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A spectacular new way for stars to die

  1. May 21, 2008 #1

    SF

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    Meet pair-instability supernova SN2006GY, the most extraordinary explosion in the cosmos. Unlike its smaller, regular supernova cousins, which blast off the outer layers of a star and pack what remains into a neutron core or a black hole, the pair-instability supernova is a much more violent celestial finale. These events happen only in stars that are at least 150 times as large as our sun and result in total annihilation of the star. Astrophysicists contend that this type of eruption helped seed the cosmos with heavy metals like iron, a process that ultimately allowed planets to form.

    http://www.popsci.com/military-aviation-space/article/2008-05/biggest-boom-universe
     
  2. jcsd
  3. May 21, 2008 #2
    From that article {#3 I believe}, "gamma rays born from nuclear fusion in the core spontaneously morph into pairs of electrons and their antimatter twins, positrons".

    .. is that possible?
     
  4. May 21, 2008 #3
    Yes. If you've heard of anti-matter annihilations (electron + positron = photons), this is just the reverse, which is totally allowed.
    Generally when photons change into a e- e+ pair, they'll soon collide reforming the photons. Sometimes another event (like a strong electric of magnetic field) will prevent them from annihilating, and you'll be left with a brand new electron and positron.
     
  5. May 21, 2008 #4

    marcus

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    As I recall we had some discussion of this at PF about a years ago---in May 2007.

    The paper referred to was this one posted December 2006 and published round that time.
    Proud to say I know one of the authors---a teacher of mine years back.

    http://arxiv.org/abs/astro-ph/0612617
    SN 2006gy: Discovery of the most luminous supernova ever recorded, powered by the death of an extremely massive star like Eta Carinae
    Authors: Nathan Smith, Weidong Li, Ryan J. Foley, J. Craig Wheeler, Dave Pooley, Ryan Chornock, Alexei V. Filippenko, Jeffrey M. Silverman, Robert Quimby, Joshua S. Bloom, Charles Hansen
    14 pages, 4 color figs
    2007, Astrophysical Journal, 666, 1116
    (Submitted on 21 Dec 2006 (v1), last revised 22 May 2007 (this version, v3))

    Abstract: (abridged) We report our discovery and observations of the peculiar Type IIn supernova SN2006gy in NGC1260, revealing that it reached a peak magnitude of -22, making it the most luminous supernova ever recorded. It is not yet clear what powers the total radiated energy of 1e51 erg, but we argue that any mechanism -- thermal emission, circumstellar interaction, or 56Ni decay -- requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star probably experienced an LBV eruption like the 19th century eruption of eta Carinae. Alternatively, radioactive decay of 56Ni may be a less objectionable hypothesis. That power source would imply a large Ni mass of 22 Msun, requiring that SN2006gy was a pair-instability supernova where the star's core was obliterated. SN2006gy is the first supernova for which we have good reason to suspect a pair-instability explosion. Based on a number of lines of evidence, we rule out the hypothesis that SN 2006gy was a ``Type IIa'' event. Instead, we propose that the progenitor may have been a very massive evolved object like eta Carinae that, contrary to expectations, failed to completely shed its massive hydrogen envelope before it died. Our interpretation of SN2006gy implies that the most massive stars can explode earlier than expected, during the LBV phase, preventing them from ever becoming Wolf-Rayet stars. SN2006gy also suggests that the most massive stars can create brilliant supernovae instead of dying ignominious deaths through direct collapse to a black hole.

    =====================

    the pair instability business is an interesting mechanism!

    Here is something I wrote about it last November which tries to make it intuitive. Wallace or others please correct me if there is something wrong with this intuitive explanation:

    I suspect that the ability of a star to become that massive, so that its core can reach that threshold temperature, without blowing the outer layers off too early, has to do with purity.

    It might happen if the material out of which the start condensed was almost metal-free----no carbon, nitrogen, oxgen to catalyze efficient fusion and provide the energy to blow off excess mass. Because of its relative purity the star isn't fighting its own condensation so much. Anybody clear me up on this?
    How do EtaCarinae type stars manage to coagulate?

    Kudos to SF the O.P. who brought this up. Interesting topic!
     
    Last edited: May 21, 2008
  6. May 21, 2008 #5

    marcus

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    More stuff.
    A November 2007 UC SantaCruz press release with some more detailed explanation
    http://www.ucsc.edu/news_events/press_releases/text.asp?pid=1742

    Some PF discussion where at the end of the thread George Jones mentions pair instability supernova
    https://www.physicsforums.com/archive/index.php/t-169612.html
    George gives link to a UC Berkeley press release
    http://www.berkeley.edu/news/media/releases/2007/05/07_supernova.shtml

    there is also a Wikipedia article about pair-instability supernova, I think
     
  7. May 21, 2008 #6
    g33,

    This has been duplicated in the lab long ago. Apposing beams of gamma radiation contact each other at twice the speed of light (collision speed). Gamma rays are the highest frequency waves (shortest waves). Upon contact with each other they produce numerous pairs of stable electrons and positrons. Conversely, when electrons and positrons come in contact they annihilate each other producing gamma rays. Within a star according to theory the same process occurs. The primarily unanswered theoretical question is: why are gamma rays somehow different in that they can produce stable particles? They are EM radiation but what does pure energy really mean? There are only a few theories concerning this question and little controversy.
     
  8. May 22, 2008 #7

    SF

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    So what, non-gamma rays are "impure" energy?
     
  9. May 22, 2008 #8
    Hey two points for public radio! They had a short report on this discovery on NPR yesterday afternoon!
     
  10. May 22, 2008 #9

    Chronos

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    One issue not well discussed in the literature is massive binaries of similar size and histories. What if a massive pop III star went SNc while its neighbor was at the brink? I would expect to see 'camel' humps in the light curve. Detonation of the first would set off its companion. The primary and secondary spectrums in such an event would be novel.
     
  11. May 23, 2008 #10

    chemisttree

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    Ah! Good question! Is it true that a metal-rich protostar ignites at a lower temperature (mass?)? Is there data suggesting that much more massive stars than our sun are all metal poor?
     
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