Federal Agency for Education
GOU VPO
Ufa State Academy of Economics and Service
department of Physics
TEST
in the discipline "Concepts of modern natural science"
on the topic "Stars and their evolution"
Completed by: Lavrinenko R.S.
group SZ-12
Checked by: A.V. Altayskaya
Ufa-2010
Introduction ………………………………………………………………………… ... 3
Stages of evolution of stars …………………………………………………………… 5
Characteristics and chemical composition of stars ……………………… ................... 11
Forecast of the evolution of the Sun ………………………………………… ................... 20
Sources of thermal energy of stars …………………………………… ......... 21
Conclusion ……………………………………………………… ..............
Literature…………………………………………………………………………
Introduction
On a clear moonless night, about 3,000 stars can be seen above the horizon with the naked eye. And every time, looking at the starry sky, we ask ourselves the question - what are the stars? A cursory glance will find similarities between stars and planets. After all, the planets, when observed with a simple eye, are visible as luminous points of various brightness. However, already several millennia before us, attentive observers of the sky - shepherds and farmers, navigators and participants in caravan crossings - came to the conviction that stars and planets are phenomena of different nature. The planets, like the Moon and the Sun, change their position in the sky, move from one constellation to another and manage to travel a considerable distance in a year, while the stars are stationary relative to one another. Even deep old people see the outlines of constellations exactly the same as they saw them in childhood.
Stars cannot belong to the solar system. If they were approximately at the same distance as the planets, then it would be impossible to find an explanation for their apparent immobility. It is natural to assume that stars also move in space, but they are far from us, that their apparent movement is negligible. The illusion of immobility of the stars is created. But if the stars are so far away, then with an apparent brightness comparable to the apparent brightness of the planets, they must study many times more powerfully than the planets. This line of reasoning led to the idea that stars are bodies similar in nature to the Sun. This idea was defended by Giordano Bruno. But the question was finally resolved after two discoveries. The first was made by Halley in 1718. He showed the convention of the traditional name "fixed stars". To clarify the constant precession, he compared his contemporary catalogs of stars with those of antiquity, and above all with the catalog of Hipparchus (about 129 BC) - the first star catalog, which is mentioned in historical documents and with the catalog in Ptolemy's "Almagest 1" (AD 138). Against the background of a uniform picture, a regular shift of all stars, Halley discovered an amazing fact: "Three stars: ... or the Eye of Taurus, Aldebaran, Sirius and Arcturus directly contradicted this rule." So the stars' own movement was discovered. It received final recognition in the 70s of the 18th century, after the measurements of the proper motions of dozens of stars by the German astronomer Tobias Mayer and the English astronomer Neville Maskelyne. The second discovery was made in 1824 by Joseph Fraunhofer, making the first observations of the spectra of stars. Further, detailed studies of the spectra of stars led to the conclusion that stars, like the Sun, consist of gas with a high temperature, and also that the spectra of all stars can be distributed into several classes and the spectrum of the Sun belongs to one of these classes. It follows from this that the light of the stars is of the same nature as the light of the Sun.
The sun is one of the stars. This is a very close star to us, with which the Earth is physically connected, around which it moves. But there are a lot of stars, they have different brilliance, different colors, they radiate a huge amount of energy into space and therefore, losing this energy, they cannot but change: they must go through some kind of evolutionary path.
Stages of evolution of stars
Stars are immense plasma systems in which physical characteristics, internal structure and chemical composition change over time. The time of stellar evolution is very long, and it is not possible to directly trace the evolution of a particular star. This is compensated by the fact that each of the many stars in the sky goes through some stage of evolution. Summarizing the observations, it is possible to restore the general direction of stellar evolution (according to the Hertzsprung - Russell diagram (Figure 1), it is displayed by the main sequence and by deviation from it up and down).
Figure 1. Hertzsprung-Russell diagram
On the Hertzsprung-Russell diagram, the stars are unevenly distributed. About 90% of the stars are concentrated in a narrow band that crosses the diagram diagonally. This strip is called the main sequence. Its upper end is located in the area of \u200b\u200bbright blue stars. The difference in the population of stars located on the main sequence and regions adjacent to the main sequence is several orders of magnitude. The reason is that the main sequence stars are in the hydrogen burning stage, which makes up the bulk of the star's lifetime. The sun is on the main sequence. The next most populous regions after the main sequence are white dwarfs, red giants, and red super-giants. Red giants and supergiants are mostly stars in the burning stage of helium and heavier nuclei.
The modern theory of the structure and evolution of stars explains the general course of stellar evolution in good agreement with observational data.
The main phases in the evolution of a star are its birth (star formation); a long period of (usually stable) existence of a star as an integral system in hydrodynamic and thermal equilibrium; and, finally, the period of her "death", i.e. irreversible imbalance, which leads to the destruction of the star or to its catastrophic contraction.
According to the generally accepted hypothesis of a gas and dust cloud, a star is born as a result of gravitational compression of an interstellar gas and dust cloud. As such a cloud thickens, a protostar is first formed, the temperature in its center steadily increases until it reaches the limit necessary for the speed of the thermal motion of particles to exceed the threshold, after which protons are able to overcome the macroscopic forces of mutual electrostatic repulsion and enter into a thermonuclear fusion reaction.
As a result of a multistage thermonuclear fusion reaction, a helium nucleus (2 protons + 2 neutrons) is ultimately formed from four protons and a whole fountain of various elementary particles is released. In the final state, the total mass of the formed particles is less than the mass of the four initial protons, which means that free energy is released during the reaction. Because of this, the inner core of a newborn star quickly heats up to ultra-high temperatures, and its excess energy begins to splash out towards its less hot surface - and out. At the same time, the pressure in the center of the star begins to rise. Thus, by “burning” hydrogen in the course of a thermonuclear reaction, the star does not allow the forces of gravitational attraction to compress itself to a superdense state, opposing continuously renewed internal thermal pressure to gravitational collapse, as a result of which a stable energy equilibrium arises. Stars that are actively burning hydrogen are said to be in the "main phase" of their life cycle or evolution. The transformation of some chemical elements into others inside a star is called nuclear fusion or nucleosynthesis.
In particular, the Sun has been in 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 star for another 5.5 billion years. The more massive the star, the more hydrogen fuel it has, but to counteract the forces of gravitational collapse, it has to burn hydrogen with an intensity that exceeds the growth rate of hydrogen reserves as the star's mass increases. For stars with a mass 15 times the solar mass, the time of stable existence is only about 10 million years. This is an extremely insignificant time by cosmic standards, because the time allotted for our Sun is 3 orders of magnitude higher - about 10 billion years.
Sooner or later, any star will use up all the hydrogen available for combustion in its thermonuclear furnace. It also depends on the mass of the star. The sun (and all stars not exceeding it in mass by more than eight times) end my life in a very banal way. As the reserves of hydrogen in the interior of the star are depleted, the forces of gravitational compression, patiently waiting for this hour from 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 thicken. This process leads to a twofold effect: The temperature in the layers immediately around the star's core rises to a level at which the hydrogen contained there enters into a thermonuclear fusion reaction to form helium. At the same time, the temperature in the core itself, which now consists of almost one helium, rises so much that helium itself - a kind of "ash" of the decaying primary nucleosynthesis reaction - enters into a new thermonuclear fusion reaction: one carbon nucleus is formed from three helium nuclei. This secondary reaction of thermonuclear fusion, fueled by the products of the primary reaction, is one of the key moments in the life cycle of stars.
With the secondary combustion of helium in the core of the star, so much energy is released that the star literally begins to swell. In particular, the shell of the Sun at this stage of life will expand beyond the orbit of Venus. In this case, the total radiation energy of the star remains approximately at the same level as during the main phase of its life, but since this energy is now radiated 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 a red giant.
For stars of the class of the Sun, after the depletion of the fuel that feeds the secondary reaction of nucleosynthesis, the stage of gravitational collapse begins again - this time the final one. The temperature inside the core is no longer able to rise to the level required for the next level of thermonuclear reaction to begin. Therefore, the star contracts until the forces of gravitational attraction are balanced by the next force barrier. Its role is played by the pressure of a degenerate electron gas. Electrons, which up to this stage played the role of unemployed extras in the evolution of a star, without participating in nuclear fusion reactions and freely moving between nuclei in the process of fusion, at a certain stage of compression are 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 down completely.
Stars more massive than the Sun will have a far more spectacular ending. After the combustion of helium, their mass during compression turns out to be sufficient to heat the core and shell to temperatures required to trigger the next nucleosynthesis reactions - carbon, then silicon, magnesium - and so on, as the nuclear masses grow. Moreover, at the beginning of each new reaction in the core of the star, the previous one continues in its envelope. In fact, all the chemical elements up to iron, of which the Universe is composed, 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 temperatures and pressures, since an influx of external energy is required both for its decay and for adding additional nucleons to it. As a result, the massive star gradually accumulates an iron core inside itself, which is not capable of serving as fuel for any further nuclear reactions.
As soon as the temperature and pressure inside the nucleus reach a certain level, the 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 it takes only a few seconds) free electrons, throughout the previous evolution of the star, literally dissolve in the protons of iron nuclei. The entire matter of the star's core turns into a continuous bunch of neutrons and begins to rapidly contract in gravitational collapse, since the pressure of the degenerate electron gas opposing it falls to zero. The outer shell of the star, from under which all support is knocked out, collapses towards the center. The collision energy of the collapsed outer shell with the neutron core is so high that it bounces and scatters in all directions from the core with great speed - and the star literally explodes in a blinding supernova explosion. In a matter of seconds, during a supernova explosion, more energy can be released into space than all the stars of the galaxy combined during the same time.
After a supernova explosion and the expansion of the envelope, in stars with a mass of about 10-30 solar masses, the continuing gravitational collapse leads to the formation of a neutron star, the substance of which is compressed until the pressure of degenerate neutrons begins to make itself felt. In other words, now neutrons (just as electrons did before) begin to resist further compression, demanding living space for themselves. This usually occurs when the star reaches about 15 km in diameter. The result is a rapidly rotating neutron star that emits electromagnetic pulses at its rotational frequency; such stars are called pulsars. Finally, if the mass of the star's core exceeds 30 solar masses, nothing can stop its further gravitational collapse, and as a result of a supernova explosion, a black hole is formed.
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Thermonuclear fusion in the bowels of stars
At this time, for stars with a mass greater than 0.8 times the mass of the Sun, the core becomes transparent for radiation, and radiant energy transfer in the core will prevail, while the upper envelope remains convective. Nobody knows for certain which stars of lower mass arrive on the main sequence, since the time spent by these stars in the category of young ones exceeds the age of the Universe. All our ideas about the evolution of these stars are based on numerical calculations.
As the star shrinks, the pressure of the degenerate electron gas begins to increase, and at some radius of the star, this pressure stops the growth of the central temperature, and then begins to decrease it. And for stars less than 0.08, this turns out to be fatal: the energy released during nuclear reactions will never be enough to cover the cost of radiation. Such under-stars are called brown dwarfs, and their fate is constant compression until the pressure of the degenerate gas stops it, and then gradual cooling with the cessation of all nuclear reactions.
Young stars of intermediate mass
Young stars of intermediate mass (from 2 to 8 solar masses) evolve qualitatively in the same way as their smaller sisters, with the exception that they have no convective zones up to the main sequence.
Objects of this type are associated with the so-called. Herbit stars Ae \\ Be as irregular variables of spectral type B-F5. They also have bipolar jet disks. The outflow rate, luminosity, and effective temperature are substantially higher than those for τ Taurus, so they effectively heat and disperse the remnants of the protostellar cloud.
Young stars with masses greater than 8 solar masses
In fact, these are already normal stars. While the mass of the hydrostatic core was accumulating, the star managed to skip all intermediate stages and heat up nuclear reactions to such an extent that they compensated for the radiation losses. These stars have an outflow of mass and luminosity is so great that it not only stops the collapse of the remaining outer regions, but pushes them back. Thus, the mass of the formed star is noticeably less than the mass of the protostellar cloud. Most likely, this explains the absence in our galaxy of stars greater than 100-200 solar masses.
Mid-life of a star
Among the formed stars, there is a huge variety of colors and sizes. In spectral type, they range from hot blue to cold red, in mass - from 0.08 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, depending on the parameters of the star. That is, we are talking, in fact, only about changing the parameters of the star.
What happens next again depends on the mass of the star.
Later years and the death of the stars
Old stars with low mass
To date, it is not known for certain what happens to light stars after the depletion of their hydrogen reserves. Since the age of the universe is 13.7 billion years, which is not enough to deplete the supply of hydrogen fuel, modern theories are based on computer simulations of the processes occurring in such stars.
Some stars can only synthesize helium in some active regions, which causes instability and strong solar 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.
But a star with a mass of less than 0.5 solar will never be able to synthesize helium even after the reactions with the participation of hydrogen in the core cease. Their stellar shell is not massive enough to overcome the pressure produced by the core. These stars include red dwarfs (such as Proxima Centauri), which have lived on the main sequence for hundreds of billions of years. After the termination of thermonuclear reactions in their core, they, gradually cooling down, will continue to emit weakly in the infrared and microwave ranges of the electromagnetic spectrum.
Medium stars
When a star reaches an average size (from 0.4 to 3.4 solar masses) of the red giant phase, its outer layers continue to expand, the core shrinks, and the reactions of carbon synthesis from helium begin. The fusion releases a lot of energy, giving the star a temporary respite. 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, which include changes in size, surface temperature, and energy release. The energy release is shifted towards low frequency radiation. All this is accompanied by an increasing loss of mass due to strong solar winds and intense pulsations. The stars in this phase are named late-type stars, OH -IR stars or World-like stars, depending on their exact 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 envelope and cools as it moves away from the star, allowing dust particles and molecules to form. The strong infrared radiation of the central star in such envelopes forms ideal conditions for the activation of masers.
Helium combustion reactions are very temperature sensitive. This sometimes leads to great instability. Violent pulsations occur, which ultimately impart enough kinetic energy to the outer layers to be ejected and turn into a planetary nebula. In the center of the nebula, the core of the star remains, which, while cooling, turns into a helium white dwarf, usually having a mass of up to 0.5-0.6 solar and a diameter of the order of the Earth's diameter.
White dwarfs
The overwhelming majority of stars, including the Sun, end their evolution, contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases a hundred times and the density becomes a million times that of water, the star is called a white dwarf. It is devoid of energy sources and, gradually cooling down, becomes dark and invisible.
In stars more massive than the Sun, the pressure of degenerate electrons cannot contain the compression of the core, and it continues until most of the particles turn into neutrons packed so tightly that the size of the star is measured in kilometers, and the density is 100 million times the density water. Such an object is called a neutron star; its equilibrium is maintained by the pressure of the degenerate neutron matter.
Supermassive stars
After the outer layers of a star, with a mass greater than five solar masses, scattered to form a red supergiant, the core begins to shrink due to gravitational forces. As the compression proceeds, the temperature and density increase, and a new sequence of thermonuclear reactions begins. In such reactions, heavy elements are synthesized, 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. Up to this point, the synthesis of elements released a large amount of energy, but it is the iron -56 nucleus that has the maximum mass defect and the formation of heavier nuclei is disadvantageous. Therefore, when the iron core of a star reaches a certain value, the pressure in it is no longer able to withstand the colossal force of gravity, and an immediate collapse of the core occurs with neutronization of its matter.
What happens next is not entirely clear. But whatever it is, it in a matter of seconds leads to a supernova explosion of incredible power.
The accompanying neutrino burst provokes a shock wave. Strong jets of neutrinos and a rotating magnetic field expel most of the material accumulated by the star - the so-called seating elements, including iron and lighter elements. The scattering matter is bombarded by neutrons ejected from the nucleus, capturing them and thereby creating a set of elements heavier than iron, including radioactive ones, up to uranium (and possibly even to californium). Thus, supernova explosions explain the presence of elements heavier than iron in interstellar matter.
The blast wave and jets of neutrinos carry material away from the dying star into interstellar space. Subsequently, moving through space, this supernova material can collide with other space debris, and possibly participate in the formation of new stars, planets or satellites.
The processes taking place during the formation of a supernova are still being studied, and so far there is no clarity on this issue. It is also questionable what actually remains of the original star. However, two options are being considered:
Neutron stars
It is known that in some supernovae, strong gravity in the interior of a supergiant forces electrons to fall onto the atomic nucleus, where they merge with protons to form neutrons. The electromagnetic forces separating nearby nuclei disappear. The star's core is now a dense ball of atomic nuclei and individual neutrons.
Such stars, known as neutron stars, are extremely small - no more than the size of a large city - and have an unimaginably high density. Their period of revolution becomes extremely short as the size of the star decreases (due to the conservation of angular momentum). Some make 600 revolutions per second. When the axis connecting the north and south magnetic poles of this rapidly rotating star points to the Earth, a pulse of radiation can be recorded repeating at intervals equal to the period of the star's revolution. Such neutron stars were called "pulsars" and became the first neutron stars to be discovered.
Black holes
Not all supernovae become neutron stars. If the star has a sufficiently large 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. After that, the star becomes a black hole.
The existence of black holes was predicted by general relativity. According to general relativity, matter and information cannot leave a black hole under any conditions. However, quantum mechanics makes possible exceptions to this rule.
A number of open questions remain. Chief among them: "Are there 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. All attempts to do this have ended in failure. But there is still hope, since some objects cannot be explained without attracting accretion, and accretion onto an object without a solid surface, but the very existence of black holes does not prove this.
The questions are also open: is it possible for a star to collapse directly into a black hole, bypassing a supernova? Are there supernovae that will later become black holes? What is the exact effect of the initial mass of a star on the formation of objects at the end of its life cycle?
Each of us at least once in his life looked into the starry sky. 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 dimensions in the Universe are colossal. We rarely think about the fact that the evolution of galaxies and stars is constantly taking place before our eyes. Every object in endless space is a consequence of certain physical processes. Galaxies, stars, and even planets have major phases of development.
Our planet and we are all dependent 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 in millions and billions of years? In this regard, it is curious to know more about what are the stages of the evolution of astronomical objects, where the 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 is, for the most part, well studied. In space, the laws of physics are unshakable, which help to understand the origin of space objects. In this case, it is accepted 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, by cosmic standards, is lightning fast. For space, moments pass from the birth of a star to its death. Great distances create the illusion of the constancy of the universe. A star that flared up in the distance shines for us for billions of years, while it may no longer exist.
The theory of the evolution of galaxies and stars is a development of the Big Bang theory. The doctrine of the birth of stars and the emergence of stellar systems differs in 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.
Studying the life cycle of stars, you can use the example of the closest star to us. The sun is one of a hundred trillion 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 allow us to understand in detail how other stars are arranged, how quickly these gigantic heat sources are depleted, what are the stages of a star's development and what will be the final 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 contraction and expansion. Compression of cosmic gas in clouds arose under the influence of its own gravity and similar processes in new stars in the vicinity. The expansion arose from the internal pressure of the interstellar gas and from the magnetic fields inside the gas cloud. The cloud rotated freely around its center of mass.
The gas clouds formed after the explosion are 98% composed of atomic and molecular hydrogen and helium. Only 2% in this massif are dust and solid microscopic particles. Previously it was believed that in the center of any star lies the 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. Light, together with a part of the released energy, spreads outward, creating a subzero temperature and a low pressure zone inside a dense accumulation of gas. While in this state, the cosmic gas is rapidly compressed, the influence of the forces of gravitational attraction leads to the fact that the particles begin to form stellar matter. When a gas accumulation is dense, intense compression causes a star cluster to form. When the size of the gas cloud is small, the compression results in 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 a protostar. Slow compression occurs already 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 temperatures leads to the formation of a future star of its own center of gravity.
In this state, the protostar remains for millions of years, slowly giving off heat and gradually shrinking, decreasing in size. As a result, the contours of a new star are outlined, and the density of its matter becomes comparable to the density of water.
The average density of our star is 1.4 kg / cm3 - almost the same as the density of water in the salty Dead Sea. In the center, the Sun has a density of 100 kg / cm3. Stellar matter is not in a liquid state, but in the form of plasma.
Under the influence of enormous pressure and temperature of about 100 million K, thermonuclear reactions of the hydrogen cycle begin. The compression stops, the mass of the object increases when the energy of gravity is converted into a thermonuclear combustion of hydrogen. From this moment on, the new star, emitting energy, begins to lose mass.
The above version of the formation of a star 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 a few new stars have been observed. On the scale of the Universe, this figure can be increased hundreds and thousands of times.
For most of their life, protostars are hidden from the human eye by a dusty shell. Radiation from the core can only be observed in the infrared range, 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, whose radiation temperature was 700 degrees Kelvin. Subsequently, it turned out that the birthplace of protostars are compact sources that are available not only in our galaxy, but also in other corners of the Universe far from us. In addition to infrared radiation, the birthplaces of new stars are marked by intense radio signals.
The process of studying and the diagram of the evolution of stars
The whole process of knowing the stars can be roughly 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, how long the light goes from it, gives an idea of \u200b\u200bwhat happened to the star throughout this time. After a person learned to measure the distance to distant stars, it became clear that stars are the same suns, only of different sizes and with different destinies. Knowing the distance to the star, the process of thermonuclear fusion of the star can be traced by the level of light and the amount of emitted energy.
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 were able to study the nature of starlight. This device can determine and measure the gas composition of stellar matter, which a star possesses at different stages of its existence.
By studying the spectral analysis of the energy of the Sun and other stars, scientists have come 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 (up to iron) as our planet. The difference is only in the amount of certain elements and in the processes taking place on the Sun and inside the earth's firmament. This is what distinguishes stars from other objects in the universe. The origin of stars should also be viewed in the context of another physical discipline, quantum mechanics. According to this theory, the matter that determines the 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 our star and many other stars is only two elements - hydrogen and helium. A theoretical model describing the structure of a star will make it possible 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. Hot gas is a combination of atoms that are loosely bound to each other. Millions of years after the formation of a star, the cooling of the surface layer of stellar matter begins. The star gives off most of its energy to outer space, decreasing or increasing in size. Heat and energy transfer occurs from the interior of the star to the surface, affecting the intensity of radiation. In other words, one and the same star looks different at different periods of its existence. Thermonuclear processes based on hydrogen cycle reactions promote the conversion 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 does thermonuclear nuclear fusion not end with the explosion of such a reactor? The thing is that the forces of the gravitational field in it can keep the stellar matter within the stabilized volume. From this, an unambiguous conclusion can be drawn: any star is a massive body that retains its size due to the balance between the forces of gravity and the energy of thermonuclear reactions. The result of this ideal natural design is a heat source that can work 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 as it does now. Consequently, our star has changed little, despite the fact that the scale of radiated heat and solar energy is colossal - more than 3-4 million tons every second.
It is not difficult to calculate how much over the years of its existence our star has lost weight. This will be a huge figure, however, due to its enormous mass and high density, such losses on the scale of the Universe look negligible.
Stellar evolution stages
The fate of the star in 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 towards an increase in the size of a star, it means that the main source for thermonuclear fusion has dried up. The long final path of transformation of the celestial body began.
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 hydrogen reserves and live their lives quite calmly.
The majority of such stars in the Universe and our star - a yellow dwarf - belongs to them. With the onset of old age, the 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 in comparison with the Sun, but also the youngest. Astrophysicists and astronomers call these stars blue supergiants. In the end, they will face the same fate that trillions of other stars are experiencing. First, a rapid birth, a brilliant and ardent life, after which a period of slow decay sets in. Stars as large as the sun have long life cycles in the main sequence (in the middle).
Using data on the mass of a star, one can assume its evolutionary path of development. A clear illustration of this theory is the evolution of our star. Nothing is everlasting. As a result of thermonuclear fusion, hydrogen is converted into helium, therefore, its initial reserves are consumed and reduced. Sometime, not very soon, these stocks 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 a star can still last approximately 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 contract. 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 condition is called collapse, which can be caused by the passage of thermonuclear reactions in the upper layers of the star. As a result of high pressure, thermonuclear reactions are triggered with the participation of helium.
The reserves of hydrogen and helium in this part of the star will last for another millions of years. It will not be very soon that the depletion of hydrogen reserves will lead to an increase in radiation intensity, to an increase in the size of the envelope and the size of the star itself. As a consequence, our Sun will become very large. If we imagine this picture after tens of billions of years, then instead of a dazzling bright disk, a hot red disk of gigantic dimensions will hang in the sky. Red giants are a natural phase of a star's evolution, its transitional state into the category of variable stars.
As a result of such a 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 will begin to "fry" in it. The temperature on the planet's surface will rise tenfold, which will lead to the disappearance of the atmosphere and to the evaporation of water. As a result, the planet will turn into a lifeless rocky desert.
The final stages of star 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 proceed calmly, without impulses and explosive reactions. The white dwarf will die for a long time, burning to ashes.
In cases where the star originally had 1.4 times the mass of the Sun, the white dwarf will not be the final stage. With a large mass inside the star, the processes of stellar matter compaction begin at the atomic, molecular level. Protons turn into neutrons, the density of the star increases, and its size is rapidly decreasing.
The neutron stars known to science have a diameter of 10-15 km. At 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 star of large mass, the final stage of evolution takes on 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 increases the gravitational forces that drive the compressive forces. It is not possible to suspend this process. The density of matter grows until it turns into infinity, 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 much more black holes if massive and supermassive stars occupied most of the space in 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 space object.
Supernova birth is the most spectacular final stage in stellar evolution. Here the natural law of nature operates: the cessation of the existence of one body gives rise to a new life. The period of a cycle such as a supernova birth mainly concerns massive stars. The spent reserves of hydrogen lead to the fact that helium and carbon are included in the process of thermonuclear fusion. As a result of this reaction, the pressure rises again, and an iron core forms in the center of the star. Under the influence of the strongest gravitational forces, the center of mass shifts to the central part of the star. The core becomes so heavy that it is unable to withstand its own gravity. As a consequence, a rapid expansion of the nucleus 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, therefore, such a 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 explains their rather rare detection.
Finally
The evolution of stars is a process that spans tens of billions of years. Our idea of \u200b\u200bthe ongoing processes is just a mathematical and physical model, theory. Terrestrial time is only a moment in the huge time cycle that our Universe lives on. We can only observe what was happening billions of years ago and guess what the next generations of earthlings might face.
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The lifetime of stars consists of several stages, passing through which for millions and billions of years the stars are steadily striving for an inevitable ending, turning into bright flares or into gloomy black holes.
The lifetime of a star of any type is an incredibly long and complex process, accompanied by phenomena of a cosmic scale. Its versatility is simply impossible to fully trace and study, even using the entire arsenal of modern science. But on the basis of that 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 the luminaries into relatively coherent theories and simulate their development. What are these stages?
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Episode I. Protostars
The life path of the 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 also 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 fast compression of its constituent particles with mass occurs, that is, gravitational collapse, does a future star begin to form. The reason for this is the burst of gravitational energy, part of which compresses 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 star grows and becomes visible after the pressure of the emitted light literally sweeps all the dust to the outskirts.
Find protostars in the Orion Nebula!
This huge panorama of the Orion Nebula is taken from the 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 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: young stars 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 of a star
Sun shot in H alpha line. Our star is in its prime.
In the middle of their lives, cosmic luminaries can have a wide variety of colors, masses and dimensions. The color palette ranges from bluish shades to reds, 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 runs out in the core of the space body. 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 the newly begun contraction of the star, collapse begins, which leads to the appearance of thermonuclear reactions already with the participation of helium. This process stimulates an incredible expansion of the star. And now she 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, etc. As for objects with a small mass, it is still impossible to say exactly what processes occur with them in the last stages of their existence. All such phenomena are hypothetically described using computer simulations, and not on the basis of careful observations of them. After the final burnout of carbon and oxygen, the star's atmospheric envelope increases and the gas component is rapidly lost by it. At the end of their evolutionary path, the luminaries are repeatedly compressed, and their density, on the contrary, increases significantly. Such a star is considered to be a white dwarf. Then in its life phase follows the period of the red supergiant. The last in the cycle of a star's existence 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), go 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 space is that the vast majority of luminaries in ours are at the stage of red dwarfs. Such objects have a mass significantly less than that of the Sun.
It is also quite interesting that the magnetic attraction of neutron stars is billions of times higher than that of a terrestrial star.
Effect of mass on a star
Another equally 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 the solar mass, their release of energy is also many times greater, sometimes even millions of times. Consequently, the period of their life lasts much less. In some cases, their existence fits only a few million years, versus billions of years of life for 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 mass, and the latter, on the contrary, from the smallest ones.
There is a huge number of unique phenomena in the Universe, about which we can talk endlessly, because the cosmos is extremely poorly studied and explored. All human knowledge about stars and their life cycles that modern science possesses 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 accumulating, supplemented and changed, thus becoming more accurate, reliable and comprehensive.
\u003e Life cycle of a star
Description life and death of stars: stages of development with a photo, molecular clouds, protostar, T Tauri, main sequence, red giant, white dwarf.
Everything in this world is developing. Any cycle begins with birth, growth and ends with death. Of course, in stars, these cycles run in a special way. Let us at least recall that their time frames are more extensive and are measured in millions and billions of years. In addition, their death has certain consequences. How does it look 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 safely exist in the universe without any changes. But suddenly a supernova explodes not far from it, or it hits another cloud. Due to this push, the destruction process is activated. It is divided into small parts, each of which is drawn into itself. As you already understood, all these heaps are preparing to become stars. Gravity heats up the temperature, and the stored momentum supports 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 star life cycle:Protostar
The material thickens 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. Part is attracted to the object, increasing its mass. The rest of the debris will group 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. It is a variable star located 600 light years away.
It can become very bright 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 a celestial body rises to the required level, activating nuclear fusion. All the stars go through this. Hydrogen is transformed into helium, releasing a huge amount of heat and energy.
Energy is released as gamma rays, but due to the slow motion of the star, it falls off with wavelength. Light is pushed outward and confronts gravity. It can be considered that a perfect balance is created here.
How long will she be in the main sequence? You need to proceed from the mass of the star. Red dwarfs (half the solar mass) are capable of spending hundreds of billions (trillions) of years of fuel. Average stars (like) live 10-15 billion. But the largest ones are billions or millions of years. See what the evolution and death of stars of different classes looks like on 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 vigorous reactions freeze, and the star begins to contract due to gravity. The hydrogen envelope around the core heats up and ignites, causing the object to grow 1,000 to 10,000 times. At a certain moment, our Sun will repeat this fate, increasing to the earth's orbit.
Temperature and pressure peaks and helium fuses to carbon. At this point, the star contracts 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 star with a solar mass does not 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.