During solar flares, there are mysterious shadows of falling material in the atmosphere of the Sun.
The shadows were thought to be related to the magnetic field interactions that cause solar eruptions. Solar physicists have found that these downflows are the result of fluid interactions in the sun.
The phenomenon is very similar to structures seen at the shock interface in supernova remnants, where instabilities result in long, finger-like structures. The finding will help us understand the Sun's behavior.
Since the Sun has a very complicated and messy magnetic field, the structures may have something to do with it.
Our star is a ball of hot plasma made up of charged particles that interacts with the force of the universe. The equator rotates faster than the poles because the Sun is a sphere. The solar magnetic field grows tangled and can produce strong magnetic fields all over the Sun, opening up sunspots from which flares emerge.
The field lines can grow chaotic in these magnetic fields. The opposing lines connect at the roots of solar flares. The core solar flare region has sheets of electric current. The release of energy and electrons is caused by a magnetic reconnection.
On the Sun, there are a lot of magnetic fields that are pointing in different directions. The magnetic fields are pushed together to the point where they release a lot of energy in the form of a solar flare.
It is like stretching out a rubber band and cutting it in the middle. It is stretched thin and stressed so it will snap back.
Downflows embedded in fan-like structures resemble outflows seen in simulations of the movement of fluids. They are 15 percent slower than the simulations, which is a huge problem.
A team of researchers led by astronomer Chengcai Shen of the Harvard & Smithsonian Center for Astrophysics wanted to get to the bottom of this strange discrepancy, so they took and carefully studied images of the downflows from NASA's space-based Solar Dynamics Observatory.
They ran simulations of solar flares and compared them to observation data. The majority of the shadows are not caused by magnetic reconnection.
When magnetic reconnection downflows meet the flare's closed loops of magnetic field, they create a termination shock. The researchers noted that supra-arcade downflows are the result of fluids of different densities interacting.
The region sandwiched between two shocks in a supernova remnant is similar to the interface region.
The dark, finger-like voids are not filled with plasma. The density is lower there than in the surrounding area.
The results show that the interface region might be more complex than we thought, which could help us understand how magnetic energy is released during solar flares. 3D simulations of solar phenomena will continue to be conducted by the team.
Nature Astronomy has published the research.
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