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The Sun has a strong magnetic field similar to solar storms, which create sunspots on the star’s surface and cover much of the planet in beautiful auroras this month.
But exactly how this magnetic field is generated inside the sun is a puzzle that has vexed astronomers for centuries, dating back to the time of Italian astronomer Galileo, who made the first observations of sunspots in the early 1600s and noticed how they changed over time. .
Researchers behind an interdisciplinary study put forward a new theory in a report published Wednesday in the journal Nature. Unlike previous research that assumed the Sun’s magnetic field originates deep within the celestial body, they suspect the 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 space weather forecasts that can disrupt GPS and communications satellites and dazzle night sky watchers with auroras.
“This study proposes a new hypothesis for how the sun’s magnetic field is generated that better matches solar observations, and we hope it can be used to make better predictions of solar activity,” said Daniel Lecoanet, assistant professor of engineering sciences. He is a member of the Center for Interdisciplinary Research and Research in Mathematics and Astrophysics at Northwestern University’s McCormick School of Engineering.
“We want to predict whether the next solar cycle will be particularly strong or weaker than usual. Previous models (assuming the solar magnetic field is generated deep within the Sun) were unable to make accurate predictions or (determine) whether the next solar cycle will be strong or weak,” he said. added.
Sunspots help scientists track the sun’s activity. These are the starting point for explosive flares and launch events that release light, solar material, and energy into space. The latest solar storm is evidence that the sun is approaching its “solar maximum,” the point at which there are the largest number of sunspots in its 11-year cycle.
“Since we think the number of sunspots matches the strength of the Sun’s magnetic field, we think the 11-year sunspot cycle reflects a cycle in the strength of the Sun’s internal magnetic field,” Lecoanet said.
Modeling the sun’s magnetic field
The Sun’s magnetic field lines are difficult to see as they travel through the Sun’s atmosphere, forming a complex network of magnetic structures much more complex than the 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 developed by Lecoanet and colleagues explained a phenomenon called torsional oscillation; Magnetically driven flows of gas and plasma in and around the sun that contribute to sunspot formation.
In some regions the rotation of this solar feature accelerates or slows down, in others it remains constant. Like the 11-year solar magnetic cycle, torsional oscillations experience an 11-year cycle.
“Solar observations gave us a good idea of how matter moves inside the Sun. For our supercomputing calculations, we solved equations to determine how the magnetic field on the Sun changes due to the observed motions.” said Lecoanet.
“No one had ever done this calculation before because no one knew how to perform 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 assumed. Other models suggested it was much deeper; approximately 130,000 miles (209,200 kilometers).
“Our new hypothesis provides a natural explanation for torsional oscillations that was missing in previous models,” Lecoanet said.
‘Astrophysical mystery’
Lecoanet said a key breakthrough was developing new numerical algorithms to carry out calculations. Lecoanet said the paper’s lead author, Geoff Vasil, a professor at the University of Edinburgh in the United Kingdom, came up with the idea about 20 years ago, but it took more than 10 years to develop the algorithms and required a powerful NASA supercomputer to run the idea. simulations.
“We used approximately 15 million CPU hours for this research,” he said. “This means that if I tried to do the calculations on my laptop, it would take me about 450 years.”
The initial results are intriguing and will help inform future models and research, Ellen Zweibel, a professor of astronomy and physics at the University of Wisconsin-Madison, said in a commentary published alongside the study. She did not participate in the research.
Zweibel said the team added “a provocative component to the theoretical mix that could be the key to solving this astrophysical mystery.”
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