Ah, the sounds of late summer. Pass a pool, and hear the happy yelps of kids splashing around. Sit outside at night, and bask in the soothing buzz of cicadas hidden in the trees. You can hear outer space’s terrifying howling through the internet.
Thank NASA for that last one. The space agency recently shared a clip online of sound coming from a cluster of galaxies about 250 million light-years from Earth. The space agency is always keen to showcase its ability to create cosmic wonders. shared a clip online of sound coming from a cluster of galaxies located about 250 million light-years from Earth.
The noise sounds like a ghostly wail, or the horror-movie music just before a jump scare, or, as several people have pointed out, the cries of untold souls trapped in eternal darkness. It’s just nothing; it is more terrifying than it sounds. Does space really sound this scary?
The answer is, sort of. And there is a perfectly horror-free explanation for it. Some parts of space are full of hot gas, including the medium between the distant, sparkly galaxies huddled together. In 2002, when a NASA space telescope named Chandra studied the Perseus cluster, it detected wavelike movements in the gas, propagating outward like ripples in water. Scientists determined that the ripples were caused by the central supermassive dark hole of the cluster. When the black hole sucks in cosmic material, it burps some out–explosive behavior that pushes around the gas nearby. The resulting waves, astronomers concluded, were sound waves, with a frequency much too deep for any of us to hear.
It wasn’t until recent that Chandra’s visualization scientist Kimberly Arcand decided to make those low-frequency cosmic sounds audible. She wanted the public, and particularly those who are blind or have reduced vision, to be able to experience the wonder of the Perseus cluster with senses besides sight. Arcand told me she was inspired by Wanda Diaz-Merced, a blind astrophysicist who developed a program to convert sunlight into sound so that she could hear a solar eclipse sweeping across the United States in 2017. Arcand extracted the sound data from Chandra’s observations and then, with some mathematical work and sound editing, brought them into the range of human hearing, a couple hundred quadrillion times higher than the original frequency. The result: a spooky, cosmic wail.
Arcand and her team at Chandra have previously made a variety of celestial images into music through a process known as sonification, but those projects were based on light, not sound. Take a look at the star-filled, glittering center of our Milky Way Galaxy. To hear it, scientists assigned different sonic features to the cosmic material in a snapshot of the galaxy. Stellar stuff at the top of the image corresponds to higher pitches; the brightest bits play at top volume. Short notes represent stars, and a drawn-out hum indicates clouds of gas and dust. This image shows observations at multiple wavelengths that scientists use to create a beautiful song.
The melody from our galactic centre sounds beautiful and peaceful. Most of the sonifications in Chandra’s library do, even the clips that lack instrumental elements and feature only a jumble of notes. They are nothing like the primal scream of the Perseus cluster, which the Chandra team released in May this year. Arcand stated that the Perseus sound is one of the most powerful because it’s based on sound waves. It’s more objective, which makes the noise feel a bit more real. The cosmic wail would not sound quite the same if the Perseus cluster had a helmet, superpowered hearing and a helmet. It is made up of sound waves coming from different directions and not one scream at a time. Still, “this is as close as we know how to get,” she said.
When I asked Arcand what she thought about the sound freaking people out, she cracked up. “I just feel bad,” she said. Arcand was raised singing in choirs and the Perseus audio for her is musical. It’s like listening to a Hans Zimmer song with dramatic lyrics. She has worked on the Chandra mission for more than two decades, and being so intimately familiar with the data, she was unlikely to be spooked by it, even when it sounds like, you know, that. She said that she didn’t find anything frightening in the video, though scientists and sound engineers can edit it to reduce its creepiness, adding chimes or nice chords. But this is space putting on a little performance, and we may as well experience it as the artist intended.