Like any body in nature, stars also cannot remain unchanged. They are born, developed and, finally, “die”. The evolution of stars takes billions of years, but there is debate about the time of their formation. Previously, astronomers believed that the process of their "birth" from stardust took millions of years, but not so long ago, photographs of a region of the sky from the composition of the Great Nebula of Orion were obtained. In a few years, a small star cluster appeared there.
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 after another five years, these objects broke up into separate ones. So for the first time the process of birth of stars took place literally in front of astronomers.
Let's take a closer look at how the structure and evolution of stars goes, with what their endless, by human standards, life begins and ends.
Scientists traditionally suggest that stars are formed as a result of condensation of clouds of a gas-dust medium. Under the influence of gravitational forces, an opaque gas sphere is formed from the formed clouds, which is dense in structure. Its internal pressure cannot balance the gravitational forces compressing it. Gradually, the ball contracts so much that the temperature of the stellar interior rises, 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 stars suggests a very high temperature in their bowels, which contributes to continuous thermonuclear processes (the hydrogen that forms them turns into helium). It is these processes that cause the intense emission of stars. The time it takes for them to consume an available supply of hydrogen is determined by their mass. The duration of radiation also depends on this.
When hydrogen reserves are depleted, the evolution of stars comes to the stage of the formation of the red giant. This happens as follows. After the cessation of energy release, gravitational forces begin to compress the core. 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 boundary of the nucleus.
This process is accompanied by an increase in the temperature of the contracting helium nucleus and the conversion of helium nuclei into carbon nuclei.
According to forecasts, our sun can turn into a red giant in eight billion years. At the same time, its radius will increase several dozen times, and the luminosity will increase hundreds of times compared with current indicators.
The life span of a star, as already noted, depends on its mass. Objects with a mass that is smaller than the sun are very economically “consuming” 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 to those of them whose mass is close to the mass of the Sun, i.e. does not exceed 1.2 from it.
Giant stars tend to quickly deplete their nuclear fuel supply. This is accompanied by a significant loss of mass, in particular, due to the dumping of the outer shells. As a result, only the gradually cooling central part remains, in which the nuclear reactions have completely ceased. Over time, such stars cease their radiation and become invisible.
But sometimes the normal evolution and structure of stars is disturbed. Most often this applies to massive objects that have exhausted all types of thermonuclear fuel. Then they can be transformed into neutron, supernovae or black holes. And the more scientists learn about these objects, the more new questions arise.