What is the function of carbon, nitrogen, and oxygen isotopes during hydrogen fusion in massive stars?

Answer

They act as temporary catalysts

The CNO cycle utilizes carbon, nitrogen, and oxygen isotopes as temporary catalysts to facilitate the conversion of hydrogen into helium, making the process highly temperature-sensitive.

What is the function of carbon, nitrogen, and oxygen isotopes during hydrogen fusion in massive stars?
ElementastronomystarFusionnucleosynthesis