A star is a cosmic plasma (gaseous) body that has its own source of radiation. Thermonuclear fusions take place in the star’s core, burning hydrogen to helium (this phenomenon occurs in most stars in the universe). Thanks to these thermonuclear fusions, the star can emit radiation.
Stars form from the originally cold, sparse and cold clouds of interstellar matter. The cold, dust-gas cloud usually begins to shrink under the influence of some external factor (supernova explosion, collision with another cloud, collision of galaxies). As soon as the region reaches a sufficient density of matter and meets the criterion of Jeans’ instability, it begins to collapse under its own gravity. The most numerous stars in the universe, red dwarfs.
Star properties: Radiation, Chemical composition, Weight, Limit weight, Density, Size, Age, Variability, Rotation, Temperature, Magnetic field.
Paradoxically, more massive stars live shorter because thermonuclear reactions in their nuclei are much more turbulent than in less massive stars. The life of a star with the mass of the Sun lasts billions of years, the life of much more massive giants and forever only millions or even only hundreds of thousands of years. For most stars, the amount of mass lost by the stellar wind is negligible due to their mass.
The remnants of the star are the White Dwarf (Black Dwarf), the Neutron Star (Pulzar and Magnetar) and the Black Hole.

Star construction:
The core – the hottest and densest part of the star. Nuclei are the energy sources of stars,
Layer of radiant balance – a very thick layer of plasma that surrounds the core.
convective zone – an even cooler layer of a star in which energy is transferred by flow.
photosphere – the visible (but not solid) surface of a star.
Chromosphere – the lower part of the star’s atmosphere.
corona – the highest, hottest and least dense outer atmosphere of a star, which gradually dissolves into interstellar space.
The stars are sorted:
According to the temperature and luminosity of the supernatants, bright giants, giants, subfields of stars of the main sequence (the most numerous group), dwarves and dwarfs.

According to the energy source
plasma stars – stars in which thermonuclear reactions take place and generate their own radiation
degenerate stars – stars in which thermonuclear reactions no longer take place and their mass is in a degenerate state.
There are multi-star systems formed by two or more gravitationally coupled stars orbiting each other. The most common example of a multi-star system is a binary, but systems of three or more stars are also common. Such multi-star systems are often hierarchically organized sets of orbiting stars due to the stability of their orbits. There are also larger groups, i. star clusters.

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