Researchers started cataloguing them with the Kepler space telescope a few years ago. They're easy to spot, even on distant stars, since they crank out about 10,000 times more energy than normal flares.
And in a new study published in Nature, researchers say the sun is capable of emitting a superflare of its own — even if that's unlikely.
Most superflares come from stars that are more magnetically active than our home star, but about 10 percent of the superflare examples researchers analyzed came from stars with similar or even weaker fields.
See photos of solar flares:
Solar flares (the sun)
We probably don't need to worry about a solar superflare
The sun emitted a significant solar flare, peaking at 7:28 p.m. EST on Dec. 19, 2014. NASA’s Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. (Photo via NASA/SDO)
On Feb. 24, 2014, the sun emitted a significant solar flare, peaking at 7:49 p.m. EST. NASA's Solar Dynamics Observatory (SDO), which keeps a constant watch on the sun, captured images of the event. These SDO images from 7:25 p.m. EST on Feb. 24 show the first moments of this X-class flare in different wavelengths of light -- seen as the bright spot that appears on the left limb of the sun. Hot solar material can be seen hovering above the active region in the sun's atmosphere, the corona.
Solar flares are powerful bursts of radiation, appearing as giant flashes of light in the SDO images. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however -- when intense enough -- they can disturb the atmosphere in the layer where GPS and communications signals travel. (Photo via NASA/SDO)
The bright flash of an X1.6-class flare can be seen on the right side of the sun in this image captured by NASA's Solar Dynamics Observatory. This image shows extreme ultraviolet light of 131 Angstroms, which highlights the intensely hot material of a flare and which is typically colorized in teal. (Photo via NASA/SDO)
On Oct. 25, 2014, the sun emitted its fifth substantial flare since Oct.19. This flare was classified as an X1-class flare and it peaked at 1:08 p.m. EDT, as seen as a bright flash of light in this image from NASA's SDO. The image shows extreme ultraviolet light in the 131-angstrom wavelength, which highlights the intensely hot material in a flare and which is typically colorized in teal. (Photo via NASA/SDO)
NASA's Solar Dynamics Observatory captured this image of an X2.0-class solar flare bursting off the lower right side of the sun on Oct. 27, 2014. The image shows a blend of extreme ultraviolet light with wavelengths of 131 and 171 Angstroms. (Photo via NASA/SDO)
The bright flash of an M-class flare is seen exploding on the left side of the sun in this image from Nov. 5, 2014. The image was captured by NASA's Solar Dynamics Observatory in extreme ultraviolet light that was colorized in red and gold. (Photo via NASA/SDO)
On Jan. 27, 2012, a large X-class flare erupted from an active region near the solar west limb. X-class flares are the most powerful of all solar events. Seen here is an image of the flare captured by the X-ray telescope on Hinode. This image shows an emission from plasma heated to greater than eight million degrees during the energy release process of the flare. (Photo via JAXA/Hinode)
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The closest thing we've ever seen to a superflare from the sun is probably the Carrington Event.
In 1859, the sun launched a flare so energetic it damaged Earth's ozone layer and set telegraph offices on fire.
Experts say a flare that powerful today could do billions of dollars in long-term damage to satellite networks and electrical transformers. Those aren't the sort of things we keep plenty of spares for.
And Carrington was a relatively weak example compared to the energies involved in superflares.