Listen to the Center of the Milky Way Translated Into Sound

The cosmos have long been an inspiration for artists on Earth. In the early 20th century, Gustav Holst composed his suite The Planets, in which each movement is named after a planet in the solar system and based on its astrological character. John Cage wrote Atlas Eclipticalis in the 1960s by superimposing musical staffs onto star charts. Frank Sinatra asked in song to be flown to the moon.

Now, a collaboration between a NASA sonification project and composer Sophie Kastner has turned astronomical data collected by telescopes into music that can be played by a small ensemble.

Two years ago, Kimberly Arcand, an expert in astronomy visualization at the Center for Astrophysics, Harvard & Smithsonian, and her collaborators translated the information contained in a composite image of the center of the Milky Way galaxy into sound. Kastner’s new composition, a piece of music titled Where Parallel Lines Converge, expands on the original project and tells a story based on the telescope data.

“The first time I heard it, I kind of got chills,” Arcand says to Smithsonian magazine. “It translated how I feel about these data sometimes that I can’t always communicate through words or through images.”

Typically, astronomical data is represented visually, in colorful depictions of starry skies. But creating these images often requires some degree of translation—telescope data is not always inherently visual. For example, NASA’s Chandra X-Ray Observatory, which Arcand works with, aptly captures X-rays, which can’t be seen by the human eye.

“It dawned on me quite a few years back that that was prioritizing a visual when it wasn’t necessarily always the best case or the only case that that should be created,” Arcand says. “Why couldn’t we use some other sense to be able to explore this data, particularly for people who are blind or low vision?”

At first, Arcand and her colleagues did this in a tactile way—they developed 3D-printed models and Lego builds to represent telescope data. But the Covid-19 pandemic disrupted this work, forcing their efforts to go digital. Arcand joined up with astrophysicist and musician Matt Russo and musician and sound engineer Andrew Santaguida of System Sounds, a science and art outreach project. Together, they started to “sonify” NASA’s data.

Translating telescope data into sound

Since 2020, the team has translated a number of astronomical images into sounds, called sonifications, that you can listen to. Each one—from the Pillars of Creation to the Carina Nebula—tells a scientific story that a person can follow just by listening. The translation process involves computers that use algorithms to map telescope data as noises.

One image, for example, depicts the center of our own galaxy, the Milky Way. It’s a combination of data from Chandra, the Hubble Space Telescope and the Spitzer Space Telescope. The sonification takes the listener from the left to the right of the image, with higher-pitched sounds representing light in the top region and lower-pitched sounds representing the bottom. The brightness of the light determines the volume of the sound, and each telescope’s data is played by a different set of instruments.

Plucked strings represent individual bright sources from Hubble’s optical imaging. Spitzer’s infrared swirls of dust and gas clouds are portrayed by a piano. The sound swells near Sagittarius A*, the black hole at the galaxy’s center, seen in the lower right region of the image.

Data Sonification: Galactic Center (Multiwavelength)

Watch on

Arcand says that when she gave talks about the sonifications, musicians would ask her if they could play the pieces. That idea led to the recent collaboration with composer Kastner to create a playable representation of the data.

“As an artist and a musician, I was fascinated by the idea of taking something that’s scientific and turning it into art or music,” Kastner tells Smithsonian magazine. “Those two things aren’t as far removed as one might think.”

Sounds of the Milky Way’s center

The resulting piece, Where Parallel Lines Converge, is a composition for a small ensemble of strings, woodwinds, percussion and piano. Kastner used the original sonification of the center of the Milky Way as inspiration for which types of sound to include, and she similarly featured piano and glockenspiel with the occasional plucked string.

Kastner also based her composition on the same image of the Milky Way’s center. She says she often begins with a text when writing music, and she found starting with an image to be a similar storytelling process.

Instead of moving from left to right, Kastner wove together the story in her composition by zooming in on three sections of the image and writing a minute-long vignette about each part. She compares the process to writing a film score accompanying the data.

Sounds of Space: Where Parallel Lines Converge, performed by Ensemble Éclat

Watch on

The piece opens with the galaxy’s X-ray binary—a pair of stars, one regular and one a neutron star that has exploded in a supernova, orbiting each other and emitting large amounts of X-ray radiation. Kastner says she noticed a lot of empty space around the binary, and the music starts with soft, wind-like noise created by a cello, violin and snare drum. The low registers of the bass clarinet and cello then evoke clouds of infrared light. Percussive sounds represent dim stars. The pitches climb higher and grow purer as the music takes the listener closer to the binary system.

In the second section, wispy, breathy strings come in, representing more diffuse structures called arched filaments. The other instruments, meanwhile, chime in as surrounding stars. In the final stage, interweaving, fast-moving phrases send the listener spiraling toward the supermassive black hole as chords crescendo beneath.

Throughout the piece, Kastner maps different types of data to different musical textures and registers. X-ray data is represented with high-register, pure and bright sounds, mid-register sounds portray optical information and the infrared data is translated into lower, darker tones. Foggy, cloud-like structures are recreated using more sustained notes, while stars translate to a sharper staccato. Like the original sonification, the music’s volume corresponds to brightness in the image.

Kastner also experimented with textures in the music. The violin and cello not only use their bows and pluck their strings—they even draw their bows while dampening the strings to create more nebulous sounds. The pianist sometimes reaches inside the instrument to pluck its strings, instead of pressing the keys. These diverse tones can convey “the feeling behind the note,” Kastner says.

Montreal-based Ensemble Éclat recorded the piece at McGill University in Canada in July, with the Analysis, Creation and Teaching of Orchestration Project providing the space to record and the recording equipment. The composition’s title, Where Parallel Lines Converge, is inspired by a verse in the poem “Relativity” by Sarah Howe, and Kastner feels like it evokes the idea of spiraling into a center.

Beyond focusing on different parts of the heart of the Milky Way, Kastner tried to represent “vastness, or a sense of endlessness.”

“I wanted to convey … feeling small in comparison to something so huge,” she says.

Kastner hopes to expand the piece into a longer version in the future or write other short pieces for different images, as Arcand’s team continues to work on communicating scientific information acoustically.

“I think sound is a valid way of making meaning,” Arcand says.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.