Supernova explosion is a violent explosion experienced by some stars when they are near the end of their evolution.This kind of explosion is extremely brightelectromagnetic radiationIt can often illuminate the whole galaxy where it is located, and can last for weeks to months before gradually fading into invisibility.During this period, the energy radiated by a supernova can be comparable to the total energy radiated by the sun in its lifetime[1]。The explosion of a star will scatter most or almost all of its material outward at a speed as high as one tenth of the speed of light[2], and to the surroundingInterstellar matterRadiation shock[3]。This shock wave will lead to the formation of an expanded shell structure of gas and dust, which is calledSupernova remnant。Supernovae is a potentially powerful source of galactic gravitational waves[4]。A large proportion of primary cosmic rays come from supernovae[5]。
A supernova is more energetic than a nova.The English name of a supernova is supernova. nova means "new" in Latin, which means that it appears to be a new bright star on the celestial sphere (in fact, it already exists, and is considered to be new due to the increase in brightness). The super at the beginning is to distinguish a supernova from a common nova, which also means that a supernova has higher brightness.The term supernova was coined by Walter Budd and Fritz Zweiki in 1931[6]。
A supernova can be triggered in one of two ways: a degenerate star that suddenly reignites the fire of nuclear fusion, or a gravitational collapse of the core of a massive star.In the first case, a degenerate white dwarf can accumulate enough mass from the companion star through accretion, or accretion or merger, to raise the core temperature, ignite carbon fusion, and trigger runaway nuclear fusion to completely destroy the star.In the second case, the core of a massive star may suffer a sudden gravitational collapse, releasing gravitational potential energy and creating a supernova explosion.
White dwarf;Neutron star;Black hole;Stellar evolution
Earliest observation
China
Noun Creator
Walter Bader and Fritz Zweiki
Nouns create time
1931
Causes
The stars radiate electron photons in outer space, transform heavy element carbon and sodium layer, and the carbon and sodium hail increases as the constant wind rises and falls. At the same time, the carbon and sodium heavy element hail continues to hit the constant sun center, causing damage to the solar foreskin, and the constant loss turns to supernova sodium explosion.
The earliest supernova record is SN 185 seen by Chinese astronomers in AD 185.The brightest supernova on record is SN 1006, which has been described in detail by Chinese and Islamic astronomers.[7]The most widely observed supernova is SN 1054, which formedCrab Nebula。Supernovae SN 1572 and SN 1604 are the last two galactic supernovae observed with the naked eye, which have a significant impact on the development of European astronomy, because they are used to refute the Aristotelian universe that is unchangeable beyond the moon and planets.John Kepler observed it on the peak of SN 1604 on October 17, 1604, and continued to estimate its brightness until the brightness became dim and invisible to the naked eye the next year.[8]It was the second supernova observed by people at that time (after the Cassiopeia SN 1572 of Tycho Brahe).
With the development of telescopes, the field of discovering supernovae has nearly expanded to other galaxies.It was observed in 1885 thatAndromeda galaxyThe supernova S Andromeda.American astronomers Rudolf Minkowski and Fritz Zweiki launched the modern supernova classification plan in 1941.In the 1960s, astronomers found that the maximum intensity of supernova explosions could be taken as the astronomical distanceStandard candle, thus measuring the distance of the celestial body.Recently, some of the most distant supernovae have been observed to be darker than expected, which supports the view that the expansion of the universe is accelerating.[9]In order to reconstruct the observation of supernovae without written records, new technologies have been developed to detect the echo events from the nebula from the date of supernova Cassiopeia A.[10]From temperature measurement andγX-ray decay, estimatedSupernova remnantRX J0852.0-4622.In 2009, the matching of nitric acid content in Antarctic ice sediments revealed the time of past supernova events.[11]
Famous supernovae
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On December 7, 185, the second year of Zhongping in the Eastern Han Dynasty, Yichou, Chinese astronomers observed Supernova 185, the first supernova in human history.[12]The supernova shone in the night sky for eight months.According to the Chronicles of Astronomy in the Later Han Dynasty, "In October of the second year of Zhongping (185), the guest star came out of the south gate, as big as a half feast, with five colors of joy and anger, and slightly smaller, until June of the next year".
April 30, 1006: SN 1006 burst in the constellation of Jackal. It may be the most luminous supernova ever recorded. It is inferred that its brightness has reached - 9.According to modern astronomers, "in the spring of 1006, people may even be able to read in the middle of the night with the help of its light."[13]In the Song Dynasty of China, this supernova was discovered by Sitianjian, Zhou Keming and others, so it was called Zhou Boxing.In the fifth and sixth volumes of the Chronicles of Astronomy in the History of the Song Dynasty, it is recorded that: "In April of the third year of Jingde, when Wu Yin and Zhou Boxing saw each other, they left the southern part of the country and rode once to the west of the country. They looked like half moons with awned horns. They could learn things from each other and go to the east of the library. In August, they went into the turbid state along with the heavenly wheel. In November, they came back to the country. Since then, they often saw the east in November, and went into the turbid state in the southwest in August."
July 4, 1054: A supernova explosion that produced the Crab Nebula. The appearance of the guest star was recorded in detail by astronomers in the Song Dynasty of China《Continuation of Zizhi Tongjian》Volume 176 contains: "In May of the first year of the Zhihe era, the guest star appeared at the southeast of the Tianguan in the morning, which can be measured by inches (since March of the first year of Jiayou era)." Japanese and American aborigines also have records of observation.
Early November 1572 (probably between 2 and 6): supernova in Cassiopeia（Tycho supernova）Outbreak, Danish astronomer Tycho has observation records, and therefore published the book De Nova Stella, which is the source of the Latin name nova of nova.It is estimated that the absolute magnitude of this supernova is - 15.4, 7500 light-years away from the Earth;Its highest apparent brightness is - 4, which can be compared with Venus.
October 9, 1604: Supernova in Ophiuchus（Kepler supernova）The German astronomer Kepler has detailed observation records. This is the last supernova found in the Milky Way so far, with an apparent magnitude of - 2.5 and a distance of 6000 light-years from the Earth.It was used by Galileo to refute the Aristotelian school's theory that heaven is always the same.
August 19, 1885: The supernova SN 1885A (Andromeda S) in the Andromeda galaxy was discovered by Irish amateur astronomer Issac Ward in Belfast, which is the first time that humans have discovered itExtragalactic galaxyThe supernova in the Andromeda galaxy is also the only supernova found so far in the Andromeda galaxy.
February 24, 1987: atLarge Magellanic CloudOfSupernova 1987AThe discovery within a few hours after the explosion is the first opportunity for modern supernova theory to be compared with actual observations.It is about 51400 seconds away from the earth, and its apparent magnitude at its brightest is 3.[14]
September 18, 2006: SN 2006gy, a supernova 238 million light-years away from the Earth (once assumed to be unstable to supernova, but not confirmed), is the strongest supernova explosion ever observed.[15]
Current model
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The classification code given by astronomers to supernovae is a natural classification: the value of the type of light given by supernovae is not necessarily its cause.For example,Ia supernovaIts ancestor star is a degenerated white dwarf star, which was generated by out of control fusion ignition;The ancestor star of Ib/c supernovae with similar spectral types is the massive Wolf Rayet star, which was ignited by the core collapse.The following summarizes what astronomers think is the most reasonable explanation for supernovae
Thermal runaway
The white dwarf may accumulate enough mass from its companion star to raise the core temperature enough to ignite carbon fusion, at which time it will lose control and completely destroy it.In theory, this explosion can occur in three ways: from the stable accretion mass of the companion star, the collision of two white dwarfs, or ignition in the accretion shell, and then ignition.But it is still unclear which is the main mechanism.[16]Although it is not sure how Ia supernova came into being, Ia supernova has a very uniform property and is a useful standard candle for intergalactic distance.However, for the gradual change in nature or the abnormal luminosity with high redshift at different frequencies, the photometric curve and spectrum are different small changes, and some compensation on calibration is required.[17-18]
Normal Ia supernova
There are several ways to form this type of supernova, but they share a basic mechanism.If a carbon oxygenWhite dwarf accretionTo enough mass to reach the Chandraseka limit of about 1.44 solar mass (M☉）(For non rotating stars), it will no longer be able toElectronic degeneracy pressureSupport its huge plasma body and start to collapse.However, the view is that this limit has not been reached, and enough temperature and density have been obtained to ignite carbon fusion in the core.It usually collapses before reaching the limit (approximately 1%).
In a few seconds, a considerable part of the material of the white dwarf will undergo nuclear fusion, releasing enough energy (1 – 2 × 10forty-fourJ) , release the binding of the star, and a supernova explosion occurs.The outward expanding shock wave and material can reach 5000-20000km/s, or about 3% of the speed of light.At the same time, the brightness also increased significantly, and the absolute magnitude could reach - 19.3 (or 500 million times brighter than the sun), with only a small amount of variation.
These supernovae are formed by closely connected stars.The big one of the two stars first evolved out of the main sequence belt and expanded into a red giant star.The two stars share an envelope, causing their orbits to shrink.The larger star then dumped most of its envelope and lost mass until its core could no longer undergo nuclear fusion.At this point, it becomes a white dwarf composed mainly of carbon and oxygen.Finally, its companion star also evolved out of the main sequence belt to become a red giant.The matter from the giant star is accreted by the white dwarf, resulting in the continuous increase of the mass of the white dwarf.Although the basic model is generally accepted, the precise details of the heavy elements generated by the initiation and explosion are still unclear.
Ia nova follows a characteristic photometric curve - the relationship diagram of brightness as a function of time - after explosion, this brightness changes due to radioactive decay from Ni-56 through Cobalt-56 to Fe-56.The peak value of photometric curve of normal Ia supernova is very consistent, and the maximum value is absolute magnitude - 19.3, etc.This makes it a secondary standard candle, which can be used to measure the distance of its host galaxy.[19]
Non-standard Ia supernova
The explosion of another Ia super star involves the merger of two white dwarfs, and the combined mass may exceedChandraseka limit。[20]There are still many changes in this type of explosion, and in many cases there may be no supernovae, but their photometric curves are expected to be wider and lower than the normal Ia supernova explosion.
When the mass of a white dwarf star exceeds the Chandraseka limit, there will be an Ia supernova with abnormal luminosity, and the asymmetry may have a further enhanced type, but the kinetic energy of the ejected matter will be less than the normal kinetic energy.
There is no formal subcategory for non-standard Ia superstars.It has been suggested that helium should be accreted on white dwarfs, and the dimmer supernovae should be classified as Iax. This type of supernova may not completely destroy the Zubai dwarfs, but can leave a zombie star.
A special non-standard type of Ia supernova developed hydrogen and others, and the emitted spectral lines give the mixture between Ia and IIn supernovae with normal appearance, such as SN 2002ic and SN 2005gj.This supernova was once labeled Ia/IIn, Ian, IIa, IIan.[21]
Core collapse
When a massive star suddenly becomes unable to support its core and resist its own gravity, it will experience core collapse;This is the reason for the formation of all types of supernovae except Ia supernovae.The result of this collapse will cause the outer layer of the star to explode violently and become a supernova, or the gravitational potential energy released will be insufficient and collapse into a black hole or neutron star with a small amount of radiant energy.There are several different mechanisms that can cause core collapse: electron trapping, exceeding the Chandraseka limit, pair instability, or photoinduced disintegration.When a star develops an iron core, because the electron degeneracy pressure is not enough to support the mass beyond the Chandraseka limit, the core collapses into a neutron star or a black hole.Following the explosion of oxygen fusion, the electron capture in the oxygen/neon/magnesium core is the cause of gravitational collapse, with very similar results.After burning a large amount of core helium, electron positron pairs are generated to remove thermodynamic support, guide the initial collapse and subsequent runaway nuclear fusion, and the result is a pair of unstable supernovae.A sufficiently large and hot stellar core may produceγX-rays, which have enough energy to directly cause light induced disintegration, will lead to the complete collapse of the core.
The following table lists the massive stars with known causes of core collapse, the types of stars, the associated types of supernovae, and the resulting debris.The amount of metal is the ratio of other elements except hydrogen and helium to the content in the sun.The initial mass is several times the mass of the sun before it became a supernova. However, the mass of this supernova may have been much lower at that time.
IIn supernovae are not listed in the table.They may be formed by different types of potential progenitor stars through different ways, and may even be ignited by Ia's white dwarf stars.Although it seems that most of them are formed in bright giants or supergiants (including LBVs) through the collapse of the iron core.Narrow spectral lines are the reason why they are so named, because the arch material of such supernovae is small and dense.[22]It seems that IIn supernova is a genuine fake supernova, butHigh luminosity blue variable starLarge scale eruption, similar to Haishan II.In these events, the newly erupted matter interacts with the previously erupted matter through the shock wave to produce narrow absorption spectral lines.[23]
Scenario of core collapse mass and metal quantity
Cause of collapse
Estimated initial mass of progenitor star
Supernova type
wreckage
Electron capture in degenerate O+Ne+Mg core
8–10
Dark II-P
neutron star
Iron core collapse
10–25
Dark II-P
neutron star
25 – 40 Same or lower than the amount of metal and the sun
Ordinary II-P
It started as a neutron star, and the matter fell back into a black hole
25 – 40 and high metal content
II-L or II-b
neutron star
40 – 90 and low metal content
nothing
black hole
≥ 40 Similar to the amount of metal and the sun
Dim Ib/c, or GRB supernova
It started as a neutron star, and the matter fell back into a black hole
For a long time, a mystery surrounding the research of supernovae is how to explain that the residual dense matter generated after explosion has such a high speed relative to the core.[25](It has been observed that the pulsar as a neutron star has a very high speed, and theoretically, the black hole will also have a very high speed, but it is difficult to confirm it through isolated observation at present.) In any case, the force that can push matter to produce such a speed should be considerable, because it can make an object with a mass greater than the sun produce a speed of 500 km/s or more.It is generally believed that this velocity is caused by the spatial asymmetry of supernova explosion, but the specific mechanism through which this momentum is transferred is still unknown.Some explanations suggest that this driving force includes the convection during the collapse of stars and the jet generated during the formation of neutron stars.
This composite image of X-ray and visible light depicts the electromagnetic radiation emitted from the core region of the Crab Nebula.The speed of particles released from a pulsar near the center can be close to the speed of light.The velocity of this neutron star is about 375 km/s
Specifically, the large-scale convection generated above the core can cause local changes in element abundance, thus leading to uneven distribution of nuclear reactions during collapse, and then causing explosion after rebound.The jet interpretation believes that the accretion of gas by the central neutron star will form an accretion disk and generate a highly directional jet, which will eject the material at a high speed and generate a transverse shock wave to completely destroy the star.These jets may be important factors leading to supernova explosion.(A similar model is also used to explain the longGamma ray burstsGeneration of.)
The initial existence of spatial asymmetry in the explosion of type Ia supernovae has been confirmed by observation.This result may mean that the initial luminosity of such supernovae is related to the observation angle, but the explosion will become more symmetrical over time.This asymmetry can be detected by measuring the polarization of the outgoing light in the initial state.[26]
Type Ia nuclear collapse
Because Ib, Ic and many types of Type II supernovae have similar mechanism models, they are collectively called nuclear collapse supernovae.The basic difference between type Ia supernovae and nuclear collapse supernovae is the energy source of the radiation released near the peak of the photometric curve.The original stars of nuclear collapse supernovae all have extended outer layers, and the expansion amount required for such outer layers to reach a certain transparency is small.Most of the energy required for the light radiation at the peak of the photometric curve comes from the shock wave that heats and ejects the outer layer material.
In contrast, the original star of type Ia supernova is compact and much smaller than the sun (but still much larger in mass). Therefore, if this compact star wants to become transparent, it needs to undergo a large expansion (and cooling).The heat generated by the explosion is consumed during the expansion of the star, which can not promote the generation of photons.In fact, the energy radiated by type Ia supernova comes entirely from the explosionradio isotopeIt mainly includes Ni-56 (half life 6.1 days) and its decay product Cobalt-56 (half life 77 days).The gamma rays radiated from radioactive decay will be absorbed by the ejected materials, which will therefore be heated to incandescent state.
In nuclear collapse supernovae, as the ejected material expands and cools, radioactive decay will eventually become the main source of light radiation.A bright type Ia supernova can release nickel - 56 of 0.5 to 1 times the mass of the sun,[27]However, the nickel - 56 released by nuclear collapse supernovae is usually about 0.1 times the mass of the sun.[28]
Energy output
Although the supernova event we are thinking about is mainly the part of visible light emission, electromagnetic radiation is only a minor side effect of explosion.In particular, a supernova with a collapsed core emits only a small part of its total energy.
In different types of supernovae, the difference and balance of energy generation is the fundamental difference between them.In type Ia, the explosion of a white dwarf star, most of the energy flows to the kinetic energy of heavy element synthesis and ejecta.Most of the energy of a collapsed supernova is emitted through neutrinos. When the main explosion is obvious, more than 99% of neutrinos have escaped within a few minutes after the collapse began.
Type Ia super star out of control from nuclear fusionCarbon oxygen white dwarfGet their energy.However, the energy details have not yet been completely shaped, and the final result is to eject the original mass of the whole star with high kinetic energy.About half the solar mass of Ni is burned from silicon.Ni is a radioactive material with a half-life of 6 days, which will be radiated by positron emissionγThe rays degenerate into Co.Co itself will decay into stable Fe via positron with a half-life of 77 days.These two processes are responsible for providing electromagnetic radiation from the Ia supernova.In combination with the changes in the transparency of the eruptive materials, they produce a sharp decline in the light curve.[29]
Core collapse supernovaThe average brightness of type Ia supernovae is low, but the total energy is much higher.This comes from the gravitational potential energy of core collapse, which is initially generated from the collapsed atomic nucleusElectron neutrinoThen all the flavors are released from the core of the superheated neutron star.Only about 1% of these neutrinos have enough energy to cause the supernova explosion in the outer layer of the star, but the current model is not enough to provide details.The amount of kinetic energy and nickel is lower than that of Ia supernova, so the apparent brightness is relatively low, but the contribution of ionization energy from several times the solar mass hydrogen can decline more slowly, and make the brightness of the core collapse supernova at a higher stage.
Some supernovae with collapsed cores will retreat to the black hole to driveRelativistic jet, which can produce transient, high-energy and directionalGamma ray burstAnd further transmits energy to the jet of substance.This is generatedsuper-luminous supernovae One of the schemes is considered to be the cause of extremely supernovae and long duration gamma ray bursts.If the relativistic jet is too short to penetrate the outer envelope of the star, then a low brightness gamma ray burst may occur, and the supernova may be low brightness.
When a supernova occurs in a low-density peripheral cloud, it may generate shock waves, which can effectively convert a large amount of kinetic energy into electromagnetic radiation.Although the initial explosion energy is a completely normal supernova, it will also have high brightness and extended duration, because it does not rely on exponential radioactive decay.This type of event may cause IIn type supernovae.
Although the unstable supernova is a core collapsing supernova, its spectrum and light variation curve are similar to those of IIp supernovae, and the natural explosion following the core collapse is more like a giant type Ia supernova with carbon oxygen and silicon nuclear fusion out of control.The total energy release of the event with the highest mass is comparable to that of other core collapsing supernovae, but the production of neutrinos is considered very low, so the kinetic energy and electromagnetic radiation energy are very high.The core of these stars is far larger than any white dwarf, and the amount of radioactive nickel and other elements thrown out will also be more, so the visual luminosity will be several poles higher.
Recent observations
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The last supernova observed in the Milky Way was Kepler's star in 1604 (SN 1604);Retrospective analysis has found two new debris[30]。Observations of other galaxies show that there are three supernovae in the Milky Way every century on average, and with astronomical observation equipment, these galactic supernovae will almost certainly be observed[31]。Their roles enrich interstellar matter and high-quality chemical elements[32]。In addition, the outward expanding shock wave from the supernova can trigger the formation of new stars[33-35]。
An international research team led by researcher Dong Subo of Peking University in China announced on the 14th that they had observed the strongest supernova explosion ever recorded in human history, with the highest brightness equivalent to 570 billion suns.[36]
Domestic research
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According to《National Astronomy of China》Magazine news, byBeijingAn international team led by Dong Subo, a "" researcher at the Kevley Institute of Astronomy and Astrophysics, University, has discovered a supernova.
This latest research achievement was discovered in the summer of 2015, and then was published in the journal Science on January 15, 2016 as the first and corresponding author of East Soviet Union.This article introduces that ASASSN-15lh is 3.8 billion light years away from the Earth, and it is a member of the rare "extremely bright supernova" family.Its discovery is expected to provide important clues for astronomers to uncover the mystery of the explosion of extremely bright supernovae.
According to China National Astronomy, supernovae are violent explosions of stars at the end of life.Nearly 2000 years ago, Chinese astronomersThe Book of the Later Han DynastyThe first supernova explosion in human history was recorded in.This supernova, now called SN 185, is classified as type Ia by astronomers.Since then, humans have recorded tens of thousands of supernovae, of which the most common type is type Ia.The discovery of a supernova in the summer of 2015 shocked the astronomical world - its explosion intensity was about 200 times more than that of Type Ia supernova, more than twice that of the record holder.
The maximum luminosity of ASASSN-15lh is 570 billion times stronger than that of the sun, about 20 times the total luminosity of hundreds of billions of stars in the entire Milky Way.In his research achievements, East Supo said: "ASASSN-15lh is the strongest supernova explosion recorded by humans so far. Because of its high radiation energy, it is difficult for the supernova theory to give a satisfactory explanation of its explosion mechanism and energy source."
ASASSN-15lh was discovered by two 14cm telescopes in June 2015.On the day of discovery of ASASSN-15h, East Supo and its collaborators immediately disclosed relevant information to global supernova researchers so that people could observe more quickly and better.ASASSN-15lh has aroused strong interest of astronomers. Many large telescopes andU.S.ANASA's SwiftSpace telescopeImmediately began the follow-up observation.To this day, researchers are still observing this supernova in many wave bands from optics to X-ray to radio.
After discussion with colleagues Professor Jos é Preiet (University of Santiago de Badaris, Chile) and Professor Stanick, East Supo suddenly realized that ASASSN-15lh might belong to extremely bright supernova.According to his conjecture, if ASASSN-15lh is 3.8 billion light-years away from us, then its most prominent spectral line features match the spectrum of an extremely bright supernova found in 2010.If this inference is correct, it should be possible to see the absorption spectrum line of supernova light passing through the gas in the host galaxy at a specific wavelength.However, the expected characteristic absorption spectral line has a short wavelength, which can only be observed with an instrument covering enough blue end spectrum.In the next few days, East Sober and his colleagues contacted three telescopes that could shoot the blue end spectrum. Unfortunately, several observations failed due to weather and instrument failures.Ten days later, 10 meter caliber“South AfricaThe huge telescope "(SALT) finally succeeded in capturing the required spectrum, and the inference of East Supo was confirmed.
According to the National Astronomy of China, at 2:00 a.m. Beijing time on July 1, 2015, East Subo received the observation information from the South African telescope.He said: "When I saw the spectrum taken by the South African telescope and realized that we had discovered the strongest supernova explosion in history, I was too excited to sleep all night."
East Soviet Union is the core member of the strategic pilot project of the Chinese Academy of Sciences on the origin of the cosmic structure.This strategic pilot project led by the National Astronomical Observatory has created a comprehensive observation network of advanced telescopes at home and abroad, focusing on fostering the development and breakthrough of many scientific frontier fields, including time domain astronomy.The discovery of this extreme supernova is also a great achievement of Chinese scientists in the field of time-domain astronomy.
Astronomical circles believe that supernovae are at the intersection of many different branches of astronomical research.As the final destination of many kinds of stellar life, supernovae can be used to test the current stellar evolution theory.[37]
