Sun's Flare 'Footprints' Show Explosions Release Energy in Bursts

Solar flares can interfere with radio signals, GPS and power grids, yet the explosions behind them happen in a part of the Sun that is hard to watch. A new study in The Astrophysical Journal describes a way to read what is going on there by studying the bright marks a flare leaves lower down, according to Universe Today.

The researchers found that a flare does not dump its energy in one smooth event. The glowing patch it leaves behind breaks into fragments of different sizes, and the energy arrives in bursts.

Why flares reach into everyday life

Universe Today noted that the Sun, unlike distant objects in astronomy, affects daily life on Earth. Flares are the most powerful explosions in the Solar System, the outlet reported, releasing energy comparable to millions or even billions of hydrogen bombs going off at once.

Astronomers sort flares by X-ray brightness into the classes A, B, C, M and X, from weakest to strongest. Each step up the scale means a ten-fold increase in energy output.

The trigger is magnetic. The Sun's magnetic fields are constantly twisted and rotated until they snap and reconnect in a simpler, more stable arrangement. That process, called reconnection, frees energy that had been held in the fields and sends it out as a flare.

What the researchers looked at

Flares begin in the corona, the Sun's outermost layer. The glare of the Sun makes the corona difficult to observe, so the team turned to flare ribbons instead. Universe Today described these as a kind of footprint: plasma and high-energy particles that crash back into the Sun during reconnection, follow magnetic field lines and light up brilliantly where they hit the chromosphere.

The team, led by Marcel Corchado Albelo of the U.S. National Science Foundation, worked out a way to measure how the fine detail of those ribbons changes over time. The idea is that small features where the energy lands carry clues about what is happening far above, where it is released.

They first built a model and tested it against synthetic observations. They then applied it to a real event, an M6.5-class flare on June 22, 2015, which was observed by NASA's Interface Region Imaging Spectrograph, or IRIS, a solar observation satellite launched in 2013.

What they found

The ribbon split into fragments of different sizes, and the energy was deposited in bursts rather than evenly. According to the report, Corchado Albelo said in a press release that this was the first experimental demonstration of a physical link between the irregular shapes seen on the Sun and the structure of the region where energy is converted.

Maria Kazachenko, a co-author and scientist at the National Solar Observatory, said simulations had suggested for years that ribbon edges should behave in a particular way, but there had been no way to confirm it with observations. She described the study as the first quantitative observational test of those simulations. The measuring tool was adapted from a completely different field, and it showed that ribbon complexity rose along with the rate of reconnection, she said.

What it means for the rest of us

The study does not predict when the next flare will strike, and the report does not claim it does. Its value is in understanding. Flares can cause radio blackouts when they hit the ionosphere, disrupting aviation and maritime communications. They can introduce errors in GPS by altering the altitude of satellites, and they can cause electronics on spacecraft to malfunction. The coronal mass ejections that often accompany flares can disrupt power grids and also produce aurorae.

Because the corona is so hard to observe directly, ribbons offer a more accessible signal. The study authors wrote that ribbon substructure could serve as a unique diagnostic tool for physical processes in the flare's current sheet, the region where reconnection takes place. In practical terms, better knowledge of how flares release energy could improve the models scientists use to understand these events, though the report does not say how soon that might happen.

The result comes from one flare, so it is a first test rather than the final word. Universe Today said the research is part of an ongoing effort to understand solar flaring.

Around Prague, based on reporting by Universe Today