Astronomers have captured the most detailed images of the sun's surface, revealing golden bands and swirling vortices that may explain a decades-old mystery: why the corona, the sun's outer atmosphere, is millions of degrees hotter than its surface.
Unprecedented Resolution
The images were taken with the Inouye solar telescope in Hawaii, the world's most powerful solar telescope. They show features smaller than 20km (12 miles) across in a magnetically active region near a sunspot.
“These are the highest spatial resolution images of the solar surface ever acquired,” said Dr Friedrich Wöger, a senior scientist at the US National Solar Observatory, which operates the telescope near the summit of the Haleakalā volcano on Maui.
Earlier observations with the telescope captured the sun's surface as a patchwork of granular structures each about the size of France, picking out details as small as 30km across. The latest images push the telescope to its limits.
Swirling Vortices and Kelvin-Helmholtz Instabilities
In the new images, small whirlpool-like structures were identified as signatures of Kelvin-Helmholtz instabilities (KHIs). These occur when fast-moving plasma slides past slower-moving fluid, creating shear at the interface. This sets up disturbances that grow into spiralling vortices resembling breaking waves.
KHIs have been observed in lakes, oceans, clouds on Earth, and even in the atmospheres of Jupiter and Saturn, but never before confirmed on the sun. The findings are published in Nature.
Implications for Solar Physics
Explosive events on the sun, such as solar flares and coronal mass ejections, are powered by extreme magnetic fields. These explosions can disrupt power grids, satellites, GPS, and communications on Earth.
The magnetic fields are generated by the movement of hot, charged plasma, but the physics is not fully understood. Astronomers know that magnetic field lines can twist like braided hair, releasing tension when they break. The swirling vortices are now a key suspect in explaining why the field lines become braided and why the corona is heated to a few million degrees while the surface is only 6,000°C.
“This could solve the biggest mystery of the last half a century for solar physics and astrophysics,” said Dr David Kuridze, an astronomer on the team. “When you have this instability in the system, it is very easy to cascade the energy into smaller scales. And at some point, it just dissipates as heat. This could make hot coronas, hot outer atmospheres of the sun and similar stars.”
