Twinkle loudly, little star

Science Daily has the story of a research team at Northwestern University that has determined the way any particular star should twinkle – which is a phenomenon based in part on how the superhot gas on their surfaces move. But to do that, they’ve also figured out how those stellar surges and vibrations would sound:

“Motions in the cores of stars launch waves like those on the ocean,” said Northwestern’s Evan Anders, who led the study. “When the waves arrive at the star’s surface, they make it twinkle in a way that astronomers may be able to observe. For the first time, we have developed computer models which allow us to determine how much a star should twinkle as a result of these waves. This work allows future space telescopes to probe the central regions where stars forge the elements we depend upon to live and breathe.”

After convection generates waves, those waves bounce around inside of the simulated star. While some waves eventually emerge to the star’s surface to produce a twinkling effect, other waves become trapped and continue to bounce around. To isolate the waves that launch to the surface and create twinkling, Anders and his team built a filter that describes how waves bounce around inside of the simulations.

“We first put a damping layer around the star — like the padded walls you would have in a recording studio — so we could measure exactly how the core convection makes waves,” Anders explained.

Anders compares it to a music studio, which leverages soundproof padded walls to minimize the acoustics of an environment so musicians can extract the “pure sound” of the music. Musicians then apply filters and engineer those recordings to produce the song how they want.

Similarly, Anders and his collaborators applied their filter to the pure waves they measured coming out of the convective core. They then followed waves bouncing around in a model star, ultimately finding that their filter accurately described how the star changed the waves coming from the core.

Because these waves are outside the range of human hearing, the researchers uniformly increased the frequencies of the waves to make them audible.

Depending on how large or bright a massive star is, the convection produces waves corresponding to different sounds. Waves emerging from the core of a large star, for example, make sounds like a warped ray gun, blasting through an alien landscape. But the star alters these sounds as the waves reach the star’s surface. For a large star, the ray gun-like pulses shift into a low echo reverberating through an empty room. Waves at the surface of a medium-sized star, on the other hand, conjure images of a persistent hum through a windswept terrain. And surface waves on a small star sound like a plaintive alert from a weather siren.

Next, Anders and his team passed songs through different stars to listen to how the stars change the songs. They passed a short audio clip from “Jupiter”(a movement from “The Planets” orchestral suite by composer Gustav Holst) and from “Twinkle, Twinkle, Little Star” through three sizes (large, medium and small) of massive stars. When propagated through stars, all songs sound distant and haunting — like something from “Alice in Wonderland.”

“We were curious how a song would sound if heard as propagated through a star,” Anders said. “The stars change the music and, correspondingly, change how the waves would look if we saw them as twinkling on the star’s surface.”

You can find videos at the link, and can read more the Northwestern research here, in Nature.