After "burnout" thermonuclear fuel in the star, the mass of which is comparable to the mass of the Sun, in the Central part of the kernel density of matter becomes so high that gas properties change drastically. This gas is called degenerate, and the stars, he composed, - degenerate stars.

After the formation of a degenerate kernel thermonuclear burning continues in the source around him, having the form of a spherical layer. A star becomes a red giant in the chart of Hertzsprung - Resell. The envelope of the red giant is waste of mammoth proportions in hundreds of Solar radii and for a time of about 10-100 thousand years scattered in space. Reset the shell is sometimes seen as a planetary nebula. The remaining hot core slowly cools down and becomes a white dwarf, in which the forces of gravity resists the pressure of the degenerate electron gas, thereby ensuring the sustainability of the stars. When the mass of about solar radius of the white dwarf is only a few thousand kilometers. The average density of matter in it often exceeds 109 kg/m3 (ton per cubic centimeter!).

Nuclear reactions inside a white dwarf not go, but the glow is due to the slow cooling. The main supply of thermal energy white dwarf contains oscillatory movements of ions, which at temperatures below 15 thousand Kel-responsible crystal lattice. Figuratively speaking, white dwarfs is a giant hot crystals. Gradually the temperature of the surface of the white dwarf is reduced and the star ceases to be white (color) - this is rather brown or brown dwarf.

Mass white dwarfs cannot exceed a certain value is the so - called limit Chand-racecar (on behalf of the American astrophysics, of Indian origin, Subrahmanyan Chandrasekhar-RA), it is equal to about 1.4 the mass of the Sun. If the mass of a star more pressure degenerate electrons cannot withstand the forces of gravitation and in seconds is catastrophic compression white dwarf - collapse. During the collapse of density is rising sharply, protons are combined with degenerate electrons to form neutrons (called stoichiometric ernization substances), and the gravitational energy released carry mainly neutrinos. What ends this process? In the modern view, collapse can either stop when reaching densities of the order of th"7 kg/m3, when the neutrons themselves become degenerate, and then formed a neutron star; or emitted energy is completely destroys the white dwarf and a collapse in fact converted into an explosion.