What is the primary energy-generating reaction sustaining a main-sequence star's luminosity for billions of years?
Answer
The fusion of hydrogen into helium through the proton-proton chain reaction
During the lengthy main-sequence phase of stellar life, the star maintains hydrostatic equilibrium by generating energy primarily through nuclear fusion in its core. For the majority of stars, including those around solar mass, this energy comes from the proton-proton chain reaction, which systematically fuses hydrogen nuclei (protons) into helium nuclei. While more massive stars utilize the CNO cycle, the proton-proton chain is cited as the primary mechanism sustaining luminosity for the longest duration, slowly converting the star's most abundant fuel, hydrogen, into its first ash, helium.
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