Put into music, telescope observations of the center of the Milky Way create a tranquil tune, glittering with xylophone and piano notes. The iconic Pillars of Creation in the Eagle Nebula, meanwhile, sound like an eerie sci-fi score. And the supernova remnant Cassiopeia A is a sweeping symphony.
These musical renditions, or sonifications, were released on September 22 by NASA’s Chandra X-ray Center. “Listening to the data gives [people] another dimension to experience the universe,” says Matt Russo, an astrophysicist and musician at the astronomy outreach project SYSTEM Sounds in Toronto.
Sonification can make cosmic wonders more accessible to people with blindness or visual impairments, and complement images for sighted learners. SYSTEM Sounds teamed up with Kimberly Arcand, a visualization scientist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., to create the new pieces.
Christine Malec, a musician and astronomy enthusiast who is blind, vividly recalls the first sonification she ever heard — a rendering of the TRAPPIST-1 planetary system that Russo played during a planetarium show in Toronto (SN: 2/22/17). “I had goosebumps, because I felt like I was getting a faint impression of what it’s like to perceive the night sky, or a cosmological phenomenon,” she says. Music affords data “a spatial quality that astronomical phenomena have, but that words can’t quite convey.”
The new renditions combine data from multiple telescopes tuned to different types of light. The sonification of an image of the Milky Way’s center, for instance, includes observations from the Chandra X-ray Observatory, optical images from the Hubble Space Telescope and infrared observations from the Spitzer Space Telescope. Users can listen to data from each telescope alone or the trio in harmony.
As a cursor pans from left to right across the image of the galactic center, showing a 400-light-year expanse, Chandra X-ray observations, played on the xylophone, trace filaments of superhot gas. Hubble observations on the violin highlight pockets of star formation, and Spitzer’s piano notes illuminate infrared clouds of gas and dust. Light sources near the top of the image play at higher pitches, and brighter objects play louder. The song crescendos around a luminous region in the lower-right corner of the image, where glowing gas and dust shroud the galaxy’s supermassive black hole.
Layering the instruments on top of each other gives the observations an element of texture, Malec says. “It appealed to my musical sense, because it was done in a harmonious way — it was not discordant.”
That was on purpose. “We wanted to create an output that was not just scientifically accurate, but also hopefully nice to listen to,” Arcand says. “It was a matter of making sure that the instruments played together in symphony.”
But discordant sounds can also can be educational, Malec says. She points to the new sonification of supernova remnant Cassiopeia A: The sonification traces chemical elements throughout this great plume of celestial debris using notes played on stringed instruments (SN: 2/19/14). Those notes make a pretty harmony, but they can be difficult to tell apart, Malec says. “I would have picked very different instruments” to make it easier for the ear to follow — perhaps a violin paired with a trumpet or an organ.
While sonification is a valuable tool to get the public interested in astronomy, it also has untapped potential to help professional astronomers analyze data, says Wanda Díaz-Merced, an astronomer who is also at the Harvard-Smithsonian Center for Astrophysics but was not involved in the project (SN: 10/22/14).
Astronomers including Díaz-Merced, who is blind, have used sonifications to study stars, solar wind and cosmic rays. And in experiments, Díaz-Merced has demonstrated that sighted astronomers can better pick out signals in datasets by analyzing audio and visual information together rather than relying on vision alone.
Still, efforts to sonify astronomy datasets for research have been rare. Making data sonification a mainstream research method would not only break down barriers to pursuing astronomy research, but may also lead to many new discoveries, she says.