The birth and death of supernovae. Supernova - death or the beginning of a new life

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 various types Of nonstationary 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 dual system. For example, in the “white dwarf – ordinary star (low luminosity)” system, explosions causing the phenomenon 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 on final stages evolution of stars whose mass 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. Remains of shells discarded supernovas, visible for a long time like expanding gases.

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 classified as rare events. 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 of the largest ground-based observatories, the Astron orbital observatory and X-ray telescopes on the Kvant module orbital station“Mir”, it was possible for the first time to trace the entire process of the outbreak. 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.

The sky on a clear day presents, in general, a rather boring and monotonous picture: a hot ball of the Sun and a clear, endless expanse, sometimes decorated with clouds or rare clouds.

The sky on a cloudless night is another matter. It is usually all strewn with bright clusters of stars. It should be taken into account that in the night sky with the naked eye you can see from 3 to 4.5 thousand night luminaries. And they all belong to the Milky Way, in which our solar system is located.

According to modern concepts, stars are hot balls of gas, in the depths of which thermonuclear fusion of helium nuclei from hydrogen nuclei occurs, releasing a colossal amount of energy. It is this that ensures the luminosity of stars.

The closest star to us is our Sun, the distance to which is 150 million kilometers. But the star Proxima Centauri, the next most distant, is located at a distance of 4.25 light years from us, or 270 thousand times further than the Sun.

There are stars that are hundreds of times larger in size than the Sun and the same number of times inferior to it in this indicator. However, the masses of stars vary within much more modest limits - from one twelfth of the mass of the Sun to 100 of its masses. More than half visible stars are double and sometimes triple systems.

In general, the number of stars in the Universe visible to us can be designated by the number 125,000,000,000 with eleven additional zeros.

Now, in order to avoid confusion with zeros, astronomers no longer keep records of individual stars, but of entire galaxies, believing that on average there are about 100 billion stars in each of them.

American astronomer Fritz Zwicky first began to engage in a targeted search for supernovae

Back in 1996, scientists determined that 50 billion galaxies can be seen from Earth. When the Hubble Orbital Telescope was put into operation, which is not interfered with by interference from the Earth's atmosphere, the number of visible galaxies jumped to 125 billion.

Thanks to the all-seeing eye With this telescope, astronomers penetrated such universal depths that they saw galaxies that appeared just one billion years after the Great Explosion that gave birth to our Universe.

Several parameters are used to characterize stars: luminosity, mass, radius and chemical composition atmosphere, as well as its temperature. And using a number of additional characteristics of a star, you can also determine its age.

Each star is a dynamic structure that is born, grows and then, having reached a certain age, quietly dies. But it also happens that it suddenly explodes. This event leads to large-scale changes in the area adjacent to the exploding star.

Thus, the disturbance that followed this explosion spreads with gigantic speed, and over the course of several tens of thousands of years covers a huge space in the interstellar medium. In this region, the temperature rises sharply, up to several million degrees, and the density of cosmic rays and the magnetic field strength increase significantly.

Such features of the material ejected by an exploding star allow it to form new stars and even entire planetary systems.

For this reason, both supernovae and their remnants are studied very closely by astrophysicists. After all, the information obtained during the study of this phenomenon can expand knowledge about the evolution of normal stars, about the processes occurring during the birth of neutron stars, as well as clarify the details of those reactions that result in the formation of heavy elements, cosmic rays, etc.

At one time, those stars whose brightness unexpectedly increased by more than 1000 times were called new by astronomers. They appeared in the sky unexpectedly, making changes to the usual configuration of the constellations. Having suddenly increased several thousand times at maximum, their brightness after some time sharply decreased, and after a few years their brightness became as weak as before the explosion.

It should be noted that the periodicity of flares, during which a star is freed from one thousandth of its mass and which is thrown into outer space at enormous speed, is considered one of the main signs of the birth of new stars. But, at the same time, strangely enough, explosions of stars do not lead to significant changes in their structure, or even to their destruction.

How often do such events occur in our Galaxy? If we take into account only those stars whose brightness did not exceed the 3rd magnitude, then, according to historical chronicles and observations of astronomers, no more than 200 bright flares were observed over the course of five thousand years.

But when studies of other galaxies began, it became obvious that the brightness of new stars that appear in these corners of space is often equal to the luminosity of the entire galaxy in which these stars appear.

Of course, the appearance of stars with such luminosity is an extraordinary event and absolutely different from the birth of ordinary stars. Therefore, back in 1934, American astronomers Fritz Zwicky and Walter Baade proposed that those stars whose maximum brightness reaches the luminosity of ordinary galaxies be classified as a separate class of supernovae and the most bright stars. It should be borne in mind that supernova explosions in current state our Galaxy is an extremely rare phenomenon, occurring no more often than once every 100 years. The most striking outbreaks, which were recorded by Chinese and Japanese treatises, occurred in 1006 and 1054.

Five hundred years later, in 1572, a supernova explosion in the constellation Cassiopeia was observed by the outstanding astronomer Tycho Brahe. In 1604, Johannes Kepler saw the birth of a supernova in the constellation Ophiuchus. And since then, such grandiose events have not been celebrated in our Galaxy.

This may be due to the fact that the Solar system occupies such a position in our Galaxy that it can be observed in optical instruments Supernova explosions from the Earth are possible only in half of its volume. In the rest of the region, this is hampered by interstellar absorption of light.

And since in other galaxies these phenomena occur with approximately the same frequency as in Milky Way, the main information about supernovae at the time of the explosion was obtained from observations of them in other galaxies...

For the first time, astronomers W. Baade and F. Zwicky began to engage in a targeted search for supernovae in 1936. During three years of observations in different galaxies, scientists discovered 12 supernova explosions, which were subsequently subjected to more thorough study using photometry and spectroscopy.

Moreover, the use of more advanced astronomical equipment has made it possible to expand the list of newly discovered supernovae. And the introduction of automated searches led to the fact that scientists discovered more than a hundred supernovae per year. In total for a short time 1,500 of these objects were recorded.

IN last years by using powerful telescopes In one night of observations, scientists discovered more than 10 distant supernovae!

In January 1999, an event occurred that shocked even modern astronomers, accustomed to the many “tricks” of the Universe: in the depths of space, a flash ten times brighter than all those previously recorded by scientists was recorded. It was noticed by two research satellites and a telescope in the mountains of New Mexico, equipped with an automatic camera. This unique phenomenon occurred in the constellation Bootes. A little later, in April of the same year, scientists determined that the distance to the outbreak was nine billion light years. This is almost three-quarters of the radius of the Universe.

Calculations made by astronomers showed that in the few seconds during which the flare lasted, many times more energy was released than the Sun produced over the five billion years of its existence. What caused such an incredible explosion? What processes gave rise to this enormous energy release? Science cannot yet answer these questions specifically, although there is an assumption that great amount energy could occur in the event of the merger of two neutron stars.

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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 was unclear for a long time. 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

Modern classification supernovas

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
	Silicon lines are weak or absent	Ib Helium (He I) lines are present.			Gravitational collapse
		Ic Helium lines are weak or absent
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
				II-L Magnitude decreases linearly with time
		IIn There are narrow lines
	IIb The spectrum changes over time and becomes similar to the Ib spectrum.

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 supernova spectra various types, let's dwell on what was not included. The first and very important feature, which for a long time prevented the decoding of the obtained spectra - 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 flares its magnitude 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:

1. Possible compact remainder; usually a pulsar, but possibly a black hole
2. External shock wave propagating in interstellar matter.
3. A return wave propagating in the supernova ejecta material.
4. 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 it is known about the latter 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 during the ejection there are active nuclear reactions. 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 way to release the required amount of energy is sharp increase 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 affect 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

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
• Turbulent fast combustion

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 for various groups elements and even their own 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 had 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 solar system unchanged. 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. Now supernovae give 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.

January 22, 2014 in the M82 galaxy, located in the constellation Big Dipper, the supernova SN 2014J erupted. 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 Middle and Far East(does not appear 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.

SUPERNOVA

SUPERNOVA, a stellar explosion in which almost the entire STAR is destroyed. Within a week, a supernova can outshine all other stars in the Galaxy. The luminosity of a supernova is 23 magnitudes (1000 million times) greater than the luminosity of the Sun, and the energy released during the explosion is equal to all the energy emitted by the star during its entire previous life. After a few years, the supernova increases in volume so much that it becomes rarefied and translucent. Over hundreds or thousands of years, remnants of the ejected material are visible as remnants of a supernova. The supernova is about 1000 times brighter than the nova. Every 30 years, a galaxy like ours experiences about one supernova, but most of these stars are obscured by dust.

Supernovae come in two main types, distinguished by their light curves and spectra. Supernovae are stars that suddenly flare up, sometimes acquiring a brightness 10,000 million times greater than the brightness of the Sun. This happens in several stages. At the beginning (A), a huge star develops very quickly to the stage where various nuclear processes begin to occur simultaneously inside the star. Iron may form in the center, which means the end of nuclear energy production. The star then begins to undergo gravitational collapse (B). This, however, heats the center of the star to such an extent that disintegrate, and new reactions occur with explosive force (C). Most of the star's material is ejected into space, while the remnants of the star's center collapse until the star becomes completely dark, possibly becoming a very dense neutron star (D). One such supernova was visible in 1054. in the constellation Taurus (E). The remnant of this star is a cloud of gas called the Crab Nebula (F).

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Kepler supernova remnant

A supernova or supernova explosion is a phenomenon during which its brightness sharply changes by 4-8 orders of magnitude (a dozen magnitudes) followed by a relatively slow attenuation of the outbreak. It is the result of a cataclysmic process, accompanied by the release of enormous energy and arising at the end of the evolution of some stars.

Supernova remnant RCW 103 with neutron star 1E 161348-5055 at the center

As a rule, supernovae are observed after the fact, that is, when the event has already occurred and their radiation has reached . Therefore, their nature was unclear for quite a long time. 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 star matter into interstellar space, and from the remaining part of the matter of the exploding star, as a rule, a compact object is formed - a neutron star or a black hole. 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 substance ejected during the flare largely contains products of thermonuclear fusion that occurred throughout the life of the star. It is thanks to supernovae in general and each in particular that chemically evolves.

The name reflects the historical process of studying stars whose brightness changes significantly over time, the so-called novae. Similarly, among supernovae a subclass is now distinguished - hypernovae.

The name is made up of the tag SN, followed by the year of opening, ending with a one- or two-letter designation. The first 26 supernovae of the current year receive single-letter designations, at the end of their name, from capital letters A through Z. The remaining supernovae receive two-letter designations from lowercase letters: aa, ab, and so on. Unconfirmed supernovae are designated by the letters PSN (possible supernova) with celestial coordinates in the format: Jhhmmssss+ddmmsss.

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.

But the light curves of type II are quite diverse. 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.

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.

The frequency of flares depends on the number of stars in the galaxy or, which is the same for ordinary galaxies, luminosity.

In this case, supernovae Ib/c and II gravitate towards spiral arms.

Crab Nebula (X-ray image) showing internal shock wave, free-flowing wind, and jet

The canonical scheme of the young remainder is as follows:

Possible compact remainder; usually a pulsar, but possibly a black hole
An 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 TS ≥ 107 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 emission from the young remnant creates gas in clumps behind the secondary wave front. 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.

The fibers in Cassiopeia A make it clear that the origin of the clumps of matter can be twofold. The so-called fast filaments fly away at a speed of 5000-9000 km/s and emit only in the O, S, Si lines - that is, these are clumps formed at the moment of the supernova explosion. Stationary condensations have a speed of 100-400 km/s, and normal concentrations of H, N, O are observed in them. Together, this indicates that this substance was ejected long before the supernova explosion and was later heated by an external shock wave.

Synchrotron radio emission from relativistic particles in a strong magnetic field is the main observational signature for the entire remnant. The area of ​​its localization is the frontal areas of external and return waves. Synchrotron radiation is also observed in the X-ray range.

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 1010 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 us 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⊙.

Dominant scenario

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; everything can change only when approaching the Chandrasekhar limit. This leads to the unambiguous conclusion that a thermonuclear explosion is possible only in stellar 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 degeneration.

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.

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 1051 erg.

The further behavior of the light curve is mainly determined by the decay chain.

The 56Ni isotope is unstable and has a half-life of 6.1 days. Further, e-capture leads to the formation of a 56Co 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 surface matter of the star 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, 56Ni has already decayed and energy release occurs due to the β-decay of 56Co to 56Fe (T1/2 = 77 days) with excitation energies up to 4.2 MeV.

Model of the gravitational collapse mechanism

The second scenario for the release of the necessary energy is the collapse of the star's core. Its mass must be exactly equal to the mass of its remnant - a neutron star.

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 compression is the process of neutronization.

Neutrinos from these reactions carry away 10%. The main role in cooling is played by URKA processes (neutrino cooling).

Instead of protons and neutrons, atomic nuclei can also act, forming an unstable isotope that experiences beta decay.

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.

Note that neutronization processes occur only at densities of 1011/cm3, 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.

Supernova remnant evolution theory

Free flight.
Adiabatic expansion (Sedov stage). A supernova explosion at this stage appears as a strong point explosion in a medium with constant heat capacity. Sedov’s self-modal solution, tested for nuclear explosions in the earth's atmosphere.
Stage of intense illumination. It begins when the temperature behind the front reaches a maximum on the radiation loss curve.

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.

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
Turbulent fast combustion

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. As an example, we can cite models when two detonate at once. Naturally, this is only possible in scenarios where both components have evolved.

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.

Almost all elements heavier than He and up to Fe are the result of classical thermonuclear fusion, occurring, for example, in the interior of stars or during supernova explosions during the p-process. It is worth mentioning here that it is extremely small part nevertheless was obtained during primary nucleosynthesis.
All elements heavier than 209Bi are the result of the r-process
The origin of the others is the subject of debate; s-, r-, ν-, and rp-processes are proposed as possible mechanisms.

The structure and processes of nucleosynthesis in the pre-supernova and in the next instant after the outburst for a 25M☉ star, not to scale.

The r-process is the process of formation of heavier nuclei from lighter ones by sequential capture of neutrons during (n, γ) reactions and continues as long as the rate of neutron capture is higher than the rate of β− decay of the isotope.

The 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 7Li, 11B, 19F, 138La and 180Ta.

The Crab Nebula as a remnant of supernova SN 1054

Hipparchus's interest in the fixed stars may have been inspired by the observation of a supernova (according to Pliny). The earliest record identified as supernova SN 185 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 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 light echoes from the nebula, while the age of supernova remnant RX J0852.0-4622 was estimated from measurements of temperature and γ-ray emissions from the decay of titanium-44. In 2009, nitrates were discovered in Antarctic ice corresponding to the time of the supernova explosion.

On January 22, 2014, a supernova SN 2014J exploded 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).