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a quasar, astronomy The noun, Active galactic nucleus, is one of the brightest and most active objects in the universe^[11] 。 The name comes from a pair of similar fixed star The abbreviation of celestial body, also known as quasi-stellar , Kuisa or Quasar radio source , and Pulsar 、 Microwave background radiation and Interstellar molecules Together, they were called the "four major discoveries" of astronomy in the 1960s.

As one of the brightest objects in the universe, active galactic nuclei (AGNs) have attracted a lot of attention from researchers since their discovery. Bright AGNs can easily be distinguished from ordinary quiet galaxies by their brightness alone. These high luminosity AGNs are still easy to observe even in the distant universe, while the radiation of the host galaxy is usually submerged in the light of AGN and is difficult to study. The image of such active galaxies is dominated by star shape and point spread function (PSF) characteristics, so they are also called quasars.^[11]

Quasars are very distant objects observed by human beings. High redshift quasars can reach more than 10 billion light years from the Earth. Quasars are a kind of high luminosity objects measured at an extremely remote distance, and more than 80% of quasars are radio quiet. Quasars are much smaller than galaxies, but the energy released by quasars is more than a thousand times that of galaxies. The extraordinary brightness of quasars makes their light energy reach 10 billion Light year It is observed at a distance beyond.

It is estimated that there were more quasars 10 billion years ago.

Chinese name: a quasar
Foreign name: quasar
Alias: quasi-stellar 、 Kuisa 、 Quasar radio source

Discovery time: 1960
Field: astronomy
Brief description: Active galactic nucleus

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Discovery history

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In 1960, American astronomer Alan Sandwich Use a 5-meter caliber Optical telescope eureka Cambridge Radio Power Samsung Meter Upper 48th celestial body (3C 48) Optical counterpart 。 He found that 3C 48 spectrum In the middle, there are some wide and bright emission lines in a strange position. Later, people Cambridge Third Radio Astrolabe Middle (3C) radio waves The following discoveries have been made continuously:

① Their optical volume is very small (optical diameter<1 "), and fixed star It's hard to distinguish: from the pictures taken by the 5m telescope of the Palo Alto Observatory, it is just a light spot like the stars.

② They have extremely bright (unusually bright) surfaces: visible light And radio wave band have this characteristic.

Atomic hydrogen spectroscopy

④ Their spectra are Continuous spectrum And strong Emission line 。

In 1962/63, M. Schmidt measured this and those known Radio galaxy spectrum Same.

In fact, the measured spectrum mainly consists of three parts: synchrotron radiation Non thermal continuous spectrum caused; accretion The action causes extremely bright emission spectral lines; Interstellar medium Caused by the absorption spectrum. Their spectra are huge Red shift Quantity (displacement index Z=△ λ/λ）。 Therefore, by Hubble's law By inference, they are extremely far away Blue galaxy The absolute brightness of visible light is 100 times higher than that of normal galaxies, and the radio wave intensity is comparable to that of CygA galaxy.

The exploration at this stage will be crowned with quasar (or quasar radio source).

In 1963, Dutch born American astronomer Martin Schmidt found that 3C 273 There is a phenomenon similar to 3C 48 in the spectrum of hydrogen The emission lines of red shift , making it difficult to identify spectral lines. Following the clue of red shift, we analyzed the spectrum of 3C 48 and found that its red shift was even greater.

The huge energy of quasars

If we assume that the redshift is caused by the expansion effect of the space, then 3C 273 and 3C 48 have great Retrogression speed , respectively light speed 1/6 and 1/3 of. Astronomers have named these celestial bodies, which look like stars in optical photos, but whose essence is quite different Quasar radio source 。 As observed in optical telescopes, quasars are different from ordinary fixed star It seems that there is no difference.

In 1965, A. Sandage discovered many quasars, whose optical properties are the same as those of quasar radio sources; All have compact structure, extremely bright surface and blue color; But they do not radiate radio waves (perhaps too weak to be detected). They are also very similar to stars in shape, and also have a large red shift, but there is no radio radiation. They are called radio quiet quasars^[1] 。

Therefore, they can be divided into two categories:

QSR's: QSR's can be measured by optical and radio bands, which is relatively rare, accounting for 1/20 of the total number of quasars.

QSO's (or radio quiet quasar): the radio wave is weak and can only be measured optically.

Quasars represent the same kind of celestial bodies , but the radiation intensity of some radio waves is different; Scientists believe that quasars with strong radio radiation may be the product of a short period of "high fever" in a quasar's "life". Therefore, it can be called quasars or quasar objects; If necessary, pay attention to whether it radiates radio waves. Thousands of quasars have been found in the sky search in the visible and radio wave bands; For example, M.P. Veron CETY and P. Veron (1989) Catalogue There are 4170 quasars in the catalog, A There are 3570 quasars with redshift data in the catalogue of Hewit and G. Burbidge (1987).

On November 8, 2011, with the help of Hubble Space Telescope , astronomers first photographed black hole Discoid structure exists.^[2]

In January 2013, according to the data from Sloan Digital Sky Survey Project, an international team of astronomers found a record quasar cluster structure, which extends more than 4 billion Light year 。 Quasars are young active galaxies. The first author of the study, University of Central Lancashire Astronomer Roger Clowes said: "This discovery is a surprise to a large extent, because it really breaks through the scale of the largest structure in the universe that we know." In contrast, the diameter of our Milky Way is only hundreds of thousands of light years, and the upper structure of the Milky Way is virgo cluster Its extension is only hundreds of millions of light years.

On March 3, 2015, a research team led by Chinese astronomers found a super bright quasar 12.8 billion light years away from the Earth, 430 trillion times the solar luminosity, and the mass of the central black hole is about 12 billion solar masses. This is the most luminous quasar with the largest mass of the central black hole in the distant universe that has been observed.^[3]

In May 2015, according to foreign media reports Hawaii Of Keck Observatory Astronomers at the Max Planck Institute for Astronomy discovered the scene of four quasars gathering for the first time. These four active black holes are very close to each other. The research team was led by astronomer Joseph Hennawi. It is reported that these four quasars are located in a super massive structure in the remote space, and a huge cooling dense gas is surrounding them Nebula 。 Since the probability of this phenomenon is only one in ten million, cosmologists may need to reconsider the evolution model of quasars and the formation of super mass structures. Relevant research results were published in the《 science 》(Science) magazine.^[4]

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Dust surrounded quasars are found

The term "quasar" derives from the abbreviation of quasi stellar [star like] radio source. In 1964, Qiu Hongyi, a Chinese astrophysicist, published a review on Physics Today, which shortened quasi stellar [star like] radio source to quasar for the first time.^[12]

The discovery of quasars, and Cosmic microwave background radiation 、 Pulsar 、 Interstellar molecule They were listed as the four major discoveries of astronomy in the 1960s.

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The bright light of quasars

Quasars are a special kind of celestial bodies discovered in 1960^[12] 。 They are named because they look like "star like objects", but actually they are distant objects with huge energy outside the Milky Way. Their center is a super mass that devours surrounding materials violently and has a mass of more than 10 million solar masses black hole 。 Although these black holes do not emit light themselves, due to their strong gravity, the surrounding matter releases huge energy in the process of rapidly falling to the black hole in a manner similar to "friction heat generation", making quasars the most dazzling objects in the universe. Astronomers have found more than 200000 quasars through large-scale sky surveys, but only 40 of them are more than 12.7 billion light-years away.^[5]

The remarkable feature of quasars is that red shift , indicating that it is moving away from the earth at a fast speed. Quasars are far from the earth, about 10 billion Light year In addition, it may be the most distant object discovered at present. Astronomers can see quasars because they are light , radio waves or X ray It emits huge energy.^[1]

① Quasars have stellar like images on photographic negatives, which means that their Angular diameter Less than 1 ″. Very few quasars have weak nebular envelope, such as 3C48. Some quasars have Jet Shape structure.

a quasar

② There are many strong and wide emission lines in the spectrum of quasars, including allowable and forbidden lines. The most common is the spectral line of hydrogen, oxygen, carbon, magnesium and other elements. The helium line is very weak or does not appear, which can only be explained by the low abundance of helium. It is generally believed that the emission lines of quasars are generated from a gas envelope, and the process of generation is similar to that of general Gas nebula similar. The wide emission line of quasars indicates that there must be violent turbulent motion in the gas envelope. Some quasars have very sharp absorption lines in their spectra, which means that the turbulence velocity in the area where the absorption lines are generated is very small.

③ Quasars emit strong ultraviolet radiation, so the color appears very blue. The energy distribution of the continuous spectrum in the optical band is in the form of a power law spectrum, which is the radiation intensity, and v is the frequency, α Is the spectral index, which is often greater than zero. Optical radiation It is polarized and has Nonthermal radiation Properties (see thermal radiation and non thermal radiation). In addition, quasar infrared radiation Also very strong.

④ The quasar radio source emits strong non heat Radio radiation 。 Most of the radio structures are of dual source type, a few of them are of complex structure, and a few are of compact single source, whose angular diameter is less than 0 ″. 001, which has not been distinguished up to now. The position of the compact source usually coincides with the optical source. Spectral index of radio radiation α The average is 0.75. General, α> 0.4; α< 0.4. Steep spectrum Radio source Most are dual sources; Most of the flat spectrum radio sources are compact single sources, and their centimeter band radiation is particularly strong.

⑤ Quasars generally have light changes, and the time scale is several years. The light of a few quasars changes violently, and the time scale is several months or days. From the light variable time scale, we can estimate the size of the area where the quasar emits optical radiation (from several light days to several light years). The radio radiation of quasar radio sources also changes frequently. It was also found that the two sub sources of several double source type stellar radio sources separated outward at a very high speed. The changes of optical radiation and radio radiation are not periodic.

⑥ The emission lines of quasars have a large red shift. The maximum redshift observed so far is 3.53 (OQ 172). For quasars with absorption lines, the red shift z absorption of absorption lines is generally smaller than that of emission lines. Some quasars have several groups of absorption lines corresponding to different redshifts, called Multiple redshift 。 For example, the emission line red shift of quasar PHL 957 is 2.69, and the absorption line red shift has five groups: 2.67, 2.55, 2.54, 2.31, 2.23.

⑦ Observations show that some quasars also emit X-ray Radiation.

Historical Studies

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Research measurement

The most recent quasar - 3C273 (discovered by M. Schmidt):

The apparent magnitude mv=12.8 (the rest are darker than 16), and the redshift z=0.158 (equivalent to 950 Mpc., which is about 290 million light-years away).

The brightest quasar - S50014+81:

Absolute magnitude Mv=- 33, etc. (mv=16.5); The value of z is 3.14.

The quasar with the maximum redshift index (equivalent to the farthest) - PKS2000-300:

mv=19，z=3.78

However, after 1986, more and more quasars with larger redshifts were found, about 30 of which had z values greater than 4; The most recent report (1990) indicates that the z value of PC1247+3406 is 4.90. It is worth mentioning that the number of quasars seems to be bounded by Z=2; The number of quasars with redshift less than 2 increases with the increase of z value, while the distribution trend is opposite for those with redshift greater than 2, and the number of quasars with larger z value is smaller.

The first discovery of giant quasars Redshift phenomenon M Schmidt had an insight when analyzing 3c 273 spectrum; He felt that the relative arrangement order of those strong emission spectral lines was the same as hydrogen atom Several spectral lines of the spectrum are very similar; The difference is that the whole spectrum moves a large part towards the red end (long wave).

The redshift of a quasar is so huge that its distance cannot be determined simply by Hubble's law (the distance d is proportional to the value of z); It must be explained by the universe model based on general relativity.

Research progress

The farthest known quasar is about 15 billion light years. In 2001, NASA（ NASA ）The scientists of.

In 2003, Israel TEL AVIV University and Harvard University The scientists of Dark matter halo Evidence. [2]

In 2006, European scientists said they had discovered mysterious and rare "orphan" quasars.

In 2007, scientists found the very rare quasar triplets for the first time.

In 2008, scientists found that rare X-ray The quasar of.

For scientists in 2011 hubble space telescope The veil of a mysterious celestial body has been unveiled. In 2007, a German biology teacher found a mysterious green celestial body in the night sky, which is about 650 million light years away from the Earth Hanni 。 It turns out that this is a dead quasar.

Hanny's Voorwerp (Voorwerp means "object" in Dutch) is one of the most mysterious celestial bodies in the universe. But on January 10, 2011 American Astronomical Society Opened at the 217th meeting Hubble Space Telescope The fine photos and X-ray observation data finally revealed the mystery of Hanni Celestial Body. By many ground and Space telescope The original image taken shows that Hanni is a huge hot gas. Astronomers speculate that the light emitted by the Hani object comes from the radiation of an adjacent galaxy named IC2497.

Scientists believe that there is a huge black hole in the core of IC2497, which once swallowed up various gases and stars, and released two opposite streams of hot gas and high-energy radiation. Such active galaxies are also called quasars. When the radiation from quasars hits the gas cloud, it will excite oxygen atoms, making the gas cloud emit green light.

Yale University Kevin Schawinski, an astronomer of, found that this quasar is no longer active after X-ray observation, which may be because the black hole in its center has no "food" to eat. But scientists believe that this quasar died soon, because the Hani object is still glowing. Considering that the light of IC2497 will take tens of thousands of years to arrive Hanni Therefore, astronomers speculate that quasars should have died out less than 200000 years ago. This also means that it goes out much faster than scientists think.

The latest images observed by the Hubble Space Telescope in April 2010 also confirmed the hypothesis of death quasars. It is worth mentioning that the observation found that there are some young star clusters in the Hani object, some of which are not more than 1 million years old.

Research explanation

Quasar Absolute magnitude Mv is between - 25 and - 33 (from Hubble constant Ho=50km/s · Mpc), which can infer that its luminosity is between 1012 - 1014L ⊙ (about 4 * 1038 - 1041W), which means that quasars are the brightest objects in the universe; They are extremely bright nuclei and Seyfert galaxies The continuation of intense activity in galaxies N, N, and radio waves. The outlines of these galaxies are only recognized in the optical image of the recent quasar 3C273, showing fuzzy, expanding, cloud like spots; Usually, the galaxy is obscured by the light of a much brighter core, which shows the phenomenon of quasars. Only with extremely sensitive CCD Detectors and modern image expansion technology, which makes it possible to detect quasars with z ≤ 0.5 and their related galaxies (because the smaller the z value, the closer the quasars are, which is related to them Parent galaxy Not too dark). The absolute magnitude of the galaxy after subtracting the quasar luminosity is between - 21 and 23 degrees, which is 40-150 kpc in diameter Elliptical galaxy or spiral galaxy 。 The observation results suggest that quasars with strong radio radiation may belong to elliptical galaxies, while quasars without radio radiation may belong to vortex galaxies.

In addition, in some quasars, there is separation between their discrete sub radio sources relative velocity Faster than the speed of light Superluminal motion Phenomenon. For example, 3C273; From 1977 to 1980, the observation results of the giant antenna array (VLA) in the radio wave band with a wavelength of 2.8 cm showed that the separation speed between the two discrete radio wave sources was up to 11 times the speed of light.

Although the speed of light is an object Movement speed The limit of energy transfer Speed limit; But this seemingly incredible phenomenon of superluminal speed may be caused visually. For example, when a searchlight is shot into the sky at night a bank of clouds The sky will show bright spots; When the searchlight on the ground rotates slowly, the bright spot in the sky moves at an extremely fast speed. If the clouds are high enough, the speed of bright spots can even exceed the speed of light. This model is used to explain the phenomenon in the quasar, and it is believed that the two opposite directions are ejected from the central parent body of the quasar Particle Flow (equivalent to the light of a searchlight), which shines on the interstellar medium (equivalent to clouds in the sky), thus arousing radio wave radiation (equivalent to bright spots); Therefore, as long as the central matrix has a small swing, the radiation area aroused by the particle flow irradiation will move rapidly; In this way, it is highly possible that the speed of the two radiation regions is faster than the speed of light.

The Mystery of Redshift

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Gravitational lens and quasars

Synchronize by Electron radiation The principle infers that the mass of the black hole in the quasar -- 10 ^ 8M ⊙, all radiant energy (luminosity) -- 10 ^ 39W ≈ 10 ^ 13L ⊙. according to relativity E=m · c2, its life is estimated to be about 10 ^ 8 years. The calculation of such a huge energy has led some astronomers to question whether the basis for determining distance is Hubble redshift Relationship?

It is generally believed that there are three possibilities represented by redshift:

Hubble redshift

Farther Galaxy redshift The greater the effect; Quasars are the farthest galaxies discovered so far, and they may represent the edge of the universe or the earliest universe.

Gravitational redshift

It is observed from a place far away from the strong gravitational field, and the spectral line will move to the direction of long wave; But the required gravitational field is huge (about 100 million Solar mass And the spectral pattern is not consistent with that of quasars.

Local redshift

It is believed that it may be a local phenomenon caused by the high-speed ejection of matter from some galaxies (the same as the superluminal principle of the above line of sight); The supporting evidence is that many galaxies and quasars often appear in pairs or groups, and their redshifts are quite different. The objection is that there are also many groups of cooperative quasars cluster They have the same redshift as their parent galaxies.

Among them, the evidence supporting Hubble's redshift theory is the most powerful.

Look for low redshift quasars with redshifts similar to galaxies:

With z ≤ 0.5 as the range, we found many quasars related to elliptical or spiral galaxies with similar redshifts; High redshift galaxies are too dark to be detected, so this method is not applicable.

Evidence for twin quasars:

In 1979, D. Walsh, R.F. Carswell and R.J. Weymann were surprised to find that quasars are not only very close (5.7 "), but also have a magnitude of 17, a z value of 1.41, and even the same spectrum. It is doubtful that they are the same celestial body, but are only Gravity lens Affects the deflection of light rays to form a double image. Later, a blurry cloud was found next to quasar B. The measurement results showed that it was an intermediate galaxy (between the Earth and such a star) that caused the optical double image effect z=0.39. This discovery is of great significance, which not only confirms Einstein The prediction of gravity lens in general relativity also proves that stars with large redshift (z=1.41) support the Hubble redshift theory after galaxies with small redshift (z=0.39).

Light variation caused by gravity lens:

When Intermediary star When the system rotates, the luminosity of quasars behind it changes due to gravity; Theoretically observable light change time and image of quasars Spatial angle , to calculate the quasar distance, and then to verify whether the distance calculated by Hubble redshift is correct. Unfortunately, there are always countless substances between quasars and the earth, causing multiple effects of gravity, which is not easy to be measured by this method, and further improvement of observation technology is needed in the future.

Absorber support:

The z values of the absorption and emission lines in quasars are different, generally Zabs ≤ Z; If the z value of the emission line represents the position (distance) of the quasar, the Zabs of its absorption line is caused by the absorption of many interstellar materials between the quasar and the Earth (as shown in Figure 1, L α Forest area, L α The line is absorbed by substances at different distances, resulting in multiple redshifts). When (Z Zabs)/Z ≥ 0.01, it means that it is caused by holes outside many galaxies between quasars and the Earth.

In addition, the absorption line system of low redshift galaxies (and quasars) is found in the absorption line of high redshift quasars, while the absorption line of high redshift quasars is not found in the absorption line of low redshift galaxies, which indicates that the high redshift stars are indeed behind the low redshift galaxies (quasars). In addition, a strange thing very similar to quasars was discovered in 1929 and named BL Scorpio Celestial bodies; It is characterized by almost no features. The photometric change is irregular, only continuous spectrum, and its spectral line cannot be measured (may be too weak). Therefore, it is difficult to determine its distance. Its non thermal continuous spectrum is steeper in visible light than that of quasars. About 100 have been found.

What kind of objects are quasars? Its appearance is like a star, its spectrum is like Seyfert galaxy, and its radio wave nature is like radio wave galaxy? At present, it is believed that it is the predecessor of the first "galaxy" formed in the universe after the big bang. But undoubtedly, it is a very active celestial body; If cosmological redshift The theory is really right, that kind of stars will play a very important role in the universe; It represents the farthest and oldest universe. Therefore, it can reflect the evolution of the whole universe from the side. Because of its high brightness and mysterious absorption line, it is also used to study the universe Intermediary substances The best weapon (between the earth and the edge of the universe).

Theoretical hypothesis

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Construction principle

When a galaxy with a galactic nucleus runs at super high speed in the universe, when it catches up with another galaxy with a galactic nucleus, if the speed of the two is similar, they will devour each other and form a larger galaxy. If the galactic nuclei of these two galaxies meet, they will circle each other to form a faster rotating galactic nucleus with greater mass. The high-speed rotating galactic nucleus is like a huge generator, which bursts out powerful particles from its poles and ejects them into the distance.

Galactic nucleus The greater the energy, the greater the flow of the jet particle flow, and the farther the jet will be. Quasars are ejecting High-energy particle When flowing, it will consume its own energy. However, when it captures other star clusters or galaxies, it will add energy. In the process of super high speed running in the universe, quasars devour all the objects they encounter. Quasars are the brightest objects in the universe.

Define Hypothesis

In the more than 20 years after the discovery of quasars, people have put forward various models to try to explain the energy problem of quasars. The representative ones are as follows:

Black hole hypothesis: At the center of the quasar is a huge black hole, which constantly consumes the surrounding material and radiates energy.

White hole hypothesis: Like black holes, white holes are also a class of celestial bodies predicted by general relativity. Contrary to the fact that black holes constantly devour matter, white holes continuously radiate energy and matter.

The antimatter hypothesis: It is believed that the energy of quasars comes from the annihilation of matter and antimatter in the universe.

Giant pulsar hypothesis: Think quasars are huge Pulsar The kink of the magnetic field lines causes the eruption of energy.

Proximity Celestial Hypothesis: It is believed that quasars are not at the edge of the universe, but Galaxy The huge redshift of the objects moving outward at high speed is caused by the Doppler effect of the relative motion with the earth.

Hypothesis of supernova chain explosion It is believed that at the beginning, stars in the universe were of high mass and short-lived type, so supernovae were very common Galactic nucleus The density of stars in this region is extremely high, so there are Supernova explosion 。

Stellar collision explosion It is believed that in the early days when the universe was small, the density of galactic nuclei was very high, so star collisions and explosions often occurred.

Active galactic nucleus theory

Quasars are strange objects with extremely high luminosity and far distance.

More and more evidence shows that quasars are actually a class Active galactic nucleus (AGN)。 However, a widely accepted model of active galactic nuclei believes that there is a Supermassive black hole ，

Under the strong gravitational force of the black hole, nearby dust, gas and some stellar matter surround the black hole, forming a huge rotating Accretion disk 。 At the inner side of the accretion disk near the event horizon of the black hole, matter falls into the black hole, accompanied by huge energy radiation, forming a matter jet. The strong magnetic field restricts the jet of these substances, so that they can only eject at high speed along the direction of the magnetic axis, usually perpendicular to the plane of the accretion disk. If these jets are at an angle to the observer, quasars can be observed.

Just when the problem of galaxy redshift became so serious, the redshift of quasars appeared in the 1960s, which made the problem more complicated. According to the research on the physical properties of quasars. It is certain that quasars are extragalactic objects. It belongs to the level of galaxies. In that case, can their redshifts also be interpreted as retrogression and meet Hubble's law, as normal galaxies do? It is difficult to verify this directly, because it is still impossible to calculate the distance of quasars. The statistics of quasars show that their distribution is irregular on the redshift apparent magnitude diagram. What is the reason?

Most astronomers insist that the redshift of quasars is the cosmic redshift, that is, redshift reflects retrogression, and there is a Hubble relationship 。 The evidence is that the physical properties of quasars and some Active galaxy Similarly, active galaxies have been shown to satisfy Hubble's law. In addition, it has been found that several quasars are close to a base cluster or within a galaxy cluster, and the redshifts of quasars and galaxy clusters are approximately equal. It is also found that some quasars are very close to some galaxies, and the redshifts of quasars and galaxies are roughly the same. They believe that the reason why quasars disperse on the redshift apparent magnitude diagram is that the absolute magnitude dispersion of quasars is too large, rather than that Hubble's law is not tenable.

A few astronomers believe that Quasar redshift Not cosmological. The sampling statistical study of some quasars and bright galaxies shows that some galaxies that are associated with each other (that is, linked together) or the redshifts of associated galaxies and quasars are completely different or very different from each other. In addition, it is found that in the spectra of some quasars, the redshifts of their absorption lines and emission lines are different from each other, and different absorption lines also have different redshifts, that is, multiple redshifts. However, the different redshifts of the associated objects and the multiple redshifts of the same object cannot be explained by the Doppler effect, so it is necessary to find a new redshift mechanism. In addition to the proposed red shift mechanisms such as gravitational red shift, photon aging, and physical constant change, there is also a so-called "transverse Doppler effect". The huge redshift of a quasar may indicate that its Lateral velocity Very big.

Some of the above views are just hypotheses, and some have theoretical basis, but they cannot explain the redshift of quasars well Cosmological redshift Those who believe that the redshift of quasars is a challenge to modern physics. The observation and study of the redshift of spectral lines that are common in galaxies have strongly promoted the Observable universe The structure, origin and evolution of modern cosmology are the subject of rapid development. Once the truth of galaxy redshift is revealed, human understanding of the universe will have a greater leap.

Active galactic nucleus model

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In the mid-1990s, with the improvement of observation technology, the mystery of quasars began to be revealed gradually. One of the important results is that the "host galaxies" of quasars have been observed and their redshifts have been measured. Because the light of quasars is too bright, covering the relatively dim light of the host galaxy, the host galaxy has not attracted people's attention before. The host galaxies of quasars were not observed until instruments similar to the coronagraph used to observe the solar atmosphere were installed on the telescope to block the bright light of quasars.

Now the scientific community has reached a consensus that quasars are actually a class of active galactic nuclei (AGNs). At the same time, Seyfert galaxy And the scorpion tiger BL objects are also confirmed to be active galactic nuclei, an attempt to unify Radio galaxy The models of active galactic nuclei of quasars, seyfert galaxies and scorpion tiger BL objects have gradually been widely accepted.

This model believes that there is a supermassive black hole at the core of the galaxy. Under the strong gravitational force of the black hole, nearby dust, gas and some stellar matter surround the black hole, forming a huge accretion disk rotating at high speed. At the inner side of the accretion disk near the event horizon of the black hole, matter falls into the black hole, accompanied by huge energy radiation, forming a matter jet. The strong magnetic field restricts the jet of these substances, so that they can only eject at high speed along the direction of the magnetic axis, usually perpendicular to the plane of the accretion disk. If these jets are directly facing the observer, quasars will be observed. If the observer's perspective of observing AGN is different, AGN will be shown as radio galaxy, Seiffert galaxy and Scorpio BL object respectively. In this way, the energy problem of quasars has been preliminarily solved.

The difference between quasars and ordinary "quiet" galactic nuclei is that quasars are young and active galactic nuclei. From the fact that quasars have large redshifts and are far away, it can be inferred that the quasars we see are actually what they looked like many years ago, and quasars themselves may be a stage commonly experienced in the early evolution of galaxies. As the "fuel" near the galactic core gradually runs out, quasars will evolve into ordinary Spiral galaxy And elliptical galaxies.^[6]

Cutting edge achievements

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Peking University

The discovery of super black holes and brightest quasars in the early universe by small telescopes in China^[5]^[7]

Schematic diagram of quasars with giant black holes in the distant universe^[5]

Peking University recently announced that a team led by Wu Xuebing, a professor in the Department of Astronomy at its School of Physics, had discovered a super bright quasar 12.8 billion light-years away from humans. Its luminous intensity is 430 trillion times that of the sun, and the mass of the central black hole is about 12 billion solar mass. It is the brightest quasar known in the universe and the largest mass of the central black hole. This super "monster" in the early universe was used by Chinese scholars Lijiang, Yunnan It is also the only early cosmic quasar with redshift of more than 6 found by a 2-meter telescope in the world. The discovered 6.3 redshift quasar SDSS J0100+2802 has the largest luminosity and black hole mass among all high redshift quasars.

This latest research achievement was published in the latest issue of the international scientific journal Nature on February 26, 2015.

Famous astronomer Academician of CAS Chen Jiansheng commented on this discovery and said: "Chinese astronomers can use domestic 2-meter small telescopes to find objects that usually need a 10 meter telescope to find internationally, which shows that Chinese astronomers are full of innovative ideas."^[8]

Found red shift 6.3 quasar SDSS J0100+2802^[5]

The magazine also specially made a news release entitled "Young black hole with rapid growth spurt" for this article, and invited Dr. Bram Venemans of the Max Planck Institute of Astronomy in Germany to write a special article entitled "Giant in the Young Universe" in the "News and Review" column of the contemporary journal (A gift in the young universe).

In just a few days, foreign news media, including CNN, Reuters, Washington Post, Time Weekly, NBC, National Geographic, Discovery Channel, Scientific American, and domestic news media, such as CCTV, Xinhua News Agency, People's Daily, Guangming Daily, China Daily, and China Science News, The discovery was reported as important news. Peking University also held a special press conference for this purpose, which was attended by more than 20 journalists from major domestic media.

In August 2022, researchers from the National Astronomical Observatory of the Chinese Academy of Sciences released the first batch of wide field X-ray images and energy spectra of celestial bodies observed by EP-WXT pathfinders. This instrument X-rays of quasars 814 million light years away from Earth were detected.^[9]

University of Science and Technology of China

In October 2023, Associate Professor Cai Zhenyi and Professor Wang Junxian of the Department of Astronomy of the University of Science and Technology of China found that the extreme ultraviolet radiation spectrum of the accretion of the supermassive black hole at the quasar center was irrelevant to the intrinsic brightness of the quasar, which overturned the traditional understanding in this field. Further research by researchers found that the average extreme ultraviolet energy spectrum of quasars is much softer than expected by the classical accretion disk theory, posing a serious challenge to the classical accretion disk radiation model, and strongly supporting the accretion model with universal disk wind. Relevant achievements have been published online in Nature Astronomy in the form of long research articles.^[10]

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