Do all black holes produce sound?
October 24, 2022 5:34 PM Subscribe
There is a supermassive black hole that rings a very low B-flat. As I understand it, the surrounding gas is affected by pressure waves from the black hole in such a way that they can be translated into sound (or could be theoretically heard, if you were in the surrounding gas). Is this a special case, or would all black holes surrounded by appreciable amounts of gas make a sound?
Additionally: Is there any way to calculate what note a given black hole would sound, given its size? Are other factors involved, like rotation?
Additionally: Is there any way to calculate what note a given black hole would sound, given its size? Are other factors involved, like rotation?
Best answer: Sound waves are compression waves in a medium (gas,liquid,solid,plasma). Any compression wave can be regarded as a "sound" wave effectively.
The article states that the sound that the black hole is making is 57 octaves below middle C. Middle-C is 262 Hz, or 262 oscillations per second. With a sound that is 57 octaves below the oscillations per second will be much much lower - there's some maths here but I'm not entirely clear this actually works with notes / frequencies way beyond a standard piano / human hearing (I punched the numbers in and it gave me one oscillation every 33 years, so not sure this is right).
Do the tides on earth make a sound? Twice a day the water will rise and fall, compressing the atmosphere meaning there's a compression wave being generated there. Is this a sound? Only if "compression wave" == "sound" here. It's certainly not audible and has a frequency of approximately 0.0002Hz, a long long way from middle-C.
> Is there any way to calculate what note a given black hole would sound, given its size?
No, because the "sound" that's generated by this black hole is likely to be clumps of gas/plasma in slightly different orbits smashing into each other periodically - it'll be more to do with the rate that these clumps of matter are orbiting the black hole rather than a particular property like angular momentum of that particular black hole.
posted by BigCalm at 1:52 AM on October 26, 2022 [1 favorite]
The article states that the sound that the black hole is making is 57 octaves below middle C. Middle-C is 262 Hz, or 262 oscillations per second. With a sound that is 57 octaves below the oscillations per second will be much much lower - there's some maths here but I'm not entirely clear this actually works with notes / frequencies way beyond a standard piano / human hearing (I punched the numbers in and it gave me one oscillation every 33 years, so not sure this is right).
Do the tides on earth make a sound? Twice a day the water will rise and fall, compressing the atmosphere meaning there's a compression wave being generated there. Is this a sound? Only if "compression wave" == "sound" here. It's certainly not audible and has a frequency of approximately 0.0002Hz, a long long way from middle-C.
> Is there any way to calculate what note a given black hole would sound, given its size?
No, because the "sound" that's generated by this black hole is likely to be clumps of gas/plasma in slightly different orbits smashing into each other periodically - it'll be more to do with the rate that these clumps of matter are orbiting the black hole rather than a particular property like angular momentum of that particular black hole.
posted by BigCalm at 1:52 AM on October 26, 2022 [1 favorite]
Response by poster: No, because the "sound" that's generated by this black hole is likely to be clumps of gas/plasma in slightly different orbits smashing into each other periodically - it'll be more to do with the rate that these clumps of matter are orbiting the black hole rather than a particular property like angular momentum of that particular black hole.
Searching further on this point seems to have answered my question: The Perseus black hole is unusual in the clumps of gas surrounding it, and there's no easy way to generalize this to other black holes.
(I punched the numbers in and it gave me one oscillation every 33 years, so not sure this is right).
Another source I can't find now suggested the waves were caused from black hole jets switching on and off over a timescale of tens of thousands of years. So 33 years sounds reasonable.
posted by solarion at 4:14 PM on October 26, 2022
Searching further on this point seems to have answered my question: The Perseus black hole is unusual in the clumps of gas surrounding it, and there's no easy way to generalize this to other black holes.
(I punched the numbers in and it gave me one oscillation every 33 years, so not sure this is right).
Another source I can't find now suggested the waves were caused from black hole jets switching on and off over a timescale of tens of thousands of years. So 33 years sounds reasonable.
posted by solarion at 4:14 PM on October 26, 2022
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But the kind of sound depends on the gas densities and circumstances. Here's another more recent example of sound being extracted from black hole observations. In that case the sound is far outside of the range of human hearing, but they've transposed it up.
Many celestial objects make noise. Our sun would be deafeningly loud if there were air in space to transmit its sound to Earth.
Black holes can also ring like a bell when they merge. And that "ringing" doesn't need gas to propagate. It spreads through the universe in the form of gravitation waves, which we can observe.
The gravitational waves aren't audible, but they do happen at audible frequencies and you can listen to an example from LIGO.
posted by mcbaya at 5:43 AM on October 25, 2022 [4 favorites]