As compression clouds and growth what is saturated steam of its density gravitational force stronge

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The idea of the formation of stars from the rarefied interstellar matter was discussed Newton (1643-1727), but make sure it is finally allowed to justice astronomical observations in the second half of XX century. what is saturated steam With the help of infrared and radio telescopes what is saturated steam were not only found suitable clouds of interstellar gas, but managed to see to it that these clouds become unstable and are compressed by gravity, since its transformation into a star. It turned out that immediately prior to the compression temperature of the gas in the depths of such clouds what is saturated steam is only 10-30 K, and sometimes even 3-5 K, then there is the coldest objects in the Universe. They consist mainly of hydrogen molecules and helium atoms. Other chemical elements are present in small numbers and are concentrated mainly in dust particles of about 0.1 microns. Although the "interstellar standards" what is saturated steam these clouds are considered very dense, by earthly what is saturated steam standards, they are very sparse: the average distance between the dust particles of a few meters, and in 1 m of gas is present about 2 billion molecules, which is 10 16 times less than in air at normal conditions. Therefore, the gas-dust nebula from which 5 billion years ago formed the Sun was about 10 million times greater what is saturated steam than the size of our modern luminaries. Although the terrestrial habit we call the field of interstellar gas concentration "clouds", it should be understood that in their behavior they are significantly different from the usual for us, atmospheric clouds. For example, what is saturated steam ground floating clouds in the atmosphere, because their density is practically the same as that of the ambient air and clouds in interstellar hundred times denser medium between moving and therefore orbits in galactic as individual objects, almost like a star. But the main difference between the atmospheric and interstellar clouds - in their mass: in interstellar clouds, it reaches millions of solar masses, making gravity important factor in their evolution. Small clouds for some time able to withstand the force of gravity. But accidentally colliding and merging with each other, they increase their mass, and with it - the role of gravity.
Began to shrink under its own gravity, the cloud can no longer return to the original state of equilibrium. The fact that a decrease in the size of the cloud (R) the force of gravity (GM / R 2) is growing much faster than the opposing force her gas pressure (P). The reason for this is very effective cooling substances: all the heat released when the compression is leaving the cloud in the form of infrared what is saturated steam radiation dust. However, when compressing cloud becomes less transparent to radiation, because the number of absorbing particles in the beam path increases (ρR ~ M / R 2). But while the cloud is not reached very high density at which the infrared quanta difficult to leave it, it keeps the temperature almost constant and very low point - just a few degrees Kelvin. Therefore, the pressure gradient (the buoyancy force) is growing rather slowly (P / R ~ ρT / R ~ ρ 4/3), and the weight of a volume element of the cloud increases noticeably faster (ρΜ / R 2 ~ ρ 5/3).
As compression clouds and growth what is saturated steam of its density gravitational force stronger dominates the force of the gas pressure. For this reason, the rate of contraction is continuously increasing clouds, and about half a million years, its size is reduced to a thousand times. The volume of the cloud while decreasing a billion times, and as many times increases the average gas density. Due to the fact that the compression proceeds nonuniformly, what is saturated steam the density of the most rapidly growing areas in the central. This leads to the fact that exactly in the center of the cloud material what is saturated steam becomes opaque to infrared radiation, and this greatly reduces the effectiveness of cooling. Central regions what is saturated steam are beginning what is saturated steam to heat up quickly and the pressure of the gas inside what is saturated steam them begins to grow much faster than before, slowing compression. Soon the pressure becomes so great that the compression what is saturated steam at all stops and inside the cloud formed hydrostatic equilibrium core - the germ stars whose mass is only a few percent of the mass of clouds. Outside the core gas remains transparent to infrared radiation and continues to free fall almost to the center. Compresses the cloud within which formed the core of the equilibrium is called a protostar.
Falling at a rate of several kilometers per second gas shell encounters what is saturated steam a stationary core material and sharply decelerated down to a complete stop. Thus, the kinetic energy is converted into heat, which is about 50% goes into heating the gas, and the remainder is emitted to the outside. Initially, this radiation consists of infrared photons, but as rasut mass of the nucleus and its temperature, the emission spectrum of an increasing number of visible