Mini solar flares produced in the safety of a laboratory have revealed how the sun fires out energetic particles and X-rays at incredibly high speeds.
The sun regularly spits out solar flares when arcs of plasma, called coronal loops, break. We don’t fully understand how they are made, as even our most detailed pictures of the sun can’t make out details below a resolution of about 10,000 metres, but one idea is that these loops are twisted like braided rope, in a fractal pattern, where smaller and smaller structures of braids form as you look more closely, says at the California Institute of Technology. These small braids make it easier to break the loops apart and release X-rays as part of a solar flare.
To study a flare up close and try to see this fractal structure, Bellan and his colleagues created miniature coronal loops by injecting jets of hydrogen gas into a vacuum chamber that contained high-voltage electrodes, turning the gas into a plasma. They then used a magnetic field to loop the plasma, filming it with video and X-ray cameras operating at millions of frames per second.
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The high current flowing through these loops produces their own magnetic field, which chaotically tugs back and forth with the initial field and creates the patterns seen in solar flares. “If you have too much current, then things start falling apart, and that’s what leads to the X-rays,” says Bellan.
By watching how the loops developed and matching this up with when the X-rays were released, Bellan and his team could see where and how the loops collapsed into a solar flare. One of the main ways is what is known as a kink instability, which happens when a rope-like flare bunches up, making it longer, increasing its resistance and so lowering its voltage. This voltage drop creates a pressure drop, accelerating the particles to a high speed – which Bellan and his team think might be happening to produce the X-rays we see from the sun.
“This is a major step in the direction of understanding the physics of flares,” says at the University of Sheffield, UK. However, not everyone agrees about the fractal nature of coronal loops. More data and experiments will be needed until we can definitively say that this is what is happening in the sun, says Fay-Siebenburgen.
Nature Astronomy
