Inouye Solar Telescope Sees the Sun Closer Than Ever

Scientists observing the Sun with the Daniel K. Inouye Solar Telescope have caught a wave-like shape that’s never been seen on the Sun’s visible surface. The highest-resolution image of the Sun's surface (photosphere) ever captured, taken at 416 nm by the Inouye Solar Telescope, reveals deformed boundaries of magnetic elements and ultra-fine scale stripes, both associated with Kelvin-Helmholtz instability.NSF / NSO / AURA / MPS The sharpest images ever of the Sun’s visible surface have revealed beautiful wave-like structures never seen there before. They’re mesmerizing to watch, but they’re also key to the transformation of energy in the Sun’s atmosphere. When two fluids flow past each other at significantly different speeds, something beautiful happens. The smallest of disturbances along such boundaries can grow into swirling vortices in a process known as the Kelvin-Helmholtz instability. We see these wave-like shapes throughout the solar system: We see them in Earth’s clouds and wind-swept ocean and between stripes in Saturn’s upper atmosphere. We’ve even seen hints of such swirls in the solar corona. But we’ve never seen them on the Sun’s visible surface, where the corona and the solar wind originate. Now, the National Science Foundation’s 4-meter Daniel K. Inouye Solar Telescope, near the summit of Maui’s Haleakalā, has given us a view fine enough to reveal such details, published August 5th in Nature. The highest-resolution image of the Sun's surface (photosphere) ever captured, taken at 416 nm by the Inouye Solar Telescope, reveals deformed boundaries of magnetic elements and ultra-fine scale stripes, both associated with Kelvin-Helmholtz instability.NSF / NSO / AURA / MPS Zooming into an active region near a sunspot, David Kuridze (National Solar Observatory) and colleagues watched the boiling motions of plasma on the Sun at a wavelength of 416 nanometers (violet light). Like in a pot of boiling water, the solar plasma wells up at the center of convection cells, known as granules. At the surface, the plasma releases radiation and heat into space, cooling and sinking down again at the granule edges. (Just like in sunspots, the edges of granules appear darker because the plasma there is cooler.) There, where the plasma flows converge, so, too, do the magnetic field lines that the plasma is carrying. Like dry pasta packed in a bundle, closer-together magnetic field lines represent stronger fields. Stronger magnetic fields in turn stymie the flow of plasma. The result is a sudden change in velocity — exactly the condition needed to set up Kelvin-Helmholtz instabilities. Using the Inouye Telescope to zoom in on granule edges, the researchers found not the blurry, smooth interfaces seen in previous images, but clear vortices forming and dissipating. Computer simulations of magnetized plasma in the solar atmosphere, known as MURaM, confirm that the swirls are Kelvin-Helmholtz instabilities. “The smallest resolve features in these images are around 19 km, which is also diffraction limit (highest achievable resolution) of the telescope,” Kuridze says. “Resolving structures as small as 19 kilometers and tracking their rapid motions over just a few seconds is an extraordinary technological achievement in observational solar physics.” This compilation of data from the Solar Dynamics Orbiter, the Inouye Solar Telescope, the MPS camera, and the High Altitude Observatory's MuRAM simulation demonstrates the sharpness of Inouye's images. The last part of the movie shows the simulated brightness and vertical magnetic field component, demonstrating their distribution in 3D. NSF / NSO / AURA / MPS / HAO Just as pilots might use wave-shaped clouds as an indicator of turbulent atmosphere ahead, solar physicists see these instabilities as signs of turbulence and energy dissipation on the Sun’s visible surface. The energy from pent-up magnetic fields drives most solar activity, but there’s still a lot we don’t understand about how that energy turns into solar flares and explosions called coronal mass ejections. Mechanisms of energy release at the smallest scales are key to almost every process we see on our nearest star. “The Kelvin-Helmholtz instability is an extremely efficient process for transferring, transforming, and dissipating energy, as well as reshaping magnetic fields,” Kuridze explains. “This makes it critical for tackling fundamental open problems in solar and stellar astrophysics, including why outer layers of stellar atmospheres are much hotter than their surfaces.”