The old adage, courtesy of Ridley Scott, is that in space nobody can hear you scream. But in reality, what you can or cannot hear in space is all a matter of technology.
Sound is a mechanical wave: To propagate it requires a material and it cannot spread through a vacuum. And while space is very empty, it is not exactly a vacuum. The universe is filled with particles. Yes, there are huge swathes of space with less than half a proton per cubic meter, but planetary systems and nebulae are denser and they do transmit sounds.
Those sounds are not audible within the limited range of the human ear, but they can be measured and converted into something we can all listen to.
Among the famous (and somewhat terrifying) sounds of space, a spot of honor belongs to the Voyager recording of interstellar plasma waves. The recording is 12 seconds long and incredibly significant. We have sent a man-made object, the Voyager 2, so far away from our planet that it is now capable of detecting waves of particles in interstellar space.
Mechanical waves play an important role in star formation. The collapse of gas into a star depends on the speed of sound. And even the beautiful structures seen in supernova remnants have a sound connection. The material the star ejects moves at supersonic speeds and slams into the interstellar medium, heating it up to millions of degrees, eventually forming spectacles like the Crab Nebula.
Scientists also enjoy making audible what’s not normally in that form. Radio waves are a good example of this. Scientists take the frequency of the radio signal (from 300 GHz to 3kHz) and convert them into sounds (with shifted frequency, 20 kHz to 20 Hz). So, although radio waves are just a type of light, it’s more effective to hear them as sound than to see a radio map of a source. You can listen to the sound of radio communication on Earth, to the lightning on Jupiter, and even the radio emission of Saturn.
But it’s not just radio waves. Any kind of wave can be converted into sound. Physicists have even turned the signal of gravitational waves detected last year into a nice chirp. And the sounds are not just used for science – these cosmic noises are even used for art. Queen Mary University is currently running a short-film competition on space sounds.
Sometimes it’s for fun and other times because it's useful. We rely heavily on our hearing, and thanks to millennia of music, we are good with tunes and patterns. By listening, we might pick up on something not easily seen in the data. And with the right tech, we can listen to the music of spacetime itself.