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

Star-- a celestial body in which thermonuclear reactions are occurring, have occurred, or will occur. Stars are massive luminous balls of gas (plasma). Formed from a gas-dust environment (hydrogen and helium) as a result of gravitational compression. The temperature of matter in the interior of stars is measured in millions of kelvins, and on their surface - in thousands of kelvins. The energy of the vast majority of stars is released as a result of thermonuclear reactions converting hydrogen into helium, occurring at high temperatures in the internal regions. Stars are often called the main bodies of the Universe, since they contain the bulk of luminous matter in nature. Stars are huge, spherical objects made of helium and hydrogen, as well as other gases. The energy of a star is contained in its core, where helium interacts with hydrogen every second. Like everything organic in our universe, stars arise, develop, change and disappear - this process takes billions of years and is called the process of “Star Evolution”.

1. Evolution of stars

Evolution of stars-- the sequence of changes that a star undergoes during its life, that is, over hundreds of thousands, millions or billions of years while it emits light and heat. A star begins its life as a cold, rarefied cloud of interstellar gas (a rarefied gaseous medium that fills all the space between stars), compressing under its own gravity and gradually taking the shape of a ball. When compressed, gravitational energy (the universal fundamental interaction between all material bodies) turns into heat, and the temperature of the object increases. When the temperature in the center reaches 15-20 million K, thermonuclear reactions begin and compression stops. The object becomes a full-fledged star. The first stage of a star's life is similar to that of the sun - it is dominated by reactions of the hydrogen cycle. It remains in this state for most of its life, being on the main sequence of the Hertzsprung-Russell diagram (Fig. 1) (showing the relationship between absolute magnitude, luminosity, spectral type and surface temperature of the star, 1910), until its fuel reserves run out at its core. When all the hydrogen in the center of the star is converted into helium, a helium core is formed, and thermonuclear burning of hydrogen continues at its periphery. During this period, the structure of the star begins to change. Its luminosity increases, its outer layers expand, and its surface temperature decreases—the star becomes a red giant, which forms a branch on the Hertzsprung-Russell diagram. The star spends significantly less time on this branch than on the main sequence. When the accumulated mass of the helium core becomes significant, it cannot support its own weight and begins to shrink; if the star is massive enough, the increasing temperature can cause further thermonuclear transformation of helium into heavier elements (helium into carbon, carbon into oxygen, oxygen into silicon, and finally silicon into iron).

2. Thermonuclear fusion in the interior of stars

By 1939, it was established that the source of stellar energy is thermonuclear fusion occurring in the bowels of stars. Most stars emit radiation because in their core four protons combine through a series of intermediate steps into a single alpha particle. This transformation can occur in two main ways, called the proton-proton, or p-p, cycle, and the carbon-nitrogen, or CN, cycle. In low-mass stars, energy release is mainly provided by the first cycle, in heavy stars - by the second. The supply of nuclear fuel in a star is limited and is constantly spent on radiation. The process of thermonuclear fusion, which releases energy and changes the composition of the star's matter, in combination with gravity, which tends to compress the star and also releases energy, as well as radiation from the surface, which carries away the released energy, are the main driving forces of stellar evolution. The evolution of a star begins in a giant molecular cloud, also called a stellar cradle. Most of the "empty" space in a galaxy actually contains between 0.1 and 1 molecule per cm?. The molecular cloud has a density of about a million molecules per cm?. The mass of such a cloud exceeds the mass of the Sun by 100,000-10,000,000 times due to its size: from 50 to 300 light years in diameter. While the cloud rotates freely around the center of its home galaxy, nothing happens. However, due to the inhomogeneity of the gravitational field, disturbances may arise in it, leading to local concentrations of mass. Such disturbances cause gravitational collapse of the cloud. One of the scenarios leading to this is the collision of two clouds. Another event causing collapse could be the passage of a cloud through the dense arm of a spiral galaxy. Also a critical factor could be the explosion of a nearby supernova, the shock wave of which will collide with the molecular cloud at enormous speed. It is also possible that galaxies collide, which could cause a burst of star formation as the gas clouds in each galaxy are compressed by the collision. In general, any inhomogeneities in the forces acting on the mass of the cloud can initiate the process of star formation. Due to the inhomogeneities that have arisen, the pressure of the molecular gas can no longer prevent further compression, and the gas begins to gather around the center of the future star under the influence of gravitational attraction forces. Half of the released gravitational energy goes to heating the cloud, and half goes to light radiation. In clouds, pressure and density increase towards the center, and the collapse of the central part occurs faster than the periphery. As it contracts, the mean free path of photons decreases, and the cloud becomes less and less transparent to its own radiation. This leads to a faster rise in temperature and an even faster rise in pressure. As a result, the pressure gradient balances the gravitational force, and a hydrostatic core is formed, with a mass of about 1% of the mass of the cloud. This moment is invisible. The further evolution of the protostar is the accretion of matter that continues to fall onto the “surface” of the core, which due to this grows in size. The mass of freely moving matter in the cloud is exhausted, and the star becomes visible in the optical range. This moment is considered the end of the protostellar phase and the beginning of the young star phase. The process of star formation can be described in a unified way, but the subsequent stages of a star's development depend almost entirely on its mass, and only at the very end of stellar evolution can chemical composition play a role.

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 inside 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 lifespan of stars consists of several stages, passing through which for millions and billions of years the luminaries steadily strive towards the inevitable finale, turning into bright flares or gloomy black holes.

The lifetime of a star of any type is an incredibly long and complex process, accompanied by phenomena on a cosmic scale. Its versatility is simply impossible to fully trace and study, even using the entire arsenal of modern science. But based on the unique knowledge accumulated and processed over the entire period of the existence of terrestrial astronomy, whole layers of the most valuable information become available to us. This makes it possible to link the sequence of episodes from the life cycle of luminaries into relatively coherent theories and model their development. What are these stages?

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Episode I. Protostars

The life path of stars, like all objects of the macrocosm and microcosm, begins with birth. This event originates in the formation of an incredibly huge cloud, within which the first molecules appear, therefore the formation is called molecular. Sometimes another term is used that directly reveals the essence of the process - the cradle of stars.

Only when in such a cloud, due to insurmountable circumstances, an extremely rapid compression of its constituent particles that have mass occurs, i.e., gravitational collapse, does a future star begin to form. The reason for this is a surge of gravitational energy, part of which compresses gas molecules and heats up the mother cloud. Then the transparency of the formation gradually begins to disappear, which contributes to even greater heating and an increase in pressure in its center. The final episode in the protostellar phase is the accretion of matter falling onto the core, during which the nascent star grows and becomes visible after the pressure of the emitted light literally sweeps away all the dust to the outskirts.

Find protostars in the Orion Nebula!

This huge panorama of the Orion Nebula comes from images. This nebula is one of the largest and closest cradles of stars to us. Try to find protostars in this nebula, since the resolution of this panorama allows you to do this.

Episode II. Young stars

Fomalhaut, image from the DSS catalogue. There is still a protoplanetary disk around this star.

The next stage or cycle of a star’s life is the period of its cosmic childhood, which, in turn, is divided into three stages: young stars of minor (<3), промежуточной (от 2 до 8) и массой больше восьми солнечных единиц. На первом отрезке образования подвержены конвекции, которая затрагивает абсолютно все области молодых звезд. На промежуточном этапе такое явление не наблюдается. В конце своей молодости объекты уже во всей полноте наделены качествами, присущими взрослой звезде. Однако любопытно то, что на данной стадии они обладают колоссально сильной светимостью, которая замедляет или полностью прекращает процесс коллапса в еще не сформировавшихся солнцах.

Episode III. The heyday of a star's life

The sun photographed in the H alpha line. Our star is in his prime.

In the middle of their lives, cosmic luminaries can have a wide variety of colors, masses and dimensions. The color palette varies from bluish shades to red, and their mass can be significantly less than the solar mass or more than three hundred times greater. The main sequence of the life cycle of stars lasts about ten billion years. After which the core of the cosmic body runs out of hydrogen. This moment is considered to be the transition of the object’s life to the next stage. Due to the depletion of hydrogen resources in the core, thermonuclear reactions stop. However, during the period of renewed compression of the star, collapse begins, which leads to the occurrence of thermonuclear reactions with the participation of helium. This process stimulates a simply incredible expansion of the star. And now it is considered a red giant.

Episode IV. The end of the existence of stars and their death

Old stars, like their young counterparts, are divided into several types: low-mass, medium-sized, supermassive stars, and. As for objects with low mass, it is still impossible to say exactly what processes occur with them in the last stages of existence. All such phenomena are hypothetically described using computer simulations, and not based on careful observations of them. After the final burnout of carbon and oxygen, the star’s atmospheric envelope increases and its gas component rapidly loses. At the end of their evolutionary path, the stars are compressed many times, and their density, on the contrary, increases significantly. Such a star is considered to be a white dwarf. Its life phase is then followed by a red supergiant period. The last thing in the life cycle of a star is its transformation, as a result of very strong compression, into a neutron star. However, not all such cosmic bodies become like this. Some, most often the largest in parameters (more than 20-30 solar masses), become black holes as a result of collapse.

Interesting facts about the life cycles of stars

One of the most peculiar and remarkable information from the stellar life of space is that the vast majority of the luminaries in ours are at the stage of red dwarfs. Such objects have a mass much less than that of the Sun.

It is also quite interesting that the magnetic attraction of neutron stars is billions of times higher than the similar radiation of the earth’s star.

Effect of mass on a star

Another equally interesting fact is the duration of existence of the largest known types of stars. Due to the fact that their mass can be hundreds of times greater than that of the sun, their energy release is also many times greater, sometimes even millions of times. Consequently, their life span is much shorter. In some cases, their existence lasts only a few million years, compared to the billions of years of life of low-mass stars.

An interesting fact is also the contrast between black holes and white dwarfs. It is noteworthy that the former arise from the most gigantic stars in terms of mass, and the latter, on the contrary, from the smallest.

There are a huge number of unique phenomena in the Universe that we can talk about endlessly, because space is extremely poorly studied and explored. All human knowledge about stars and their life cycles that modern science possesses is mainly derived from observations and theoretical calculations. Such little-studied phenomena and objects provide the basis for constant work for thousands of researchers and scientists: astronomers, physicists, mathematicians, and chemists. Thanks to their continuous work, this knowledge is constantly accumulated, supplemented and changed, thus becoming more accurate, reliable and comprehensive.

TOPIC No. 5. UNIVERSE

Concepts

Plasma, star, red giant, white dwarf, neutron star, “black hole”, galaxy, Metagalaxy, “red spectral shift”, parsec, quasar.

Scientists

William Herschel, Robert Julius Trumpler, Edwin Hubble, Albert Einstein, Vesto Slifer, Christian Doppler, Georgiy Antonovich Gamow, Arno Penzias, Robert Wilson.

Questions

1. The birth and evolution of stars.

2. Galaxies.

3. Model of the expanding Universe.

4. The Big Bang Theory.

THE BIRTH AND EVOLUTION OF STARS

Star - plasma ball

It seems that there are an unimaginable number of stars in the sky. In fact, with the naked eye, with the sharpest vision, on the darkest night you can see no more than 3,000 stars, and in both hemispheres - no more than 6,000. Over hundreds of years of observations, astronomers have cataloged about a million stars.

To understand what a star is, we need to remember what states of matter exist. In addition to the well-known solid, liquid and gaseous states, a substance can also be in a plasma state, when there are many ions. An ion is a charged atom. If there is an excess or deficiency of electrons on the outer shell of an atom, it becomes an ion, positive or negative, respectively. So, an ion is an electrically charged atom. If a gas contains a significant proportion of ions, it is called plasma.

Plasma is an ionized gas, i.e. a gas in which positive ions and electrons cancel each other out on average.

A star is a plasma ball.

Sources of stellar energy

Stars have been releasing enormous amounts of energy into the surrounding space for billions of years. Modern physics names two possible sources of it - gravitational compression and thermonuclear reactions.

In order to understand how gravity feeds stars with energy, imagine, for example, a lead ball that we hold at a height H above the surface of a lead plate. The gravitational force acts on it from the Earth. The ball has energy, which in physics is called potential, in other words, stored. According to the formula known from the school physics course, it is equal to

where E p is potential energy, m is the mass of the ball, g is the acceleration of gravity. More precisely, it expresses the value of the mutual energy of two bodies - the ball and the Earth. If we let go of the ball, it will begin to fall, the distance to the plate will decrease and, therefore, its potential energy will decrease. But it will pick up speed, which means it will increase its kinetic energy, in other words, the energy of movement. In this case, the sum of potential and kinetic energy – the total mechanical energy of the “Earth-ball” system – will be conserved. This is evidenced by the most important law of mechanics - the law of conservation of total mechanical energy.

When the ball falls on the slab, it will not fly up, but will flatten out somewhat. But where did the total mechanical energy go? It did not disappear, but turned into another type of energy - internal (sometimes inaccurately called thermal). Both the ball and the place on the lead plate where it hit will heat up somewhat. Thus, gravity led to the convergence of the ball and the plate and to their heating.

The Birth of Stars

Let us imagine in the vastness of outer space a huge cloud of dust and gas, say, many times larger in size than the solar system. Under the influence of gravitational forces, dust and gas particles will condense and heat up. A similar process was described by Kant in his nebular hypothesis. The cloud can take millions of years to thicken and warm up. When the temperature inside it reaches a value of about 10 million K, thermonuclear fusion reactions will begin. The most common of these is probably the fusion reaction of the nuclei of a hydrogen atom to form the nuclei of a helium atom. Its beginning will mean the birth of a new star. This is one of the models for the origin of stars. Thus, gravitational compression “switches on” the thermonuclear reaction.

Evolution of stars

Gravitational compression is the first stage in the evolution of a star. As a result, the central part of the star is heated to a temperature of approximately 10 - 15 million K - before the start of the thermonuclear fusion reaction. It is accompanied by the release of a large amount of energy.

Young stars are at the stage of initial gravitational compression. They glow due to the conversion of the potential energy of particle interaction into internal energy.

The process of star evolution is a confrontation between two powerful forces. The gravitational forces of interaction between different regions of the star tend to compress it, since they are attractive forces. Internal pressure prevents this compression. It consists of at least three components. Firstly, this is gas pressure. If, for example, you squeeze a rubber ball with your hands, you can feel the pressure of the air inside. Secondly, light pressure. (Remember the pressure of the sun's rays on the comet's tail). Thirdly, the pressure arising from the flying fragments of thermonuclear reactions. When nuclei merge, neutrons are released. Their flows also exert pressure. (Let us remember what gas pressure is. Its molecules collide with the walls of the vessel. Their combined effect is the gas pressure). The explosion of a thermonuclear bomb causes a wave that has enormous destructive power. Thermonuclear bombs explode inside the star every second. But their action is restrained by powerful gravitational forces. Amazingly, the duel between two equal forces - the combined internal pressure and gravity - lasts for billions of years.

Red giants

Since the thermonuclear fusion reaction occurs in the central region of the Sun, as hydrogen is converted into helium, an ever-increasing helium core is formed in it. Thermonuclear reactions continue, but in a thin layer near the surface of this core and gradually move to the periphery of the star. The shell swells to colossal sizes, the external temperature becomes low, and the star enters the red giant stage - entering the final stage of its life. The star's matter is lost and ejected into interstellar space. In just ten to one hundred thousand years, only the central helium core remains from the red giant.

The final stage of star evolution

Nothing lasts forever in the material world. No matter how large the supply of hydrogen inside a star is, it is not infinite. After a few billion years, all the hydrogen turns into helium as a result of thermonuclear fusion reaction.

Finally, all remaining hydrogen is converted to helium, and thermonuclear reactions stop. Then the internal pressure of the star is significantly weakened, since it no longer includes a powerful component - the impact of particles that are released during the thermonuclear reaction, primarily neutrons. In other words, the explosions of thermonuclear bombs stop inside the star. Of course, this leads to a decrease in internal pressure.

Then the previous balance of opposing forces is disrupted. Gravitational forces gain an advantage over the forces of internal pressure, and this process grows like a snowball. To make this easier to understand, let us turn to the law of universal gravitation:

For our specific case, F is the force of interaction between the opposite regions of the star that compress it, G is the gravitational constant (it is unchanged), m is the mass of matter in these regions, R is the distance between these regions, and it does not exceed the diameter of the star. Since the gravitational forces compress the star, this leads to a decrease in the value of R. This value is in the denominator, and as the denominator decreases, the fraction increases, and R is in the second power. Increasing fraction, i.e. force F, compresses the star even more, which leads to a decrease in its size R and, accordingly, to an increase in force F. Etc. Within a few tens of seconds, the star's core contracts. This process is called gravitational collapse, which means gravitational catastrophe.

The further fate of a star depends, first of all, on its mass. The most probable three options for the final stage of stellar evolution are white dwarfs, neutron stars and “black holes”.

White dwarfs

If a star has a mass of approximately 1.4 solar masses or less, it becomes a state called a white dwarf. Why white? Because the star shines very brightly. Why dwarf? Because the star is sharply compressed, and, consequently, its density increases. Let's imagine the Sun, which has shrunk to the size of the Earth. The density of such a star will be billions of times greater than the density of water. The substance of a white dwarf is a very dense ionized gas. It consists of atomic nuclei and individual electrons. Such a gas is called degenerate.

The white dwarf is slowly cooling. Its shell is gradually thrown into space. Young white dwarfs are surrounded by remnants of an envelope that resembles a ring around a white dot. Such formations are called planetary nebulae.

Thermonuclear reactions do not occur in the interior of white dwarfs. They can only occur in their atmosphere, where hydrogen penetrates from the interstellar medium. White dwarfs shine due to their enormous reserves of internal energy. They cool down over hundreds of millions of years. As a white dwarf cools, its color changes from white to yellow, and then to red. Finally, it turns into a black dwarf - a dead, cold star.

Fate of the Sun

Currently, the nuclear reaction of converting hydrogen into helium is still taking place in the depths of our Sun. According to experts, its gravitational collapse will occur no earlier than in 5 billion years. The sun will swell and turn into a red giant. Its outer shell will reach the orbit of Mercury or perhaps Venus. The oceans on Earth will evaporate, and what will be left behind is charred rocks.

Neutron stars

If the mass of a star that has reached a state of gravitational collapse exceeds the mass of the Sun by more than 1.4 times, then it turns into a neutron star. In a very simplified way, one can imagine that gravitational forces are so strong that they seem to “press” negatively charged electrons into positively charged protons, and as a result, neutral particles - neutrons - are formed. So, a neutron star is mainly made of neutrons. The question arises, which star is denser, more densely packed, a white dwarf or a neutron star? Let us remember that a white dwarf contains positively charged protons. Likely charged particles repel each other. Therefore, to compress a white dwarf, gravitational forces have to overcome the electrical repulsion of protons. On the contrary, a neutron star consists of neutrons - particles that have no electrical charge, between which there is no electrical repulsion. Therefore, gravitational forces are capable of compressing a neutron star to a denser state than a white dwarf. The density of a neutron star is even higher than the density of atomic nuclei - 10 15 g/cm 3 . Its temperature is about 1 billion degrees.

Black holes

If the mass of the collapsing star, i.e. star in a state of gravitational collapse exceeds 2 – 3 solar masses, then it turns into a “black hole”. Let's find out why it is black and why the hole?

On Earth, any body thrown up falls under the influence of gravity. If some body reaches a speed of 7.9 km/s, then it will become an artificial satellite of the Earth. This speed is called the first escape velocity. If this value is exceeded, then the body will leave the limits of the Earth’s gravity and will be able to move away from it. The “black hole” has such powerful gravity that even the speed of light - 300,000 km/s is not enough to overcome it. The “black hole” does not shine, that’s why it’s called that.

In the general theory of relativity, gravity is explained by the curvature of space. Let's remember the analogy between gravity and a sheet of rubber. The greater the mass of a body, for example a ball, the larger the depression it creates in the rubber. A ball of enormous mass will create such a large depression that it will resemble a funnel or hole. Figuratively speaking, a “black hole” creates such a deep funnel in space that all matter at enormous distances from it is absorbed into it.