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A team of solar scientists have uncovered the possible originals of the engine that drives much of the sun鈥檚 volatile nature鈥攇enerating the sunspots that move like storm clouds over the surface and causing the sun鈥檚 activity levels to rise and fall over 11-year cycles.

The secret behind this engine, also known as the 鈥渟olar dynamo,鈥� may be among the oldest 鈥渦nsolved problems of physics,鈥� said Benjamin Brown, a solar physicist at CU Boulder.

In new research, he and his colleagues used mathematical equations to simulate the behavior of the sun, arguing that the dynamo may begin in the star鈥檚 outermost layers鈥攏ot deep in its interior as many scientists have believed for decades.

It鈥檚 a pursuit that, in many ways, started with the famed astronomer Galileo Galilei in 1612 A.D.

鈥淕alileo first observed the sunspots 400 years ago, and he learned quite a bit about them, including how they move over the sun鈥檚 surface,鈥� said Brown, a co-author of the research and associate professor in the Department of Astrophysical and Planetary Sciences. 鈥淏ut he couldn鈥檛 figure out where they came from. We鈥檝e struggled with the question ever since.鈥�

The researchers, led by Geoffrey Vasil of the University of Edinburgh in the United Kingdom, in the journal Nature. Co-authors of the study included Keith Julien, an applied mathematician from CU Boulder who died in April after a short illness.

The findings hinge on the dynamo, the term for the complex physics and chemistry in the sun that produce its听wild magnetic fields. Earth boasts its own dynamo that powers the planet鈥檚 magnetic field鈥攖he reason why all compasses on the ground point north.

The sun鈥檚 inner workings matter a lot for people, Brown said. The sun鈥檚 dynamo generates听solar storms that, among other things, pose risks to human power grids. Such storms also caused the auroras that appeared in the skies above the United States earlier this month.

For the researchers, the study represents an achievement decades in the making.听

鈥淕eoff Vasil and I have been thinking about these ideas ever since we were both grad students at CU Boulder 20 years ago,鈥� Brown said.

Wild yet orderly

In general, scientists agree that the solar dynamo begins in the sun鈥檚 鈥渃onvection zone,鈥� or roughly the outer one-third of its interior. There, plumes of hot and charged particles, known as plasma, climb toward the surface.

While Earth鈥檚 magnetic field is mostly uniform, the churn of plasma throughout the sun鈥檚 convection zone warps and twists its magnetic field lines into a pattern that looks a like a bowl of noodles.

Despite that chaos, the solar dynamo powers behavior that is surprisingly predictable, Brown said. Every 11 years or so, the sun moves from a period of low activity, when sunspots pop up less often, to a period of frenzied activity, when sunspots abound鈥攖hen it flips and starts all over again. Right now, the sun鈥檚 activity is on the frenzied side. 听

鈥淵ou could practically set a calendar to the solar dynamo,鈥� he said. 鈥淗ow is it so wild yet also so orderly?鈥�

Spinning dancers

To find out, researchers first need to know exactly where in the sun the dynamo begins. In the 1990s, scientists proposed that the dynamo emerged roughly 130,000 miles below the sun鈥檚 surface鈥攁 theory nicknamed the 鈥渄ynamo in the deep.鈥�

That notion, however, struggles to explain the order that emerges from the sun鈥檚 chaos. Instead, Vasil, Brown and their colleagues turned to a phenomenon in physics called a 鈥渕agnetorotational instability.鈥� It鈥檚 a sort of imbalance that forms whenever magnetic fields interact with rotating plasmas where those flows move faster as you go deeper.

鈥淚t鈥檚 kind of like dance partners slinging each other around in a spin while holding arms,鈥� Brown said.

Researchers have long examined how this phenomenon arises in the disks of hot gases that circle black holes. Its role in the sun is less clear.听

In the current study, Vasil, Brown and their colleagues ran a series of calculations on computers to study how such an instability could influence the sun鈥檚 activity. They discovered that the process could easily whip up the sun鈥檚 insides to form the solar dynamo and explain how the 11-year cycles start. Those physics would also take place in the outer 10% of the sun, or a paltry 20,000 miles from the surface. The solar dynamo, in other words, might be powerful, but it鈥檚 also a little on the shallow side.听

The researchers have a lot of work to do before they can fully cast off the dynamo in the deep theory. But Brown is hopeful that the study could become its own dynamo鈥攇enerating a wave of new research in the field.

Vasil added that the work is a testament to his colleague and friend, Julien.

As a doctoral student at CU Boulder, 鈥淢y advisors and mentors were Nic Brummell, Juri Toomre and Keith Julien,鈥� Vasil said. 鈥淚 recall first having a 鈥榟uh, that's funny鈥� moment about sun's the near-surface instability one morning in 2004 while flipping through an astrophysics textbook. Keith was the first person I literally ran to tell about it. He was such a fantastic friend all these years. He supported ideas and gave encouragement to a generation of energetic young researchers, like I was back then. It's astonishing he won't be here anymore. But he was thrilled this work happened and was to be published in Nature. The silver lining is that his ideas and personality will live on in the astonishing number of people that he inspired over the years.鈥�