Like any body in nature, stars also can notremain unchanged. They are born, develop and, finally, "die." The evolution of stars takes billions of years, but there are disputes over the time of their formation. Previously, astronomers believed that the process of their "birth" of stellar dust requires millions of years, but not so long ago, photographs of the sky region from the Great Orion Nebula were obtained. For a few years there was a small star cluster.
In the photographs of 1947 in this place wasrecorded a small group of star-like objects. 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 take a closer look at how the structure and evolution of the stars go, what begins and ends with their endless, by human standards, life.
Traditionally, scientists suggest that the starsare formed as a result of the condensation of clouds of the 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 hightemperature in their bowels, 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 starsapproaches 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. The 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.
Under forecasts, our Sun can turn into athe red giant in eight billion years. Its radius in this case will increase by several tens of times, and the luminosity will increase hundreds of times in comparison with the current indicators.
The lifetime of a star, as alreadyit was noted, depends on its mass. Objects with a mass that is less than solar, very economically "expend" their nuclear fuel reserves, 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 exhaustits own 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 ceased. Over time, such stars cease their radiation and become invisible.
But sometimes the normal evolution and structure of the starsis violated. 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.
