Introduction

   Stellar evolution in astronomy - the sequence of changes, which star is exposed during its life, that is, for hundreds of thousands, millions or billions of years until it radiates light and warmth. During such enormous periods of time changes are very significant.

   The star begins its life as a cold rarefied cloud of interstellar gas, compressed under its own gravity and gradually taking the form of a ball. Compression energy of gravity is moving in the heat and the temperature of the object increases. When the temperature in the center reaches a few million K, thermonuclear reactions begin and compression stops. The object becomes a full-fledged star. In this state, it remains for most of his life while on the main sequence diagrams Gertsshprunga - Rassella, until the fuel in its nucleus. When the star in the center of the entire hydrogen turns into helium, helium nucleus is formed, and the thermonuclear hydrogen burning continues at its periphery.

   During this period, the structure of the star begins to evolve. Its luminosity increases, the outer layers expand and the surface temperature is reduced - the star becomes a red giant, which form a branch in the diagram Gertsshprunga-Russell. This branch star holds much less time than on the main sequence. When the accumulated mass of helium nucleus becomes large, it does not hold its own weight and begins to shrink, if the star is massive, with increasing temperature may cause further thermonuclear conversion of helium into heavier elements.

   The study of stellar evolution can not be observed for only one star - many changes in the stars proceed too slowly to be noticed, even after many centuries. Therefore, scientists are exploring a lot of stars, each of which is at a certain stage in the life cycle. Over the past few decades, widespread in astrophysics been modeling the structure of stars, using computing technology.