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Initiating mechanism of supernovae

  1. Feb 22, 2014 #1

    ChrisVer

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    I think that our current knowledge on the initiating mechanism of supernovae is that they happen due to neutrinos interacting with the inner layers of a star and then accelerating them away from the core.
    I am having some trouble in understanding that idea. Of course this could be plausible if neutrinos interacted strongly with matter, but that's not the case... At least it's not the case for pushing away 80++ % of the star's mass....
    Of course it doesn't have to be neutrinos at all (the inner layers will drift the outer ones etc). But I can't even understand how this can really happen...

    Can someone please give a satisfactory explanation?

    At first we would have to admit that the neutrino emission for some reason raises in extreme numbers (also I am not sure if this could overcome neutrinos' weakly interacting nature)...why would that happen to a dying star's core?
     
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  3. Feb 22, 2014 #2

    SteamKing

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    I don't know anything about neutrinos being responsible for initiating a supernova. The loss of the envelope of the star, as far as I know, is due to the shock waves created by the collapse of the stellar core once its nuclear fuel has been exhausted and fusion no longer occurs.

    Do you have a reference for any articles which discuss this neutrino initiation theory?
     
  4. Feb 22, 2014 #3

    mfb

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    Neutrinos are always produced at high speed, so neutrinos produced in the core that interact in the outer part will accelerate this a bit outwards - but it would surprise me if that is a significant effect in supernovae.

    In the extremely hot and dense core, many nuclear reactions happen, so many unstable nuclei are produced and decay quickly afterwards.
     
  5. Feb 22, 2014 #4

    ChrisVer

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    I had heard of the neutrino initiating mechanism at a seminar... For now I can quote something I found online (see attachment).

    As for the whole, the neutrinos play the role of initiating mechanism (they don't move the whole procedure)- they somehow "push" the inner layers and so the everything is pushed. But for me still it's weird to think of weakly interacting particles to cause something so spectacular...
     

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  6. Feb 22, 2014 #5

    Drakkith

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    From wiki:http://en.wikipedia.org/wiki/Supernova

    Reference number 75: http://adsabs.harvard.edu/doi/10.1086/169405
     
  7. Feb 22, 2014 #6

    SteamKing

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    This article is only partially quoted, so I can't say that a neutrino initiating mechanism is discussed.

    This article: http://en.wikipedia.org/wiki/Type_II_supernova

    has the following description of the events surrounding core collapse:

    The neutrinos produced during the core collapse are an important mechanism whereby energy is carried away from the core, without which, the succeeding neutron star could not form. The loss of the core's surrounding envelope is still caused by the shock of the initial core collapse and the rebound when the core cannot collapse further, due to nuclear forces.
     
  8. Feb 22, 2014 #7

    Chronos

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  9. Feb 23, 2014 #8
    The neutrino cross section rises rapidly with energy, see below. With the graph below and some simplifications should you be able to come up with a rough estimate for the momentum transfer due to neutrinos.

    Image from,

    http://www.google.com/imgres?safe=o...hBwwCg&iact=rc&dur=737&page=1&start=0&ndsp=15

    Is there such a thing as an index of refraction for a neutrino beam through matter?

    Edit, I guess we need the neutrino cross section for iron nuclei?
     

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  10. Feb 23, 2014 #9
    In the rest frame of an escaping neutrino it "sees" a severe density increase in the matter because of a Lorentz contraction (in addition to already high densities), does this possibly increase the actual cross section?
     
  11. Feb 23, 2014 #10

    ChrisVer

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    Not really iron (the external layers of a star should not be composed of iron). I guess the proton is enough.

    As for the increase of density, I am not sure, but almost all neutrinoes are considered (in SM) to run at the speed of light, so Lorentz contraction is taken in account eversince we consider them...

    I thought that the neutrino interaction with matter followed a logarithmic relation (with respect to energy). I am not sure how this came in my mind.

    Does that mean that Ultra relativistic neutrinos leave a better/more clear signature when we measure them on earth? (if their energies allowed them to interact better with matter this must play a role in how we measure them here)
     
  12. Feb 23, 2014 #11
    This is a quick and dirty estimate of the odds a super nova neutrino interacts on its way out.

    Pack the matter of our sun into a shell of radius 1000km and thickness 1E-15m thick. We then have about,

    [(2E30kg/sun)/(2E-27kg/proton)]/[4∏1E16cm^2] protons/cm^2 ≈ 1E40protons/cm^2

    and as the cross section for a 30MeV neutrino is of order 1E-40cm^2 we should expect each neutrino to interact once on average on its way out of a super nova?

    What amount of momentum can we expect on average to be transferred per neutrino?

    Edit, the results depend strongly on the radius above, more care needed!
     
    Last edited: Feb 23, 2014
  13. Feb 24, 2014 #12

    ChrisVer

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    In this I would question why doesn't the same mechanism/logic work with the sun neutrinos?
    except for if their interaction rate grows really much with respect to energy... (from the graph I don't see such a relationship)
     
  14. Feb 24, 2014 #13

    mfb

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    It also decreases the length of the material, keeping the area density the same => no.

    All neutrinos we can measure (so far) are ultrarelativistic. For neutrinos of very high energy: yes. They are just much more rare.
     
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