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A Hayashi limit is a limit on the temperature (or radius) of a star (or any object that adheres approximately to the idea gas law) dependent on its mass and luminosity. A star of higher temperature (or equivalently, of small radius, given its luminosity) is necessarily internally unstable, i.e., convection is inevitable until stability (hydrostatic equilibrium) is reached. The region of the H-R diagram beyond the Hayashi limit is termed the forbidden zone. Protostars can form within this forbidden zone, i.e., unstable, but after convection (and presumably other changes), they can leave it. A star right at the Hayashi limit is fully convective. Hayashi tracks for different stellar masses fall near the corresponding Hayashi limit. Metallicity also affects the Hayashi limit, and a magnetic field can affect a star's interior so as to leave a star in the forbidden zone longer than otherwise possible.