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What force is created before supernova explosion?

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  1. Jun 7, 2015 #1
    how antigravity force is created before supernova explosion? why it is not created in a body less than chandrashekhar limit?
     
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  3. Jun 7, 2015 #2

    wabbit

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    What do you mean by "antigravity force" ?
     
  4. Jun 7, 2015 #3
    I think he means an outward force so big that the whole star expands.


    And in that case it is produced in every single star in the universe other than brown and red dwarfs(brown and red dwarfs just gradually die off like how a battery gradually dies off so no outward force other than the one produced by fusion is involved) from small ones like our sun that will never supernova to large ones like betelgeuse that will definetely supernova within the next 10,000 years.
     
  5. Jun 7, 2015 #4

    wabbit

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    Ah you lost me here, what is this outward force you are referring to ?

    Also, do you have a reference to the fact that Betelgeuse will go supernova in the next 10,000 years ? This seems extremely precise, I wonder how we can get such accuracy ?
     
    Last edited: Jun 7, 2015
  6. Jun 7, 2015 #5
    This outward force that I am referring to is the pressure produced by the star's core to counteract gravity which always trys to shrink the star. When you have a massive star(more massive than our sun) at some point pressure is greater than gravity so the star expands. Before that though some stars will actually shrink right before helium fusion starts. This is a helium flash. Then after years of being a red giant or supergiant(and in rare cases hypergiant(hypergiants are the biggest stars in the universe)) the pressure gets so big that while the core contracts due to gravity forming a neutron star or if the star is supermassive, a black hole the outer layers continue to expand at a rapid pace. This is a type II supernova
     
  7. Jun 7, 2015 #6

    wabbit

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    OK I see - pressure is nothing one would call antigravity, but also, as I understand it this is not what causes a supernova explosion. On the contrary, if I recall correctly, it is insufficient pressure to counteract gravity that provokes a collapse, and the explosion is the resulting rebound. Describing this as antigravity seems very weird, if anything the force causing the explosion is gravity.

    Regarding Betelgeuse, I found this article, which is reporting on http://arxiv.org/abs/1406.3143 : Evolutionary tracks for Betelgeuse (Michelle M. Dolan, Grant J. Mathews, Doan Duc Lam, Nguyen Quynh Lan, Gregory J. Herczeg, David S. P. Dearborn). They estimate ~100k years, which seems quite precise already. Very interesting stuff.
     
  8. Jun 7, 2015 #7

    Vanadium 50

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    Roughly 20x as much writing has been expended guessing what the OP means. Why not wait for him to explain what he means?
     
  9. Jun 7, 2015 #8

    Chronos

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    The outward force in a supernova is created by matter recoiling from the degenerate core during collapse. There are also significant neutrino emissions involved as well - no antigravity required.
     
  10. Jun 8, 2015 #9
    Below is a good brief description of what goes on in a red supergiant just before supernova-
    http://aether.lbl.gov/www/tour/elements/stellar/stellar_a.html

    I suppose you could say that it is the mass of the original star that results in there being a supernova or not. A star with an original mass of up to 8 sol will result in a white dwarf, a star with an original mass of between 8 and 18 sol will result in a supernova & neutron star, and a star with an original mass of more than 18 sol will result in a supernova & black hole.

    source-
    http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit3/extreme.html
     
  11. Jun 8, 2015 #10
    A Hypothetical question: What would happen to our solar system if there is a supernovae exploding at a distance of our closest star Proxima Centauri at approx 4.2 light years away? What would be the consequences?
     
  12. Jun 8, 2015 #11
    It really depends on what kind of supernova explosion takes place. In general, supernovae release huge amounts of x-rays and gamma rays, and these could significantly damage the ozone layer in the atmosphere when they reach the Earth. A depletion of the ozone layer could have catastrophic effects for the biosphere, as primary producers would significantly be affected after exposure UV radiation from the Sun, which could lead to a collapse in food webs globally.
    I'm not 100% sure, but IMO the radiation should affect human satellites near Earth as well.
     
  13. Jun 8, 2015 #12
    The blast from a supernova can be somewhat directional, so the exact consequences for Earth could vary because of that,
    However even if Earth were located well away from the regions of maximum blast, I'm pretty sure that the amount of gamma radiation received from a supernova that close to Earth would likely sterilize all life, and probably fry the atmosphere into a highly ionized state.
     
  14. Jun 8, 2015 #13
    the outward force that is created during supernova explosion is antigravity force.. at that time gravity collapses.
     
  15. Jun 8, 2015 #14

    Drakkith

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    The outward force certainly works against gravity, but it is not antigravity in the usual sense of the word. Not anymore than the thrust propelling a rocket away from Earth is antigravity.
     
  16. Jun 8, 2015 #15

    Chronos

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  17. Jun 8, 2015 #16

    SteamKing

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    You were misinformed somewhere. Gravity doesn't "collapse" during the microseconds preceding the supernova event.

    If anything, once fusion stops in the core of the star, gravity is able to cause the core to compress to a tiny fraction of its original size, since there is nothing, no force, which counteracts it.

    You should read something about supernova formation, to get the correct idea about the sequence of events:

    http://en.wikipedia.org/wiki/Type_II_supernova
     
  18. Jun 11, 2015 #17

    Ken G

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    That Wiki entry promotes some common misconceptions. I knew it would, it's not alone there-- textbooks say similarly misleading things. But it's worth pointing them out to try to set the record straight. For example, the Wiki says "As there is no fusion to further raise the star's temperature to support it against collapse, it is supported only by degeneracy pressure of electrons." This is incorrect, it is never necessary to raise temperature to support against collapse, what you actually need to support against collapse is to maintain the temperature-- you need to replace lost heat. When lost heat is not replaced, what actually happens is temperature rises, so we can see that a constant temperature is a sign of something that is being supported, and a rising temperature is a sign of something that is not being supported. Worse, the Wiki goes on to say "In this state, matter is so dense that further compaction would require electrons to occupy the same energy states."
    That's also incorrect, further compaction is certainly possible if sufficient work is supplied, degeneracy never prevents collapse any differently from any other kind of pressure, it simply sets the requirements for collapse like any pressure does. Degeneracy pressure is, in that sense, a completely mundane type of pressure, and a natural aspect of pressure is that work is required to produce compaction. But like with any nonrelativistic gas pressure, the work that would be supplied to produce compaction causes an increase in pressure which exceeds the increase in gravity, this is normal gas-pressure stability no different from an ideal gas. So it bounces back-- gravity does not contract gas pressure supported objects unless there is net heat loss. So what neutron degeneracy really does, which has no direct connection with producing pressure, is to eliminate further heat loss, and gravity always requires heat loss in order to obtain further contraction. Degeneracy is a thermodynamic effect that inhibits heat loss, not a mechanical effect that produces pressure.
     
  19. Jun 11, 2015 #18

    Drakkith

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    Note that Ken's referring to the Kelvin-Helmholtz mechanism here. (I think)
     
  20. Jun 11, 2015 #19

    Ken G

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    Right. That mechanism says that if there is net heat loss, gravity will slightly exceed pressure. It is a misconception to say that the heat loss ever causes temperature drop, however-- the temperature can rise monotonically everywhere, throughout the process. The key is that the slight excess of gravity is always causing contraction, allowing gravity to do work that pumps kinetic energy into the system-- usually at a rate twice as large as the net heat loss that is driving the whole business. Thus the excess kinetic energy piles up and causes the continuing temperature rise, but even though the temperature is steadily rising, the rising gravity continues to slightly exceed the pressure.

    Anything that short-circuits the net heat loss will stop this process, and either fusion or degeneracy can do that-- fusion by replacing lost heat, degeneracy by preventing heat loss in the first place.
     
    Last edited: Jun 11, 2015
  21. Jun 12, 2015 #20
    The "outward force" is caused by electron degeneracy. It can resist further compression by the gravity of the star. Bigger stars could overcome even that and create black holes.
     
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