A star is born lasts millions of years, and is hidden from us in the depths of dark clouds, so the process is virtually inaccessible to direct observation. Astrophysicists are trying to explore it in theory, with the help of computer simulation. Turning a fragment of clouds in the star accompanied by gigantic change in the physical conditions: the temperature of the substance increases by approximately 106 times, and the density - 1020 times. Tremendous changes all the characteristics of the emerging stars are the main difficulty theoretical consideration of its evolution. At the stage of such changes, the original object is not a cloud, but not a star. Therefore, it is called a protostar (from the Greek. "protos" - "first").

In General terms, the evolution of proto-stars can be divided into three stages, or phases. The first stage - separation portion of the cloud and its seal - we have already considered. After him comes the stage of fast compression. At the beginning of the radius of the protostar about a million times more sun. It is completely opaque to visible light, but transparent to infrared radiation with a wavelength greater than 10 microns. Radiation carries away the excess heat produced by compression, so that the temperature does not rise and the pressure of the gas shall not prevent the collapse. There is a fast compression, almost free fall substances to the center of the cloud.

However, as the compression protosses-let all things be done less transparent, which makes the output radiation and causes a rise in temperature of the gas. At some point protostar is practically transparent for own thermal radiation. The temperature, and with it the gas pressure increase rapidly, the contraction is slowing.

Warmer temperatures cause significant changes of properties of substances. At a temperature of several thousand degrees molecules are split into individual atoms, and at a temperature of about 10 thousand degrees ionised atoms, i.e. destroyed their electron shell. These energy-intensive processes for some time delay the growth of temperature, but then he resumed. Protostar quickly reaches the state where gravity is almost balanced by the internal pressure of the gas. But because the heat is still a little goes outside, and other energy sources, in addition to compression, protostar no, she continues to slowly shrink and the temperature in its depths is increasing.

Finally, the temperature in Central protostar reaches several million degrees, and start the fusion reaction. Heat due to the heat fully offset the cooling protostar from the surface. Compression stops. Protostar becomes a star.