Scientists noticed strange movements inside a solar flare in January 1999.
Unlike most solar flares, which show dazzling energy bursting away from the Sun, this one had a downward flow of motion, as if material was flowing back toward the Sun. Astronomers were perplexed by what they saw, which they described as “downward-moving black gaps.”
In a paper published today in Nature Astronomy, astronomers from the Center for Astrophysics | Harvard & Smithsonian (CfA) propose a novel explanation for the poorly understood downflows, now known as supra-arcade downflows (SADs) by scientists.
“We wanted to know how these formations happen,” explains Chengcai Shen, a CfA astronomer who described the structures as “black finger-like characteristics.” “What is it that motivates them, and are they actually linked to magnetic reconnection?”
Since their discovery in the 1990s, scientists have thought that SADs are linked to magnetic reconnection. When magnetic fields break, fast-moving and very intense radiation is released, and when the field reforms, the process happens.
“What occurs on the Sun is that there are a lot of magnetic fields pointing in all different directions. The magnetic fields are eventually pushed together to the point where they rearrange and unleash a large amount of energy as a solar flare “Kathy Reeves, a CfA astronomer and research co-author, states
Reeves continues, “It’s like stretching a rubber band and cutting it in half. It will snap back because it is pressured and stretched thin.”
The black downflows were thought to be indicators of the fractured magnetic fields “snapping back” to the Sun following a solar flare explosion, according to scientists.
However, there was a snag.
According to co-author Bin Chen, an astronomer at the New Jersey Institute of Technology, most of the downflows detected by scientists are “puzzlingly sluggish.”
Shen clarifies, “Classic reconnection models suggest that downflows should be substantially faster, but this is not the case. It’s a dilemma that necessitates a different explanation.”
The scientists used downflow photos obtained by NASA’s Solar Dynamics Observatory’s Atmospheric Imaging Assembly (AIA) to figure out what was going on. The AIA, which was largely designed and developed at the CfA and is directed by the Lockheed Martin Solar Astrophysics Laboratory, captures photos of the Sun every twelve seconds in seven distinct wavelengths to detect fluctuations in the Sun’s atmosphere.
After that, they created 3D models of solar flares and compared them to the data.
The findings suggest that magnetic reconnection is not the cause of most SADs. Instead, they arise spontaneously in a chaotic environment as a consequence of the interaction of two fluids of differing densities.
According to Reeves, scientists are seeing the same phenomenon that occurs when water and oil are mixed: the two differing fluid densities become unstable and eventually separate.
“The lack of plasma is shown by the dark, finger-like spaces. There’s a lot less density there than in the surrounding plasma “According to Reeves.
To further understand magnetic reconnection, the team hopes to continue investigating SADs and other solar phenomena using 3D models. They want to build methods to anticipate space weather and lessen its effects by better understanding the mechanisms that cause solar flares and eruptions.
Xiaoyan Xie of the CfA, Sijie Yu of the New Jersey Institute of Technology, and Vanessa Polito of the Bay Area Environmental Research Institute are also co-authors on the research.
The National Science Foundation provided funding for this study.