Modern cosmological models of the universe briefly. Cosmological models of the evolution of the universe. Hot bang model
Introduction The Structure of the Universe in Antiquity
3Heliocentric model of the universe. Cosmological models of the universe
1Cosmology
2Stationary Model of the Universe
3Unsteady Model of the Universe
4Modern studies of cosmological models of the Universe. Nobel Prize for discovering the accelerated expansion of the universe
5 Dark matter
6Dark energy
Conclusion
Literature
Introduction
The Universe as a whole is the subject of a special astronomical science - cosmology, which has an ancient history. Its origins go back to antiquity. Cosmology has long been under the significant influence of a religious worldview, being not so much a subject of knowledge as a matter of faith.
Since the XIX century. cosmological problems are not a matter of faith, but the subject of scientific knowledge. They are solved with the help of scientific concepts, ideas, theories, as well as instruments and tools to understand what the structure of the universe is and how it was formed. In the XX century. Substantial progress has been made in the scientific understanding of the nature and evolution of the Universe as a whole. Of course, an understanding of these problems is still far from completion, and, undoubtedly, the future will lead to new great upheavals in the current views on the picture of the universe. Nevertheless, it is important to note that here we are dealing specifically with science, with rational knowledge, and not with beliefs and religious beliefs.
The relevance of this work is caused, on the one hand, by a great interest in the structure of the Universe in modern science, on the other hand, by its insufficient development, as well as attention to the Universe in the modern world.
Object of study: the Universe.
Subject of research: models of the structure of the Universe.
Purpose of work: to consider modern cosmological models of the Universe.
To achieve this goal it is necessary to solve the following tasks:
)To analyze the literature on the course of general physics and astronomy, in connection with the choice of the subject of study.
)Trace the history of cosmological research.
)Consider modern cosmological models.
)Pick up illustrative material.
Course work consists of introduction, three chapters, conclusion and bibliography. Chapter 1 is devoted to the history of the structure of the Universe, Chapter 2 considers cosmological models of the Universe, Chapter 3 opens up modern studies of cosmological models, and in conclusion, the results of the work done are summarized.
Chapter 1. The structure of the Universe in Antiquity
.1 Pyrocentric model of the universe
The path to understanding the position of our planet and humanity living on it in the Universe was very difficult and sometimes very dramatic. In ancient times, it was natural to believe that the Earth is motionless, flat and located in the center of the world. It seemed that in general the whole world was created for the sake of man. Similar representations were called anthropocentrism (from the Greek. Antropos - man). Many ideas and thoughts that were subsequently reflected in modern scientific ideas about nature, in particular in astronomy, originated in Ancient Greece, a few centuries before our era. It is difficult to list the names of all thinkers and their ingenious guesses. The outstanding mathematician Pythagoras (VI century BC) was convinced that "the number rules in the world." It is believed that it was Pythagoras who was the first to express the idea that the Earth, like all other celestial bodies, has a spherical shape and is in the Universe without any support. The Pythagoreans proposed a pyrocentric model of the Universe, in which the stars, the Sun, the Moon, and six planets revolve around the Central Fire (Hestia). In order to make the sacred number - ten - of spheres, the sixth planet was declared the Anti-Earth (Antichthon). Both the Sun and the Moon, according to this theory, shone with the reflected light of Hestia. This was the first mathematical system in the world - the rest of the ancient cosmogonists worked more like imagination than logic. The distances between the spheres of the luminaries of the Pythagoreans corresponded to musical intervals in gamma; while rotating them, “music of the spheres” sounds, inaudible by us. The Pythagoreans believed the Earth to be spherical and rotating, which is why the day and night change. The Pythagoreans first arose the concept of ether. This is the topmost, cleanest and most transparent layer of air, the place of the gods.
1.2 Geocentric Model of the Universe
Another no less famous scientist of antiquity, Democritus, the founder of ideas about atoms, who lived 400 years BC, believed that the Sun is many times larger than the Earth, that the Moon itself does not shine, but only reflects sunlight, and the Milky Way consists of a huge number of stars. Summarize all the knowledge that was accumulated by the IV century. BC BC., could the outstanding philosopher of the ancient world Aristotle (384-322 BC. E.).
Fig. 1. The geocentric system of the world of Aristotle-Ptolemy.
His work encompassed all natural sciences - information about heaven and Earth, about the laws of body movement, about animals and plants, etc. The main merit of Aristotle as an encyclopedic scientist was the creation of a unified system of scientific knowledge. For nearly two millennia, his opinion on many issues has not been questioned. According to Aristotle, everything heavy tends to the center of the Universe, where it accumulates and forms a spherical mass - the Earth. Planets are placed on special spheres that revolve around the Earth. Such a system of the world was called geocentric (from the Greek name of the Earth - Gaia). It was not by chance that Aristotle proposed to consider the Earth as the fixed center of the world. If the Earth moved, then, in the right opinion of Aristotle, a regular change in the relative positions of stars in the celestial sphere would be noticeable. But none of the astronomers observed anything like this. Only at the beginning of the XIX century. it was finally discovered and measured the displacement of stars (parallax), occurring due to the motion of the Earth around the Sun. Many of Aristotle's generalizations were based on such conclusions, which at that time could not be verified by experience. So, he argued that the movement of the body cannot occur if force does not act on it. As you know from the course of physics, these ideas were refuted only in the XVII century. in the days of Galileo and Newton.
1.3 Heliocentric model of the universe
Among the scholars of antiquity stands out by the courage of his guesses Aristarchus of Samos, who lived in the III century. BC e. He was the first to determine the distance to the Moon, calculate the size of the Sun, which, according to his data, turned out to be more than 300 times larger than the Earth in volume. Probably, these data became one of the grounds for concluding that the Earth, together with other planets, moves around this largest body. Today, Aristarchus of Samos began to be called "Copernicus of the ancient world." This scientist introduced a new doctrine of the stars. He believed that they are immeasurably further from the Earth than the Sun. For that era, this discovery was very important: from a cozy home world, the Universe turned into an immense gigantic world. In this world, the Earth, with its mountains and plains, with forests and fields, with seas and oceans, became a tiny speck of dust, lost in a grandiose empty space. Unfortunately, the works of this remarkable scientist practically did not reach us, and for more than one and a half thousand years, mankind was confident that the Earth was the motionless center of the world. To a large extent, this was facilitated by the mathematical description of the visible movement of the bodies, which was developed for the geocentric system of the world by one of the outstanding mathematicians of antiquity - Claudius Ptolemy in the II century. AD The most difficult task was to explain the loop-like motion of the planets.
Ptolemy in his famous essay “Mathematical Treatise on Astronomy” (it is more commonly known as the “Almagest”) argued that each planet uniformly moves along an epicyclic small circle, the center of which moves around the Earth along a deflector - a large circle. Thus, he managed to explain the special nature of the motion of the planets, which distinguished them from the Sun and Moon. The Ptolemy system gave a purely kinematic description of planetary motion - science could not offer otherwise. You have already seen that the use of the model of the celestial sphere in describing the motion of the sun, moon and stars allows us to make many calculations useful for practical purposes, although such a sphere does not really exist. The same is true for epicycles and deferents, on the basis of which one can calculate the position of the planets with a certain degree of accuracy.
Fig. 2. The motion of the Earth and Mars.
However, over time, the requirements for the accuracy of these calculations have steadily increased; we had to add more and more epicycles for each planet. All this complicated the Ptolemy system, making it unnecessarily cumbersome and inconvenient for practical calculations. Nevertheless, the geocentric system remained unshakable for about 1000 years. Indeed, after the heyday of ancient culture in Europe, a long period began, during which no significant discoveries were made in astronomy and many other sciences. Only in the Renaissance does the rise in the development of sciences begin, in which astronomy becomes one of the leaders. In 1543, a book was published by the outstanding Polish scientist Nicholas Copernicus (1473-1543), in which he substantiated the new - heliocentric - the system of the world. Copernicus showed that the daily movement of all the luminaries can be explained by the rotation of the Earth around the axis, and the loop-like movement of the planets - by the fact that all of them, including the Earth, revolve around the Sun.
The figure shows the motion of the Earth and Mars during the period when, as it seems to us, the planet describes a loop in the sky. The creation of the heliocentric system marked a new stage in the development of not only astronomy, but also the entire natural sciences. A particularly important role was played by the idea of \u200b\u200bCopernicus that behind the visible picture of occurring phenomena, which seems true to us, it is necessary to search and find the essence of these phenomena inaccessible for direct observation. The heliocentric system of the world, justified, but not proven by Copernicus, was confirmed and developed in the works of such outstanding scientists as Galileo Galilei and Johannes Kepler.
Galileo (1564-1642), one of the first to direct the telescope to the sky, interpreted the discoveries made at the same time as arguments in favor of the Copernican theory. Having discovered the phase change of Venus, he came to the conclusion that such a sequence of them can be observed only if it revolves around the Sun.
Fig. 3. The heliocentric system of the world.
The four satellites of the planet Jupiter that he discovered also refuted the notion that the Earth is the only center in the world around which other bodies can rotate. Galileo not only saw the mountains on the moon, but even measured their height. Along with several other scientists, he also observed spots on the Sun and noticed their movement on the solar disk. On this basis, he concluded that the Sun rotates and, therefore, has such a motion that Copernicus attributed to our planet. So it was concluded that the Sun and Moon have a certain similarity with the Earth. Finally, observing in the Milky Way and outside it many faint stars inaccessible to the naked eye, Galileo concluded that the distances to the stars are different and no “sphere of fixed stars” exists. All these discoveries have become a new stage in understanding the position of the Earth in the Universe.
Chapter 2. Cosmological models of the Universe
.1 Cosmology
Translated from Greek, cosmology means "a description of the world order." This is a scientific discipline designed to find the most general laws of motion of Matter and build an understanding of the Universe as a harmonious whole. Ideally, in it (in cosmological theory) there should not be a place for chance, but all the phenomena observed in the Cosmos should be presented as manifestations of the general laws of motion of Matter. Thus, cosmology is the key to understanding everything that happens both in the macrocosm and in the microcosm.
Cosmology is a branch of astronomy and astrophysics that studies the origin, large-scale structure and evolution of the universe. Cosmology data is mainly derived from astronomical observations. For their interpretation, the general theory of relativity by A. Einstein (1915) is currently used. The creation of this theory and the corresponding observations made it possible to put cosmology in a number of exact sciences in the early 1920s, whereas before that it was more likely to be a field of philosophy. Now there are two cosmological schools: empiricists confine themselves to the interpretation of observational data, without extrapolating their models to unexplored areas; theorists are trying to explain the observable Universe using some hypotheses selected on the basis of simplicity and elegance. The cosmological model of the Big Bang is now widely known, according to which the expansion of the Universe began some time ago from a very dense and hot state; The stationary model of the Universe is also discussed, in which it exists forever and has no beginning or end.
2.2 Stationary model of the universe
The beginning of a new theory of the origin of the Universe was laid by the publication in 1916 of Albert Einstein's work "Fundamentals of the General Theory of Relativity."
This work is the basis of the Relativistic Theory of Gravity, which, in turn, is based on modern cosmology. The general theory of relativity is already applied to all reference frames (and not just to those moving at a constant speed relative to each other) and looks mathematically much more complicated than the special one (which explains the gap of eleven years between their publication). It includes, as a special case, the special theory of relativity (and, therefore, Newton's laws). Moreover, the general theory of relativity goes much further than all its predecessors. In particular, it gives a new interpretation of gravity. The general theory of relativity makes the world four-dimensional: time is added to the three spatial dimensions. All four dimensions are inextricable, so we are no longer talking about the spatial distance between two objects, as is the case in the three-dimensional world, but about the space-time intervals between events that combine their remoteness from each other - both in time and in space . That is, space and time are considered as a four-dimensional space-time continuum or, simply, space-time. Already in 1917, Einstein himself proposed a model of space that he derived from his field equations, now known as the Model of the Einstein Universe. At its core, it was a stationary model. In order not to conflict with static, Einstein modified his theory by introducing the so-called cosmological constant into the equations. He introduced a new “anti-gravity” force, which, unlike other forces, was not generated by any source, but was embedded in the very structure of space-time. Einstein argued that space - time itself always expands, and with this expansion the attraction of all the rest of the matter in the Universe is precisely balanced, so that as a result the Universe turns out to be static.
Given the cosmological constant, the Einstein equations have the form:
where ? - cosmological constant, g ab is the metric tensor, R ab is the Ricci tensor, R is the scalar curvature, T ab is the energy-momentum tensor, c is the speed of light, G is the Newtonian gravitational constant.
“The universe depicted by Einstein's theory of relativity is like a swelling soap bubble. She is not his inside, but a film. The surface of the bubble is two-dimensional, and the bubble of the Universe has four dimensions: three spatial and one temporal, ”said the once prominent English physicist James Jeans. This modern scientist (he died in 1946), as it were, revived the old idea of \u200b\u200bthe followers of Plato and Pythagoras that everything around is pure mathematics, and the god who created this mathematical universe was himself a great mathematician.
But Einstein was also a great mathematician. His formulas allow us to calculate the radius of this universe. Since its curvature depends on the mass of the bodies that make up it, one must know the average density of matter. For many years, astronomers studied the same small patches of sky and meticulously calculated the amount of matter in them. It turned out that the density is approximately 10 -30 g / cm 3. If we substitute this figure in Einstein's formulas, then, firstly, we get a positive value of curvature, that is, our Universe is closed! - and, secondly, its radius is equal to 35 billion light years. This means that although the Universe is finite, it is huge - a ray of light, rushing along the Great Cosmic Circle, will return to the same point after 200 billion Earth years!
This is not the only paradox of the Einstein universe. It is not only finite, but unlimited, it is also unstable. Albert Einstein formulated his theory in the form of ten very complex, so-called non-linear differential equations. However, not all scholars treated them as the Ten Commandments, admitting only one single interpretation. Yes, this is not surprising - after all, modern mathematics cannot exactly solve such equations, and there can be many approximate solutions.
2.3 Unsteady Model of the Universe
The first fundamentally new revolutionary cosmological consequences of the general theory of relativity was discovered by the outstanding Soviet mathematician and theoretical physicist Alexander Alexandrovich Fridman (1888-1925).
The basic equations of the general theory of relativity are Einstein's “world equations”, which describe the geometric properties, or metrics, of four-dimensional curved space — time.
Their solution allows in principle to build a mathematical model of the universe. The first such attempt was made by Einstein himself. Assuming that the radius of curvature of space is constant (i.e., based on the assumption that the Universe as a whole is stationary, which seemed most reasonable), he came to the conclusion that the Universe should be spatially finite and have the shape of a four-dimensional cylinder. In the years 1922-1924. Friedman criticized Einstein’s findings. He showed the groundlessness of his original postulate - the stationarity, the immutability in time of the universe. After analyzing world equations, Friedman came to the conclusion that their solution under no circumstances can be unambiguous and cannot give an answer to the question of the shape of the Universe, its finiteness or infinity.
Based on the opposite postulate - about a possible change in the radius of curvature of world space in time, Friedman found unsteady solutions to the "world equations". As an example of such decisions, he built three possible models of the universe. In two of them, the radius of curvature of space monotonously grows, and the Universe expands (in one model - from a point, in the other - starting from some finite volume). The third model painted a picture of a pulsating universe with a periodically changing radius of curvature.
The Friedman model is based on the idea of \u200b\u200bthe isotropic, homogeneous and non-stationary state of the Universe:
Ø Isotropy indicates that in the Universe there are no distinguished points of directions, that is, its properties are independent of direction.
Ø The homogeneity of the universe characterizes the distribution of matter in it. This uniform distribution of matter can be justified by counting the number of galaxies to a given apparent magnitude. According to observations, the density of matter in the visible part of space is on average the same.
Ø Non-stationary means that the Universe cannot be in a static, unchanging state, but must either expand or contract
In modern cosmology, these three statements are called cosmological postulates. The totality of these postulates is a fundamental cosmological principle. The cosmological principle directly follows from the postulates of the general theory of relativity. A.Fridman, on the basis of the postulates put forward by him, created a model of the structure of the Universe, in which all galaxies are removed from each other. This model is similar to a uniformly inflating rubber ball, all points of the space of which are moving away from each other. The distance between any two points increases, however, none of them can be called the center of expansion. Moreover, the greater the distance between the points, the faster they move away from each other. Friedman himself considered only one model of the structure of the Universe, in which space changes according to a parabolic law. That is, at first it will expand slowly, and then, under the influence of gravitational forces, the expansion will be replaced by compression to its original size. His followers showed that there are at least three models for which all three cosmological postulates are fulfilled. A. Friedman's parabolic model is one of the possible options. A slightly different solution to the problem was found by the Dutch astronomer W. de Sitter. The space of the Universe in its model is hyperbolic, that is, the expansion of the Universe occurs with increasing acceleration. The expansion rate is so high that the gravitational impact cannot interfere with this process. He actually predicted the expansion of the universe. The third version of the behavior of the Universe was calculated by the Belgian priest J. Lemetre. In his model, the Universe will expand to infinity, however, the rate of expansion will constantly decrease - this dependence is of a logarithmic nature. In this case, the expansion speed is only sufficient to avoid compression to zero. In the first model, space is curved and self-enclosed. This is a sphere, therefore its dimensions are finite. In the second model, space is curved differently, in the form of a hyperbolic paraboloid (or saddle), space is infinite. In the third model with a critical expansion rate, the space is flat, and therefore also infinite.
Initially, these hypotheses were perceived as an incident, including by A. Einstein. However, already in 1926, a landmark event in cosmology took place, which confirmed the correctness of the calculations of Friedman - De Sitter - Lemaitre. Such an event that influenced the construction of all existing models of the Universe was the work of the American astronomer Edwin P. Hubble. In 1929, when conducting observations with the largest telescope at that time, he established that the light reaching the Earth from distant galaxies is shifted toward the long-wavelength part of the spectrum. This phenomenon, known as the "Red Shift Effect", is based on the principle discovered by the famous physicist K. Doppler. The Doppler effect indicates that in the spectrum of a radiation source approaching the observer, the lines of the spectrum are shifted to the short-wave (violet) side, in the spectrum of a source moving away from the observer, the spectral lines are shifted to the red (long-wave) side.
The redshift effect indicates the removal of galaxies from the observer. With the exception of the famous Andromeda Nebula and a few star systems closest to us, all other galaxies are moving away about us. Moreover, it turned out that the speed of expansion of galaxies is not the same in different parts of the universe. They move away from us the faster the further they are located. In other words, the redshift value was proportional to the distance to the radiation source - such is the strict formulation of the open Hubble law. The regular relationship of the speed of removal of galaxies with the distance to them is described using the Hubble constant (N, km / s per 1 megaparsec distance).
V \u003d hr ,
where V is the speed of removal of galaxies, H is the Hubble constant, r is the distance between them.
The value of this constant has not yet been finally established. Various scientists determine it in the range of 80 ± 17 km / s for each megaparsec of distance. The phenomenon of redshift has been explained in the phenomenon of "recession of galaxies." In this regard, the problems of studying the expansion of the Universe and determining its age by the duration of this expansion are highlighted.
Most modern cosmologists understand this expansion as an expansion of the really conceivable and existing Universe ... Unfortunately, early death did not allow the genius theorist of the Universe A.A. Fridman, whose ideas have been guiding the idea of \u200b\u200bcosmologists for more than half a century, to take part in further revolutionary development of the process Updates of the cosmological picture of the world. The experience of the history of the development of knowledge about the world suggests, however, that the modern relativistic cosmological picture of the world, being the result of extrapolation to the entire conceivable "whole" of knowledge about a limited part of the Universe, is inevitably inaccurate. Therefore, one might think that it rather reflects the properties of a limited part of the Universe (which can be called the Metagalaxy), and, perhaps, only one of the stages of its development (which allows for relativistic cosmology and that can become clear with the refinement of the average density of matter in the Metagalaxy). At present, however, at this point, the picture of the world remains uncertain.
Chapter 3. Modern studies of cosmological models of the Universe
.1 Nobel Prize for the discovery of the accelerated expansion of the Universe
Modern cosmology is a complex, complex and rapidly developing system of natural - scientific (astronomy, physics, chemistry, etc.) and philosophical knowledge of the Universe as a whole, based on both observational data and theoretical conclusions relating to part of the universe covered by astronomical observations. .
More recently, a discovery was made in the field of modern cosmology, which in the future will be able to change our ideas about the origin and evolution of our Universe. Scientists who have made a huge contribution to the development of this discovery have been awarded the Nobel Prize for their work.
The Nobel Prize was awarded to American Saul Perlmutter, Australian Brian Schmidt and American Adam Rees for the discovery of the accelerated expansion of the universe.
In 1998, scientists discovered that the universe is expanding with acceleration. The discovery was made through the study of type Ia supernovae. Supernovae are stars that flare up from time to time in the sky and then quickly fade. Due to their unique properties, these stars are used as markers to determine how cosmological distances change over time. A supernova flash is a moment in the life of a massive star when it experiences a catastrophic explosion. Supernovae come in many types, depending on the specific circumstances preceding the cataclysm. In observations, the type of flash is determined by the spectrum and shape of the light curve. The supernovae, designated Ia, arise during the thermonuclear explosion of a white dwarf whose mass exceeded the threshold value of ~ 1.4 of the mass of the Sun, called the Chandrasekhar limit. As long as the mass of the white dwarf is less than the threshold value, the star’s gravitational force is balanced by the pressure of a degenerate electron gas. But if in a close binary system a substance flows onto it from a neighboring star, then at a certain moment the electron pressure is insufficient and the star explodes, and astronomers record another type Ia supernova burst. Since the threshold mass and the reason why the white dwarf explodes are always the same, such supernovae at the maximum brightness should have the same, and very large luminosity, and can serve as a “standard candle” for determining intergalactic distances. If we collect data on many such supernovae and compare the distances to them with the redshifts of galaxies in which flares occurred, we can determine how the rate of expansion of the Universe has changed in the past and select the corresponding cosmological model.
Studying supernovae remote from the Earth, scientists found that they are at least a quarter fainter than theory predicts - this means that the stars are too far away. Having calculated, thus, the parameters of the expansion of the Universe, scientists have established that this process occurs with acceleration.
3.2 Dark matter
Dark matter is akin to ordinary matter in the sense that it is able to collect in clusters (the size of, say, a galaxy or a cluster of galaxies) and participates in gravitational interactions just like ordinary matter. Most likely, it consists of new particles that have not yet been discovered in terrestrial conditions.
In addition to cosmological data, the existence of dark matter is supported by measurements of the gravitational field in clusters of galaxies and in galaxies. There are several ways to measure the gravitational field in clusters of galaxies, one of which is gravitational lensing, illustrated in Fig. 4.
Fig. 4. Gravity lensing.
The gravitational field of the cluster bends the rays of light emitted by the galaxy behind the cluster, i.e. the gravitational field acts like a lens. In this case, sometimes several images of this distant galaxy appear; on the left half of fig. 7 they are blue. The curvature of light depends on the distribution of mass in the cluster, regardless of which particles create this mass. The mass distribution reconstructed in this way is shown in the right half of Fig. 7 blue; it can be seen that it is very different from the distribution of the luminous substance. The masses of galaxy clusters measured in this way are consistent with the fact that dark matter contributes about 25% to the total energy density in the Universe. Recall that the same number is obtained from a comparison of the theory of the formation of structures (galaxies, clusters) with observations.
Dark matter is also present in galaxies. This again follows from measurements of the gravitational field, now in galaxies and their environs. The stronger the gravitational field, the faster the stars and clouds of gas rotate around the galaxy, so that measurements of rotation speeds depending on the distance to the center of the galaxy can restore the mass distribution in it.
What are particles of dark matter? It is clear that these particles should not decay into other, lighter particles, otherwise they would decay during the existence of the Universe. This fact itself indicates that a new conservation law, which has not yet been discovered, is in force in nature, which prohibits these particles from decaying. The analogy here is with the law of conservation of electric charge: an electron is the lightest particle with an electric charge, and that is why it does not decay into lighter particles (for example, neutrinos and photons). Further, dark matter particles interact extremely weakly with our substance, otherwise they would have already been discovered in terrestrial experiments. Then begins the area of \u200b\u200bhypotheses. The most plausible (but by no means the only one!) Hypothesis is that the particles of dark matter are 100-1000 times heavier than the proton, and that their interaction with ordinary matter is comparable in intensity with the interaction of neutrinos. It is within the framework of this hypothesis that the modern density of dark matter finds a simple explanation: particles of dark matter were intensively born and annihilated in a very early Universe at extremely high temperatures (about 1015 degrees), and some of them survived to this day. With the indicated parameters of these particles, their current amount in the Universe is obtained exactly as needed.
Can we expect the discovery of dark matter particles in the near future in terrestrial conditions? Since today we do not know the nature of these particles, it is completely impossible to answer this question. However, the outlook seems very optimistic.
There are several ways to search for dark matter particles. One of them is associated with experiments on future high-energy accelerators - colliders. If dark matter particles are really 100-1000 times heavier than a proton, then they will be born in collisions of ordinary particles, which are accelerated at colliders to high energies (there are not enough energies achieved at existing colliders). The immediate prospects here are connected with the Large Hadron Collider (LHC) under construction at the CERN international center near Geneva, on which colliding proton beams with an energy of 7x7 Teraelectron-volts will be obtained. I must say that according to popular hypotheses today, dark matter particles are only one representative of a new family of elementary particles, so along with the discovery of dark matter particles, one can hope for the discovery of a whole class of new particles and new interactions on accelerators. Cosmology suggests that the world of elementary particles known today by the "bricks" is far from being exhausted!
Another way is to register particles of dark matter that fly around us. They are by no means few: with a mass equal to 1000 proton masses, these particles here and now should be 1000 pieces per cubic meter. The problem is that they interact extremely weakly with ordinary particles, the substance is transparent to them. However, dark matter particles occasionally collide with atomic nuclei, and these collisions can hopefully be recorded. Search in this direction is carried out using a number of highly sensitive detectors placed deep underground, where the background from cosmic rays is sharply reduced.
Finally, another way is associated with the registration of products of annihilation of dark matter particles among themselves. These particles must accumulate in the center of the Earth and in the center of the Sun (the substance for them is almost transparent, and they can fall into the Earth or the Sun). There they annihilate with each other, and other particles are formed, including neutrinos. These neutrinos freely pass through the thickness of the Earth or the Sun, and can be detected by special installations - neutrino telescopes. One of these neutrino telescopes is located deep in Lake Baikal, the other (AMANDA) - deep in ice at the South Pole. There are other approaches to the search for dark matter particles, for example, the search for products of their annihilation in the central region of our Galaxy. Which of all these paths will be the first to succeed, time will tell, but in any case, the discovery of these new particles and the study of their properties will be a major scientific achievement. These particles will tell us about the properties of the Universe 10–9 s (one billionth of a second!) After the Big Bang, when the temperature of the Universe was 1015 degrees, and dark matter particles interacted intensively with cosmic plasma.
3.3 Dark energy
Dark energy is a much stranger substance than dark matter. To begin with, it is not going to clumps, but is uniformly “spilled” in the Universe. In galaxies and clusters of galaxies there are as many of it as outside of them. The most unusual thing is that dark energy in a sense experiences antigravity. We have already said that modern astronomical methods can not only measure the current rate of expansion of the Universe, but also determine how it changed over time. So, astronomical observations indicate that today (and in the recent past) the Universe is expanding with acceleration: the rate of expansion increases with time. In this sense, we can talk about antigravity: ordinary gravitational attraction would slow down the scattering of galaxies, but in our Universe, it turns out, the opposite is true.
heliocentric cosmological gravitational universe
Fig. 5. Illustration of dark energy.
Such a picture, generally speaking, does not contradict the general theory of relativity, but for this the dark energy must have a special property - negative pressure. This sharply distinguishes it from ordinary forms of matter. It is no exaggeration to say that the nature of dark energy is the main mystery of fundamental physics of the 21st century.
One of the candidates for the role of dark energy is vacuum. The energy density of the vacuum does not change with the expansion of the universe, and this means the negative pressure of the vacuum. Another candidate is a new superweak field permeating the entire Universe; the term quintessence is used for it. There are other candidates, but in any case, the dark energy is something completely unusual.
Another way of explaining the accelerated expansion of the Universe is to suggest that the laws of gravity themselves mutate at cosmological distances and cosmological times. Such a hypothesis is far from harmless: attempts to generalize the general theory of relativity in this direction encounter serious difficulties. Apparently, if such a generalization is possible at all, then it will be connected with the idea of \u200b\u200bthe existence of additional dimensions of space, in addition to the three dimensions that we perceive in everyday experience.
Unfortunately, the direct experimental study of dark energy in terrestrial conditions is now not visible. This, of course, does not mean that new brilliant ideas in this direction cannot appear in the future, but today the hopes for clarifying the nature of dark energy (or, more broadly, the reasons for the accelerated expansion of the Universe) are connected exclusively with astronomical observations and with obtaining new accurate cosmological data. We have to learn in detail how the Universe expanded at a relatively late stage of its evolution, and this, hopefully, will allow us to make a choice between various hypotheses.
Conclusion
In this course work I have considered the cosmological models of the universe. After analyzing the literature on the course of general physics and astronomy, I traced the history of cosmological research, examined modern cosmological models of the Universe and selected illustrative material for the research topic. Having proved the relevance of the chosen topic, I summed up the work done.
Literature
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Modern physics considers the megaworld as a system that includes all celestial bodies, diffuse (diffusion - scattering) matter existing in the form of separated atoms and molecules, as well as in the form of denser formations - giant clouds of dust and gas, and matter in the form of radiation.
Cosmology is the science of the Universe as a single whole. In modern times, it is separated from philosophy and turns into an independent science. Newtonian cosmology was based on the following postulates:
· The universe has always existed, it is the "world as a whole" (the universe).
· The Universe is stationary (unchanged), only space systems are changing, but not the world as a whole.
· Space and time are absolute. Metrically, space and time are infinite.
· Space and time are isotropic (isotropy characterizes the same physical properties of the medium in all directions) and homogeneous (uniformity characterizes the average distribution of matter in the Universe).
Modern cosmology is based on the general theory of relativity and therefore it is called relativistic, in contrast to the previous, classical.
In 1929, Edwin Hubble (an American astrophysicist) discovered the phenomenon of "redshift." Light from distant galaxies is shifted toward the red end of the spectrum, which indicated the removal of galaxies from the observer. The idea arose of the unsteadiness of the universe. Alexander Alexandrovich Fridman (1888 - 1925) for the first time theoretically proved that the Universe cannot be stationary, but must periodically expand or contract. The problems of studying the expansion of the Universe and determining its age have come to the fore. The next stage in the study of the Universe is connected with the work of the American scientist George Gamow (1904-1968). The physical processes that took place at different stages of the expansion of the universe began to be investigated. Gamow discovered "relict radiation." (Relic - the remnant of the distant past).
There are several models of the universe: common to them is the idea of \u200b\u200bits unsteady, isotropic and homogeneous nature.
By the way of existence - the model of the "expanding Universe" and the model of the "pulsating Universe".
Depending on the curvature of space, they distinguish - an open model in which the curvature is negative or equal to zero, it presents an open, infinite Universe; a closed model with positive curvature, in it the Universe is finite, but unlimited, unlimited.
The discussion of the question of the finiteness or infinity of the Universe gave rise to several so-called cosmological paradoxes, according to which, if the Universe is infinite, then it is finite.
1. The expansion paradox (E. Hubble). Accepting the idea of \u200b\u200binfinite extent, we come to a contradiction with the theory of relativity. Removing the nebula from the observer at an infinitely large distance (according to the theory of “redshift” by V. M. Slifer and the “Doppler effect”) must exceed the speed of light. But it is the limiting (according to Einstein's theory) speed of propagation of material interactions, nothing can move at a faster speed.
2. Photometric paradox (J. F. Chesault and V. Olbers). This is the thesis of infinite luminosity (in the absence of light absorption) of the sky according to the law of illumination of any site and according to the law of an increase in the number of light sources as the volume of space increases. But infinite luminosity contradicts empirical evidence.
3. The gravitational paradox (K. Neumann, G. Zeeliger): an infinite number of cosmic bodies should lead to infinite gravity, and therefore to infinite acceleration, which is not observed.
4. Thermodynamic paradox (or the so-called "thermal death" of the Universe). The transfer of thermal energy to other types is difficult compared to the reverse process. Result: the evolution of matter leads to thermodynamic equilibrium. The paradox speaks of the final nature of the spatio-temporal structure of the Universe.
The evolution of the universe. The Big Bang Theory"
From ancient times to the beginning of the 20th century, space was considered unchanged. The starry world personified absolute peace, eternity and unlimited length. The discovery in 1929 of the explosive scattering of galaxies, that is, the rapid expansion of the visible part of the Universe, showed that the Universe is unsteady. By extrapolating this process of expansion into the past, scientists concluded that 15-20 billion years ago the Universe was enclosed in an infinitesimal volume of space at an infinitely high density (the “singularity point”), and the entire current Universe is finite, i.e. It has a limited volume and lifetime.
The starting point of the life time of the evolving Universe begins from the moment when the Big Bang occurred and the singularity state suddenly broke. The weakest single link in this beautiful theory is considered the problem of the Beginning - a physical description of the singularity.
Scientists agree that the original Universe was in conditions that are difficult to imagine and reproduce on Earth. These conditions are characterized by the presence of high temperature and high pressure in the singularity in which matter was concentrated.
The evolutionary time of the universe is estimated at about 20 billion years. Theoretical calculations showed that in the singular state its radius was close to the radius of the electron, i.e. it was a micro-object of negligible proportions. It is assumed that here the quantum laws characteristic of elementary particles began to affect.
The universe went on to expand from its original singular state as a result of the Big Bang, which filled all of space. There was a temperature of 100,000 million degrees. according to Kelvin, in which molecules, atoms and even nuclei cannot exist. The substance was in the form of elementary particles, among which electrons, positrons, neutrinos, and photons predominated, and there were fewer protons and neutrons. At the end of the third minute after the explosion, the temperature of the Universe dropped to 1 billion degrees. according to Kelvin. Atom nuclei began to form - heavy hydrogen and helium, but the substance of the Universe at that time consisted mainly of photons, neutrinos and antineutrinos. Only a few hundred thousand years later, hydrogen and helium atoms began to form, forming a hydrogen-helium plasma. Astronomers discovered "relict" radio emission in 1965 - the emission of hot plasma, which has been preserved since the time when there were no stars and galaxies. From this mixture of hydrogen and helium in the process of evolution, the whole diversity of the modern Universe arose. According to the theory of JH Jeans, the main factor in the evolution of the Universe is its gravitational instability: matter cannot be distributed with constant density in any volume. Homogeneous plasma initially broke up into huge clots. From them then clusters of galaxies formed, which broke up into protogalaxies, and protostars arose from them. This process continues in our time. Around the stars formed planetary systems. This model (standard) of the Universe is not sufficiently substantiated, many questions remain. The arguments in her favor are only the established facts of the expansion of the Universe and the relict radiation.
The famous American astronomer Carl Sagan has built a visual model of the evolution of the Universe, in which the space year is 15 billion Earth years, and 1 second. - 500 years; then in terrestrial units of time evolution will appear as follows:
The standard model of the evolution of the Universe assumes that the initial temperature inside the singularity was more than 10 13 on the Kelvin scale (in which the reference point corresponds to - 273 ° С). The density of the substance is approximately 10 93 g / cm 3. Inevitably, a “big bang” was to happen, with which the beginning of evolution was associated. It is assumed that such an explosion occurred about 15-20 billion years ago and was accompanied first by rapid, and then more moderate expansion and, accordingly, gradual cooling of the Universe. By the degree of expansion of the universe, scientists judge the state of matter at different stages of evolution. After 0.01 sec. after the explosion, the density of the substance dropped to 10 10 g / cm 3. Under these conditions, apparently, photons, electrons, positrons, neutrinos and antineutrinos, as well as a small number of nucleons (protons and neutrons) should have existed in the expanding Universe. In this case, continuous conversion of electron + positron pairs into photons and vice versa - of photons into an electron + positron pair took place. But just 3 minutes after the explosion, a mixture of light nuclei forms from nucleons: 2/3 of hydrogen and 1/3 of helium, the so-called stellar substance, the rest of the chemical elements are formed from it by nuclear reactions. At the moment when hydrogen and helium atoms arise, the substance became transparent to photons, and they began to radiate into world space. Currently, such a residual process is observed in the form of relict radiation (the remainder from that distant pore of formation of neutral hydrogen and helium atoms).
With expansion and cooling in the Universe, processes of destruction of previously existing and the emergence on this basis of new structures took place, which led to a violation of the symmetry between matter and antimatter. When the temperature after the explosion fell to 6 billion degrees Kelvin, the first 8 seconds. there was mainly a mixture of electrons and positrons. While the mixture was in thermal equilibrium, the number of particles remained approximately the same. Continuous collisions occur between particles, resulting in photons, and from photons - an electron and a positron. There is a continuous transformation of matter into radiation and, conversely, radiation into matter. At this stage, the symmetry between matter and radiation is maintained.
The violation of this symmetry occurred after a further expansion of the Universe and a corresponding decrease in its temperature. Heavier nuclear particles appear - protons and neutrons. An extremely insignificant excess of matter over radiation is formed (1 proton or neutron per billion photons). From this surplus in the process of further evolution, that enormous wealth and variety of the material world arises, from atoms and molecules to various mountain formations, planets, stars and galaxies.
So, 15-20 billion years is the approximate age of the universe. What happened before the birth of the universe? The first cosmogonic scheme of modern cosmology claims that the entire mass of the Universe was compressed to a certain point (singularity). It is not known, by virtue of what reasons this initial, point state was violated and what is called today the words "Big Bang" happened.
The second cosmological scheme of the birth of the Universe describes this process of emergence from “nothing,” vacuum. In the light of new cosmogonic concepts, the very understanding of vacuum has been revised by science. Vacuum is a special state of matter. At the initial stages of the Universe, an intense gravitational field can generate particles from a vacuum.
We find an interesting analogy to these modern ideas among the ancients. The philosopher and theologian Origen (II-III century AD) mentioned the transition of matter to another state, even the “disappearance of matter” at the time of the death of the Universe. When the universe arises again, “matter,” he wrote, “receives being again, forming bodies ...”.
According to the scenario of the researchers, the entire observable Universe of 10 billion light-years now appeared as a result of expansion, which lasted only 10-30 seconds. Expanding, expanding in all directions, matter pushed aside “nonexistence”, creating space and starting the countdown. This is how modern cosmogony sees the formation of the Universe.
The conceptual model of the "expanding universe" was proposed by A. A. Friedman in 1922-24. Decades later, it received practical confirmation in the works of the American astronomer E. Hubble, who studied the motion of galaxies. Hubble discovered that the galaxies were rapidly scattering, following a certain impulse. If this scattering does not stop, continues indefinitely, then the distance between space objects will increase, tending to infinity. According to Friedman’s calculations, this is how the further evolution of the Universe should have passed. However, under one condition - if the average density of the mass of the Universe turns out to be less than a certain critical value, this value is approximately three atoms per cubic meter. Some time ago, the data obtained by American astronomers from a satellite that examined the x-ray radiation of distant galaxies made it possible to calculate the average mass density of the universe. It turned out to be very close to that critical mass at which the expansion of the Universe cannot be infinite.
It was necessary to turn to the study of the Universe through the study of X-rays because a significant part of its substance is not optically perceived. About half the mass of our Galaxy, we "do not see." The existence of this substance not perceived by us is indicated, in particular, by gravitational forces, which determine the motion of our and other galaxies, the motion of stellar systems. This substance can exist in the form of "black holes", the mass of which is hundreds of millions of masses of our Sun, in the form of neutrinos or some other unknown forms. Not perceived, like "black holes", the corona of galaxies can be, as some researchers believe, 5-10 times the mass of the galaxies themselves.
The assumption that the mass of the Universe is much larger than is commonly believed has found a new, very weighty confirmation in the work of physicists. They obtained the first data that one of the three types of neutrinos has a rest mass. If the remaining neutrinos have the same characteristics, then the mass of neutrinos in the Universe is 100 times larger than the mass of ordinary matter in stars and galaxies.
This discovery allows us to say with greater certainty that the expansion of the Universe will continue only until a certain moment after which the process will reverse - the galaxies will begin to converge, again contracting to a certain point. Following matter, space will shrink to a point. What happens is what astronomers today call the words “Collapse of the Universe.”
Will people or inhabitants of other worlds, if they exist in space, notice the contraction of the Universe, the beginning of its return to pristine chaos? Not. They will not be able to notice the turn of time that will have to happen when the universe begins to shrink.
Scientists, speaking of the rotation of the flow of time on the scale of the Universe, draw an analogy with time on a shrinking, "collapsing" star. Conditional clocks located on the surface of such a star will first have to slow down, then when the compression reaches a critical point, they will stop. When the star “fails” from our space-time, the conditional arrows on the conditional clock will move in the opposite direction - time will go back. But the hypothetical observer on such a star will not notice all this. Slowing, stopping and changing the direction of time could be observed from the outside, being outside the “collapsing” system. If our Universe is the only one and there is nothing outside of it - no matter, no time, no space - then there cannot be a certain view from the side, which could notice when time changes its course and flows back.
Some scientists believe that this event in our Universe has already happened, galaxies are falling on each other, and the Universe has entered the era of its death. There are mathematical calculations and considerations confirming this idea. What will happen after the universe returns to a certain starting point? After this, a new cycle will begin, the next “Big Bang” will occur, the foremother will rush in all directions, pushing apart and creating space, galaxies, star clusters, life will arise again. Such, in particular, is the cosmological model of the American astronomer J. Wheeler, the model of the Universe, which is expanding and “collapsing” alternately.
The famous mathematician and logician Kurt Godel mathematically substantiated the position that under certain conditions our Universe really must return to its starting point in order to then complete the same cycle again, completing it with a new return to its original state. The model of the English astronomer P. Davis, the model of the "pulsating Universe", also corresponds to these calculations. But what’s important - the Davis Universe includes closed time lines, in other words, the time in it moves in a circle. The number of occurrences and deaths experienced by the Universe is infinite.
But how does modern cosmogony imagine the death of the Universe? The famous American physicist S. Weinberg describes it this way. After the start of compression for thousands and millions of years, nothing will happen that could cause concern for our distant descendants. However, when the Universe shrinks to 1/100 of its present size, the night sky will exude as much heat on the Earth as daylight today. After 70 million years, the universe will shrink another ten times and then "our heirs and successors (if they will) will see the sky unbearably bright." After another 700 years, space temperature will reach ten million degrees, stars and planets will begin to turn into a “space soup” of radiation, electrons and nuclei.
After compression to a point, after what we call the “death of the Universe,” but that, perhaps, is not its death at all, a new cycle begins. An indirect confirmation of this conjecture is the already mentioned relict radiation, the echo of the Big Bang that gave rise to our Universe. According to scientists, this radiation, it turns out, comes not only from the past, but also “from the future”. This is a reflection of the “world fire” emanating from the next cycle in which the new Universe is born. Not only relict radiation permeates our world, coming as if from two sides - from the past and the future. Matter, which makes up the world, the Universe and us, possibly carries some information in itself. Researchers with some conventionality, but are already talking about a kind of "memory" of molecules, atoms, elementary particles. Atoms of carbon that has been in living beings are “biogenic”.
Since at the moment the Universe converges to a point, matter does not disappear, it does not disappear, the information it carries is also indestructible. Our world is filled with it, as it is filled, with the matter that constitutes it.
The universe that will replace ours, will it be its repetition?
It is possible, some cosmologists answer.
Not at all necessary, others object. There is no physical justification, says, for example, Dr. R. Dick from Princeton University, so that every time the Universe is formed, the physical laws are the same as at the beginning of our cycle. If these patterns will differ even in the most insignificant way, then the stars will not be able to subsequently create heavy elements, including the carbon from which life is built. Cycle by cycle, the Universe can arise and be destroyed without generating a spark of life. This is one of the points of view. It could be called the point of view of the "discontinuity of being." It is intermittent, even if life arises in the new Universe: no threads connect it with the past cycle. According to another point of view, on the contrary, “the Universe remembers its entire history, no matter how far (even infinitely far) it goes into the past”.
No global evolutionary theory of the development of the Universe until the twentieth century existed, since classical natural sciences focused primarily on the study of not the dynamics, but the statics of systems. In classical science, there was a so-called theory stationarystate of the universe, according to which the universe has always been almost the same as it is now. Astronomy was static: the movements of planets and comets were studied, stars were described, their classifications were created. However the question of evolution The universe was not set.
Classical Newtonian Cosmology explicitly or implicitly accepted the following postulates:
· The Universe is “the world as a whole”. Cosmology cognizes the world as it exists on its own, regardless of the conditions of cognition.
· Space and time of the Universe are absolute, they do not depend on material objects and processes.
· Space and time are metrically infinite.
· Space and time are homogeneous and isotropic.
· The Universe is stationary, does not undergo evolution. Specific space systems can change, but not the world as a whole.
However, in Newtonian cosmology two paradoxrelated to the postulate of infinity of the universe.
The first paradox is called gravitational: if the Universe is infinite and there is an infinite number of celestial bodies, then the gravitational force will be infinitely large, and the Universe should collapse, and not exist forever.
The second paradox is called photometric: if there is an infinite number of celestial bodies, then there must be an infinite luminosity of the sky, which is not observed.
These paradoxes turned out to be insoluble within the framework of Newtonian cosmology.
Modern cosmological models The universe are based on general relativity A. Einstein, according to which the metric of space and time is determined by the distribution of gravitational masses in the Universe. Such models rely on basic gravity equationintroduced by A. Einstein in the general theory of relativity. This equation has not one, but several solutions, which is due to the presence of many cosmological models of the universe.
The first cosmological model was developed by L. Einstein himself in 1917. In accordance with this model, world space uniformly and isotropicallymatter is distributed on average in it evenly, gravitational attraction of masses is compensated by universal cosmological repulsion. Universe in the cosmological model of A. Einstein stationary, infinite in time and unlimited in space. This model at that time seemed quite satisfactory, since it was consistent with all known facts.
Another model, which is also a solution of gravitational equations, was proposed by the Dutch astronomer in the same 1917 Willem de Sitter. This solution would exist even in the case of an “empty” Universe free of matter. If masses appeared in such a Universe, then the solution ceased to be stationary: a cosmic repulsion between the masses arose, striving to remove them from each other and dissolve the entire system.
In 1922, the Russian mathematician and geophysicist A. A. Friedman rejected the postulate of classical cosmology about the stationary nature of the Universe and received solutions of Einstein's equations describing the Universe with an "expanding" space.
Proposed A. A. Friedman solutions allow three possibilities.
· If the average density of matter and radiation in the Universe is equal to some critical value ( ρ \u003d 10 -29 g / cm 3), the world space turns out to be Euclidean and the Universe expands unlimitedly from the initial point state.
· If the density is less than critical, space has Lobachevsky geometry and also expands unlimitedly.
· And finally, if the density is more than critical, the space of the Universe turns out to be Riemannian, expansion at some stage is replaced by compression, which continues up to the initial point state.
Since the average density of matter in the Universe is unknown, today we do not know in which of these spaces of the Universe we live.
In 1929, an American astronomer Edwin P. Hubble (1889 - 1953) established that light coming from distant galaxies shifts toward the red end of the spectrum. This phenomenon is called redshift. , according to the Doppler effect, removing galaxies from the observer. Thus, the expansion of the Universe is considered a scientifically established fact, however, it is not currently possible to unambiguously resolve the issue in favor of a particular model.
Common to solving these models is the idea of \u200b\u200bthe unsteady, isotropic and homogeneous nature of its models.
Instability means that the Universe cannot be in a static, unchanging state, but must either expand or contract.
Isotropy indicates that in the Universe there are no distinguished points and directions, that is, its properties do not depend on the direction.
Uniformity characterizes the uniform distribution of matter in the Universe on average.
These statements are often called cosmological postulates. A plausible requirement is added to it that there are no forces in the Universe that impede gravitational forces. Under such assumptions, cosmological models turn out to be the simplest.
The problem of the origin and evolution of the universe. Now it’s obvious that our universe evolves. In 1927, the Belgian abbot and scholar J. Lemeter introduced the concept of the beginning of the universe as a singularity (i.e. superdense state). According to the theoretical calculations of J. Lemetre, in a singular state, the Universe was a micro-object of negligible size: the radius of the Universe was 10 -12 cm, which is close in size to the radius of the electron, and its density is 10 96 g / cm 3. From the initial singular state, the Universe went on to expand as a result of the Big Bang.
Since the end of the 40s. XX century attracts more and more attention in cosmology process physics at different stages of cosmological expansion. Student A.A. Friedman G.A. Gamow developed a model hot Universe, considering the nuclear reactions taking place at the very beginning of the expansion of the Universe, and called it "The cosmology of the Big Bang."Such a model of the “hot” Universe was subsequently named standard.
Standard Big Bang Model leans on the following data:
Firstly, on the empirical facts of extragalactic astronomy about continuous removal the farthest galaxies from us;
· Secondly, the discovery in 1965 of microwave radiation, subsequently named relictbecause it carries information about the early history of the universe;
· Thirdly, on the postulate of symmetry breaking between microparticles, on the one hand, and forces acting between them, on the other.
About the state of the universe before the explosion no reliable data exists yet. Only a few assumptions and hypotheses are made. Therefore, the standard model assumes that initially the Universe could consist of electrons, positrons and photons, as well as neutrinos and antineutrinos. Currently becoming popular quark model due to the fact that these hypothetical particles are now considered the basis for constructing existing elementary particles. Relatively more reliable are the ideas about the evolution of the universe. after the explosion and its expansion that has begun.
Retrospective calculations determine the age of the universe at 13 - 20 billion years. G. A. Gamov suggested that the temperature of the substance was high and fell with the expansion of the Universe, which contributed to the formation of chemical elements and cosmological structures. In modern cosmology, for clarity, the initial stage of the evolution of the Universe is divided into "era".
Hadron era (heavy particles entering into strong interactions). The duration of the era is 0.0001 s, the temperature is 10 12 degrees Kelvin, the density is 10 14 g / cm 3. At the end of the era, particles and antiparticles are annihilated, but some protons, hyperons, mesons remain. In the first hundredth of a second after the explosion, matter was a kind of substance mixture (consisting of electrons and positrons) and radiation(photons) that continuously interacted with each other. Electrons and positrons turned into photons, and the latter, as a result of interaction, formed a pair of electron and positron: e - + e + ↔ 2γ.
Interconversion of matter and radiation continued until there was a thermodynamic equilibrium between them. There was also symmetry how between substance and radiationbetween and substance and antimatter.
As a result of the separation of antimatter from matter and the destruction of symmetry between matter and radiation, one can only guess. It is believed that in the distant past, our real the world was somehow isolated from antimatterfor otherwise everything would turn into radiation.
Era of leptons (light particles entering into electromagnetic interaction). The duration of the era is 10 s, the temperature is 10 10 degrees Kelvin, the density is 10 4 g / cm 3. The main role is played by light particles participating in reactions between protons and neutrons.
Photon era. Duration 1 million years. The bulk of the mass-energy of the universe - accounted for by photons. By the end of the era, the temperature drops from 10 10 to 3000 degrees Kelvin, the density - from 10 21 g / cm 3 to 10 4 g / cm 3. The main role is played by radiation, which at the end of an era is separated from matter. When electrons and nuclei begin to form stable atoms of light elements, mainly hydrogen and helium, then the separation of matter and radiation occurs. One of its first consequences was star formation. Another consequence was that The universe has become transparent to radiation. It was then that cosmic microwave radiation with a temperature of 3 degrees Kelvin arises, which is now often called relict, because it recalls the history of the origin of the Universe.
Star era occurs 1 million years after the birth of the universe. In the stellar era, the process of the formation of protostars and protogalaxies begins. Then a grandiose picture of the formation of the structure of the Metagalaxy unfolds.
In the standard hypothesis of the formation of the Universe there are many more obscure and controversial. First of all, questions about the structure and state of matter remain unresolved. initial The universe.
For this reason, in addition to the standard model, hypothesis of a pulsating universe, which suggests that during its evolution, the Universe undergoes periodic expansion and contraction. According to her defenders, she satisfactorily explains the presence of a giant number of photons in the Universe during the cycles of its expansion and contraction. However, no empirical facts showing the contraction of the universe have yet been discovered.
A quarter century ago was put forward inflationary modelwho is trying to uncover the state of the universe before the explosion. She sees the universe as giant fluctuation of vacuum, and seeks to explain the destruction of symmetries in it between matter and antimatter, as well as various forces of interaction between particles and fields. According to this model, the Universe arose from the initial vacuum, which possessed tremendous energy but was in an unstable state. In this vacuum called excited, or false, cosmic repulsive forces dominated, which “inflated” the space occupied by it, and the energy released during this quickly heated the Universe. A huge increase in temperature and pressure during the rapid expansion of the excited vacuum led to the explosion of superhot matter. After the explosion, a sharp drop in temperature and pressure occurred, and subsequently the expansion of the Universe occurred according to the scenario of the standard model.
The greatest difficulty for scientists arises when explaining causes of cosmic evolution. If we discard particulars, we can distinguish two basic concepts that explain the evolution of the universe: self-organization and creationism.
For self organization conceptsthe material Universe is the only reality; no other reality exists besides it. The evolution of the Universe is described in terms of self-organization: there is a spontaneous ordering of systems in the direction of the formation of increasingly complex structures. Dynamic chaos gives rise to order. Question about the goals cosmic evolution is not posed, because it makes no sense.
Within creationism concepts, those. creations, the evolution of the Universe is associated with the implementation of a program that was formulated by a higher order reality than the material world (for example, God). Proponents of creationism draw on the anthropic principle as an additional argument.
Essence anthropic principle lies in the fact that the existence of the Universe in which we live depends on the numerical values \u200b\u200bof the fundamental physical constants - Planck's constant, gravity constant, interaction constants, etc. If these values \u200b\u200bdiffered from the existing ones even by a negligible amount, then not only life would be impossible, but the Universe itself as a complex ordered structure would be impossible. The conclusion is drawn from this: the physical structure of the Universe programmedand the final target cosmic evolution supposedly lies in the appearance of man in the universe in accordance with the intentions of the Creator.
It is regrettable to note that in some modern textbooks the idea of \u200b\u200bcreationism is considered in the framework of the concepts of natural science. However, the idea of \u200b\u200bcreationism is connected with the world supernatural and therefore goes beyond the scope of natural science studying natural laws of the world. In addition, the anthropic principle explains why the appearance of man has become possible, but in no way can serve as evidence programmed such an appearance.
Cosmology -a section of modern astronomy that studies the origin, properties and evolution of the Universe as a whole. Physical cosmology deals with observations that provide information about the universe as a whole, and theoretical cosmology with the development of models that should describe the observable properties of the universe in mathematical terms. Cosmology in the broadest sense encompasses physics, astronomy, philosophy and theology. Indeed, she seeks to provide a picture of the world explaining why the Universe has exactly the properties that it has. Greek cosmology already sought to build a mathematical model of planetary motion. Modern cosmology is based entirely on the laws of physics and mathematical constructions.
Only in the 20th century was an understanding of the universe developed as a whole. The first important step was taken in the 1920s, when scientists came to the conclusion that our Galaxy is one of many galaxies, and the Sun is one of the millions of stars of the Milky Way. A subsequent study of galaxies showed that they are moving away from the Milky Way, and the further they are, the greater the speed of their removal. Scientists have realized that we live in an expanding universe. The recession of galaxies occurs in accordance with the Hubble law, according to which the redshift of a galaxy is proportional to its distance. The proportionality constant, called the Hubble constant, has a value in the range of 60-80 km / s per Megapar-s (1 pc - 3.26 light years) with an error of 20%. According to Hubble’s law, the recession speeds of distant galaxies are directly proportional to their distances from us, the observers. The darkness of the night sky is due to the expansion of the universe. The explanation of this fact is a very important cosmological observation. The advent of radio astronomy in the 1950s made it possible to establish that most radio sources (for example, quasars and radio galaxies) are distant objects. Since the distances calculated by the redshift constitute a significant fraction of the size of the Universe, radio waves and light require a period of time comparable to the age of the Universe in order to reach the Earth. Because of this, observing weak radio sources, the researcher sees the early stages of the evolution of the universe.
All cosmological theories (models) include the postulate according to which there are no distinguished points and directions in the Universe, that is, all points and directions are equal for any observer. Usually, it is also assumed that the laws of physics and fundamental constants, in particular the gravitational constant G, do not change with time. There are no facts to the contrary. Einstein's general theory of relativity is the starting point for most cosmological models. Cosmological models differ in the choice of two values \u200b\u200b- the Einstein cosmological constant and density, depending on the amount of matter in the Universe and on the Hubble constant.
IN stationary universe models,created by the English astronomers F. Hoyle and G. Bondi and the American astronomer T. Gold, it is argued that the Universe is the same everywhere and at any time for all observers. In order to bring this model into line with the observed expansion of the Universe, F. Hoyle postulated the continuous generation of a new substance with the C-field (“creating field”), which fills the voids remaining after the scattering of existing galaxies. However, the Hoyle-Bondi-Gold model was not consistent with other empirical data, for example with relict radiation. Nevertheless, this model gave a significant impetus to the development of the theory of nuclear fusion in stars, since, if there were no Big Bang, heavy elements could be formed only in exploding stars. This position of the theory, not related to the choice of the cosmological model, has remained fully valid.
Friedman Universe -a model in which the density and radius of the Universe can change over time, that is, the Universe is in a state of continuous expansion or contraction. The Friedman universe can be closed if the density of matter in it is high enough to stop expansion. This fact led to the search for the so-called missing mass, that is, “dark” matter that fills the non-radiating regions of the Metagalaxy. Back in 1922-1924, the Russian mathematician A. A. Fridman, based on Einstein's theory of relativity, proved that due to the action of gravitational forces, matter in the Universe cannot be at rest - it is unsteady. The most important argument in favor of this theory is the discovery in 1965 by American physicists A. Penzias and R. Wilson of microwave background radiation, equivalent to radiation from a completely black body with a temperature of 2.7 K (Kelvin).
Pulsating Universe ~a model of the Universe in which it periodically goes through cycles of expansion and contraction to the so-called Big Clap (squeezing). Each compression cycle is replaced by the next Big Bang following it, opening a new expansion cycle, and so on to infinity. If this happens, then the universe is closed.
The Shuffling Universe -a chaotic model of the early Universe, in which, as a result of gigantic convulsions and oscillations, the light “floats” around it and contributes to the transformation of the heterogeneous Universe into a homogeneous one. It is established that this model is not viable.
Open universe- a cosmological model in which the Universe appears to be infinite in space. For this model to be true, the expansion of the Universe must continue or slow down, but not be replaced by compression, as in the models of a pulsating Universe. To do this, it should contain less substance than is necessary to create dos-42
a sufficiently strong gravitational field capable of stopping its expansion. Currently, the average density of matter in the Universe is not precisely determined, therefore, it is too early to conclude in favor of a particular model.
Expanding Universe Model- A model of the evolution of the Universe, according to which it arose in an infinitely dense hot state and has been expanding ever since. This event occurred 13 to 20 billion years ago and is known as the Big Bang. The Big Bang theory is now generally accepted, as it explains both of the most significant facts of cosmology: the expanding Universe and the existence of cosmic background radiation. This relict radiation of a primary expanding hot ball was predicted by an American physicist of Russian origin J. Gamow in 1948. Background radiation was studied at all wavelengths from the radio to the gamma range. In recent decades, much attention has been paid to the isotropy of CMB radiation, which provides information on the earliest stages of evolution.
You can use the well-known laws of physics and calculate in the opposite direction all the states the Universe was in, starting from 10? 43 s (quantum of time) after the Big Bang. During the first million years, matter and energy in the Universe formed an opaque plasma, sometimes called the primary flame By the end of this period, the expansion of the Universe caused the temperature to drop below 3000 K: the era of recombination had begun, that is, the substance was separated from radiation, so that protons and electrons could unite to form I’m hydrogen atoms. At this stage, the Universe became transparent to radiation. The density of matter reached a value higher than the value of the radiation density, although before the situation was reversed, which determined the rate of expansion of the Universe. Background microwave radiation is all that remains of the highly cooled radiation of Universe: The first galaxies began to form from the primary clouds of hydrogen and helium in only one or two billion years. The term “Big Bang” can be applied to any model of an expanding Universe that was hot and dense in the past.
A special class of Big Bang models make up inflationary modelsor swelling universe models.In these models, at an early stage in the evolution of the Universe, there is a finite period of accelerated expansion. Under such conditions, a tremendous amount of energy would be released that was previously contained in the original physical vacuum of space-time. For some time, the horizon of the Universe would expand at a speed far exceeding the speed of light. This theory is able to satisfactorily explain the existing expansion of the Universe and its homogeneity, however, most physicists and cosmologists have doubts about the possibility of moving at a speed exceeding the speed of light.
Based on the ideas about the unified nature of the four fundamental physical interactions (gravitational, electromagnetic, strong and weak nuclear), which determines their relationship at all stages of the evolution of the Universe, starting with! 970s cosmologists and physicists are trying to build theory of great unification.The creation of The Theory of Everything, as S. Hawking 1 calls this grandiose project of modern science, would greatly expand our understanding of the Universe and its evolution.
Currently, cosmology is developing rapidly thanks to the discoveries of elementary particle physics and astronomical observations of various objects in the Universe.
1. Introduction.
2. Modern cosmological models of the universe.
3. Stages of cosmic evolution.
4. Planets.
5. Comets.
6. Asteroids.
7. The stars.
8. The used literature.
Introduction
Megamir, or cosmos, modern science considers as an interacting and developing system of all celestial bodies. Megamir has a systematic organization in the form of planets and planetary systems that arise around stars, stars and stellar systems - galaxies; galaxy systems - Metagalaxies.
Matter in the Universe is represented by condensed cosmic bodies and diffuse matter. Diffuse matter exists in the form of separated atoms and molecules, as well as more dense formations - giant clouds of dust and gas - gas-dust nebulae. A significant proportion of matter in
Along with diffuse formations, the universe is occupied by matter in the form of radiation. Therefore, cosmic interstellar space is by no means empty.
Modern cosmological models of the universe.
As indicated in the previous chapter, in classical science there was a so-called theory of the stationary state of the Universe, according to which
The universe has always been almost the same as it is now. Astronomy was static: the movements of planets and comets were studied, stars were described, their classifications were created, which was, of course, very important. But the question of the evolution of the universe was not raised.
Classical Newtonian cosmology explicitly or implicitly accepted the following postulates:
The universe is an omnipresent, "world as a whole." Cosmology cognizes the world as it exists on its own, regardless of the conditions of cognition.
The space and time of the Universe is absolute, they do not depend on material objects and processes.
Space and time are metrically infinite.
Space and time are homogeneous and isotropic.
The universe is stationary, does not undergo evolution. Specific space systems may change, but not the world as a whole.
Modern cosmological models of the Universe are based on A. Einstein's general theory of relativity, according to which the metric of space and time is determined by the distribution of gravitational masses in the Universe. Its properties as a whole are due to the average density of matter and other specific physical factors. Modern relativistic cosmology builds models of the Universe, starting from the basic equation of gravitation, introduced by A. Einstein in the general theory of relativity.
Einstein's gravitational equation has not one, but many solutions, which is due to the presence of many cosmological models of the Universe. The first model was developed by L. Einstein himself in 1917. He rejected the postulates of Newtonian cosmology about the absoluteness and infinity of space and time. In accordance with the cosmological model of the Universe
A. Einstein’s world space is homogeneous and isotropic, matter is distributed uniformly on average, the gravitational attraction of the masses is compensated by universal cosmological repulsion.
This model at that time seemed quite satisfactory, since it was consistent with all known facts. But the new ideas put forward by A. Einstein stimulated further research, and soon the approach to the problem drastically changed.
In the same 1917, the Dutch astronomer W. de Sitter proposed another model, which is also a solution of the gravitational equations. This solution had the property that it would exist even in the case of "empty"
Universe free of matter. If masses appeared in such a Universe, then the solution ceased to be stationary: a kind of cosmic repulsion between the masses arose, striving to remove them from each other and dissolve the entire system. The expansion trend, according to V. de Sitter, became noticeable only at very large distances.
In 1922, the Russian mathematician and geophysicist L.A. Friedman o (dropped the postulate of classical cosmology about the stationarity of the Universe and gave the currently accepted solution to the cosmological problem.
Solution of the equations A.A. Friedman, allows three possibilities. If the average density of matter and radiation in the Universe is equal to some critical value, world space is Euclidean and
The universe expands unlimitedly from its original point state.
If the density is less than critical, space has a geometry
Lobachevsky is also expanding unlimitedly. And finally, if the density is more than critical, the space of the Universe turns out to be Riemannian, the expansion at some stage is replaced by compression, which continues up to the initial point state. According to modern data, the average density of matter in the Universe is less than critical, so the Lobachevsky model is considered more likely, i.e. spatially infinite expanding universe. It is possible that some types of matter, which are of great importance for the average density, remain unaccounted for. In this regard, it is still premature to draw final conclusions about the finiteness or infinity of the Universe.
The expansion of the universe is considered a scientifically established fact. The first to search for data on the motion of spiral galaxies turned V. de Sitter.
The discovery of the Doppler effect, which indicated the removal of galaxies, gave impetus to further theoretical research and new improved measurements of the distances and velocities of spiral nebulae.
In 1929, the American astronomer E.P. Hubble discovered the existence of a strange relationship between the distance and the speed of galaxies: all galaxies are moving away from us, and with a speed that increases in proportion to the distance, the galaxy system expands.
But the fact that the Universe is currently expanding does not yet allow to unambiguously resolve the issue in favor of a particular model.
Stages of cosmic evolution.
No matter how the question of the diversity of cosmological models is resolved, it is obvious that our Universe is expanding, evolving. The time of its evolution from the initial state is estimated at approximately 20 billion years.
Perhaps, an analogy not with an elementary particle, but with a supergene possessing a huge set of potential possibilities realized in the process of evolution is more suitable. In modern science, a so-called anthropic principle in cosmology has been advanced. Its essence lies in the fact that life in the Universe is possible only at those values \u200b\u200bof universal constants, physical constants, which actually take place. If the value of physical constants would have at least a negligible deviation from existing ones, then the emergence of life would be in principle impossible. This means that even in the initial physical conditions of the existence of the Universe, the possibility of the emergence of life is inherent.
From the initial singular state, the Universe passed to expansion as a result of the Big Bang, which filled all space. As a result, each particle of matter rushed away from any other.
Just one hundredth of a second after the explosion, the Universe had a temperature of about 100,000 million degrees, according to Kelvin. At that temperature
(above the temperature of the center of the hottest star) molecules, atoms and even atomic nuclei cannot exist. The substance of the Universe was in the form of elementary particles, among which electrons, positrons, neutrinos, photons predominated, as well as a relatively small number of protons and neutrons. The density of the substance of the Universe was huge 0.01 seconds after the explosion - 4,000 million times more than that of water
At the end of the first three minutes after the explosion, the temperature of the substance of the Universe, continuously decreasing, reached 1 billion degrees. At this still very high temperature, nuclei of atoms began to form, in particular, nuclei of heavy hydrogen and helium. However, the substance of the universe at the end of the first three minutes consisted mainly of photons, neutrinos and antineutrinos.
Planets.
Mercury, Venus, Mars, Jupiter and Saturn were known in antiquity. Uranus was discovered in 1781 by W. Herschel.
In 1846, the eighth planet, Neptune, was discovered. In 1930, the American astronomer C. Tombo found on negatives a slowly moving star-shaped object, which turned out to be a new, ninth planet. She was called Pluto. The search for and discovery of the satellites of the planets of the solar system continues to this day.
The planets Mercury, Venus, Earth and Mars are combined into one group of terrestrial planets. In their characteristics, they significantly differ from Jupiter, Saturn, Uranus and Neptune, which form a group of giant planets.
On the disks of Mars, Jupiter and Saturn, a lot of interesting details are noticeable. Some of them belong to the surface of the planets, others to their atmosphere (cloud formations)
When observing Mars during the period of confrontation, you can see polar caps that change over the seasons, light continents, dark areas (seas) and periodic cloud cover.
The visible surface of Jupiter is a cloud cover. The most noticeable are dark reddish stripes elongated parallel to the equator.
The rings of Saturn are one of the most beautiful objects that can be observed with a telescope. The outer ring is separated from the middle by a dark gap called the Cassini gap. The middle ring is the brightest. It is also separated from the inner ring by a dark gap. The inner dark and translucent ring is called crepe. Its edge is blurred, the ring gradually disappears.
Experienced observers note the presence of foggy spots on the disk of Venus, the appearance of which varies from day to day. These spots can only be details of a cloud structure. The clouds on Venus form a powerful continuous layer that completely hides the surface of the planet from us.
Uranus cannot be observed with the naked eye. It is visible only through a telescope and looks like a small greenish disk.
Pluto, the most distant among the planets of the solar system known to us, looks like a star in a telescope. Its luster experiences periodic changes, apparently related to rotation (period of 6.4 days).
Spacecraft flights have brought more information for planetary exploration. However, ground-based observations of the planets are important, if only for the reason that these devices do not yet allow a sufficiently long tracking of the planets necessary to study all kinds of changes (seasonal changes on Mars, the movement of clouds on Jupiter, etc.). Ground-based astronomical observations for a long time will provide interesting data.
Comets. Presumably, long-period comets fly to us from the Oort Cloud, which contains a huge number of cometary nuclei. Bodies located on the outskirts of the solar system, as a rule, are composed of volatile substances (water, methane and other ice) that evaporate when approaching the sun.
To date, more than 400 short-period comets have been discovered. Of these, about 200 were observed in more than one perihelion passage. Many of them belong to the so-called families. For example, approximately 50 of the shortest-period comets (their full revolution around the Sun lasts 3-10 years) form the Jupiter family. A little smaller than the families of Saturn, Uranus and Neptune (the latter, in particular, includes the famous comet Halley).
Comets emerging from the depths of space look like foggy objects, followed by a tail, sometimes reaching a length of millions of kilometers. The nucleus of a comet is a body of solid particles and ice, shrouded in a foggy shell called a coma. A core with a diameter of several kilometers may have around itself a coma of 80 thousand kilometers across. Streams of sun rays knock out gas particles from a coma and throw them back, pulling them into a long smoky tail, which drags behind it in space.
The brightness of comets is very dependent on their distance from the sun. Of all the comets, only a very small part approaches the Sun and the Earth so much that they can be seen with the naked eye. The most notable of them are sometimes called "large (great) comets."
Asteroids. To date, hundreds of thousands of asteroids have been discovered in the solar system. As of September 26, 2009, there were 460,271 objects in the databases, 219,018 had precisely defined orbits and they were assigned an official number. 15361 of them at that moment had officially approved names. It is estimated that between 1.1 and 1.9 million objects with dimensions greater than 1 km can be in the solar system. Most of the currently known asteroids are concentrated within the asteroid belt located between the orbits of Mars and Jupiter.
The largest asteroid in the solar system was Ceres, measuring approximately 975 × 909 km, but since August 24, 2006, it received the status of a dwarf planet. The other two largest asteroids 2 Pallas and 4 Vesta have a diameter of ~ 500 km. 4 Vesta is the only object of the asteroid belt that can be observed with the naked eye. Asteroids moving in other orbits can also be observed during passage near the Earth.
The total mass of all asteroids of the main belt is estimated at 3.0-3.6 × 10 21 kg, which is only about 4% of the mass of the moon. The mass of Ceres is 0.95 × 10 21 kg, that is, about 32% of the total, and together with the three largest asteroids 4 Vesta (9%), 2 Pallas (7%), 10 Hygea (3%) - 51%, i.e. absolute most asteroids have insignificant, by astronomical standards, mass.
Stars.
The most common object in the universe are stars. They arise as follows: particles of a gas-dust cloud are slowly attracted to each other due to gravitational forces. The density of the cloud is growing, the resulting opaque sphere begins to rotate, capturing more and more particles from the surrounding space. The outer layers put pressure on the inner, pressure and temperature in depth grow, according to the laws of thermodynamics, gradually reaching several million degrees. Then, in the protostar core, conditions are created for the thermonuclear fusion of helium from hydrogen. About this "notify the world" neutrino fluxes released during such a reaction. As a result, a powerful flow of electromagnetic radiation presses on the outer layers of the substance, counteracting gravitational compression. When the forces of radiation and gravity are balanced, the protostar becomes a star. To go through this stage of its evolution, a protostar needs from several million years (with a mass greater than the sun) to several hundred million years (with a mass less than the sun). Double and multiple stars are widespread, we can say that this is a common occurrence. They form nearby and revolve around a common center of mass. They account for about 50% of all stars.
The chemical composition of stars according to spectral analysis is on average the following: for 10,000 hydrogen atoms there are 1,000 helium atoms, 5 for oxygen, 2 for nitrogen, 1 for carbon, and even fewer other elements. Due to high temperatures, the atoms are ionized and are in a plasma state - a mixture of ions and electrons. Depending on the mass and chemical composition of the protostellar cloud, a young star falls on a certain part of the Hertzsprung-Russell diagram, which is a coordinate plane, the vertical axis of which depicts the luminosity of the star (the amount of energy emitted per unit time), and the horizontal - spectral class (star color depending on surface temperature). In this case, blue stars are hotter than red ones. For convenience, the entire sequence of spectra is divided into several sections, or spectral classes. These spectral classes are indicated by Latin letters: O - B - A - F - G - K - M - L - T The spectra of the stars of two neighboring spectral classes are still very different from each other. Therefore, it was necessary to introduce a finer gradation — dividing the spectra within each spectral class into 10 subclasses. After this separation, part of the sequence of spectra will look like this: ... - B9 - A0 - A1 - A2 - A3 - A4 - A5 - A6 - A7 - A8 - A9 - F0 - F1 - F2 - ... (the yellow Sun has class G2, i.e. it is in the middle of the diagram, with a surface temperature of 6000 o). For convenience, the entire sequence of spectra is divided into several sections, or spectral classes. These spectral classes are indicated by Latin letters: O - B - A - F - G - K - M - L - T The spectra of the stars of two neighboring spectral classes are still very different from each other. Therefore, it was necessary to introduce a finer gradation — dividing the spectra within each spectral class into 10 subclasses. After this separation, part of the sequence of spectra will look like this: ... - B9 - A0 - A1 - A2 - A3 - A4 - A5 - A6 - A7 - A8 - A9 - F0 - F1 - F2 - ... Most of the stars in the diagram are located along the main sequence - a smooth curve going from the upper left to the lower right corner of the diagram. As hydrogen is consumed, its mass changes, and the star shifts to the right along the main sequence. Stars with masses of the order of the sun are in the main sequence of 10-15 billion years (the Sun on it is already about 4.5 billion years old). Gradually, the energy in the center of the star runs out, the pressure drops. Since it does not resist gravity, the core shrinks, and the temperature there again rises, but reactions now proceed only at the boundary of the core inside the star. A star swells, its luminosity also grows. It leaves the main sequence in the upper right corner of the diagram, turning into a red giant with a radius greater than the radius of the orbit of Mars. When the temperature of the compressing helium (after all, hydrogen “burned out”) the core of the red giant reaches 100-150 million degrees, the synthesis of carbon from helium begins. When this reaction has exhausted itself, the external layers are reset. The hot inner layers of the star appear on the surface, blowing the separated shell by radiation into a planetary nebula. After several tens of thousands of years, the shell dissipates, and a small, very hot, dense star remains. As it cools, it goes into the lower left corner of the diagram and turns into a white dwarf with a radius of no more than the radius of the Earth. White dwarfs are a miserable finish to the normal evolution of most stars.
Some stars flash from time to time, dropping part of the shell and turning into New stars. Moreover, each time they lose about a hundredth of a percent of their mass. Disasters destroying a star are rarer - supernova explosions, in which more energy is emitted in a short time than from an entire galaxy. During an explosion, a star discharges its outer gas envelope (this is how it occurred during the supernova explosion of 1054. The crab nebula inside of which now lies a “star cinder” - a pulsar PSR0531, emitting even in the gamma range). The last supernova erupted nearby in 1987, in the Large Magellanic Cloud, 60 kiloparsecs from us. From this supernova, neutrino radiation was first recorded. If the mass of the star remaining after the disaster exceeds the solar by 2.5 times, a white dwarf cannot be formed. Gravity destroys even the structure of atoms. In this case, according to the laws of physics, rotation is sharply accelerated.
In 1963, mysterious quasistellar objects (quasars) were discovered, which are compact formations, the size of a star, but radiating like a whole galaxy. In their spectrum, against a continuous radiation background, bright lines are visible, strongly shifted to the red side, which indicates that quasars are moving away from us at great speed (and are located very far from our galaxy). The nature of quasars has not been fully explained. Recall that, according to the hypothesis of the Russian physicist A. Kushelev, the “redshift” has a different nature, to explain which there is no need to imagine the Big Bang (although in this case, quasars are one of the oldest objects in the Universe). And yet it is precisely the explosive version that most researchers adhere to so far.
