What determines the end of a star's evolution? How stars die

Stars, like people, can be newborn, young, old. Every moment some stars die and others are formed. Usually the youngest of them are similar to the Sun. They are at the stage of formation and are actually protostars. Astronomers call them T-Taurus stars, after their prototype. In terms of their properties - for example, luminosity - protostars are variable, since their existence has not yet entered a stable phase. Around many of them there is a large number of matter. Powerful wind currents emanate from T-type stars.

Protostars: the beginning of their life cycle

If matter falls onto the surface of a protostar, it quickly burns and turns into heat. As a consequence, the temperature of protostars is constantly increasing. When it rises so high that stars are launched in the center nuclear reactions, the protostar acquires the status of an ordinary one. With the start of nuclear reactions, the star has a constant source of energy that supports its life for a long time. How long a star's life cycle in the Universe will be depends on its original size. However, it is believed that stars the diameter of the Sun have enough energy to exist comfortably for about 10 billion years. Despite this, it also happens that even more massive stars live only a few million years. This is due to the fact that they burn their fuel much faster.

Normal sized stars

Each of the stars is a clump of hot gas. In their depths, the process of generating nuclear energy constantly occurs. However, not all stars are like the Sun. One of the main differences is color. Stars are not only yellow, but also bluish and reddish.

Brightness and Luminosity

They also differ in characteristics such as shine and brightness. How bright a star observed from the Earth's surface will be depends not only on its luminosity, but also on its distance from our planet. Given their distance from Earth, stars can have completely different brightnesses. This indicator ranges from one ten-thousandth of the brilliance of the Sun to a brightness comparable to more than a million Suns.

Most stars are at the lower end of this spectrum, being dim. In many ways, the Sun is an average, typical star. However, compared to others, it has much greater brightness. A large number of dim stars can be observed even with the naked eye. The reason stars vary in brightness is due to their mass. Color, shine and change in brightness over time are determined by the amount of substance.

Attempts to explain the life cycle of stars

People have long tried to trace the life of stars, but the first attempts of scientists were rather timid. The first advance was the application of Lane's law to the Helmholtz-Kelvin hypothesis of gravitational contraction. This brought a new understanding to astronomy: theoretically, the temperature of a star should increase (its indicator is inversely proportional to the radius of the star) until an increase in density slows down the compression processes. Then the energy consumption will be higher than its income. At this moment, the star will begin to rapidly cool down.

Hypotheses about the life of stars

One of the original hypotheses about the life cycle of a star was proposed by astronomer Norman Lockyer. He believed that stars arise from meteoric matter. Moreover, the provisions of his hypothesis were based not only on theoretical conclusions available in astronomy, but also on data from spectral analysis of stars. Lockyer was convinced that chemical elements, which take part in the evolution of celestial bodies, consist of elementary particles- “protoelements”. Unlike modern neutrons, protons and electrons, they do not have a common, but individual character. For example, according to Lockyer, hydrogen decays into what is called “protohydrogen”; iron becomes “proto-iron”. Other astronomers also tried to describe the life cycle of a star, for example, James Hopwood, Yakov Zeldovich, Fred Hoyle.

Giant stars and dwarf stars

Stars large sizes are the hottest and brightest. They are usually white or bluish tint. Despite the fact that they are gigantic in size, the fuel inside them burns so quickly that they are deprived of it in just a few million years.

Small stars, as opposed to giant ones, are usually not so bright. They are red in color and live long enough - for billions of years. But among the bright stars in the sky there are also red and orange ones. An example is the star Aldebaran - the so-called “eye of the bull”, located in the constellation Taurus; and also in the constellation Scorpio. Why are these cool stars able to compete in brightness with hot stars like Sirius?

This is due to the fact that they once expanded very much, and their diameter began to exceed huge red stars (supergiants). The huge area allows these stars to emit an order of magnitude more energy than the Sun. This is despite the fact that their temperature is much lower. For example, the diameter of Betelgeuse, located in the constellation Orion, is several hundred times larger than the diameter of the Sun. And the diameter of ordinary red stars is usually not even a tenth the size of the Sun. Such stars are called dwarfs. Each celestial body can go through these types of star life cycles - the same star at different stages of its life can be both a red giant and a dwarf.

As a rule, luminaries like the Sun support their existence due to the hydrogen found inside. It turns into helium inside the star's nuclear core. The sun has a huge amount of fuel, but even it is not infinite - over the past five billion years, half of the supply has been used up.

Lifetime of stars. Life cycle of stars

Once the supply of hydrogen inside a star is depleted, major changes occur. The remaining hydrogen begins to burn not inside its core, but on the surface. At the same time, the lifespan of a star is increasingly shortened. During this period, the cycle of stars, at least most of them, enters the red giant stage. The size of the star becomes larger, and its temperature, on the contrary, decreases. This is how most red giants and supergiants appear. This process is part of the general sequence of changes occurring in stars, which scientists call stellar evolution. The life cycle of a star includes all its stages: ultimately, all stars age and die, and the duration of their existence is directly determined by the amount of fuel. Big stars end their lives with a huge, spectacular explosion. More modest ones, on the contrary, die, gradually shrinking to the size of white dwarfs. Then they just fade away.

How long does the average star live? The life cycle of a star can last from less than 1.5 million years to 1 billion years or more. All this, as has been said, depends on its composition and size. Stars like the Sun live between 10 and 16 billion years. Very bright stars, like Sirius, live relatively short-lived - only a few hundred million years. The star life cycle diagram includes the following stages. This molecular cloud is the gravitational collapse of the cloud - birth above nova- evolution of a protostar - the end of the protostellar phase. Then follow the stages: the beginning of the young star stage - mid-life - maturity - red giant stage - planetary nebula - white dwarf stage. The last two phases are characteristic of small stars.

The nature of planetary nebulae

So, we briefly looked at the life cycle of a star. But what is Transforming from a huge red giant to a white dwarf, sometimes stars shed their outer layers, and then the core of the star becomes exposed. The gas shell begins to glow under the influence of energy emitted by the star. This stage got its name due to the fact that luminous gas bubbles in this shell often look like disks around planets. But in reality they have nothing to do with planets. The life cycle of stars for children may not include all the scientific details. One can only describe the main phases of the evolution of celestial bodies.

Star clusters

Astronomers love to explore. There is a hypothesis that all luminaries are born in groups, and not individually. Since stars belonging to the same cluster have similar properties, the differences between them are true and not due to the distance to the Earth. Whatever changes occur to these stars, they originate at the same time and at equal conditions. Especially a lot of knowledge can be obtained by studying the dependence of their properties on mass. After all, the age of the stars in the clusters and their distance from the Earth are approximately equal, so they differ only in this indicator. Clusters will be of interest not only to professional astronomers - every amateur will be happy to make beautiful photo, admire them exclusively beautiful view in the planetarium.

Although stars seem eternal on the human time scale, they, like everything in nature, are born, live and die. According to the generally accepted gas-dust cloud hypothesis, a star is born as a result of gravitational compression of an interstellar gas-dust cloud. As such a cloud thickens, it first forms protostar, the temperature at its center steadily increases until it reaches the limit necessary for the speed of thermal motion of particles to exceed the threshold after which protons are able to overcome the macroscopic forces of mutual electrostatic repulsion ( cm. Coulomb's Law) and enter into a thermonuclear fusion reaction ( cm. Nuclear decay and fusion).

As a result of a multi-stage thermonuclear fusion reaction, four protons ultimately form a helium nucleus (2 protons + 2 neutrons) and a whole fountain of various elementary particles is released. In the final state, the total mass of the formed particles is less the masses of the four initial protons, which means that free energy is released during the reaction ( cm. Theory of relativity). Because of this, the internal core of the newborn star quickly heats up to ultra-high temperatures, and its excess energy begins to splash towards its less hot surface - and out. At the same time, the pressure in the center of the star begins to increase ( cm. Equation of state of an ideal gas). Thus, by “burning” hydrogen in the process of a thermonuclear reaction, the star does not allow the forces of gravitational attraction to compress itself to a super-dense state, countering the gravitational collapse with continuously renewed internal thermal pressure, resulting in a stable energy equilibrium. Stars actively burning hydrogen are said to be in the "primary phase" of their life cycle or evolution ( cm. Hertzsprung-Russell diagram). The transformation of one chemical element into another inside a star is called nuclear fusion or nucleosynthesis.

In particular, the Sun has been at the active stage of burning hydrogen in the process of active nucleosynthesis for about 5 billion years, and the reserves of hydrogen in the core for its continuation should be enough for our luminary for another 5.5 billion years. The more massive the star, the greater the supply of hydrogen fuel it has, but to counteract the forces of gravitational collapse it must burn hydrogen at an intensity that exceeds the growth rate of hydrogen reserves as the mass of the star increases. Thus, the more massive the star, the shorter its lifetime, determined by the depletion of hydrogen reserves, and the largest stars literally burn out in “some” tens of millions of years. The smallest stars, on the other hand, live comfortably for hundreds of billions of years. So, on this scale, our Sun belongs to the “strong middle class”.

Sooner or later, however, any star will use up all the hydrogen suitable for combustion in its thermonuclear furnace. What's next? It also depends on the mass of the star. The sun (and all stars not exceeding its mass by more than eight times) end my life in a very banal way. As the reserves of hydrogen in the bowels of the star are depleted, the forces of gravitational compression, which have been patiently waiting for this hour since the very moment of the birth of the star, begin to gain the upper hand - and under their influence the star begins to shrink and become denser. This process has a twofold effect: The temperature in the layers immediately around the star's core rises to a level at which the hydrogen contained there finally undergoes thermonuclear fusion to form helium. At the same time, the temperature in the core itself, now consisting almost entirely of helium, rises so much that the helium itself - a kind of “ash” of the fading primary nucleosynthesis reaction - enters into a new thermonuclear fusion reaction: from three helium nuclei one carbon nucleus is formed. This process of secondary thermonuclear fusion reaction, fueled by the products of the primary reaction, is one of the key moments in the life cycle of stars.

During the secondary combustion of helium in the core of the star, so much energy is released that the star literally begins to inflate. In particular, the shell of the Sun at this stage of life will expand beyond the orbit of Venus. In this case, the total energy of the star's radiation remains approximately at the same level as during the main phase of its life, but since this energy is now emitted through a much larger surface area, the outer layer of the star cools down to the red part of the spectrum. The star turns into red giant.

For solar-class stars, after the fuel feeding the secondary nucleosynthesis reaction has been depleted, the stage of gravitational collapse begins again—this time final. The temperature inside the core is no longer able to rise to the level necessary to initiate the next level of thermonuclear reaction. Therefore, the star contracts until the forces of gravitational attraction are balanced by the next force barrier. His role is played by degenerate electron gas pressure(cm. Chandrasekhar limit). Electrons, which until this stage played the role of unemployed extras in the evolution of the star, not participating in nuclear fusion reactions and freely moving between nuclei in the process of fusion, at a certain stage of compression find themselves deprived of “living space” and begin to “resist” further gravitational compression of the star. The state of the star stabilizes, and it turns into a degenerate white dwarf, which will radiate residual heat into space until it cools completely.

Stars more massive than the Sun face a much more spectacular end. After the combustion of helium, their mass during compression turns out to be sufficient to heat the core and shell to the temperatures necessary to launch the next nucleosynthesis reactions - carbon, then silicon, magnesium - and so on, as the nuclear masses grow. Moreover, with the start of each new reaction in the core of the star, the previous one continues in its shell. In fact, all the chemical elements, including iron, that make up the Universe, were formed precisely as a result of nucleosynthesis in the depths of dying stars of this type. But iron is the limit; it cannot serve as fuel for nuclear fusion or decay reactions at any temperature or pressure, since both its decay and the addition of additional nucleons to it require an influx of external energy. As a result, a massive star gradually accumulates an iron core inside itself, which cannot serve as fuel for any further nuclear reactions.

Once the temperature and pressure inside the nucleus reach a certain level, electrons begin to interact with the protons of the iron nuclei, resulting in the formation of neutrons. And in a very short period of time - some theorists believe that this takes a matter of seconds - the electrons free throughout the previous evolution of the star literally dissolve in the protons of the iron nuclei, the entire substance of the star’s core turns into a solid bunch of neutrons and begins to rapidly compress in gravitational collapse , since the counteracting pressure of the degenerate electron gas drops to zero. The outer shell of the star, from under which all support is knocked out, collapses towards the center. The energy of the collision of the collapsed outer shell with the neutron core is so high that it rebounds with enormous speed and scatters in all directions from the core - and the star literally explodes in a blinding flash supernova stars. In a matter of seconds, a supernova explosion can release more energy into space than all the stars in the galaxy put together during the same time.

After a supernova explosion and the expansion of the shell of stars with a mass of about 10-30 solar masses, the ongoing gravitational collapse leads to the formation of a neutron star, the matter of which is compressed until it begins to make itself felt pressure of degenerate neutrons - in other words, now neutrons (just as electrons did earlier) begin to resist further compression, requiring to myself living space. This usually occurs when the star reaches a size of about 15 km in diameter. The result is a rapidly rotating neutron star, emitting electromagnetic pulses at the frequency of its rotation; such stars are called pulsars. Finally, if the star's core mass exceeds 30 solar masses, nothing can stop its further gravitational collapse, and a supernova explosion results in

It is quite natural that stars are not living beings, but they also go through evolutionary stages similar to birth, life and death. Like a person, a star undergoes radical changes throughout its life. But it should be noted that they clearly live longer - millions and even billions of earthly years.

How are stars born? Initially, or rather after Big Bang, matter in the Universe was unevenly distributed. Stars began to form in nebulae—giant clouds of interstellar dust and gases, mostly hydrogen. This matter is affected by gravity, and part of the nebula is compressed. Then round and dense gas and dust clouds are formed - Bok globules. As such a globule continues to condense, its mass increases due to the attraction of matter from the nebula. In the inner part of the globule, the gravitational force is strongest, and it begins to heat up and rotate. This is already a protostar. The hydrogen atoms begin to bombard each other and thereby generate a large amount of energy. Eventually the temperature of the central part reaches a temperature of about fifteen million degrees Celsius, and the core of a new star is formed. The newborn flares up, begins to burn and glow. How long this will continue depends on the mass of the new star. What I told you at our last meeting. The greater the mass, the shorter the life of the star.
By the way, it depends on the mass whether a protostar can become a star. According to calculations, in order for this contracting celestial body to turn into a star, its mass must be at least 8% of the mass of the Sun. A smaller globule, condensing, will gradually cool and turn into a transitional object, something between a star and a planet. Such objects are called brown dwarfs.

The planet Jupiter, for example, is too small to become a star. If Jupiter were more massive, perhaps thermonuclear reactions would begin in its depths, and our solar system would be a double star system. But this is all lyrics...

So, the main stage of a star’s life. For most of its existence, the star is in an equilibrium state. The force of gravity tends to compress the star, and the energy released as a result of thermonuclear reactions occurring in the star forces the star to expand. These two forces create a stable equilibrium position - so stable that the star lives like this for millions and billions of years. This phase of a star's life ensures its place in the main sequence. -

After shining for millions of years, a large star, that is, a star at least six times heavier than the Sun, begins to burn out. When the core runs out of hydrogen, the star expands and cools, becoming a red supergiant. This supergiant will then shrink until it finally explodes in a monstrous and dramatic, brilliant explosion called a supernova. It should be noted here that very massive blue supergiants bypass the stage of transformation into a red supergiant and explode into a supernova much faster.
If the remaining core of the supernova is small, then its catastrophic compression (gravitational collapse) begins into a very dense neutron star, and if it is large enough, it will compress even more, forming a black hole.

The demise of an ordinary star is somewhat different. Such a star lives longer and dies a more peaceful death. The sun, for example, will burn for another five billion years before its core runs out of hydrogen. Its outer layers will then begin to expand and cool; a red giant is formed. In this form, a star can exist for about 100 million years on helium formed during its life in its core. But helium also burns out. To top it all off, the outer layers will be carried away - they will form a planetary nebula, and a dense white dwarf will shrink from the core. Although the white dwarf is quite hot, it will eventually cool, becoming a dead star called a black dwarf.

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. In fact, the Universe is a giant physical laboratory where enormous transformations occur, 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 allow us to understand the complex process of nuclear fusion that allows a star to exist, 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 a brilliant sunset 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 with bright light and emits 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. 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. The greater the mass of the star, 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 in the center of the gas ball, the higher temperature inside the object. From this moment on, heat becomes the main energy of the celestial body. The greater the density and the higher the temperature, the greater the pressure in the depths 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 is 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. The further evolution of the star will occur in accordance with the thermal time scale, much slower and more consistent.

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 the period of time spent on the formation of a full-fledged star. A star with a mass of 15 M 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. The kinetic energy released during the compression of an object fades into the background. Achieved balance ensures a long and quiet life for a star that finds itself 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 phase of the main sequence, which is an important part of the 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 nuclear fuel is consumed, 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 for 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 duration life cycle. Of the stars known today, some have a mass of 70M. Objects whose mass exceeds the upper limit of 100M may not form at all.

Heavenly bodies whose mass is less than 0.08 M do not have the opportunity to overcome the critical mass required for the onset of thermonuclear fusion and remain cold throughout their lives. The smallest protostars collapse and form planet-like dwarfs.

A planet-like brown dwarf compared to a 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:

1. live your life calmly and rest peacefully in the vast expanses of the Universe;
2. enter the red giant phase and slowly age;
3. become a white dwarf, explode as a supernova, and become a neutron star.

Possible options for the evolution of protostars depending on time, the chemical composition of objects and their mass

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 reactions shift to 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 the influence of 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 all thermodynamic processes occur in the helium core and in the discharged outer shell.

The structure of a solar-type main sequence star 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 stars with large masses, the processes listed above are not so catastrophic. Helium combustion is replaced by the nuclear fission reaction of carbon and silicon. In the end stellar 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. 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. Due to the high density, the core becomes degenerate, and 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 real existence 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 black hole – nothingness.

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, depleted by long-term nuclear reactions, can explain the appearance of 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. Mass loss occurs constantly, the density of interstellar space decreases in one part 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 molecules of hydrogen, which is building material for the 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, you rely only on the laws of nuclear, quantum physics and thermodynamics. The theory of relative probability should be included in the study of this issue, which allows for the curvature of space, allowing the transformation of one energy into another, one state into another.

Like any bodies in nature, stars also cannot remain unchanged. They are born, develop and finally “die”. The evolution of stars takes billions of years, but there is debate about the time of their formation. Previously, astronomers believed that the process of their “birth” from stardust took millions of years, but not so long ago photographs of the sky region from the Great Orion Nebula were obtained. Over the course of several years, a small

Photographs from 1947 showed a small group of star-like objects in this location. By 1954, some of them had already become oblong, and five years later these objects broke up into separate ones. Thus, for the first time, the process of star birth took place literally before the eyes of astronomers.

Let's look in detail at the structure and evolution of stars, where their endless, by human standards, life begins and ends.

Traditionally, scientists assume that stars are formed as a result of the condensation of clouds of gas and dust. Under the influence of gravitational forces, an opaque gas ball, dense in structure, is formed from the resulting clouds. Its internal pressure cannot balance the gravitational forces compressing it. Gradually, the ball contracts so much that the temperature of the stellar interior rises, and the pressure of the hot gas inside the ball balances the external forces. After this, the compression stops. The duration of this process depends on the mass of the star and usually ranges from two to several hundred million years.

The structure of stars suggests very high temperature in their depths, which contributes to continuous thermonuclear processes (the hydrogen that forms them turns into helium). It is these processes that cause intense radiation from stars. The time during which they consume the available supply of hydrogen is determined by their mass. The duration of radiation also depends on this.

When hydrogen reserves are depleted, the evolution of stars approaches the formation stage. This happens as follows. After the release of energy ceases, gravitational forces begin to compress the core. At the same time, the star increases significantly in size. The luminosity also increases as the process continues, but only in a thin layer at the core boundary.

This process is accompanied by an increase in the temperature of the contracting helium core and the transformation of helium nuclei into carbon nuclei.

It is predicted that our Sun could become a red giant in eight billion years. Its radius will increase several tens of times, and its luminosity will increase hundreds of times compared to current levels.

The lifespan of a star, as already noted, depends on its mass. Objects with a mass that is less than the Sun “use up” their reserves very economically, so they can shine for tens of billions of years.

The evolution of stars ends with the formation. This happens to those of them whose mass is close to the mass of the Sun, i.e. does not exceed 1.2 of it.

Giant stars tend to quickly deplete their supply of nuclear fuel. This is accompanied by a significant loss of mass, in particular due to the shedding of outer shells. As a result, only a gradually cooling central part remains, in which nuclear reactions have completely stopped. Over time, such stars stop emitting and become invisible.

But sometimes normal evolution and the structure of stars is disrupted. Most often this concerns massive objects that have exhausted all types of thermonuclear fuel. Then they can be converted into neutrons, or And the more scientists learn about these objects, the more new questions arise.