Still in XIX century Lord Kelvin has made a conclusion that the gravitation is one of stellar power sources, that is the potential energy of particles of interstellar environment dropping into stellar gravitational hole (in other words the accretion of gas). The glow duration of such stars equal on mass and luminosity to the Sun makes time about 10⁷ years, and for giant stars it is 10⁸... 10⁹ years and more depending on presence of influx of interstellar material. Though relativists and believers in the nuclear concept of stellar power have scarified Kelvin's hypothesis, but really, this source is the main for such stars as red giants.

Except of gravitational energy the kinetic energy of particles and energy of neutralization of ions goes with accretion material. A small part of energy of red giants receive comes from aether, however, in connection with their low temperature that is low speed of molecules, this share can not be large.

The beginning of formation of Kelvin star, that is real proto-star, the star of the first generation, occurs at local holding the condition of virial stability, Clausius, 1870, but not hypothetical condition of Jeansean instability, 1903.

Virial stability in this case is determined by a threshold of steady integrity of gas volume in space, it means that the kinetic energy of particles of gravitating system should be less than half of potential energy. Such condition is observed in gathering gas cloud under condition of outflow of sufficient part of kinetic energy by emission. This condition is observed in steady Kelvin stars. In spite of Jeans' speculative reasoning conducting to for the huge proto-star size, Clausius virial stability can be keep for gas of modest volume that is really observed by astronomers.

The red giants and supergiants, the stars of globular clusters and other stars of the "population II" (according to Walter Baade, 1944 [10]), the stars of galactic halo filling all elliptical volume of galaxy. They are formed and exist due to accretion, the fall of primary intergalactic material on them, hydrogen and helium.

It is established by study of many astronomers that on periphery of our Galaxy the protons and alpha-particles prevail. The author was found out that "dust" of calibrated size 0,1 micron observable in a halo and galactic corona, is actually free electrons spreaded in absence of an external electrical field up to Rydberg radius [29]. Thus, the initial intergalactic broth consists of practically not changed products of explosions of galaxies.

Inside a galactic halo these particles repeatedly collide, lose kinetic energy and pass in a condition of neutral atomic hydrogen and neutral helium. Than, closer to center of a Galaxy, there are less originally ionized particles. In vicinities of the Sun already the half of atomic hydrogen is incorporated in molecules H₂, and closer to center of Galaxy the molecular hydrogen is already prevails above atomic HI.

In the red giants there are no nuclear reactions in general. Their temperature rather low, and its volumes are extremely great. It is known that Betelgeuse has density in hundred thousand times less than density of air on the Earth surface. It means that such stars represent extremely rarefied gas clouds transparent in its whole volume.

Really brightness of such stars decreased to edge of its visible disk is explained by transparency of atmosphere of the star. Its absolute luminosity depends on two major factors:

• The density of interstellar gas in space circumjacent the star;
• Value and form of a gravitational hole, that is accumulated mass of the star and volumetric temperature dependent on value of recent accretion.

Fig. 1. (a) - photo of Betelgeuse (a) from [30], (b) - same snapshot with the extreme increased contrast for delimitation of a star, (c) - end-to-end transparency of the star;
(d) - temperature, as a function of stellar radius (depth of layers of gas).

Metal-poor Kelvin stars are the first generation of stars formed from intergalactic gas. Existence and permanent origin of Kelvin stars filling elliptical volume of galaxy is caused by constant influx of hydrogen - helium mixture from intergalactic space. Actually it is one type of proto-stars born and dying on our eyes in condition of practically fixed during many billions years Galaxy.

Usually these stars are formed on a place of a huge hydrogen - helium cloud, in mass of which the ensemble of such stars can be arise at once. They grow for the account accretion and get speed during fall to center of a cluster. So globular clusters are formed.