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The scariest sound in astronomy

The scariest sound in astronomy

Ah, the sounds of late summer. Run by a swimming pool, and listen to the happy cries of babies splashing around. Sit outside at night and enjoy the soothing hum of cicadas hidden in the trees. Open the internet, and listen to the terrifying howl of outer space.

I thank NASA for that last one. The space agency recently shared a clip online of sound coming from a group of galaxies about 250 million light-years from Earth. NASA, always eager to show off its ability to produce cosmic wonders, Introduce the sound enthusiastically, as if to say, Wow, check out this cool thing! And while turning a space phenomenon into something detectable by our human ears certainly sounds like an exciting exercise, the reality is — well, listen up.

The noise sounds like ghostly howling, horror movie music right before a jump scare, or as many people do has indicated, the cries of countless souls trapped in eternal darkness. Only nothing good is less terrifying, and more terrible. Does space really look that scary?

The answer is, sort of. And there is a completely devoid of horror explanation for this. Some parts of space are filled with hot gas, including the middle between the distant, sparkling galaxies clustered together. In 2002, when a NASA space telescope called Chandra studied the Perseus cluster, it detected wave-like motions in the gas, spreading outward like ripples in water. Scientists determined that the ripples were caused by the supermassive black hole in the cluster’s central galaxy. When a black hole sucks in cosmic matter, it regurgitates some — explosive behavior that pushes around nearby gas. The astronomers concluded that the resulting waves were sound waves of a frequency too deep for any of us to hear.

It wasn’t until recently that Chandra visualization scientist Kimberly Arcand decided to shift those impossibly low cosmic notes into the audible range. She wanted the audience, especially those who are blind or have a low vision, to be able to experience the wonders of the Perseus collection with the senses besides the sight. Arcand told me she was inspired by Wanda Diaz-Merced, a blind astrophysicist who developed software to convert sunlight into sound so she could hear a solar eclipse sweeping the United States in 2017. Arcand and her team extracted audio data from Chandra observations and then, with some math work and editing sound, I made them within the range of human hearing, a few hundred quadrillion times higher than the original frequency. The result: a frightening cosmic howl.

Arcand and her team at Chandra had previously turned a variety of celestial images into music through a process known as sonication, but those projects were based on light, not sound. Consider the shimmering, star-filled center of the Milky Way. To hear it, scientists assigned different sonic features of cosmic matter to a snapshot of the galaxy. Star material at the top of the image corresponds to higher pitches; The brightest bits are played at the highest volume. Short tones represent stars, and long tones indicate clouds of gas and dust. The image features notes in multiple wavelengths, which scientists used to make an even sweeter song: X-ray xylophone, optical light violin, and infrared piano.

Our galactic center melody sounds beautiful and calm. Most of the voices in Chandra’s library do as well, even passages that lack instrumental elements and contain only a mixture of notes. It’s not like the primal scream of Perseus, which Team Chandra released in May of this year. “Perseus is probably the most evocative because it is actually based on sound waves,” said Arcand. It’s more objective, which makes noises look more realistic. At the same time, cosmic wailing wouldn’t sound quite like this if you could hang out in the Perseus galaxy cluster with a helmet and powerful hearing aid. The eerie sound is a mixture of sound waves emitted from the central galaxy in different directions, not a single cry at the right time. Still, she said, “This is as close to what we know as it gets.”

When I asked Arcand what she thought about the sound that frightens people, she cracked. She said: “I just feel bad.” Arcand grew up singing in choirs, and to her, Perseus’ voice is musical, like a dramatic melody from Hans Zimmer’s sentimental track. I’ve worked on the Chandra mission for more than two decades, and being intimately familiar with the data, you weren’t likely to intimidate it, even when it seemed, you know, that. She said, “I haven’t heard anything scary about it, but I completely understand that other people have a different perspective.” Scientists and sound engineers could certainly tweak the clip to make it less scary, mixing in some nice bells or harp chords. But this is a space that offers little performance, and we might as well experience it as the artist intended it to be.



#scariest #sound #astronomy

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