Active galactic nucleus (AGN) has violent activity, and its core is generally believed to be ablack hole, attractive andJet, will happen againGalactic nuclear explosion。Galaxy nuclear explosion is one of the most spectacular astronomical phenomena in the universe.
The galactic nucleus is the central part of most galaxies.Based on the radiation pressure and gravitational phase balance, it can be inferred that the mass M of galactic nuclei is about 108Solar massM⊙。The galactic nucleus containsfixed starAnd ionized gas, magnetic field andHigh-energy particle。Normal galaxyThe core is usually "peaceful".Stars of various spectral types have been observed from quiet nuclei, and there may also be various neutron starsCompact star。It is known from the spectral lines of some galactic nuclei that there is a mass of plasma (one thousandth of the mass of the nucleus) in the nucleus, the temperature is about several thousand degrees, and the number of electrons per cubic centimeter is n ε ≈ 10 ^ 3~10 ^ 6.
Quiet nuclei often produce radio radiation, and the distribution of radio spectrum intensity is in the form of power law, that is, I ν ∝ν ^ (- α);For most nuclei, α=0.7. Its radio radiation spectral intensity I ν≈ 10 ^ - 8 ergs/cm ² at the frequency ν≈ 10 ^ 9 Hz.Observations show that 90% of the luminosity of galactic nuclei is generated in a very narrow infrared region.Infrared radiation maximum frequency ν maximum=2.5 × 10 ^ 13 Hz (i.e. λ maximum=70 μ m);On both sides of the maximum frequency, the intensity decreases rapidly (when ν<ν max, I ν ∝ ν ^ 35; when ν>ν max, I ν ∝ ν ^ - 35).
For most galactic nuclei, although their properties are very different, the maximum frequency of their infrared radiation is the same.Galaxies with obviously active nuclei account for 1~5% of the total number of galaxies.The galaxy with the strongest nuclear activity isa quasar, followed byN galaxy (SeeSpecial galaxy）AndSeyfert galaxies 。The active period of galactic nuclei is estimated to be 10 ^ 5~10 ^ 7 years.
Activity form
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① Severe gas movement:Measure fromSeyfert galaxies It can be estimated that the air velocity can reach several thousand kilometers per second.This air flow can sometimes extend to thousands of seconds outside the nucleus.
② Huge non thermal radiation:Similar to quiet nuclei, strong nonthermal radiation also reaches its maximum in the infrared region, and the infrared maximum frequency is ν maximum ≈ 2.5 × 10 ^ 13 Hz, but the intensity is several orders of magnitude larger than that in quiet nuclei, and the radiation power can reach 10 ^ 46 ～ 10 ^ 47 ergs/second;The total energy can even reach 10 ^ 62 ergs.
③ Strong light variation:The radiation intensity of optics and radio varies greatly with time.For example, 3C273, sometimes within two months, the change of luminosity is twice as bad.At the same time, for different wavelengths, the time-varying amplitude of spectral intensity is also different: the shorter the wavelength, the stronger the time-varying.For the majorityActive galactic nucleusFor example, the light variable time scale is nearly one year, so it can be inferred that its size is about 10 ^ 18 cm (equivalent to a one second gap).
④ A huge outbreakSome galactic nuclei throw out large masses of matter and relativistic particle streams, forming so-called matter jets.M87 is an example.EjectaLocated in the northwest of M87 core, there are three bright condensates and three dark condensates.The condensed matter is connected with the core by a luminous "fiber";In addition, a small jet structure with two condensates was also found in the opposite direction of these jets.SomeGalactic nuclear explosionWhen, matter is ejected in all directions, the famous examples are M82 and NGC1275;manyRadio galaxyanda quasarThere is a dual source structure, which may also be the result of some kind of explosion.
theoretical model
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Tight cluster hypothesis
At the center of the galactic nucleus,fixed starThe density is so high that inelastic collision occurs, releasing huge energy.However, to make collisions become the energy source of galactic nuclei, the density of star clusters at the center of the galaxy must be as high asCubic second gap10 ^ 11 stars, which contradicts the observation.
Black hole hypothesis
It is considered to be the result of gravitational collapse.Although the energy released by gravitational collapse can reach the order of 2 × 10 ^ 54M/M ⊙ Erg, and M/M ⊙ is the mass ratio of the galactic nucleus to the sun, the transformation mechanism is still unclear;More importantly, gravitational collapse was completed in 10 ^ - 5M/M ⊙ seconds, which conflicts with the observed quasi steady state of active nuclei.Admittedly, accretion can temporarily ease this difficulty.However, the matter ejection will greatly inhibit the accretion, so the difficulties remain unsolved.
Large Mass Rotating Magnetic Multilayer Sphere Model
That is, the magnetic rotor model: qualitatively speaking, the rotation causes the distortion of the magnetic field to produce a neutral line (see magnetic merging), and the dynamic dissipation of the magnetic field occurs near the neutral line, so that the accumulated magnetic energy is converted into the kinetic energy of the particles, and the particlesRelativistic velocityThis is the explosive mechanism of the magnetic rotor.The thrown electrons whirl along the dumbbell shaped magnetic field lines outside the nucleus and emit synchrotron acceleration radiation, which is received by us.
The magnetic rotor model is being interpretedActive galactic nucleusIn fact, although some achievements have been made in the main observations of, the theory requires that the luminosity of galactic nuclei should be quasi periodic, which is not consistent with the observation data.In addition, the magnetic rotor model has not been successfully used to explain the extreme infrared radiation and large-scale explosions of AGN.
Gravitational slingshot and bubble model
According to the gravitational slingshot modelfixed starCollision, forming a number of large pieces of material.The calculation shows that if more than three large blocks are formedGravitational instability, eject matter.However, this model cannot explain the symmetric ejection of galactic nuclei.The bubble model is a hydrodynamic projection, which assumes thatRelativistic particleA "bubble" is formed in the core, and then it splits into two hot gas bubbles, which are blown out of the galaxy by the intergalactic wind, or ejected by the surrounding cold air, forming a mass (bubble) ejection.This model requires sufficient buoyancy. It seems that onlyGalaxy clusterInternalActive galactic nucleusThis kind of casting is possible.
Plasma turbulent reactor model
This model can clarify the following three main problems:Plasma waveCan accelerate particles to extremeRelativistic velocity；In the reactor, the power law spectrum of relativistic particles can be formed;The characteristics of the radiation spectrum are given, especially the explanation of the maximum infrared radiation of galactic nuclei, and the reason why various galactic nuclei have almost the same maximum infrared frequency is explained.However, this model cannot give a convincing explanation for the ejected matter of galactic nuclei.
Bibliography
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E.H.Avrett ed.,Frontiers of Astrophysics,p.438，Harvard Univ.Press,Cambridge,1976.
A. Ambartsumian,The Nuclei of Galaxies and their Activity,Interscience Publ.,London,1964.
According to foreign media reports, a new astronomical observation and research report shows that scientists have found a giant galactic nucleus in a distant galaxy, which is the largest galactic nucleus ever seen. Its formation mechanism may be due to the merger of two black holes.The newly discovered giant galactic nucleus spans 10000 light-years, and the researchers named it A2261-BCG.
Astronomers use NASA'sHubble Space TelescopeAfter the discovery of its existence, the galactic nucleus shows an unimaginable huge size. The span of the galaxy where it is located is 10 times that of our Milky Way. The starlight emitted by the galactic nucleus area appears strange, and there is no star concentration phenomenon that can be seen in the galactic nucleus area.
The last point in the detailed description of the observation of A2261-BCG objects is somewhat surprising, because supermassive black holes are believed to be hidden near the core of the galaxy, and of course not all galaxies exist in the centerSupermassive black hole。According to the co-author of this study, astronomer Todd?Tod Lauer said: "When we use the Hubble Space Telescope to observe the core region of this galaxy, it is like cutting the largest peach, but we have not found a peach kernel. We cannot say for sure that there is no black hole in the center of this galaxy, buthubble space telescope Our observation shows that there is no star concentration in the core region of the galaxy. "
The galaxy A2261-BCG is one of the brightest objects in the Abel 2261 galaxy cluster. It has relatively bright characteristics. Its width reaches 1 million light-years, and it is 3 billion light-years away from the Earth. What surprised scientists is that the galaxy has a bright, bloated core, three times as many as other extremely luminous cores.Astronomers believe that a black hole merger event occurred in the center of the galaxy, and a black hole with a mass of billions of times the sun may make the galaxy core appear "bloated".The reason why a large number of light emitted by star clusters are not found in the nuclear region is that one scheme believes that black hole merging events scatter the positions of stars in the galaxy, and one black hole loses its power source and falls into another black hole.
Another proposal is that black hole merging events can create gravitational waves, which is a unique space-time structure ripple, and reflects the strongest radiation release in one direction, makingSupermassive black holeWas kicked out of the Central Nuclear Zone.National Optical Astronomy Observatory astronomer Todd?Raul believes that black holes are somewhat like the "anchorage" of stars. Under the action of gravity, stars can orbit around black holes. If we remove them, galaxies will suddenly lose a lot of mass.The stars in A2261-BCG objects do not seem to be so concentrated, and they are in the process of outward movement.
Based in BaltimoreInstitute of Space Telescope ScienceMark?Marc Postman believes that the theory of celestial "ejection" sounds strange, but it is very interesting to observe the universe. Sometimes you will find something strange.The research team is looking for evidence of the A2261-BCG central black hole. If it exists, it can detect the radio waves generated by the black hole.The team of astronomers is in contact withradio telescopeArray, hoping to observe through this telescope.The study was published in the September 10 issue of Astrophysics.[1]
Under normal circumstances, the earth's atmosphere will be constantly exposed to high-energy rays from the universe. Scientists have been looking for the source of this mysterious cosmic ray.An international scientific research team announced on the 8th that, according to the latest observation results, they believe that the source of cosmic rays is likely to beActive galactic nucleus。
The observation and research team, composed of more than 200 physicists from more than 10 countries, published a report in the journal Science scheduled to be published on the 9th, saying that they had detected about 80 cosmic high-energy ray activities using the Pierre Ohel Observatory in Argentina, South America.The results show that the sources of rays in the universe are not evenly distributed.Among the cosmic rays detected by experts, the most energetic rays usually come from the space region with more active galactic nuclei nearby.The so-called active galactic nucleus refers to the compact central location of the galaxy, which is usually the location of large black holes, and will erupt hugeplasma jet To the space between galaxies.
Cosmic rays scatter among galaxiescosmic raysSome ray particles still have quite high energy when they fly into the atmosphere and collide with it.Scientists said that some ray particles that arrived near the earth after a long journey were still like fast moving baseball.They speculate that maybeActive galactic nucleusThe black hole magnetic field at is like an accelerator of cosmic rays, which enables ray particles to obtain extremely high energy and fly at super high speed.In the past decades, scientists have been trying to determine the source of cosmic rays through various ways.Previously, the scientific community also theoretically regarded active galactic nuclei as a possible source of cosmic rays. The above latest observation and research results made them more convinced that cosmic rays are likely to come from active galactic nuclei.
