How does the core of a star $>10 ext{M}_{\odot}$ differ structurally from the Sun's core region?
The massive star's core is convective due to the high energy generation from the CNO cycle.
The internal structure, particularly concerning energy transport, varies significantly based on mass. In stars much more massive than the Sun, specifically those exceeding roughly $10 ext{M}_{ ext{odot}}$, the energy generation via the highly efficient CNO cycle is intensely concentrated very close to the center. This results in an extremely steep temperature gradient, which drives the inner core region into a state of convection. This convective core is highly advantageous for the star's main sequence longevity because the constant churning motion effectively mixes the helium 'ash' away from the immediate fusion zone, allowing a larger volume of hydrogen fuel to remain accessible for burning over time. In contrast, stars similar in mass to the Sun feature a stable, purely radiative core, which prevents mixing and leads to the buildup of a helium-rich core surrounded by the hydrogen shell.
