<p>Nothing comes out from the BH (well, with a single known, very small <a href="https://en.wikipedia.org/wiki/Hawking_radiation" rel="nofollow noreferrer">exception</a>).</p>

<p>The <a href="https://en.wikipedia.org/wiki/Accretion_disk" rel="nofollow noreferrer">accretion disk</a> of the Black Holes most likely has various streams, pressure differences and so in it. Calculating it or measuring it is surely a very hard task, if you have luck, a professional explains the results in a better answer.</p>

<p>The accretion disc of the typical, star-sized black holes is much smaller as 1AU. And sound doesn't propagates in vacuum. Thus, from 1AU distance from the Black Hole we most likely wouldn't hear anything.</p>

<p>Other radiations (mainly gamma from the disc) may be deadly even from 1AU, but not its sound.</p>

CC BY-SA 4.0
2018-06-14T17:40:57.810Z
Also I think think that this question would deserve a professional answer.
peterh
CC BY-SA 4.0
2018-06-16T07:09:41.410Z
A professional answer can talk about phonons, and Sonic Black Holes. a SNB can  envelop normal black holes if the speed of phonons is space is slower than light, which it theoretically is. So if phonons travel at 0.1 times the speed of light in a vacuum by phonon tunneling, the the sonic black hole would exist where matter falls in at that speed.
bandybabboon
CC BY-SA 4.0
2018-06-18T21:03:31.253Z
BTW, you're going to get a lot of nitpicking for saying the Hawking radiation originates from "inside" the event horizon. :)
Florin Andrei
CC BY-SA 4.0
2018-06-14T17:26:22.740Z
2018-06-18T22:31:35.017Z
2018-06-18T22:31:35.017Z
peterh
<p>Physicists talk about phonons to describe energy transmission in elastic media similar to sound. There hasn't been much research about phonon transmission through the void of space because it is a forbidden event in physics. There is no sound in space. Some scientists have studied phonon tunneling through few angstroms of vacuum. <a href="https://physicsworld.com/a/phonons-tunnel-across-the-vacuum/" rel="nofollow noreferrer">https://physicsworld.com/a/phonons-tunnel-across-the-vacuum/</a></p>

<p>To find out more, you can read about phonons and sonic black holes. </p>

<p>Ears and microphones require air pressure and displacement of mass onto the auditory diaphragm. The mass and pressure of the interstellar medium is too low to actively move sound-sensing diaphragms, unless you have a lot of ions/gas massive objects to do that. In space there is a vacuum. if an astronaut played drums beside you in space, they would not displace any air pressure. there would be no noise. </p>

<p>If you had a 1000Watt studio speaker beside you in space, it's quite possible that you would receive less than a single electron worth of sound pressure energy from that speaker per m2. something like 10^-20 watts. 100 dB is about 0.01W/m2 and is at the limit of hearing impairment.</p>

<p>Do you know the warning: "In Space, No one can hear you scream"... the film aliens...</p>

CC BY-SA 4.0
2018-06-14T20:54:51.513Z
There _is_ sound in space, just with typical sound speeds of the order of tens of kilometers per second. Sound plays a very significant role e.g. in such diverse fields as collapse of protostellar clouds and in the "baryonic acoustic oscillations" in the early Universe.
pela
CC BY-SA 4.0
2018-06-16T02:17:57.460Z
We would have to disagree about what sound is, and sound volume... What is the transmission medium and physical strength of the sound that you describe? The sound pressure level generated by a violin in space would be how much in terms of SPL? any microphone in space would register 0 dB unless a gas/ion mass moved the diaphragm. the mass of a vacuum is not sound-transmitting.
bandybabboon
CC BY-SA 4.0
2018-06-16T05:06:17.840Z
I agree that the sound is too… dim?…low?… to be heard by humans, but in physics we cannot disagree what sound is: it is the oscillating compressions/rarefactions of particles in a fluid. In space, that fluid is usually an extremely dilute atomic gas or plasma. But nevertheless, "sound in space" is term used frequently by astronomers. For instance, in the "warm neutral medium", you could have n = 1 atom per cm$^3$ at a temperature of T = 1e4 K, so the pressure would be $P = n k_B T$ ~ 1e-13 Pa, corresponding to an SPL of 20 log(P/20µPa) = –163 dB.
pela
CC BY-SA 4.0
2018-06-16T07:28:00.913Z
that's a very qualified response, so I have read about phonons and sonic black holes, and measurements of phonons in low pressure, I didn't find that space can actually transmit phonons, perhaps no more than a few microns. There is also a graph of sound dampening of different frequencies for different media. If the interstellar medium only contains 1 atom per cm3, then the atoms would not interact very often at most frequencies?
bandybabboon
CC BY-SA 4.0
2018-06-16T08:44:08.487Z
I don't know anything about sonic BHs, but as far as I know, phonons are a way to describe sound waves primarily in solid, where waves can be both longitudinal and tranversal, though it might also have a use in some quantum description of BHs. That's not how it works in a gas, especially not such a dilute gas as in the interstellar medium. I don't think I've ever heard the term used in astronomy; usually we just call it "sound waves", and they work exactly the same as a sound wave in, say, our atmosphere, with the speed of sound calculated e.g. as c = √(∂p/∂ρ).
pela
CC BY-SA 4.0
2018-06-16T08:47:26.143Z
Because the mean free path of particles in the interstellar and intergalactic is so long, sound frequencies are extremely small — wavelengths are typically measured in AU or lightyears. The [baryon acoustic oscillations](https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations) have wavelengths of roughly half a billion lightyears.
pela
CC BY-SA 4.0
2018-06-16T09:22:00.287Z
The Baryon Acoustic Oscillations are thermal imprints of 14.3 billion year old thermal pressure waves that occured in a plasma medium that was too dense to transmit light. The resemblance between the BAO and acoustics is similar to the similiarity of macro-galactic matrix to a sponge, it's not the same thing. I thought that phonons transmit radially and are described as a radiation, I think that phonons can happen in any state of matter which is dense. here is a 2d pic of phonons: http://slideplayer.com/slide/4173889/
bandybabboon
CC BY-SA 4.0
2018-06-16T11:39:37.687Z
I don't really know anything about phonons. And you're right, the BAOs are not sound waves anymore. But they _were_, when the gas/photon fluid was oscillating in the gravitational wells of dark matter halos. When free electrons disappeared and photons started free-streaming, the fluid was relieved of pressure and the sound waves were essentially frozen in space and stopped propagating (though their wavelength expanded with the Universe). I don't agree that it's just an analogy, though, like comparing galaxy filaments to a sponge. It really _was_ sound waves.
pela
CC BY-SA 4.0
2018-06-14T19:43:26.550Z
2018-06-16T09:33:08.660Z
2018-06-16T09:33:08.660Z
bandybabboon
<p>If we could hear black holes, how loud would they be? I know that this is basically the same question as the question "How loud would the Sun be?", except this time there is a black hole. But since the black hole sucks in stuff like a passenger jet engine sucks in air, about how many decibels would it be? Also, would it lethal to humans if we were 1 AU away and what would it do to our planet?</p>

CC BY-SA 4.0
2018-06-14T04:46:51.687Z
-1. If light can’t escape a black hole, why do you think sound could? Also, black holes don’t “suck”. You might find it useful to read up on black holes in Wikipedia before asking about them. Or look through the questions and answers on Astronomy SE or Physics SE (search the tag black-hole).
Chappo Hasn't Forgotten
CC BY-SA 4.0
2018-06-14T17:18:34.047Z
@Chappo I think the sound strength in the accretion disc could be calculated with (general) relativistic aerodynamics. Most probably it is not an easy calculation, and it hardly depends on the circumstances, but interpreting the question in this view makes it, in my opinion, on-topic.
peterh
CC BY-SA 4.0
2018-06-14T21:25:48.230Z
@peterh yes, I’d expect some extreme acoustic effects within a BH accretion disk. The question is on-topic but borderline in quality: inexperienced OPs need to demonstrate some basic effort before posting their questions, to avoid us having to infer a related matter to make the question valid.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2018-06-14T21:32:45.377Z
@Chappo Btw, it is probably the only place in the Universe, where doppler effect of *sound* due to general relativity plays an experimentally verifiable role. But I don't know, this what the OP really asked for. But I think this is what he asked. If he wanted to know some different, then he may ask a new question :-)
peterh
CC BY-SA 4.0
2018-06-15T02:00:31.580Z
Wait. But the point of no return is the event horizon, not the accretion disk. Also, what about the jets?
Leo Pan
CC BY-SA 4.0
2018-06-15T05:59:36.523Z
@LeoPan Jets have typically not a very high density, although they are probably deadly from 1AU.
peterh
CC BY-SA 4.0
2018-06-15T06:48:28.313Z
@LeoPan Not all BHs have accretion disks. Once the matter in the accretion disk has fallen in to the BH, the local space outside the event horizon has effectively been cleared.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2018-06-15T23:58:47.577Z
That is true. But, wouldn't we hear the stuff falling in?
Leo Pan
CC BY-SA 4.0
2018-06-16T07:36:20.220Z
Research sonic black holes and phonons if you want. a black hold would be enveloped with a sonic black hole if space had a phonon transmission medium heavier than one atom per cm3, which it perhaps doesn't.
bandybabboon
<black-hole><sound>
How loud would a black hole be?
Leo Pan
# How loud would a black hole be?

(Asked by: username_0 on 2018-06-13)

If we could hear black holes, how loud would they be? I know that this is basically the same question as the question "How loud would the Sun be?", except this time there is a black hole. But since the black hole sucks in stuff like a passenger jet engine sucks in air, about how many decibels would it be? Also, would it lethal to humans if we were 1 AU away and what would it do to our planet?

**Tags:** black-hole, sound

> **Comments:**
> **username_1**: -1. If light can’t escape a black hole, why do you think sound could? Also, black holes don’t “suck”. You might find it useful to read up on black holes in Wikipedia before asking about them. Or look through the questions and answers on Astronomy SE or Physics SE (search the tag black-hole).  
> **username_2**: @username_1 I think the sound strength in the accretion disc could be calculated with (general) relativistic aerodynamics. Most probably it is not an easy calculation, and it hardly depends on the circumstances, but interpreting the question in this view makes it, in my opinion, on-topic.  
> **username_1**: @username_2 yes, I’d expect some extreme acoustic effects within a BH accretion disk. The question is on-topic but borderline in quality: inexperienced OPs need to demonstrate some basic effort before posting their questions, to avoid us having to infer a related matter to make the question valid.  
> **username_2**: @username_1 Btw, it is probably the only place in the Universe, where doppler effect of *sound* due to general relativity plays an experimentally verifiable role. But I don't know, this what the OP really asked for. But I think this is what he asked. If he wanted to know some different, then he may ask a new question :-)  
> **username_0**: Wait. But the point of no return is the event horizon, not the accretion disk. Also, what about the jets?  
> **username_2**: @username_0 Jets have typically not a very high density, although they are probably deadly from 1AU.  
> **username_1**: @username_0 Not all BHs have accretion disks. Once the matter in the accretion disk has fallen in to the BH, the local space outside the event horizon has effectively been cleared.  
> **username_0**: That is true. But, wouldn't we hear the stuff falling in?  
> **username_3**: Research sonic black holes and phonons if you want. a black hold would be enveloped with a sonic black hole if space had a phonon transmission medium heavier than one atom per cm3, which it perhaps doesn't.  

---

## 2 answers

### Answer by username_2 on 2018-06-14. Score: 3 | Accepted answer

Nothing comes out from the BH (well, with a single known, very small [exception](https://en.wikipedia.org/wiki/Hawking_radiation)).

The [accretion disk](https://en.wikipedia.org/wiki/Accretion_disk) of the Black Holes most likely has various streams, pressure differences and so in it. Calculating it or measuring it is surely a very hard task, if you have luck, a professional explains the results in a better answer.

The accretion disc of the typical, star-sized black holes is much smaller as 1AU. And sound doesn't propagates in vacuum. Thus, from 1AU distance from the Black Hole we most likely wouldn't hear anything.

Other radiations (mainly gamma from the disc) may be deadly even from 1AU, but not its sound.

> **Comments:**
> **username_2**: Also I think think that this question would deserve a professional answer.  
> **username_3**: A professional answer can talk about phonons, and Sonic Black Holes. a SNB can  envelop normal black holes if the speed of phonons is space is slower than light, which it theoretically is. So if phonons travel at 0.1 times the speed of light in a vacuum by phonon tunneling, the the sonic black hole would exist where matter falls in at that speed.  
> **username_4**: BTW, you're going to get a lot of nitpicking for saying the Hawking radiation originates from "inside" the event horizon. :)  

---

### Answer by username_3 on 2018-06-14. Score: 2

Physicists talk about phonons to describe energy transmission in elastic media similar to sound. There hasn't been much research about phonon transmission through the void of space because it is a forbidden event in physics. There is no sound in space. Some scientists have studied phonon tunneling through few angstroms of vacuum. <https://physicsworld.com/a/phonons-tunnel-across-the-vacuum/>

To find out more, you can read about phonons and sonic black holes.

Ears and microphones require air pressure and displacement of mass onto the auditory diaphragm. The mass and pressure of the interstellar medium is too low to actively move sound-sensing diaphragms, unless you have a lot of ions/gas massive objects to do that. In space there is a vacuum. if an astronaut played drums beside you in space, they would not displace any air pressure. there would be no noise.

If you had a 1000Watt studio speaker beside you in space, it's quite possible that you would receive less than a single electron worth of sound pressure energy from that speaker per m2. something like 10^-20 watts. 100 dB is about 0.01W/m2 and is at the limit of hearing impairment.

Do you know the warning: "In Space, No one can hear you scream"... the film aliens...

> **Comments:**
> **username_5**: There _is_ sound in space, just with typical sound speeds of the order of tens of kilometers per second. Sound plays a very significant role e.g. in such diverse fields as collapse of protostellar clouds and in the "baryonic acoustic oscillations" in the early Universe.  
> **username_3**: We would have to disagree about what sound is, and sound volume... What is the transmission medium and physical strength of the sound that you describe? The sound pressure level generated by a violin in space would be how much in terms of SPL? any microphone in space would register 0 dB unless a gas/ion mass moved the diaphragm. the mass of a vacuum is not sound-transmitting.  
> **username_5**: I agree that the sound is too… dim?…low?… to be heard by humans, but in physics we cannot disagree what sound is: it is the oscillating compressions/rarefactions of particles in a fluid. In space, that fluid is usually an extremely dilute atomic gas or plasma. But nevertheless, "sound in space" is term used frequently by astronomers. For instance, in the "warm neutral medium", you could have n = 1 atom per cm$^3$ at a temperature of T = 1e4 K, so the pressure would be $P = n k_B T$ ~ 1e-13 Pa, corresponding to an SPL of 20 log(P/20µPa) = –163 dB.  
> **username_3**: that's a very qualified response, so I have read about phonons and sonic black holes, and measurements of phonons in low pressure, I didn't find that space can actually transmit phonons, perhaps no more than a few microns. There is also a graph of sound dampening of different frequencies for different media. If the interstellar medium only contains 1 atom per cm3, then the atoms would not interact very often at most frequencies?  
> **username_5**: I don't know anything about sonic BHs, but as far as I know, phonons are a way to describe sound waves primarily in solid, where waves can be both longitudinal and tranversal, though it might also have a use in some quantum description of BHs. That's not how it works in a gas, especially not such a dilute gas as in the interstellar medium. I don't think I've ever heard the term used in astronomy; usually we just call it "sound waves", and they work exactly the same as a sound wave in, say, our atmosphere, with the speed of sound calculated e.g. as c = √(∂p/∂ρ).  
> **username_5**: Because the mean free path of particles in the interstellar and intergalactic is so long, sound frequencies are extremely small — wavelengths are typically measured in AU or lightyears. The [baryon acoustic oscillations](https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations) have wavelengths of roughly half a billion lightyears.  
> **username_3**: The Baryon Acoustic Oscillations are thermal imprints of 14.3 billion year old thermal pressure waves that occured in a plasma medium that was too dense to transmit light. The resemblance between the BAO and acoustics is similar to the similiarity of macro-galactic matrix to a sponge, it's not the same thing. I thought that phonons transmit radially and are described as a radiation, I think that phonons can happen in any state of matter which is dense. here is a 2d pic of phonons: http://slideplayer.com/slide/4173889/  
> **username_5**: I don't really know anything about phonons. And you're right, the BAOs are not sound waves anymore. But they _were_, when the gas/photon fluid was oscillating in the gravitational wells of dark matter halos. When free electrons disappeared and photons started free-streaming, the fluid was relieved of pressure and the sound waves were essentially frozen in space and stopped propagating (though their wavelength expanded with the Universe). I don't agree that it's just an analogy, though, like comparing galaxy filaments to a sponge. It really _was_ sound waves.  

---

