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The sun has a powerful magnetic field that creates sunspots on the star’s surface and unleashes solar storms like the one that bathed much of the planet in beautiful auroras this month.
But exactly how that magnetic field is generated in the sun is a puzzle that has puzzled astronomers for centuries, dating back to the time of the Italian astronomer Galileo. who made the first observations of sunspots in the early 17th century and noted how they varied over time.
Researchers behind an interdisciplinary study have put forward a new theory in a report published Wednesday in the journal Nature. Unlike previous research that assumed the Sun’s magnetic field comes from deep within the celestial body, they suspect its source is much closer to the surface.
The model developed by the team could help scientists better understand the 11-year solar cycle and improve the prediction of space weather, which can disrupt GPS and communications satellites and dazzle night sky observers with auroras.
“This work proposes a new hypothesis about how the Sun’s magnetic field is generated, which better fits solar observations and, we hope, could be used to make better predictions of solar activity,” says Daniel Lecoanet, assistant professor of engineering and applied science. mathematics at Northwestern University’s McCormick School of Engineering and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics.
“We want to predict whether the next solar cycle will be particularly strong, or perhaps weaker than normal. “The previous models (assuming the Sun’s magnetic field is generated deep within the Sun) have failed to make accurate predictions or determine whether the next solar cycle will be strong or weak,” he added.
Sunspots help scientists track the sun’s activity. They are the starting point of the explosive eruptions and eruptions that release light, solar material and energy into space. The recent solar storm is evidence that the sun is approaching ‘solar maximum’ – the point in its eleven-year cycle when the highest number of sunspots occur.
“Because we think that the number of sunspots corresponds to the strength of the Sun’s magnetic field, we think that the eleven-year sunspot cycle reflects a cycle in the strength of the Sun’s internal magnetic field,” says Lecoanet.
It is difficult to see the sun’s magnetic field lines, which run through the solar atmosphere and form an intricate web of magnetic structures that are much more complex than Earth’s magnetic field. To better understand how the sun’s magnetic field works, scientists are turning to mathematical models.
In a scientific first, the model Lecoanet and his colleagues developed took into account a phenomenon called torsional oscillation: magnetically driven gas and plasma flows in and around the sun that contribute to the formation of sunspots.
In some areas the rotation of this solar feature speeds up or slows down, while in other areas it remains stable. Like the 11-year solar magnetic cycle, torsional oscillations also undergo an 11-year cycle.
“Solar observations have given us a good idea of how material moves within the sun. For our supercomputer calculations, we solved equations to determine how the magnetic field in the Sun changes due to the observed movements,” Lecoanet said.
“No one had done this calculation before because no one knew how to do the calculation efficiently,” he added.
The group’s calculations showed that magnetic fields could be generated about 20,000 miles (32,100 kilometers) below the sun’s surface—much closer to the surface than previously thought. Other models had suggested it was much deeper: about 209,200 kilometers.
“Our new hypothesis provides a natural explanation for the torsional oscillations missing in previous models,” Lecoanet said.
An important breakthrough was the development of new numerical algorithms for performing the calculations, according to Lecoanet. The paper’s lead author, Geoff Vasil, a professor at the University of Edinburgh in the United Kingdom, came up with the idea 20 years ago, Lecoanet said, but it took more than a decade to develop the algorithms and there was requires a powerful NASA supercomputer. the simulations.
“We used approximately 15 million CPU hours for this study,” he said. “That means if I had tried to do the calculations on my laptop, it would have taken me about 450 years.”
In a commentary published alongside the study, Ellen Zweibel, a professor of astronomy and physics at the University of Wisconsin-Madison, said the initial results were intriguing and would help inform future modeling and research. She was not involved in the investigation.
Zweibel said the team had “added a provocative ingredient to the theoretical mix that could prove key to unraveling this astrophysical enigma.”