What Happens to Sound Waves Near Black Holes?

AI Thread Summary
The discussion centers on the nature of sound waves in relation to black holes, addressing misconceptions about sound traveling in space. Participants clarify that sound requires a medium, such as gas, to propagate, and while black holes can produce sound waves in surrounding gas, these are not sound in the traditional sense. The conversation also touches on the influence of gravitational waves and the conditions necessary for sound to exist near black holes. Some participants express interest in the broader implications of sound in space, including the presence of magnetic fields and electrical currents. Ultimately, the complexities of sound waves and their interaction with black holes remain a topic of intrigue and debate.
freddy123
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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
 
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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?)
 
Actually, let me ask a different question.

Do black holes make sound ?
 
freddy123 said:
Actually, let me ask a different question.

Do black holes make sound ?

In WHAT?
 
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?
 
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.
 
That's all :-)
 
freddy123 said:
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.

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.
 
  • #10
A similar situation arises in the case of baryon acoustic oscillations in the surface of last scattering. You can google that too.
 
  • #11
freddy123 said:
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.

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.
 
  • #12
ImaLooser said:
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.

The bolded part is incorrect. electromagnetic waves do NOT require a medium such as is required by sound.
 
  • #13
Just to be clear, here's wikipedia's definition of sound:
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations

Nothing in space falls under this definition, so I personally wouldn't call it sound. But to each their own.
 
  • #14
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.
 
  • #15
phinds said:
The bolded part is incorrect. electromagnetic waves do NOT require a medium such as is required by sound.

Yes. I wrote "electromagnetic waves and electrical currents." By "and" I meant both, not and/or.
 
  • #16
Chronos said:
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.

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"
 
  • #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?
 
  • #18
Holesarecool said:
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?

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.
 
  • #19
Interesting video about the sound of black holes

http://www.ted.com/talks/view/lang///id/1095
 
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