Astronomers have seen swirling vortices on the surface of the sun for the first time, in the sharpest solar images ever taken. The observations come from the Daniel K. Inouye Solar Telescope on Maui and were published in the journal Nature on 5 August.
The swirls matter because they offer an answer to an old puzzle. The sun's visible surface sits at roughly 6,000C, while the corona above it reaches millions of degrees. Something must carry energy upward, and physicists have argued about what for half a century.
The telescope, run by the US National Solar Observatory near the summit of the Haleakalā volcano, was pointed at a magnetically active region beside a sunspot. It resolved structures smaller than 20 kilometres across, the Guardian reports. Earlier pictures from the same instrument reached about 30 kilometres, enough to show granules the size of France. The new frame covers roughly the radius of the Earth, and its finest details are the size of a city, according to NASA's Astronomy Picture of the Day.
"These are the highest spatial resolution images of the solar surface ever acquired," said Dr Friedrich Wöger, a senior scientist at the observatory.
The fine dark striations in the images are signatures of a Kelvin-Helmholtz instability. It arises wherever fast-moving fluid slides past slower fluid, creating shear that grows into spiralling vortices. The pattern is familiar from lakes, from cloud formations and from the atmospheres of Jupiter and Saturn.
"A beautiful example of KHIs happens at the boundaries of Jupiter's cloud bands, leading to vortices along the edges," Dr Maria Weber of Delta State University told CNN. Weber was not involved in the study. Theory had long allowed for the same process on the sun. Nobody had confirmed it there.
Why the swirls could heat the corona
Solar flares and coronal mass ejections draw their power from the sun's twisted magnetic fields. Those field lines braid around each other, build tension, then snap and rearrange. What starts the braiding has been unclear. The vortices are now a leading suspect.
"For the first time, we have identified both their origin and their driving mechanism," lead author Dr David Kuridze of the National Solar Observatory wrote to CNN. Once the instability sets in, he told the Guardian, energy cascades to ever smaller scales until it dissipates as heat.
The conclusion rests on the images combined with computer simulations, and how much of the corona's heat the swirls actually supply is not yet quantified. That number bears on space weather forecasting, since flares and ejections aimed at Earth can knock out satellites, power grids and navigation signals.