Bester description. Bester is a hybrid: bester for ponds
Interstellar medium rarefied matter, interstellar gas and tiny dust particles that fill the space between the stars in our and other Galaxy x. The composition of M. s. In addition, they include cosmic rays, interstellar magnetic fields (See Interstellar magnetic field), as well as quanta of electromagnetic radiation of various wavelengths. Near the Sun (and other stars) M. s. passes into the interplanetary medium (See Interplanetary medium). The space between galaxies is filled by the Intergalactic Medium. For the first time, V. Ya. Struve (1847) came to the conclusion about the existence of a solar system that absorbs the light of stars; however, its existence was proven only in the 30s of the 20th century ( American astronomer R. Trampler and Soviet astronomer B. A. Vorontsov-Velyaminov). Interstellar gas consists of neutral and ionized atoms and molecules. The bulk of the gas consists of hydrogen and helium atoms (about 90% and 10% by number of atoms, respectively) with a small admixture of oxygen, carbon, neon, and nitrogen (about 0.01% each). Of the molecules, the most abundant is H 2, concentrated in clouds. In addition, there are small amounts of CH, OH, H 2 O, NH 3, CH 2 O and other organic and inorganic molecules. Interstellar gas is almost uniformly mixed with interstellar dust, consisting of particles measuring 10 -4 -3 10 -6 cm. Small particles consist of Fe, SiO 2, larger ones have partially graphite cores, possibly with an admixture of iron, and shells of frozen gases CH 4, NH 3, H 2 O and others. Gas and dust are almost completely absent in elliptical galaxies, while in S-type spiral galaxies a , S a b c constitute, respectively, about 1%, 3%, 10% of the mass of the galaxy, and in irregular galaxies - on average 16%. Interstellar gas and dust are highly concentrated towards the plane of galaxies, forming a disk whose thickness averages several hundred ps , increasing towards the periphery sometimes up to several KPS . The gas concentration in the disks is on average about 1 or several atoms per 1 cm 3 (density about 10 -24 g/cm 3 ); Outside the disk and at its edges, the gas density is much lower. In spiral galaxies gas and dust are concentrated in spiral arms (branches): the density of gas between the arms of the galaxy is 3-10 times less than in the arms. In the arms, about 80-90% of the gas is concentrated in interstellar clouds, which often combine to form gas-dust complexes, located mainly on the inner (concave) side of the spiral arms. The parameters of interstellar clouds are extremely diverse. In our Galaxy, the diameters of interstellar clouds are usually 5-40 constitute, respectively, about 1%, 3%, 10% of the mass of the galaxy, and in irregular galaxies - on average 16%. Interstellar gas and dust are highly concentrated towards the plane of galaxies, forming a disk whose thickness averages several hundred, the concentration of atoms in them is from 2 to 100 in 1 . The gas concentration in the disks is on average about 1 or several atoms per 1, temperature 20-100 K. Clouds occupy about 10% of the volume of the Galaxy's disk. Gas and dust M. s. together with the stars, they move in the disk of galaxies around its center in orbits close to circular, with average speeds of 100-200 km/sec. Individual clouds interstellar gas have their own (peculiar) velocities, the average value of which is 10 km/sec, sometimes reaching 50-100 km/sec. In the galactic corona, gas is observed falling onto the galactic plane at speeds of tens and hundreds (up to 200) km/sec; The origin of this gas is not clear. The concentration of atoms between clouds is 0.02-0.2 in 1 . The gas concentration in the disks is on average about 1 or several atoms per 1, temperature 7-10 thousand K. Hydrogen, helium and other elements, the ionization potential of which is greater than that of hydrogen, are very weakly ionized in clouds, and between clouds the ionization of hydrogen is several tens of percent. The remaining elements are singly ionized by starlight. Such clouds and the medium between them are called HI (neutral hydrogen) regions and occupy the bulk of the disk of galaxies. Around hot O-class stars, hydrogen is highly (up to 99%) ionized by ultraviolet radiation. Such regions are called HII (ionized hydrogen) regions or Strömgren zones. the temperature of the HII regions reaches 6000-8000 K, their sizes, depending on the temperature of the star and the density of the gas, vary from fractions constitute, respectively, about 1%, 3%, 10% of the mass of the galaxy, and in irregular galaxies - on average 16%. Interstellar gas and dust are highly concentrated towards the plane of galaxies, forming a disk whose thickness averages several hundred up to several dozen, and in exceptional cases - up to hundreds constitute, respectively, about 1%, 3%, 10% of the mass of the galaxy, and in irregular galaxies - on average 16%. Interstellar gas and dust are highly concentrated towards the plane of galaxies, forming a disk whose thickness averages several hundred. Usually, around hot stars, not just ionized interstellar clouds are observed, but much denser diffuse nebulae, in which the concentration reaches tens and hundreds of atoms per 1 . The gas concentration in the disks is on average about 1 or several atoms per 1. Perhaps these are the remnants of the dense complex from which the hot stars formed. Such HII regions gradually expand under the influence of hot gas. If on the path of such a region there is a compaction belonging to the HI region, then the boundary of the HII region goes around this compaction, exposing it on all sides. This is how dark (against the background of luminous HII regions) cold dense HI regions are formed, having the form of elongated ropes (the so-called elephant trunks) or spherical clots (globules). In the spectrum of the HII regions, bright lines of hydrogen and forbidden lines of oxygen, nitrogen, sulfur and some other elements are observed, as well as weak continuous spectrum. In the radio range, these regions glow in a continuous spectrum and in hydrogen and helium lines, which arise during quantum transitions between very high energy levels. In areas of HI gas optical rays does not light up. It is studied by the absorption lines of light from stars located behind these regions. Especially a lot of information is provided by the resonance absorption lines of atoms and ions located in the ultraviolet region and observed from space probes. Information about neutral hydrogen in the Galaxy and other galaxies, about its distribution and movement is obtained by observing radio lines of neutral hydrogen with a wavelength of 21 cm. In this line, however, only a small fraction of the thermal energy of the gas of the HI regions is emitted. The main share of energy is emitted by HI regions in the far infrared spectral lines of O atoms, C, Si, Fe ions and others. The average density of dust in the galactic disk is 10 -26 g/cm(0.01 gas density). This dust absorbs starlight, with blue rays being stronger than red rays. Therefore, due to dust, the light of distant stars is visible not only weakened, but also redder. The presence of dust does not allow us to observe stars lying in the plane of the Galaxy at distances exceeding 3 , increasing towards the periphery sometimes up to several from the earth. Dense clouds of gas and dust that absorb light appear dark against a light background Milky Way. Dark gas and dust clouds stand out even more sharply if they are projected onto a light nebula. Close enough bright stars(mostly Class B) dust is illuminated enough to be photographed from Earth; such light clouds are called reflection nebulae. The layer of gas and dust in other edge-on galaxies is visible as a dark stripe (see, for example, ill.
). Interstellar dust grains have a nonspherical shape and are oriented on average in a certain way relative to magnetic field Galaxies, which causes polarization of star light. The masses of large gas-dust complexes reach tens and hundreds of thousands of solar masses. In their central parts the temperature is very low (sometimes only 5-6 K) with a concentration of atoms up to hundreds per 1 . The gas concentration in the disks is on average about 1 or several atoms per 1 and more. The density of dust in them is more than 1/100th the density of gas. The last circumstance is due to the fact that when low temperatures and high densities, molecules, including polyatomic ones, form and stick to dust particles. Stars can form in such places. In this regard, it has important the fact that compact objects (about 10 15 in size) are observed in the central parts of the complexes cm and less), from which stars (see Protostars) and planets may possibly form. They emit very intensely in the radio lines of OH, H 2 O and other molecules, the nature of the radiation of which is sometimes similar to that of lasers. Particles that make up cosmic rays and have enormous energies - from 10 6 to 10 20 ev, in M. p. much less than its other components, but their total energy is 1 . The gas concentration in the disks is on average about 1 or several atoms per 1 is about 1 ev, that is, exceeds the energy of thermal movements of interstellar gas. High-energy cosmic rays weakly interact with gas and dust, occasionally causing nuclear reactions. Less energetic particles (10 6 -10 7 ev) are capable of heating and ionizing interstellar gas; they are one of the main sources of heating of HI regions. The strength of the interstellar magnetic field is low (10 5 times weaker than the Earth's magnetic field), but its energy is approximately equal to the energy of cosmic rays. Therefore, the pressure of cosmic rays and the magnetic field play a significant role in the dynamics of magnetism. Electromagnetic quanta in MS. have frequencies from the radio range to hard gamma radiation. The greatest impact on interstellar gas and dust is exerted by optical, ultraviolet and soft X-rays (with photon energies less than 1 kev). The latter partly come from intergalactic space, and partly arise in X-ray sources inside the Galaxy and cause (together with cosmic rays) heating and partial ionization of HI regions. Optical and ultraviolet quanta in MS. are the result of radiation from the stars of the Galaxy. In galaxies, there is a constant exchange of matter between magnets. and stars. M. s. serves as material for the formation of stars, and the stars, in turn, eject part of the matter into the solar system, simultaneously informing the gas kinetic energy. This happens both at the quiet stages of the development of stars, and at the end of their evolution, when the stars shed their shell, forming a planetary nebula, or explode as a supernova (See Supernovae). There is a constant circulation of matter, in which the amount of gas in M. s. is gradually depleted. In particular, the latter circumstance explains that there is no gas in elliptical galaxies, while in irregular galaxies there is a lot of it: here it is least depleted. Since during the evolution of stars and especially during explosions supernovas nuclear reactions change chemical composition gas, the composition of the solar system changes over time, and consequently, the composition of the stars formed from it. In addition, gas exchange occurs between galactic nuclei and stars. Lit.: Pikelner S.B., Physics of the interstellar medium, M., 1959; Kaplan S. A., Pikelner S. B., Interstellar environment, M., 1963; Grinberg M., Interstellar dust, translation from English, M., 1970; Space gas dynamics, [translation from English], M., 1972; Bakulin P.I., Kononovich E.V., Moroz V.I., Course of General Astronomy, M., 1970; Martynov D, Ya., Course of general astrophysics, M., 1971; Aller L., Astrophysics, translation from English, vol. 2, M., 1957. S. B. Pikelner, N. G. Bochkarev.
Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what “Interstellar medium” is in other dictionaries:
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Even from the above brief overview one can see how complex the structure of the interstellar medium is. Let us list the components of which it should consist.
Compact regions with Te Clouds have such characteristics, which are studied by their molecular radio lines. They are characterized by a wide range of densities, many of them associated with regions of recent star formation. In table 17.2, borrowed from the review, shows the values of densities, sizes, degrees of ionization and root-mean-square velocity dispersions characteristic of these regions.
Diffuse neutral hydrogen. Most of what is shown in Fig. 17.1 neutral hydrogen is diffuse, i.e. it does not enter the clouds. It is clear that the density varies from point to point, but on average the value can be used with a reasonable degree of accuracy. Some of this gas may be hot, but of course it is not ionized.
Ionized gas. The regions, which are one of the most interesting astronomical objects in the Galaxy, are directly associated with young, bright, hot stars of spectral types, of course, not typical for the interstellar medium. Many of the methods described above are used for a comprehensive study of these objects. As an example in Fig. Figure 17.3 shows the results of observations of the source in different ranges. In general, it represents a source of diffuse thermal bremsstrahlung radio emission. At higher resolution, individual areas are visible, some of them have a shell structure, meaning that they arose as a result of a recent outbreak
(click to view scan)
(see scan)
star formation. The areas associated with powerful infrared sources are even more compact. Finally, smallest sizes have sources of maser radiation on molecules and the corresponding physical parameters are shown in Fig. 17.3.
There is also an ionized component of the diffuse interstellar gas. Its density is best determined by measuring the dispersion of pulsars. The values found in this way have a large scatter, which is not surprising, since physical conditions in the interstellar medium vary widely. A reasonable average value for the density of interstellar gas is
Hot phase Observations of highly ionized elements, for example, show that a much hotter phase must be present in the interstellar gas. It is noteworthy that its temperature is not very different from the temperatures of old supernova remnants. As can be shown, a significant part of the interstellar gas is constantly heated shock waves, arising at the boundaries of old supernova remnants. This provides a rather attractive explanation for the hot phase.
It is clear that the structure of the interstellar medium is very complex. However, it is useful to have a simple model for calculations. The regions are concentrated near the Galactic plane. The half-thickness of the neutral hydrogen layer (i.e., the distance between half-density levels) is approximately On the other hand, judging by the rotational measures, the bremsstrahlung absorption at low frequencies and measures of pulsar dispersion, the half-thickness of the layer is much greater, about The accuracy of these values is low, but they give a correct order-of-magnitude idea of the distribution of the various components of the gaseous disk of the Galaxy. These values refer to the vicinity of the Sun. Closer to the center of the Galaxy, the situation changes significantly and within a radius from the center most of the hydrogen is in the molecular state.
Finally, we did not even try to understand the mechanisms of heating and ionization of interstellar gas. Many of them are developed in detail. Among them: heating and ionization by cosmic rays, i.e. ionization losses, which were discussed in detail in Chap. 2; heating during cloud collisions; heating with hard ultraviolet and soft x-ray radiation; heating during supernova explosions. By virtue of great variety structures in the interstellar medium, it would be surprising if for each of the listed mechanisms there were not a point in the Galaxy where it predominates.
The mechanism of supernova heating provides an attractive explanation for the existence of a very hot phase. The original work by Cox and Smith suggested that further heating could occur through collisions of old supernova remnants. According to these authors, the intersection of old shells and their heating during collisions lead to the formation of a network of hot gas that permeates the galactic disk.
And sterlet milk. The name was formed from the first letters of the “parents”, and if translated from English (“best”), you get “the best”. This is exceptional Russian work, started by Professor N.I. Nikolyukin and subsequently continued by his students under the leadership of I.A. Burtseva.
Today bester is a fish that is grown in industrial scale not only in Russia, but also in the USA, the Baltic states, France, Belarus, and Italy. Perhaps years will pass before the first human-created species of animals will begin the whole group domesticated fish.
Bester is a fish obtained after many failed experiments, since Nikolyukin carried out various crosses of sturgeons, but did not even think about connecting beluga and sterlet. Not only are their masses incomparable (beluga grows up to a ton, and sterlet - up to 2 kg), they spawn in different time and in different places, so they also belong to different genera of sturgeon. And with intergeneric crossing, as is known, the offspring are sterile. A study of the genetics of these fish species revealed that they the same number chromosomes, that is, a “marriage” between them is possible.
The efforts of our scientists have paid off. for which any change in their usual habitat turned out to be disastrous, it became possible to grow in
ponds like carp. It turned out that the hybrid requires deeper bodies of water. And he can live like in sea water, and in fresh. Bester began to be grown in cages, that is, fenced areas of the sea or reservoirs with a “roof” and “bottom” so that the fish would not swim away.
Took it from my “parents” best fish bester. The photo confirms this. The beluga gave rise to intensive growth and predatory image nutrition, and from sterlet - excellent-tasting meat and early ripening. In addition, this hybrid is quite prolific. A female can lay up to 150 thousand eggs (more than a sterlet, but less than a beluga).
In matters of nutrition, there were also advantages. Bester is a lazy fish, it doesn’t have enough food, like salmon or trout, for example, but takes it as if reluctantly. It is impossible to overfeed him. By the way, trout even die from gluttony. The hybrid can live without food for a couple of months.
Bester is not a schooling fish. Each individual is individual, moves in the pool (cage) on its own or stands still, not paying attention to others. Reflexes are developed well. For example, the boat from which feeding is carried out
They recognize her very well and swim up to her. Hybrids are little susceptible to disease, which cannot be said about other mass-grown fish. They are hardy, balanced and calm.
Considering that most of the caviar is used for food, doubts may arise as to whether there are enough beluga and sterlet in the wild to obtain sufficient quantities bestera. Undoubtedly, because from every kilogram of fertilized eggs you can get tons of fish.
Since the production of third-generation hybrids, deviations from the norm began to appear in the form of underdeveloped eyes, fused bugs, and others. The offspring of besters are very variable in snout length, growth rate, and mouth shape. Breeders have yet to stabilize the hereditary system and increase the viability of the offspring. Science does not stand still, and there is hope that scientists will be able to solve the problems.
Sometimes amateur fishermen come across fish species that are difficult to recognize on a fishing rod or in a net. These are hybrids that appear as a result of random crossing (hybridization) of fish belonging to different types. But fish breeding scientists carry out targeted hybridization of fish to obtain hybrids with certain qualities beneficial to humans. An example of a successful hybrid among sturgeons is the bester fish, characterized by rapid growth, early maturation and having delicious meat and caviar.
The path from a hybrid of sturgeon and sterlet to bester
To increase the supply of sturgeon fish, which have excellent gastronomic qualities (tasty and healthy meat and caviar), hybridization is very important. Obtaining a hybrid and sterlet opens up broad prospects for its cultivation in many inland water bodies (reservoirs, pond farms, and others).
The very first experience in producing hybrid sturgeon fish was undertaken back in 1869. Academician Philip Ovsyannikov and Professor Alexander Kovalevsky conducted an experiment on artificial fertilization of sterlet eggs in the middle Volga, where the spawning grounds of sterlet and sturgeon were located. Some of the caviar was fertilized with sturgeon milk, and for the first time, hybrid sturgeon offspring were obtained. Over the next 80 years, these bold experiments were not continued.
Directed experiments on sturgeon hybridization
The resumption of work on obtaining sturgeon hybrids occurred in 1949 by Nikolai Nikolaevich Nikolyukin, the author of a successfully defended doctoral dissertation"Interspecific hybridization of fish."
As a result of many years of work carrying out numerous experiments, a hybrid was obtained that inherited the best qualities of its parents - bester fish, the name of which was coined by Professor Nikolyukin N.I. It is composed of the first syllables of the names of the parent species (beluga and sterlet). It coincided completely by chance that with in English the word “best” is translated as “the best.” And the resulting hybrid 100 percent justified the meaning hidden in its name.
Setting goals and getting started
When starting to study the hybridization of sturgeons, Professor Nikolyukin set his goal to obtain new forms of these fish that would be able to live sedentary lives in reservoirs without making long migrations for reproduction. He conducted his experiments at a small fish hatchery on the Volga near Saratov.
For successful crossbreeding, it is necessary that the caviar and milt from the producers be fully ripe. This circumstance was difficult to overcome: it was necessary to constantly catch new fish. And only with the advent of the methodology of Professor N.L. Gerbilsky. to stimulate the maturation of eggs and milk by introducing a pituitary injection, experiments began to be carried out much faster. After the fish received such an injection, the eggs and milt matured in one to two days.
Nikolyukin conducted experiments on crossing sturgeons very carefully, crossing each species with all. Receiving natural hybrids from fishermen (natural crosses among sturgeons were always found), he crossed them with pure species. Example: a male hybrid (sterlet and stellate sturgeon) was crossed with a female sterlet.
In this sequence of experiments, the attempt to fertilize beluga eggs with milt obtained from sterlet turned out to be almost complete. And it was as a result of this experiment that the famous bester fish was obtained.
Success of an unplanned experiment
His wife (Timofeeva Nina Apollonovna) also worked with Nikolai Nikolaevich. It was she who began the experiment by crossing beluga and sterlet. IN natural conditions Hybrids of these two fish have never been found, probably because their spawners do not meet each other.
The reasons for this were obvious:
- The spawning grounds of beluga and sterlet are located far from each other, and their spawning times do not coincide.
- Their size is very different: the beluga can weigh up to one ton, while the sterlet can reach up to two kilograms (very rarely more).
Another important circumstance usually stops breeders: intergeneric crossing does not distinguish the fertility of the offspring. Therefore, in his experiments Nikolyukin considered different variants crossing fish only of the genus Acipenser (thorn, sturgeon, sterlet and stellate sturgeon) from the Aral and Caspian seas. Beluga belongs to another genus Huso, just like the one that lives on far east. It turns out that the experiment started by Nina Apollonovna to produce a hybrid of beluga and sterlet was unplanned. But he gave the best result.
During the experiment, second-generation hybrids were even obtained, both parents of which were hybrid individuals, that is, offspring were obtained from a sexually mature female and male Bester. It was a real sensation.
Genetic characteristics of producers are important when crossing
The reason for the successful experiment to obtain bester lies in genetic characteristics sturgeon fish. All sturgeons (excluding sturgeon) have the same number of chromosomes. The reason for the sterility of hybrids based on sturgeon, which has 2 times more chromosomes than all the others, has become clear.
Due to genetic similarity, that is, the presence of an equal number of chromosomes, the beluga (which is the most big fish sturgeon family) and the smallest of this family (sterlet) can successfully “marry” and produce viable offspring that have other advantages.
Bester's appearance and biology
A photo of a bester fish is remotely very similar to a photo of any other sturgeon fish: along the body there are clearly visible five rows of bone bugs (one on the back, two on the sides and two on the ventral side).
A closer look at the appearance of the bester reveals the features of each of the “parents”:
- Antennae located under the snout in two pairs, like a beluga: flattened or slightly wavy with leafy appendages.
- The mouth has intermediate form: in the beluga it is semilunar, and in the sterlet it is transverse.
- The color varies from sterlet to beluga: from light gray and light brown shades to black, brown and gray-brown.
The contrast between the dark back and light belly is more pronounced than in other sturgeons, which is also noticeable in the photo of the bester fish.
Features of bester biology and breeding
Bester fish are capable of reproduction, but in aquaculture conditions this hybrid is bred artificially. Offspring are always obtained artificial insemination beluga caviar with sperm from a male sterlet. For this purpose, spawners are caught in natural reservoirs and the development and maturation of their reproductive products (caviar and milt) is accelerated. The eggs of one female beluga are fertilized with a mixture of sperm taken from several male sterlet. Incubation of eggs lasts five to ten days (this depends on the water temperature). The hatched larvae are first planted in trays. After the juveniles move to self-catering it is transferred to special nursery ponds.
What is the value of bester
Bester fish has best qualities, inherited from parents:
- High growth rate (like beluga). Maximum length bodies up to 180 centimeters and weight up to thirty kilograms.
- Increased endurance and vitality: withstands a wide range of salinity (from) to 18 ppm) and temperatures increased to 30 degrees (with a high oxygen content in the water).
- Early maturation (like sterlet): males become sexually mature at three to four years, and females at six to eight years.
- High taste qualities meat and caviar. From females weighing twelve to eighteen kilograms, two to three kilograms of black caviar are obtained.
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