribution of matter, and compare with the observation work to see whether it supports or refutes different cosmological theories. Observations indicate that most universes must contain Cold dark matter , Assumption Hot dark matter or Baryon dark matter The model of is not consistent with the observation. Cosmic microwave background radiation And high red shift Supernova Similarly, these models are comprehensively suppressed, and these methods also give us more opportunities to live Accelerating universe Discuss the evidence.

Endless knowledge

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According to many years of exploration, what human beings can observe（ Extragalactic galaxy ）Probably 100~200 billion^[1] 。 only andromeda The Milky Way contains nearly 1 trillion planets. So the stars to the Milky Way are just a drop in the ocean. There are many stars in the universe, just like the sand grains on the river beach, which can't be counted. So it is no exaggeration to say that the universe is boundless.

On the mystery of cosmic scale, German philosopher Kant put forward the famous“ Space-time paradox ”, emphasizing that there must be contradictions in people's understanding of the finite and infinite universe. In 1917, Einstein proposed that Cosmic model He proposed that "the universe should be regarded as a closed continuous area with limited spatial scale". On the premise of uniform distribution of cosmic matter, a four-dimensional continuum of "boundless and limited" and "limited and closed" is built mathematically. That is, the universe is a closed "cosmic ball". According to this view, the light emitted from any point in the universe will return to its starting point in 10 billion years along the space-time surface. Such a wonderful theory cannot be fully understood. Spatiotemporal curvature Is it positive or negative? Or zero (Ehrlich himself tends to agree with the existence of positive curvature)? People can't answer for sure. However, when an American scientist used an electronic computer to process and observe the cosmic light, he did see the light emitted by a galaxy in the form of a light circle, which undoubtedly supported and verified Einstein's "cosmic sphere" theory. Finally, there is still time to explore the cosmic scale and other issues. But it can be said that the understanding of the universe is endless.

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