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cosmogony(koz-mog -ŏ-nee) The study of the origin and evolution of cosmic objects and in particular the Solar System. See galaxies, formation and evolution; Solar System, origin; stellar evolution. Compare cosmology.
Cosmogony(religion, spiritualism, and occult)
A religion's cosmogony is its model of the creation of the universe. Jewish, Christian, and Islamic cosmogony begins with a six-day period of activity some six to ten thousand years ago. Some believe this to be a symbolic myth, others a historical fact.
Hindu and Buddhist cosmogony, along with many indigenous traditions, involve a cyclical understanding of the concept of time. There is no beginning or end. The wheel of samsara, the unending wheel of life (see Hinduism), turns forever.
Scientific theories now postulate a Big Bang, a beginning point when both time and space began.
A religion's cosmogony is expressed in Creation myths, stories that explain how things began. Jewish stories of God's six-day work week are contrasted with Hindu concepts of Vishnu sleeping on the cosmic ocean and dreaming a world into existence.
But it is a mistake to choose a religion based on its cosmogony. Within each tradition there are those believers who accept the latest scientific evidence while maintaining their traditional mythology. Mythological cosmogonies were not meant simply to explain how the universe was created. They almost always have a spiritual, moral, or ethical point to make as well.
the field of science that studies the origin and evolution of cosmic bodies and systems: stars and star clusters, galaxies, nebulae, and the solar system and all its members—the sun, the planets (including the earth) and their satellites, asteroids, comets, and meteoroids. The study of cosmogonical processes is one of the principal tasks of astrophysics. Insofar as all celestial bodies originate and develop, ideas about their evolution are closely linked with concepts of the nature of these bodies in general. The laws of physics and chemistry are widely used in modern cosmogony.
|Table 1. Technical characteristics of American launch complexes|
|1One launching pad in reserve; it was used only for launch of Apollo 10 2One launching pad in reserve 330–60 days includes prelaunch preparation as well as postlaunch repair time|
|Launch complex 39 for Saturn 5 launch vehicle||Launch complex 37 for Saturn 1 launch vehicle||Launch complex 40–41 for Titan 3C launch vehicle|
|Total area (ha) ..........||48.6||48||8.4|
|Cost (million dollars) ........||800||65||176|
|Number of launching pads ...||21||22||2|
|Type of transportation of rockets or stages ..........||Caterpillar||Two wheeled transporters for first and second stages||Two locomotives, 735.5 kW (1 ,000 hp) each|
|Prelaunch preparation time (days)||50–70||25||1|
|Postlaunch repair time (days) ...||14–42||30–603||up to 14|
Cosmogonical hypotheses in the 18th and 19th centuries were mainly concerned with the origin of the solar system. Only in the 20th century did the development of observational and theoretical astrophysics and physics make possible the serious study of the origin and evolution of the stars. The study of the origin and evolution of galaxies, whose nature was elucidated only in the 1920’s, was begun in the 1960’s.
The processes of the formation and evolution of most cosmic bodies and their systems proceed exceedingly slowly and take millions or billions of years. However, rapid changes are also observed, including processes of an explosive nature. In the study of the cosmogony of stars and galaxies, the results of observations of many similar objects that originated at different times and are at different stages of development can be used. However, in studying the cosmogony of the solar system we are forced to rely solely on the particulars of its structure and on the structure and composition of the bodies within it.
Historical outline of cosmogonical research. The period in which the general concepts of the evolution of the celestial objects were those of the Greek philosophers of the fourth to the first century B.C. (Leucippus, Democritus, Lucretius) was followed by a period of many centuries in which theology prevailed. Only in the 17th century did R. Descartes reject the myth of the creation of the world and present a picture of the formation of all celestial bodies as the result of the vortical motion of minute particles of matter. The foundation of scientific planetary cosmogony was laid by I. Newton, who drew attention to the laws of planetary motion. Having discovered the basic laws of mechanics and the law of universal gravitation, he arrived at the conclusion that the arrangement of the planetary system could not be the result of a coincidence. In 1745, G. L. Buffon advanced the hypothesis that the planets arose from globules of matter torn from the sun by the impact of an enormous comet (at that time comets were considered to be massive bodies). In 1755,1. Kant published The Universal Natural History and Theory of the Heavens, in which he first gave a cosmogonical explanation of the laws of planetary motion. At the end of the 18th century, W. Herschel, observing the sky though large telescopes of his own construction, discovered oval-shaped nebulae having varying degrees of concentration toward the central bright nucleus. This led to the speculation that the stars formed from nebulae by means of “condensation.” Relying on HerschePs observations and on the laws of planetary motion, P. Laplace formulated a hypothesis on the origin of the solar system that in many respects resembled Kant’s hypothesis. (When interested chiefly in the idea of the natural formation of the solar system out of an extended diffuse medium, we often speak of a unified Kant-Laplace hypothesis.) The Laplace hypothesis quickly won recognition, and as a result, astronomy was one of the first sciences to introduce the idea of evolution into modern natural science. However, in the course of the 19th century, new difficulties appeared in the Laplace hypothesis that could not be successfully resolved at that time. In particular, the hypothesis could not successfully explain why the sun now rotates very slowly, although earlier, during its contraction, it was rotating at a rate so rapid that matter separated from it under the action of centrifugal force.
At the end of the 19th century, the American scientists F. Moulton and T. Chamberlin advanced the hypothesis that the planets were formed from small solid particles, which they called “planetesimals.” They erroneously believed that the planetesimals rotating around the sun could have arisen through solidification of material ejected from the sun in the form of enormous prominences. (Such formation of planetesimals contradicts the law of conservation of angular momentum.) At the same time, the planetesimal hypothesis correctly described many features of the process of planet formation. Widely known in the 1920’s and 1930’s was the hypothesis of J. Jeans, who believed that the planets were formed out of hot material pulled from the sun by the gravitational attraction of a closely passing massive star.
The concept of the formation of stars through the condensation of diffuse nebular matter continues to be analyzed by most researchers. After the discovery of the mechanical equivalent of heat, the energy liberated during a star’s contraction was calculated (H. Helmholtz, 1854; W. Thomson [Lord Kelvin], 1862). It proved to be sufficient to sustain the sun’s radiation for a period of 107–108 years. At that time, such a length of time seemed sufficient. However, later, the study of the history of the earth showed that the sun has been radiating incomparably longer.
At the beginning of the 20th century unsuccessful attempts were made to solve the problem of stellar energy sources with the help of the newly discovered radioactive elements. The establishment of the mass-energy relation, which indicated that stars lose mass by radiating, led to hypotheses that matter was being annihilated in stellar interiors, that is, by the transformation of matter into energy. In this case, the transformation of massive stars into stars of small mass would take 1013–1015 years. The correct hypothesis proved to be that of the transmutation of elements, that is, the formation of more complex atomic nuclei from simple ones, primarily of helium from hydrogen. In 1938–39 specific nuclear reactions capable of supplying the radiation of stars were investigated (C. von Weizsäcker [Germany], H. Bethe). This was the beginning of the modern stage in the development of stellar cosmogony.
Only a few steps have been taken in working out the cosmogony of the galaxies. The classification of galaxies and clusters of galaxies is being carried out. Evolutionary changes in stars and the gaseous component of galaxies and their chemical composition and other parameters are being studied. The nature of the initial perturbations, whose development led to the disintegration of the expanding gas of the metagalaxy into individual condensations is being investigated. Calculations are being made of how the morphological type and other properties of galaxies depend on the mass and rotation of these primary condensations. Compact dense nuclei present in a number of galaxies are attracting great attention. The nature of the powerful radio emissions from certain galaxies is being studied, as well as the link between these emissions and explosive processes in the nuclei. Powerful explosions occurring in quasars and nuclei of active galaxies—for example, Seyfert galaxies, N-galaxies—are essential stages in the evolution of galaxies. Cosmogony develops on the basis of numerous facts encompassing the varied properties of celestial bodies.
Planetary cosmogony. In investigations of the earlier condition of the matter now forming the solar system, important roles are played by the regularities of the motion of the planets—their revolution around the sun in near-circular orbits lying almost in the same plane—and by the division of the planets into two groups differing in mass and composition—the group of terrestrial planets near the sun and the group of giant, or Jovian, planets distant from the sun. Furthermore, in seeking to clarify where the preplanetary material around the sun came from, an important role is played by the problem of the distribution of angular momentum between the sun and the planets: why is 2 percent of the total angular momentum of the entire solar system contained in the sun’s rotation while 98 percent belongs to the orbital motion of the planets, whose total mass is 750 times smaller than that of the sun?
In the 1940’s, after Jeans’ hypothesis was refuted, planetary cosmogony returned to the classical ideas of Kant and Laplace on the formation of the planets from diffuse matter. At present (1970’s) it is generally acknowledged that most of the planets accumulated from solid matter, while Jupiter and Saturn accumulated from solid and gaseous matter. Apparently, the cloud of gas and dust that existed near the sun’s equatorial plane extended to the present boundaries of the solar system.
Proceeding from the prevailing concepts of the formation of the sun from a contracting and rotating nebula, most astronomers consider that a protoplanetary cloud of a certain mass separated under the action of centrifugal force from this nebula at the final stage of its contraction (F. Hoyle [Great Britain], A. Cameron [USA], E. Schatzman [France]). However, in contrast to Laplace, who regarded this separation as a purely mechanical phenomenon, astronomers now take into account effects associated with the presence of the magnetic field and the corpuscular radiation of the sun. This has allowed them to explain the distribution of angular momentum between the sun and the planets within the framework of hypotheses of the joint formation of the sun and the protoplanetary cloud. Together with these hypotheses, a hypothesis on the capture of matter by the already-formed sun has been proposed (O. lu. Shmidt, H. Alfvén).
If the protoplanetary cloud was initially hot and consisted only of gases, then solid dust particles formed as it cooled. The first to condense were the less volatile substances, including silicates and iron, followed by the more volatile ones. The inner zone of the protoplanetary cloud was heated by the sun, and only nonvolatile substances could form there, primarily stony dust particles, whereas in the cold outer zone the volatile substances also condensed. Although the presence of dust made the cloud opaque, which enabled the outer zone to reach a very low temperature, the most volatile substances—hydrogen and helium— were unable to condense even there.
However, if the protoplanetary cloud was initially cold and the dust particles primarily consisted of volatile substances, then they could be retained in the cold outer zone of the cloud, whereas in the inner zone the volatile substances evaporated leaving only small stony residues.
Cosmic (solar) material contains a greater amount of volatile substances than nonvolatile ones. Therefore, an enormous difference must have arisen not only in the composition but also in the total quantity of dust matter in the inner and outer zones. These zonal differences subsequently led to differences in composition and masses of the terrestrial and Jovian planets.
Attempts to detect the occurrence of the process of condensation (or evaporation) of dust particles in the asteroid zone have been made through careful analysis of meteorites, which are fragments of asteroids and in certain cases may serve as examples of preplanetary matter little altered by subsequent processes. Some researchers see in the results of such an analysis an indication that the condensation of dust particles proceeded parallel with the accumulation of these particles into larger bodies. However, this does not agree with the results of theoretical computations, which show that the accumulation must have lasted hundreds or thousands of times longer than the cooling and condensation.
The formation of the planets from a protoplanetary cloud has been thoroughly investigated by O. lu. Shmidt and his col-leagues and proponents. This process may conveniently be divided into two stages. In the first stage, which probably lasted less than 106 years, numerous “intermediate” bodies, with diameters of the order of hundreds of kilometers, were formed from the dust components of the cloud. In the second stage, lasting about 108 years, the planets accumulated out of the swarm of intermediate bodies. (For the most distant planets—Uranus, Neptune, and Pluto—whose matter was scattered over enormous ring-shaped regions, the second stage may have lasted about 109 years.) In their principal stage of accumulation, the largest planets—Jupiter and Saturn—absorbed gases as well as solid bodies.
Different hypothetical variants of the formation process of the cloud lead to different variants in the course of the first stage. The intermediate bodies must have been formed either as a result of the accumulation of the dust into a thin disk and the disintegration of this disk into globules or as a result of coagulation of the dust particles, that is, “adhesion.”
The course of the accumulation of planets from the swarm of intermediate bodies essentially does not depend on the mechanism of formation. At first, these bodies moved in circular orbits in the plane of the dust layer that engendered them. They grew, merging with one another and scooping up the surrounding diffuse matter—the remnants of the “primary” dust and fragments that formed when the intermediate bodies collided with large relative velocities. With the growth of the intermediate bodies, their gravitational interaction increased and gradually changed the orbits of the bodies, increasing the mean eccentricity and mean inclination to the central plane. Those intermediate bodies that broke loose first in the growth process became the seeds of the future planets. During the consolidation of many bodies into planets, the individual properties of motion of the separate bodies averaged out, and therefore the orbits of the planets became almost circular and coplanar. The analysis of the process of accumulation of the planets from a swarm of solid bodies permitted O. lu. Shmidt to propose an explanation of the origin of the direct rotation of the planets and the law of planetary distances.
The growth of the terrestrial planets ceased when they had absorbed practically all the solid material in the vicinity of their orbits (only in the case of Mars was part of the matter in its “feeding zone” probably absorbed by massive Jupiter). However, the growth of the Jovian planets ceased when all intermediate bodies and their fragments were ejected from their zone of formation by gravity; at the same time the gases were ejected, in whose dispersion the intense corpuscular radiation of the young sun may have played an important role.
Inelastic collisions of bodies, which had occurred in the neighborhood of the growing planets, resulted in some bodies’ moving into satellite orbits. As a result, swarms of solid bodies and particles arose around the planets. The satellites of the planets accumulated from them. The moon probably accumulated from a near-earth swarm at a distance of about ten earth radii and then moved out to its present distance from the earth as a result of tidal interactions with the earth. Other hypotheses of the origin of the moon also existed. G. Darwin’s hypothesis, according to which the moon separated from the earth, and the hypothesis of the earth’s capture of the moon, which had formed in an orbit close to that of earth’s. The radius of the moon’s orbit after the capture was small, subsequently increasing as in the aforementioned hypothesis. The possibility of a smooth separation of the moon from the earth, which Darwin proposed, was refuted by the works of A. M. Liapunov and E. Cartan.
In the case of Jupiter and Saturn, systems of satellites, which moved in the direction of rotation of each planet in circular orbits lying in the equatorial plane of the planet, accumulated from the swarms around these planets. Such systems of satellites are similar to the solar system. Those satellites of Jupiter, Saturn, and Neptune that possess retrograde motion were probably captured from among the intermediate bodies. The remnants of these bodies are the present asteroids (stony bodies of the inner zone) and the nuclei of comets (icy bodies of the outer zone). Collisions among the asteroids lead to their fragmentation.
The study of meteorites has shown that the structure of some of them has been changed under the effect of high pressure (up to hundreds of kilobars) arising during collisions. The content in meteorites of short-lived isotopes, which originate from the action of cosmic rays, indicates that the disintegration processes engendering these meteorites occurred 107–108 years ago. The icy nuclei of comets form a cloud, extending out to 100–150,000 astronomical units from the sun, around the planetary system. There, at low temperatures, the ices are preserved indefinitely. Under the influence of stellar and later also planetary perturbations, individual nuclei move into smaller orbits and are transformed into short-period comets. Frequently approaching the sun, they evaporate and are destroyed in the course of several tens or hundreds of revolutions. Measurements of radioactive isotopes and their decay products show that the oldest meteorites are about 4.7 billion years old. Since asteroids, which are the parent bodies of meteorites, quickly accumulated at the very beginning of the formation of the solar system, this figure is taken to be the age of the entire solar system. Calculation of the age of lunar samples has shown that the moon was formed at the same time as the earth. The flows of dark lava that filled the basins of the lunar “seas” occurred a billion years later (3.1–3.6 billion years ago).
As the planets accumulated, they heated up. However, the mean surface temperature on the terrestrial planets was primarily determined by solar heating and the greenhouse effect. In general, heat escapes slowly from the deeper layers. A residue of 3–4 percent was sufficient to heat the interior of the earth and Venus to 1000°-1500°C, and the interiors of the Jovian planets to tens of thousands of degrees. The initial heating up of the earth and the moon was connected with the liberation of gravitational energy during the contraction of these bodies and, probably, with tidal deformations of these two initially close bodies. The subsequent evolution of the earth, moon, and the terrestrial planets was primarily determined by the accumulation of the heat liberated during the slow decay of radioactive elements— uranium, thorium, and others—which are found in negligibly small amounts in all rocks. The heating up and partial fusion of the interiors of these planets led to the melting of the crust and the liberation of gases and vapors. On planets of small mass (Mercury, Mars) and on the moon the gases and vapors were completely or to a significant degree dispersed into space; on the more massive planets, however, they were basically retained, forming an atmosphere and a hydrosphere (on the earth) or only an atmosphere (on Venus).
REFERENCESVoprosy kosmogonii, vols. 1–10. Moscow, 1952–64.
Shmidt, O. lu. Chetyre lektsii o teorii proiskhozhdeniia Zemli, 3rd. ed. Moscow. 1957.
Levin, B. lu. “Proiskhozhdenie Zemli.” Izv. AN SSSR. Fizika Zemli, 1972, no. 7.
Safronov, V. S. Evoliutsiia doplanetnogo oblaka i obrazovanie Zemli i planet. Moscow, 1969.
Symposium on the Origin of the Solar System. Nice, April, 1972. Paris, 1972.
B. IU. LEVIN
Stellar cosmogony. The problems of the origin and evolution of the stars and stellar systems are studied in the branch of cosmogony called stellar cosmogony.
In the course of its evolution a star passes through stages that are determined by changes in the conditions of mechanical and thermal equilibrium in its interior. As a result of nuclear reactions involving the conversion of hydrogen into helium (which serve as the energy source of stars on the main sequence of the Hertzsprung-Russell diagram and some giant stars), the chemical composition of the star’s core gradually changes; moreover, the mean molecular weight of the gas increases and the core becomes denser and hotter. Studies show that this is accompanied by an increase in the luminosity and radius of the star.
On the Hertzsprung-Russell diagram, the star, which was located on the main sequence at the start of its evolution, rises above it. As the hydrogen in a star of small mass continues to burn up, a core is formed with a density hundreds of thousands of times greater than that of water and a temperature of more than 107°K. The gas at such a density becomes degenerate. There is no longer any hydrogen in the star’s core, as a result of which nuclear reactions occur only in the core’s envelope, where the temperature is sufficiently high and there is hydrogen. The star expands; at this stage, its radius is tens of times greater than when the star was on the main sequence; the luminosity also increases greatly, and the star becomes a giant. The point corresponding to the star on the Hertzsprung-Russell diagram moves to the upper right portion owing to the star’s evolution. Gradually, the envelope, expanding, becomes transparent and the hot core becomes visible. The ultraviolet radiation from the core causes the gas in the envelope to glow, and a planetary nebula is formed from the giant star. After the core cools, the star becomes a white dwarf, which has no source of energy and slowly cools in the course of billions of years.
In stars that at the initial stage have a somewhat larger mass, the evolutionary changes proceed differently. In such stars, the temperature of the core increases at 120–140 million°C, and the conversion of helium to carbon begins; at still higher temperatures, even heavier nuclei are synthesized. The enormous amount of energy released expands the star’s core. The corresponding point on the Hertzsprung-Russell diagram moves in a complex manner between the branch of giants and the left part of the main sequence. After disposing of about half its mass, the star also becomes a white dwarf.
Still more massive stars (up to two solar masses) abruptly move off the main sequence into the region of the red super-giants. Heavier elements, up to the most densely packed nucleus, that of the iron atom, are formed in their cores. With a further increase in temperature, the iron nuclei are transformed into nuclei of other elements; however, in this case, energy is no longer liberated but absorbed and the star’s core does not heat up during contraction. The pressure of the degenerate gas cannot balance the weight of the core if the star’s mass is greater than 1.4 solar masses, and it continues to contract until the density of matter in it is on the order of the density of atomic nuclei. As this occurs, the electrons, under the influence of enormous pressure, combine with the nuclei, forming neutrons. Such neutron stars, with a radius of about 10 km, are pulsars. Some of the gravitational energy liberated during the contraction is transmitted to the envelope, which is ejected with a velocity of several thousand km/sec; an outburst of a Type II supernova occurs. Type I supernovas are formed at the end of the evolution of stars of smaller mass.
If the mass of a star’s core exceeds 2 solar masses, then the contraction does not cease even at nuclear density but occurs with increasing speed. When the speed of the collapse of matter toward the sun’s center approaches that of light, the star, because of relativistic effects, appears to solidify and stops radiating. Such a collapsed star can only be observed by its gravitation or by the radiation of gas falling on it. The time it takes for a star to evolve depends essentially on its mass. For the sun it is about 1010 years, and for a star of spectral class 0, several million years (in such stars, the reserves of hydrogen are quickly depleted). Therefore, all observable hot stars are young, recently formed, stars. The concentration of young stars in clusters and associations shows that stars are formed in groups. The connection of these groups with the interstellar medium, in particular with the dark band of compressed gas on the edge of the spiral arms, and a number of other facts have led to the idea that stars are formed during the contraction and fractionation of large, gas-dust clouds into individual globules, which continue to contract under the influence of their own gravitation.
At the initial stage of its evolution (up to the time that it arrives on the main sequence of the Hertzsprung-Russell diagram), a star shines through the energy of gravitational contraction. At this time, the points corresponding to the stars are located on the diagram above and to the right of their eventual position on the main sequence. Typical representatives of young stars of average mass that have not yet fully contracted are the T Tauri stars. Stars of very small mass contract for billions of years; such contracting stars are the flare stars of the UV Ceti type.
Magnetic fields play an important role in the formation of stars. Interstellar gas, under the influence of gravitational forces, glides along the lines of force and accumulates from great distances into dense complexes. When the mass of a complex becomes sufficiently large, the complex contracts across the lines of force. As it contracts, its rotation accelerates. Further contraction becomes possible only on the condition that part of the angular momentum can be transferred to the surrounding gas. This happens as a consequence of the twisting of the lines of force, whose pull transfers the rotation to the outer medium.
Galactic cosmogony. Various types of stars make up specific subsystems in the Milky Way Galaxy; these subsystems were formed at different stages in the formation of the Milky Way Galaxy.
At first, our galaxy was an extended, slowly rotating gaseous cloud. The gas contracted toward the center, forming star clusters in the process, most of which later dissipated. The stars that were formed at this time move in very elongated orbits and fill a slightly oblate spheroid—that volume that the gas formerly occupied. These stars are part of stellar subsystems belonging to the spherical component of the galaxy. In contrast to the stars that essentially move without friction, the gas loses kinetic energy as a result of its chaotic motions and therefore contracts. The radius of the spheroid decreases and its rotation accelerates until the centrifugal force balances gravity at the equator. After this, contraction occurs chiefly toward the equatorial plane. At this stage, subsystems belonging to the intermediate component of the Milky Way Galaxy were formed.
After the formation of subsystems of the planar component, the gas no longer contracted; it was restrained not so much by its motions as by the pressure of the magnetic field. The stars that formed from the gas at this stage belong to subsystems of the planar component. Hot stars and the clusters that they make up are young; they also belong to the planar component.
There are no massive stars in the other components of our galaxy, since their evolution has already ended. Clusters belonging to different components are also distinguished. In the planar components they contain- several hundred or several thousand stars and are called open clusters, while in the spherical components they contain tens or hundreds of thousands of stars and are called, because of their appearance, globular clusters. In the planar components the stars generally move in near-circular orbits and oscillate with respect to the galactic plane. In the intermediate components they move in more elongated orbits, while in the spherical components the plane of the elongated orbits is oriented almost randomly. The thicker the subsystem, the larger the variation of the stellar velocities perpendicular to the galactic plane.
In addition to age and kinematic differences, subsystems are also distinguished by the chemical composition of their stars. In subsystems of the intermediate components, the ratio of heavy elements to hydrogen and helium is several times less than in the planar components, and in the spherical components it is tens or even hundreds of times less. Moreover, the older the group of stars and the greater its mean distance from the galactic plane, the less its content of heavy elements. This feature is explained by the fact that heavy elements are formed within stars during nuclear reactions and supernova explosions. Together with supernova envelopes and stellar wind, the heavy elements enter the interstellar medium and the next generation of stars is formed from gas enriched with these elements. Helium is also formed during nuclear reactions, but the bulk of it was apparently formed in the prestellar stage of the evolution of the universe. Differences in chemical composition affect the spectra and internal structure of stars. In particular, subdwarfs are also main-sequence stars, but in spherical and intermediate subsystems they do not coincide with the main sequence owing to the difference in chemical composition, which alters their color.
Stars and the interstellar medium are two phases in the evolution of matter in galaxies. In time, the interstellar medium will become depleted, young stars will disappear in the Milky Way Galaxy, and a large part of the mass will become concentrated in stars of small mass, which evolve slowly, as well as in the remains of stars, that is, in white dwarfs, neutron stars, and more massive remnants in a state of collapse.
In the conception outlined, it is significant that both the stars themselves and the galaxies were formed as a result of the condensation of an initially diffuse gas. This conception follows from an enormous quantity of facts, in particular from the aforementioned differences among the subsystems. In fact, younger stars do include a large amount of those elements that are dissipated in the interstellar medium during the implosions of supernovas. The shape of subsystems of various ages shows that the material from which stars were formed was flattened; however, only a diffuse medium can be flattened, since dense bodies move almost without friction. Compact regions, which are surrounded by dense, cold gas, have been discovered with the aid of radio-astronomical observations. This phenomenon may be interpreted as the result of the formation of a hot star in the center of a cold, dense globule.
V. A. Ambartsumian has advanced another cosmogonical conception, based on observed explosions and nonstationary phenomena in objects of the most varied sizes (from white dwarfs to galactic nuclei) and on the presumed breakup of certain stellar systems and clusters of galaxies. According to this conception, galactic nuclei contain superdense “prestellar” matter, which also serves as the material for the formation of galaxies. Stellar associations, which are part of galaxies, are formed from “fragments” of this matter. The explosions that are observed on the surface of dwarf stars are also explained by the breakup of this prestellar matter. Clusters of galaxies are also assumed to be relatively young (in the astronomical sense of the word), having been formed from this prestellar matter. The properties of the prestellar matter are still unknown. However, in Ambartsumian’s conception it is assumed that the fundamental laws of modern physics may prove to be invalid for this matter.
REFERENCESSchwarzschild, M. Stroenie i evoliutsiia zvezd. Moscow, 1961. (Translated from English.)
Frank-Kamenetskii, D. A. Fizicheskie protsessy vnutri zvezd. Moscow, 1959.
Kaplan, S. A. Fizika zvezd, 2nd ed. Moscow, 1970.
Problemy sovremennoi kosmogonii, 2nd ed. Edited by V. A. Ambartsumian. Moscow, 1972.
S. B. PIKEL’NER