The limit and the measurement
The visible surface of the Sun is covered by granules, cells of rising and sinking plasma between 500 and 2,000 km across. Observations with the NSF Daniel K. Inouye Solar Telescope, the first 4 metre class solar telescope, have now resolved something at their edges: fringed structures, some little more than 20 km wide, that repeatedly curl over like a breaking wave. The team reporting them in Nature on 5 August is explicit that 20 km sits at the limit of what the largest solar telescope and current simulations can reach, and that reaching it took a broadband imaging camera and an image restoration step.[1]
What the fringes are read as matters as much as their size. The authors identify them as magnetized Kelvin-Helmholtz instabilities at the edges of magnetic flux concentrations, the shear-driven roll-up that appears wherever two fluids slide past each other at different speeds, and they describe the observation as experimental confirmation of a long-standing theoretical prediction. High-resolution numerical simulations reproduce the same structures. That pairing is the strongest part of the paper: a predicted effect, an image at the predicted scale, and a simulation that lands in the same place.[1]
What could be twisting the field lines?
The Sun stores magnetic energy as field lines twist and coil, and releases it when they snap open and reconnect. What sets the twisting going has been an open question, and the new observation offers a candidate, because the swirls appear wherever the field is strong enough to support them. The same swirls mix magnetized and unmagnetized plasma, which bears on a second gap: activity turns over on an 11-year cycle, and existing models cannot move magnetic flux out of the surface layers fast enough to keep up. Two other readings survive this evidence. The mixing could be a consequence of granular flow that the twisting also happens to follow, in which case the vortices mark the process without driving it; and at the resolution limit part of an apparent swirl can be produced by the restoration step rather than by the plasma.[1]
The useful question is what evidence would sustain this reading of the image. A second observing run at the same 20 km, or another instrument reaching that scale, would either recover fringes at the edges of flux concentrations or not; a different restoration pipeline applied to the same sequence would either leave them standing or thin them out. Until one of those happens, this is one telescope's first look at a scale nothing else can currently reach, which is a real thing to have and a thin thing to build on.[1]