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Why is pressure in the outermost layer of a star lower than at its center?

I have done the math and I have obtained the hydrostatic pressure in a star is lower at the outermost layer of a star than in its center, where the pressure is actually maximum. Although the equations tell me this is right, I can't provide an intuitive explanation as to why this happens. Considering the only force keeping the star together is gravitational in nature, then shouldn't pressure be null in the center, where there is no mass to exert any force in nearby layers, and maximum in the outermost layer, where there is the most mass enclosed?

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  • $\begingroup$ Yes and in that sense the difference between the two problems is interesting. $\endgroup$
    – Not a chance
    Commented Jul 2 at 14:18
  • 1
    $\begingroup$ Interesting idea that the pressure inside a rigid body could indeed be zero because the layers around it act like vaults in architecture, carrying all the load. But note that "rigid" on the planetary scale is not obvious: What's rigid on the human scale, e.g. rock, behaves essentially like a fluid on the planetary scale which is why they take on a spherical shape. Indeed, this is one criterion of a planet. $\endgroup$
    – Peter - Reinstate Monica
    Commented Jul 3 at 12:58
  • $\begingroup$ @Peter-ReinstateMonica Good point, I've edited my answer. $\endgroup$
    – C.M.O.B.
    Commented Jul 4 at 1:44

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