Sun-like stars emit a gigantic outburst of radiation on average about once every hundred years per star. These superflares are much more powerful than anything we’ve seen before, releasing more energy than a trillion hydrogen bombs combined.
This estimate comes from a study of 56,450 sun-like stars conducted by an international team of researchers led by the Max Planck Institute for Solar System Research (MPS) in Germany. The findings show that earlier studies greatly underestimated these stars’ eruption potential.
Using data from NASA’s Kepler space telescope, the team discovered that sun-like stars experience superflares 10 to 100 times more often than previously thought. This suggests that the Sun may also be capable of similarly powerful eruptions.
The new study aims to learn about our Sun’s long-term behavior. Modern space telescopes observe thousands of stars and track their brightness changes in visible light. Superflares, which release more energy than one octillion joules in a short time, appear in the data as brief, sharp spikes in brightness.
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For this study, the team analyzed the data from 56450 sun-like stars as seen by NASA’s space telescope Kepler between 2009 and 2013. The data offers evidence of 220000 years of stellar activity.
A key part of the study was carefully selecting the stars to include. The researchers focused on stars that were close “relatives” of the Sun, meaning they had similar surface temperatures and brightness. They also ruled out potential errors, like cosmic radiation, passing asteroids or comets, and non-sun-like stars that might flare up near a sun-like star in the Kepler images.
To do this, the team carefully analyzed the images of each potential superflare, which were only a few pixels in size and counted only events that could be linked to one of the selected stars.
The researchers identified 2,889 superflares on 2,527 of the 56,450 observed stars through this method. This suggests that, on average, a sun-like star produces a superflare about once every century.
Coauthor Dr. Allan Sacha Brun of the Commissariat of Atomic and Alternative Energies of Paris-Saclay and the University of Paris-Cité said, “High-performance dynamo computations of these solar-type stars easily explain the magnetic origins of the intense energy release during such superflares.”
A complete picture of a superflare on a star
First author Dr. Valeriy Vasilyev from the MPS said, “We were very surprised that sun-like stars are prone to such frequent superflares.”
Previous surveys by other research groups found that extreme solar events, like superflares, happened on average once every thousand or even ten thousand years. However, these studies couldn’t pinpoint the exact source of the observed flares, so they had to focus on stars with few nearby neighbors in the telescope images. The current study, however, is the most precise and sensitive one to date.
Other studies have also suggested longer time intervals between extreme solar events by looking for signs of violent solar storms that have impacted Earth. When a burst of high-energy particles from the Sun reaches Earth’s atmosphere, they create detectable amounts of radioactive atoms, like the carbon isotope 14C.
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These atoms get trapped in natural archives, such as tree rings and glacial ice. Even thousands of years later, scientists can use modern technology to measure the amount of 14C in these archives to detect past solar storms.
Using this method, researchers identified five extreme solar particle events and three possible candidates from the past 12,000 years of the Holocene. This results in an average occurrence rate of about once every 1,500 years. The most powerful event is believed to have happened in 775 AD. However, there were likely more violent particle events and superflares on the Sun in the past, which haven’t yet been detected.
Coauthor Prof. Dr. Ilya Usoskin from the University of Oulu in Finland pointed out, “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. Looking at the terrestrial evidence of past extreme solar events could, therefore, underestimate the frequency of superflares.”
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The new study does not reveal when the Sun will throw its next fit. However, the results urge caution: Even the most extreme solar events are part of the Sun’s natural repertoire.
Journal Reference:
- Valeriy Vasilyev, Timo Reinhold, Alexander I. Shapiro et al. Sun-like stars produce superflares roughly one per century, Science. DOI: 10.1126/science.adl5441
