The Sun is a rare astronomical object whose behavior directly affects people on Earth. Its flares can disrupt radio communications, GPS operation and power grids, and their emissions cause auroras. That is why it is important for scientists to understand exactly how energy is released.
Flares are classified by brightness in the X-ray range, from weak class A to the most powerful class X. They are born in the corona, the outer layer of the Sun's atmosphere, which is hidden by the dazzling glow of the disk. It is almost impossible to see the processes there directly.
Flare ribbons help: bright traces of plasma and high-energy particles that strike the chromosphere, the lower layer of the Sun's atmosphere, along magnetic field lines. From their shape, scientists try to understand what is happening far above.
A study in The Astrophysical Journal led by Marcel Corchado Albelo of the U.S. National Science Foundation proposes a new approach. The authors created a model, tested it on synthetic data, and then applied it to a real M6.5-class flare recorded on June 22, 2015, by the IRIS satellite, launched in 2013.
It turned out that the ribbons are inhomogeneous: they break up into fragments of different sizes, and energy is released in separate pulses rather than as a uniform flow. "For the first time, we have experimentally shown a physical connection between the observed irregular shapes and the structure of the energy conversion region," a press release quoted Corchado Albelo as saying.
Co-author Maria Kazachenko of the National Solar Observatory noted that models had long predicted a certain behavior of ribbon boundaries, but observations had not been able to confirm it. Now, according to her, a quantitative test has been carried out for the first time: the complexity of the ribbons grows with the rate of magnetic line reconnection.
Magnetic reconnection is a process in which tangled magnetic fields suddenly rearrange into a simpler configuration, releasing stored energy. It is this process that triggers flares.
The authors emphasize that their findings do not make it possible to predict flares directly, but they help understand how energy is released and will become the basis for more accurate models. "Our analysis is the first step toward a quantitative link between ribbon shape and reconnection dynamics," they conclude.