Sun’s largest sunspots may have potential to trigger superflares

The sun is capable of great things. In massive eruptions, it repeatedly hurls particles and radiation into space. This solar bombardment can be dangerous for technical infrastructure on Earth: For example, satellites and transformers in substations can be damaged.

The sun offered an impressive demonstration of its strength in 1859. The solar storm that struck Earth during the so-called Carrington Event was so powerful that auroras were visible as far as the Caribbean, and sparks flew from the receivers in telegraph offices.

But can the sun accomplish even more? Can it rage even more violently and generate so-called superflares? These are bursts of radiation that release more energy than trillions of hydrogen bombs and have so far been observed directly only on distant stars.

Researchers at the Max Planck Institute for Solar System Research (MPS) in Germany and the University of Colorado in the U.S. explore this question in their latest paper, published in the journal Philosophical Transactions of the Royal Society A, and find further evidence of our star’s eruptive skills.

A look at distant stars and into the past

The amount of energy the sun releases during a flare can be measured directly only outside Earth’s atmosphere or determined indirectly from data and images from space probes. Both have been possible only since the beginning of the space age about 70 years ago. There has been no superflare since then. But this period is merely the blink of an eye in the life of our 4.6-billion-year-old star.

“There is some evidence to suggest that the sun, too, can produce superflares at great intervals. However, there is no direct proof,” explained MPS scientist Natalie Krivova, lead author of the new study.

Such clues can be found, for example, by looking at the sun’s peer group, which comprises many thousands of stars. In late 2024, researchers at the MPS were able to show that superflares occur about once a century on stars that resemble the sun in key characteristics.

Natural archives of solar activity also point to our star’s tempestuous nature: Isolated, short-lived and exceptionally strong spikes in the concentrations of radioactive isotopes in historical tree trunks or in ice cores from the Arctic’s permafrost suggest that Earth has repeatedly been exposed to particularly intense bombardment by high-energy solar particles in the past.

It is unclear whether these extreme particle eruptions were accompanied by superflares. A flare itself, no matter how strong, leaves no long-term traces.

“According to the current state of research, extreme particle eruptions and particularly intense flares often—but not always—occur together,” explained MPS scientist Valeriy Vasilyev. He is the lead author of a review article on this topic, also published in Philosophical Transactions of the Royal Society A.

A promising outlier

In their new publication, the research team led by Krivova took a new approach to gauging the sun’s potential for violent activity. They analyzed observational data collected by NASA’s Solar Dynamics Observatory from 2010 to 2016.

The team correlated the amount of energy released by the 300 strongest flares during this period with the size of the corresponding active region on the sun’s visible surface. These are areas where the magnetic field is particularly strong and complex in structure. Active regions are associated with sunspots—dark areas on the sun’s surface—and are considered potential starting points for eruptions.

“Of course, we knew that no superflares had occurred during the observation period,” explained Krivova. “But the statistical relationship we found between the released energy and the size of the active region should hold true for more powerful events as well,” she added.

In a second step, the researchers turned their attention to the largest known sunspots that have ever covered our star. “Sunspots have been systematically and regularly recorded for about 400 years,” said MPS scientist Theodosios Chatzistergos, a co-author of the new study.

They offer us another way to look into the history of our star, he added. Based on the size of the sunspot, the researchers were able to infer the size of the associated active region—and thus the strength of a possible eruption. They were particularly interested in the rare outliers with exceptionally high energy.

The 1947 sunspot benchmark

One of the largest sunspots the sun has displayed since the beginning of systematic solar observations was the large sunspot of April 1947. It covered approximately 0.6% of the visible solar disk; its diameter was about 40 times that of Earth’s. There was no superflare at that time. But the new study shows that a sunspot of this size can trigger a superflare in statistically rare cases.

“Our sun has superflare potential. It can produce massive sunspots that, in principle, can serve as the starting point for the most extreme bursts of radiation,” said Krivova.

Has such a superflare ever actually occurred on the sun? That remains one of our star’s mysteries.

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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