(ORDO NEWS) — The luminary, to which our planet, and its biosphere, and human civilization owe their existence, is quite banal from the point of view of astronomers. And what will happen if the Sun goes out forever is not a big secret for them either.
Before you understand whether the Sun can go out, you should find out how the star closest to us was born. According to generally accepted estimates, the Sun arose 4.59 billion years ago: of course, our daytime luminary was not born from scratch.
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 the father also took place in the face of a cosmic event that increased the gravitational instability of the cloud and spurred its collapse (such could be a meeting with a massive star or a supernova explosion). In the center of the disk, a sphere of luminous plasma arose with a surface temperature of several thousand degrees, transferring part of its gravitational energy into heat.
The newborn luminary continued to shrink, warming up its bowels more and more. After a few million years, their temperature reached 10 million degrees Celsius, and self-sustaining fusion reactions began there. The young protostar evolved into a normal main sequence star.
The substance of the near and far periphery of the disk condensed into cold bodies – planets and planetoids. Therefore, when the Sun cools down, firstly, it will not happen, by human standards, also not quickly, and secondly, the nearest celestial bodies will clearly be under the influence of the fading luminary.
Hear the sun
If anyone knows that the Sun will ever go out, it is clearly scientists who are actively engaged in its study. At present, they 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, the typical periods of which are several minutes,” explains Alexander Kosovichev, a senior researcher at Stanford University. “They were discovered back in the early 1960s. In particular, in this The Crimean Astrophysical Observatory, led by Academician Severny, has done a lot in the region. 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 of generation of magnetic fields. Helioseismology has already made it possible to determine the depth of the convective zone, elucidate the nature of the rotation of the solar layers, and refine our ideas about the origin of sunspots, which are actually clots of the 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.” clarify our understanding of the occurrence of sunspots, which are actually clots of the 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.” clarify our understanding of the occurrence of sunspots, which are actually clots of the 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.”
Here are some passport data of the Sun. Age – 4.59 billion years; weight – 1.989×1030 kg; average radius – 696,000 km; average density – 1.409 g / cm ^ 3 (the density of terrestrial 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 – 3.83×1023 kW.
Understanding how many years the Sun will go out can help not only the study of the chemical composition of a given star. but also the structure of its surface. The photosphere (the so-called surface of the Sun) even in a calm state when viewed through a telescope (of course, 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 up”, and cold gas sinks down at the boundaries of the granules, which are visible as dark areas. The typical granule size 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 shown in light tones, towards the observer – in dark. Left – composite picture (top and counterclockwise): the internal structure of the Sun with the core and the convective zone; photosphere with a dark spot; chromosphere; solar flare; top right – prominence.
Since the Sun does not rotate around its own axis as a whole, it does not have a strictly defined day. The surface of its equatorial zone makes a complete revolution in 27 Earth days, and the circumpolar zones – in 35 days.
The axial rotation of the solar interiors is even more complex and is still unknown in all details. The receipt of such data by mankind in the near future will allow not only to assume when the Sun will go out, but also with a high degree of probability to understand how this will happen. In the meantime, it remains to observe the life of similar stars and pay attention to the composition of our luminary.
The chemical composition of solar matter is naturally dominated by hydrogen (about 72% of the mass) and helium (26%). A little less than a percent is oxygen, 0.4% is carbon, about 0.1% is neon. And one of the answers to the question of why the Sun will go out lies precisely in this proportion of these elements.
If these ratios are expressed in terms of the number of atoms, then it turns out that there are 98,000 helium atoms, 850 oxygen atoms, 360 carbon atoms, 120 neon atoms, 110 nitrogen atoms, and 40 iron and silicon atoms per million hydrogen atoms.
The layered structure of the Sun is often compared to an onion. This analogy is not very successful, since the layers themselves are permeated with powerful vertical flows of matter and energy. But in the first approximation, it is acceptable.
Our star shines due to thermonuclear energy, which is generated in the core. Accordingly, without the presence of this type of energy or its significant change, the Sun will soon go out. But at the moment it is known that the temperature of the core reaches 15 million degrees Celsius, the density is 160 g / cm ^ 3, the pressure is 3.4×1011 atm.
Under these hellish conditions, several chains of thermonuclear reactions are carried out that make up the proton-proton cycle (pp-cycle). He owes this name to the initial reaction, where two protons, colliding, give rise to a deuterium nucleus, a positron and an electron neutrino.
During these transformations (and there are quite a few of them), hydrogen burns out 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 not reacting with its matter. Each reaction of the pp cycle releases 26.73 MeV in the form of the kinetic energy of the generated particles and gamma rays. Of course, when the Sun goes out, these transformations will be irrelevant, and their significant slowdown will mean the cooling of our star.
The sun may go out, but the importance of these metamorphoses shows one of the options when this could happen even earlier in time. If the protosolar cloud consisted exclusively of elements that arose during the Big Bang (hydrogen and helium-4 with a very small admixture of deuterium, helium-3 and lithium-7), then everything would have ended with these reactions.
However, the composition of the protosolar matter was much richer, as 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 luminaries, where temperatures reach billions of degrees.
The sun is not one of them. If there is iron there, it is only because the primary cloud has already been contaminated with this metal and many other elements.
This circumstance does not greatly change the above scheme of intrasolar thermonuclear fusion, but still introduces some amendments into it, allowing us to understand how long the Sun will go out. 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 are produced.
Nitrogen swallows the third proton with the release of a gamma quantum and oxygen-15, which is transformed into nitrogen-15, a positron and a 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 the 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 reappears in the last one. It’s not a fuel, it’s a catalyst.
The sun rotates around its axis, but not as a whole. Because of this, it is quite possible that the Sun will soon go out, but this extinction will also be uneven. The figure shows a computer model compiled on the basis of data from 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). Sections of hot plasma moving at different speeds form “ribbons” at the boundaries of which perturbations of local magnetic fields arise, as a result of which it is precisely here that sunspots most often appear.
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 a very young Sun was 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 will burn out.
However, it will be enough for another five years. The processes in the thermonuclear furnace of the Sun are sometimes compared with the explosion of a hydrogen bomb, but the similarity here is very arbitrary. Dozens of kilograms of stuffing 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 a 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 fusion does not “explode” but slowly, slowly “smolders” – to our great happiness. Hence, the scientific understanding of how long the Sun will go out is inexorably pessimistic, because the processes taking place inside our star indicate that it is already going out, albeit at a minimum speed for humanity.
The outer boundary of the core is located 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 the electrostatic repulsion and merge into the deuterium nucleus. Reactions of the CNO cycle do not occur there either, since their temperature threshold is even higher.
Therefore, at the boundary of the core, the solar fusion comes to naught. But under current conditions, the moment that the Sun will soon go out should not worry both us and our immediate descendants.
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 plane of the section is extended up to 24 thousand kilometers. Colors indicate areas with different sound speeds (as they decrease, from red to blue to black). The spots themselves are places where strong magnetic fields enter the solar atmosphere. When the Sun cools down, they will also cease to be active. Now the spots are visible as areas with a lower temperature on the surface of the Sun, usually they are surrounded by hotter active regions – torches.
The core is surrounded by a powerful spherical layer, which ends at a vertical mark of 0.7 solar radius. This is the radiative zone, and thanks to it, or rather the processes inside it, the Sun will not go out soon. It is filled with hydrogen-helium plasma, the density of which, as it moves from the inner boundary of the zone to the outer one, decreases by a factor of a hundred, from 20 to 0.2 g/cm^3.
Although the outer plasma layers are colder than the inner layers, the temperature gradient there is not so large that vertical flows of matter arise that carry heat away from the lower layers to the upper ones (such a heat transfer mechanism is called convection).
There is no convection in the supranuclear layer and cannot be. The energy released in the nucleus passes through it in the form of electromagnetic radiation quanta.
How does this happen? Gamma quanta born in the center of the nucleus scatter in its substance, gradually losing energy. It seems that the Sun itself will explode when this energy becomes too excessive. But in fact, gamma quanta reach the nuclear boundary in the form of soft X-rays (wavelength of the order of one nanometer and energy of 400–1300 eV).
The local plasma is almost opaque for them, photons can cover a distance of only a fraction of a centimeter in it.
When colliding with hydrogen and helium ions, the 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 longer quanta. So photons gradually diffuse through the plasma, dying and being born again. Wandering quanta go up (where the matter is less dense) more easily than down,
Since matter is immobile in the zone of radiative transfer, it rotates around the solar axis as a whole. But only for the time being.
As they move toward the surface of the Sun, photons travel ever 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 is hotter at greater depths than at shallower ones.
As a result, the plasma is destabilized and conditions arise in it for the physical movement of matter. Ideal conditions explaining at a fundamental level why the Sun will go out in the near future, by the standards of the Universe. The radiative transfer zone passes into the convective zone.
A photo of the solar corona, taken during the total solar eclipse of February 26, 1998, helps experts better understand when the Sun goes out. 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 represent the decreasing brightness of the corona as it moves away from the Sun (the blue with a pink spot in the center is the Moon).
It starts at a depth of 0.3 radius and extends up to the surface of the Sun (or rather, its atmosphere). Its sole is heated up to 2 million degrees, while the temperature of the outer border does not even reach 6000˚С. It is separated from the radial zone by a thin intermediate layer, the tachocline.
Interesting things happen in it, but so far not too studied things that can determine how long the Sun will go out. In any case, there are reasons to believe that the 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 the solar matter inevitably discharges as it moves away from the center. At the lower boundary of the zone, the plasma density is equal to 0.2 of the density of water.
Matter in the convective zone moves in a very confusing way. Powerful but slow streams of hot plasma rise from its sole (with a diameter of a hundred thousand kilometers), 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 ascending high-temperature plasma is divided into giant cells. The largest of them have linear dimensions of the order of 30-35 thousand kilometers – they are called supergranules.
Closer to the surface, microgranules with a characteristic size of 5000 km are formed, and even closer, granules 3–4 times smaller are formed. Supergranules live for about a day, granules – usually no more than a quarter of an hour.
All their activity suggests that if the Sun ever goes out, it’s certainly not in our lifetime. When these products of the collective motion of the plasma reach the solar surface, they are easy to see in a telescope with a special filter.
It is rather complicated. All sunlight escapes into space from its lowest 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, but it is not entirely correct to say that because of this the Sun will soon go out.
In the photosphere, areas of low (up to 3700 K) temperature constantly appear, which glow more weakly and are found in the form of dark spots. The number of sunspots changes with a period of 11 years, but they never cover more than 0.5% of the area of the solar disk, which means that the Sun may not go out because of their number.
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 perfectly 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 neighboring countries watched the Moon close 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 eclipse of 1860, it was possible not only to better examine such flares, but also to obtain their spectrograms. Nine years later, the English astronomer Norman Lockyer named this zone the chromosphere. And thanks to its study, you can also understand how long the Sun will go out.
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˚С, which does not allow the Sun to go out in the sky.
In the chromosphere, dark elongated structures are constantly observed – chromospheric filaments (their variety 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 are also visible – flocculi. Finally, elongated plasma structures—spicules—constantly appear in the chromosphere and disappear after a few minutes. These are a kind of viaducts through which matter flows from the photosphere to the corona.
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 poorly understood, but they allow us to give some idea of what will happen if the Sun goes out forever. The crown is also saturated with various structures – holes, loops, streamers.
When the sun goes out
What will happen to the Earth if the Sun goes out? Unfortunately, here it is worth disappointing those who hypothesize about a new ice age and eternal cold. Scientists do not exclude that the star closest to us will begin to expand significantly and simply “swallow” our planet.
In general, the future fate of our luminary directly depends on the processes taking place in the solar interior. As hydrogen reserves decrease, the core gradually contracts and heats up, which increases the luminosity of the Sun.
Since turning into 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 light up in its center (with the formation of carbon and oxygen).
At the periphery, at this time, hydrogen will be afterburner, and the zone of its combustion will move somewhat towards the surface. Does this mean that when the Sun explodes, it will start destroying its own system?
The sun will lose hydrostatic stability, its outer layers will swell greatly, and it will turn into a gigantic, but not particularly bright luminary – a red giant. The luminosity of this giant will exceed the current luminosity of the Sun by two orders of magnitude, but its lifespan will be much shorter.
After that, the Sun will soon go out. 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.
When the Sun finally cools down, it will become a white dwarf. Approximately this will happen in 5 billion years.
The rate of thermonuclear combustion of helium increases extremely rapidly with an increase in temperature and falls with its decrease. 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 ejected into the surrounding space at a speed of tens of kilometers per second.
At first, the expanding stellar shell, under the influence of ionizing ultraviolet radiation from the underlying stellar layers, will shine 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 down, darken and dissipate in space.
As for the core, there the transformation of elements will stop altogether, and it will shine only due to the accumulated thermal energy, cooling down and fading more and more. It will not be able to shrink into a neutron star or a black hole, there will not be enough mass.
Such cooling remnants of solar-type stars that died in the Bose are called white dwarfs. The sun will become a dwarf, but before that it will absorb Mercury, Venus and the Earth, so that further metamorphoses of the star will quite possibly take place without us.
Despite the fact that the Sun is the largest and most visible object in the earth’s sky, there are enough unsolved problems in the physics of our star. The fact that the Sun will someday go out is not a reason for the scientific community to stop studying the 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 propagates in the plasma has not yet been clarified,” Steven Cale, director of the American National Solar Observatory, answers the question of “PM”.
In second place, I would put the decoding of the mechanism of the occurrence of solar flares. These are short-term, but extremely powerful ejections of fast electrons and protons, combined with the generation of equally powerful electromagnetic radiation fluxes of various wavelengths.
A lot of information has been collected about outbreaks, however, there are no reasonable models of their occurrence yet. Finally, we need to understand how the photosphere feeds energy to the corona and heats it up 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 values are far from being fully known.”
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