Active galaxy model

The unified model of active galactic nuclei tries to describe two or more active galactic nuclei with one model, and different types of active galactic nuclei are only due to different observation angles. Radio quiet active galactic nuclei and radio TV active galactic nuclei have their own unified models: radio quiet unified model and radio TV unified model. According to the weak unified model of radio waves, SIFO type ⅰ galaxy is a low luminosity active galactic nucleus directly observed, while SIFO type ⅱ galaxy is blocked out of sight by the shielding ring around the accretion disk. If the luminosity of active galactic nuclei is very high, then the galaxies directly observed are quasars rather than Sifo I galaxies. The unified model of radio wave intensity mainly focuses on radio wave intensity quasars with high luminosity, which can be unified with radio wave galaxies with narrow emission lines in a way similar to the weak unified model of radio waves, that is, radio wave galaxies are shielded by shielding rings, while quasars are not. If the angle between the line of sight and the jet is small, the Tokamak BL quasars will be observed.

Lead: Astronomers have been puzzled by the huge energy mystery of active galaxies and quasars for decades. It is generally believed that their energy comes from supermassive black holes rotating at high speed in the center of galaxies.

After the 1920s, astronomers finally realized that there are countless galaxies of different sizes and shapes scattered in the vast space outside the Milky Way. However, until the mid-20th century, astronomers believed that galaxies were quite calm, with only rare supernova explosions with the same luminosity as the whole galaxy, occasionally breaking through the silence in the depths of the universe. With the development of radio astronomy, astronomers have discovered the radio source in the center of our galaxy and the strong radio sources in many galaxies. It is worth noting that these extragalactic radio sources emit much more energy in the radio band than in the center of the Milky Way, thus opening the prelude to understanding the activities of galaxies.

Since then, with the development of space astronomy, the activities of galaxies, especially those related to the nuclei of some types of galaxies, have been detected in the infrared and X bands. In this way, astronomers realize that the activity of galaxies is quite common. But most galaxies (about 98%) are very low in activity, such as our Milky Way, which we call normal galaxies. Only 2% of galaxies are active and are classified as active galaxies.

A normal galaxy is a group of celestial bodies formed by a large number of stars bound by gravity. Most of its radiation is emitted by stars, and the radiation is mainly concentrated in the optical band. Active galaxies radiate the entire electromagnetic wave range from radio to gamma rays. Moreover, the energy emitted in radio, infrared, ultraviolet and X-ray bands is greater than that in optical bands, indicating that these radiations are emitted by a large number of non-stellar substances. Under the special physical conditions of active galaxies, these substances are accretion, turbulence and explosion on a large scale. Jet structures have been observed near some active galaxies, which are obviously formed by materials thrown by galaxies. There are many types of active galaxies, but there is no unified and accurate classification so far. Buthus BL celestial bodies, Seyfert galaxies and radio galaxies are some of the main types.

1929, Scorpio discovered a celestial body, and the light changed very quickly. Its apparent magnitude fluctuates from 14 to 16, and occasionally it can be brightened to 13, that is, the brightness of visible light band changes by about 15 times, and can change by 10% ~ 32% in one day. At first, astronomers thought it was a variable star, and according to the naming method of variable stars, it was called Scorpio BL. Weak absorption lines are observed in the spectrum of Scorpio BL, and these absorption lines are produced by nebula materials around celestial bodies. According to Hubble's law, the red shift of the measured spectral line is 590 MPC (1MPC = 3.26×106 light years). Now astronomers have strong evidence that it is an extragalactic object. Later, more than 300 celestial bodies with the same characteristics as the East Asian scorpion BL were discovered, commonly known as the East Asian scorpion BL celestial body. The same characteristics of the BL-shaped celestial bodies in Scorpio are as follows: generally, they are star-shaped and have no structure, but some of them have weak cladding; The brightness of radio, infrared and visible light bands changes rapidly, and the time scale ranges from a few days to several months. There are neither absorption lines nor emission lines in the spectrum, only a continuous radiation spectrum with no characteristics; Many of them are compact radio sources with strong radio radiation at their core.

1943, American astronomer C.K.Seyfert discovered six spiral galaxies with unusually wide emission lines in the spectrum, and later confirmed that they were active galaxies and were named Seyfert galaxies. They are spiral galaxies with exceptionally bright nuclei, which occupy almost all the light emitted by galaxies, and are easily mistaken for stars on short-time exposure films, while hazy spiral structures around the nuclei are revealed on long-time exposure films. The galactic nucleus is filled with ionized gas with the mass of 10 to 103 solar mass, the ion density of 107/cm3 ~ 109/cm3, and the gas moves randomly at high speed with the speed of 103 km/sec. This speed may be caused by a violent explosion. Seyfert galaxies have stronger radio emission and infrared radiation than normal spiral galaxies, and some Seyfert galaxies have detected X-ray radiation.

Since the 1940s, radio astronomers have discovered tens of thousands of radio sources. At first, some of the strongest signal sources were represented by constellation names followed by a large Latin letter. For example, the strong radio source of Cygnus is called Swan A, and the strong radio source of Virgo is called Virgo A. Most of the radio sources are located outside the river, of which about 1/3 ~ 1/2 has been confirmed as a galaxy.

Galaxies with strong radio emission (higher than1034W) are called radio galaxies. Their radiation power in the radio band is not only far greater than that of normal galaxies, but also far greater than their radiation power in the optical band. Most of these galaxies are elliptical galaxies. The main types are Shuang Yuan type and intensive type. A typical Shuang Yuan radio galaxy has a small radio source near the center of the galaxy, but there are two large radio sources far away from the galaxy itself. The width of these two sources, or radio lobes, may be 105 parsec ~ 107 parsec and 104 parsec ~ 106 parsec. Sometimes you can see many pairs of petals. The structure of these sources shows that they point to the center of the galaxy and are actually substances ejected from the galaxy. Each radio lobe is a high-energy electron cloud with a magnetic field. The radio lobe is far away from the central galaxy, and the front end faces the vast galaxy space, compressing a huge amount of galaxy material, causing violent collisions and forming hot spots at the front end. Observations by X-ray detection satellites show that they are also strong X-ray sources. The energy stored in a typical radio lobe is about equal to the energy radiated by all the stars in the Milky Way 1 100 million years!

The radio source Swan A was discovered in 1948, and 1954 was confirmed as an extragalactic galaxy with brightness of 16. It is 734 million light years away from the Milky Way, and its radiation power is about 107 times stronger than that of the Milky Way. It is the strongest known extragalactic radio source and the first radio galaxy to be discovered. Centauri A is the nearest radio galaxy, with a distance of 1, 065,438+0 billion light years. Although not as powerful as Swan A, it is similar in other aspects. They are typical examples of Shuang Yuan-type radio galaxies. The radio emission area of compact radio galaxies is usually very small, which is no larger than the optical image range of galaxies on the negative. Some are not even more than a few light years. M87 is a huge elliptical galaxy, located near the center of the Virgo cluster, and is the optical counterpart of Virgo. It is 500,000 light-years in diameter and 65 million light-years away from the Earth, and its opening angle in the sky is over half a degree (about the size of a full moon). It is a typical compact radio galaxy.

1960, astronomers discovered that the optical counterpart of the radio source 3C 48 was a star-like object with an apparent magnitude of 16, surrounded by dark nebula material. It is puzzling that there are several completely unfamiliar lines in the spectrum. 1962, another "star" with a magnitude of 13 was found at the position of radio source 3C 273. Astronomers are also puzzled by the unusual lines in their spectra.

1963, finally someone recognized the true colors of the 3C 273 spectral line. It was originally the spectral line of hydrogen atom, but it experienced a great red shift, which made it difficult to identify the spectral line. According to the clue of red shift, the spectrum of 3C 48 is analyzed, and the conclusion is that the red shift is bigger. Assuming that the red shift is caused by Doppler effect, both 3C 273 and 3C 48 have great retrogression speeds, reaching 1/6 and 1/3 of the speed of light, respectively. Astronomers name this celestial body that looks like a star in optical photos, but its essence is quite different. Further observation and research revealed another celestial body, which is also very similar to a star, with a great red shift but no radio emission, so it is called a radio quiet quasar. Later, both of them were called quasars.

What exactly is a quasar? This poses a difficult problem for astronomers. In the decades after their discovery, the debate has not completely subsided. The focus of the debate is the reason for the red shift of quasar spectral lines. Most people advocate "cosmological redshift", that is, quasars are located in the distant depths of the universe outside the Milky Way, and the farther the distance, the greater the redshift. If quasars are really so far away, there is still a problem, and that is how to explain their huge energy output. The emission power of quasars is 102 ~ 104 times higher than that of ordinary spiral galaxies. What is even more surprising is that the area emitting energy is very small, and its diameter is only the order of magnitude of light or even light. It was a mystery at that time that quasars could release so much energy in such a small volume. Another view is that quasars are celestial bodies thrown by the Milky Way or other extragalactic galaxies, and they gain great speed in the ejection. The greater the speed, the greater the redshift.

Comparing quasars with Buthus BL celestial bodies, Seyfert galaxies, radio galaxies and other active galaxies, it is found that there are many similar observation characteristics, especially the understanding of radio galaxies, which is enough for astronomers to realize that quasars are different manifestations of the same phenomenon. In addition, since the 1980s, a large number of high-energy phenomena in the universe have been observed and understood, and the energy problem of quasars can also be reasonably explained.

On the premise that redshift is cosmological redshift, redshift from big to small means that celestial bodies change from young to old. As far as redshift is concerned, quasars are the largest, followed by Buthus BL celestial bodies and Seyfert galaxies, and radio galaxies are the smallest. Thus, an evolutionary sequence can be roughly discharged: quasars, Buthus BL celestial bodies, Seyfert galaxies and radio galaxies, ending in normal galaxies.

As mentioned above, active galaxies (including quasars) only account for about 2% of the total number of galaxies, which shows that the evolution process of galaxies from birth to "maturity" is very short in its life. So quasars are the infancy of normal galaxies. Then quasars are extremely active galactic nuclei. There are galactic disks around them. Because quasars are too far away, the silver disk looks very dim and the angular diameter is too small to be observed. In fact, for some relatively close quasars, such as 3C 273, evidence of galactic disks has been found.

The violent activity of active galaxies and quasars originated from the central nucleus. Then, relative to the whole galaxy, it is difficult to explain how to release so much energy in such a small galactic nucleus. This problem has puzzled astrophysicists for a long time. It is generally believed that almost every large normal galaxy contains a supermassive black hole at its center. More and more observational evidence supports this hypothesis. Astronomers used VLA (Very Large Array Radio Telescope) and VLBA (Very Long Baseline Interferometry Array) in New Mexico, USA, to make a complete survey of 100 neighboring galaxies, and found that at least 30% of the samples showed tiny and compact central radio sources, which had the unique characteristics of quasar phenomenon.

In addition, the background of the universe is also full of weak X-ray glow, covering the whole sky. Different from microwave background radiation, microwave background radiation is the residue of the Big Bang, and the photon energy in X-ray smoke is too high to be generated in the early universe. Moreover, the microwave background radiation presents a basically uniform and continuous distribution, and this all-day distribution of X-ray radiation is the contribution of countless discrete sources. The Chandra X-ray Observatory in the United States is equipped with a grazing X-ray imaging telescope, formerly known as the Advanced X-ray Astrophysics Satellite, which was launched by the Space Shuttle in 1999. It was renamed in memory of the late Indian-American Nobel Prize winner surat Horse Chandraseka. It has deeply exposed the selected sky area and can decompose at least 80% of X-ray glow into a point light source. Extrapolating to the whole sky, it shows that there are about 70 million in total. Then some of these celestial bodies are tracked and studied, and their radiation in other bands is detected, and it is concluded that some of them are quite normal galaxies. They have dust-covered nuclei that emit X-rays-a sign of the central black hole.

It is generally believed that such a huge energy source is because there is a supermassive black hole hidden in the center of the galaxy, and its mass is at least 107 times that of the sun. The black hole attracts the surrounding matter with its great gravity, and spirals down there to form an accretion disk around it. The gas in the disc is compressed and heated. When the temperature exceeds 1 100 million k, a strong radiation field will be formed, so that the high-energy plasma jet will be ejected from the core to the two poles perpendicular to the disk surface at a speed close to the speed of light.