Unveiling the Invisible: Exploring the “Shimmer” of Stars with Groundbreaking 3D Simulations and Astronomy Sound Waves

2023-08-04 10:03:59
Stars have an instinctive “shimmer” as a result of gaseous heat waves rippling on their surfaces, but they are imperceptible to current Earth-bound telescopes. Stars twinkle to us because our atmosphere bends their light as it travels to Earth. But stars also have a “shimmer” as a result of gaseous waves rippling on their surfaces, imperceptible to current Earthbound telescopes. In a new study, a team of researchers from Northwestern University in the US developed the first 3D simulation of energy ripple from the core of a massive star to its outer surface. Using these new models, the researchers determined, for the first time, the innate amount of star blinking. In another first, the team also converted these gas waves into sound waves in an effort to find out what the stars’ inner sound and “flashing” might be like. The results of the study were published on July 27 in the journal Nature Astronomy. “Motions in the core of stars trigger waves like those in the ocean,” said Evan Anders of Northwestern, who led the study. “When the waves reach the surface of the star, they cause it to flicker in a way that astronomers might be able to notice.” “For the first time we have developed computer models that allow us to quantify the amount of star blinking as a result of these waves. This work allows future space telescopes to explore the central regions, where stars form the elements we depend on to live and breathe,” he added. The waves make the heat that produces the flashes. To understand, the press release explains that all stars have a convection zone, a disorderly place where gases churning to push heat out. For massive stars (stars with a mass of at least 1.2 times the mass of our sun) this convection zone lies in their cores. “Convection within stars is similar to the process that fuels thunderstorms,” ​​says Anders, where cold air falls to warm up and rises again, a turbulent process that transfers heat inside the stars. Convection creates ripples, tiny galaxies that dim and brighten starlight, resulting in a subtle twinkle. Because the cores of massive stars are hidden from view, Anders and his team sought to model the hidden convection, building on studies that examined the properties of turbulent core convection, wave properties, and potential observations of those waves. the star depending on the waves generated by convection. After convection generates waves, they bounce back inside the simulated star, while some waves eventually appear on the surface of the star to create a shimmering effect, then other waves get trapped and continue to bounce back. To isolate the waves that bounce off the surface and create a flicker, Anders and his team built a filter that describes how the waves bounce back inside the simulation. “We first put an inhibitory layer around the star – like the lining walls you might have in a recording studio – so we can measure exactly how convection makes the waves,” Anders explained. He compares it to a music studio, which benefits from padded, soundproof walls to reduce ambient sounds so musicians can extract “pure sound”. They then apply filters and engineer those recordings to produce the song just the way they want it. Similarly, Anders and his collaborators applied their filter to the pure waves emerging from the convection core. Then they tracked waves bouncing back inside a typical star, and eventually found that their filter accurately described how the star changed the waves coming from the core. The researchers then developed a different filter for how the waves would bounce back inside a real star. With this filter applied, the resulting simulation shows how astronomers would expect the waves to appear if viewed through a powerful telescope. “Stars become brighter or darker depending on different things that are dynamically going on inside the star,” Anders says. “The shimmer caused by these waves is very subtle, and our eyes are not sensitive enough to see it. But powerful future telescopes may be able to detect it.” Stars get brighter or darker depending on different things happening dynamically inside the star (Shutterstock) How did the researchers turn the waves into audible sound? Taking the recording studio analogy with the team a step further, Anders and his collaborators then used their own simulations to generate the sound. Since these waves lie outside the range of human hearing, they uniformly increased the frequencies of the waves to make them audible. Depending on the massive star’s size or brightness, convection produces waves that correspond to different sounds. Waves emerging from the core of a massive star, for example, make sounds like a distorted beam gun, exploding in a strange way. But the star changes these sounds when the waves reach the surface of the star. For the massive star, the ray gun-like pulsations turn into a low echo that reverberates through an empty room. On the other hand, waves on the surface of an average-sized star evoke images of a continuous hum across windswept terrain. Surface waves on a young star sound like a sad alert from a weather siren. Then, Anders and his team passed songs through different stars to hear how the stars changed the songs. “We were curious what the song would sound like if it was heard through a star,” he said, adding, “The stars change the music, and therefore, the state of the waves change if we see them sparkling on the surface of the star.”
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