We have already seen that, unlike the Sun and other stationary stars, physical variable stars change in size, temperature of the photosphere, and luminosity. Among the various types of non-stationary stars, novae and supernovae are of particular interest. In fact, these are not newly appeared stars, but pre-existing ones that attracted attention by a sharp increase in brightness.
During the outbursts of new stars, the brightness increases thousands and millions of times over a period of several days to several months. There are known stars that have repeatedly flared up as novae. According to modern data, new stars are usually part of binary systems, and outbursts of one of the stars occur as a result of the exchange of matter between the stars forming the binary system. For example, in the “white dwarf – ordinary star (low luminosity)” system, explosions that cause the phenomenon of a nova can occur when gas falls from an ordinary star onto a white dwarf.
Even more grandiose are the explosions of supernovae, the brightness of which suddenly increases by about 19 m! At maximum brightness, the radiating surface of the star approaches the observer at a speed of several thousand kilometers per second. The pattern of supernova explosions suggests that supernovae are exploding stars.
During supernova explosions, enormous energy is released over several days - about 10 41 J. Such colossal explosions occur at the final stages of the evolution of stars, the mass of which is several times greater than the mass of the Sun.
At its maximum brightness, one supernova can shine brighter than a billion stars like our Sun. During the most powerful explosions of some supernovae, matter can be ejected at a speed of 5000 - 7000 km/s, the mass of which reaches several solar masses. The remnants of shells ejected by supernovae are visible for a long time as expanding gas.
Not only the remains of supernova shells have been discovered, but also what remains of the central part of the once-exploded star. These “stellar remnants” turned out to be amazing sources of radio emission, which were called pulsars. The first pulsars were discovered in 1967.
Some pulsars have an amazingly stable repetition rate of radio pulses: pulses are repeated at strictly equal intervals of time, measured with an accuracy exceeding 10 -9 s! Open pulsars are located from us at distances not exceeding hundreds of parsecs. It is assumed that pulsars are rapidly rotating super-dense stars with radii of about 10 km and masses close to the mass of the Sun. Such stars consist of densely packed neutrons and are called neutron stars. Only part of the time of their existence do neutron stars manifest themselves as pulsars.
Supernova explosions are rare phenomena. Over the past millennium, only a few supernova explosions have been observed in our star system. Of these, the following three have been most reliably established: an outbreak in 1054 in the constellation Taurus, in 1572 in the constellation Cassiopeia, in 1604 in the constellation Ophiuchus. The first of these supernovae was described as a “guest star” by Chinese and Japanese astronomers, the second by Tycho Brahe, and the third was observed by Johannes Kepler. The brilliance of the supernovae of 1054 and 1572 exceeded the brilliance of Venus, and these stars were visible during the day. Since the invention of the telescope (1609), not a single supernova has been observed in our star system (it is possible that some explosions went unnoticed). When the opportunity arose to explore other star systems, new stars and supernovae were often discovered in them.
On February 23, 1987, a supernova exploded in the Large Magellanic Cloud (constellation Doradus), the largest satellite of our Galaxy. For the first time since 1604, a supernova could be seen even with the naked eye. Before the explosion, there was a 12th magnitude star at the site of the supernova. The star reached its maximum brightness of 4 m in early March, and then began to slowly fade. Scientists who observed the supernova using telescopes from the largest ground-based observatories, the Astron orbital observatory and X-ray telescopes on the Kvant module of the Mir orbital station were able to trace the entire outbreak process for the first time. Observations were carried out in different spectral ranges, including visible optical range, ultraviolet, X-ray and radio ranges. Sensational reports appeared in the scientific press about the detection of neutrino and, possibly, gravitational radiation from an exploding star. The model of the structure of the star in the phase preceding the explosion was refined and enriched with new results.
How many impressions are associated with these words among amateurs and professionals - space explorers. The word “new” itself carries a positive meaning, and “super” has a super positive meaning, but, unfortunately, it deceives the very essence. Supernovae can rather be called super-old stars, because they are practically the last stage of the development of a Star. So to speak, a bright eccentric apotheosis of star life. The flare sometimes eclipses the entire galaxy in which the dying star is located, and ends with its complete extinction.
Scientists have identified 2 types of Supernovae. One is affectionately nicknamed the explosion of a white dwarf (type I) which, compared to our sun, is denser, and at the same time much smaller in radius. Small, heavy White dwarf is the penultimate normal stage of the evolution of many stars. There is practically no hydrogen in the optical spectrum anymore. And if a white dwarf exists in a symbiosis of a binary system with another star, it draws its matter until it exceeds its limit. S. Chandresekhar in the 30s of the 20th century said that each dwarf has a clear limit of density and mass, exceeding which collapse occurs. It is impossible to shrink endlessly and sooner or later an explosion must occur! The second type of supernova formation is caused by the process of thermonuclear fusion, which forms heavy metals and contracts into itself, causing the temperature in the center of the star to rise. The core of the star is compressed more and more and neutronization processes (“grating” protons and electrons, during which both turn into neutrons) begin to occur in it, which leads to a loss of energy and cooling of the center of the star. All this provokes a rarefied atmosphere, and the shell rushes towards the core. Explosion! Myriads of small pieces of a star scatter throughout space, and a bright glow from a distant galaxy, where millions of years ago (the number of zeros in years of visibility of a star depends on its distance from Earth) the star exploded, is visible today to scientists of planet Earth. News of the tragedy of the past, another life cut short, a sad beauty that we can sometimes observe for centuries.
For example, the Crab Nebula, which can be seen through the telescope eye of modern observatories, is the consequences of a supernova explosion, which was seen by Chinese astronomers in 1054. It is so interesting to realize that what you are looking at today was admired for almost 1000 years by a person who no longer existed on Earth for a long time. This is the whole mystery of the Universe, its slow, drawn-out existence, which makes our life like a flash of a spark from a fire, it amazes and leads to some awe. Scientists have identified several of the most famous supernova explosions, which are designated according to a clearly defined scheme. Latin SuperNova is abbreviated to the characters SN, followed by the year of observation, and at the end the serial number in the year is written. Thus, the following names of famous supernovae can be seen:
The Crab Nebula - as mentioned earlier, it is the result of a supernova explosion, which is located at a distance of 6,500 light years from Earth, with a diameter today of 6,000 light years. This nebula continues to fly apart in different directions, although the explosion occurred just under 1000 years ago. And in its center there is a neutron star-pulsar, which rotates around its axis. Interestingly, at high brightness this nebula has a constant flow of energy, which allows it to be used as a reference point in the calibration of X-ray astronomy. Another find was supernova SN1572; as the name suggests, scientists observed the explosion in November 1572. By all indications, this star was a white dwarf. In 1604, for a whole year, Chinese, Korean, and then European astrologers could observe the explosion-glow of supernova SN1604, which was located in the constellation Ophiuchus. Johannes Kepler devoted his main work to its study, “On a new star in the constellation Ophiuchus,” and therefore the supernova was named after the scientist - SuperNova Kepler. The closest supernova explosion occurred in 1987 - SN1987A, located in the Large Magellanic Cloud 50 parsecs from our Sun, a dwarf galaxy - a satellite of the Milky Way. This explosion overturned some of the already established theories of stellar evolution. It was supposed that only red giants could flare up, but then, inopportunely, a blue one exploded! Blue supergiant (mass more than 17 solar masses) Sanduleak. The very beautiful remains of the planet form two unusual connecting rings, which scientists are studying today. The next supernova amazed scientists in 1993 - SN1993J, which before the explosion was a red supergiant. But the surprising thing is that the remnants, which were supposed to fade out after the explosion, on the contrary, began to gain brightness. Why?
A few years later, a satellite planet was discovered that was not damaged by the supernova explosion of its neighbor and created the conditions for the glow of the shell of the companion star that was torn off shortly before the explosion (neighbors are neighbors, but you can’t argue with gravity...), observed by scientists. This star is also predicted to become a red giant and a supernova. The explosion of the next supernova in 2006 (SN206gy) is recognized as the brightest glow in the entire history of observing these phenomena. This allowed scientists to put forward new theories of supernova explosions (such as quark stars, the collision of two massive planets, and others) and call this explosion a hypernova explosion! And the last interesting supernova is G1.9+0.3. For the first time, its signals as a radio source of the Galaxy were caught by the VLA radio telescope. And today the Chandra Observatory is studying it. The rate of expansion of the remains of the exploded star is amazing; it is 15,000 km per hour! Which is 5% of the speed of light!
In addition to these most interesting supernova explosions and their remnants, of course, there are other “everyday” events in space. But the fact remains that everything that surrounds us today is the result of supernova explosions. Indeed, in theory, at the beginning of its existence, the Universe consisted of light gases of helium and hydrogen, which, during the burning of stars, were transformed into other “building” elements for all currently existing planets. In other words, the Stars gave their lives for the birth of a new life!
Their occurrence is a rather rare cosmic phenomenon. On average, three supernovae explode per century in the observable universe. Each such flare is a gigantic cosmic catastrophe, releasing an incredible amount of energy. According to the roughest estimate, this amount of energy could be generated by the simultaneous explosion of many billions of hydrogen bombs.
There is no sufficiently rigorous theory of supernova explosions yet, but scientists have put forward an interesting hypothesis. They suggested, based on complex calculations, that during the alpha synthesis of elements the core continues to shrink. The temperature in it reaches a fantastic figure - 3 billion degrees. Under such conditions, various processes in the core are significantly accelerated; As a result, a lot of energy is released. The rapid compression of the core entails an equally rapid compression of the star's shell.
It also heats up greatly, and the nuclear reactions occurring in it, in turn, are greatly accelerated. Thus, literally in a matter of seconds, a huge amount of energy is released. This leads to an explosion. Of course, such conditions are not always achieved, and therefore supernovae flare quite rarely.
This is the hypothesis. The future will show how right scientists are in their assumptions. But the present has also led researchers to absolutely amazing guesses. Astrophysical methods have made it possible to trace how the luminosity of supernovae decreases. And this is what turned out to be: in the first few days after the explosion, the luminosity decreases very quickly, and then this decrease (within 600 days) slows down. Moreover, every 55 days the luminosity weakens exactly by half. From a mathematical point of view, this decrease occurs according to the so-called exponential law. A good example of such a law is the law of radioactive decay. Scientists have made a bold assumption: the release of energy after a supernova explosion is due to the radioactive decay of an isotope of an element with a half-life of 55 days.
But which isotope and which element? These searches continued for several years. Beryllium-7 and strontium-89 were “candidates” for the role of such “generators” of energy. They disintegrated by half in just 55 days. But they did not have the chance to pass the exam: calculations showed that the energy released during their beta decay was too small. But other known radioactive isotopes did not have a similar half-life.
A new contender has emerged among elements that do not exist on Earth. It turned out to be a representative of transuranium elements synthesized artificially by scientists. The name of the applicant is Californian, his serial number is ninety-eight. Its isotope californium-254 was prepared in an amount of only about 30 billionths of a gram. But this truly weightless amount was enough to measure the half-life of the isotope. It turned out to be equal to 55 days.
And from here a curious hypothesis arose: it is the decay energy of California-254 that ensures the unusually high luminosity of a supernova for two years. The decay of californium occurs through the spontaneous fission of its nuclei; With this type of decay, the nucleus seems to split into two fragments - the nuclei of the elements in the middle of the periodic table.
But how is californium itself synthesized? Scientists give a logical explanation here too. During the compression of the nucleus preceding the supernova explosion, the nuclear reaction of the interaction of the already familiar neon-21 with alpha particles is unusually accelerated. The consequence of this is the appearance within a fairly short period of time of an extremely powerful neutron flux. The process of neutron capture occurs again, but this time it is fast. The nuclei manage to absorb the next neutrons before they undergo beta decay. For this process, the instability of transbismuth elements is no longer an obstacle. The chain of transformations will not break, and the end of the periodic table will also be filled. In this case, apparently, even transuranium elements are formed that have not yet been obtained under artificial conditions.
Scientists have calculated that each supernova explosion produces a fantastic amount of California-254 alone. From this quantity it would be possible to make 20 balls, each of which would weigh as much as our Earth. What is the further fate of the supernova? She dies pretty quickly. At the site of its outbreak, only a small, very faint star remains. It is distinguished, however, by the unusually high density of the substance: a matchbox filled with it would weigh tens of tons. Such stars are called "". We don’t yet know what happens to them next.
Matter that is ejected into outer space can condense and form new stars; they will begin a new long path of development. Scientists have so far made only general rough strokes of the picture of the origin of elements, a picture of the work of stars - grand factories of atoms. Perhaps this comparison generally conveys the essence of the matter: the artist sketches on the canvas only the first outlines of the future work of art. The main idea is already clear, but many, including significant, details still have to be guessed.
The final solution to the problem of the origin of elements will require enormous work by scientists of various specialties. It is likely that much that now seems undoubted to us will in fact turn out to be roughly approximate, or even completely incorrect. Scientists will probably have to face patterns that are still unknown to us. Indeed, in order to understand the most complex processes occurring in the Universe, there will undoubtedly be a need for a new qualitative leap in the development of our ideas about it.
SUPERNOVA, explosion that marked the death of a star. Sometimes a supernova explosion is brighter than the galaxy in which it occurred.
Supernovae are divided into two main types. Type I is characterized by a deficiency of hydrogen in the optical spectrum; therefore, it is believed that this is an explosion of a white dwarf - a star with a mass close to the Sun, but smaller in size and more dense. A white dwarf contains almost no hydrogen, since it is the end product of the evolution of a normal star. In the 1930s, S. Chandrasekhar showed that the mass of a white dwarf cannot be above a certain limit. If it is in a binary system with a normal star, then its matter can flow onto the surface of the white dwarf. When its mass exceeds the Chandrasekhar limit, the white dwarf collapses (shrinks), heats up and explodes. see also STARS.
A type II supernova erupted on February 23, 1987 in our neighboring galaxy, the Large Magellanic Cloud. She was given the name of Ian Shelton, who was the first to notice a supernova explosion using a telescope, and then with the naked eye. (The last such discovery belongs to Kepler, who saw a supernova explosion in our Galaxy in 1604, shortly before the invention of the telescope.) Simultaneously with the optical supernova explosion of 1987, special detectors in Japan and in the United States. Ohio (USA) recorded a flux of neutrinos - elementary particles born at very high temperatures during the collapse of the star's core and easily penetrating through its shell. Although the stream of neutrinos was emitted by a star along with an optical flare approximately 150 thousand years ago, it reached Earth almost simultaneously with photons, thereby proving that neutrinos have no mass and move at the speed of light. These observations also confirmed the assumption that about 10% of the mass of the collapsing stellar core is emitted in the form of neutrinos when the core itself collapses into a neutron star. In very massive stars, during a supernova explosion, the cores are compressed to even greater densities and probably turn into black holes, but the outer layers of the star are still shed. Cm. Also BLACK HOLE.
In our Galaxy, the Crab Nebula is the remnant of a supernova explosion, which was observed by Chinese scientists in 1054. The famous astronomer T. Brahe also observed a supernova that broke out in our Galaxy in 1572. Although Shelton's supernova was the first nearby supernova discovered since Kepler, hundreds of supernovae in other, more distant galaxies have been seen by telescopes over the past 100 years.
Carbon, oxygen, iron and heavier elements can be found in the remnants of a supernova explosion. Consequently, these explosions play an important role in nucleosynthesis, the process of formation of chemical elements. It is possible that 5 billion years ago the birth of the Solar system was also preceded by a supernova explosion, as a result of which many elements that became part of the Sun and planets arose. NUCLEOSYNTHESIS.
Supernova or supernova explosion- a phenomenon during which a star sharply changes its brightness by 4-8 orders of magnitude (a dozen magnitudes) followed by a relatively slow attenuation of the flare. It is the result of a cataclysmic process that occurs at the end of the evolution of some stars and is accompanied by the release of enormous energy.
As a rule, supernovae are observed after the fact, that is, when the event has already occurred and its radiation has reached the Earth. Therefore, the nature of supernovae has long been unclear. But now quite a lot of scenarios are proposed that lead to outbreaks of this kind, although the main provisions are already quite clear.
The explosion is accompanied by the ejection of a significant mass of matter from the outer shell of the star into interstellar space, and from the remaining part of the matter from the core of the exploded star, as a rule, a compact object is formed - a neutron star, if the mass of the star before the explosion was more than 8 solar masses (M ☉), or a black star a hole with a star mass over 20 M ☉ (the mass of the core remaining after the explosion is over 5 M ☉). Together they form a supernova remnant.
A comprehensive study of previously obtained spectra and light curves in combination with the study of remnants and possible progenitor stars makes it possible to build more detailed models and study the conditions that existed at the time of the outburst.
Among other things, the material ejected during the flare largely contains products of thermonuclear fusion that occurred throughout the life of the star. It is thanks to supernovae that the Universe as a whole and each galaxy in particular chemically evolves.
The name reflects the historical process of studying stars whose brightness changes significantly over time, the so-called novae.
The name is made up of the label SN, followed by the year of opening, followed by a one- or two-letter designation. The first 26 supernovae of the current year receive single-letter designations, at the end of the name, from capital letters from A before Z. The remaining supernovae receive two-letter designations from lowercase letters: aa, ab, and so on. Unconfirmed supernovae are designated by letters PSN(eng. possible supernova) with celestial coordinates in the format: Jhhmmssss+ddmmsss.
The big picture
| Class | Subclass | Mechanism | ||||||
|---|---|---|---|---|---|---|---|---|
| I No hydrogen lines |
Strong lines of ionized silicon (Si II) at 6150 | Ia | Thermonuclear explosion | |||||
| Iax At maximum brightness they have lower luminosity and lower Ia in comparison |
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| Silicon lines are weak or absent | Ib Helium (He I) lines are present. |
Gravitational collapse | ||||||
| Ic Helium lines are weak or absent |
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| II Hydrogen lines present |
II-P/L/N The spectrum is constant |
II-P/L No narrow lines |
II-P The light curve has a plateau |
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| II-L Magnitude decreases linearly with time |
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| IIn Narrow lines present |
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| IIb The spectrum changes over time and becomes similar to the Ib spectrum. |
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Light curves
The light curves for type I are highly similar: there is a sharp increase for 2-3 days, then it is replaced by a significant drop (by 3 magnitudes) for 25-40 days, followed by a slow weakening, almost linear on the magnitude scale. The average absolute magnitude of the maximum for Ia flares is M B = − 19.5 m (\textstyle M_(B)=-19.5^(m)), for Ib\c - .
But the light curves of type II are quite varied. For some, the curves resembled those for type I, only with a slower and longer decline in brightness until the linear stage began. Others, having reached a peak, stayed at it for up to 100 days, and then the brightness dropped sharply and reached a linear “tail.” The absolute magnitude of the maximum varies widely from − 20 m (\textstyle -20^(m)) before − 13 m (\textstyle -13^(m)). Average value for IIp - M B = − 18 m (\textstyle M_(B)=-18^(m)), for II-L M B = − 17 m (\textstyle M_(B)=-17^(m)).
Spectra
The above classification already contains some basic features of the spectra of supernovae of various types; let us dwell on what is not included. The first and very important feature, which for a long time prevented the interpretation of the obtained spectra, is that the main lines are very broad.
The spectra of type II and Ib\c supernovae are characterized by:
- The presence of narrow absorption features near the brightness maximum and narrow undisplaced emission components.
- Lines , , , observed in ultraviolet radiation.
Observations outside the optical range
Flash rate
The frequency of flares depends on the number of stars in the galaxy or, which is the same for ordinary galaxies, luminosity. A generally accepted quantity characterizing the frequency of flares in different types of galaxies is SNu:
1 S N u = 1 S N 10 10 L ⊙ (B) ∗ 100 y e a r (\displaystyle 1SNu=(\frac (1SN)(10^(10)L_(\odot )(B)*100year))),
Where L ⊙ (B) (\textstyle L_(\odot )(B))- luminosity of the Sun in filter B. For different types of flares its value is:
In this case, supernovae Ib/c and II gravitate towards spiral arms.
Observing supernova remnants
The canonical scheme of the young remainder is as follows:
- Possible compact remainder; usually a pulsar, but possibly a black hole
- External shock wave propagating in interstellar matter.
- A return wave propagating in the supernova ejecta material.
- Secondary, propagating in clumps of the interstellar medium and in dense supernova emissions.
Together they form the following picture: behind the front of the external shock wave, the gas is heated to temperatures T S ≥ 10 7 K and emits in the X-ray range with a photon energy of 0.1-20 keV; similarly, the gas behind the front of the return wave forms a second region of X-ray radiation. Lines of highly ionized Fe, Si, S, etc. indicate the thermal nature of the radiation from both layers.
Optical radiation from the young remnant creates gas in clumps behind the front of the secondary wave. Since the propagation speed in them is higher, which means the gas cools faster and the radiation passes from the X-ray range to the optical range. The impact origin of the optical radiation is confirmed by the relative intensity of the lines.
Theoretical description
Decomposition of observations
The nature of supernovae Ia is different from the nature of other explosions. This is clearly evidenced by the absence of type Ib\c and type II flares in elliptical galaxies. From general information about the latter, it is known that there is little gas and blue stars there, and star formation ended 10 10 years ago. This means that all massive stars have already completed their evolution, and only stars with a mass less than the solar mass remain, and no more. From the theory of stellar evolution it is known that stars of this type cannot be exploded, and therefore a life extension mechanism is needed for stars with masses of 1-2M ⊙.
The absence of hydrogen lines in the Ia\Iax spectra indicates that there is extremely little hydrogen in the atmosphere of the original star. The mass of the ejected substance is quite large - 1M ⊙, mainly containing carbon, oxygen and other heavy elements. And the shifted Si II lines indicate that nuclear reactions are actively occurring during the ejection. All this convinces that the predecessor star is a white dwarf, most likely carbon-oxygen.
The attraction to the spiral arms of type Ib\c and type II supernovae indicates that the progenitor star is short-lived O-stars with a mass of 8-10M ⊙ .
Thermonuclear explosion
One of the ways to release the required amount of energy is a sharp increase in the mass of the substance involved in thermonuclear combustion, that is, a thermonuclear explosion. However, the physics of single stars does not allow this. Processes in stars located on the main sequence are in equilibrium. Therefore, all models consider the final stage of stellar evolution - white dwarfs. However, the latter itself is a stable star, and everything can change only when approaching the Chandrasekhar limit. This leads to the unambiguous conclusion that a thermonuclear explosion is possible only in multiple star systems, most likely in the so-called double stars.
In this scheme, there are two variables that influence the state, chemical composition and final mass of the substance involved in the explosion.
- The second companion is an ordinary star, from which matter flows to the first.
- The second companion is the same white dwarf. This scenario is called double degeneracy.
- An explosion occurs when the Chandrasekhar limit is exceeded.
- The explosion occurs before him.
What all supernova Ia scenarios have in common is that the exploding dwarf is most likely carbon-oxygen. In the explosive combustion wave traveling from the center to the surface, the following reactions occur:
12 C + 16 O → 28 S i + γ (Q = 16.76 M e V) (\displaystyle ^(12)C~+~^(16)O~\rightarrow ~^(28)Si~+~\gamma ~ (Q=16.76~MeV)), 28 S i + 28 S i → 56 N i + γ (Q = 10.92 M e V) (\displaystyle ^(28)Si~+~^(28)Si~\rightarrow ~^(56)Ni~+~\ gamma ~(Q=10.92~MeV)).The mass of the reacting substance determines the energy of the explosion and, accordingly, the maximum brightness. If we assume that the entire mass of the white dwarf reacts, then the energy of the explosion will be 2.2 10 51 erg.
The further behavior of the light curve is mainly determined by the decay chain:
56 N i → 56 C o → 56 F e (\displaystyle ^(56)Ni~\rightarrow ~^(56)Co~\rightarrow ~^(56)Fe)The isotope 56 Ni is unstable and has a half-life of 6.1 days. Further e-capture leads to the formation of a 56 Co nucleus predominantly in an excited state with an energy of 1.72 MeV. This level is unstable, and the transition of the electron to the ground state is accompanied by the emission of a cascade of γ quanta with energies from 0.163 MeV to 1.56 MeV. These quanta experience Compton scattering, and their energy quickly decreases to ~100 keV. Such quanta are already effectively absorbed by the photoelectric effect, and, as a result, heat the substance. As the star expands, the density of matter in the star decreases, the number of photon collisions decreases, and the material on the star's surface becomes transparent to radiation. As theoretical calculations show, this situation occurs approximately 20-30 days after the star reaches its maximum luminosity.
60 days after the onset, the substance becomes transparent to γ-radiation. The light curve begins to decay exponentially. By this time, the 56 Ni isotope has already decayed, and the energy release is due to the β-decay of 56 Co to 56 Fe (T 1/2 = 77 days) with excitation energies up to 4.2 MeV.
Gravitational core collapse
The second scenario for the release of the necessary energy is the collapse of the star's core. Its mass should be exactly equal to the mass of its remnant - a neutron star, substituting typical values we get:
E t o t ∼ G M 2 R ∼ 10 53 (\displaystyle E_(tot)\sim (\frac (GM^(2))(R))\sim 10^(53)) erg,where M = 0, and R = 10 km, G is the gravitational constant. The characteristic time for this is:
τ f f ∼ 1 G ρ 4 ⋅ 10 − 3 ⋅ ρ 12 − 0 , 5 (\displaystyle \tau _(ff)\sim (\frac (1)(\sqrt (G\rho )))~4\cdot 10 ^(-3)\cdot \rho _(12)^(-0.5)) c,where ρ 12 is the density of the star, normalized to 10 12 g/cm 3 .
The resulting value is two orders of magnitude greater than the kinetic energy of the shell. A carrier is needed that, on the one hand, must carry away the released energy, and on the other, not interact with the substance. Neutrinos are suitable for the role of such a carrier.
Several processes are responsible for their formation. The first and most important for the destabilization of a star and the beginning of contraction is the process of neutronization:
3 H e + e − → 3 H + ν e (\displaystyle ()^(3)He+e^(-)\to ()^(3)H+\nu _(e))
4 H e + e − → 3 H + n + ν e (\displaystyle ()^(4)He+e^(-)\to ()^(3)H+n+\nu _(e))
56 F e + e − → 56 M n + ν e (\displaystyle ()^(56)Fe+e^(-)\to ()^(56)Mn+\nu _(e))
Neutrinos from these reactions carry away 10%. The main role in cooling is played by URKA processes (neutrino cooling):
E + + n → ν ~ e + p (\displaystyle e^(+)+n\to (\tilde (\nu ))_(e)+p)
E − + p → ν e + n (\displaystyle e^(-)+p\to \nu _(e)+n)
Instead of protons and neutrons, atomic nuclei can also act, forming an unstable isotope that experiences beta decay:
E − + (A , Z) → (A , Z − 1) + ν e , (\displaystyle e^(-)+(A,Z)\to (A,Z-1)+\nu _(e) ,)
(A , Z − 1) → (A , Z) + e − + ν ~ e .
(\displaystyle (A,Z-1)\to (A,Z)+e^(-)+(\tilde (\nu ))_(e).) The intensity of these processes increases with compression, thereby accelerating it. This process is stopped by the scattering of neutrinos on degenerate electrons, during which they are thermolyzed and locked inside the substance. A sufficient concentration of degenerate electrons is achieved at densitiesρ n u c = 2, 8 ⋅ 10 14 (\textstyle \rho _(nuc)=2,8\cdot 10^(14))
g/cm 3 .
Note that neutronization processes occur only at densities of 10 11 /cm 3, achievable only in the stellar core. This means that hydrodynamic equilibrium is disturbed only in it. The outer layers are in local hydrodynamic equilibrium, and collapse begins only after the central core contracts and forms a solid surface. The rebound from this surface ensures the release of the shell.
Model of a young supernova remnant
Supernova remnant evolution theory
There are three stages in the evolution of the supernova remnant:
The expansion of the shell stops at the moment when the pressure of the gas in the remnant equals the pressure of the gas in the interstellar medium. After this, the residue begins to dissipate, colliding with chaotically moving clouds. Resorption time reaches: T m a x = 7 E 51 0.32 n 0 0.34 P ~ 0 , 4 − 0.7 (\displaystyle t_(max)=7E_(51)^(0.32)n_(0)^(0.34)(\tilde (P))_( 0.4)^(-0.7))
years
Theory of the occurrence of synchrotron radiation
Construction of a detailed description
Search for supernova remnants
Search for precursor stars
Supernova Ia theory
- In addition to the uncertainties in the supernova Ia theories described above, the mechanism of the explosion itself has been a source of much controversy. Most often, models can be divided into the following groups:
- Instant detonation
- Delayed detonation
- Pulsating delayed detonation
At least for each combination of initial conditions, the listed mechanisms can be found in one variation or another. But the range of proposed models is not limited to this. An example is a model where two white dwarfs detonate at once. Naturally, this is only possible in scenarios where both components have evolved.
Chemical evolution and impact on the interstellar medium
Chemical evolution of the Universe. Origin of elements with atomic number higher than iron
Supernova explosions are the main source of replenishment of the interstellar medium with elements with atomic numbers greater (or as they say heavier) He . However, the processes that gave rise to them are different for different groups of elements and even isotopes.
R process
r-process is the process of the formation of heavier nuclei from lighter ones through the sequential capture of neutrons during ( n,γ) reactions and continues until the rate of neutron capture is higher than the rate of β − -decay of the isotope. In other words, the average time of capture of n neutrons τ(n,γ) should be:
τ (n , γ) ≈ 1 n τ β (\displaystyle \tau (n,\gamma)\approx (\frac (1)(n))\tau _(\beta ))where τ β is the average time of β-decay of nuclei forming a chain of the r-process. This condition imposes a limitation on the neutron density, because:
τ (n , γ) ≈ (ρ (σ n γ , v n) ¯) − 1 (\displaystyle \tau (n,\gamma)\approx \left(\rho (\overline ((\sigma _(n\gamma ),v_(n))))\right)^(-1))Where (σ n γ , v n) ¯ (\displaystyle (\overline ((\sigma _(n\gamma),v_(n)))))- product of the reaction cross section ( n,γ) on the neutron velocity relative to the target nucleus, averaged over the Maxwellian spectrum of the velocity distribution. Considering that the r-process occurs in heavy and medium nuclei, 0.1 s< τ β < 100 с, то для n ~ 10 и температуры среды T = 10 9 , получим характерную плотность
ρ ≈ 2 ⋅ 10 17 (\displaystyle \rho \approx 2\cdot 10^(17)) neutrons/cm 3 .Such conditions are achieved in:
ν-process
Main article: ν-process
ν-process is a process of nucleosynthesis through the interaction of neutrinos with atomic nuclei. It may be responsible for the appearance of the isotopes 7 Li, 11 B, 19 F, 138 La and 180 Ta
Impact on the large-scale structure of the galaxy's interstellar gas
Observation history
Hipparchus's interest in the fixed stars may have been inspired by the observation of a supernova (according to Pliny). Earliest record identified as supernova SN 185 (English), was made by Chinese astronomers in 185 AD. The brightest known supernova, SN 1006, has been described in detail by Chinese and Arab astronomers. The supernova SN 1054, which gave birth to the Crab Nebula, was well observed. Supernovae SN 1572 and SN 1604 were visible to the naked eye and were of great importance in the development of astronomy in Europe, as they were used as an argument against the Aristotelian idea that the world beyond the Moon and the Solar System is unchanging. Johannes Kepler began observing SN 1604 on October 17, 1604. This was the second supernova that was recorded at the stage of increasing brightness (after SN 1572, observed by Tycho Brahe in the constellation Cassiopeia).
With the development of telescopes, it became possible to observe supernovae in other galaxies, starting with observations of the supernova S Andromeda in the Andromeda Nebula in 1885. During the twentieth century, successful models for each type of supernova were developed and understanding of their role in star formation increased. In 1941, American astronomers Rudolf Minkowski and Fritz Zwicky developed a modern classification scheme for supernovae.
In the 1960s, astronomers discovered that the maximum luminosity of supernova explosions could be used as a standard candle, hence a measure of astronomical distances. Supernovae now provide important information about cosmological distances. The most distant supernovae turned out to be fainter than expected, which, according to modern ideas, shows that the expansion of the Universe is accelerating.
Methods have been developed to reconstruct the history of supernova explosions that have no written observational records. The date of supernova Cassiopeia A was determined from the light echo from the nebula, while the age of supernova remnant RX J0852.0-4622 (English) estimated by measuring temperature and γ emissions from the decay of titanium-44. In 2009, nitrates were discovered in Antarctic ice, consistent with the timing of the supernova explosion.
On February 23, 1987, supernova SN 1987A, the closest to Earth observed since the invention of the telescope, exploded in the Large Magellanic Cloud at a distance of 168 thousand light years from Earth. For the first time, the neutrino flux from the flare was recorded. The flare was intensively studied using astronomical satellites in the ultraviolet, X-ray and gamma-ray ranges. The supernova remnant was studied using ALMA, Hubble and Chandra. Neither a neutron star nor a black hole, which, according to some models, should be located at the site of the flare, have yet been discovered.
On January 22, 2014, the supernova SN 2014J erupted in the M82 galaxy, located in the constellation Ursa Major. Galaxy M82 is located 12 million light-years from our galaxy and has an apparent magnitude of just under 9. This supernova is the closest to Earth since 1987 (SN 1987A).
The most famous supernovae and their remnants
- Supernova SN 1604 (Kepler Supernova)
- Supernova G1.9+0.3 (The youngest known in our Galaxy)
Historical supernovae in our Galaxy (observed)
| Supernova | Outbreak date | Constellation | Max. shine | Distance yaniye (saint years) |
Flash type shki |
Length tel- visibility bridges |
Remainder | Notes |
|---|---|---|---|---|---|---|---|---|
| SN 185 | , December 7 | Centaurus | −8 | 3000 | Ia? | 8-20 months | G315.4-2.3 (RCW 86) | Chinese records: observed near Alpha Centauri. |
| SN 369 | unknown | not from- known |
not from- known |
not from- known |
5 months | unknown | Chinese chronicles: the situation is very poorly known. If it was near the galactic equator, it was very likely that it was a supernova; if not, it was most likely a slow nova. | |
| SN 386 | Sagittarius | +1,5 | 16 000 | II? | 2-4 months | G11.2-0.3 | Chinese chronicles | |
| SN 393 | Scorpion | 0 | 34 000 | not from- known |
8 months | several candidates | Chinese chronicles | |
| SN 1006 | , 1st of May | Wolf | −7,5 | 7200 | Ia | 18 months | SNR 1006 | Swiss monks, Arab scientists and Chinese astronomers. |
| SN 1054 | , 4th of July | Taurus | −6 | 6300 | II | 21 months | Crab Nebula | in the Near and Far East (not listed in European texts, apart from vague hints in Irish monastic chronicles). |
| SN 1181 | , August | Cassiopeia | −1 | 8500 | not from- known |
6 months | Possibly 3C58 (G130.7+3.1) | works of University of Paris professor Alexandre Nequem, Chinese and Japanese texts. |
| SN 1572 | , November 6 | Cassiopeia | −4 | 7500 | Ia | 16 months | Supernova Remnant Quiet | This event is recorded in many European sources, including in the records of the young Tycho Brahe. True, he noticed the flaring star only on November 11, but he followed it for a whole year and a half and wrote the book “De Nova Stella” (“On the New Star”) - the first astronomical work on this topic. |
| SN 1604 | , October 9 | Ophiuchus | −2,5 | 20000 | Ia | 18 months | Kepler's supernova remnant | From October 17, Johannes Kepler began to study it, who outlined his observations in a separate book. |
| SN 1680 | , 16 August | Cassiopeia | +6 | 10000 | IIb | not from- known (no more than a week) |
Supernova remnant Cassiopeia A | possibly seen by Flamsteed and cataloged as 3 Cassiopeiae. |