IRIS and Hinode a stellar research team
A filament stretches across the lower half of the Sun in this image captured by NASA’s Solar Dynamics Observatory on 10 February 2015. Filaments are huge tubes of relatively cool solar material held high up in the corona by magnetic fields. Researchers simulated how the material moves in filament threads to explore how a particular type of motion could contribute to the extremely hot temperatures in the Sun’s upper atmosphere, the corona.
Modern telescopes and satellites have helped us measure the blazing hot temperatures of the Sun from afar. Mostly the temperatures follow a clear pattern: The Sun produces energy by fusing hydrogen in its core, so the layers surrounding the core generally get cooler as you move outwards — with one exception. Two NASA missions have just made a significant step towards understanding why the corona — the outermost, wispy layer of the Sun’s atmosphere — is hundreds of times hotter than the lower photosphere, which is the Sun’s visible surface.
The researchers focused on a solar feature called a filament. Filaments are huge tubes of relatively cool plasma held high up in the corona by magnetic fields. Researchers developed a computer model of how the material inside filament tubes moves, then looked for signatures of these motions with Sun-observing satellites.
This image taken on 19 October 2013, shows a filament on the Sun — a giant ribbon of relatively cool solar material threading through the Sun’s atmosphere, the corona. The individual threads that make up the filament are clearly discernible in this photo. This image was captured by the Solar Optical Telescope onboard JAXA/NASA’s Hinode solar observatory. Researchers studied this filament to learn more about how material gets heated in the corona.
“Through numerical simulations, we show that the observed characteristic motion matches well what is expected from resonant absorption,” said Antolin.
The signatures of these motions appear in three dimensions, making them difficult to observe without the teamwork of several missions. Hinode’s Solar Optical Telescope was used to make measurements of motions that appear, from our perspective, to be up-and-down or side-to-side, a perspective that scientists call plane-of-sky. The resonant absorption model relies on the fact that the plasma contained in a filament tube moves in a specific wave motion called an Alfvénic kink wave, caused by magnetic fields. Alfvénic kink waves in filaments can cause motions in the plane-of-sky, so evidence of these waves came from observations by Hinode’s extremely high-resolution optical telescope.
This is a simulation of a cross-section of a thread of solar material, called a filament, hovering in the Sun’s atmosphere. The yellow area is the thread itself, where the material is denser, and the black area is the surrounding, less dense material. The characteristic wave motion leads to complex turbulence around the edges of the yellow thread, which heats the surrounding black material. This model was created with the Aterui supercomputer at the Center for Computational Astrophysics at the National Astronomical Observatory of Japan.