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Physics of Hydrogen under great Pressur

Physics of Hydrogen under great Pressur - Below this regime...

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Physics of Hydrogen under great Pressur e We see that as Hydrogen is added the body does not grow linearly with mass (note the left hand axis is a log scale - the bottom axis is linear). This is because ttom axis is linear). This is because as we add more material the total mass goes up and so the material that was there already is compressed. Eventually we see that we getto a point where there is a balance - as we add more mass the body stays the same size as the added volume of material is compensated for exactly by the compression of the material that is already there. This behaviour goes some way to explaining why Saturn is roughly the same size as Jupiter even though it is much lighter. Above the turn-over point, of course, we see that the body actually shrinks as we add material, the added volume being more than compensated for by the added mass's compression effect. Above 10 29 kg the body reaches critical mass where the nuclei are forced so close toghether that fission is initiated and Hydrogen burns to Helium - the body has become a sun.
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Unformatted text preview: Below this regime we see that we have first, at around 10 26 kg, the region we have described where Hydrogen becomes metallic in nature, and then at around 10 28 kg we have a region of electron degeneracy. We have marked on this diagram the positions of the giant planets (and sub-giants). We see that Neptune and Uranus are nowhere near the regim where metallic hydrogen is formed. We see also that Jupiter and Saturn are inside the curve, since they are not pure Hydrogen and the extra mass of their cores makes them smaller than a pure hydrogen bodan a pure hydrogen body. There is an added difference in that this curve is for 0K - if the temperature is also taken into account it is possible that Saturn moves out of the metallization region. Thus, it is not entirely sure that metallic hydrogen is found inside Saturn, as it undoubtedly is in Jupiter. The cross-sections above assume it is, but there is a large scope for uncertainty in these models....
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