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Black Hole Music and Really Low Notes

Posted July 13, 2017 12:00 AM by Hannes
Pathfinder Tags: black hole organ pitch

A colleague of mine recently heard from a friend that certain black holes make musical pitches—specifically, scientists have observed a black hole “emitting” a B-flat. As it turns out, he was correct: in 2003 Cambridge researcher Andy Fabian discovered that the satellite-borne Chandra X-ray Observatory spotted music-like ripples emanating from a black hole at the center of NGC 1275, a distant galaxy.

The researchers treated these gas ripples as musical sound waves and came up with some pretty wild observations. They calculated that the waves work out to “sound” a B-flat 57 octaves below middle C; for comparison, a standard piano range reaches to a little over 3 octaves below middle C. A keyboard purpose-built to play the black hole’s note would be over 45 feet wide. The wave had a frequency of about 10 million years, which is infinitely far below that perceived by human hearing. In September 2003 Nature magazine proclaimed it the “deepest-ever note.”

Here on Earth, the real deepest-sounding notes belong to the trusty pipe organ. Interestingly, organ builders have used two different methods for accomplishing low notes.

The simplest method is to build a really tall pipe, but this usually isn’t practical. The lowest organ pipe of any musical value would be around 64 feet tall, a dimension not possible in even the largest halls. There are only two true pipes of this size: one resides in the world’s largest pipe organ (and musical instrument) at Boardwalk Hall in Atlantic City, and the other in the Sydney Town Hall Grand Organ in Australia. The sound from these pipes is described as more felt than heard: their pitch resides around 8 Hz, and human hearing sensitivity cuts off around 20 Hz. As the videos below prove, the Atlantic City organ sounds like a rumble, and the Sydney one sounds like, well, flatulence.

The second method relies on the psychoacoustic phenomenon of resultant tones. When pure sine waves are sounded together, they produce two additional sounds whose frequencies are the sum and difference of the two originals. For example, combining two tones at 32 Hz and 48 Hz result in two additional tones of 80 Hz and 16 Hz. Organ builders in the late 18th century were aware of this phenomenon and realized they could use it to produce very low sounds without building massive, costly pipes. So, to get the same 8 Hz as the Boardwalk organ, a builder could simply sound two pipes—one 32’ in length and one 21 1/3’—to generate the desired pitch. One might imagine this effect to be jarring, but the pitches are usually so low that a listener only perceives the low note and doesn’t hear the two combined pitches that produced it (a good audio example is here).

Organs also take the prize for the highest instruments, but that’s a topic for the next blog.

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#1

Re: Black Hole Music and Really Low Notes

07/13/2017 4:55 AM

A "major blasket in the basey-profundole", then? [With apologies to the late Professor Stanley Unwin].

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#3
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Re: Black Hole Music and Really Low Notes

07/13/2017 1:37 PM

Presumably not the Sir Stanley Unwin who co-founded the publisher?

Those words are perfectly expressive! Love them!

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#7
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Re: Black Hole Music and Really Low Notes

07/14/2017 8:00 AM

No. This one.

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#8
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Re: Black Hole Music and Really Low Notes

07/14/2017 8:11 AM

Beware the Jabberwock, my friend!

Thanks for the link. Why have I never heard of Prof. Unwin until now!

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#2

Re: Black Hole Music and Really Low Notes

07/13/2017 7:00 AM

Q: What sound does a black hole make?

A: B Flat

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#4

Re: Black Hole Music and Really Low Notes

07/13/2017 1:41 PM

Dumb question of the day: when the organ builder uses the two-pipe solution, does the organist have to play one key or two?

Really interesting post. I'm going to bring it up tomorrow when I see the young woman who just got her acoustical engineering degree. She probably doesn't know about the black hole note.

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#5
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Re: Black Hole Music and Really Low Notes

07/13/2017 2:09 PM

Just one. The organist pulls the Resultant stop, which tells the instrument to sound the two pipes at once for each key. Compound stops are pretty common...some sound as many as seven or eight pipes for one key.

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#6

Re: Black Hole Music and Really Low Notes

07/13/2017 11:01 PM

"The wave had a frequency of about 10 million years, which is infinitely far below that perceived by human hearing."

Any audiophile worth his ego can easily hear it and not only that he would gladly spend at least $30K on a custom filter to out of any original 50+ year old vinyl record he was listening to.

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#9

Re: Black Hole Music and Really Low Notes

07/14/2017 4:52 PM

I would have imagined a black hole making a sound more like that thang standing on the corner of Hollywood and Vines, saying, "Come hither big fella, and I will make your world."

You don't get to hear her say "vanish" until you pay.

Sorry about the sleaze, I just could not resist.

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#10

Re: Black Hole Music and Really Low Notes

07/15/2017 9:15 AM

I wonder is this conclusive? Seeing how the very nature of a black hole is that nothing escapes not even light. The music like ripples may be coming from some other nearby as yet unknown object. I do find this interesting and the part sounding like a "fart" well I guess when a black hole gobbles up a nearby star the gas has to come out somewhere. As My mother used to say "more room on the outside then inside"

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#12
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Re: Black Hole Music and Really Low Notes

07/15/2017 10:11 AM

Spinning black holes do eject jets of matter along the axis of rotation.

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#11

Re: Black Hole Music and Really Low Notes

07/15/2017 10:06 AM

One interesting application of mixing two sound to produce a lower sound with a sound projector which transmits two ultrasonic sound signals together. Because of its short wavelength, an ultrasonic signal can be transmitted in a tight beam with a reasonable sized projector. Two ultrasonic signals are generated such that an audio signal can be heard when nonlinearities in the target generate the difference frequency. A private message can be sent to a person without anyone else hearing it. One application would be for museum displays.

https://en.m.wikipedia.org/wiki/Sound_from_ultrasound

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#16
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Re: Black Hole Music and Really Low Notes

07/17/2017 9:20 AM

I find that possibility fascinating! Does anyone here know what the nonlinear element is made of for breaking the beam down to sonic frequency? I did not bother to google that this morning.

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#13

Re: Black Hole Music and Really Low Notes

07/15/2017 11:03 AM

I don't follow the last bit. If two notes are played together you hear a chord. If the two notes are close together - as when the orchestra tunes to the oboe - you still hear both notes as well as the resultant (beat) note. Now the organ builder uses two short pipes to generate the subtraction resultant frequency. By definition the two frequencies are higher than the resultant, so they must be more audible. How are they suppressed?

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#18
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Re: Black Hole Music and Really Low Notes

07/17/2017 8:44 PM

If you work out the math, the sum of 32 hz and 48 hz sine waves is equivalent to the product of 8 hz and 40 hz sine waves.

sin α sin β = 1/2 [cos(α - β) - cos(α + β)]

Here, α = 40, β = 8, α - β = 32, and α + β = 48.

So you have a 8 hz sine wave modulating a 40 hz sine wave. Your ears cannot hear 8 hz as a continuous tone, but a series of pulses. Apparently, the modulated 40 hz wave generates the same sensation.

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#19
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Re: Black Hole Music and Really Low Notes

07/18/2017 5:57 AM

I'm consider myself informed by your maths. My grasp of the mixing of frequencies (coming from the generation of intermediate frequencies in a superhet receiver, as in this paper) has been that the components are strictly the addition/subtraction of frequencies. Never mind, the same principle applies. The 32Hz and the 48Hz tones by definition are of higher intensity than the interference generated. I expect to hear both 32 and 48Hz tomes as well as a strange sensation corresponding to the subtraction, and possibly the addition component as well.

I would have expected the situation where only the subtraction component was audible to arise only when both fundamentals are in the ultrasound range. Maybe the organ builders were devising high-powered ultrasonic pipes?

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#22
In reply to #19

Re: Black Hole Music and Really Low Notes

07/18/2017 9:09 AM

ultrasonic or infrasonic? There seems a bit of confusion in this thread about terms.

Aren't trigonometric identities wonderful?

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#23
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Re: Black Hole Music and Really Low Notes

07/18/2017 9:09 AM

I think that what you hear is 40 hz modulated by 8 hz. (I don't have my PC available, but in a few days I can attach a plot.) What you feel is your gut shaking every 1/8 second.

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#21
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Re: Black Hole Music and Really Low Notes

07/18/2017 9:08 AM

They're suppressed because organists are never supposed to play a resultant stop on its own. A competent organist would layer more stops at fundamental pitch (16' and 8') above the Resultant to "cover" the sound of 21 1/3' pipe.

Organs have a bunch of stops called "mutations" that sound pitches other than the fundamental. The most common one is a 2 2/3' stop, so if you pull that alone and play a middle C the sound you hear would be a G a 12th higher. So yes, if you use that stop with a fundamental stop you would technically play a chord with every note--theoretically it should sound terrible, but the mutation stops are voiced so using them actually makes the sound a little nasal and unsteady. (The 2 2/3' stop is actually called a "Nazard," which was corrupted from the French word for "nose.")

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#24
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Re: Black Hole Music and Really Low Notes

07/18/2017 9:33 AM

Thank you. I shall investigate our parish church organ, but I'm not sure that it "sinks that low".

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#14

Re: Black Hole Music and Really Low Notes

07/15/2017 11:07 AM

And how do you measure a frequency of 1 in 10 million years anyway?

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#15
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Re: Black Hole Music and Really Low Notes

07/15/2017 11:59 AM

They should have said "period of 10 million years".

I suspect they know the distance between ripples and the velocity of the jet. Dividing velocity by distance gives frequency and dividing distance by velocity is period. Determining the "musical note" requires about 6 percent accuracy in the frequency.

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#17
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Re: Black Hole Music and Really Low Notes

07/17/2017 9:21 AM

So if the dinosaurs heard the beginning of one of these tones (somehow), then we are about to hear the rest of the story?

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#20
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Re: Black Hole Music and Really Low Notes

07/18/2017 6:14 AM

Then the question becomes: how do you measure distance and velocity. The NASA image shows ripples from which one can calculate the distance, but it would take eons to observe the velocity. Conversely you can measure the velocity in the viewer'e direction from the red or blue shift, but then you cannot observe the distance. Can you assume that the ripples in this extraordinary system are uniform in all axes?

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#25
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Re: Black Hole Music and Really Low Notes

07/18/2017 8:53 PM

I should have said the sound propagation velocity, not jet velocity. Perhaps the sound velocity can be determined from the gas pressure, density and composition.

c = sqrt(γp/ρ) where p is pressure, ρ is density, and γ is the adiabatic index of the gas.

https://en.m.wikipedia.org/wiki/Speed_of_sound

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#26
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Re: Black Hole Music and Really Low Notes

07/19/2017 6:01 AM

My assumption was indeed that the streaks in the image corresponded to peaks in the pressure wave and that their movement represented the propagation velocity which it would take eons to measure. As for pressure, density and adiabatic index, how do you measure those at astronomical distances?

I now harbour the unworthy suspicion that some of these numbers are made up to attract public attention as a means of securing research funding. Perish the thought.

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#27
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Re: Black Hole Music and Really Low Notes

07/19/2017 9:25 AM

I am sure that this presents a non-issue to a qualified astrophysicist. They are better than magicians at pulling rabbis out of their black hats.

Silly rabbis, anyway, trying to hide in there.

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#28
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Re: Black Hole Music and Really Low Notes

07/19/2017 9:43 AM

As a practising Christian I must protest at the wanton cruelty involved in pulling rabbis out of their hats.

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#29
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Re: Black Hole Music and Really Low Notes

07/19/2017 9:51 AM

Yes, sir, I would be joining you in that line! Who wants to harm rabbis while making such films, anyway?

BTW - Breaking News, Fakey Quakey News (FQN) has confirmed from unreliable anonymous sources that in the OP of this thread, that is actually POTUS Donald J. Trump playing "Rite of Spring" on that organ - talk about Russian collision!

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#30
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Re: Black Hole Music and Really Low Notes

07/19/2017 8:39 PM

I would think it boils down to pressure and composition of the gases. Composition can be determined spectrographically. Then, given composition, you can find density and adiabatic index. Not sure how they could determine pressure...

If you know the speed of sound and the distance between pressure peaks, you can determine the period, the inverse of frequency.

Having said that, I'm thinking your suspicion might be "spot on". :)

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