How the Core of a Star Causes it to 'Twinkle'

Monday - September 25 2023, 13:34 UTC - 1 year ago

In a new study conducted by Northwestern University, a team used 3D simulations to determine how stars should twinkle due to waves generated by their core convection. The team also converted these rippling waves of gas into sound waves to hear what the stars should sound like. This discovery could help astronomers better investigate the processes deep within certain stars.

Many people know that stars appear to twinkle because our atmosphere bends starlight as it travels to Earth. But stars also have an innate "twinkle" — caused by rippling waves of gas on their surfaces — that is imperceptible to current Earth-bound telescopes.

In a new study, a Northwestern University-led team of researchers developed the first 3D simulations of energy rippling from a massive star’s core to its outer surface. Using these new models, the researchers determined, for the first time, how much stars should innately twinkle.

And, in yet another first, the team also converted these rippling waves of gas into sound waves, enabling listeners to hear both what the insides of stars and the "twinkling" should sound like. And it is eerily fascinating.

The study was published in the journal Nature Astronomy."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 that 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." .

Anders is a postdoctoral fellow in Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). He is advised by study coauthor Daniel Lecoanet, an assistant professor of engineering sciences and applied mathematics in Northwestern’s McCormick School of Engineering and member of CIERA.

A 3D simulation of how turbulent convection in the core of a large star (center) can generate waves that ripple outward and power resonant vibrations near the star’s surface. By studying changes in the star’s brightness caused by the vibrations, scientists could one day better understand the processes deep in the hearts of large stars. Credit: E.H. Anders et al./Nature Astronomy 2023 .

All stars have a convection zone, a volatile and chaotic region where gases churn to push heat outward. For massive stars (stars at least about 1.2 times the mass of our sun), this convection zone resides at their cores.

"Convection within stars is similar to the process that fuels thunderstorms," Anders said. "Cooled air drops, warms and rises again. It’s a turbulent process that transports heat." .

It also makes waves — small rivulets that cause starlight to dim and brighten, producing a subtle twinkle. Because the cores of massive stars are shrouded from view, Anders and his team sought to model their hidden convection. Building upon studies that examined properties of turbulent core convection, characteristics of waves, and possible observational features of those waves, the team’s new simulations include all relevant physics to accurately predict how a star’s brightness changes depending upon convection-generated waves.

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 effec, others dissipate, or hit other waves and merge, dampening their effects.