Superflare
Since superflares can occur on stars apparently equivalent in every way to the Sun, it is natural to ask if they can occur on the Sun itself. An estimate based on the original Kepler photometric studies suggested a frequency on solar-type stars (early G-type and rotation period more than 10 days) of once every 800 years for an energy of 10 erg and every 5000 years at 10 erg. One-minute sampling provided statistics for less energetic flares and gave a frequency of one flare of energy 10 erg every 5–600 years for a star rotating as slowly as the Sun; this would be rated as X100 on the solar flare scale. This is based on a straightforward comparison of the number of stars studied with the number of flares observed. An extrapolation of the empirical statistics for solar flares to an energy of 10 erg suggests a frequency of one in 10,000 years.
Kappa1 Ceti
According to recent hypotheses, unusually intense stellar flares from a solar twin star could be caused by the interaction of the magnetic field of a giant planet in tight orbit with that star's own magnetic field. Some Sun-like stars of spectral class F8 to G8 have been found to undergo enormous magnetic outbursts to produce so-called superflares (coronal mass ejections) that release between 100 and 10 million times more energy than the largest flares ever observed on the sun, making them brighten briefly by up to 20 times. In 1998, nine Solar twin stars (including Kappa Ceti) were observed to have produced superflares, on average, about once per century. None of these stars rotate particularly fast, have close binary companions, or are very young. Previously, such large flares had not been observed in solar-type main sequence stars, although they are common in a group of dim main-sequence, reddish M dwarfs known as flare stars.