Extreme solar flares may be surprisingly more frequent than thought, scientists say

Stars like our sun seem to produce superflares once every century

Stars like our sun may eject extremely violent flares about once per century, which is “surprisingly” often, scientists say in a new study.

“We were very surprised that sun-like stars are prone to such frequent superflares,” study first author Valeriy Vasilyev from the Max Planck Institute for Solar System Research in Germany said.

While solar storms today are usually associated with auroras, there is evidence of extremely violent outbursts from the sun, found in prehistoric tree trunks and glacial ice, causing significant damage on the earth.

One such superflare, which struck the plant in 772AD, is recorded in history as “fire in heaven” or “red cross” in the sky. It was apparently as strong as the infamous Carrington event of 1859AD which collapsed early telegraph networks in large parts of Europe and North America.

Artist’s impression of a star exhibiting a superflare as seen in visible light (MPS/Alexey Chizhik)

The frequency of solar superflares remains undetermined as the sun can’t be observed over thousands of years into the past. So researchers turned their attention to the behaviour of stars similar to the sun.

“We can monitor the behaviour of thousands of stars very similar to the sun over short periods,” Sami Solanki, another author of the study, said. “This helps us to estimate how frequently superflares occur.”

Researchers analysed data from 56,450 stars observed by Nasa’s Kepler telescope between 2009 and 2013, totalling 220,000 years of stellar activity.

Researchers ruled out sources of error in their observations such as cosmic radiation, passing asteroids or comets, or another star that may have flared up in the vicinity by chance.

This enabled them to identify 2,889 superflares on 2,527 of the observed stars with surface temperatures and brightness levels similar to the sun.

They concluded that a sun-like star produces a superflare once per century on average.

This contradicts previous research that calculated an average interval of 1,000 or even 10,000 years between solar superflares.

Tree rings of a buried subfossil tree in the Drouzet river (Cécile Miramont)

A growing body of research is finding evidence of violent solar flares deposited in natural archives like tree rings and glacial ice.

Scientists have so far identified five extreme solar particle events, three within the past 12,000 years, suggesting a rate of once every 1,500 years.

However, researchers say more superflares likely occurred on the sun in the past.

Previous studies could not determine the exact source of the observed flares and had to be limited to stars without any close neighbours in the telescope images.

“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,” Ilya Usoskin, another of the study’s authors, explained.

“This requires further investigation.”

The new research is the most precise and sensitive to date, scientists say.

While the latest study does not reveal when the sun will release its next superflare, it urges caution as the planet’s current infrastructure such as satellites are at risk.

“The new data are a stark reminder that even the most extreme solar events are part of the Sun’s natural repertoire,” Natalie Krivova, who was also involved in the study, said.