How does the evolution of stars

Like any body in nature, stars also can not remain unchanged. They are born, develop and, finally, "die." The evolution of stars takes billions of years, but there are disputes about the time of their formation. Earlier, astronomers believed that the process of their "birth" of stellar dust requires millions of years, but not so long ago, photos of the sky area from the Great Orion Nebula were obtained. For a few years there was a small star cluster.

In the photographs of 1947, a small group of star-like objects was recorded in this place. By 1954, some of them had already become oblong, and five years later, these objects were divided into separate ones. So for the first time the process of the birth of stars passed literally in front of astronomers.

Let's examine in detail how the structure and evolution of the stars go, where begins and ends their endless, by human standards, life.

Traditionally, scientists believe that the stars are formed as a result of the condensation of clouds of gas-dust medium. Under the influence of gravitational forces, an opaque gas ball is formed from the formed clouds, dense in structure. Its internal pressure can not balance the gravitational forces that compress it. Gradually, the ball shrinks to such an extent that the temperature of the stellar interior increases, and the pressure of the hot gas inside the ball balances the external forces. After that, the compression stops. The duration of this process depends on the mass of the star and usually ranges from two to several hundred million years.

The structure of the stars assumes a very high temperature in their interior, which contributes to the continuous thermonuclear processes (the hydrogen that forms them, turns into helium). It is these processes that cause the intense emission of stars. The time for which they expend the available supply of hydrogen is determined by their mass. The duration of the radiation also depends on this.

When the hydrogen reserves are depleted, the evolution of the stars approaches the stage of formation of the red giant. This happens as follows. After the cessation of the release of energy, the gravitational forces begin to compress the nucleus. In this case, the star significantly increases in size. Luminosity also increases, as the process of thermonuclear reactions continues, but only in a thin layer at the core boundary.

This process is accompanied by an increase in the temperature of the contracting helium core and the conversion of helium nuclei to carbon nuclei.

According to forecasts, our Sun can turn into a red giant in eight billion years. Its radius in this case will increase by several tens times, and the luminosity will grow hundreds of times in comparison with the current indicators.

The lifetime of a star, as already noted, depends on its mass. Objects with a mass that is less than solar, very economically "expend" the reserves of their nuclear fuel, so they can shine for tens of billions of years.

The evolution of stars ends with the formation of white dwarfs. This happens with those of them whose mass is close to the mass of the Sun, i. E. Does not exceed 1.2 of it.

Giant stars, as a rule, quickly deplete their stock of nuclear fuel. This is accompanied by a significant loss of mass, in particular, due to the dumping of external shells. As a result, only the gradually cooling central part remains, in which nuclear reactions have completely stopped. Over time, such stars stop their radiation and become invisible.

But sometimes the normal evolution and structure of stars is disrupted. Most often this concerns massive objects that have exhausted all types of thermonuclear fuel. Then they can be transformed into neutron, supernovas or black holes. And the more scientists learn about these objects, the more new questions arise.