Space - stars and planets, galaxies and nebulae - a huge mysterious world that people have wanted to understand from ancient times. First, astrology, and then astronomy sought to know the laws of life flowing on its open spaces. Today we can safely say that we know a lot, but the impressive part of the processes and phenomena has only a hypothetical explanation. The physical nature of stars is one of the widely discussed issues in astronomy. Today, in general, the picture is clear, but gaps remain in our knowledge of celestial bodies.
Countless
Any star is a gas ball that constantly emits light. The forces of gravity and internal pressure prevent its destruction. The physical nature of stars is such that thermonuclear reactions constantly occur in its bowels . They cease only at certain stages of the development of the luminary, as will be discussed below.
Under good weather conditions and the absence of artificial lighting in the sky, you can see up to 3,000 thousand stars in each hemisphere. However, this is only a small part of the amount that fills the cosmos. The star closest to us is the Sun. Studying his behavior, scientists learn a lot about the stars in general. The closest star outside the solar system is Proxima Centauri. It is separated from us by approximately 4.2 light years.
Parameters
The science of stars today knows enough to understand how basic characteristics affect their evolution. The most important parameters for any luminary are mass and composition. They determine the duration of existence, especially the passage of different stages and all other characteristics, for example, spectrum, size, gloss. However, due to the enormous distance that separates us from all the stars except the Sun, it is not always possible to obtain accurate data about them.
Weight
In modern conditions, more or less accurate data on the mass of stars can be obtained only if they are companions of the binary system. However, such calculations give a rather high error - from 20 to 60%. For other stars, mass is calculated indirectly. It is derived from various known relationships (for example, mass - luminosity).
The physical nature of stars with a change in this parameter remains the same, but many processes begin to flow in a slightly different plane. Mass directly affects the thermal and mechanical equilibrium of the entire cosmic body. The larger it is, the greater the gas pressure and temperature in the center of the star, as well as the amount of thermonuclear energy generated. To maintain thermal equilibrium, the luminary must emit as much as was formed in its bowels. For this, a change in the diameter of the star occurs. Similar changes continue until both types of equilibrium are established.
Chemical composition
The base of the star is hydrogen and helium. In addition to them, the composition in a different ratio includes heavier elements. “Complete set” indicates the age and generation of the luminary, indicates some of its other properties.
The percentage of heavier elements is extremely small, but it is they that affect the rate of thermonuclear fusion. Its deceleration and acceleration is reflected in the brightness, color and longevity of the body. Knowledge of the chemical composition of a star makes it easy to determine the time of its formation.
The birth of a star
The process of formation of luminaries is still not well understood. Enormous distances and the impossibility of direct observation hinder the full understanding of the picture. However, today there is a generally accepted concept that describes the birth of a star. Let us briefly dwell on it.
Apparently, luminaries are formed from interstellar gas, which is compressed by its own gravity. In this case, the gravitational energy is converted into heat - the temperature of the formed globule increases. This process ends when the core heats up to several million Kelvin and starts the formation of elements heavier than hydrogen (nucleosynthesis). Such a star remains for quite a long time, being located on the Main sequence of the Hertzsprung-Russell diagram.
Red giant
The next stage of evolution begins after the core has exhausted all the fuel. All hydrogen in the center of the star turns into helium and its combustion continues in the outer shells of the star. The cosmic body begins to change. Its luminosity increases, the outer layers expand, and the inner ones, on the contrary, are compressed, the brightness temporarily decreases, and the surface temperature drops. A star goes off the Main sequence and becomes a red giant. In this state, the star spends much less time in its life than in the previous stage.
Irreversible changes
Soon (by cosmic standards), the core begins to shrink again, not sustaining its own weight. The increasing temperature at the same time stimulates the onset of the synthesis of heavier elements from helium. On such fuel, a star can also exist for a long time. Further events depend on the initial parameters of the luminary. Massive stars go through several more stages when, first, carbon (formed from helium) and then silicon (formed from carbon) begin to act as fuel. As a result of processing the latter, iron is formed. At this point, the final stage of the star’s life begins, when it can transform into the neutron. However, most luminaries after burning all the hydrogen in the red giant turn into white dwarfs.
Not so new
It should be noted that not every bright star that suddenly lights up in the sky is a “newborn”. As a rule, this is the so-called variable - the star, whose brilliance changes over time. Objects designated in astronomy as the “new star” also do not apply to the bodies that have just appeared. They relate to cataclysmic variables that change their brightness quite sharply. However, supernovae are significantly ahead of them in this: the amplitude of the change in them can be up to 9 values. However, both of these types of bodies are a topic for separate articles.
The physical nature of stars is largely understood today, although there is no guarantee that new data will not refute established theories. Accepted hypotheses and ideas dominate science only until they can explain the observed phenomena. Each new star discovered in the vastness of the universe reveals the unsolved problems of astronomy. The existing understanding of space processes is far from complete, it has quite extensive gaps regarding, for example, the process of formation of black holes, supernovae and so on. However, regardless of the state of the theory, heavenly bodies continue to delight us at night. In fact, a bright star will not cease to be beautiful if we fully know its nature. Or, conversely, we stop all study.