With the naked eye in the sky on a moonless night and far from the city you can see a huge number of stars. Using the telescope, you can observe even more luminaries. Professional equipment allows you to determine their color and size, as well as luminosity. The question "what are the stars made of?" for a long time in the history of astronomy remained one of the most controversial. However, it was possible to solve it. Today, scientists know what the Sun and other stars consist of and how this parameter changes during the evolution of cosmic bodies.
Method
Astronomers learned to determine the composition of luminaries only in the middle of the 19th century. It was then that spectral analysis appeared in the arsenal of space researchers. The method is based on the property of atoms of various elements to emit and absorb light at strictly defined resonant frequencies. Correspondingly, the spectrum shows dark and light bands located at the sites characteristic of this substance.
Different light sources can be distinguished by a pattern of absorption and radiation lines. Spectral analysis has been successfully applied to determine the composition of stars. His data help researchers understand a great many processes occurring inside the luminaries and inaccessible to direct observation.
What does a star in heaven consist of?
The sun and other luminaries are huge, hot balls of gas. Stars consist mainly of hydrogen and helium (73 and 25%, respectively). About 2% of the substance is accounted for by heavier elements: carbon, oxygen, metals and so on. In general, the planets and stars known today consist of the same material as the entire Universe, however, differences in the concentration of individual substances, the mass of objects and internal processes give rise to the whole variety of existing cosmic bodies.
In the case of luminaries, the main criteria for differences between their types are mass and the very 2% of elements that are heavier than helium. The relative concentration of the latter is called metallicity in astronomy. The magnitude of this parameter helps determine the age of the star and its future.
Internal structure
The "filling" of stars does not fly across the galaxy due to the forces of gravitational compression. They also contribute to the distribution of elements in the internal structure of the stars in a certain way. All metals rush to the center, to the core (in astronomy, any element heavier than helium is called that). A star is formed from a cloud of dust and gases. If only helium and hydrogen are present in it, the first forms the core, and the second - the shell. At the moment when the mass reaches a critical point, a thermonuclear reaction begins and the star ignites.
Three generations of stars
The nuclei, consisting exclusively of helium, had luminaries of the first generation (they are also called stars of the population III). They formed some time after the Big Bang and were characterized by impressive sizes, comparable to the parameters of modern galaxies. In the process of synthesis, other elements (metals) gradually formed in their bowels from helium. Such stars ended their lives exploding in a supernova. The elements synthesized in them became the building material for the next luminaries. Stars of the second generation (population II) are characterized by low metallicity. The youngest of the luminaries known today belong to the third generation. These include the sun. A feature of such luminaries is a higher metallicity compared to their predecessors. Younger stars were not discovered by scientists, but it can be confidently stated that they will be characterized by an even larger size of this parameter.
Defining parameter
What stars are made of affects their lifespan. Metals falling to the core affect the thermonuclear reaction. The more of them, the earlier the star lights up and the smaller the size of its core will be. The consequence of the latter fact is a lower amount of energy emitted by such a luminary per unit time. As a result, such stars live much longer. Their fuel supply is enough for many billions of years. For example, according to scientists, the Sun is now in the middle of its life cycle. It has existed for about 5 billion years and the same is yet to come.
The sun, according to the theory, was formed from a gas-dust cloud saturated with metals. It belongs to the stars of the third generation, or, as they are also called, the population of I. The metals in its core, in addition to the slower burning of fuel, provide uniform heat generation, which has become one of the conditions for the origin of life on our planet.
Star evolution
The composition of the luminaries is unstable. Let's see what stars consist of at different stages of their evolution. But first, let us recall what stages the luminary goes through from the moment it appears to the end of its life cycle.
At the beginning of evolution, stars are located on the main sequence of the Hertzsprung-Russell diagram. At this time, the main fuel in the core is hydrogen, of which four atoms form one helium atom. The star spends most of his life in this state. The next stage of evolution is the red giant. Its dimensions are much larger than the original, and the surface temperature, on the contrary, is lower. Stars like the Sun end their life in the next stage - they become white dwarfs. More massive luminaries turn into neutron stars or black holes.
First stage of evolution
Thermonuclear processes in the bowels are the cause of the transition of the star from one stage to another. Combustion of hydrogen leads to an increase in the amount of helium, and hence, the size of the nucleus and the reaction area. As a result, the temperature of the star increases. Hydrogen begins to enter into the reaction, previously not involved in it. There is an imbalance between the shell and the core. As a result, the first begins to expand, and the second - to narrow. In this case, the temperature rises significantly, which provokes the burning of helium. Heavier elements are formed from it: carbon and oxygen. A star goes off the main sequence and turns into a red giant.
Next part of the cycle
The red giant is an object with a highly swollen shell. When the Sun reaches this stage, it will occupy the entire space up to the Earth’s orbit. Of course, there is no need to talk about life on our planet in such conditions. In the bowels of the red giant, carbon and oxygen are synthesized. At the same time, the star regularly loses mass due to stellar wind and constant ripple.
Further events differ for objects with medium and large mass. Pulsations of stars of the first type lead to the fact that their outer shells are discarded and form a planetary nebula. The fuel runs out in the core, it cools and turns into a white dwarf.
The evolution of supermassive bodies
Hydrogen, helium, carbon and oxygen - not all of which are composed of stars with huge masses at the last stage of evolution. At the stage of the red giant, the nuclei of such luminaries are compressed with great force. In conditions of constantly increasing temperature, the combustion of carbon and then its products begins. Oxygen, silicon, and iron are successively formed. The synthesis of elements does not go any further, since the formation of heavier nuclei from iron with the release of energy is impossible. When the mass of the nucleus reaches a certain value, it collapses. A supernova lights up in the sky. The further fate of the object again depends on its mass. A neutron star or a black hole may form in the place of the star.
After a supernova explosion, the synthesized elements scatter in the surrounding space. Of them, quite possibly, after a while new stars will form.
Examples
A special feeling arises when it is possible not only to recognize the familiar luminaries in the sky, but also to remember to which class they belong, of which they consist. Let's see what stars Ursa Major consists of. Asterism bucket includes seven bodies. The brightest of them are Aliot and Dubhe. The second luminary is a system of three components. In one of them, the burning of helium has already begun. The other two, like Aliot, are located on the main sequence. The same part of the Hertzsprung-Russell diagram includes Fekda and Benetas, who also make up the bucket.
The brightest star in the night sky, Sirius, consists of two components. One of them refers to the main sequence, the second is a white dwarf. On the branch of the red giants are Pollux (alpha Gemini) and Arcturus (alpha Bootes).
What luminaries does each galaxy consist of? From how many stars is the universe formed? It is quite difficult to answer such questions accurately. Several hundred billion luminaries are concentrated in the Milky Way alone. Many of them have already fallen into the lenses of telescopes and new ones are regularly discovered. What gases constitute the stars, we also generally know, but new luminaries often do not correspond to the prevailing idea. Cosmos still has many secrets and many objects and their properties are waiting for their discoverers.