Beneath the Surface: The Hidden Source of the Sun’s Magnetic Field

The Sun's magnetic field may not be as deep as we thought. For decades, scientists thought the Sun's dynamo, the region that generates the powerful magnetic field, was located far inside the star. Now there is evidence that the dynamo lurks just below the Sun's surface.

The strength of the sun's magnetic field fluctuates on an 11-year cycle. During the strongest periods of the cycle, sunspots and powerful winds appear near the Sun's equator, as well as eruptions of material that cause Earth's aurora borealis. Ideas about how magnetic fields are generated have struggled to explain how all these phenomena are related.

Essentially, he says, the sun behaves like a giant clock, with its many vortices and currents of plasma acting as the gears that keep it running. Jeffrey Vasil Researchers from the University of Edinburgh in the UK say: “No one really knows how these elements fit together, or what they are all about, unless we know how a clock starts. “I can't explain the whole watch.”

Vasil and his colleagues suggest that the Sun's magnetic field could result from instabilities in the rotation of plasma inside the star, a phenomenon also commonly seen in other astrophysical objects, such as disks of hot material orbiting black holes. Such instabilities could arise in the outermost 5 to 10 percent of the Sun.

The researchers modeled how these instabilities churn through the plasma that makes up the Sun's outer layer, and found that they could produce sunspots during periods of maximum solar activity and create powerful winds that sweep around the Sun. They also found other magnetic phenomena. Simulations of a dynamo near the surface matched observed magnetic patterns on the Sun much better than simulations of a deeper dynamo.

“There are all these clues, and we've been piecing these things together for almost 20 years,” Vassil says, “and it's been very satisfying to see a lot of things falling into place and making sense.”

If the solar dynamo were generated close to the surface, it could be much easier to study the solar magnetic field and predict its behavior. “If there is a magnetic field out there, the best hope is that we can actually study it,” Vasil said.

This could help better predict the solar activity that produces surprising aurora borealis and disrupts the Earth's power grid.