Rocking to the Sounds of Pulsar Beats
Music is a core component of humanity’s culture and experience, but it’s always been terrestrial-based. Now, scientists are transforming their astronomical data and teaming up with musicians and sound engineers to capture light from the sky and turn this music for our ears.
Music has been a part of humanity’s culture, experience, and storytelling for, well, tens of thousands of years if we are to look at the evidence of some of the first instruments. Song and dance, as a form of communication, ritual and ecstatic release of emotion are likely to go back much further.
For all its glory (and it is glorious), music has been a terrestrial-based activity, as sound requires air to travel, and there is not much of the stuff the further we go into space. But that doesn’t mean the cosmos doesn’t give us music - in fact, there is music coming from all over the sky at this very moment - we just need to know how to observe it, and turn it into the familiar audio sounds that we are used to.
Enter stage right pulsars.
One of nature’s most remarkable objects is the ticking clocks of the cosmos that sound like they are out of a science fiction movie. Discovered in 1967 by (then PhD student) Dame Professor Jocelyn Bell Burnell, these exotic objects are no bigger than a small town (about 20 kilometres in diameter) yet pack in about 1.4 times the mass of the Sun into them. This makes them incredibly dense - a single teaspoon would weigh as much as all of humanity combined.
They’ve also got these ultra-strong magnetic fields, and spin rapidly - properties that are vital to them generating beams of electromagnetic radiation that beam away from their magnetic poles, like giant lighthouses in space. Except, instead of the visible light we see with our eyes, these beams are of radio waves - similar to what comes through on your Wi-Fi.
Many of the pulsars that we know of (and there are about 3,300 so far) were discovered here in Australia, by CSIRO’s Parkes radio telescope, Murriyang (it’s Wiradjuri name, which means ‘Skyworld’). Astronomers use pulsars to probe some of the most extreme scenarios - which we could never re-create here on Earth - to answer questions about how matter behaves under such strong densities, test Einstein’s theories of relativity, and look for gravitational waves.
When pulses arrive at Earth (as radio waves) we use large radio telescopes to detect them. But the signal coming in is still electromagnetic radiation (similar to the light coming out of our light bulb, but at lower frequencies) and not sound (the stuff that we hear: your favourite song, birds chirping, the neighbour's relentless barking dog, etc.).
So how do we get from electromagnetic light (radio waves) to music?
Data from space (which is mostly in the form of light, but can also include gravitational waves, neutrinos and cosmic rays), can be converted into sound. This process is known as sonification - where the electromagnetic signals are attributed to different sounds. This has some benefits around accessibility, it opens up the possibility for people with vision impairment to also enjoy and participate in exploring astronomical data through sound. Humans also seem to have a better-tuned connection between their ears and brain, as opposed to their eyes and brain - e.g., our eyes are directional-based tools, whereas our ears can hear sounds isotropically.
So why pulsars then, as opposed to the weird squeals of the Sun, or the pitter-patter of micrometeorites that bombard the Lunar surface?
Well, pulsars rotate at a very regular period and are very stable. When converted to sound, they can act as a sort of backing beat to be used in music and tracks. With the wide variety of pulsars, each with its own spin period, and thus, its own beat, musicians and scientists can work together to get the music flowing. The beat of a pulsar is so steady that you can use it to keep an orchestra in time. Or maybe use it as the base of a house track, played by one of the world’s leading DJs at a 20,000-strong crowd festival. French composer Gerard Grisey included a pulsar as one of the percussionists in the piece, 'Le Noir de l’Étoile'.
For example, PSR J1056-6258 has a 142 beats-per-minute (BPM) spin period, so it would be perfectly suited to go well with Kylie Minogue’s ‘Padam Padam’, Britney Spears ‘Toxic’, Blondie’s ‘Call Me’ and Mumford & Sons ‘The Cave’. This pulsar was discovered in the 1970s by another famous Australian telescope - the University of Sydney’s Molongolo telescope, which is located just outside Canberra.
Another Molongolo discovery is PSR J1752-2806, which would work well with Elive Presley’s ‘Farther Along’, with its slowish 33 BPM. Unlike the intense PSR J1559-4438, with a BPM of 233 making it more suitable for Metallica’s ‘Killing Time’.
Other pulsars spin so fast that their BPM is in thousands and tens of thousands - these are known as Millisecond Pulsars and they spin hundreds of times on their axis. These have also been sonified, but their rapid rotation produces a high-pitch constant sound, which my dog didn’t seem to like too much.
Sonification of astronomical data is ongoing, and with accessibility as a driver, it is likely to get bigger over time. The logical next step is for musicians, sound engineers, and astronomers to work together to find pulsars that can be used as backing tracks for a variety of music genres.
Better get those dance shoes on for these extraordinary astronomical objects. Padam. Padam.
Listen to the pulsars here:
This article is an expansion from ‘Rock Stars – Music from the Cosmos’ by Australia’s national science agency, CSIRO and has been shared with permission.