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Sound and Black Holes

  1. Apr 24, 2012 #1
    Hi,

    I'm doing some research on sound. I'm interested in finding out what happens to a sound wave just BEFORE it reaches a black hole and what happens when it ACTUALLY reaches a black hole ?

    Can someone direct me to the right place for this ?

    Thanks for the help
     
  2. jcsd
  3. Apr 24, 2012 #2

    marcusl

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    Are you asking about pressure disturbances in a plasma? (You do know, I presume, that sound won't travel in a vacuum?)
     
  4. Apr 24, 2012 #3
    Actually, let me ask a different question.

    Do black holes make sound ?
     
  5. Apr 24, 2012 #4

    phinds

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    In WHAT?
     
  6. Apr 24, 2012 #5
  7. Apr 24, 2012 #6

    phinds

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    So do you not believe what it says in the article? I mean, you've just posted a link in post #5 to a thread where NASA says it has found sound waves from a black hole in the surrounding gas cloud, just after asking in post #3 if black holes make sound? Do you figure NASA is lying about it?
     
  8. Apr 24, 2012 #7
    No i don't believe NASA is lying. I'm very excited that I have discovered this. I posted here to see if you guys here, the experts, have got any more information about this. Not just about this specific article but about sound in space in general (i'm fully aware that sound doesn't travel in vacuum). I'm just asking the experts for some more information that's all. I just wanted to know if you ever come across anything about sound in space and specifically about sound near black holes.
     
  9. Apr 24, 2012 #8
    That's all :-)
     
  10. Apr 24, 2012 #9

    Drakkith

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    The "sound" in space that is referred to is simply a very long wavelength wave within a very very thin gas. While you can call this sound, I personally wouldn't. It's kind of like calling a 10 hz EM wave light. You can do it, but it really doesn't make much sense.
     
  11. Apr 24, 2012 #10

    Chronos

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    A similar situation arises in the case of baryon acoustic oscillations in the surface of last scattering. You can google that too.
     
  12. Apr 25, 2012 #11
    I'm very interested in this too. When I was a kid they taught us that outer space was empty and not much happened there. Not so. There are magnetic fields and electrical currents out there, and once you have those you can get sound waves too. The fields may be very diffuse, but get enough space and the total power can be considerable.
     
  13. Apr 25, 2012 #12

    phinds

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    The bolded part is incorrect. electromagnetic waves do NOT require a medium such as is required by sound.
     
  14. Apr 25, 2012 #13

    Drakkith

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    Just to be clear, here's wikipedia's definition of sound:
    Nothing in space falls under this definition, so I personally wouldn't call it sound. But to each their own.
     
  15. Apr 25, 2012 #14

    Chronos

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    Sound waves are influenced by the density of the medium through which they propogate. Space contains matter, like gas molecules, but, at low density. Sound is propogated by collisions between molecules. In space the distance between collisions is merely greater than say for air on earth.
     
  16. Apr 26, 2012 #15
    Yes. I wrote "electromagnetic waves and electrical currents." By "and" I meant both, not and/or.
     
  17. Apr 27, 2012 #16
    exactly. sound waves need to "travel" through gas, like said above, in our case air

    to quote the movie Aliens "in space, no one can hear you scream"
     
  18. May 1, 2012 #17
    If a black hole has strong gravitational waves, couldn't that induce disturbances in the density of whatever material is in the path of the waves? So in affect, couldn't a black hole create sound in any close medium by jiggling spacetime?
     
  19. May 1, 2012 #18

    Drakkith

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    I don't believe so. First, a lone black hole shouldn't be producing gravitational waves, as it would need another massive object to orbit with it. Second, gravitational waves are in the metric of spacetime itself, so I don't think they would have the effect you imagine they would. Space would curve back and forth a little bit as each wave passes through, but I don't believe this would create any sound waves.
     
  20. May 1, 2012 #19
    Interesting video about the sound of black holes

    http://www.ted.com/talks/view/lang///id/1095 [Broken]
     
    Last edited by a moderator: May 6, 2017
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