Vortices a few dozen kilometers wide have been observed directly in the photosphere, the visible surface of the Sun. They appear at the edge of small concentrations of magnetic field. Their presence confirms a mechanism predicted long ago and could help understand how energy is transported to the upper layers of the solar atmosphere.
The images come from the Daniel K. Inouye Solar Telescope, installed in Hawaii. Its 4 m mirror can distinguish much finer details than previous instruments. During observations made on April 14, 2025, the team achieved a resolution of about 19 km on the surface of the Sun.
Overview of the MURaM simulation.
a - Vertical magnetic flux density at the height where the mean optical thickness τ 500 is equal to 1 near the interface between magnetic and non-magnetic regions.
b - Horizontal velocity field at the same height.
c - Synthetic emergent intensity at 500 nm at disk center, calculated from the MURaM cube.
d to f - Enlarged images of the regions indicated by the yellow boxes in the upper panels: vertical magnetic flux density (d), horizontal velocity field (e) and synthetic emergent intensity (f). The arrows in e indicate the direction of plasma flows.
The researchers studied an active region near a sunspot for about three minutes. They spotted 47 vortices in the images. Their size ranges from about 25 to 170 km, with a characteristic distance of about 65 km between neighboring structures.
To understand their origin, one must look at what happens when two flows move at different speeds on either side of a boundary. This situation can trigger a Kelvin-Helmholtz instability: small undulations grow and then roll up into vortices.
On the Sun, the boundary here separates plasma subjected to different magnetic conditions.
The images alone do not, however, provide all the plasma velocities. The team therefore compared them with numerical simulations of magnetoconvection, which reproduce the motions of a conducting plasma subjected to the solar magnetic field. The simulations produce structures very close to the observations, with 94 analyzed occurrences and a characteristic scale of about 49 km.
Concretely, these vortices stir magnetized and less magnetized material. They can also deform field lines, promote their entanglement and feed small turbulent structures.
The next question is to determine how much energy these instabilities actually transport toward the chromosphere and corona. Longer observations, covering several active regions and different magnetic field strengths, will make it possible to measure their contribution to the phenomena that fuel solar activity and space weather.