Scientists have found superflares more than 1 million times more powerful than flares generated by the sun occurring on sun-like stars being studied by NASA's Kepler space telescope.
The finding, culled from 120 days of observations of 83,000 stars, is the first to detail how often and how energetic flares on other stars can be.
The discovery, however, raises a question about how the massive outbursts, believed to be caused by complex magnetic interactions, can physically occur.
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Scientists previously theorized a close-flying Jupiter-sized planet would be needed to ground a super-flaring stars' magnetic fits. For the size flares our sun experiences, magnetic reconnection occurs within the sun itself, with one twisted magnetic field snapping and then linking up to another -- releasing energy in the process as a solar flare.
But the 365 superflares found by scientists crunching Kepler data need another explanation, said astrophysicist Bradley Schaefer, with Louisiana State University.
Kepler, whose prime mission is to look for planets transiting the face of their parent stars, should have found big, close-by planets (so-called "hot-Jupiters") circling about 10 percent of the superflaring stars. Instead the team, led by Kyoto University astronomer Hiroyuki Maehara, found none.
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"Maehara's point that the 365 superflares don't show hot-Jupiters is a pretty strong argument against the hot-Jupiter theory," Schaefer told Discovery News. "No one has proposed any alternative."
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Maehara thinks they could be caused by starspots much larger than any sunspot found on the sun.
"However it is not well understood why and how such large starspots are formed on solar-type stars," he wrote in an email to Discovery News.
"This very much is a mystery and a challenge for classic astrophysics," Schaefer said.
Scientists don't believe our sun has ever generated such a superflare. If one had, it likely would have triggered enough chemical change in the atmosphere to set off a mass-extinction of life on Earth. The only mass extinctions in geologic record have been tied to asteroid strikes, volcanic activity and related climatic change.
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Ironically, a superflaring star may be a good place to look for habitable planets, Schaefer adds.
"Superflares might provide the high-energy radiation required to create organic molecules, so perhaps superflare systems are a good place to look for alien life that has evolved to avoid the effects of the huge flares," he said.
The research is published in this week's Nature.