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Let's say that there existed a non-rotating hollow shell of hydrogen gas in space. This shell of gas was collapsing under its own weight. Is it possible to form a star that is hollow inside? If the density of the gas in the shell got high enough to start nuclear fusion and the pressure of the radiation prevented the shell from collapsing into a solid sphere?

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There is an obvious flaw in your scheme. It is pressure gradient that supports a star against gravity. In your hollow star there is a sudden drop in the pressure at the centre. This is unstable and the star would collapse.

Real stars have a pressure that increases towards a maximum at the centre.

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it is not possible to have a hollow star because the gravitational force of the star would pull all of the hydrogen back into the centre of the star, creating a smaller star.

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  • $\begingroup$ I guess I do not understand your comment about the pressure gradient. Certainly one can have a solid with a hollow core even if that solid is the size of the moon, right? Or am I missing something. If the integrity of the solid material is strong enough in compression then it can be stable. Here we are talking about compressed gas in the shell. I realize that it is an unstable condition but mathematically can't it exist? If the pressure from radiation is great enough to counter the inward force of gravity? Maybe you can explain a bit more for me. Thanks :-) $\endgroup$ – Paul Dec 4 '16 at 16:13
  • $\begingroup$ Now I understand after reading some other posts. Pressure differential. You cannot have a high density object floating above lower density. $\endgroup$ – Paul Dec 5 '16 at 14:45

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