No one can hear any sound in space but that really does not means that there aren’t any. Astronomers detected something truly astonishing in 2003. Acoustic waves propagate through the gas surrounding a supermassive black hole, 250 million light-years away.
Nobody can hear them at their current pitch. Emanating from the supermassive black hole at the center of the Perseus cluster of galaxies, the waves include the lowest note in the Universe ever detected by humans – well below the limits of human hearing.
A new sonification (data turned into sound) however, has not only added to the notes detected from the black hole but brought them up 57 and 58 octaves so we can get a sense of what they would sound like, ringing through intergalactic space.
It’s the first time these sound waves have been extracted and made audible.
The lowest note, the one identified back in 2003, is a B-flat, just over 57 octaves below middle C; at that pitch, its frequency is 10 million years. The lowest note detectable by humans has a frequency of one-twentieth of a second.
The sound waves were extracted radially, or outwards from the supermassive black hole at the center of the Perseus cluster, and played in an anticlockwise direction from the center so that we can hear the sounds in all directions from the supermassive black hole at pitches 144 quadrillions and 288 quadrillion times higher than their original frequency.
The result is an eerie one, a sort of unearthly (obviously) howling, like many of the waves recorded from space and transposed into audio frequencies.
The sounds aren’t just a scientific curiosity, though. The tenuous gas and plasma that drifts between the galaxies in galaxy clusters – known as the intracluster medium – is denser and much, much hotter than the intergalactic medium outside galaxy clusters.
Sound waves propagating through the intracluster medium is one mechanism whereby the intracluster medium can be heated, as they transport energy through the plasma.