Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core even though it is producing millions of times more energy per second?

Answer 1

The high-mass star enters a phase called "core helium burning" where energy production in the core increases due to the fusion of heavier elements such as helium into carbon and oxygen. The increase in energy production counterbalances the higher energy loss through radiation, maintaining a relatively constant luminosity. This equilibrium regulates the star's luminosity despite the increased energy output.