What Happens to Sound Waves Near Black Holes?

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Discussion Overview

The discussion revolves around the behavior of sound waves in the vicinity of black holes, particularly what occurs to sound waves before and after they reach a black hole. Participants explore the nature of sound in space, the conditions under which sound can exist, and the implications of black holes on sound propagation.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question whether sound can exist near black holes, noting that sound requires a medium and cannot travel in a vacuum.
  • There is a discussion about whether black holes can produce sound, with references to NASA's claims about sound waves detected in surrounding gas clouds.
  • Some participants express skepticism about the definition of sound in the context of space, arguing that the conditions do not meet traditional definitions of sound as mechanical waves.
  • Others suggest that sound waves can be influenced by the density of the medium, even in low-density environments like space, where gas molecules exist.
  • A hypothesis is raised about whether gravitational waves from black holes could induce disturbances in nearby materials, potentially creating sound, though this is contested by others who argue against the feasibility of such effects.
  • There are references to the concept of baryon acoustic oscillations and the nature of electromagnetic waves, with some participants clarifying that electromagnetic waves do not require a medium like sound does.

Areas of Agreement / Disagreement

Participants express a range of views, with no consensus reached on the nature of sound near black holes or the validity of claims regarding sound in space. Disagreements persist regarding definitions and the physical mechanisms involved.

Contextual Notes

Participants highlight limitations in understanding sound in space, including the dependence on definitions and the conditions under which sound can propagate. The discussion reflects varying interpretations of scientific concepts without resolving these ambiguities.

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 propagate. 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 propagate. 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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