When does the physical principle of convection become dominant over radiation for energy transport?
Answer
When the temperature gradient becomes too steep for radiation efficiency
Convection is initiated as a thermal regulation mechanism when the internal temperature gradient—the rate at which temperature changes over distance—increases beyond a critical threshold. If radiation alone were relied upon under such steep gradients, the star could not efficiently move the necessary amount of energy outward to maintain hydrostatic equilibrium. When the plasma effectively becomes opaque due to high density or steep thermal variations, the material becomes unstable, triggering bulk fluid motion (convection) to rapidly transfer heat through the physical movement of the plasma itself.
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