Like all bodies in nature, stars do not remain unchanged, they are born, evolve, and finally “die.” To trace the life path of stars and understand how they age, you need to know how they arise. In the past, this seemed like a big mystery; modern astronomers can already with great confidence describe in detail the paths leading to the appearance of bright stars in our night sky.
Not so long ago, astronomers believed that it takes millions of years to form a star from interstellar gas and dust. But in recent years, striking photographs have been taken of the area of the sky that is part of the Great Orion Nebula, where a small cluster of stars has appeared over the course of several years. In the pictures of 1947. in this place a group of three star-like objects was visible. By 1954 some of them became oblong, and by 1959 these oblong formations broke up into separate stars – for the first time in the history of mankind, people observed the birth of stars literally before our eyes, this unprecedented case showed astronomers that stars can be born in a short period of time, and the previously strange arguments that stars usually appear in groups or star clusters turned out to be fair.
What is the mechanism of their occurrence? Why for many years of astronomical visual and photographic observations of the sky only now for the first time managed to see the “materialization” of stars? The birth of a star cannot be an exceptional event: in many parts of the sky there are conditions necessary for the appearance of these bodies.
As a result of a careful study of photographs of foggy areas of the Milky Way, it was possible to detect small black spots of irregular shape, or globules, which are massive accumulations of dust and gas. They look black, because they do not emit their own light and are between us and the bright stars, from which they obscure the light. These gas-dust clouds contain dust particles that absorb very strongly the light coming from the stars behind them. The size of the globules is huge – up to several light years across. Despite the fact that the matter in these clusters is very sparse, their total volume is so large that it is enough to form small clusters of stars, by mass close to the Sun. In order to imagine how stars arise from globules, we recall that all stars emit and their radiation exerts pressure. Sensitive instruments have been developed that respond to the pressure of sunlight penetrating the earth’s atmosphere. In a black globule, under the influence of radiation pressure emitted by surrounding stars, compression and compaction of matter occurs. A “wind” walks inside the globule, scattering gas and dust particles in all directions, so that the substance of the globule is in continuous turbulent motion.
The globule can be considered as a turbulent gas-dust mass, on which radiation presses from all sides. Under the influence of this pressure, the volume filled with gas and dust will shrink, becoming smaller and smaller. Such compression proceeds for some time, depending on the radiation sources surrounding the globule and the intensity of the latter. Gravitational forces arising from the concentration of mass in the center of the globule also tend to compress the globule, causing the substance to fall to its center. As particles fall, they acquire kinetic energy and heat a gas-dust cloud.
The fall of a substance can last hundreds of years. At first it happens slowly, slowly, because the gravitational forces that attract particles to the center are still very weak. After a while, when the globule becomes smaller, and the gravitational field intensifies, the fall begins to occur faster. But, as we already know, the globule is huge, no less than a light year in diameter. This means that the distance from its outer border to the center can exceed 10 trillion kilometers. If a particle from the edge of the globule begins to fall towards the center with a speed of a little less than 2 km / s, then it will reach the center only after 200,000 years. Observations show that the velocities of gas and dust particles are actually much greater, and therefore gravitational compression occurs much faster.
The fall of matter toward the center is accompanied by very frequent collisions of particles and the transition of their kinetic energy into heat. As a result, the temperature of the globule increases. The globule becomes a protostar and begins to glow, since the energy of particle movement has transferred to heat, heated dust and gas.
At this stage, the protostar is barely visible, since the bulk of its radiation falls on the far infrared region. A star has not yet been born, but its germ has already appeared. Astronomers still do not know how long it takes for the protostar to reach the stage when it begins to glow like a dim red ball and becomes visible. According to various estimates, this time ranges from thousands to several million years.