What limits the theoretical upper boundary for how large and bright a stable star can become?

Answer

Internal radiation pressure overpowering the inward crush of gravity.

A star remains stable only when fusion pressure balances gravity; if a star exceeds a certain mass threshold (e.g., 150 solar masses), radiation pressure becomes too intense, leading to catastrophic loss of outer layers.

What limits the theoretical upper boundary for how large and bright a stable star can become?

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Why Would The Size Of A Star Affect Its Luminosity? - Physics Frontier

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