1. In outer space under absence of any external force (like gravity) can a free liquid develop pressure due to cohesive forces? Will the liquid be in spherical shape and will pressure increase towards its centre? As external force is absent, that is there is no external pressure, will the liquid expand and radiate heat then cool down to solidify?

  2. In a similar isolated situation as above (say in outer space without celestial bodies), will a finite volume of gas expand infinitely? If it expands and the molecules become cooler and solidify, then how small would it be? Will it form a fermionic condensate or a Bose-Einstein condensate (though method of preparation is very different)? But how do then nebulas maintain their shape and don't expand but rather contract to form a star?


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In astrophysical regimes, gravity becomes less like an 'external' force --- as "self-gravity" is usually important between each particle. The fate of a material in space depends on its initial configuration: the total mass, and energy of it. If there is enough mass (like in nebulae, or other large clouds) it will be "bound" by self-gravity, keeping it from expanding out to infinity. If, on the other hand, you imagine placing a cup of water in space, the near-zero pressure will cause it to boil/evaporate almost instantly - and the initial temperature will provide enough energy to keep it from re-collapsing. In this case the gas will likely just continue to expand --- and despite how cold it gets, it will not form a solid because the density (and pressure) are too low. It will become more and more like individual molecules/atoms freely moving through space.


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