What elements act as catalysts during the CNO Cycle for energy generation in massive stars?
Answer
Carbon, nitrogen, and oxygen
In stars significantly more massive than the Sun, which possess substantially higher core temperatures and pressures (generally above 17 million K), the dominant method of hydrogen fusion shifts to the Carbon-Nitrogen-Oxygen (CNO) Cycle. This cycle relies on the presence of carbon, nitrogen, and oxygen atoms which function specifically as catalysts within the reaction sequence. A catalyst is consumed and then regenerated during the reaction steps, meaning these heavier elements facilitate the conversion of hydrogen to helium without being permanently incorporated into the final helium product, allowing for a much faster rate of fuel burning compared to the P-P chain.
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