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# The lowest note: that of a black hole

The lowest note ever measured would be the "B flat^{-54}" of a supermassive black hole located at the center of the Perseus galaxy cluster. That is 54 octaves below octave 0, or 57 octaves below the middle C octave (C^{3}).

## Basic Concepts

Sound is the audible vibration of matter around a source. A drum vibrates, causing the air around it to vibrate, allowing our ears to capture its vibrations. Matter can be air, water, metal, or anything else...

The human ear can only hear from 20 to 20,000 vibrations per second (from 20 to 20,000 "Hz", for "Hertz").

## Musical Notions

The reference note "A" (the one from the phone in France) is 440 vibrations per second (440 Hz). It is the note "A^{3}", of the third octave, that of the middle "C" (C^{3}).

If we divide this number by two, we get the lower (graver) "A" of the lower octave, and so on. If we double this number, it is the higher (sharper) "A" of the higher octave, and so on.

The lowest audible "A" note for humans is therefore the "A at octave -1", which is 27.5 Hz. Since the previous "A", the "A^{-2}", would be 13.75 Hz (inaudible for humans, as it is below 20 Hz).

## And this black hole then?

In space, there is no matter to vibrate, at least not enough to transmit sound. But there are objects that vibrate. This is the case of the supermassive black hole located at the center of the Perseus galaxy cluster.

This black hole does not vibrate at 440Hz like our "A^{3}", nor at 466.1 Hz like a "B flat^{3}". Not even at 233.1 Hz like a "B flat^{2}"... No, it generates the equivalent of one oscillation every 9.8 million years, which is 0.000000000000003234 Hz, the frequency of a "B flat^{-54}"!

## Sonification

Since "sonification" of data is in vogue, researchers have multiplied all their figures by 2^57 (x2^{57}), to obtain a sound audible to the human ear.

Here, to illustrate these points, is the sound this black hole would make:

https://www.youtube.com/embed/ioR5np1fmEc
What do you think?

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08/02/2024