Sophie Kastner is a musical composer who translated the unlistenable into song, turning nuanced data emanating from the heart of our Milky Way into the notes of a dissonant symphony.
"It's like writing a fictional story that is largely based on real facts," she said in a statement.
Her piece, "Where Parallel Lines Converge," draws from one specific portrait of our home galaxy's central region, aptly known as the Galactic Center. Physically viewing this image can be a little disorienting. It's captured in a variety of light wavelengths — X-ray, infrared and optical — by several powerful deep space imagers — NASA's Chandra, Hubble and Spitzer telescopes. As such, there are tons of random swirls and streaks representing stunning entities in the area, like bright bubbles of gas and luminous star explosions, thick hyphens of dust and glowing stellar nurseries.
So rather than try and make sonic sense of this 2009 composite image in its entirety, Kastner decided to focus on three key elements. The first is a double star system revealed in X-ray wavelengths, indicated with a bright blue orb at the left of the image; the second is the group of arched filaments we see; and the third is the grandest of them all: The supermassive black hole Sagittarius A* that lurks at the heart of our Milky Way. "I wanted to draw the listener's attention to smaller events within the greater data set," Kastner said in an overview of the composition.
But let me back up a little. You might be wondering: What does this translation actually mean? How can telescopic data be turned into the universe's own soundtrack? Well, as the saying goes, "In space, no one can hear you scream."
Someone can, however, watch and interpret your scream.
Related: James Webb Space Telescope could soon solve mysteries of the Milky Way's heart
In a sense, sound waves can be thought of as vibrations propagating through atoms and molecules floating in the air. On Earth, there are lots of different things in our air — the waves associated with a knock on your door, for instance, can travel through your house's air to your ears. But in space, there is no "air." It's a vacuum.
If you screamed in space, the sound waves you'd create wouldn't have anything to vibrate, really, so someone standing a few meters away from you wouldn't hear you. Even if the Galactic Center were filled with incredible noises, we wouldn't be able to hear them unless there were enough surrounding atoms for those sound waves to propagate through. And more often than not when it comes to space objects, there aren't enough atoms.
The "sonification project" at NASA's Chandra X-ray center is an organization dedicated to getting around this hurdle, aiming to introduce another human sense to space exploration.
Much as scientists take X-ray telescope data, captured in wavelengths unseeable by human eyes, and translate it into visible forms we can admire, the sonification project takes such data and turns it into sounds we can listen to. Already, the organization has done this with a solid amount of space marvels like the supernova remnant Cassiopeia A, a gaggle of galaxies known as Stephan's Quintet and the Carina Nebula as seen by the trailblazing James Webb Space Telescope.
Sonification efforts like these are particularly lauded by the scientific community because "listening" to a deep space image can allow visually impaired space enthusiasts to establish a deeper connection to what lies in the faraway reaches of space.
To be clear, none of the songs associated with those aforementioned images are made with sounds literally recorded in space. They're audio interpretations of data, just like the JWST's images are optical interpretations of infrared signals.
"In some ways, this is just another way for humans to interact with the night sky just as they have throughout recorded history," Kimberly Arcand, Chandra visualization and emerging technology scientist, said in the statement. "We are using different tools, but the concept of being inspired by the heavens to make art remains the same."
Such interpretation is precisely what Kastner did with her new composition, truly converging the parallel lines of science and song — and the sheet music for the piece is actually available online for anyone to take a stab at.
"I like to think of it as creating short vignettes of the data, and approaching it almost as if I was writing a film score for the image," Kastner said. "I wanted to draw listeners' attention to smaller events in the greater data set."
As to what exactly we're hearing, Kastner's song is divided into three parts "played" from left to right. "The light of objects located towards the top of the image are heard as higher pitches, while the intensity of the light controls the volume," the sonification team says. "Stars and compact sources are converted to individual notes, while extended clouds of gas and dust produce an evolving drone."
The crescendo of the song happens when the composition hits the bright region to the lower right of the image. This is where Sgr A* resides, and where clouds of gas and dust shine the brightest.
"I approached the form from a different perspective than the original sonifications: Rather than scanning the image horizontally and treating the x-axis as time, I instead focused on small sections of the image creating short vignettes corresponding with these occurrences, approaching the piece as if I was writing a film score to accompany the image," Kastner said. A more detailed outline of the composer's notes can be found here.
This isn't to say, however, that scientists have never tried to enhance literal waves captured in space. Remember how the general lack of air in space means there's not much for sound waves to vibrate thorough? Well, sometimes, there are things that can propagate those vibrations.
Last year, for instance, scientists determined that a black hole in the Perseus cluster was surrounded with enough gas that pressure waves sent out from the void created a signature detectable by our instruments.
"A galaxy cluster … has copious amounts of gas that envelop the hundreds or even thousands of galaxies within it, providing a medium for the sound waves to travel," NASA scientists had said.
The resultant ripples were translated into an actual musical note, but the note was unfortunately 57 octaves below middle C. That's way too low for the human ear to perceive. So, the team resynthesized the signals to the range of human hearing, 57 and 58 octaves higher. That's 144 quadrillion and 288 quadrillion times higher than their original frequency.
It sounded exactly like you'd expect a black hole to sound.
