Successful models were developed to explain the interiors of stars and stellar evolution. It occurs in stars during stellar evolution. Planetary nebulae came to be understood as a final stage of stellar evolution. The star is bright with low levels of stellar activity. Most stars are born within molecular clouds known as stellar nurseries. This is typical of stellar separations in galactic discs. Be star with a stellar classification of B3IIIpe. These hypothetical models could potentially explain a number of observations of stellar black hole candidates. This allowed the chemical composition of the stellar atmosphere to be determined. Metals condense in planets as a result of stellar evolution and destruction processes. Heavy metals condense in planets as a result of stellar evolution and destruction processes. There are also fifty observations of stellar altitude. The variability is highly periodic and attributed to stellar rotation. This was a preliminary step toward the idea of stellar nucleosynthesis. Other sources of complex molecules have been postulated, including extraterrestrial stellar or interstellar origin.