Plasma corkscrews form on sun during stellar eruption

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A twist on the sun is throwing solar scientists for a loop.

For the first time, researchers have watched the sun’s magnetic field force plasma into a spring-shaped curl during a powerful solar eruption known as a coronal mass ejection, or CME. The new observations contradict previous research suggesting that the twisted plasma structures are precursors of CMEs, which can disable satellites and disrupt air travel when directed toward Earth. The new findings appear August 28 in Astrophysical Journal Letters.

Understanding the interplay between the magnetic curls and CMEs could help solar scientists spot impending solar storms well in advance, says astrophysicist Angelos Vourlidas of the U.S. Naval Research Laboratory in Washington, D.C., who was not involved with the new study. “A reconciled theory would potentially allow us to see the early stages of a CME and issue warnings days instead of hours before it reaches Earth,” he says.

Scientists detect the sun’s invisible magnetic field by watching how it steers glowing solar plasma. In the aura of plasma that surrounds the sun, called the corona, the field can bend into large loops of plasma more than 10 times as wide as Earth. When two loops cross paths, they can spiral around each other into a coil-shaped structure known as a flux rope.

Plasma physicists have produced two competing hypotheses to explain the formation of the spring-shaped structures and their connection to CMEs. In one, the rope forms before a solar eruption. After drifting for hours or days, it suddenly kinks like an overtwisted phone cord, pushing solar material outward as a CME.

In the second hypothesis, CMEs instead erupt when the ends of magnetic loops disconnect from the sun’s surface. As the CME’s blob of solar material bursts outward, the severed loops connect to one another, forming a flux rope. The debate boils down to whether ropes form before or during CMEs.

The first hypothesis gained credence in July 2012 when NASA’s Earth-orbiting Solar Dynamics Observatory satellite spotted a flux rope form and float around for eight hours before it kinked and triggered a CME. The event seemed to settle the debate.

But in November 2013, the probe recorded the birth of another flux rope that supported the second explanation. The rope formed during a CME when severed magnetic loops fused together into a slinky-shaped spiral. Solar physicist Hongqiang Song of Shandong University in Weihai, China, who led the analysis, says that the eruption’s location on the sun’s edge, when viewed from the probe’s perspective, allowed researchers to clearly see the plasma outlining the rope.

Song says his team’s finding demonstrates that neither theory can completely explain the relationship between CMEs and flux ropes, which complicates efforts to improve solar storm prediction. “We still have a long way to answer why, when and where solar outbursts will take place,” he says.