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I Core collapse supernova: the "void" left by the collapsed core?

  1. Jun 5, 2018 #26

    Ken G

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    They woudn't disagree that this thread is about core-collapse supernovae, so they would know it has nothing to do with fusion design.
     
  2. Jun 5, 2018 #27

    Ken G

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    That's not entirely true, some simulations have succeeded in getting an outgoing shock and an explosion using that physics. Rotation seems to matter, perhaps magnetic fields matter, certainly neutrinos matter. They don't think they are missing any important luminosity effects, because the energy is way short, though I agree it is still strangely difficult to get it to work.
    Well, the neutron star is formed by infalling gas, the shock merely decides what of that infalling gas ends up in the neutron star and what ends up getting blasted out. The void left behind comes outside all the action of interest, including the shock.
    It isn't the void that prevents that, voids don't really do much of anything. The defeat of the shock wave happens inside the infalling gas, it's all over by the time it gets to the void. The difficult part is to keep the shock from turning into a standing accretion shock, which is a stalled shock that cannot make headway against the gas falling into it. It requires some additional push from underneath to get it going again, so that it can advance through the infalling gas and energize the stellar envelope. The leading idea is that this additional push comes from neutrino heating, but it doesn't work in one dimension because of the need for instabilities. This seems to be the problem that hampered 1D simulations, they didn't realize the crucial role of higher-dimensional instabilities and convection.
     
    Last edited: Jun 5, 2018
  3. Jun 6, 2018 #28
    If in fusion design a ~100 million kelvin photon gas can drive a ~1000km/s shock that compresses LiD to 1000 times its STP density, why do you completely discount effects of ~10 billion kelvin photon gas on star's internal layers?
     
  4. Jun 6, 2018 #29
    Ok, please try to answer this. Suppose the shock is "defeated" and all the dense core material ends up falling on the proto-NS and all of it ends up being the material of the newly-created NS. This new NS is more than 100 billion kelvins hot. Above it, there is a relatively low density gas, which continues to fall on it from the farther-up, less dense layers of the star.

    What will be happening in the next ~10 seconds?
     
  5. Jun 6, 2018 #30

    Ken G

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    Because of decades of supernova research, not done by me, but I am aware of it. Perhaps you need to be.
     
  6. Jun 6, 2018 #31
    So am I aware of it too.

    The simulations have computing power restrictions. The simulated volume can't be too big; the time the simulation runs can't be too long.

    Researchers make sensible decisions based on the availability of CPU power.

    If simulating a (400km)^3 cube for 1 second takes 2 days, then simulating (4000km)^3 cube for 10 seconds on the same hardware would take 5000 days (~15 years). It makes sense to _not_ try that as the first (or second, or tenth) attempt to figure out why simulation does not match expectations. "Maybe we overlooked something. Maybe it's magnetic fields?" etc. Completely sensible. I'd do the same. I don't want to wait 15 years for one test run! And I'm not ready to give up on my codes simply because they didn't work in the first few tries. Bugs are a fact of life.

    However, maybe the simulations _were_ mostly correct. Maybe they do show what really happens in (400km)^3 cube for 1 first second. Maybe star's explosion is not generated in this volume.

    I'd be happy to hear this was looked at, and shown not to be the case, by people who did work on it.
     
  7. Jun 6, 2018 #32

    Ken G

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    Of course, but none of that justifies an expectation that a region where there is no material and no energy has anything to do with getting an explosion. Also, none of that justifies thinking that radiation is important, when simulations include radiation and find that it is not important.
     
  8. Jun 6, 2018 #33

    JMz

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    Yes, but they have no neutrinos to make use of, right?
     
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