Stars are known to get their energy from reactions thermonuclear fusion, and every star sooner or later comes to a point when its thermonuclear fuel runs out. The higher the mass of a star, the faster it burns up everything it can and enters the final stage of its existence. Further events may follow different scenarios, which one depends primarily on the masses.
While the hydrogen “burns out” in the center of the star, a helium core is released in it, compressing and releasing energy. Subsequently, combustion reactions of helium and subsequent elements may begin in it (see below). The outer layers expand many times under the influence of increased pressure coming from the heated core, the star becomes a red giant.
Depending on the mass of the star, different reactions can occur in it. This determines what composition the star will have by the time the fusion dies out.

White dwarfs

For stars with masses up to about 10 MC, the core weighs less than 1.5 MC. After the completion of thermonuclear reactions, the radiation pressure ceases, and the core begins to shrink under the influence of gravity. It contracts until the pressure of the degenerate electron gas, due to the Pauli principle, begins to interfere. The outer layers are shed and dissipate, forming planetary nebula. The first such nebula was discovered by the French astronomer Charles Messier in 1764 and cataloged it under the number M27.
What emerges from the core is called a white dwarf. White dwarfs have a density greater than 10 7 g/cm 3 and a surface temperature of the order of 10 4 K. The luminosity is 2-4 orders of magnitude lower than the luminosity of the Sun. Thermonuclear fusion does not occur in it; all the energy emitted by it was accumulated earlier. Thus, white dwarfs slowly cool down and cease to be visible.
A white dwarf still has a chance to be active if it is part of a binary star and pulls the mass of a companion onto itself (for example, the companion became a red giant and filled its entire Roche lobe with its mass). In this case, either the synthesis of hydrogen in the CNO cycle can begin with the help of carbon contained in the white dwarf, ending with the release of the outer hydrogen layer (a “new” star). Or the mass of the white dwarf could grow so large that its carbon-oxygen component ignites in a wave of explosive combustion coming from the center. As a result, heavy elements are formed with the release large quantity energy:

12 C + 16 O → 28 Si + 16.76 MeV
28 Si + 28 Si → 56 Ni + 10.92 MeV

The star's luminosity increases strongly for 2 weeks, then rapidly decreases over another 2 weeks, after which it continues to decrease by approximately 2 times in 50 days. The main energy (about 90%) is emitted in the form of gamma rays from the decay chain of the nickel isotope. This phenomenon is called a type 1 supernova.
There are no white dwarfs with a mass of 1.5 or more solar masses. This is explained by the fact that for a white dwarf to exist, it is necessary to balance gravitational compression pressure of the electron gas, but this happens at masses of no more than 1.4 M C, this limitation is called the Chandrasekhar limit. The value can be obtained as the condition of equality of pressure forces to the forces of gravitational compression under the assumption that the electron momenta are determined by the uncertainty relation for the volume they occupy, and they move at a speed close to the speed of light.

Neutron stars

In the case of more massive (> 10 M C) stars, everything happens a little differently. High temperature in the core activates energy absorption reactions, such as the knocking of protons, neutrons and alpha particles from the cores, as well as the e-capture of high-energy electrons, compensating for the mass difference two cores. The second reaction creates an excess of neutrons in the nucleus. Both reactions lead to its cooling and general compression of the star. When the nuclear fusion energy runs out, the compression turns into an almost free fall of the shell onto the collapsing core. At the same time, the rate of thermonuclear fusion in the outer falling layers sharply accelerates, which leads to the emission of a huge amount of energy in a few minutes (comparable to the energy that light stars emit during their entire existence).
Due to its high mass, the collapsing core overcomes the pressure of the electron gas and contracts further. In this case, reactions p + e - → n + ν e occur, after which there are almost no electrons remaining in the nucleus that interfere with compression. Compression occurs to sizes of 10 − 30 km, corresponding to the density established by the pressure of the neutron degenerate gas. The matter falling onto the core receives a shock wave reflected from the neutron core and part of the energy released during its compression, which leads to a rapid ejection of the outer shell to the sides. The resulting object is called a neutron star. Most (90%) of the energy released from gravitational compression is carried away by neutrinos in the first seconds after the collapse. The above process is called a type 2 supernova explosion. The energy of the explosion is such that some of them are (rarely) visible to the naked eye even in daytime. The first supernova was recorded by Chinese astronomers in 185 AD. Currently, several hundred outbreaks are recorded per year.
The resulting neutron star has a density of ρ ~ 10 14 − 10 15 g/cm 3 . Conservation of angular momentum during star compression leads to very short orbital periods, usually ranging from 1 to 1000 ms. For ordinary stars such periods are impossible, because Their gravity will not be able to counteract the centrifugal forces of such rotation. A neutron star has a very large magnetic field, reaching 10 12 -10 13 Gas at the surface, which leads to strong electromagnetic radiation. A magnetic axis that does not coincide with the rotation axis leads to the fact that the neutron star sends periodic (with a rotation period) pulses of radiation in a given direction. Such a star is called a pulsar. This fact aided their experimental discovery and is used for detection. Detecting a neutron star using optical methods is much more difficult due to its low luminosity. The orbital period gradually decreases due to the transition of energy into radiation.
The outer layer of a neutron star consists of crystalline matter, mainly iron and its neighboring elements. Most of the rest of the mass is neutrons; pions and hyperons can be found in the very center. The density of the star increases towards the center and can reach values ​​noticeably greater than the density of nuclear matter. The behavior of matter at such densities is poorly understood. There are theories about free quarks, including not only the first generation, at such extreme densities of hadronic matter. Superconducting and superfluid states of neutron matter are possible.
There are 2 mechanisms for cooling a neutron star. One of them is the emission of photons, as everywhere else. The second mechanism is neutrino. It prevails as long as the core temperature is above 10 8 K. This usually corresponds to a surface temperature above 10 6 K and lasts 10 5 −10 6 years. There are several ways to emit neutrinos:

Black holes

If the mass of the original star exceeded 30 solar masses, then the core formed in the supernova explosion will be heavier than 3 M C. At this mass, the pressure of the neutron gas can no longer hold back gravity, and the core does not stop at the neutron star stage, but continues to collapse (however, experimentally detected neutron stars have masses of no more than 2 solar masses, not three). This time nothing will prevent the collapse, and a black hole is formed. This object has a purely relativistic nature and cannot be explained without general relativity. Despite the fact that matter, according to theory, has collapsed into a point - a singularity, the black hole has a non-zero radius, called the Schwarzschild radius:

R Ш = 2GM/s 2.

The radius marks the boundary of the black hole's gravitational field, which is insurmountable even for photons, called the event horizon. For example, the Schwarzschild radius of the Sun is only 3 km. Outside the event horizon, the gravitational field of a black hole is the same as that of an ordinary object of its mass. A black hole can only be observed by indirect effects, since it itself does not emit any noticeable energy.
Even though nothing can escape the event horizon, a black hole can still create radiation. In the quantum physical vacuum, virtual particle-antiparticle pairs are constantly being born and disappearing. The strong gravitational field of a black hole can interact with them before they disappear and absorb the antiparticle. If the total energy of the virtual antiparticle was negative, the black hole loses mass, and the remaining particle becomes real and receives energy sufficient to fly away from the field of the black hole. This radiation is called Hawking radiation and has a black body spectrum. A certain temperature can be attributed to it:

The effect of this process on the mass of most black holes is negligible compared to the energy they receive even from the cosmic microwave background radiation. The exception is relic microscopic black holes, which could have formed in the early stages of the evolution of the Universe. Small sizes speed up the evaporation process and slow down the process of mass gain. The final stages of evaporation of such black holes should end in an explosion. No explosions matching the description were ever recorded.
Matter falling into a black hole heats up and becomes a source of X-ray radiation, which serves as an indirect sign of the presence of a black hole. When matter falls into a black hole big moment momentum, it forms a rotating accretion disk around it, in which particles lose energy and angular momentum before falling into the black hole. In the case of a supermassive black hole, two distinct directions appear along the axis of the disk, in which the pressure of the emitted radiation and electromagnetic effects accelerate particles ejected from the disk. This creates powerful jets of substance in both directions, which can also be registered. According to one theory, this is how active galactic nuclei and quasars are structured.
A spinning black hole is a more complex object. With its rotation, it “captures” a certain region of space beyond the event horizon (“Lense-Thirring effect”). This region is called the ergosphere, its boundary is called the limit of staticity. The static limit is an ellipsoid that coincides with the event horizon at the two poles of the black hole's rotation.
Rotating black holes have an additional mechanism of energy loss through the transfer of energy to particles trapped in the ergosphere. This loss of energy is accompanied by a loss of angular momentum and slows down the rotation.

References

1. S.B.Popov, M.E.Prokhorov "Astrophysics of single neutron stars: radio-quiet neutron stars and magnetars" SAI MSU, 2002
2. William J. Kaufman "The Cosmic Frontiers of Relativity" 1977
3. Other Internet sources

December 20 10 g.

The Universe is a constantly changing macrocosm, where every object, substance or matter is in a state of transformation and change. These processes last for billions of years. Compared to duration human life this incomprehensible period of time is enormous. On a cosmic scale, these changes are quite fleeting. The stars that we now see in the night sky were the same thousands of years ago, when the Egyptian pharaohs could see them, but in fact all this time the change did not stop for a second physical characteristics heavenly bodies. Stars are born, live and certainly age - the evolution of stars goes on as usual.

The position of the stars of the constellation Ursa Major in different historical periods in the interval 100,000 years ago - our time and after 100 thousand years

Interpretation of the evolution of stars from the point of view of the average person

For the average person, space appears to be a world of calm and silence. In fact, the Universe is a giant physical laboratory where enormous transformations are taking place, during which the chemical composition, physical characteristics and structure of stars change. The life of a star lasts as long as it shines and gives off heat. However, such a brilliant state does not last forever. The bright birth is followed by a period of star maturity, which inevitably ends with the aging of the celestial body and its death.

Formation of a protostar from a gas and dust cloud 5-7 billion years ago

All our information about stars today fits within the framework of science. Thermodynamics gives us an explanation of the processes of hydrostatic and thermal equilibrium in which stellar matter resides. Nuclear and quantum physics provide insight into complex process nuclear fusion, thanks to which a star exists, emitting heat and giving light to the surrounding space. At the birth of a star, hydrostatic and thermal equilibrium is formed, maintained by its own energy sources. At the end of a brilliant stellar career, this balance is disrupted. A series of irreversible processes begins, the result of which is the destruction of the star or collapse - a grandiose process of instantaneous and brilliant death heavenly body.

A supernova explosion is a bright finale to the life of a star born in the early years of the Universe.

Changes in the physical characteristics of stars are due to their mass. The rate of evolution of objects is influenced by their chemical composition and, to some extent, by existing astrophysical parameters - rotation speed and state magnetic field. It is not possible to talk exactly about how everything actually happens due to the enormous duration of the processes described. The rate of evolution and the stages of transformation depend on the time of birth of the star and its location in the Universe at the time of birth.

The evolution of stars from a scientific point of view

Any star is born from a clump of cold interstellar gas, which, under the influence of external and internal gravitational forces, is compressed to the state gas ball. The process of compression of the gaseous substance does not stop for a moment, accompanied by a colossal release of thermal energy. The temperature of the new formation increases until thermonuclear fusion starts. From this moment, the compression of stellar matter stops, and a balance is reached between the hydrostatic and thermal states of the object. The Universe has been replenished with a new full-fledged star.

The main stellar fuel is the hydrogen atom as a result of a launched thermonuclear reaction.

In the evolution of stars, their sources of thermal energy are of fundamental importance. The radiant and thermal energy escaping into space from the surface of the star is replenished by cooling the inner layers of the celestial body. Constantly occurring thermonuclear reactions and gravitational compression in the bowels of the star make up for the loss. As long as there is sufficient nuclear fuel in the bowels of the star, the star glows with bright light and emits heat. As soon as the process of thermonuclear fusion slows down or stops completely, the mechanism of internal compression of the star is activated to maintain thermal and thermodynamic equilibrium. At this stage, the object is already emitting thermal energy, which is visible only in the infrared range.

Based on the processes described, we can conclude that the evolution of stars represents a consistent change in sources of stellar energy. IN modern astrophysics star transformation processes can be arranged in accordance with three scales:

• nuclear timeline;
• thermal period of a star's life;
• dynamic segment (final) of the life of a luminary.

In each individual case, the processes that determine the age of the star, its physical characteristics and the type of death of the object are considered. The nuclear timeline is interesting as long as the object is powered by its own heat sources and emits energy that is a product of nuclear reactions. The duration of this stage is estimated by determining the amount of hydrogen that will be converted into helium during thermonuclear fusion. The greater the mass of the star, the greater the intensity of nuclear reactions and, accordingly, the higher the luminosity of the object.

Sizes and masses of various stars, ranging from a supergiant to a red dwarf

The thermal time scale defines the stage of evolution during which a star expends all its thermal energy. This process begins from the moment when the last reserves of hydrogen are used up and nuclear reactions stop. To maintain the object's balance, a compression process is started. Stellar matter falls towards the center. In this case, the kinetic energy is converted into thermal energy, which is spent on maintaining the necessary temperature balance inside the star. Some of the energy escapes into outer space.

Considering the fact that the luminosity of stars is determined by their mass, at the moment of compression of an object, its brightness in space does not change.

A star on its way to the main sequence

Star formation occurs according to a dynamic time scale. Stellar gas falls freely inward toward the center, increasing the density and pressure in the bowels of the future object. The higher the density at the center of the gas ball, the higher the temperature inside the object. From this moment on, heat becomes the main energy of the celestial body. The higher the density and the higher the temperature, the more pressure in the depths of a future star. The free fall of molecules and atoms stops, and the process of compression of stellar gas stops. This state of an object is usually called a protostar. The object is 90% molecular hydrogen. When the temperature reaches 1800K, hydrogen passes into the atomic state. During the decay process, energy is consumed, and the temperature increase slows down.

The Universe consists of 75% molecular hydrogen, which during the formation of protostars turns into atomic hydrogen - the nuclear fuel of a star.

In this state, the pressure inside the gas ball decreases, thereby giving freedom to the compression force. This sequence is repeated each time all the hydrogen is ionized first, and then the helium is ionized. At a temperature of 10⁵ K, the gas is completely ionized, the compression of the star stops, and hydrostatic equilibrium of the object arises. The further evolution of the star will occur in accordance with the thermal time scale, much slower and more consistent.

The radius of the protostar has been decreasing from 100 AU since the beginning of formation. up to ¼ a.u. The object is in the middle of a gas cloud. As a result of the accretion of particles from the outer regions of the stellar gas cloud, the mass of the star will constantly increase. Consequently, the temperature inside the object will increase, accompanying the process of convection - the transfer of energy from the inner layers of the star to its outer edge. Subsequently, with increasing temperature in the interior of the celestial body, convection is replaced by radiative transfer, moving towards the surface of the star. At this moment, the luminosity of the object rapidly increases, and the temperature of the surface layers of the stellar ball also increases.

Convection processes and radiative transfer in a newly formed star before the onset of thermonuclear fusion reactions

For example, for stars with a mass identical to the mass of our Sun, the compression of the protostellar cloud occurs in just a few hundred years. As for the final stage of the formation of the object, the condensation of stellar matter has already been stretched for millions of years. The Sun is moving towards the main sequence quite quickly, and this journey will take hundreds of millions or billions of years. In other words, the greater the mass of the star, the longer gap time spent on the formation of a full-fledged star. A star with a mass of 15 M will move along the path to the main sequence for much longer - about 60 thousand years.

Main sequence phase

Although some fusion reactions are started at more low temperatures, the main phase of hydrogen combustion starts at a temperature of 4 million degrees. From this moment the main sequence phase begins. Comes into play new form reproduction of stellar energy - nuclear. The kinetic energy released during the compression of the object fades into the background. The achieved equilibrium ensures a long and quiet life for a star that finds itself in the initial phase of the main sequence.

The fission and decay of hydrogen atoms during a thermonuclear reaction occurring in the interior of a star

From this moment on, observation of the life of a star is clearly tied to the phase of the main sequence, which is an important part of the evolution of celestial bodies. It is at this stage that the only source of stellar energy is the result of hydrogen combustion. The object is in a state of equilibrium. As nuclear fuel is consumed, only the chemical composition of the object changes. The Sun's stay in the main sequence phase will last approximately 10 billion years. This is how long it will take for our native star to use up its entire supply of hydrogen. As for massive stars, their evolution occurs faster. By emitting more energy, a massive star remains in the main sequence phase for only 10-20 million years.

Less massive stars burn in the night sky for much longer. Thus, a star with a mass of 0.25 M will remain in the main sequence phase for tens of billions of years.

Hertzsprung–Russell diagram assessing the relationship between the spectrum of stars and their luminosity. Points on the diagram - location famous stars. The arrows indicate the displacement of stars from the main sequence into the giant and white dwarf phases.

To imagine the evolution of stars, just look at the diagram characterizing the path of a celestial body in the main sequence. Upper part the graphics look less object-saturated since this is where the massive stars are concentrated. This location is explained by their short life cycle. Of the stars known today, some have a mass of 70M. Objects whose mass exceeds the upper limit of 100M may not form at all.

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

A planet-like brown dwarf compared to a normal star (our Sun) and the planet Jupiter

At the bottom of the sequence are concentrated objects dominated by stars with a mass equal to the mass of our Sun and slightly more. The imaginary boundary between the upper and lower parts of the main sequence are objects whose mass is – 1.5M.

Subsequent stages of stellar evolution

Each of the options for the development of the state of a star is determined by its mass and the length of time during which the transformation of stellar matter occurs. However, the Universe is multifaceted and complex mechanism, so the evolution of stars can take other paths.

When traveling along the main sequence, a star with a mass approximately equal to the mass of the Sun has three main route options:

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

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

After the main sequence, the giant phase begins. By this time, the reserves of hydrogen in the bowels of the star are completely exhausted, the central region of the object is a helium core, and thermonuclear reactions shift to the surface of the object. Under the influence of thermonuclear fusion, the shell expands, but the mass of the helium core increases. An ordinary star turns into a red giant.

Giant phase and its features

In stars with low mass, the core density becomes colossal, turning stellar matter into a degenerate relativistic gas. If the mass of the star is slightly more than 0.26 M, an increase in pressure and temperature leads to the beginning of helium synthesis, covering the entire central region of the object. From this moment on, the temperature of the star increases rapidly. Main feature The process is that the degenerate gas does not have the ability to expand. Under the influence high temperature only the rate of helium fission increases, which is accompanied by an explosive reaction. At such moments we can observe a helium flash. The brightness of the object increases hundreds of times, but the agony of the star continues. The star transitions to a new state, where all thermodynamic processes occur in the helium core and in the discharged outer shell.

Structure of a solar-type main sequence star and a red giant with an isothermal helium core and a layered nucleosynthesis zone

This condition is temporary and not stable. Stellar matter is constantly mixed, and a significant part of it is ejected into the surrounding space, forming a planetary nebula. A hot core remains at the center, called a white dwarf.

For stars with large masses, the processes listed above are not so catastrophic. Helium combustion is replaced by the nuclear fission reaction of carbon and silicon. Eventually the star core will turn into star iron. The giant phase is determined by the mass of the star. The greater the mass of an object, the lower the temperature at its center. This is clearly not enough to trigger the nuclear fission reaction of carbon and other elements.

The fate of a white dwarf - a neutron star or a black hole

Once in the white dwarf state, the object is in an extremely unstable state. The stopped nuclear reactions lead to a drop in pressure, the core goes into a state of collapse. Energy released in in this case, is spent on the decay of iron into helium atoms, which further decays into protons and neutrons. The running process is developing at a rapid pace. The collapse of a star characterizes the dynamic segment of the scale and takes a fraction of a second in time. The combustion of nuclear fuel residues occurs explosively, releasing a colossal amount of energy in a split second. This is quite enough to blow up the upper layers of the object. Final stage A white dwarf is a supernova explosion.

The star's core begins to collapse (left). The collapse forms a neutron star and creates a flow of energy into the outer layers of the star (center). Energy released as a result of dumping outer layers stars during a supernova explosion (right).

The remaining superdense core will be a cluster of protons and electrons, which collide with each other to form neutrons. The Universe has been replenished with a new object - a neutron star. Because of high density the core becomes degenerate, the process of core collapse stops. If the star's mass were large enough, the collapse could continue until the remaining stellar matter finally fell into the center of the object, forming a black hole.

Explaining the final part of stellar evolution

For normal equilibrium stars, the described evolution processes are unlikely. However, the existence of white dwarfs and neutron stars proves the real existence of compression processes of stellar matter. Minor amount similar objects in the Universe indicates the transience of their existence. The final stage of the evolution of stars can be represented as a sequential chain of two types:

• normal star - red giant - shedding of outer layers - white dwarf;
• massive star – red supergiant – supernova explosion – neutron star or black hole – nothingness.

Diagram of the evolution of stars. Options for the continuation of the life of stars outside the main sequence.

It is quite difficult to explain the ongoing processes from a scientific point of view. Nuclear scientists agree that in the case of the final stage of stellar evolution, we are dealing with fatigue of matter. As a result of prolonged mechanical, thermodynamic influence, matter changes its physical properties. The fatigue of stellar matter, exhausted by long nuclear reactions, one can explain the appearance of a degenerate electron gas, its subsequent neutronization and annihilation. If all the listed processes take place from beginning to end, stellar matter ceases to be a physical substance - the star disappears in space, leaving nothing behind.

Interstellar bubbles and gas and dust clouds, which are the birthplace of stars, cannot be replenished only by disappeared and exploded stars. The Universe and galaxies are in an equilibrium state. Mass loss occurs constantly, the density of interstellar space decreases in one part outer space. Consequently, in another part of the Universe, conditions are created for the formation of new stars. In other words, the scheme works: if a certain amount of matter was lost in one place, in another place in the Universe the same amount of matter appeared in a different form.

In conclusion

By studying the evolution of stars, we come to the conclusion that the Universe is a gigantic rarefied solution in which part of the matter is transformed into molecules of hydrogen, which is building material for the stars. The other part dissolves in space, disappearing from the sphere of material sensations. A black hole in this sense is the place of transition of all material into antimatter. It is quite difficult to fully comprehend the meaning of what is happening, especially if, when studying the evolution of stars, we rely only on the laws of nuclear power, quantum physics and thermodynamics. Theory should be included in the study of this issue. relative probability, which allows for the curvature of space, allowing the transformation of one energy into another, one state into another.

Our Sun has been shining for more than 4.5 billion years. At the same time, it constantly consumes hydrogen. It is absolutely clear that no matter how large its reserves are, they will someday be exhausted. And what will happen to the luminary? There is an answer to this question. The life cycle of a star can be studied from other similar cosmic formations. After all, there are real patriarchs in space, whose age is 9-10 billion years. And there are very young stars. They are no more than several tens of millions of years old.

Consequently, by observing the state of the various stars with which the Universe is “strewn”, one can understand how they behave over time. Here we can draw an analogy with an alien observer. He flew to Earth and began to study people: children, adults, old people. Thus, in a very short period of time, he understood what changes happen to people throughout life.

The Sun is currently a yellow dwarf - 1
Billions of years will pass, and it will become a red giant - 2
And then it will turn into a white dwarf - 3

Therefore, we can say with all confidence that when the hydrogen reserves in the central part of the Sun are exhausted, the thermonuclear reaction will not stop. The zone where this process will continue will begin to shift towards the surface of our star. But at the same time, gravitational forces will no longer be able to influence the pressure that is generated as a result of the thermonuclear reaction.

As a consequence, 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 also happens at an early stage during star formation. Only in the second case does the red giant shrink and turn into main sequence star. That is, one in which the reaction of synthesis of helium from hydrogen takes place. In a word, where the life cycle of a star begins is where it ends.

Our Sun will increase in size so much that it will engulf nearby planets. These are Mercury, Venus and Earth. But don't be afraid. The star will begin to die in a few billion years. During this time, dozens, and maybe hundreds of civilizations will change. A person will pick up a club more than once, and after thousands of years he will sit down at a computer again. This is the usual cyclicity on which the entire Universe is based.

But becoming a red giant doesn't mean the end. The thermonuclear reaction will throw the outer shell into space. And in the center there will remain an energy-deprived helium core. Under the influence of gravitational forces, it will compress and, ultimately, turn into an extremely dense cosmic 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 its luminosity will decrease by 10 thousand times. In this case, the mass will be comparable to the current solar one, and the density will be a million times greater. There are a lot of such white dwarfs in our Galaxy. Their number is 10% of total number stars

It should be noted that white dwarfs are hydrogen and helium. But we will not go into the wilds, but will only note that with strong compression, gravitational collapse can occur. And this is fraught with a colossal explosion. In this case, a supernova explosion is observed. The term "supernova" does not describe the age, but the brightness of the flash. It’s just that the white dwarf was not visible for a long time in the cosmic abyss, and suddenly a bright glow appeared.

Most of the exploding supernova scatters through space at tremendous speed. And the remaining central part is compressed into an even denser formation and is called neutron star. It is the end product of stellar evolution. Its mass is comparable to that of the sun, and its radius reaches only a few tens of kilometers. One cube cm neutron star can weigh millions of tons. There are quite a lot of such formations in space. Their number is about a thousand times less than the ordinary suns with which the Earth's night sky is strewn.

It must be said that the life cycle of a star is directly related to its mass. If it matches the mass of our Sun or is less than it, then a white dwarf appears at the end of its life. However, there are luminaries that are tens and hundreds of times larger than the Sun.

When such giants shrink as they age, they distort space and time so much that instead of a white dwarf a white dwarf appears. black hole. Its gravitational attraction is so strong that even those objects that move at the speed of light cannot overcome it. The dimensions of the hole are characterized by gravitational radius. This is the radius of the sphere bounded by event horizon. It represents a space-time limit. Any cosmic body, having overcome it, disappears forever and never returns 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 of the Universe. And its main quality is versatility. At least, today not a single space object has been discovered that lacks gravitational interaction.

There is an assumption that through black hole you can get into parallel world. That is, it is a channel to another dimension. Anything is possible, but any statement requires practical evidence. However, no mortal has yet been able to carry out such an experiment.

Thus, the life cycle of a star consists of several stages. In each of them, the luminary appears in a certain capacity, which is radically different from previous and future ones. This is the uniqueness and mystery of outer space. Getting to know him, you involuntarily begin to think that a person also goes through several stages in his development. And the shell in which we exist now is only a transitional stage to some other state. But this conclusion again requires practical confirmation..

> Life cycle of a star

Description life and death of stars: stages of development with photos, molecular clouds, protostar, T Tauri, main sequence, red giant, white dwarf.

Everything in this world is evolving. Any cycle begins with birth, growth and ends with death. Of course, stars have these cycles in a special way. Let us at least remember that their time frames are larger and are measured in millions and billions of years. In addition, their death carries certain consequences. What does it look like life cycle of stars?

The first life cycle of a star: Molecular clouds

Let's start with the birth of a star. Imagine a huge cloud of cold molecular gas that can quietly exist in the Universe without any changes. But suddenly a supernova explodes not far from it or it collides with another cloud. Due to such a push, the destruction process is activated. It is divided into small parts, each of which is retracted into itself. As you already understand, all these groups are preparing to become stars. Gravity heats up the temperature, and the stored momentum maintains the rotation process. The lower diagram clearly demonstrates the cycle of stars (life, stages of development, transformation options and death of a celestial body with a photo).

Second life cycle of a star: Protostar

The material condenses more densely, heats up and is repelled by gravitational collapse. Such an object is called a protostar, around which a disk of material forms. The part is attracted to the object, increasing its mass. The remaining debris will group and create a planetary system. Further development of the star all depends on mass.

Third life cycle of a star: T Taurus

When material hits a star, a huge amount of energy is released. The new stellar stage was named after the prototype - T Tauri. It is a variable star located 600 light years away (near).

It can reach great brightness because the material breaks down and releases energy. But the central part does not have enough temperature to support nuclear fusion. This phase lasts 100 million years.

Fourth life cycle of a star:Main sequence

At a certain moment, the temperature of the celestial body rises to the required level, activating nuclear fusion. All stars go through this. Hydrogen transforms into helium, releasing enormous heat and energy.

The energy is released as gamma rays, but due to the slow motion of the star, it falls with the same wavelength. Light is pushed out and comes into conflict with gravity. We can assume that an ideal balance is created here.

How long will she be in the main sequence? You need to start from the mass of the star. Red dwarfs (half the mass of the sun) can burn through their fuel supply for hundreds of billions (trillions) of years. Average stars (like ) live 10-15 billion. But the largest ones are billions or millions of years old. See what the evolution and death of stars of different classes looks like in the diagram.

Fifth life cycle of a star: Red giant

During the melting process, hydrogen runs out and helium accumulates. When there is no hydrogen left at all, all nuclear reactions stop, and the star begins to shrink due to gravity. The hydrogen shell around the core heats up and ignites, causing the object to grow 1,000 to 10,000 times larger. At a certain moment, our Sun will repeat this fate, increasing to the Earth’s orbit.

Temperature and pressure reach a maximum and helium fuses into carbon. At this point the star shrinks and ceases to be a red giant. With greater massiveness, the object will burn other heavy elements.

Sixth life cycle of a star: White dwarf

A solar-mass star doesn't have enough gravitational pressure to fuse the carbon. Therefore, death occurs with the end of helium. The outer layers are ejected and a white dwarf appears. It starts out hot, but after hundreds of billions of years it cools down.

Evolution of Stars of Different Masses

Astronomers cannot observe the life of one star from beginning to end, because even the shortest-lived stars exist for millions of years - longer than the life of all humanity. Changes over time in physical characteristics and chemical composition stars, i.e. stellar evolution, astronomers study by comparing the characteristics of many stars located on different stages evolution.

Physical patterns connecting the observed characteristics of stars are reflected in the color-luminosity diagram - the Hertzsprung - Russell diagram, on which the stars form separate groups - sequences: the main sequence of stars, sequences of supergiants, bright and faint giants, subgiants, subdwarfs and white dwarfs.

For most of its life, any star is on the so-called main sequence of the color-luminosity diagram. All other stages of the star's evolution before the formation of a compact remnant take no more than 10% of this time. This is why most of the stars observed in our Galaxy are modest red dwarfs with the mass of the Sun or less. The main sequence contains about 90% of all observed stars.

The lifespan of a star and what it turns into at the end life path, is completely determined by its mass. Stars with masses greater than the Sun live much less than the Sun, and the lifetime of the most massive stars is only millions of years. For the vast majority of stars, the lifetime is about 15 billion years. After a star exhausts its energy sources, it begins to cool and contract. The end product of stellar evolution is compact, massive objects whose density is many times greater than that of ordinary stars.

Stars different masses end up in one of three states: white dwarfs, neutron stars or black holes. If the mass of the star is small, then the gravitational forces are relatively weak and the compression of the star (gravitational collapse) stops. It transitions to a stable white dwarf state. If the mass exceeds critical value, compression continues. At very high densities, electrons combine with protons to form neutrons. Soon, almost the entire star consists of only neutrons and has such an enormous density that the huge stellar mass is concentrated in a very small ball with a radius of several kilometers and the compression stops - a neutron star is formed. If the mass of the star is so great that even the formation of a neutron star will not stop the gravitational collapse, then the final stage of the star’s evolution will be a black hole.