Sun-like stars release massive superflares every 100 years

The Sun, our life-giving star, has a reputation for being temperamental. This year alone, unusually strong solar storms have dazzled the world with auroras at unexpectedly low latitudes. But how furious can our star become?

Evidence of the most violent solar “tantrums” – superflares – lies hidden in prehistoric tree trunks and millennia-old glacial ice.

However, these indirect sources leave us unable to determine the frequency of such events. Direct measurements, available only since the space age began, provide a limited perspective.

Superflares of sun-like stars

A recent study offers a fresh approach: studying stars similar to our Sun to better understand its long-term behavior.

By observing thousands of sun-like stars with space telescopes, an international team of researchers set out to estimate how often superflares occur.

“We cannot observe the Sun over thousands of years,” explained Dr. Sami Solanki, director at the Max Planck Institute for Solar System Research (MPS).

“Instead, however, we can monitor the behavior of thousands of stars very similar to the Sun over short periods of time. This helps us to estimate how frequently superflares occur.”

Finding the Sun’s stellar relatives

The researchers, in collaboration with NASA’s Kepler mission, analyzed data from 56,450 sun-like stars observed between 2009 and 2013. These observations covered an astounding 220,000 years of stellar activity.

“In their entirety, the Kepler data provide us with evidence of 220,000 years of stellar activity,” said Dr. Alexander Shapiro from the University of Graz.

To ensure accuracy, the researchers selected stars closely resembling the Sun in surface temperature and brightness. They meticulously excluded errors caused by cosmic radiation, passing asteroids, or comets, and ensured that flares were reliably attributed to sun-like stars.

This rigorous process identified 2,889 superflares on 2,527 stars. On average, each sun-like star produced a superflare about once per century.

“High performance dynamo computations of these solar-type stars easily explain the magnetic origins of the intense release of energy during such superflares,” noted Dr. Allan Sacha Brun of the University of Paris-Cité.

Unexpected frequency of star superflares

The findings were unexpected. “We were very surprised that sun-like stars are prone to such frequent superflares,” said study first author Dr. Valeriy Vasilyev from the MPS.

Earlier surveys had suggested much longer intervals between such events – ranging from 1,000 to 10,000 years.

The superior precision of this study clarified uncertainties in earlier research, which often struggled to pinpoint flare sources due to neighboring stars in telescope images.

Extreme solar particle events

Past studies of extreme solar events on Earth also hinted at less frequent occurrences of superflares.

By analyzing radioactive isotopes like carbon-14 in tree rings and glacial ice, researchers have identified five extreme solar particle events over the last 12,000 years.

The most violent occurred in 775 AD, with an estimated average interval of 1,500 years. However, this data may underestimate the true frequency of superflares.

“It is unclear whether gigantic flares are always accompanied by coronal mass ejections and what is the relationship between superflares and extreme solar particle events. This requires further investigation,” noted Dr. Ilya Usoskin from the University of Oulu.

The current study suggests that evidence from terrestrial sources might miss many solar superflares.

Implications for space weather

While the study on sun-like stars doesn’t predict when the next superflare might occur, it highlight the need for vigilance.

“The new data are a stark reminder that even the most extreme solar events are part of the Sun’s natural repertoire,” said Dr. Natalie Krivova from the MPS.

The Carrington Event of 1859, one of the most powerful solar storms in history, caused widespread telegraph failures in Europe and North America. Its associated flare released only a fraction of the energy of a superflare.

Today, a similar event would endanger satellites and modern infrastructure, highlighting the importance of accurate forecasting.

Preparing for the Sun’s unpredictable behavior

ESA’s upcoming space mission, Vigil, aims to improve solar storm forecasting. Set to launch in 2031, the probe will monitor the Sun’s activity from a vantage point in space, offering early warnings of potential solar storms.

The MPS is currently developing the Polarimetric and Magnetic Imager for Vigil, which will help detect processes that drive dangerous space weather. With this technology, humanity could better prepare for the Sun’s unpredictable “fits.”

Superflares, while rare, remain a possibility for our Sun. Understanding their frequency and impact is critical for safeguarding our technological civilization.

This remarkable study on sun-like stars and their superflares opens new doors to forecasting space weather and mitigating the risks posed by our temperamental star.

The study is published in the journal Science.

Image Credit: MPS/Alexey Chizhik

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