Our Sun has been shining for more than 4.5 billion years. At the same time, it constantly consumes hydrogen. It is absolutely clear that no matter how large its reserves are, they will be exhausted someday. And what will happen to the luminary? There is an answer to this question. The life cycle of a star can be studied from other similar cosmic formations. After all, there are real patriarchs in space, whose age is 9-10 billion years. And there are very young stars. They are no more than several tens of millions of years old.
Consequently, by observing the state of the various stars with which the Universe is “strewn”, one can understand how they behave over time. Here we can draw an analogy with an alien observer. He flew to Earth and began to study people: children, adults, old people. Thus, in a very short period of time, he understood what changes happen to people throughout life.
The Sun is currently a yellow dwarf - 1
Billions of years will pass, and it will become a red giant - 2
And then it turns into white dwarf - 3
Therefore, we can say with all confidence that when the hydrogen reserves in the central part of the Sun are exhausted, the thermonuclear reaction will not stop. The zone where this process will continue will begin to shift towards the surface of our star. But at the same time, gravitational forces will no longer be able to influence the pressure that is generated as a result of the thermonuclear reaction.
Consequently, the star will begin to grow in size and gradually turn into a red giant. This is a space object of a late stage of evolution. But he also happens to be the same early stage during star formation. Only in the second case does the red giant shrink and turn into star main sequence . That is, one in which the reaction of synthesis of helium from hydrogen takes place. In a word, where the life cycle of a star begins is where it ends.
Our Sun will increase in size so much that it will engulf nearby planets. These are Mercury, Venus and Earth. But don't be afraid. The star will begin to die in a few billion years. During this time, dozens, and maybe hundreds of civilizations will change. A person will pick up a club more than once, and after thousands of years he will sit down at a computer again. This is the usual cyclicity on which the entire Universe is based.
But becoming a red giant doesn't mean the end. The thermonuclear reaction will throw the outer shell into space. And in the center there will remain an energy-deprived helium core. Under the influence of gravity, it will compress and eventually become extremely dense with a large mass. space education. Such remnants of extinct and slowly cooling stars are called white dwarfs.
Our white dwarf will have a radius 100 times smaller than the radius of the Sun, and its luminosity will decrease by 10 thousand times. In this case, the mass will be comparable to the current solar one, and the density will be a million times greater. There are a lot of such white dwarfs in our Galaxy. Their number is 10% of total number stars
It should be noted that white dwarfs are hydrogen and helium. But we will not go into the wilds, but will only note that with strong compression, gravitational collapse can occur. And this is fraught with a colossal explosion. At the same time, a flash is observed supernova. The term "supernova" does not describe the age, but the brightness of the flash. It’s just that the white dwarf was not visible for a long time in the cosmic abyss, and suddenly a bright glow appeared.
Most of the exploding supernova scatters in space with enormous speed. And the remaining central part compresses into an even denser formation and is called neutron star. It is the end product of stellar evolution. Its mass is comparable to that of the sun, and its radius reaches only a few tens of kilometers. One cube cm neutron star can weigh millions of tons. There are quite a lot of such formations in space. Their number is about a thousand times less than the ordinary suns with which the Earth's night sky is strewn.
It must be said that the life cycle of a star is directly related to its mass. If it matches the mass of our Sun or is less than it, then a white dwarf appears at the end of its life. However, there are luminaries that are tens and hundreds of times larger than the Sun.
When such giants shrink as they age, they distort space and time so much that instead of a white dwarf a white dwarf appears. black hole. Her gravitational attraction so great that even those objects that move at the speed of light cannot overcome it. The dimensions of the hole are characterized by gravitational radius. This is the radius of the sphere bounded by event horizon. It represents a space-time limit. Any cosmic body Having overcome it, it disappears forever and never comes back.
There are many theories about black holes. All of them are based on the theory of gravity, since gravity is one of the the most important forces Universe. And its main quality is versatility. At least not a single one has been discovered these days. space object, which would have no gravitational interaction.
There is an assumption that through black hole you can get into a parallel world. That is, it is a channel to another dimension. Everything is possible, but any statement requires practical evidence. However, no mortal has yet been able to carry out such an experiment.
Thus, the life cycle of a star consists of several stages. In each of them, the luminary appears in a certain capacity, which is radically different from previous and future ones. This is where the uniqueness and mystery lie. outer space. Getting to know him, you involuntarily begin to think that a person also goes through several stages in his development. And the shell in which we exist now is only a transitional stage to some other state. But this conclusion again requires practical confirmation..
> Life cycle of a star
Description life and death of stars: stages of development with photos, molecular clouds, protostar, T Tauri, main sequence, red giant, white dwarf.
Everything in this world is evolving. Any cycle begins with birth, growth and ends with death. Of course, stars have these cycles in a special way. Let us at least remember that their time frames are larger and are measured in millions and billions of years. In addition, their death carries certain consequences. What does it look like life cycle of stars?
The first life cycle of a star: Molecular clouds
Let's start with the birth of a star. Imagine a huge cloud of cold molecular gas that can quietly exist in the Universe without any changes. But suddenly a supernova explodes not far from it or it collides with another cloud. Due to such a push, the destruction process is activated. It is divided into small parts, each of which is retracted into itself. As you already understand, all these groups are preparing to become stars. Gravity heats up the temperature, and the stored momentum maintains the rotation process. The lower diagram clearly demonstrates the cycle of stars (life, stages of development, transformation options and death celestial body with photo).
Second life cycle of a star: Protostar
The material condenses more densely, heats up and is repelled by gravitational collapse. Such an object is called a protostar, around which a disk of material forms. The part is attracted to the object, increasing its mass. The remaining debris will group and create planetary system. Further development of the star all depends on mass.
Third life cycle of a star: T Taurus
When material hits a star, a huge amount of energy is released. The new stellar stage was named after the prototype - T Tauri. This variable star, located 600 light years away (near).
It can reach great brightness because the material breaks down and releases energy. But the central part does not have enough temperature to support nuclear fusion. This phase lasts 100 million years.
Fourth life cycle of a star:Main sequence
At a certain moment, the temperature of the celestial body rises to the required level, activating nuclear fusion. All stars go through this. Hydrogen transforms into helium, releasing enormous heat and energy.
The energy is released as gamma rays, but due to the slow motion of the star, it falls with the same wavelength. Light is pushed out and comes into conflict with gravity. We can assume that an ideal balance is created here.
How long will she be in the main sequence? You need to start from the mass of the star. Red dwarfs (half the mass of the sun) can burn through their fuel supply for hundreds of billions (trillions) of years. Average stars (like ) live 10-15 billion. But the largest ones are billions or millions of years old. See what the evolution and death of stars of different classes looks like in the diagram.
Fifth life cycle of a star: Red giant
During the melting process, hydrogen runs out and helium accumulates. When there is no hydrogen left at all, all nuclear reactions stop, and the star begins to shrink due to gravity. The hydrogen shell around the core heats up and ignites, causing the object to grow 1,000 to 10,000 times larger. At a certain moment, our Sun will repeat this fate, increasing to the Earth’s orbit.
Temperature and pressure reach their maximum and helium fuses into carbon. At this point the star shrinks and ceases to be a red giant. With greater massiveness, the object will burn other heavy elements.
Sixth life cycle of a star: White dwarf
A solar-mass star doesn't have enough gravitational pressure to fuse the carbon. Therefore, death occurs with the end of helium. The outer layers are ejected and a white dwarf appears. It starts out hot, but after hundreds of billions of years it cools down.
Studying stellar evolution is impossible by observing just one star - many changes in stars occur too slowly to be noticed even after many centuries. Therefore, scientists study many stars, each of which is at a certain stage of its life cycle. Over the past few decades wide use in astrophysics received modeling of the structure of stars using computer technology.
Encyclopedic YouTube
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✪ Stars and stellar evolution (narrated by astrophysicist Sergei Popov)
✪ Stars and stellar evolution (narrated by Sergey Popov and Ilgonis Vilks)
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✪ Surdin V.G. Stellar Evolution Part 1
✪ S. A. Lamzin - “Stellar Evolution”
Subtitles
Thermonuclear fusion in the interior of stars
Young stars
The process of star formation can be described in a unified way, but the subsequent stages of a star's evolution depend almost entirely on its mass, and only at the very end of the star's evolution can its chemical composition play a role.
Young low mass stars
Young low-mass stars (up to three solar masses) [ ], which are approaching the main sequence, are completely convective - the convection process covers the entire body of the star. These are essentially protostars, in the centers of which nuclear reactions are just beginning, and all radiation occurs mainly due to gravitational compression. Until hydrostatic equilibrium is established, the star's luminosity decreases at a constant effective temperature. On the Hertzsprung-Russell diagram, such stars form an almost vertical track called the Hayashi track. As the compression slows, the young star approaches the main sequence. Objects of this type are associated with T Tauri stars.
At this time, for stars with a mass greater than 0.8 solar masses, the core becomes transparent to radiation, and radiative energy transfer in the core becomes predominant, since convection is increasingly hampered by the increasing compaction of stellar matter. In the outer layers of the star’s body, convective energy transfer prevails.
It is not known for certain what characteristics do stars of lower mass have at the moment they enter the main sequence, since the time these stars spent in the young category exceeds the age of the Universe [ ] . All ideas about the evolution of these stars are based only on numerical calculations and mathematical modeling.
As the star contracts, the pressure of the degenerate electron gas begins to increase and when a certain radius of the star is reached, the compression stops, which leads to a stop in the further increase in temperature in the core of the star caused by the compression, and then to its decrease. For stars smaller than 0.0767 solar masses, this does not happen: the energy released during nuclear reactions is never enough to balance the internal pressure and gravitational compression. Such “understars” emit more energy than is produced during thermonuclear reactions, and are classified as so-called brown dwarfs. Their fate is constant compression until the pressure of the degenerate gas stops it, and then gradual cooling with the cessation of all thermonuclear reactions that have begun.
Young intermediate mass stars
Young stars of intermediate mass (from 2 to 8 solar masses) [ ] evolve qualitatively in exactly the same way as their smaller sisters and brothers, with the exception that they do not have convective zones up to the main sequence.
Objects of this type are associated with the so-called. Ae\Be Herbig stars with irregular variables of spectral class B-F0. They also exhibit disks and bipolar jets. The rate of outflow of matter from the surface, luminosity and effective temperature are significantly higher than for T Tauri, so they effectively heat and disperse the remnants of the protostellar cloud.
Young stars with a mass greater than 8 solar masses
Stars with such masses already have the characteristics of normal stars, since they went through all the intermediate stages and were able to achieve such a rate of nuclear reactions that compensated for the energy lost to radiation while mass accumulated to achieve hydrostatic equilibrium of the core. For these stars, the outflow of mass and luminosity are so great that they not only stop the gravitational collapse of the outer regions of the molecular cloud that have not yet become part of the star, but, on the contrary, disperse them away. Thus, the mass of the resulting star is noticeably less than the mass of the protostellar cloud. Most likely, this explains the absence in our galaxy of stars with a mass greater than about 300 solar masses.
Mid-life cycle of a star
Stars come in a wide variety of colors and sizes. By spectral class they range from hot blue to cold red, by mass - from 0.0767 to about 300 solar masses. latest estimates. The luminosity and color of a star depend on its surface temperature, which in turn is determined by its mass. All new stars “take their place” on the main sequence according to their chemical composition and mass. Naturally, we are not talking about the physical movement of the star - only about its position on the indicated diagram, depending on the parameters of the star. In fact, the movement of a star along the diagram corresponds only to a change in the parameters of the star.
The thermonuclear “burning” of matter, resumed at a new level, causes a monstrous expansion of the star. The star "swells", becoming very "loose", and its size increases approximately 100 times. So the star becomes a red giant, and the helium burning phase lasts about several million years. Almost all red giants are variable stars.
Final stages of stellar evolution
Old stars with low mass
At present, it is not known for certain what happens to light stars after the supply of hydrogen in their cores is depleted. Since the age of the Universe is 13.7 billion years, which is not enough for the hydrogen fuel supply in such stars to be depleted, modern theories are based on computer modeling processes occurring in such stars.
Some stars can only synthesize helium in certain active zones, causing instability and strong stellar winds. In this case, the formation of a planetary nebula does not occur, and the star only evaporates, becoming even smaller than a brown dwarf [ ] .
A star with a mass less than 0.5 solar is not able to convert helium even after reactions involving hydrogen stop in its core - the mass of such a star is too small to provide a new phase of gravitational compression to a degree sufficient to “ignite” helium Such stars include red dwarfs, such as Proxima Centauri, whose residence time on the main sequence ranges from tens of billions to tens of trillions of years. After the cessation of thermonuclear reactions in their cores, they, gradually cooling, will continue to weakly emit in the infrared and microwave ranges of the electromagnetic spectrum.
Medium sized stars
Upon reaching star average size(from 0.4 to 3.4 solar masses) [ ] of the red giant phase, hydrogen runs out in its core, and reactions of synthesis of carbon from helium begin. This process occurs at higher temperatures and therefore the energy flow from the core increases and, as a result, the outer layers of the star begin to expand. The beginning of carbon synthesis marks a new stage in the life of a star and continues for some time. For a star similar in size to the Sun, this process can take about a billion years.
Changes in the amount of energy emitted cause the star to go through periods of instability, including changes in size, surface temperature and energy release. Energy output shifts towards low frequency radiation. All this is accompanied by increasing mass loss due to strong stellar winds and intense pulsations. Stars in this phase are called “late-type stars” (also “retired stars”), OH -IR stars or Mira-like stars, depending on their exact characteristics. The ejected gas is relatively rich in heavy elements produced in the interior of the star, such as oxygen and carbon. The gas forms an expanding shell and cools as it moves away from the star, making possible education dust particles and molecules. With strong infrared radiation The source star in such shells creates ideal conditions for the activation of cosmic masers.
Thermonuclear combustion reactions of helium are very sensitive to temperature. Sometimes this leads to great instability. Strong pulsations arise, which as a result impart sufficient acceleration to the outer layers to be thrown off and turn into a planetary nebula. In the center of such a nebula, the bare core of the star remains, in which thermonuclear reactions stop, and as it cools, it turns into a helium white dwarf, usually having a mass of up to 0.5-0.6 solar masses and a diameter on the order of the diameter of the Earth.
The vast majority of stars, including the Sun, complete their evolution by contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases by a hundred times, and the density becomes a million times higher than the density of water, the star is called a white dwarf. It is deprived of energy sources and, gradually cooling, becomes an invisible black dwarf.
In stars more massive than the Sun, the pressure of degenerate electrons cannot stop further compression nuclei, and electrons begin to “press” into atomic nuclei, which turns protons into neutrons, between which there are no electrostatic repulsion forces. This neutronization of matter leads to the fact that the size of the star, which is now, in fact, one huge atomic nucleus, is measured in several kilometers, and the density is 100 million times greater than the density of water. Such an object is called a neutron star; its equilibrium is maintained by the pressure of the degenerate neutron matter.
Supermassive stars
After a star with a mass greater than five solar masses enters the red supergiant stage, its core begins to shrink under the influence of gravity. As compression increases, temperature and density increase, and new sequence thermonuclear reactions. In such reactions, increasingly heavier elements are synthesized: helium, carbon, oxygen, silicon and iron, which temporarily restrains the collapse of the core.
As a result, as increasingly heavier elements of the Periodic Table are formed, iron-56 is synthesized from silicon. At this stage, further exothermic thermonuclear fusion becomes impossible, since the iron-56 nucleus has a maximum mass defect and the formation of heavier nuclei with the release of energy is impossible. Therefore, when the iron core of a star reaches a certain size, the pressure in it is no longer able to withstand the weight of the overlying layers of the star, and immediate collapse of the core occurs with neutronization of its matter.
What happens next is not yet completely clear, but, in any case, the processes taking place in a matter of seconds lead to a supernova explosion of incredible power.
Strong jets of neutrinos and a rotating magnetic field push out most material accumulated by the star [ ] - so-called seating elements, including iron and lighter elements. The exploding matter is bombarded by neutrons escaping from the stellar core, capturing them and thereby creating a set of elements heavier than iron, including radioactive ones, up to uranium (and perhaps even californium). Thus, supernova explosions explain the presence in interstellar matter elements heavier than iron, but this is not the only possible way their formation, which, for example, is demonstrated by technetium stars.
blast wave And neutrino jets carry matter away from dying star [ ] V interstellar space. Subsequently, as it cools and moves through space, this supernova material can collide with other cosmic “salvage” and, possibly, participate in the formation of new stars, planets or satellites.
The processes occurring during the formation of a supernova are still being studied, and so far there is no clarity on this issue. Also questionable is what actually remains of the original star. However, two options are being considered: neutron stars and black holes.
Neutron stars
It is known that in some supernovae strong gravity in the depths of a supergiant, it forces electrons to be absorbed by the atomic nucleus, where they, merging with protons, form neutrons. This process is called neutronization. The electromagnetic forces separating nearby nuclei disappear. The star's core is now a dense ball of atomic nuclei and individual neutrons.
Such stars, known as neutron stars, are extremely small - no more than large city, and have an unimaginably high density. Their orbital period becomes extremely short as the size of the star decreases (due to the conservation of angular momentum). Some neutron stars rotate 600 times per second. For some of them, the angle between the radiation vector and the axis of rotation may be such that the Earth falls into the cone formed by this radiation; in this case, it is possible to detect a radiation pulse repeating at intervals equal to the star’s orbital period. Such neutron stars were called “pulsars”, and became the first neutron stars to be discovered.
Black holes
Not all stars, after going through the supernova explosion phase, become neutron stars. If the star has a sufficiently large mass, then the collapse of such a star will continue, and the neutrons themselves will begin to fall inward until its radius becomes less than the Schwarzschild radius. After this, the star becomes a black hole.
The existence of black holes was predicted by the general theory of relativity. According to this theory,
Thermonuclear fusion in the interior of stars
At this time, for stars with a mass greater than 0.8 solar masses, the core becomes transparent to radiation, and radiative energy transfer in the core prevails, while the shell at the top remains convective. No one knows for sure how stars of lower mass arrive on the main sequence, since the time these stars spend in the young category exceeds the age of the Universe. All our ideas about the evolution of these stars are based on numerical calculations.
As the star contracts, the pressure of the degenerate electron gas begins to increase, and at a certain radius of the star, this pressure stops the increase in the central temperature, and then begins to lower it. And for stars smaller than 0.08, this turns out to be fatal: the energy released during nuclear reactions will never be enough to cover the costs of radiation. Such sub-stars are called brown dwarfs, and their fate is constant compression until the pressure of the degenerate gas stops it, and then gradual cooling with the stop of all nuclear reactions.
Young intermediate mass stars
Young stars of intermediate mass (from 2 to 8 times the mass of the Sun) evolve qualitatively in exactly the same way as their smaller sisters, except that they do not have convective zones until the main sequence.
Objects of this type are associated with the so-called. Ae\Be Herbit stars with irregular variables of spectral type B-F5. They also have bipolar jet disks. The outflow velocity, luminosity and effective temperature are significantly higher than for τ Taurus, so they effectively heat and disperse the remnants of the protostellar cloud.
Young stars with a mass greater than 8 solar masses
In fact, these are already normal stars. While the mass of the hydrostatic core was accumulating, the star managed to jump through all the intermediate stages and heat up nuclear reactions to such an extent that they compensated for losses due to radiation. For these stars, the outflow of mass and luminosity is so great that it not only stops the collapse of the remaining outer regions, but pushes them back. Thus, the mass of the resulting star is noticeably less than the mass of the protostellar cloud. Most likely, this explains the absence in our galaxy of stars more than 100-200 times the mass of the Sun.
Mid-life cycle of a star
Among the formed stars there is a huge variety of colors and sizes. They range in spectral type from hot blue to cool red, and in mass - from 0.08 to more than 200 solar masses. The luminosity and color of a star depends on the temperature of its surface, which, in turn, is determined by its mass. All new stars “take their place” on the main sequence according to their chemical composition and mass. We are not talking about the physical movement of the star - only about its position on the indicated diagram, depending on the parameters of the star. That is, we are talking, in fact, only about changing the parameters of the star.
What happens next again depends on the mass of the star.
Later years and death of stars
Old stars with low mass
To date, it is not known for certain what happens to light stars after their hydrogen supply is depleted. Since the age of the universe is 13.7 billion years, which is not enough to deplete the supply of hydrogen fuel, modern theories are based on computer simulations of the processes occurring in such stars.
Some stars can only fuse helium in certain active regions, causing instability and strong solar winds. In this case, the formation of a planetary nebula does not occur, and the star only evaporates, becoming even smaller than a brown dwarf.
But a star with a mass less than 0.5 solar will never be able to synthesize helium even after reactions involving hydrogen cease in the core. Their stellar envelope is not massive enough to overcome the pressure generated by the core. These stars include red dwarfs (such as Proxima Centauri), which have been on the main sequence for hundreds of billions of years. After the cessation of thermonuclear reactions in their core, they, gradually cooling, will continue to weakly emit in the infrared and microwave ranges of the electromagnetic spectrum.
Medium sized stars
When a star of average size (from 0.4 to 3.4 solar masses) reaches the red giant phase, its outer layers continue to expand, the core contracts, and reactions begin to synthesize carbon from helium. Fusion releases a lot of energy, giving the star a temporary reprieve. For a star similar in size to the Sun, this process can take about a billion years.
Changes in the amount of energy emitted cause the star to go through periods of instability, including changes in size, surface temperature and energy output. Energy output shifts towards low frequency radiation. All this is accompanied by increasing mass loss due to strong solar winds and intense pulsations. Stars in this phase are called late type stars, OH -IR stars or Mira-like stars, depending on their exact characteristics. The ejected gas is relatively rich in heavy elements produced in the star's interior, such as oxygen and carbon. The gas forms an expanding shell and cools as it moves away from the star, allowing the formation of dust particles and molecules. Under strong infrared radiation central star In such shells, ideal conditions are formed for the activation of masers.
Helium combustion reactions are very temperature sensitive. Sometimes this leads to great instability. Violent pulsations occur, which eventually impart enough kinetic energy to the outer layers to be ejected and become a planetary nebula. In the center of the nebula, the core of the star remains, which, as it cools, turns into a helium white dwarf, usually having a mass of up to 0.5-0.6 solar and a diameter on the order of the diameter of the Earth.
White dwarfs
The vast majority of stars, including the Sun, end their evolution by contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases by a hundred times, and the density becomes a million times higher than the density of water, the star is called a white dwarf. It is deprived of energy sources and, gradually cooling down, becomes dark and invisible.
In stars more massive than the Sun, the pressure of degenerate electrons cannot contain the compression of the core, and it continues until most of the particles are converted into neutrons, packed so tightly that the size of the star is measured in kilometers and is 100 million times denser water. Such an object is called a neutron star; its equilibrium is maintained by the pressure of the degenerate neutron matter.
Supermassive stars
After the outer layers of a star with a mass greater than five solar masses have scattered to form a red supergiant, the core begins to compress due to gravitational forces. As compression increases, temperature and density increase, and a new sequence of thermonuclear reactions begins. In such reactions, heavy elements are synthesized, which temporarily restrains the collapse of the nucleus.
Ultimately, as heavier and heavier elements of the periodic table are formed, iron-56 is synthesized from silicon. Up until this point, the synthesis of elements released a large number of energy, however, it is the -56 iron nucleus that has the maximum mass defect and the formation of heavier nuclei is unfavorable. Therefore, when the iron core of a star reaches a certain value, the pressure in it is no longer able to withstand the colossal force of gravity, and immediate collapse of the core occurs with neutronization of its matter.
What happens next is not entirely clear. But whatever it is, it causes a supernova explosion of incredible power in a matter of seconds.
The accompanying burst of neutrinos provokes a shock wave. Strong jets of neutrinos and a rotating magnetic field push out much of the star's accumulated material - the so-called seed elements, including iron and lighter elements. The exploding matter is bombarded by neutrons emitted from the nucleus, capturing them and thereby creating a set of elements heavier than iron, including radioactive ones, up to uranium (and perhaps even californium). Thus, supernova explosions explain the presence of elements heavier than iron in interstellar matter.
The blast wave and jets of neutrinos carry material away from the dying star into interstellar space. Subsequently, moving through space, this supernova material may collide with other space debris, and possibly participate in the formation of new stars, planets or satellites.
The processes occurring during the formation of a supernova are still being studied, and so far there is no clarity on this issue. It is also questionable what actually remains of the original star. However, two options are being considered:
Neutron stars
It is known that in some supernovae, strong gravity in the depths of the supergiant causes electrons to fall into the atomic nucleus, where they fuse with protons to form neutrons. The electromagnetic forces separating nearby nuclei disappear. The star's core is now a dense ball of atomic nuclei and individual neutrons.
Such stars, known as neutron stars, are extremely small - no more than the size of a large city - and have an unimaginably high density. Their orbital period becomes extremely short as the size of the star decreases (due to conservation of angular momentum). Some make 600 revolutions per second. When the axis connecting north and south magnetic pole From this rapidly rotating star pointing towards the Earth, it is possible to detect a pulse of radiation repeating at intervals equal to the star’s orbital period. Such neutron stars were called “pulsars”, and became the first neutron stars to be discovered.
Black holes
Not all supernovae become neutron stars. If the star has a sufficiently large mass, then the collapse of the star will continue and the neutrons themselves will begin to fall inward until its radius becomes less than the Schwarzschild radius. After this, the star becomes a black hole.
The existence of black holes was predicted by the general theory of relativity. According to general relativity, matter and information cannot leave a black hole under any conditions. However, quantum mechanics makes exceptions to this rule possible.
There remains a number open questions. Chief among them: “Are there black holes at all?” After all, in order to say for sure that a given object is a black hole, it is necessary to observe its event horizon. All attempts to do this ended in failure. But there is still hope, since some objects cannot be explained without involving accretion, and accretion onto an object without a solid surface, but this does not prove the very existence of black holes.
Questions are also open: is it possible for a star to collapse directly into a black hole, bypassing a supernova? Are there supernovae that will later become black holes? What is the exact influence of a star's initial mass on the formation of objects at the end of its life cycle?
The Universe is a constantly changing macrocosm, where every object, substance or matter is in a state of transformation and change. These processes last for billions of years. Compared to duration human life this incomprehensible period of time is enormous. On a cosmic scale, these changes are quite fleeting. The stars that we now see in the night sky were the same thousands of years ago, when they could be seen egyptian pharaohs, however, in fact, all this time the change in the physical characteristics of the celestial bodies did not stop for a second. Stars are born, live and certainly age - the evolution of stars goes on as usual.
Position of constellation stars Big Dipper to different historical periods in the interval 100,000 years ago - our time and after 100 thousand years
Interpretation of the evolution of stars from the point of view of the average person
For the average person, space appears to be a world of calm and silence. The universe is actually gigantic physical laboratory, where grandiose transformations take place, during which the chemical composition changes, physical characteristics and the structure of stars. The life of a star lasts as long as it shines and gives off heat. However, such a brilliant state does not last forever. The bright birth is followed by a period of star maturity, which inevitably ends with the aging of the celestial body and its death.
Formation of a protostar from a gas and dust cloud 5-7 billion years ago
All our information about stars today fits within the framework of science. Thermodynamics gives us an explanation of the processes of hydrostatic and thermal equilibrium in which stellar matter resides. Nuclear and quantum physics provide insight into difficult process nuclear fusion, thanks to which the star exists, emitting heat and giving light to the surrounding space. At the birth of a star, hydrostatic and thermal equilibrium is formed, maintained by its own energy sources. At the end of a brilliant stellar career, this balance is disrupted. A series of irreversible processes begins, the result of which is the destruction of the star or collapse - a grandiose process of instant and brilliant death of the heavenly body.
A supernova explosion is a bright finale to the life of a star born in the early years of the Universe.
Changes in the physical characteristics of stars are due to their mass. The rate of evolution of objects is influenced by their chemical composition and, to some extent, by existing astrophysical parameters - rotation speed and state magnetic field. It is not possible to talk exactly about how everything actually happens due to the enormous duration of the processes described. The rate of evolution and the stages of transformation depend on the time of birth of the star and its location in the Universe at the time of birth.
The evolution of stars from a scientific point of view
Any star is born from a clump of cold interstellar gas, which, under the influence of external and internal gravitational forces, is compressed to the state of a gas ball. The process of compression of the gaseous substance does not stop for a moment, accompanied by a colossal release of thermal energy. The temperature of the new formation increases until thermonuclear fusion starts. From this moment, the compression of stellar matter stops, and a balance is reached between the hydrostatic and thermal states of the object. The Universe has been replenished with a new full-fledged star.
The main stellar fuel is the hydrogen atom as a result of a launched thermonuclear reaction.
In the evolution of stars, their sources of thermal energy are of fundamental importance. The radiant and thermal energy escaping into space from the surface of the star is replenished by cooling the inner layers of the celestial body. Constantly occurring thermonuclear reactions and gravitational compression in the bowels of the star make up for the loss. As long as there is sufficient nuclear fuel in the bowels of the star, the star glows bright light and radiates heat. As soon as the process of thermonuclear fusion slows down or stops completely, the mechanism of internal compression of the star is activated to maintain thermal and thermodynamic equilibrium. On at this stage the object is already emitting thermal energy, which is visible only in the infrared range.
Based on the processes described, we can conclude that the evolution of stars represents a consistent change in sources of stellar energy. In modern astrophysics, the processes of transformation of stars can be arranged in accordance with three scales:
- nuclear timeline;
- thermal period of a star's life;
- dynamic segment (final) of the life of a luminary.
In each individual case, the processes that determine the age of the star, its physical characteristics and the type of death of the object are considered. The nuclear timeline is interesting as long as the object is powered by its own heat sources and emits energy that is a product of nuclear reactions. The duration of this stage is estimated by determining the amount of hydrogen that will be converted into helium during thermonuclear fusion. How more mass stars, the greater the intensity of nuclear reactions and, accordingly, the higher the luminosity of the object.
Sizes and masses of various stars, ranging from a supergiant to a red dwarf
The thermal time scale defines the stage of evolution during which a star expends all its thermal energy. This process begins from the moment when the last reserves of hydrogen are used up and nuclear reactions stop. To maintain the object's balance, a compression process is started. Stellar matter falls towards the center. In this case, the kinetic energy is converted into thermal energy, which is spent on maintaining the necessary temperature balance inside the star. Some of the energy escapes into outer space.
Considering the fact that the luminosity of stars is determined by their mass, at the moment of compression of an object, its brightness in space does not change.
A star on its way to the main sequence
Star formation occurs according to a dynamic time scale. Stellar gas falls freely inward toward the center, increasing the density and pressure in the bowels of the future object. The higher the density at the center of the gas ball, the higher the temperature inside the object. From this moment on, heat becomes the main energy of the celestial body. How higher density and the higher the temperature, the greater the pressure in the bowels of the future star. The free fall of molecules and atoms stops, and the process of compression of stellar gas stops. This state of an object is usually called a protostar. The object consists of 90% molecular hydrogen. When the temperature reaches 1800K, hydrogen passes into the atomic state. During the decay process, energy is consumed, and the temperature increase slows down.
The Universe is 75% composed of molecular hydrogen, which during the formation of protostars turns into atomic hydrogen - the nuclear fuel of a star
In this state, the pressure inside the gas ball decreases, thereby giving freedom to the compression force. This sequence is repeated each time all the hydrogen is ionized first, and then the helium is ionized. At a temperature of 10⁵ K, the gas is completely ionized, the compression of the star stops, and hydrostatic equilibrium of the object arises. Further evolution stars will occur according to the thermal time scale, much more slowly and consistently.
The radius of the protostar has been decreasing from 100 AU since the beginning of formation. up to ¼ a.u. The object is in the middle of a gas cloud. As a result of the accretion of particles from the outer regions of the stellar gas cloud, the mass of the star will constantly increase. Consequently, the temperature inside the object will increase, accompanying the process of convection - the transfer of energy from the inner layers of the star to its outer edge. Subsequently, with increasing temperature in the interior of the celestial body, convection is replaced by radiative transfer, moving towards the surface of the star. At this moment, the luminosity of the object rapidly increases, and the temperature of the surface layers of the stellar ball also increases.
Convection processes and radiative transfer in a newly formed star before the onset of thermonuclear fusion reactions
For example, for stars with a mass identical to the mass of our Sun, the compression of the protostellar cloud occurs in just a few hundred years. As for the final stage of the formation of the object, the condensation of stellar matter has been stretching for millions of years. The Sun is moving towards the main sequence quite quickly, and this journey will take hundreds of millions or billions of years. In other words, the greater the mass of the star, the longer gap time spent on the formation of a full-fledged star. A star with a mass of 15M will move along the path to the main sequence for much longer - about 60 thousand years.
Main sequence phase
Although some fusion reactions are started at more low temperatures, the main phase of hydrogen combustion starts at a temperature of 4 million degrees. From this moment the main sequence phase begins. Comes into play new form reproduction of stellar energy - nuclear. Kinetic energy, released during the compression of the object, fades into the background. Achieved balance provides long and quiet life a star in the initial phase of the main sequence.
The fission and decay of hydrogen atoms during a thermonuclear reaction occurring in the interior of a star
From this moment on, observation of the life of a star is clearly tied to the main sequence phase, which is important part evolution of celestial bodies. It is at this stage that the only source of stellar energy is the result of hydrogen combustion. The object is in a state of equilibrium. As consumption nuclear fuel only the chemical composition of the object changes. The Sun's stay in the main sequence phase will last approximately 10 billion years. This is how long it will take for our native star to use up its entire supply of hydrogen. As for massive stars, their evolution occurs faster. By emitting more energy, a massive star remains in the main sequence phase for only 10-20 million years.
Less massive stars burn in the night sky much longer. Thus, a star with a mass of 0.25 M will remain in the main sequence phase for tens of billions of years.
Hertzsprung–Russell diagram assessing the relationship between the spectrum of stars and their luminosity. Points on the diagram - location famous stars. The arrows indicate the displacement of stars from the main sequence into the giant and white dwarf phases.
To imagine the evolution of stars, just look at the diagram characterizing the path of a celestial body in the main sequence. Top part The graphics look less object-saturated since this is where the massive stars are concentrated. This location is explained by their short life cycle. Of the stars known today, some have a mass of 70M. Objects whose mass exceeds upper limit- 100M, they may not form at all.
Heavenly bodies whose mass is less than 0.08 M do not have the opportunity to overcome critical mass, necessary for the start of thermonuclear fusion and remain cold all their lives. The smallest protostars collapse and form planet-like dwarfs.
Planet-like brown dwarf compared to normal star(our Sun) and the planet Jupiter
At the bottom of the sequence are concentrated objects dominated by stars with a mass equal to the mass of our Sun and slightly more. The imaginary boundary between the upper and lower parts of the main sequence are objects whose mass is – 1.5M.
Subsequent stages of stellar evolution
Each of the options for the development of the state of a star is determined by its mass and the length of time during which the transformation of stellar matter occurs. However, the Universe is a multifaceted and complex mechanism, so the evolution of stars can take other paths.
When traveling along the main sequence, a star with a mass approximately equal to the mass of the Sun has three main route options:
- live your life calmly and rest peacefully in the vast expanses of the Universe;
- enter the red giant phase and slowly age;
- become a white dwarf, explode as a supernova, and become a neutron star.
Possible options for the evolution of protostars depending on time, chemical composition objects and their masses
After the main sequence comes the giant phase. By this time, the reserves of hydrogen in the bowels of the star are completely exhausted, the central region of the object is a helium core, and thermonuclear reaction shift towards the surface of the object. Under the influence of thermonuclear fusion, the shell expands, but the mass of the helium core increases. An ordinary star turns into a red giant.
Giant phase and its features
In stars with low mass, the core density becomes colossal, turning stellar matter into a degenerate relativistic gas. If the mass of the star is slightly more than 0.26 M, an increase in pressure and temperature leads to the beginning of helium synthesis, covering the entire central region of the object. From this moment on, the temperature of the star increases rapidly. main feature The process is that the degenerate gas does not have the ability to expand. Under influence high temperature only the rate of helium fission increases, which is accompanied by an explosive reaction. At such moments we can observe a helium flash. The brightness of the object increases hundreds of times, but the agony of the star continues. The star transitions to a new state, where everything thermodynamic processes occur in the helium core and in the discharged outer shell.
Structure of a main sequence star solar type and a red giant with an isothermal helium core and a layered nucleosynthesis zone
This condition is temporary and not stable. Stellar matter is constantly mixed, and a significant part of it is ejected into the surrounding space, forming a planetary nebula. A hot core remains at the center, called a white dwarf.
For the stars large mass the listed processes are not so catastrophic. Helium combustion is replaced by the nuclear fission reaction of carbon and silicon. Eventually the star core will turn into star iron. The giant phase is determined by the mass of the star. The greater the mass of an object, the lower the temperature at its center. This is clearly not enough to trigger the nuclear fission reaction of carbon and other elements.
The fate of a white dwarf - a neutron star or a black hole
Once in the white dwarf state, the object is in an extremely unstable state. The stopped nuclear reactions lead to a drop in pressure, the core goes into a state of collapse. Energy released in in this case, is spent on the decay of iron into helium atoms, which further decays into protons and neutrons. The running process is developing at a rapid pace. The collapse of a star characterizes the dynamic segment of the scale and takes a fraction of a second in time. The combustion of nuclear fuel residues occurs explosively, releasing a colossal amount of energy in a split second. This is quite enough to blow up the upper layers of the object. The final stage of a white dwarf is a supernova explosion.
The star's core begins to collapse (left). The collapse forms a neutron star and creates a flow of energy into the outer layers of the star (center). Energy released when the outer layers of a star are shed during a supernova explosion (right).
The remaining superdense core will be a cluster of protons and electrons, which collide with each other to form neutrons. The Universe has been replenished with a new object - a neutron star. Because of high density the core becomes degenerate, the process of core collapse stops. If the star's mass were large enough, the collapse could continue until the remaining stellar matter finally fell into the center of the object, forming a black hole.
Explaining the final part of stellar evolution
For normal equilibrium stars, the described evolution processes are unlikely. However, the existence of white dwarfs and neutron stars proves the real existence of processes of compression of stellar matter. The small number of such objects in the Universe indicates the transience of their existence. The final stage of stellar evolution can be represented as a sequential chain of two types:
- normal star - red giant - shedding of outer layers - white dwarf;
- massive star – red supergiant – supernova explosion – neutron star or a black hole - non-existence.
Diagram of the evolution of stars. Options for the continuation of the life of stars outside the main sequence.
It is quite difficult to explain the ongoing processes from a scientific point of view. Nuclear scientists agree that in the case of the final stage of stellar evolution, we are dealing with fatigue of matter. As a result of prolonged mechanical, thermodynamic influence, matter changes its physical properties. The fatigue of stellar matter, exhausted by long nuclear reactions, one can explain the appearance of a degenerate electron gas, its subsequent neutronization and annihilation. If all of the above processes take place from beginning to end, stellar matter ceases to be a physical substance - the star disappears in space, leaving nothing behind.
Interstellar bubbles and gas and dust clouds, which are the birthplace of stars, cannot be replenished only by disappeared and exploded stars. The Universe and galaxies are in an equilibrium state. There is a constant loss of mass, the density of interstellar space decreases in one part of outer space. Consequently, in another part of the Universe, conditions are created for the formation of new stars. In other words, the scheme works: if a certain amount of matter was lost in one place, in another place in the Universe the same amount of matter appeared in a different form.
Finally
By studying the evolution of stars, we come to the conclusion that the Universe is a gigantic rarefied solution in which part of the matter is transformed into hydrogen molecules, which are the building material for stars. The other part dissolves in space, disappearing from the sphere of material sensations. A black hole in this sense is the place of transition of all material into antimatter. It is quite difficult to fully comprehend the meaning of what is happening, especially if, when studying the evolution of stars, we rely only on the laws of nuclear power, quantum physics and thermodynamics. To study this issue the theory of relative probability should be included, which allows for the curvature of space, allowing the transformation of one energy into another, one state into another.