The universe, with its countless stars and galaxies and nebulae, can be visually stunning, especially when we use high-powered telescopes to peer beyond the range of human vision. But what if we could hear those objects as well? That may sound counterintuitive at first—how can sound travel through the vacuum of space? Isn’t the universe silent? Far from it, says Kim Arcand, an expert on data visualization at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. Her team has found ways to amplify and manipulate distant sound waves that would otherwise be undetectable by human ears. They’ve also employed creative processing—taking visual data from optical, infrared and X-ray telescopes and assigning notes to that data—to render celestial phenomena via sounds. These “sonifications” provide a new way for people to experience those awe-inspiring objects.
Arcand, working with colleagues at the Smithsonian, Harvard University and NASA, together with a Canadian science outreach team called SYSTEM Sounds, has been making these custom-made audio tracks that bring celestial images to life. Many of the tracks can be heard on YouTube, paired up with the images that inspired them. Now, 16 of those sonifications and amplifications have been assembled into an album called Universal Harmonies, which will be available on CD, vinyl and streaming platforms beginning March 10.
Aside from bringing science to a wider audience, Arcand also believes that sonification can bolster the science itself by allowing more people to contribute to our understanding of the universe. One of her goals, she says, is to show that “people who are blind or low-vision … can also become part of the scientific enterprise.”
For University of Toronto astrophysicist Matt Russo, who runs SYSTEM Sounds together with musician Andrew Santaguida, sonification has been a chance to bring together his two great passions—astronomy and music. Russo studied jazz guitar as an undergraduate at the University of Toronto before switching to astronomy. “I was interested in rock, blues, Hendrix-type stuff,” he says. At SYSTEM Sounds, he says his mission “is simply to explore the universe through sound. That means converting any kind of astronomical data so that it can be experienced auditorily.”
That conversion can take a number of different directions. An obvious match-up is to pair brighter parts of an image with louder sounds or to render longer wavelengths of light (the red end of the spectrum) as lower-pitched sounds, and shorter wavelengths of light (the blue end of the spectrum) as higher-pitched sounds. But that’s just the beginning: An image is two-dimensional but has no time dimension, whereas music is all about time—so the element of time has to be inserted by some means. A straightforward way is to scan from left to right across an image; moving across a 1,200-pixel-wide image at 40 pixels per second, for example, yields a 30-second track to be filled with sound determined by the pattern of light.
It’s both an art and a science, and Russo was instantly drawn to the challenge. “It was just instantly obvious that it was fun and rewarding,” he says. “I got to combine all of my passions at once. And people really connected with it.”
Here are three highlights from Universal Harmonies, each of them bringing to life one facet of our dynamic cosmos.
“Galactic Center, in Multiwavelength Light”
If you’ve ever gazed up on a clear summer night, far from city lights, you’ll have seen the Milky Way—our own galaxy, viewed from within—arcing across the sky. You may have also noticed that a clumpy section near the constellation Sagittarius is noticeably thicker than the rest. That’s the heart of our galaxy, some 26,000 light-years from Earth. As beautiful as that star-strewn vista is to the naked eye, it takes on a whole new look when viewed with the various telescopes in the astronomers’ toolkit.
The sonification created for Universal Harmonies is based on data from three different telescopes: X-ray data from the Chandra X-Ray Observatory, optical data from the Hubble Space Telescope and infrared data from the Spitzer Space Telescope. Each telescope is assigned its own musical instrument: glockenspiel for Chandra, strings for Hubble and piano for Spitzer. In this case, the image is scanned left to right, with the vertical position controlling the pitch—a light source near the top of the image is presented at a higher pitch, and a source near the bottom becomes lower-pitched. Meanwhile, the volume of each note is proportional to the brightness of the particular section of the image.
For Arcand, the galactic center is analogous to a city’s urban core. “It’s like if you’re in the middle of Times Square,” she says. “There’s a lot of hustle and bustle.” Nonetheless, the resulting piece comes off sounding almost melodic, thanks to the interplay between the instruments. For Russo, the collage of sounds offers a new way to “see” the hubbub at the heart of our galaxy. “You can hear the different structures and textures that are present when you use different wavelengths of light to view the universe,” he says.
“Chandra Deep Field South, in X-Ray Light”
You may have seen the Hubble Deep Field, a galaxy-rich mosaic of photographs obtained with the Hubble Space Telescope back in 1995. But there’s more to the universe than visible light, and five years later, the Chandra X-Ray Observatory also peered into the depths of space, this time seeking out galaxies that emit X-rays. “It’s the deepest X-ray image ever taken,” notes Arcand. The reason that so many galaxies emit X-rays, she explains, is that they harbor supermassive black holes in their centers. Nothing escapes from inside a black hole, but just outside, there’s a frenzy of activity: As matter falls in, it gets heated up to temperatures in the millions of degrees, at which point it emits copious amounts of X-ray radiation.
In this sonification, lower-pitch tones correspond to less energetic X-rays, and higher-pitch sounds correspond to more energetic X-rays. Arcand explains that an earlier version of this sonification had a tempo on par with the other tracks. “But we heard feedback from people, particularly people in the blind and low-vision community, who wanted it slowed down so as to be able to spend a little bit more time with the data as it goes by.” The wavelengths of the X-ray radiation span about five octaves, Russo says—a difference that, even if rendered in visible light, would be hard for the human eye to distinguish. But our ears can do much better. “By mapping it to sound, we can actually hear that full range, because our ears are sensitive to many, many octaves of audio frequencies,” he says.
“Perseus Cluster, in X-Ray Light”
The Perseus cluster of galaxies is enormous, spanning almost a dozen light-years, and enormously far away, sitting some 240 million light-years from Earth. At its center is a galaxy harboring a supermassive black hole. As with the black holes in the Chandra Deep Field, the real action happens just outside, where gas and dust are heated up to 180 million degrees Fahrenheit—hot enough to emit X-rays. The region is so energetic that it pushes on the surrounding material, creating pressure waves—in other words, sound waves. These waves have a frequency some 57 octaves too low for humans to hear, but the musically-savvy scientists were able to raise the pitch into the realm of human hearing.
“This is definitely my favorite,” says Russo. Listening in real time, he explains, would take a while, with the interval between successive wave crests on the order of 10 million years. The solution? Speed it up—which reduces the galaxy’s “song” to a listenable length.
The sonification, which went viral when NASA tweeted it last year, provoked strong reactions. “I was happily overwhelmed by the response to it,” Arcand says. “Some people thought it sounded like a horror movie soundtrack, like something Hans Zimmer would put over a scary scene.”
Editors' Note, March 2, 2023: This article has been updated to remove erroneous information about when Arcand began working on sonifications with SYSTEM Sounds.