The temperature of the sun and the ongoing thermonuclear reaction. What is the temperature on the Sun? Temperature 1000 km from the sun
Weight:
1.99×10 30 kg;
Diameter: 1,392,000 km;
Volume: 1.41×10 18 km³;
Surface area: 6.08×10 12 km²;
Spectral class: G2V;
Surface temperature: 5778 K;
Core temperature: 13,500,000 K;
Luminosity: 3.88×10 26 W;
Galactic year:230-250 million years;
Age: about 5 billion years;
Distance from Earth: 149.6 million km.
Throughout the history of human civilization, the Sun has been an object of worship in many cultures. The cult of the Sun existed in Ancient Egypt, where Ra was the solar deity. The ancient Greeks had the sun god Helios, who, according to legend, rode across the sky every day in his chariot. The Greeks believed that Helios lived in the east in a beautiful palace, surrounded by the seasons - Summer, Winter, Spring and Autumn. When Helios leaves his palace in the morning, the stars go out, night gives way to day. The stars reappear in the sky when Helios disappears in the west, where he transfers from his chariot to a beautiful boat and sails across the sea to the place of sunrise. In the ancient Russian pagan pantheon there were two solar deities - Khors (the actual personified sun) and Dazhdbog. Even a modern person has only to look at the Sun and he begins to understand how dependent he is on it. After all, if there were no world star, then the heat necessary for biological development and life would not exist. Our Earth would turn into an ice planet frozen for centuries; a situation similar in the Southern and Northern Hemispheres would exist throughout the world.
Our Sun is a huge luminous ball of gas, within which complex processes take place and, as a result, energy is continuously released. The internal volume of the Sun can be divided into several regions. The substance in them differs in its properties, and the energy spreads through different physical mechanisms. In the central part Sun there is a source of its energy, or, in figurative language, that “stove” that heats it and does not allow it to cool down. This area is called the core. Under the weight of the outer layers, the matter inside the Sun is compressed, and the deeper, the stronger. Its density increases towards the center along with increasing pressure and temperature. In the core, where the temperature reaches 15 million Kelvin, energy is released. This energy is released as a result of the fusion of atoms of light chemical elements into atoms of heavier ones. In the depths of the Sun, one helium atom is formed from four hydrogen atoms. It was this terrible energy that people learned to release during the explosion of a hydrogen bomb. There is hope that in the near future people will be able to learn to use it for peaceful purposes. The core has a radius of approximately 150-175 thousand km(25% of the radius of the Sun). Half of the solar mass is concentrated in its volume and almost all the energy that supports the glow of the Sun is released. For every second at the center of the Sun, about 4.26 million tons of substance. This is such enormous energy that when all the fuel is used up (the hydrogen is completely converted to helium), it will be enough to support life for millions of years to come.
WITH triplicity of the Sun. At the center of the Sun is the solar core.
The photosphere is the visible surface of the Sun
which is the main source of radiation. Sun
surrounded by the solar corona, which has a very high temperature,
however, it is extremely rarefied, so it is visible to the unarmed
with the eye only during periods of total solar eclipse.
atmosphere right down to the core
Energy of sun
Why does the Sun shine and not cool down for billions of years? What “fuel” gives it energy? Scientists have been looking for answers to these questions for centuries, and only at the beginning of the 20th century. the correct solution was found. It is now known that the Sun, like other stars, shines due to thermonuclear reactions occurring in its depths.The main substance that makes up the Sun is hydrogen, accounting for about 71% of the total mass of the star. Almost 27% belongs to helium, and the remaining 2% comes from heavier elements such as carbon, nitrogen, oxygen and metals. The main “fuel” in the Sun is hydrogen. From four hydrogen atoms, as a result of a chain of transformations, one helium atom is formed. And from every gram of hydrogen participating in the reaction, 6.×10 11 J energy! On Earth, this amount of energy would be enough to heat 1000 m 3 of water from a temperature of 0 ° C to the boiling point. In the nucleus, the nucleus of atoms of light hydrogen elements merges into the nucleus of a heavier hydrogen atom (this nucleus is called deuterium). The mass of the new nucleus is significantly less than the total mass of the nuclei from which it was formed. The remainder of the mass is converted into energy, which is carried away by particles released during the reaction. This energy is almost completely converted into heat.The result of such transformation chains is the emergence of a new nucleus, consisting of two protons and two neutrons - the helium nucleus.This thermonuclear reaction of converting hydrogen into helium is called proton-proton, since it begins with the close approach of two nuclei of hydrogen atoms-protons.The reaction of hydrogen turning into helium is responsible for the fact that there is now much more helium inside the Sun than on its surface. Naturally, the question arises: what will happen to the Sun when all the hydrogen in its core burns out and turns into helium, and how soon will this happen? It turns out that in about 5 billion years, the hydrogen content in the Sun’s core will decrease so much that its “burning” will begin in the layer around the core. This will lead to an “inflation” of the solar atmosphere, an increase in the size of the Sun, a drop in temperature on the surface and an increase in its core. Gradually, the Sun will turn into a red giant - a relatively cold star of enormous size, exceeding the boundaries of its orbit. Life of the Sun it will not end there, it will undergo many more changes until it eventually becomes a cold and dense gas ball, inside which no thermonuclear reactions take place.
This is approximately what the Sun will look like from the surface of the Earth through
5 billion years, when the hydrogen in the core is completely consumed. Sun
will turn into a Red Giant, whose core will be greatly compressed,
and the outer layers are in a fairly discharged state.
Our star is so huge. that it can hold about
1,300,000 Earth volumes. Circumference of the Sun at the equator
is 4.37 million km (for example, the Earth is 40,000 km)
How the Sun was formed
Like all stars, our Sun arose as a result of prolonged exposure to interstellar matter (gas and dust). Initially, the star was a globular cluster consisting primarily of hydrogen. Then, due to gravitational forces, the hydrogen atoms began to press against each other, the density increased, and as a result, a fairly compressed core was formed. The moment the first thermonuclear reaction ignites, the official birth of a star begins.
A star as massive as the Sun, should exist for a total of about 10 billion years. Thus, now the Sun is approximately in the middle of its life cycle (at the moment its return is about 5 billion years). In 4-5 billion years it will turn into a red giant star. As the hydrogen fuel in the core burns out, its outer shell will expand and the core will contract and heat up. In about 7.8 billion years when the temperature in the core reaches approximately 100 million K, a thermonuclear reaction of synthesis of carbon and oxygen from helium will begin in it. At this phase of development, temperature instabilities inside the Sun will lead to the fact that it will begin to lose mass and shed its shell. Apparently, the expanding outer layers of the Sun will reach the modern orbit of the Earth at this time. At the same time, studies show that even before this moment, the loss of mass by the Sun will lead to it moving to an orbit farther from the Sun and, thus, avoiding absorption by the outer layers of solar plasma.
Despite this, all the water on Earth will turn into a gaseous state, and most of it will dissipate into outer space. The increase in the temperature of the Sun during this period is such that during the next 500–700 million years The Earth's surface will be too hot to support life as we know it today.
After Sun will go through a phase red giant, thermal pulsations will lead to the fact that its outer shell will be torn off and a planetary nebula will form from it. In the center of this nebula there will remain a white dwarf star formed from the very hot core of the Sun, which will gradually cool and fade over many billions of years.
Almost the entire cycle of its life, the Sun appears
like a yellow star, with the luminosity we are used to
The sun illuminates and warms our planet, without this life on it would be impossible not only for humans, but also for microorganisms. Our star is the main (although not the only) engine of processes occurring on Earth. But the Earth receives not only heat and light from the Sun. Various types of solar radiation and particle flows have a constant impact on her life. The Sun sends electromagnetic waves to the Earth from all areas of the spectrum - from multi-kilometer radio waves to gamma rays. The atmosphere of the planet is also reached by charged particles of different energies - both high (solar cosmic rays, and low and medium (solar wind flows, emissions from flares). However, a very small part of charged particles from interplanetary space enters (the rest deflect or delay the geomagnetic field) But their energy is enough to cause aurora and disturbance of the magnetic field of our planet.
Sun located from at a distance of 149.6 million km. It is this quantity in astronomy that is usually called the astronomical unit (a.e). If suddenly our star goes out at the moment, then we will not know about it for as long as 8.5 minutes - this is exactly the time it takes for sunlight to travel from the Sun to the Earth at a speed of 300,000 km/s. Our location is the most favorable for maintaining the necessary climate for the emergence of biological life. If the Earth were even a little closer to the Sun than it is now, then our planet would be incinerated from the heat, and the water cycle in nature would be disrupted, and all living things would cease to exist. At that time, the planet’s distance from the Sun would be characterized by an incredible drop in temperature, freezing of water, and the emergence of a new ice age. Which would ultimately lead to the complete extinction of all organisms on the planet.
The surface temperature of the Sun is determined by analyzing the solar spectrum. It is known that it is the source of energy for all natural processes on Earth; therefore, scientists have determined the quantitative value of the heating of various parts of our star.
The radiation intensity in individual color parts of the spectrum corresponds to a temperature of 6000 degrees. This is the temperature of the Sun's surface or photosphere.
In the outer layers of the solar atmosphere - in the chromosphere and in the corona - higher temperatures are observed. In the corona it is approximately one to two million degrees. Over places of strong outbreaks, the temperature for a short time can reach even fifty million. Due to the high heating in the corona above the flare, the intensity of X-ray and radio emissions greatly increases.
Calculations of the heating of our star
The most important process occurring on the Sun is the conversion of hydrogen into helium. It is this process that is the source of all the energy of the Sun.
The solar core is very dense and very hot. Violent collisions of electrons, protons and other nuclei often occur. Sometimes the collisions of protons are so rapid that they, overcoming the force of electrical repulsion, approach each other within the distance of their diameter. At this distance, the nuclear force begins to act, as a result of which protons combine and release energy.
Four protons gradually combine to form a helium nucleus, with two protons turning into neutrons, two positive charges being released in the form of positrons, and two imperceptible neutral particles - neutrinos - appearing. When they encounter electrons, both positrons turn into gamma ray photons (annihilation).
The rest energy of a helium atom is less than the rest energy of four hydrogen atoms.
The difference in mass turns into gamma photons and neutrinos. The total energy of all generated gamma photons and two neutrinos is 28 MeV. Scientists were able to get emission of photons.
This is the amount of energy the Sun emits in one second. This value represents the power of solar radiation.
The temperature of our nearest star is heterogeneous and varies significantly. At the core of the sun, gravitational attraction produces enormous pressure and temperature, which can reach 15 million degrees Celsius. The hydrogen atoms are compressed and fused together, creating helium. This process is called a thermonuclear reaction.
A thermonuclear reaction produces enormous amounts of energy. The energy flows to the surface of the sun, the atmosphere and beyond. From the core, the energy moves to the radiative zone, where it spends up to 1 million years, and then moves to the convective zone, the upper layer of the interior of the Sun. The temperature here drops below 2 million degrees Celsius. Huge bubbles of hot plasma form a “soup” of ionized atoms and move upward towards the photosphere.
The temperature in the photosphere is almost 5.5 thousand degrees Celsius. Here solar radiation becomes visible light. Sunspots in the photosphere are cooler and darker than those in the surrounding area. In the center of large sunspots, temperatures can drop to several thousand degrees Celsius.
The chromosphere, the next layer of the solar atmosphere, is slightly cooler at 4320 degrees. According to the National Solar Observatory, chromosphere literally means "sphere of color." Visible light from the chromosphere is usually too weak to be seen against the brighter photosphere, but during total solar eclipses, when the moon covers the photosphere, the chromosphere is visible as a red rim around the Sun.
“The chromosphere appears red because of the enormous volume of hydrogen it contains,” the National Solar Observatory writes on its website.
Temperatures rise significantly in the corona, which can also be visible during an eclipse as plasma flows upward. The corona can be surprisingly hot compared to the body of the sun. The temperature here varies from 1 million degrees to 10 million degrees Celsius.
As the corona cools, losing heat and radiation, the material is blown out in the form of the solar wind, which sometimes crosses paths with Earth.
The Sun is the largest and most massive object in the Solar System. It is located 149.5 million km from Earth. This distance is called an astronomical unit and is used to measure distances throughout the solar system. It takes about 8 minutes for sunlight and heat to reach our planet, so there is another way to determine the distance to the Sun - 8 light minutes.
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SUN
the star around which the Earth and other planets of the solar system orbit. The sun plays an exceptional role for humanity as the primary source of most types of energy. Life as we know it would not be possible if the Sun shone a little brighter or a little weaker. The Sun is a typical small star, there are billions of them. But due to its proximity to us, only it allows astronomers to study in detail the physical structure of the star and the processes on its surface, which is practically unattainable in relation to other stars even with the most powerful telescopes. Like other stars, the Sun is a hot ball of gas, mostly made of hydrogen, compressed by its own gravity. The energy emitted by the Sun is born deep in its depths during thermonuclear reactions that convert hydrogen into helium. Leaking out, this energy is radiated into space from the photosphere - a thin layer of the solar surface. Above the photosphere is the outer atmosphere of the Sun - the corona, which extends over many radii of the Sun and merges with the interplanetary medium. Because the gas in the corona is very rarefied, its glow is extremely weak. Usually invisible against the background of a bright daytime sky, the corona becomes visible only during total solar eclipses. The gas density decreases monotonically from the center of the Sun to its periphery, and the temperature, reaching 16 million K in the center, decreases to 5800 K in the photosphere, but then increases again to 2 million K in the corona. The transition layer between the photosphere and the corona, observed as a bright red rim during total solar eclipses, is called the chromosphere. The Sun has an 11-year activity cycle. During this period, the number of sunspots (dark areas in the photosphere), flares (unexpected brightenings in the chromosphere) and prominences (dense, cold clouds of hydrogen condensing in the corona) increases and decreases again. In this article we will talk about the above-mentioned areas and phenomena on the Sun. After a brief description of the Sun as a star, we will discuss its internal structure, then the photosphere, chromosphere, flares, prominences, and corona.
The sun is like a star. The Sun is located in one of the spiral arms of the Galaxy at a distance of more than half the galactic radius from its center. Together with neighboring stars, the Sun revolves around the center of the Galaxy with a period of approx. 240 million years. The Sun is a yellow dwarf of spectral class G2 V, belonging to the main sequence on the Hertzsprung-Russell diagram. The main characteristics of the Sun are given in table. 1. Note that although the Sun is gaseous right up to the center, its average density (1.4 g/cm3) exceeds the density of water, and at the center of the Sun it is significantly higher than even that of gold or platinum, which have a density of approx. 20 g/cm3. The surface of the Sun at a temperature of 5800 K emits 6.5 kW/cm2. The sun rotates around an axis in the direction of the general rotation of the planets. But since the Sun is not a solid body, different regions of its photosphere rotate at different speeds: the rotation period at the equator is 25 days, and at a latitude of 75° - 31 days.
Table 1.
CHARACTERISTICS OF THE SUN
INTERNAL STRUCTURE OF THE SUN
Since we cannot directly observe the interior of the Sun, our knowledge of its structure is based on theoretical calculations. Knowing from observations the mass, radius and luminosity of the Sun, to calculate its structure it is necessary to make assumptions about the processes of energy generation, the mechanisms of its transfer from the core to the surface and the chemical composition of matter. Geological evidence indicates that the Sun's luminosity has not changed significantly over the past few billion years. What energy source can sustain it for so long? Conventional chemical combustion processes are not suitable for this. Even gravitational compression, according to the calculations of Kelvin and Helmholtz, could only maintain the Sun's glow for approx. 100 million years. This problem was solved in 1939 by G. Bethe: the source of solar energy is the thermonuclear transformation of hydrogen into helium. Since the efficiency of the thermonuclear process is very high, and the Sun consists almost entirely of hydrogen, this completely solved the problem. Two nuclear processes provide the Sun's luminosity: the proton-proton reaction and the carbon-nitrogen cycle (see also STARS). The proton-proton reaction leads to the formation of a helium nucleus from four hydrogen nuclei (protons) with the release of 4.3×10-5 erg of energy in the form of gamma rays, two positrons and two neutrinos for each helium nucleus. This reaction provides 90% of the Sun's luminosity. It takes 1010 years for all the hydrogen in the Sun's core to turn into helium. In 1968, R. Davis and his colleagues began to measure the flux of neutrinos produced during thermonuclear reactions in the solar core. This was the first experimental test of the theory of a solar energy source. Neutrinos interact very weakly with matter, so they freely leave the depths of the Sun and reach the Earth. But for the same reason it is extremely difficult to register with instruments. Despite the improvement of equipment and refinement of the solar model, the observed neutrino flux still remains 3 times less than predicted. There are several possible explanations: either the chemical composition of the Sun's core is not the same as that of its surface; or the mathematical models of the processes occurring in the core are not entirely accurate; or on the way from the Sun to the Earth, the neutrino changes its properties. Further research in this area is needed.
see also NEUTRIN ASTRONOMY. In the transfer of energy from the solar interior to the surface, radiation plays the main role, convection is of secondary importance, and thermal conductivity is not important at all. At high temperatures in the solar interior, radiation is mainly represented by x-rays with a wavelength of 2-10. Convection plays a significant role in the central region of the core and in the outer layer lying directly below the photosphere. In 1962, the American physicist R. Layton discovered that sections of the solar surface oscillate vertically with a period of approx. 5 minutes. Calculations by R. Ulrich and K. Wolf showed that sound waves excited by turbulent gas movements in the convective zone lying under the photosphere can manifest themselves in this way. In it, like in an organ pipe, only those sounds whose wavelength fits exactly within the thickness of the zone are amplified. In 1974, the German scientist F. Debner experimentally confirmed the calculations of Ulrich and Wolf. Since then, observing 5-minute oscillations has become a powerful method for studying the internal structure of the Sun. Analyzing them, it was possible to find out that: 1) the thickness of the convective zone is approx. 27% of the radius of the Sun; 2) the core of the Sun probably rotates faster than the surface; 3) helium content inside the Sun is approx. 40% by weight. Observations of oscillations with periods between 5 and 160 minutes have also been reported. These longer sound waves can penetrate deeper into the interior of the Sun, which will help understand the structure of the solar interior and possibly solve the problem of solar neutrino deficiency.
ATMOSPHERE OF THE SUN
Photosphere. This is a translucent layer several hundred kilometers thick, representing the “visible” surface of the Sun. Since the atmosphere above is practically transparent, the radiation, having reached the photosphere from below, freely leaves it and goes into space. Without the ability to absorb energy, the upper layers of the photosphere must be cooler than the lower ones. Evidence of this can be seen in photographs of the Sun: in the center of the disk, where the thickness of the photosphere along the line of sight is minimal, it is brighter and bluer than at the edge (on the “limb”) of the disk. In 1902, calculations by A. Schuster, and later by E. Milne and A. Eddington, confirmed that the temperature difference in the photosphere is just such as to ensure the transfer of radiation through the translucent gas from the lower layers to the upper ones. The main substance that absorbs and re-emits light in the photosphere is negative hydrogen ions (hydrogen atoms with an additional electron attached).
Fraunhofer spectrum. Sunlight has a continuous spectrum with absorption lines discovered by J. Fraunhofer in 1814; they indicate that in addition to hydrogen, many other chemical elements are present in the solar atmosphere. Absorption lines form in the spectrum because atoms in the upper, cooler layers of the photosphere absorb light coming from below at certain wavelengths, and do not emit it as intensely as the hot lower layers. The distribution of brightness within the Fraunhofer line depends on the number and state of the atoms producing it, i.e. on the chemical composition, density and temperature of the gas. Therefore, a detailed analysis of the Fraunhofer spectrum makes it possible to determine the conditions in the photosphere and its chemical composition (Table 2). Table 2.
CHEMICAL COMPOSITION OF THE SUN PHOTOSPHERE
Element Logarithm of relative number of atoms
Hydrogen _________12.00
Helium___________11.20
Carbon __________8.56
Nitrogen _____________7.98
Oxygen _________9.00
Sodium ___________6.30
Magnesium___________7.28
Aluminum _________6.21
Silicon __________7.60
Sulfur _____________7.17
Calcium __________6.38
Chrome _____________6.00
Iron___________6.76
The most abundant element after hydrogen is helium, which produces only one line in the optical spectrum. Therefore, the helium content in the photosphere is not measured very accurately, and it is judged from the spectra of the chromosphere. No variations in the chemical composition in the solar atmosphere have been observed.
see also RANGE .
Granulation. Photographs of the photosphere taken in white light under very good observing conditions show small bright points - “granules” separated by dark spaces. Granule diameters approx. 1500 km. They constantly appear and disappear, lasting 5-10 minutes. Astronomers have long suspected that granulation of the photosphere is associated with convective movements of gas heated from below. Spectral measurements by J. Beckers proved that in the center of the granule, hot gas actually floats up at speed. OK. 0.5 km/s; then it spreads to the sides, cools and slowly falls down along the dark boundaries of the granules.
Supergranulation. R. Leighton discovered that the photosphere is also divided into much larger cells with a diameter of approx. 30,000 km - "super granules". Supergranulation reflects the movement of matter in the convective zone under the photosphere. In the center of the cell, the gas rises to the surface, spreads to the sides at a speed of about 0.5 km/s and falls down at its edges; Each cell lives for about a day. The movement of gas in supergranules constantly changes the structure of the magnetic field in the photosphere and chromosphere. Photospheric gas is a good conductor of electricity (since some of its atoms are ionized), so the magnetic field lines appear to be frozen into it and are transferred by the movement of gas to the boundaries of supergranules, where they are concentrated and the field strength increases.
Sun spots. In 1908, J. Hale discovered a strong magnetic field in sunspots, emerging from the interior to the surface. Its magnetic induction is so great (up to several thousand gauss) that the ionized gas itself is forced to subordinate its movement to the field configuration; in spots, the field inhibits the convective mixing of the gas, which causes its cooling. Therefore, the gas in the sunspot is cooler than the surrounding photospheric gas and appears darker. Spots usually have a dark core - a “shadow” - and a lighter “penumbra” surrounding it. Typically, their temperature is 1500 and 400 K lower, respectively, than in the surrounding photosphere.
The spot begins its growth from a small dark “pore” with a diameter of 1500 km. Most of the pores disappear within a day, but the spots that grow from them persist for weeks and reach a diameter of 30,000 km. The details of sunspot growth and decay are not fully understood. For example, it is not clear whether the magnetic tubes of the spot are compressed by the horizontal movement of the gas or whether they are ready to “emerge” from under the surface. R. Howard and J. Harvey discovered in 1970 that the spots move in the direction of the general rotation of the Sun faster than the surrounding photosphere (about 140 m/s). This indicates that the spots are associated with subphotospheric layers that rotate faster than the visible surface of the Sun. Typically, from 2 to 50 spots are combined into a group, often having a bipolar structure: at one end of the group there are spots of one magnetic polarity, and at the other - the opposite. But there are also multipolar groups. The number of sunspots on the solar disk changes regularly with a period of approx. 11 years. At the beginning of each cycle, new spots appear at high solar latitudes (± 50°). As the cycle develops and the number of sunspots increases, they appear at lower and lower latitudes. The end of the cycle is marked by the birth and decay of several sunspots near the equator (± 10°). During the cycle, most of the “leading” (western) spots in bipolar groups have the same magnetic polarity, which is different in the northern and southern hemispheres of the Sun. In the next cycle, the polarity of the leading spots is reversed. Therefore, they often talk about a complete 22-year cycle of solar activity. There is still a lot of mystery in the nature of this phenomenon.
Magnetic fields. In the photosphere, a magnetic field with an induction of more than 50 G is observed only in sunspots, in active regions surrounding the spots, and also at the boundaries of supergranules. But L. Stenflo and J. Harvey found indirect indications that the magnetic field of the photosphere is actually concentrated in thin tubes with a diameter of 100-200 km, where its induction is from 1000 to 2000 Gauss. Magnetoactive regions differ from quiet regions only in the number of magnetic tubes per unit surface. It is likely that the solar magnetic field is generated in the depths of the convective zone, where seething gas twists the weak initial field into powerful magnetic ropes. The differential rotation of matter arranges these bundles along parallels, and when the field in them becomes strong enough, they float up into the photosphere, breaking upward in separate arches. This is probably how spots are born, although there is still a lot of uncertainty about this. The process of stain decay has been studied much more fully. Supergranules floating at the edges of the active region capture the magnetic tubes and pull them apart. Gradually the general field weakens; accidental connection of tubes of opposite polarity leads to their mutual destruction.
Chromosphere. Between the relatively cold, dense photosphere and the hot, rarefied corona is the chromosphere. The faint light of the chromosphere is usually not visible against the background of the bright photosphere. It can be seen in the form of a narrow strip above the limb of the Sun when the photosphere is closed naturally (at the time of a total solar eclipse) or artificially (in a special telescope - coronagraph). The chromosphere can also be studied over the entire solar disk if observations are carried out in a narrow spectral range (about 0.5) near the center of a strong absorption line. The method is based on the fact that the higher the absorption, the shallower the depth to which our gaze penetrates into the solar atmosphere. For such observations, a spectrograph of a special design is used - a spectroheliograph. Spectroheliograms show that the chromosphere is heterogeneous: it is brighter above sunspots and along the boundaries of supergranules. Since it is in these regions that the magnetic field is strengthened, it is obvious that with its help energy is transferred from the photosphere to the chromosphere. It is probably carried by sound waves excited by the turbulent movement of gas in the granules. But the mechanisms of heating the chromosphere are not yet understood in detail. The chromosphere emits strongly in the hard ultraviolet range (500-2000), which is inaccessible for observation from the Earth's surface. Since the early 1960s, many important measurements of ultraviolet radiation from the Sun's upper atmosphere have been made using high-altitude rockets and satellites. More than 1000 emission lines of various elements were found in its spectrum, including lines of multiply ionized carbon, nitrogen and oxygen, as well as the main series of hydrogen, helium and helium ion. The study of these spectra showed that the transition from the chromosphere to the corona occurs over a segment of only 100 km, where the temperature increases from 50,000 to 2,000,000 K. It turned out that the heating of the chromosphere largely occurs from the corona by thermal conduction. Near groups of sunspots in the chromosphere, bright and dark fibrous structures are observed, often elongated in the direction of the magnetic field. Above 4000 km, uneven, jagged formations are visible, evolving quite quickly. When observing the limb at the center of the first Balmer line of hydrogen (Ha), the chromosphere at these altitudes is filled with many spicules - thin and long clouds of hot gas. Little is known about them. The diameter of an individual spicule is less than 1000 km; she lives ok. 10 min. At a speed of approx. 30 km/s spicules rise to an altitude of 10,000-15,000 km, after which they either dissolve or descend. Judging by the spectrum, the temperature of the spicules is 10,000-20,000 K, although the surrounding corona at these altitudes is heated to at least 600,000 K. It appears that spicules are regions of a relatively cold and dense chromosphere that temporarily rise into the hot, rarefied corona. Counting within the boundaries of supergranules shows that the number of spicules at the photosphere level corresponds to the number of granules; there is probably a physical connection between them.
Flashes. The chromosphere above a group of sunspots can suddenly become brighter and shoot out a burst of gas. This phenomenon, called "flare", is one of the most difficult to explain. Flares powerfully emit over the entire range of electromagnetic waves - from radio to x-rays, and often emit beams of electrons and protons at relativistic speeds (i.e. close to the speed of light). They excite shock waves in the interplanetary medium that reach the Earth. Flares more often occur near groups of spots with a complex magnetic structure, especially when a new spot begins to grow rapidly in the group; such groups produce several outbreaks per day. Weak outbreaks occur more often than strong ones. The most powerful flares occupy 0.1% of the solar disk and last for several hours. The total energy of the flare is 1023-1025 J. X-ray spectra of flares obtained by the SMM (Solar Maximum Mission) satellite have made it possible to significantly better understand the nature of flares. The beginning of the flare may be marked by an X-ray burst with a photon wavelength less than 0.05, caused, as its spectrum shows, by a flow of relativistic electrons. In a few seconds, these electrons heat the surrounding gas to 20,000,000 K, and it becomes a source of X-ray radiation in the range of 1-20, hundreds of times greater than the flux in this range from the quiet Sun. At this temperature, iron atoms lose 24 of their 26 electrons. The gas then cools, but still continues to emit X-rays. The flash also emits radio waves. P. Wild from Australia and A. Maxwell from the USA studied the development of the flare using a radio analogue of a spectrograph - a “dynamic spectrum analyzer” that records changes in the power and frequency of radiation. It turned out that the frequency of the radiation during the first few seconds of the flare drops from 600 to 100 MHz, indicating that a disturbance is propagating through the corona at 1/3 the speed of light. In 1982, US radio astronomers, using the VLA radio interferometer in pcs. New Mexico and data from the SMM satellite have resolved fine features in the chromosphere and corona during the flare. Not surprisingly, these turned out to be loops, probably of a magnetic nature, in which energy is released that heats the gas during the flare. During the final stage of the flare, relativistic electrons trapped in the magnetic field continue to emit highly polarized radio waves, moving in a spiral around magnetic field lines above the active region. This radiation can last for several hours after the outbreak. Although gas is always ejected from the flare region, its speed usually does not exceed the speed of escape from the surface of the Sun (616 km/s). However, flares often emit streams of electrons and protons that reach the Earth in 1-3 days and cause auroras and magnetic field disturbances on it. These particles, with energies reaching billions of electron volts, are very dangerous for astronauts in orbit. Therefore, astronomers try to predict solar flares by studying the configuration of the magnetic field in the chromosphere. The complex structure of the field with twisted lines of force, ready to be reconnected, indicates the possibility of a flare.
Prominences. Solar prominences are relatively cold masses of gas that appear and disappear in the hot corona. When observed with a coronagraph in the Ha line, they are visible on the solar limb as bright clouds against a dark sky background. But when observed with a spectroheliograph or Lyot interference filters, they appear as dark filaments against the background of a bright chromosphere.
The shapes of prominences are extremely diverse, but several main types can be distinguished. Sunspot prominences resemble curtains up to 100,000 km long, 30,000 km high and 5,000 km thick. Some prominences have a branched structure. Rare and beautiful loop-shaped prominences have a rounded shape with a diameter of approx. 50,000 km. Almost all prominences exhibit a fine structure of gaseous filaments, probably repeating the structure of the magnetic field; the true nature of this phenomenon is not clear. Gas in prominences usually moves downward in streams at a speed of 1-20 km/s. The exception is “sergies” - prominences that fly upward from the surface at a speed of 100-200 km/s, and then fall back more slowly. Prominences are born at the edges of sunspot groups and can persist for several revolutions of the Sun (i.e., several Earth months). The spectra of prominences are similar to those of the chromosphere: bright lines of hydrogen, helium and metals against a background of weak continuous radiation. Typically, the emission lines of quiet prominences are thinner than the chromospheric lines; This is probably due to the smaller number of atoms along the line of sight in the prominence. Analysis of the spectra indicates that the temperature of quiet prominences is 10,000-20,000 K, and the density is about 1010 at./cm3. Active prominences show lines of ionized helium, indicating a significantly higher temperature. The temperature gradient in the prominences is very large, since they are surrounded by a corona with a temperature of 2,000,000 K. The number of prominences and their distribution along latitude during the 11-year cycle follows the distribution of sunspots. However, at high latitudes there is a second belt of prominences, which shifts poleward during the maximum period of the cycle. Why prominences form and what supports them in the rarefied corona is not entirely clear.
Crown. The outer part of the Sun - the corona - shines weakly and is visible to the naked eye only during total solar eclipses or using a coronagraph. But it is much brighter in X-rays and in the radio range.
see also EXTRA-ATMOSPHERE ASTRONOMY. The corona shines brightly in the X-ray range because its temperature ranges from 1 to 5 million K, and during flares reaches 10 million K. X-ray spectra of the corona began to be obtained recently from satellites, and optical spectra have been studied for many years during total eclipses. These spectra contain lines of multiply ionized atoms of argon, calcium, iron, silicon and sulfur, which are formed only at temperatures above 1,000,000 K.
The white light of the corona, which during an eclipse is visible up to a distance of 4 solar radii, is formed as a result of the scattering of photospheric radiation by free electrons of the corona. Consequently, the change in brightness of the corona with height indicates the distribution of electrons, and since the main element is fully ionized hydrogen, so does the distribution of gas density. Coronal structures are clearly divided into open (rays and polar brushes) and closed (loops and arches); ionized gas exactly repeats the structure of the magnetic field in the corona, because cannot move across lines of force. Because the field emerges from the photosphere and is associated with the 11-year sunspot cycle, the appearance of the corona changes over the course of this cycle. During the period of minimum, the corona is dense and bright only in the equatorial belt, but as the cycle progresses, coronal rays appear at higher latitudes, and at maximum they can be seen at all latitudes. From May 1973 to January 1974, the corona was continuously observed by 3 crews of astronauts from the Skylab orbital station. Their data showed that dark coronal "holes", where the temperature and density of gas are significantly reduced, are areas from which gas flies out into interplanetary space at high speed, creating powerful flows in the calm solar wind. Magnetic fields in coronal holes are “open”, i.e. extended far into space, allowing gas to escape the corona. These field configurations are quite stable and can persist during periods of minimum solar activity for up to two years. The coronal hole and the stream associated with it rotate along with the surface of the Sun with a period of 27 days and, if the stream hits the Earth, each time they cause geomagnetic storms. Energy balance of the outer atmosphere of the Sun. Why does the Sun have such a hot corona? We don't know that yet. But there is a fairly reasonable hypothesis that energy is transferred to the outer atmosphere by sound and magnetohydrodynamic (MHD) waves, which are generated by turbulent movements of gas under the photosphere. Getting into the upper rarefied layers, these waves become shock waves, and their energy dissipates, heating the gas. Sound waves heat the lower chromosphere, and MHD waves propagate along magnetic field lines further into the corona and heat it. Part of the heat from the corona, due to thermal conductivity, goes into the chromosphere and is radiated into space there. The remaining heat maintains the coronal radiation in closed loops and accelerates solar wind flows in coronal holes.
see also
The luminary, to which our planet, its biosphere, and human civilization owe their existence, is quite banal from the point of view of astronomers.
This is an ordinary yellow star of the very common G2 class. Every 225–250 million years, it completes a full revolution in an almost circular orbit with a radius of 26,000 light years around the center of a typical large spiral galaxy with a passive core that does not emit powerful streams of energy. However, it is precisely in this ordinariness that our happiness lies. Stars that are cooler and hotter (and especially those close to active galactic centers) are much less suitable for the role of the cradle of life, at least carbon-based ones
Alexey Levin
According to generally accepted estimates, the Sun arose 4.59 billion years ago. True, recently some astronomers have started talking about the fact that its age is 6-7 billion years, but these are still only hypotheses. Of course, our daylight was not born out of nowhere. Its mother was a gigantic cloud of gas and dust, consisting mainly of molecular hydrogen, which, under the influence of its own gravity, slowly compressed and deformed until it turned into a flat disk. It is possible that there was also a father in the form of a cosmic event, which increased the gravitational instability of the cloud and spurred its collapse (this could be an encounter with a massive star or a supernova explosion). In the center of the disk, a sphere of luminous plasma appeared with a surface temperature of several thousand degrees, converting part of its gravitational energy into heat.
The newborn star continued to shrink, warming up its depths more and more. After several million years, their temperature reached 10 million degrees Celsius, and self-sustaining thermonuclear fusion reactions began there. The young protostar turned into a normal main sequence star. The matter of the near and far periphery of the disk condensed into cold bodies - planets and planetoids.
Currently, solar researchers have an extremely powerful technique for studying the convective zone - helioseismology. “This is a method of studying the Sun by analyzing its oscillations, vertical oscillations of the solar surface, typical periods of which are several minutes,” explains Alexander Kosovichev, a senior researcher at Stanford University. — They were opened in the early 1960s. In particular, the staff of the Crimean Astrophysical Observatory, led by Academician Severny, did a lot in this area. Oscillations are excited by turbulent convection in the near-surface layers of the Sun. During these processes, sound waves are generated that propagate inside the Sun. By determining the characteristics of these waves, we obtain information that allows us to draw conclusions about the internal structure of the Sun and the mechanisms by which magnetic fields are generated. Helioseismology has already made it possible to determine the depth of the convective zone, to clarify the nature of the rotation of solar layers, and to clarify our ideas about the occurrence of sunspots, which are actually clumps of a magnetic field. We now know that a solar dynamo is very different from a planetary dynamo because it operates in a highly turbulent environment. It generates both a global dipole field and many local fields. The mechanisms of interaction between fields of different scales are not yet known; they remain to be elucidated. In general, this science has a great future.”
Here are some passport details of the Sun. Age - 4.59 billion years; weight - 1.989x1030 kg; average radius - 696,000 km; average density - 1.409 g/cm 3 (the density of earthly matter is four times higher); effective surface temperature (calculated on the assumption that the Sun radiates as an absolutely black body) - 5503˚С (in terms of absolute temperature - 5778 kelvins); total radiation power - 3.83x1023 kW.
The surface of the Sun (photosphere), even in a calm state, when observed through a telescope (naturally, protected by a special filter), looks like a set of grains or a honeycomb. This structure is called solar granulation. It is formed due to convection, that is, the thermal circulation of gas flows - hot gas “floats” and cold gas sinks down at the boundaries of the granules, which are visible as dark areas. The typical size of granules is about 1000 km. In the figure - an inverted computer image calculated using the Doppler effect - the movement of gas flows from the observer is depicted in light tones, towards the observer - in dark tones. On the left is a composite picture (from top and counterclockwise): the internal structure of the Sun with the core and convective zone; photosphere with dark spot; chromosphere; solar flare; at the top right is a prominence.
Since the Sun does not rotate around its own axis as a single whole, it does not have strictly defined days. The surface of its equatorial zone makes a full revolution in 27 Earth days, and the polar zones - in 35 days. The axial rotation of the solar interior is even more complex and is still unknown in all its details.
The chemical composition of solar matter is naturally dominated by hydrogen (approximately 72% of the mass) and helium (26%). A little less than a percent is oxygen, 0.4% is carbon, and about 0.1% is neon. If we express these ratios in the number of atoms, it turns out that per million hydrogen atoms there are 98,000 helium atoms, 850 oxygen atoms, 360 carbon atoms, 120 neon atoms, 110 nitrogen atoms, and 40 iron and silicon atoms each.
Solar mechanics
The layered structure of the Sun is often compared to an onion. This analogy is not very successful, since the layers themselves are penetrated by powerful vertical flows of matter and energy. But to a first approximation it is acceptable. The sun shines due to thermonuclear energy that is generated in its core. The temperature there reaches 15 million degrees Celsius, density - 160 g/cm 3, pressure - 3.4x1011 atm. Under these hellish conditions, several chains of thermonuclear reactions take place, making up the proton-proton cycle (p-p cycle). It owes its name to the initial reaction where two protons collide and produce a deuterium nucleus, a positron and an electron neutrino.
During these transformations (and there are quite a lot of them), hydrogen is burned and various isotopes of such elements of the Periodic Table as helium, beryllium, lithium and boron are born. The last three elements enter into nuclear reactions or decay, but helium remains—or rather, its main isotope, helium-4, remains. As a result, it turns out that four protons give rise to one helium nucleus, two positrons and two neutrinos. Positrons immediately annihilate with electrons, and neutrinos leave the Sun, practically without reacting with its matter. Each p-p cycle reaction releases 26.73 megaelectronvolts in the form of kinetic energy of created particles and gamma radiation.
If the protosolar cloud consisted exclusively of elements created during the Big Bang (hydrogen and helium-4 with a very small admixture of deuterium, helium-3 and lithium-7), then these reactions would have ended everything. However, the composition of protosolar matter was much richer, an indisputable proof of which is at least the presence of iron in the solar atmosphere. This element, like its closest neighbors in the periodic table, is born only in the depths of much more massive stars, where temperatures reach billions of degrees. The sun is not one of them. If iron is still present there, it is only because the primary cloud was already contaminated with this metal and many other elements. All of them were formed in the nuclear furnaces of giant stars of previous generations, which exploded as supernovae and scattered the products of their creative activity throughout outer space.
This circumstance does not greatly change the above scheme of intrasolar thermonuclear fusion, but still introduces some amendments to it. The fact is that at 15 million degrees, hydrogen can turn into helium in the carbon-nitrogen-oxygen cycle (CNO cycle). At its beginning, a proton collides with a carbon-12 nucleus and generates a nitrogen-13 nucleus and a gamma-ray quantum. Nitrogen decays into a carbon-13 nucleus, a positron and a neutrino. The heavy carbon nucleus again collides with a proton, from which nitrogen-14 plus a gamma ray is produced. Nitrogen swallows the third proton, releasing a gamma quantum and oxygen-15, which is transformed into nitrogen-15, positron and neutrino. The nitrogen nucleus captures the last, fourth proton and splits into carbon-12 and helium-4 nuclei. The total balance is the same as in the first cycle: four protons at the beginning, an alpha particle (aka a helium-4 nucleus), a pair of positrons and a pair of neutrinos at the end. Plus, of course, the same energy output, almost 27 MeV. As for carbon-12, it is not consumed at all in this cycle; it disappears in the first reaction and appears again in the last. This is not a fuel, but a catalyst.
The sun rotates around its axis, but not as a single whole. The figure shows a computer model based on Doppler measurements of the rotation speed of individual parts of the Sun collected by the SOHO (Solar Heliospheric Observatory) space observatory. The color indicates the rotation speed (in descending order: red, yellow, green, blue). Areas of hot plasma moving at different speeds form “ribbons”, at the boundaries of which disturbances of local magnetic fields arise, as a result of which sunspots most often appear here.
The reactions of the CNO cycle inside the Sun are rather sluggish and provide only one and a half percent of the total energy output. However, they should not be forgotten, if only because otherwise the calculated power of the solar neutrino flux will be underestimated. The mysteries of the neutrino radiation of the Sun are very interesting, but this is a completely independent topic that does not fit into the scope of this article.
The core of the very young Sun consisted of 72% hydrogen. Model calculations have shown that now it accounts for only 35% of the mass of the central zone of the core and 65% of the peripheral zone. Nothing can be done, even nuclear fuel burns out. However, it will last billions for another five years. The processes in the thermonuclear furnace of the Sun are sometimes compared to the explosion of a hydrogen bomb, but the similarity here is very conditional. Tens of kilograms of powerful nuclear bombs have a yield of megatons and tens of megatons of TNT equivalent. But the solar core, with all its gigantic mass, produces only about one hundred billion megatons per second. It is easy to calculate that the average energy output is six microwatts per kilogram - the human body produces heat 200,000 times more actively. Solar thermonuclear fusion does not “explode”, but slowly, slowly “smolders” - to our great happiness.
Radiant transfer
The outer boundary of the core is approximately 150,000 km from the center of the Sun (0.2 radius). In this zone the temperature drops to 9 million degrees. With subsequent cooling, the reactions of the proton-proton cycle stop - the protons do not have enough kinetic energy to overcome electrostatic repulsion and fuse into a deuterium nucleus. The reactions of the CNO cycle do not occur there either, since their temperature threshold is even higher. Therefore, at the boundary of the core, solar thermonuclear fusion disappears.
A three-dimensional model of a sunspot, built on the basis of data obtained using one of the instruments (Michelson Doppler Imager) of the SOHO (Solar and Heliospheric Observatory) space observatory. The upper plane is the surface of the Sun, the lower plane passes at a depth of 22 thousand kilometers. The vertical sectional plane is extended to 24 thousand kilometers. The colors indicate areas with different speeds of sound (in descending order - from red to blue to black). The spots themselves are places where strong magnetic fields enter the solar atmosphere. They are visible as areas of cooler temperatures on the Sun's surface, usually surrounded by hotter active regions called faculae. The number of spots on the Sun changes with a period of 11 years (the more there are, the greater the activity of the Sun).
The core is surrounded by a thick spherical layer, which ends at a vertical mark of 0.7 solar radii. This is the radiative zone. It is filled with hydrogen-helium plasma, the density of which decreases a hundred times as it moves from the inner boundary of the zone to the outer one, from 20 to 0.2 g/cm 3 . Although the outer plasma layers are cooler than the inner ones, the temperature gradient there is not so great that vertical flows of matter arise that carry heat from the lower layers to the upper ones (this heat transfer mechanism is called convection). There is no and cannot be any convection in the supranuclear layer. The energy released in the nucleus passes through it in the form of quanta of electromagnetic radiation.
How does this happen? Gamma quanta generated in the center of the nucleus are scattered in its substance, gradually losing energy. They reach the nucleus boundary in the form of soft X-rays (wavelength on the order of one nanometer and energy 400−1300 eV). The plasma there is almost opaque to them; photons can travel only a fraction of a centimeter in it. When colliding with hydrogen and helium ions, quanta give them their energy, which is partially spent on maintaining the kinetic energy of the particles at the same level, and partially re-emitted in the form of new quanta of greater length. So photons gradually diffuse through the plasma, dying and being born again. Wandering quanta travel upward (where matter is less dense) more easily than downward, and therefore radiant energy flows from the depths of the zone to its outer boundary.
Since matter is motionless in the radiative transfer zone, it rotates around the solar axis as a single whole. But only for the time being. As photons travel toward the surface of the Sun, they travel increasingly longer distances between collisions with ions. This means that the difference in the kinetic energy of emitting and absorbing particles is increasing all the time, because solar matter at greater depths is hotter than at shallower ones. As a result, the plasma is destabilized and conditions for the physical movement of matter arise in it. The radiative transfer zone transforms into the convective zone.
Photo of the solar corona taken during the total solar eclipse of February 26, 1998. The corona is the outer part of the solar atmosphere, consisting of rarefied hydrogen heated to a temperature of about a million degrees Celsius. The colors in the image are synthetic, and indicate the decreasing brightness of the corona as it moves away from the Sun (the blue and pink spot in the center is the Moon).
Convection zone
It begins at a depth of 0.3 radii and extends all the way to the surface of the Sun (or rather, its atmosphere). Its base is heated to 2 million degrees, while the temperature of the outer boundary does not even reach 6000˚C. It is separated from the radial zone by a thin intermediate layer - the tachocline. The most interesting, but not yet well-studied things happen in it. In any case, there is reason to believe that plasma flows moving in the tachocline make the main contribution to the formation of the solar magnetic field. It is easy to calculate that the convection zone occupies about two-thirds of the volume of the Sun. However, its mass is very small - only two percent of the Sun. This is natural, because solar matter inevitably becomes rarefied as it moves away from the center. At the lower boundary of the zone, the plasma density is 0.2 the density of water, and upon entering the atmosphere it decreases to 0.0001 the density of earth's air above sea level.
Matter in the convective zone moves in a very confusing way. From its base rise powerful but slow streams of hot plasma (a hundred thousand kilometers across), the speed of which does not exceed a few centimeters per second. Not so powerful jets of less heated plasma descend towards them, the speed of which is already measured in meters per second. At a depth of several thousand kilometers, the rising high-temperature plasma is divided into giant cells. The largest of them have linear dimensions of about 30-35 thousand kilometers - they are called supergranules. Closer to the surface, mesogranules with a characteristic size of 5000 km are formed, and even closer - granules 3–4 times smaller. Supergranules live for about a day, granules usually no more than a quarter of an hour. When these products of collective plasma motion reach the solar surface, they are easily visible through a telescope with a special filter.
Atmosphere
It is quite complicated. All sunlight goes into space from its lower level, which is called the photosphere. The main source of light is the lower layer of the photosphere, 150 km thick. The thickness of the entire photosphere is about 500 km. Along this vertical, the plasma temperature decreases from 6400 to 4400 K.
Regions of low temperature (up to 3700 K) constantly appear in the photosphere, which glow weaker and are detected in the form of dark spots. The number of sunspots varies with a period of 11 years, but they never cover more than 0.5% of the solar disk.
Above the photosphere is the chromospheric layer, and even higher is the solar corona. The existence of the corona has been known since time immemorial, as it is clearly visible during total solar eclipses. The chromosphere was discovered relatively recently, only in the middle of the 19th century. On July 18, 1851, hundreds of astronomers gathered in Scandinavia and surrounding countries watched the Moon cover the solar disk. A few seconds before the appearance of the corona and just before the end of the total phase of the eclipse, scientists noticed a glowing red crescent at the edge of the disk. During the 1860 eclipse, it was possible not only to better examine such flares, but also to obtain their spectrograms. Nine years later, English astronomer Norman Lockyer called this zone the chromosphere.
The density of the chromosphere is extremely low even compared to the photosphere, only 10−100 billion particles per 1 cm³. But it is heated more strongly - up to 20,000˚C. In the chromosphere, dark elongated structures are constantly observed - chromospheric filaments (a type of them is the well-known prominences). They are clumps of denser and colder plasma, lifted from the photosphere by magnetic field loops. Areas of increased brightness—flocculi—are also visible. And finally, elongated plasma structures - spicules - constantly appear in the chromosphere and disappear after a few minutes. These are a kind of overpasses along which matter flows from the photosphere to the corona.
The future fate of our star directly depends on the processes in the solar interior. As hydrogen reserves decrease, the core gradually contracts and heats up, which increases the luminosity of the Sun. Since becoming a main sequence star, it has already grown by 25-30% - and this process will continue. In about 5 billion years, the temperature of the core will reach hundreds of millions of degrees, and then helium will ignite in its center (with the formation of carbon and oxygen). At this time, hydrogen will be burned at the periphery, and its combustion zone will move slightly towards the surface. The Sun will lose hydrostatic stability, its outer layers will greatly inflate, and it will turn into a gigantic, but not particularly bright, luminary - a red giant. The luminosity of this giant will be two orders of magnitude higher than the current luminosity of the Sun, but its lifespan will be much shorter. In the center of its core, a large amount of carbon and oxygen will quickly accumulate, which will no longer be able to flare up - there will not be enough temperature. The outer helium layer will continue to burn, gradually expanding and therefore cooling. The rate of thermonuclear combustion of helium increases extremely quickly with increasing temperature and falls with decreasing temperature. Therefore, the insides of the red giant will begin to pulsate strongly, and in the end it may come to the point that its atmosphere will be thrown into the surrounding space at a speed of tens of kilometers per second. First, the expanding stellar shell, under the influence of ionizing ultraviolet radiation from the underlying stellar layers, will glow brightly with blue and green light - at this stage it is called a planetary nebula. But after thousands or, at most, tens of thousands of years, the nebula will cool, darken and dissipate in space. As for the core, the transformation of elements will stop altogether, and it will shine only due to the accumulated thermal energy, cooling and fading more and more. It won’t be able to collapse into a neutron star or black hole; there won’t be enough mass. Such cooling remains of solar-type stars that died in Bose are called white dwarfs.
The corona is the hottest part of the atmosphere, its temperature reaches several million degrees. This heating can be explained using several models based on the principles of magnetohydrodynamics. Unfortunately, all these processes are very complex and very poorly studied. The crown is also full of various structures - holes, loops, streamers.
Solar problems
Despite the fact that the Sun is the largest and most visible object in the earth's sky, there are a lot of unsolved problems in the physics of our star. “We know that the magnetism of the Sun has an extremely strong influence on the dynamics of its atmosphere - for example, it gives rise to sunspots. But how it arises and how it spreads in plasma has not yet been clarified,” Steven Keil, director of the American National Solar Observatory, answers PM’s question. — In second place I would put deciphering the mechanism of solar flares. These are short-term, but extremely powerful emissions of fast electrons and protons, combined with the generation of equally powerful streams of electromagnetic radiation of a wide variety of wavelengths. Extensive information has been collected about outbreaks, but there are no reasonable models for their occurrence yet. Finally, it would be necessary to understand in what ways the photosphere energizes the corona and heats it to temperatures that are three orders of magnitude higher than its own temperature. And for this, first of all, it is necessary to properly determine the parameters of the magnetic fields inside the corona, since these quantities are far from being fully known.”