Physical Possibilities of Stellar Evolution

The evolution of gaseous bodies, caused by different physical processes happening in their interior and serving as energy sources, is considered qualitatively and partially quantitatively in view of possible applications for the explanation of various observed states of known stars. It is shown that the part of evolution during which the main source of energy is given by thermonuclear reactions leads to a steadily increasing luminosity and goes over continuously into the contractive stage where the energy liberation is purely gravitational. The later stages of contraction and the transition into the state of degenerate gas model are discussed, in application to the present state of white dwarfs. Some remarks are made about the possibility of neutron-core formation in heavier stars, in application to the explosion phenomena observed in supernovae. An attempt is made to explain the energy production in red giants as due to thermonuclear reactions of light elements (lithium, beryllium, and boron), and the pulsation phenomena observed for Cepheid variables is interpreted as due to instability during the transitions from the giant branch into the main sequence.