The highest-resolution images ever taken of the surface of the Sun have revealed plasma swirls that play an essential role in moving energy from the star's interior to its outer layers, according to a study published on Wednesday in the journal Nature.
Researchers captured the unprecedented spatial and temporal details of the solar photosphere using the Daniel K. Inouye Solar Telescope, the world's largest solar telescope, located on the Haleakalā volcano on the island of Maui.
An international team of scientists led by the National Solar Observatory recorded the observations, demonstrating for the first time clearly how microscopic fluid dynamics transport energy across the solar surface.
The observed plasma swirls are manifestations of Kelvin-Helmholtz instabilities, a fluid dynamics phenomenon that occurs when two layers of fluid move at different speeds where they touch. On the Sun's visible surface, hot plasma rising from the solar interior interacts with cooler plasma sinking back down, generating magnetic turbulence in the shape of waves and spirals.
The photosphere is the visible outer shell of the Sun, where solar energy escapes into space as light and heat. Understanding how energy moves through this layer is critical for solar physics, as turbulence converted from magnetic energy helps explain how the solar corona reaches millions of degrees and how the solar wind is driven outward into space.
Plasma vortices on the solar surface
Researchers found that the instability is triggered by granular plasma flows converging at the edges of magnetic regions. This movement creates strong horizontal shear layers characterized by sudden changes in velocity or direction.
The tiny turbulent structures were resolved using the 4-metre mirror of the Inouye telescope, which functions like a high-powered magnifying glass capable of detecting details just 19 kilometres wide on the solar surface. Previous solar telescopes with apertures smaller than 2 metres were unable to reach the spatial scales required to view these instabilities.
High-resolution imaging revealed that the interfaces between magnetic flux concentrations and solar granulation convection are not smooth boundaries. Instead, researchers discovered that these boundaries are composed almost entirely of vortex-shaped structures.
An analysis of 47 individual vortices showed that the average distance between them is 65 kilometres, with individual sizes ranging from 25 kilometres to 170 kilometres across. Researchers measured the apparent speeds of the vortices between 0.67 kilometres per second and 3.0 kilometres per second, while three-dimensional simulations showed that the structures extend vertically as rolls for hundreds of kilometres below the visible surface.
International research and future solar monitoring
The Daniel K. Inouye Solar Telescope is funded by the United States National Science Foundation and operated by the National Solar Observatory in partnership with the Association of Universities for Research in Astronomy. The international study also involved collaboration with researchers from the Max Planck Institute for Solar System Research in Germany and the High Altitude Observatory at the National Center for Atmospheric Research.
According to the National Solar Observatory, the research team will continue monitoring active regions of the solar photosphere using the Inouye telescope's spectropolarimeter suite. Scientists plan to map the ongoing evolution of solar magnetic fields throughout the current cycle of solar activity.
