The birth and evolution of stars: the giant factory of the Universe. The evolution of stars from the point of view of exact science and the theory of relativity

Each of us has looked at the starry sky at least once in our lives. Someone looked at this beauty, experiencing romantic feelings, another tried to understand where all this beauty comes from. Life in space, unlike life on our planet, flows at a different speed. Time in outer space lives in its own categories; distances and sizes in the Universe are colossal. We rarely think about the fact that the evolution of galaxies and stars is constantly happening before our eyes. Every object in the vast space is the result of certain physical processes. Galaxies, stars and even planets have main phases of development.

Our planet and we all depend on our star. How long will the Sun delight us with its warmth, breathing life into the Solar System? What awaits us in the future after millions and billions of years? In this regard, it is interesting to learn more about the stages of evolution of astronomical objects, where stars come from and how the life of these wonderful luminaries in the night sky ends.

Origin, birth and evolution of stars

The evolution of the stars and planets that inhabit our Milky Way galaxy and the entire Universe has, for the most part, been well studied. In space, the laws of physics are unshakable and help to understand the origin of space objects. In this case, it is customary to rely on the Big Bang theory, which is now the dominant doctrine about the process of the origin of the Universe. The event that shook the universe and led to the formation of the universe is, by cosmic standards, lightning fast. For the cosmos, moments pass from the birth of a star to its death. Vast distances create the illusion of the constancy of the Universe. A star that flares up in the distance shines on us for billions of years, at which time it may no longer exist.

The theory of evolution of the galaxy and stars is a development of the Big Bang theory. The doctrine of the birth of stars and the emergence of stellar systems is distinguished by the scale of what is happening and the time frame, which, unlike the Universe as a whole, can be observed by modern means of science.

When studying the life cycle of stars, you can use the example of the closest star to us. The Sun is one of hundreds of trillions of stars in our field of vision. In addition, the distance from the Earth to the Sun (150 million km) provides a unique opportunity to study the object without leaving the solar system. The information obtained will make it possible to understand in detail how other stars are structured, how quickly these gigantic heat sources are depleted, what are the stages of development of a star, and what will be the ending of this brilliant life - quiet and dim or sparkling, explosive.

After the Big Bang, tiny particles formed interstellar clouds, which became the “maternity hospital” for trillions of stars. It is characteristic that all stars were born at the same time as a result of compression and expansion. Compression in the clouds of cosmic gas occurred under the influence of its own gravity and similar processes in new stars in the neighborhood. The expansion arose as a result of the internal pressure of interstellar gas and under the influence of magnetic fields within the gas cloud. At the same time, the cloud rotated freely around its center of mass.

The gas clouds formed after the explosion consist of 98% atomic and molecular hydrogen and helium. Only 2% of this massif consists of dust and solid microscopic particles. Previously it was believed that at the center of any star lies a core of iron, heated to a temperature of a million degrees. It was this aspect that explained the gigantic mass of the star.

In the opposition of physical forces, compression forces prevailed, since the light resulting from the release of energy does not penetrate into the gas cloud. The light, along with part of the released energy, spreads outward, creating a subzero temperature and a low-pressure zone inside the dense accumulation of gas. Being in this state, the cosmic gas rapidly contracts, the influence of gravitational attraction forces leads to the fact that particles begin to form stellar matter. When a collection of gas is dense, the intense compression causes a star cluster to form. When the size of the gas cloud is small, compression leads to the formation of a single star.

A brief description of what is happening is that the future star goes through two stages - fast and slow compression to the state of a protostar. In simple and understandable language, rapid compression is the fall of stellar matter towards the center of the protostar. Slow compression occurs against the background of the formed center of the protostar. Over the next hundreds of thousands of years, the new formation shrinks in size, and its density increases millions of times. Gradually, the protostar becomes opaque due to the high density of stellar matter, and the ongoing compression triggers the mechanism of internal reactions. An increase in internal pressure and temperature leads to the formation of the future star’s own center of gravity.

The protostar remains in this state for millions of years, slowly giving off heat and gradually shrinking, decreasing in size. As a result, the contours of the new star emerge, and the density of its matter becomes comparable to the density of water.

On average, the density of our star is 1.4 kg/cm3 - almost the same as the density of water in the salty Dead Sea. At the center, the Sun has a density of 100 kg/cm3. Stellar matter is not in a liquid state, but exists in the form of plasma.

Under the influence of enormous pressure and temperature of approximately 100 million K, thermonuclear reactions of the hydrogen cycle begin. The compression stops, the mass of the object increases when the gravitational energy transforms into thermonuclear combustion of hydrogen. From this moment on, the new star, emitting energy, begins to lose mass.

The above-described version of star formation is just a primitive diagram that describes the initial stage of the evolution and birth of a star. Today, such processes in our galaxy and throughout the Universe are practically invisible due to the intense depletion of stellar material. In the entire conscious history of observations of our Galaxy, only isolated appearances of new stars have been noted. On the scale of the Universe, this figure can be increased hundreds and thousands of times.

For most of their lives, protostars are hidden from the human eye by a dusty shell. The radiation from the core can only be observed in the infrared, which is the only way to see the birth of a star. For example, in the Orion Nebula in 1967, astrophysicists discovered a new star in the infrared range, the radiation temperature of which was 700 degrees Kelvin. Subsequently, it turned out that the birthplace of protostars are compact sources that exist not only in our galaxy, but also in other distant corners of the Universe. In addition to infrared radiation, the birthplaces of new stars are marked by intense radio signals.

The process of studying and the evolution of stars

The entire process of knowing the stars can be divided into several stages. At the very beginning, you should determine the distance to the star. Information about how far the star is from us and how long the light has been coming from it gives an idea of ​​what happened to the star throughout this time. After man learned to measure the distance to distant stars, it became clear that stars are the same suns, only of different sizes and with different fates. Knowing the distance to the star, the level of light and the amount of energy emitted can be used to trace the process of thermonuclear fusion of the star.

After determining the distance to the star, you can use spectral analysis to calculate the chemical composition of the star and find out its structure and age. Thanks to the advent of the spectrograph, scientists have the opportunity to study the nature of starlight. This device can determine and measure the gas composition of stellar matter that a star possesses at different stages of its existence.

By studying the spectral analysis of the energy of the Sun and other stars, scientists came to the conclusion that the evolution of stars and planets has common roots. All cosmic bodies have the same type, similar chemical composition and originated from the same matter, which arose as a result of the Big Bang.

Stellar matter consists of the same chemical elements (even iron) as our planet. The only difference is in the amount of certain elements and in the processes occurring on the Sun and inside the earth's solid surface. This is what distinguishes stars from other objects in the Universe. The origin of stars should also be considered in the context of another physical discipline: quantum mechanics. According to this theory, the matter that determines stellar matter consists of constantly dividing atoms and elementary particles that create their own microcosm. In this light, the structure, composition, structure and evolution of stars is of interest. As it turned out, the bulk of the mass of our star and many other stars consists of only two elements - hydrogen and helium. A theoretical model describing the structure of stars will allow us to understand their structure and the main difference from other space objects.

The main feature is that many objects in the Universe have a certain size and shape, while a star can change size as it develops. A hot gas is a combination of atoms loosely bound to each other. Millions of years after the formation of a star, the surface layer of stellar matter begins to cool. The star gives off most of its energy into outer space, decreasing or increasing in size. Heat and energy are transferred from the interior of the star to the surface, affecting the intensity of radiation. In other words, the same star looks different at different periods of its existence. Thermonuclear processes based on reactions of the hydrogen cycle contribute to the transformation of light hydrogen atoms into heavier elements - helium and carbon. According to astrophysicists and nuclear scientists, such a thermonuclear reaction is the most efficient in terms of the amount of heat generated.

Why doesn’t thermonuclear fusion of the nucleus end with the explosion of such a reactor? The thing is that the forces of the gravitational field in it can hold stellar matter within a stabilized volume. From this we can draw an unambiguous conclusion: any star is a massive body that maintains its size due to the balance between the forces of gravity and the energy of thermonuclear reactions. The result of this ideal natural model is a heat source that can operate for a long time. It is assumed that the first forms of life on Earth appeared 3 billion years ago. The sun in those distant times warmed our planet just as it does now. Consequently, our star has changed little, despite the fact that the scale of emitted heat and solar energy is colossal - more than 3-4 million tons every second.

It is not difficult to calculate how much weight our star has lost over the years of its existence. This will be a huge figure, but due to its enormous mass and high density, such losses on the scale of the Universe look insignificant.

Stages of star evolution

The fate of the star depends on the initial mass of the star and its chemical composition. While the main reserves of hydrogen are concentrated in the core, the star remains in the so-called main sequence. As soon as there is a tendency for the size of the star to increase, it means that the main source for thermonuclear fusion has dried up. The long final path of transformation of the celestial body has begun.

The luminaries formed in the Universe are initially divided into three most common types:

• normal stars (yellow dwarfs);
• dwarf stars;
• giant stars.

Low-mass stars (dwarfs) slowly burn up their hydrogen reserves and live their lives quite calmly.

Such stars are the majority in the Universe, and our star, a yellow dwarf, is one of them. With the onset of old age, a yellow dwarf becomes a red giant or supergiant.

Based on the theory of the origin of stars, the process of star formation in the Universe has not ended. The brightest stars in our galaxy are not only the largest, compared to the Sun, but also the youngest. Astrophysicists and astronomers call such stars blue supergiants. In the end, they will suffer the same fate as trillions of other stars. First there is a rapid birth, a brilliant and ardent life, after which comes a period of slow decay. Stars the size of the Sun have a long life cycle, being in the main sequence (in its middle part).

Using data on the mass of a star, we can assume its evolutionary path of development. A clear illustration of this theory is the evolution of our star. Nothing lasts forever. As a result of thermonuclear fusion, hydrogen is converted into helium, therefore, its original reserves are consumed and reduced. Someday, not very soon, these reserves will run out. Judging by the fact that our Sun continues to shine for more than 5 billion years, without changing in its size, the mature age of the star can still last about the same period.

The depletion of hydrogen reserves will lead to the fact that, under the influence of gravity, the core of the sun will begin to rapidly shrink. The density of the core will become very high, as a result of which thermonuclear processes will move to the layers adjacent to the core. This state is called collapse, which can be caused by thermonuclear reactions in the upper layers of the star. As a result of high pressure, thermonuclear reactions involving helium are triggered.

The reserves of hydrogen and helium in this part of the star will last for millions of years. It will not be long before the depletion of hydrogen reserves will lead to an increase in the intensity of radiation, to an increase in the size of the shell and the size of the star itself. As a result, our Sun will become very large. If you imagine this picture tens of billions of years from now, then instead of a dazzling bright disk, a hot red disk of gigantic proportions will hang in the sky. Red giants are a natural phase in the evolution of a star, its transition state into the category of variable stars.

As a result of this transformation, the distance from the Earth to the Sun will decrease, so that the Earth will fall into the zone of influence of the solar corona and begin to “fry” in it. The temperature on the surface of the planet will increase tenfold, which will lead to the disappearance of the atmosphere and the evaporation of water. As a result, the planet will turn into a lifeless rocky desert.

The final stages of stellar evolution

Having reached the red giant phase, a normal star becomes a white dwarf under the influence of gravitational processes. If the mass of a star is approximately equal to the mass of our Sun, all the main processes in it will occur calmly, without impulses or explosive reactions. The white dwarf will die for a long time, burning out to the ground.

In cases where the star initially had a mass greater than 1.4 times the Sun, the white dwarf will not be the final stage. With a large mass inside the star, processes of compaction of stellar matter begin at the atomic and molecular level. Protons turn into neutrons, the density of the star increases, and its size rapidly decreases.

Neutron stars known to science have a diameter of 10-15 km. With such a small size, a neutron star has a colossal mass. One cubic centimeter of stellar matter can weigh billions of tons.

In the event that we were initially dealing with a high-mass star, the final stage of evolution takes other forms. The fate of a massive star is a black hole - an object with an unexplored nature and unpredictable behavior. The huge mass of the star contributes to an increase in gravitational forces, driving compression forces. It is not possible to pause this process. The density of matter increases until it becomes infinite, forming a singular space (Einstein's theory of relativity). The radius of such a star will eventually become zero, becoming a black hole in outer space. There would be significantly more black holes if massive and supermassive stars occupied most of the space.

It should be noted that when a red giant transforms into a neutron star or a black hole, the Universe can experience a unique phenomenon - the birth of a new cosmic object.

The birth of a supernova is the most spectacular final stage in the evolution of stars. A natural law of nature operates here: the cessation of the existence of one body gives rise to a new life. The period of such a cycle as the birth of a supernova mainly concerns massive stars. The exhausted reserves of hydrogen lead to the inclusion of helium and carbon in the process of thermonuclear fusion. As a result of this reaction, the pressure increases again, and an iron core is formed in the center of the star. Under the influence of strong gravitational forces, the center of mass shifts to the central part of the star. The core becomes so heavy that it is unable to resist its own gravity. As a result, rapid expansion of the core begins, leading to an instant explosion. The birth of a supernova is an explosion, a shock wave of monstrous force, a bright flash in the vast expanses of the Universe.

It should be noted that our Sun is not a massive star, so a similar fate does not threaten it, and our planet should not be afraid of such an ending. In most cases, supernova explosions occur in distant galaxies, which is why they are rarely detected.

Finally

The evolution of stars is a process that extends over tens of billions of years. Our idea of ​​the processes taking place is just a mathematical and physical model, a theory. Earthly time is only a moment in the huge time cycle in which our Universe lives. We can only observe what happened billions of years ago and imagine what subsequent generations of earthlings may face.

If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them

The evolution of stars is a change in physicality. characteristics, internal structures and chemistry composition of stars over time. The most important tasks of the theory of E.Z. - explanation of the formation of stars, changes in their observable characteristics, study of the genetic connection of various groups of stars, analysis of their final states.

Since in the part of the Universe known to us, approx. 98-99% of the mass of the observed matter is contained in stars or has passed the stage of stars, explanation by E.Z. yavl. one of the most important problems in astrophysics.

A star in a stationary state is a gas ball, which is in a hydrostatic state. and thermal equilibrium (i.e., the action of gravitational forces is balanced by internal pressure, and energy losses due to radiation are compensated by the energy released in the bowels of the star, see). The “birth” of a star is the formation of a hydrostatically equilibrium object, the radiation of which is supported by its own. energy sources. The “death” of a star is an irreversible imbalance leading to the destruction of the star or its catastrophe. compression.

Isolation of gravitational energy can play a decisive role only when the temperature of the star’s interior is insufficient for nuclear energy release to compensate for energy losses, and the star as a whole or part of it must contract to maintain equilibrium. The release of thermal energy becomes important only after nuclear energy reserves have been exhausted. T.o., E.z. can be represented as a consistent change in the energy sources of stars.

Characteristic time E.z. too large for all evolution to be traced directly. Therefore the main E.Z. research method yavl. construction of sequences of star models describing changes in internal structures and chemistry composition of stars over time. Evolution. The sequences are then compared with observational results, for example, with (G.-R.D.), which summarizes observations of a large number of stars at different stages of evolution. A particularly important role is played by comparison with G.-R.d. for star clusters, since all stars in a cluster have the same initial chemical. composition and formed almost simultaneously. According to G.-R.d. clusters of different ages, it was possible to establish the direction of the E.Z. Evolution in detail. sequences are calculated by numerically solving a system of differential equations describing the distribution of mass, density, temperature and luminosity over a star, to which are added the laws of energy release and opacity of stellar matter and equations describing changes in chemical properties. star composition over time.

The course of a star's evolution depends mainly on its mass and initial chemistry. composition. The rotation of the star and its magnetic field can play a certain, but not fundamental, role. field, however, the role of these factors in E.Z. has not yet been sufficiently researched. Chem. The composition of a star depends on the time at which it was formed and on its position in the Galaxy at the time of formation. Stars of the first generation were formed from matter, the composition of which was determined by cosmology. conditions. Apparently, it contained approximately 70% by mass hydrogen, 30% helium and an insignificant admixture of deuterium and lithium. During the evolution of first-generation stars, heavy elements (following helium) were formed, which were ejected into interstellar space as a result of the outflow of matter from stars or during stellar explosions. Stars of subsequent generations were formed from matter containing up to 3-4% (by mass) of heavy elements.

The most direct indication that star formation in the Galaxy is still ongoing is the phenomenon. existence of massive bright stars spectrum. classes O and B, the lifetime of which cannot exceed ~ 10 7 years. The rate of star formation in modern times. era is estimated at 5 per year.

2. Star formation, stage of gravitational compression

According to the most common point of view, stars are formed as a result of gravitational forces. condensation of matter in the interstellar medium. The necessary division of the interstellar medium into two phases - dense cold clouds and a rarefied medium with a higher temperature - can occur under the influence of Rayleigh-Taylor thermal instability in the interstellar magnetic field. field. Gas-dust complexes with mass , characteristic size (10-100) pc and particle concentration n~10 2 cm -3 . are actually observed due to their emission of radio waves. Compression (collapse) of such clouds requires certain conditions: gravity. particles of the cloud must exceed the sum of the energy of thermal motion of the particles, the rotational energy of the cloud as a whole and the magnetic field. cloud energy (Jeans criterion). If only the energy of thermal motion is taken into account, then, accurate to a factor of the order of unity, the Jeans criterion is written in the form: align="absmiddle" width="205" height="20">, where is the mass of the cloud, T- gas temperature in K, n- number of particles per 1 cm3. With typical modern interstellar clouds temperature K can only collapse clouds with a mass not less than . The Jeans criterion indicates that for the formation of stars of the actually observed mass spectrum, the concentration of particles in collapsing clouds must reach (10 3 -10 6) cm -3, i.e. 10-1000 times higher than observed in typical clouds. However, such concentrations of particles can be achieved in the depths of clouds that have already begun to collapse. It follows from this that it happens through a sequential process, carried out in several steps. stages, fragmentation of massive clouds. This picture naturally explains the birth of stars in groups - clusters. At the same time, questions related to the thermal balance in the cloud, the velocity field in it, and the mechanism determining the mass spectrum of fragments still remain unclear.

Collapsed stellar mass objects are called protostars. Collapse of a spherically symmetric non-rotating protostar without a magnetic field. fields includes several. stages. At the initial moment of time, the cloud is homogeneous and isothermal. It is transparent to its own. radiation, so the collapse comes with volumetric energy losses, Ch. arr. due to the thermal radiation of the dust, the cut transmits its kinetic. energy of a gas particle. In a homogeneous cloud there is no pressure gradient and compression begins in free fall with a characteristic time , where G- , - cloud density. With the beginning of compression, a rarefaction wave appears, moving towards the center at the speed of sound, and since collapse occurs faster where the density is higher, the protostar is divided into a compact core and an extended shell, into which the matter is distributed according to the law. When the concentration of particles in the core reaches ~ 10 11 cm -3 it becomes opaque to the IR radiation of dust grains. The energy released in the core slowly seeps to the surface due to radiative thermal conduction. The temperature begins to increase almost adiabatically, this leads to an increase in pressure, and the core becomes hydrostatic. balance. The shell continues to fall onto the core, and it appears at its periphery. The parameters of the core at this time weakly depend on the total mass of the protostar: K. As the mass of the core increases due to accretion, its temperature changes almost adiabatically until it reaches 2000 K, when the dissociation of H 2 molecules begins. As a result of energy consumption for dissociation, and not an increase in kinetic. particle energy, the adiabatic index value becomes less than 4/3, pressure changes are not able to compensate for gravitational forces and the core collapses again (see). A new core with parameters is formed, surrounded by a shock front, onto which the remnants of the first core accrete. A similar rearrangement of the nucleus occurs with hydrogen.

Further growth of the core at the expense of the shell matter continues until all the matter falls onto the star or is scattered under the influence of or, if the core is sufficiently massive (see). Protostars with a characteristic time of shell matter t a >t kn, therefore their luminosity is determined by the energy release of the collapsing nuclei.

Evolution. tracks of protostar cores with constant mass at the hydrostatic stage. compressions are shown in Fig. 1. For stars of low mass, at the moment when hydrostatic is established. equilibrium, the conditions in the nuclei are such that energy is transferred to them. Calculations show that the surface temperature of a fully convective star is almost constant. The radius of the star is continuously decreasing, because she continues to shrink. With a constant surface temperature and a decreasing radius, the luminosity of the star should also fall on the G.-R.D. This stage of evolution corresponds to vertical sections of tracks.

As the compression continues, the temperature in the interior of the star increases, the matter becomes more transparent, and stars with align="absmiddle" width="90" height="17"> have radiant cores, but the shells remain convective. Less massive stars remain completely convective. Their luminosity is controlled by a thin radiant layer in the photosphere. The more massive the star and the higher its effective temperature, the larger its radiative core (in stars with align="absmiddle" width="74" height="17"> the radiative core appears immediately). In the end, almost the entire star (with the exception of the surface convective zone for stars with a mass) goes into a state of radiative equilibrium, in which all the energy released in the core is transferred by radiation.

3. Evolution based on nuclear reactions

When the hydrogen content in the core decreases to 1%, the expansion of the shells of stars with align="absmiddle" width="66" height="17"> is replaced by a general contraction of the star necessary to maintain energy release. Compression of the shell causes heating of hydrogen in the layer adjacent to the helium core to the temperature of its thermonuclear combustion, and a layer source of energy release arises. In stars with mass , in which it depends less on temperature and the region of energy release is not so strongly concentrated towards the center, there is no stage of general compression.

E.z. after hydrogen burns out depends on their mass. The most important factor influencing the course of evolution of stars with mass . degeneracy of electron gas at high densities. Due to the high density, the number of quantum states with low energy is limited due to the Pauli principle and electrons fill quantum levels with high energy, significantly exceeding the energy of their thermal motion. The most important feature of a degenerate gas is that its pressure p depends only on the density: for non-relativistic degeneracy and for relativistic degeneracy. The gas pressure of electrons is much greater than the pressure of ions. This follows what is fundamental for E.Z. conclusion: since the gravitational force acting on a unit volume of a relativistically degenerate gas depends on density in the same way as the pressure gradient, there must be a limiting mass (see), such that at align="absmiddle" width="66" height ="15"> electron pressure cannot counteract gravity and compression begins. Limit weight align="absmiddle" width="139" height="17">. The boundary of the region in which the electron gas is degenerate is shown in Fig. 3. In low-mass stars, degeneracy plays a noticeable role already in the process of formation of helium nuclei.

The second factor determining E.z. at later stages, these are neutrino energy losses. In the depths of the stars T~10 8 K main. a role in the birth is played by: photoneutrino process, decay of plasma oscillation quanta (plasmons) into neutrino-antineutrino pairs (), annihilation of electron-positron pairs () and (see). The most important feature of neutrinos is that the star’s matter is almost transparent to them and neutrinos freely carry energy away from the star.

The helium core, in which conditions for helium combustion have not yet arisen, is compressed. The temperature in the layered source adjacent to the core increases, and the rate of hydrogen combustion increases. The need to transfer an increased energy flow leads to expansion of the shell, for which part of the energy is wasted. Since the luminosity of the star does not change, the temperature of its surface drops, and on the G.-R.D. the star moves to the region occupied by red giants. The star's restructuring time is two orders of magnitude less than the time it takes for hydrogen to burn out in the core, so there are few stars between the MS strip and the region of red supergiants. With a decrease in the temperature of the shell, its transparency increases, as a result of which an external appearance appears. convective zone and the luminosity of the star increases.

The removal of energy from the core through the thermal conductivity of degenerate electrons and neutrino losses in stars delays the moment of helium combustion. The temperature begins to increase noticeably only when the core becomes almost isothermal. Combustion of 4 He determines the E.Z. from the moment when the energy release exceeds the energy loss through thermal conductivity and neutrino radiation. The same condition applies to the combustion of all subsequent types of nuclear fuel.

A remarkable feature of stellar cores made of degenerate gas, cooled by neutrinos, is “convergence” - the convergence of tracks, which characterize the relationship between density and temperature Tc in the center of the star (Fig. 3). The rate of energy release during compression of the core is determined by the rate of addition of matter to it through a layer source, and depends only on the mass of the core for a given type of fuel. A balance of inflow and outflow of energy must be maintained in the core, therefore the same distribution of temperature and density is established in the cores of stars. By the time 4 He ignites, the mass of the nucleus depends on the content of heavy elements. In nuclei of degenerate gas, the combustion of 4 He has the character of a thermal explosion, because the energy released during combustion goes to increase the energy of the thermal motion of electrons, but the pressure remains almost unchanged with increasing temperature until the thermal energy of the electrons is equal to the energy of the degenerate gas of electrons. Then the degeneracy is removed and the core rapidly expands - a helium flash occurs. Helium flares are likely accompanied by the loss of stellar matter. In , where massive stars have long finished evolution and red giants have masses, stars at the helium burning stage are on the horizontal branch of the G.-R.D.

In the helium cores of stars with align="absmiddle" width="90" height="17"> the gas is not degenerate, 4 He ignites quietly, but the cores also expand due to increasing Tc. In the most massive stars, the combustion of 4 He occurs even when they are active. blue supergiants. Expansion of the core leads to a decrease T in the region of the hydrogen layer source, and the luminosity of the star after the helium burst decreases. To maintain thermal equilibrium, the shell contracts, and the star leaves the region of red supergiants. When the 4 He in the core is depleted, compression of the core and expansion of the shell begin again, the star again becomes a red supergiant. A layered combustion source of 4 He is formed, which dominates the energy release. External appears again. convective zone. As helium and hydrogen burn out, the thickness of the layer sources decreases. A thin layer of helium combustion turns out to be thermally unstable, because with a very strong sensitivity of energy release to temperature (), the thermal conductivity of the substance is insufficient to extinguish thermal disturbances in the combustion layer. During thermal outbreaks, convection occurs in the layer. If it penetrates into layers rich in hydrogen, then as a result of a slow process ( s-process, see) elements with atomic masses from 22 Ne to 209 B are synthesized.

Radiation pressure on dust and molecules formed in the cold, extended shells of red supergiants leads to continuous loss of matter at a rate of up to a year. Continuous mass loss can be supplemented by losses caused by instability of layer combustion or pulsations, which can lead to the release of one or more. shells. When the amount of substance above the carbon-oxygen core becomes less than a certain limit, the shell is forced to compress in order to maintain the temperature in the combustion layers until the compression is capable of maintaining combustion; star on G.-R.D. moves almost horizontally to the left. At this stage, the instability of the combustion layers can also lead to expansion of the shell and loss of matter. While the star is hot enough, it is observed as a core with one or more. shells. When layer sources shift toward the surface of the star so much that the temperature in them becomes lower than that required for nuclear combustion, the star cools, turning into a white dwarf with , radiating due to the consumption of thermal energy of the ionic component of its matter. The characteristic cooling time of white dwarfs is ~ 10 9 years. The lower limit on the masses of single stars turning into white dwarfs is unclear, it is estimated at 3-6. In c stars, the electron gas degenerates at the stage of growth of carbon-oxygen (C,O-) stellar cores. As in the helium cores of stars, due to neutrino energy losses, a “convergence” of conditions occurs in the center and at the moment of combustion of carbon in the C,O core. The combustion of 12 C under such conditions most likely has the nature of an explosion and leads to the complete destruction of the star. Complete destruction may not occur if . Such a density is achievable when the core growth rate is determined by the accretion of satellite matter in a close binary system.

> 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 of a celestial body with a 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 a 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. It is a 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.

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. Many of them have large amounts of matter around them. 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 nuclear reactions are triggered in the center of the star, 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 the chemical elements that take part in the evolution of celestial bodies consist of elementary particles - “protoelements”. Unlike modern neutrons, protons and electrons, they do not have a general, but an 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

Larger stars are the hottest and brightest. They are usually white or bluish in appearance. 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, have relatively short lives - only a few hundred million years. The star life cycle diagram includes the following stages. This is a molecular cloud - gravitational collapse of the cloud - the birth of a supernova - the 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 under 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. The clusters will be of interest not only to professional astronomers - every amateur will be happy to take a beautiful photograph and admire their exceptionally beautiful view in the planetarium.

It occupies a point in the upper right corner: it has high luminosity and low temperature. The main radiation occurs in the infrared range. The radiation from the cold dust shell reaches us. During the process of evolution, the position of the star on the diagram will change. The only source of energy at this stage is gravitational compression. Therefore, the star moves quite quickly parallel to the ordinate axis.

The surface temperature does not change, but the radius and luminosity decrease. The temperature in the center of the star rises, reaching a value at which reactions begin with light elements: lithium, beryllium, boron, which quickly burn out, but manage to slow down the compression. The track rotates parallel to the ordinate axis, the temperature on the surface of the star increases, and the luminosity remains almost constant. Finally, in the center of the star, reactions of the formation of helium from hydrogen (hydrogen combustion) begin. The star enters the main sequence.

The duration of the initial stage is determined by the mass of the star. For stars like the Sun it is about 1 million years, for a star with a mass of 10 M☉ about 1000 times less, and for a star with a mass of 0.1 M☉ thousands of times more.

Young low mass stars

At the beginning of evolution, a low-mass star has a radiant core and a convective envelope (Fig. 82, I).

At the main sequence stage, the star shines due to the release of energy in the nuclear reactions of converting hydrogen into helium. The supply of hydrogen ensures the luminosity of a star of mass 1 M☉ approximately within 10 10 years. Stars of greater mass consume hydrogen faster: for example, a star with a mass of 10 M☉ will consume hydrogen in less than 10 7 years (luminosity is proportional to the fourth power of mass).

Low mass stars

As hydrogen burns out, the central regions of the star are greatly compressed.

High mass stars

After reaching the main sequence, the evolution of a high-mass star (>1.5 M☉) is determined by the combustion conditions of nuclear fuel in the bowels of the star. At the main sequence stage, this is the combustion of hydrogen, but unlike low-mass stars, reactions of the carbon-nitrogen cycle dominate in the core. In this cycle, the C and N atoms play the role of catalysts. The rate of energy release in the reactions of such a cycle is proportional to T 17. Therefore, a convective core is formed in the core, surrounded by a zone in which energy transfer is carried out by radiation.

The luminosity of large-mass stars is much higher than the luminosity of the Sun, and hydrogen is consumed much faster. This is also due to the fact that the temperature in the center of such stars is also much higher.

As the proportion of hydrogen in the matter of the convective core decreases, the rate of energy release decreases. But since the rate of release is determined by luminosity, the core begins to compress, and the rate of energy release remains constant. At the same time, the star expands and moves into the region of red giants.

Low mass stars

By the time the hydrogen is completely burned out, a small helium core is formed in the center of a low-mass star. In the core, the density of matter and temperature reach values ​​of 10 9 kg/m and 10 8 K, respectively. Hydrogen combustion occurs on the surface of the core. As the temperature in the core rises, the rate of hydrogen burnout increases and the luminosity increases. The radiant zone gradually disappears. And due to the increase in the speed of convective flows, the outer layers of the star inflate. Its size and luminosity increase - the star turns into a red giant (Fig. 82, II).

High mass stars

When the hydrogen in a large-mass star is completely exhausted, a triple helium reaction begins to occur in the core and at the same time the reaction of oxygen formation (3He=>C and C+He=>0). At the same time, hydrogen begins to burn on the surface of the helium core. The first layer source appears.

The supply of helium is exhausted very quickly, since in the reactions described, relatively little energy is released in each elementary act. The picture repeats itself, and two layer sources appear in the star, and the reaction C+C=>Mg begins in the core.

The evolutionary track turns out to be very complex (Fig. 84). On the Hertzsprung-Russell diagram, the star moves along the sequence of giants or (with a very large mass in the supergiant region) periodically becomes a Cephei.

Old low mass stars

For a low-mass star, eventually, the speed of the convective flow at some level reaches the second escape velocity, the shell comes off, and the star turns into a white dwarf surrounded by a planetary nebula.

The evolutionary track of a low-mass star on the Hertzsprung-Russell diagram is shown in Figure 83.

Death of high-mass stars

At the end of its evolution, a large-mass star has a very complex structure. Each layer has its own chemical composition, nuclear reactions occur in several layer sources, and an iron core is formed in the center (Fig. 85).

Nuclear reactions with iron do not occur, since they require the expenditure (and not the release) of energy. Therefore, the iron core quickly contracts, the temperature and density in it increase, reaching fantastic values ​​- a temperature of 10 9 K and a pressure of 10 9 kg/m 3. Material from the site

At this moment, two important processes begin, occurring in the nucleus simultaneously and very quickly (apparently, in minutes). The first is that during nuclear collisions, iron atoms decay into 14 helium atoms, the second is that electrons are “pressed” into protons, forming neutrons. Both processes are associated with the absorption of energy, and the temperature in the core (also pressure) instantly drops. The outer layers of the star begin to fall toward the center.

The fall of the outer layers leads to a sharp increase in temperature in them. Hydrogen, helium, and carbon begin to burn. This is accompanied by a powerful stream of neutrons that comes from the central core. As a result, a powerful nuclear explosion occurs, throwing off the outer layers of the star, already containing all the heavy elements, up to californium. According to modern views, all atoms of heavy chemical elements (i.e., heavier than helium) were formed in the Universe precisely in flares