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In a recent popular science account of "pair instability" supernova, a statement was made, without explanation, that if fusion of oxygen started producing sufficiently energetic photons that most of them convert to electron positron pairs, the the outward pressure is drastically reduced and the star collapses. My hope is to get that explanation here. Why do electrons and positrons produce so much less pressure than photons? Further, why wouldn't they annihilate back to photons? (it would seem that in 100+ solar mass star, but not a neutron star, the probability of at least the positrons annihilating would near 1).
Some possible guesses I've made:
In converting much of the photons energy to mass of the electron/positron, the efficiency of momentum transfer to nucleons is much reduced; but I have done no calculations to try to justify this, and it is not obvious to me.
If a positron annihilated, the resulting photons would still have enough energy to convert right pack to a pair.
Any further explanation would be greatly appreciated.
Some possible guesses I've made:
In converting much of the photons energy to mass of the electron/positron, the efficiency of momentum transfer to nucleons is much reduced; but I have done no calculations to try to justify this, and it is not obvious to me.
If a positron annihilated, the resulting photons would still have enough energy to convert right pack to a pair.
Any further explanation would be greatly appreciated.