Introduction stellar evolution,
life history of a star
, beginning with its condensation out of the interstellar gas (see interstellar matter
) and ending, sometimes catastrophically, when the star has exhausted its nuclear fuel or can no longer adjust itself to a stable configuration. Because a star's total energy reserve is finite, a star shining today cannot continue to produce its present luminosity steadily into the indefinite future, nor can it have done so from the indefinite past. Thus, stellar evolution is a necessary consequence of the physical theory of stellar structure
, which requires that the luminosity, temperature, and size of a star must change as its chemical composition changes because of thermonuclear reactions.
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