Researchers find what happens when the sun goes to sleep

The sun often appears to be sleeping for decades to centuries. However, it does not rest even during these phases of prolonged slumber, a new study has found.

The sun’s magnetic activity does not shut down during the inactive phases, contrary to previous notions, researchers wrote in their study published in the journal Monthly Notices of the Royal Astronomical Society Letters. 

In the last 10,000 years, the sun has gone to sleep or entered the grand solar minima phase at least 23 times, the scientists found.

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During the grand solar minima, the sun’s activity stays low, lasting decades to centuries. Very few sunspots appear on the surface and the sun’s overall brightness decreases, the researchers said.

Sunspots are strong magnetic regions on the sun known to produce solar storms. These storms can damage satellites, disrupt electric grids on Earth and harm astronauts. They are dominant during the solar maxima when the star is at its most active stage.

The last grand solar minimum occurred in Maunder Minimum (1645–1710). Temperatures across much of the Northern Hemisphere dropped when the sun entered this phase, according to the National Aeronautics and Space Administration. 

“Grand minima phase can influence the global climate,” Chitradeep Saha, a PhD scholar at the Indian Institute of Science Education & Research, Kolkata and one of the study’s authors, told Down To Earth.

It is not currently possible to directly observe the sun’s poles and interiors. So, we do not understand what happens in the sun’s interior during grand minimum phases. “Many people thought the magnetic activity went off in this period,” Saha added.

So, Saha and his colleagues simulated the sun’s solar magnetic cycle in the last 10,000 years. They used data on cosmogenic isotopes, which form when cosmic rays interact with atmospheric molecules on Earth.

Cosmic particles do not accumulate in the Earth’s atmosphere during the sun’s active phase due to extremely fast solar wind, Saha explained.

But when the activity is low, he added, solar wind speed is low, allowing more cosmic particles to deposit on ice cores and tree rings.

Simulation using this data allowed the researchers to explore the “unseen” interior dynamics of the sun.

The simulation showed magnetic activity within the outermost zone of the sun, which stretches from 200,000 km right up to the visible surface or also called convection zone.

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It persists in the form of weak cycles in the convection zone. They are incapable of producing sunspots, the researchers said.

Their simulation also showed that meridional circulation — the motion of the plasma extending from the equator to the poles in the solar convection zone — continues to operate despite the sun’s inactivity.

“The meridional plasma flow threading the solar convection zone continues to function like a clock during grand solar minima,” the researchers wrote in the study.

Saha and his colleagues are examining whether grand solar minima follow a particular pattern.

In 2019, the sun entered its 25 solar cycle. Its activity is expected to peak in July 2025. “There is no possibility of another grand minimum in the near future,” Saha explained.

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