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Super Novae and emission of electromagnetic waves and gravitation wavefronts

  1. Sep 11, 2010 #1
    Hello, could you please help to clarifly the following.

    Do electromagnetic (e.g. light) and gravitational wavefronts caused by e.g. a supernova both appear at the same time seen from a distant observer perspective?

    Thank you!
     
  2. jcsd
  3. Sep 11, 2010 #2
    Is gravitation propagating at max. speed of light?

    I'd say yes, but it would be great to hear the answer from experts.

    IMO, the maximal possible speed in our Universe (being C) is set by the structure of space-time fabric.
     
  4. Sep 11, 2010 #3
    Hi, the gravitational wavefront would expand with the speed of light. The idea behind is, as gravitation folds and expands spacetime, the electromagnetic wave has to follow the path of the folded and expanded spacetime compared to gravitation, where the e.g. minima and maxima of space expand with speed of light.

    Would be nice if anyone could clarify this.
     
  5. Sep 12, 2010 #4

    Chronos

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    They arrive at the same time. Both propogate at light speed.
     
  6. Sep 13, 2010 #5
    What if Supernova exploded near a Black Hole, all matter and even light (photons) would be sucked into it, what about gravitation (gravitons), would they propagate outwards in space or would a BH suck those in too, and then increase its own gravitation force?

    Would be strange if so, I'd say gravitation cannot "suck" gravitation, right?
     
  7. Sep 13, 2010 #6
    I`d day, in the extreme (and please lets talk about extremes, all the others I don't understand).

    In the extreme I'd guess the mass of the black hole would have to be infinite to suck the gravitation of the supernova.
     
  8. Sep 13, 2010 #7

    Jonathan Scott

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    Gravitons are an idea from quantum theory and black holes are from General Relativity. So far there is no generally accepted theory which can handle both.

    Classical gravitational waves are part of General Relativity. These relate only to changes in the gravitational field, not to the field itself, and propagate at the speed of light.

    It's very difficult to produce significant changes in a gravitational field; for example, if you try shaking something, this has an equal and opposite effect on the mechanism doing the shaking, so overall the center of mass of the system is unaffected and the distant gravitational field is unchanged.

    See the Wikipedia article on http://en.wikipedia.org/wiki/Gravitational_wave" [Broken] for more information including some nice animated graphics.
     
    Last edited by a moderator: May 4, 2017
  9. Sep 13, 2010 #8
    Hello Jonathan, thank you for your reply. I will reflect on that what you wrote.

    Addendum: I will look at the pictures. but I already saw saw some pictures and read some books. However. You can't easily create a picture of a field as it changes its value in every point of space time and therefore every approximation at a point of time is, in fact, incorrect. Therefore the maximum values (in the pictures of Wikipedia) should have been spheric, meeting nearly at the north and south pole of the singularity, expanding with lightspeed c at their minma and maxima.
     
    Last edited: Sep 13, 2010
  10. Sep 13, 2010 #9
    Thank you. That was a good hint.
     
  11. Sep 13, 2010 #10
    Thanks for clarification re gravitons, gravitational waves and which theory handles which.

    So, QT doesn't handle singularities?

    Based solely on GR, isn't the space-time near the Black Hole curved so much that gravitational waves of Super Novae exploding nearby wouldn't propagate in all directions outwards in space, but just in one direction towards the BH?
     
  12. Sep 14, 2010 #11
    Hi, after reflecting a bit I dont think that gravitational waves of a supernova are completely swallowed by a black hole near by as long as the supernova is not at or "below" the event horizon.

    Philosophically said, if that would be so, the supernova would be part of the black hole (as anything behind the horizon becomes part of the hole) and if it is outside the event horizon, some gravitational waves and even photons and materia might escape.

    I do also imagine gravitational waves as a threedimensional field which manipulates spacetime. But I believe with standard mathematics you can just discuss to the point of the event horizon, but not below.
     
  13. Sep 14, 2010 #12
    Nope, both GR gives you meaningless infinities and QM doesn't include gravity at all! You'd need to accept underdeveloped theories such as string/M-theory or others which account for gravity at the Planck Scale and/or below to get a meaningful answer.

    No. G-Waves are perturbations of the same field that IS the black hole. A black hole will cause effects to be observed, but it doesn't "suck in" more than what it is. You're essentially asking of spacetime would cause all spacetime to implode on spacetime... which is a meaningless statement.
     
  14. Sep 14, 2010 #13
    Gravity is a 4 dimensional phenomenon... spaceTIME, so 3+1. Gravitational waves are perturbations in 4 dimensions.
     
  15. Sep 14, 2010 #14
    Sorry, you're right. I always make the mistake and see myself from observer perspective not as part of spacetime but outside from it.
     
  16. Sep 14, 2010 #15
    It's a common enough error, don't sweat it.
     
  17. Sep 14, 2010 #16
    We haven't yet detected gravitational waves, but we expect to see gravitational radiation from a supernova a few hours before we see any light from the explosion. Gravitational radiation is produced by the mixing processes and collapse of the SN, and gets out immediately. It takes a few hours for the shock wave to work through 20 solar masses of stuff so you don't see any visible sign of the explosion until several hours after you see a gravitational signal.

    This has been experimentally tested in another context. In SN 1987A, we recorded a very strong neutrino signal several hours before anyone visually saw the supernova. So the gravity signal should arrive at the same time as the neutrino signal. (Now whether or not it *does* is something that people are interested in seeing,)

    One thing that would be really interesting is that we've developed our neutrino telescopes and LIGO enough so that we should be able to detect a supernova in the Milky Way, even if it is in a part of the galaxy that we can't see.
     
  18. Sep 14, 2010 #17
    Also one big unresolved question is do supernova produces black holes (i.e. can you have a supernova and then have collapse into a black hole or do black holes just form quietly).
     
  19. Sep 15, 2010 #18

    Chronos

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    Good point, twofish, gravitation radiation can arrive sooner than photons - as do neutrinos, mea culpa. I have reservations about black holes forming directly from stellar collape events. See, for example http://www.space.com/scienceastronomy/massive-mega-star-challenges-black-hole-theory-100818.html
    This observation suggests neutron star mass does not scale well with progenitor star mass - which also appears consistent with the fact hardly any neutron stars are known to exceed the Chandrasekahr mass limit. I suspect stellar mass black holes most commonly originate via collisions between degenerate matter stars in binary systems.
     
    Last edited: Sep 15, 2010
  20. Sep 15, 2010 #19
    Gentlemen, I have now reflected and tried to repress the obvious question: Does this mean that information can be distributet at light speed rather than the speed of light?
     
  21. Sep 15, 2010 #20
    You just asked if information can be disseminated at c, or at c. The answer is... yes, but you only gave one option. Fortunately it's the correct option, but you're starting to worry me.
     
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