It would be make for an impressive doomsday. One moment, here we are gardening or walking to lunch in the mellow light of a spring Sun, and the next moment said Sun has shredded Earth's atmosphere and twisted up our power grids, radio communications, GPS, and most anything else electrical. And it would all stay twisted for some time because what we're talking about isn't just a bad solar storm but a full-on superflare. Life on Earth would be jeopardized.
A superflare is a solar eruption expected to be up to 10,000 times more powerful than the largest observed solar storm of the modern era: the Carrington event. Said event, which took place in 1859, wrecked havoc on the worldwide telegraph system, and, according to ice core records from Greenland, caused significant damage to the planet's ozone layer. Nonetheless, the intensity of the Carrington event is just a tiny fraction of what astronomers now know some stars to be capable of.
Since the 2012 discovery of widespread superflare phenomena among distant stars, courtesy of data collected aboard the Kepler space observatory, astronomers have wondered if the same thing could happen right here in our Solar System. Now, researchers from Aarhus University in Denmark have reached the conclusion that, yes, the Sun is indeed capable of producing a superflare. While its magnetic field is generally much weaker than those stars most likely to produce a superflare, some lesser stars still do manage to produce destructive superflares.
The deeper question the researchers sought to answer is whether or not superflares are produced by the same mechanism as solar flares, which would indicate the possibility of superflares being produced by our Sun. We know that solar flares, sudden eruptions of magnetic energy, arise as the result of collapsing magnetic fields on the surfaces of stars—events triggered by one of several possibilities, including interactions from planets and other stars—so the group examined magnetic field data collected on some 100,000 stars via the Guo Shou Jing telescope in China.
Most of the superflare-producing stars had much stronger magnetic fields than the Sun, which indicates that a superflare here is unlikely. But there is still a minority of stars out there (about 10 percent) with comparable magnetic fields to our stellar neighbor, according to the current paper. This indicates that at the very least it is not impossible that a superflare could occur here.
"Based on activity measurements of 5,648 solar-like stars, including 48 superflare stars, we show that superflare stars are generally characterized by higher activity levels than other stars, including the Sun," the Aarhus group reports. "However, superflare stars with activity levels lower than, or comparable to, the Sun do exist, but none of the stars hosting the largest superflares show activity levels lower than the Sun."
The research supports an earlier theory that Earth has indeed been subject to a small superflare in its relatively recent history. This occurred in 775 AD and is evidenced by Japanese tree ring data. At the upper limit, this event would have been 10 to 100 times more powerful than the largest solar flare activity witnessed in the space age. This upper limit coincides nicely with the theoretical limit inferred from sunspot activity observed on the Sun. To produce a really big ass superflare, it would take a sunspot, a zone of magnetic field flux on a star's surface, at least 30 percent of the total radius of the star.
Given this sunspot limitation, it's reasonable to say that we're pretty safe for the time being. It would seem, however, that this safety is provisional rather than guaranteed.