The evolution of stars from the point of view of exact science and the theory of relativity. The birth and evolution of stars: the giant factory of the universe
The lifetime of stars consists of several stages, passing through which for millions and billions of years the luminaries are steadily striving for the inevitable finale, turning into bright flashes 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 modern science. But based on those 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 connect the sequence of episodes from the life cycle of the 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 from birth. This event originates in the formation of an incredibly huge cloud, inside 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 with mass, i.e., gravitational collapse, occurs, the future star begins to form. The reason for this is a surge of gravitational energy, part of which compresses the gas molecules and heats up the parent 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 luminary 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 is derived from imagery. 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 catalog. 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: the young luminaries of the small (<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 the life path of a star
Sun shot in H line alpha. Our star is in its prime.
In the middle of their lives, cosmic bodies can have a wide variety of colors, masses and dimensions. The color palette varies from bluish hues to red, and their mass can be much less than the sun, or exceed it by more than three hundred times. The main sequence of the life cycle of stars lasts about ten billion years. After that, hydrogen ends in the core of the cosmic body. This moment is considered to be the transition of the life of the object to the next stage. Due to the depletion of hydrogen resources in the core, thermonuclear reactions stop. However, during the period of the newly begun compression of the star, a collapse begins, which leads to the occurrence of thermonuclear reactions already with the participation of helium. This process stimulates the expansion of the star, which is simply incredible in scale. And now it is considered a red giant.
Episode IV The end of the existence of stars and their death
Old luminaries, like their young counterparts, are divided into several types: low-mass, medium-sized, supermassive stars, and. As for objects with a small mass, it is still impossible to say exactly what processes take place 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 atmospheric shell of the star increases and its gas component rapidly loses. At the end of their evolutionary path, the luminaries are repeatedly compressed, while their density, on the contrary, increases significantly. Such a star is considered to be a white dwarf. Then, in its life phase, the period of a red supergiant follows. The last in the life cycle of a star is its transformation, as a result of a very strong compression, into a neutron star. However, not all such cosmic bodies become such. Some, most often the largest in terms of parameters (more than 20-30 solar masses), pass into the category of black holes as a result of collapse.
Interesting facts from the life cycles of stars
One of the most peculiar and remarkable information from the stellar life of the cosmos 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 earthly body.
Effect of mass on a star
Another no less entertaining fact is the duration of the existence of the largest known types of stars. Due to the fact that their mass is capable of hundreds of times greater than the solar mass, their release of energy is also many times greater, sometimes even millions of times. Consequently, their life span is much shorter. In some cases, their existence fits into just a few million years, against the billions of years of the life of stars with a small mass.
An interesting fact is also the opposite of black holes to 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.
In the Universe there is a huge number of unique phenomena that can be talked about endlessly, because the cosmos is extremely poorly studied and explored. All human knowledge about stars and their life cycles, which modern science has, is mainly obtained from observations and theoretical calculations. Such little-studied phenomena and objects give rise to constant work for thousands of researchers and scientists: astronomers, physicists, mathematicians, chemists. Thanks to their continuous work, this knowledge is constantly accumulated, supplemented and changed, thus becoming more accurate, reliable and comprehensive.
> Life cycle of a star
Description life and death of stars: evolutionary stages with photo, molecular clouds, protostar, T Taurus, main sequence, red giant, white dwarf.
Everything in this world is evolving. Any cycle begins with birth, growth and ends with death. Of course, the stars have these cycles in a special way. Let us recall, for example, that they have a larger time frame and are measured in millions and billions of years. In addition, their death carries certain consequences. What does it look like life cycle 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 easily exist in the universe without any changes. But suddenly a supernova explodes not far from it, or it collides with another cloud. Because of this push, the process of destruction is activated. It is divided into small parts, each of which is drawn into itself. As you already understood, all these bunches are preparing to become stars. Gravity heats up the temperature, and the stored momentum keeps the rotation going. The lower diagram clearly demonstrates the cycle of stars (life, stages of development, transformation options and death of a celestial body with a photo).
The 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 is formed. The part is attracted to the object, increasing its mass. The rest of the debris will be grouped and create a planetary system. Further development of the star all depends on the 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 Taurus. This is a variable star located 600 light years away (not far from).
It can reach great brightness because the material breaks down and releases energy. But in the central part there is not enough temperature to support nuclear fusion. This phase lasts 100 million years.
The 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 is transformed into helium, releasing a huge thermal reserve and energy.
The energy is released as gamma rays, but due to the star's slow motion, it falls off with wavelength. Light is pushed outward and confronts gravity. We can assume that a perfect balance is created here.
How long will she stay main sequence? You need to start from the mass of the star. Red dwarfs (half the solar mass) are capable of spending hundreds of billions (trillions) of years on their fuel supply. Average stars (like) live 10-15 billion. But the largest ones are billions or millions of years old. See how the evolution and death of stars of various classes looks like in the diagram.
Fifth life cycle of a star: red giant
During the melting process, hydrogen ends 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 1000-10000 times. At a certain moment, our Sun will repeat this fate, having increased to the earth's orbit.
Temperature and pressure reach a maximum, and helium fuses into carbon. At this point, the star contracts and ceases to be a red giant. With greater massiveness, the object will burn other heavy elements.
The sixth life cycle of a star: white dwarf
A solar-mass star doesn't have enough gravitational pressure to fuse carbon. Therefore, death occurs with the end of helium. The outer layers are ejected and a white dwarf appears. At first it is hot, but after hundreds of billions of years it will cool down.
Star- a celestial body in which thermonuclear reactions are going, going or will go. Stars are massive luminous gaseous (plasma) balls. Formed from a gas-dust environment (hydrogen and helium) as a result of gravitational compression. The temperature of matter in the depths 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 of the conversion of hydrogen into helium, which occur during high temperatures in the interior areas. Stars are often called the main bodies of the universe, since they contain the bulk of the luminous matter in nature. Stars are huge objects, spherical in shape, consisting of helium and hydrogen, as well as other gases. The energy of a star is contained in its core, where every second helium interacts with hydrogen. 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. The evolution of stars
Star evolution- the sequence of changes that a star undergoes during its life, that is, over hundreds of thousands, millions or billions of years, while it radiates 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), shrinking under the influence of its own gravity and gradually taking the shape of a ball. When compressed, the energy of gravity (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 the 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 the 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) (shows the relationship between the absolute magnitude, luminosity, spectral type and surface temperature of a star, 1910), until the fuel supply runs out at its core. When all the hydrogen in the center of the star turns into helium, a helium core is formed, and the thermonuclear combustion of hydrogen continues on its periphery. During this period, the structure of the star begins to change. Its luminosity increases, the outer layers expand, and the surface temperature decreases - the star becomes a red giant, which form a branch on the Hertzsprung-Russell diagram. The star spends much 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 rising temperature can cause further thermonuclear conversion 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 interiors of stars. Most stars radiate because, in their interiors, four protons combine through a series of intermediate steps into a single alpha particle. This transformation can go 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. Stock nuclear fuel in a star is limited and constantly spent on radiation. The process of thermonuclear fusion, which releases energy and changes the composition of the star's matter, combined 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 the galaxy actually contains 0.1 to 1 molecule per cm?. A 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 across. While the cloud is free to rotate around the center of the home galaxy, nothing happens. However, due to the inhomogeneity of the gravitational field, disturbances may arise in it, leading to local mass concentrations. Such perturbations cause the gravitational collapse of the cloud. One of the scenarios leading to this is the collision of two clouds. Another event causing the collapse could be the passage of a cloud through the dense arm of a spiral galaxy. Also a critical factor may be the explosion of a nearby supernova, the shock wave of which will collide with the molecular cloud at great speed. In addition, a collision of galaxies is possible, capable of causing a burst of star formation, as the gas clouds in each of the galaxies 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. Half of the released gravitational energy goes into heating the cloud, and half into light radiation. In clouds, pressure and density increase towards the center, and the collapse of the central part occurs faster than the periphery. As the contraction progresses, the mean free path of photons decreases, and the cloud becomes less and less transparent to its own radiation. This results in a faster rise in temperature and an even faster rise in pressure. As a result, the pressure gradient balances the gravitational force, 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 the substance that continues to fall on the “surface” of the core, which, due to this, grows in size. The mass of matter freely moving 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 single way, but the subsequent stages of the development of a star depend almost entirely on its mass, and only at the very end of stellar evolution can chemical composition play a role.
3. The middle of the life cycle of a star
Stars come in a wide variety of colors and sizes. They range in spectral type from hot blues to cool reds, and in mass from 0.0767 to more than 200 solar masses. The luminosity and color of a star depends on the temperature of its surface, which, in turn, is determined by its mass. All new stars "take their place" on the main sequence according to their chemical composition and mass. We are not talking about the physical movement of the star - only about its position on the indicated diagram, which depends on the parameters of the star. In fact, the movement of a star along the diagram corresponds only to a change in the parameters of the star. Small, cool red dwarfs slowly burn off their hydrogen reserves and remain on the main sequence for hundreds of billions of years, while massive supergiants leave the main sequence within a few million years of formation. Medium-sized stars like the Sun stay on the main sequence for an average of 10 billion years. It is believed that the Sun is still on it, as it is in the middle of its life cycle. As soon as the star depletes the supply of hydrogen in the core, it leaves the main sequence. After a certain time - from a million to tens of billions of years, depending on the initial mass - the star depletes the hydrogen resources of the core. In large and hot stars, this happens much faster than in small and colder ones. The depletion of the supply of hydrogen leads to the cessation of thermonuclear reactions. Without the pressure generated by these reactions to balance the star's own gravitational pull, the star begins to contract again, as it did before, during its formation. The temperature and pressure increase again, but, unlike the protostar stage, to more high level. The collapse continues until, at a temperature of approximately 100 million K, thermonuclear reactions involving helium begin. The thermonuclear combustion of matter resumed at a new level causes a monstrous expansion of the star. The star is "loosened", and its size increases by about 100 times. Thus, the star becomes a red giant, and the helium burning phase continues for about several million years. Almost all red giants are variable stars. What happens next depends again on the mass of the star.
4. Later years and the death of stars
Old stars with low mass
To date, it is not known for certain what happens to light stars after the depletion of the hydrogen supply. Since the universe is 13.7 billion years old, which is not enough to deplete the supply of hydrogen fuel in such stars, current theories are based on computer simulations of the processes occurring in such stars. Some stars can synthesize helium only in some active zones, which causes their instability and strong stellar winds. In this case, the formation of a planetary nebula does not occur, and the star only evaporates, becoming even smaller than a brown dwarf. Stars with a mass of less than 0.5 solar mass are not able to convert helium even after reactions involving hydrogen cease in the core - their mass is too small to provide a new phase of gravitational compression to the extent that initiates the "ignition" of helium . Such stars include red dwarfs, such as Proxima Centauri, whose main sequence lifetimes range from tens of billions to tens of trillions of years. After the termination of thermonuclear reactions in their core, they, gradually cooling down, will continue to weakly radiate in the infrared and microwave ranges of the electromagnetic spectrum.
medium sized stars
When a star reaches an average value (from 0.4 to 3.4 solar masses) of the red giant phase, hydrogen ends in its core and reactions of carbon synthesis from helium begin. This process occurs at higher temperatures and therefore the flow of energy from the core increases, which leads to the fact that the outer layers of the star begin to expand. The beginning of carbon synthesis marks a new stage in the life of a star and continues for some time. For a star similar in size to the Sun, this process can take about a billion years. Changes in the amount of energy emitted cause the star to go through periods of instability, including changes in size, surface temperature, and energy release. The release of energy is shifted towards low-frequency radiation. All this is accompanied by an increasing mass loss due to strong stellar winds and intense pulsations. Stars in this phase are called late-type stars, OH-IR stars, or Mira-like stars, depending on their precise characteristics. The ejected gas is relatively rich in heavy elements produced in the interior of the star, such as oxygen and carbon. The gas forms an expanding shell and cools as it moves away from the star, allowing the formation of dust particles and molecules. With strong infrared radiation from the central star, ideal conditions are formed in such shells for the activation of masers. Helium combustion reactions are very sensitive to temperature. Sometimes this leads to great instability. Strongest pulsations arise, which, in the end, give the outer layers enough acceleration to be dropped and turn into a planetary nebula. In the center of the nebula, the naked core of the star remains, in which thermonuclear reactions stop, and, cooling down, it turns into a helium white dwarf, as a rule, having a mass of up to 0.5-0.6 solar and a diameter of the order of the diameter of the Earth.
white dwarfs
Shortly after a helium flash, carbon and oxygen "light up"; each of these events causes a major rearrangement of the star and its rapid movement along the Hertzsprung-Russell diagram. The size of the star's atmosphere increases even more, and it begins to intensively lose gas in the form of expanding stellar wind streams. The fate of the central part of the star depends entirely on its initial mass: the core of the star can end its evolution as a white dwarf (low-mass stars); in the event that its mass in the later stages of evolution exceeds the Chandrasekhar limit - as a neutron star (pulsar); if the mass exceeds the limit of Oppenheimer - Volkov - like a black hole. In the last two cases, the end of stellar evolution is accompanied by catastrophic events - supernova outbursts. The vast majority of stars, including the Sun, end their evolution by contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases by a factor of a hundred and the density becomes a million times higher than that of water, the star is called a white dwarf. It is deprived of sources of energy and, gradually cooling down, becomes dark and invisible. In stars more massive than the Sun, the pressure of degenerate electrons cannot stop the further compression of the nucleus, and the electrons begin to “press” into atomic nuclei, which leads to the transformation of protons into neutrons, between which there are no electrostatic repulsion forces. Such neutronization of matter leads to the fact that the size of the star, which, in fact, now represents one huge atomic nucleus, is measured in several kilometers, and the density is 100 million times higher than the density of water. Such an object is called a neutron star.
supermassive stars
After a star with a mass greater than five solar enters the stage of a red supergiant, its core begins to shrink under the influence of gravitational forces. As the compression increases, the temperature and density increase, and a new sequence of thermonuclear reactions begins. In such reactions, increasingly heavier elements are synthesized: helium, carbon, oxygen, silicon and iron, which temporarily restrains the collapse of the nucleus. Ultimately, as more and more heavy elements of the periodic table are formed, iron-56 is synthesized from silicon. At this stage, further thermonuclear fusion becomes impossible, since the iron-56 nucleus has a maximum mass defect and the formation of heavier nuclei with energy release is impossible. Therefore, when the iron core of a star reaches a certain size, the pressure in it is no longer able to withstand the gravity of the outer layers of the star, and an immediate collapse of the core occurs with the neutronization of its substance. What happens next is still unclear to the end, but, in any case, the ongoing processes in a matter of seconds lead to the explosion of a supernova of incredible power. The accompanying burst of neutrinos provokes a shock wave. Strong neutrino jets and a rotating magnetic field push out most of the material accumulated by the star - the so-called seating elements, including iron and lighter elements. The expanding matter is bombarded by neutrons escaping from the nucleus, capturing them and thereby creating a set of elements heavier than iron, including radioactive ones, up to uranium (and possibly even California). Thus, supernova explosions explain the presence of elements heavier than iron in the interstellar matter, which, however, is not the only possible way for their formation, for example, this is demonstrated by technetium stars. The blast wave and jets of neutrinos carry matter away from the dying star into interstellar space. Subsequently, as it cools and travels through space, this supernova material may collide with other space debris, and possibly participate in the formation of new stars, planets, or satellites. The processes that take place during the formation of a supernova are still being studied, and so far this issue is not clear. Also in question is the moment what actually remains of the original star. However, two options are being considered: neutron stars and black holes.
neutron stars
It is known that in some supernovae, strong gravity in the interior of the supergiant causes electrons to be absorbed by the atomic nucleus, where they merge with protons to form neutrons. This process is called neutronization. The electromagnetic forces separating nearby nuclei disappear. The core of a star is now a dense ball of atomic nuclei and individual neutrons. Such stars, known as neutron stars, are extremely small, no larger than big city, and have an unimaginably high density. Their orbital period becomes extremely short as the size of the star decreases (due to conservation of angular momentum). Some make 600 revolutions per second. For some of them, the angle between the radiation vector and the axis of rotation may be such that the Earth falls into the cone formed by this radiation; in this case, it is possible to record a radiation pulse that repeats at time intervals equal to the rotation period of the star. Such neutron stars were called "pulsars", and became the first discovered neutron stars.
Black holes
Not all supernovae become neutron stars. If the star has a large enough mass, then the collapse of the star will continue, and the neutrons themselves will begin to fall inward until its radius becomes less than the Schwarzschild radius. The star then becomes a black hole. The existence of black holes was predicted by the general theory of relativity. According to this theory, matter and information cannot leave black hole no way. Nonetheless, quantum mechanics probably makes exceptions to this rule possible. A number of open questions remain. Chief among them: "Are there any black holes at all?". Indeed, in order to say for sure that a given object is a black hole, it is necessary to observe its event horizon. This is impossible purely by definition of the horizon, but with the help of very long baseline radio interferometry it is possible to determine the metric near the object, as well as to fix fast, millisecond variability. These properties, observed in a single object, should definitively prove the existence of black holes.
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 actually represent protostars. Astronomers call them T-Taurus stars, after their prototype. By their properties - for example, luminosity - protostars are variable, since their existence has not yet entered a stable phase. Around many of them is a large amount of matter. Powerful wind currents emanate from T-type stars.
Protostars: the beginning of the life cycle
If matter falls on the surface of a protostar, it quickly burns out and turns into heat. As a result, the temperature of protostars is constantly increasing. When it rises so much that nuclear reactions are triggered in the center of the star, the protostar acquires the status of an ordinary one. With the onset of nuclear reactions, the star has a constant source of energy that supports its vital activity for a long time. How long the life cycle of a star in the universe will be depends on its initial size. However, it is believed that stars with a 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.
Stars of normal size
Each of the stars is a bunch of hot gas. In their depths, the process of development is constantly going on. nuclear energy. However, not all stars are like the Sun. One of the main differences is in color. Stars are not only yellow, but also bluish, reddish.
Brightness and luminosity
They also differ in such features as brilliance, brightness. How bright a star observed from the surface of the Earth will be depends not only on its luminosity, but also on the distance from our planet. Given the distance to the Earth, the stars can have completely different brightness. This indicator ranges from one ten-thousandth of the brilliance of the Sun to a brightness comparable to more than a million Suns.
Most of the stars are in the lower segment of this spectrum, being dim. In many ways, the Sun is an average, typical star. However, compared to others, it has a much greater brightness. A large number of dim stars can be observed even with the naked eye. The reason stars differ in brightness is because of their mass. Color, brilliance and change in brightness over time is determined by the amount of substance.
Attempts to explain the life cycle of stars
People have long tried to trace the life of the 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 value is inversely proportional to the radius of the star) until the increase in density slows down the contraction processes. Then the energy consumption will be higher than its income. At this point, the star will begin to cool rapidly.
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. At the same time, the provisions of his hypothesis were based not only on the theoretical conclusions available in astronomy, but also on data spectral analysis stars. Lockyer was convinced that chemical elements that take part in the evolution celestial bodies, consist of elementary particles - "protoelements". Unlike modern neutrons, protons and electrons, they do not have a common, but individual character. For example, according to Lockyer, hydrogen breaks down 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 and dwarf stars
Stars large sizes are the hottest and brightest. They are usually white or bluish in appearance. Despite the fact that they have gigantic dimensions, the fuel inside them burns out so quickly that they lose it in just a few million years.
Small stars, in contrast to giant ones, are usually not as bright. They have a red color, live long enough - for billions of years. But among the brightest stars in the sky there are also red and orange ones. An example is the star Aldebaran - the so-called "bull's eye", located in the constellation Taurus; as well as 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 once they expanded very much, and in their diameter they began to exceed the huge red stars (supergiants). The huge area allows these stars to radiate an order of magnitude more energy than the Sun. And this 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 of the size of the Sun. Such stars are called dwarfs. Each celestial body can go through these types of the life cycle of stars - the same star at different segments 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 inside. It turns into helium inside the nuclear core of the star. The sun has a huge amount of fuel, but even it is not infinite - over the past five billion years, half the reserve has been used up.
Lifetime of stars. Life cycle of stars
After the reserves of hydrogen inside the star are exhausted, serious changes come. The remaining hydrogen begins to burn not inside its core, but on the surface. In this case, the lifetime of the star is decreasing more and more. The cycle of stars, at least most of them, in this segment passes into the stage of a red giant. The size of the star becomes larger, and its temperature, on the contrary, becomes smaller. This is how most red giants, as well as supergiants, appear. This process is part of the overall sequence of changes that occur with the stars, which scientists called the evolution of stars. The life cycle of a star includes all its stages: in the end, all stars grow old 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 an 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 was said, depends on its composition and size. Stars like the Sun live between 10 and 16 billion years. Highly bright stars, like Sirius, live for a relatively short time - only a few hundred million years. The life cycle diagram of a star includes the following stages. This is a molecular cloud - the gravitational collapse of the cloud - the birth of a supernova - the evolution of a protostar - the end of the protostellar phase. Then the stages follow: the beginning of the stage of a young star - the middle of life - maturity - the stage of a red giant - a planetary nebula - the stage of a white dwarf. The last two phases are characteristic of small stars.
The nature of planetary nebulae
So, we have briefly considered the life cycle of a star. But what is it? Turning from a huge red giant into a white dwarf, sometimes stars shed their outer layers, and then the core of the star becomes naked. The gas envelope begins to glow under the influence of energy emitted by the star. This stage got its name due to the fact that the luminous gas bubbles in this shell often look like disks around planets. But in fact, they have nothing to do with the 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 the heavenly bodies.
star clusters
Astronomers are very fond of exploring. There is a hypothesis that all luminaries are born precisely in groups, and not one by one. Since the 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 these stars make, they begin 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 stars in 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 make beautiful photo, admire them exclusively beautiful view in the planetarium.
Our Sun has been shining for more than 4.5 billion years. At the same time, it constantly consumes hydrogen. It is absolutely clear that no matter how great its reserves were, but someday they will be exhausted. And what will happen to the light? There is an answer to this question. The life cycle of a star can be studied from other similar space formations. Indeed, in space there are real patriarchs, whose age is 9-10 billion years. And there are very young stars. They are no more than a few tens of millions of years old.
Therefore, by observing the state of the various stars with which the Universe is "strewn", one can understand how they behave over time. Here we can draw an analogy with an alien observer. He flew to Earth and began to study people: children, adults, old people. Thus, for absolutely short period time he understood what changes occur to people during their lives.
The Sun is currently a yellow dwarf
Billions of years will pass, and it will become a red giant - 2
And then turn into a white dwarf - 3
Therefore, it can be said with certainty that when the hydrogen reserves in the central part of the Sun are exhausted, the thermonuclear reaction will not stop. The zone where this process will continue will begin to move towards the surface of our luminary. But at the same time, gravitational forces will no longer be able to influence the pressure that is formed as a result of a thermonuclear reaction.
Consequently, the star will begin to grow in size and gradually turn into a red giant. This is a space object of a late stage of evolution. But it happens the same way early stage during star formation. Only in the second case does the red giant shrink and turn into main sequence star. That is, in one in which the reaction of the synthesis of helium from hydrogen takes place. In a word, with what the life cycle of a star begins, so it ends.
Our Sun will increase in size so much that it will swallow the nearest planets. These are Mercury, Venus and Earth. But you don't have to be afraid. The luminary will begin to die in a few billion years. During this time, dozens, and maybe hundreds of civilizations will change. A person will pick up a club more than once, and after millennia, he will again sit down at a computer. This is the usual cyclicity on which the entire universe is based.
But becoming a red giant doesn't mean the end. The thermonuclear reaction will throw the outer shell into space. And in the center there will be a helium core devoid of energy. Under the influence of gravitational forces, it will shrink and, in the end, will turn into an extremely dense space formation with a large mass. Such remnants of extinct and slowly cooling stars are called white dwarfs.
Our white dwarf will have a radius 100 times smaller than the radius of the Sun, and the luminosity will decrease by 10 thousand times. At the same time, the mass will be comparable to the current solar one, and the density will be more than a million times. There are a lot of such white dwarfs in our galaxy. Their number is 10% of total number stars.
It should be noted that white dwarfs are hydrogen and helium. But we will not climb into the wilds, but only note that with strong compression, gravitational collapse can occur. And this is fraught with a colossal explosion. At the same time, a supernova explosion is observed. The term "supernova" characterizes not the age, but the brightness of the flash. It's just that the white dwarf was not visible in the cosmic abyss for a long time, and suddenly a bright glow appeared.
Most of the exploding supernova scatters in space with great speed. And the rest central part shrinks into an even denser formation and is called neutron star. It is the end product of stellar evolution. Its mass is comparable to that of the sun, and its radius reaches only a few tens of kilometers. One cube cm neutron star can weigh millions of tons. There are quite a lot of such formations in space. Their number is about a thousand times less than ordinary suns, which are strewn with the night sky of the Earth.
I must say that the life cycle of a star is directly related to its mass. If it corresponds to the mass of our Sun or less than it, then at the end of life a white dwarf appears. However, there are luminaries that are tens and hundreds of times larger than the Sun.
When such giants shrink in the process of aging, they distort space and time in such a way that instead of a white dwarf, black hole. Its gravitational attraction is so strong that even those objects that move at the speed of light cannot overcome it. The size of the hole characterizes gravity radius. This is the radius of the sphere bounded by event horizon. It represents the space-time limit. Any cosmic body, having overcome it, disappears forever and never comes back.
There are many theories about black holes. All of them are based on the theory of gravity, since gravity is one of the most important forces in the universe. And its main quality is versatility. At least, today not a single space object has been discovered that does not have gravitational interaction.
There is an assumption that through a black hole you can get into a parallel world. That is, it is a channel to another dimension. Everything is possible, but any statement requires practical evidence. However, no mortal has yet been able to carry out such an experiment.
Thus, the life cycle of a star consists of several stages. In each of them, the luminary acts in a certain capacity, which is fundamentally different from the previous and future ones. This is the uniqueness and mystery outer space. When you get to know him, you involuntarily begin to think that a person also goes through several stages in his development. And the shell in which we exist now is only a transitional stage to some other state. But this conclusion, again, requires practical confirmation..