Superflares are very strong explosions observed on solar-like stars with energy production rates at levels one million times or more that of typical solar-like flares. The stars in this class satisfy conditions which should make them solar analogues, and would be expected to be stable over very long time scales.
A Superflare star is not the same as a Flare star, which usually refers to a very late spectral type red dwarf. The term is restricted to large transient events on stars that satisfy the following conditions:
- The star is in spectral class F8 to G8
- It is on or near the main sequence
- It is single or part of a very wide binary
- It is not a rapid rotator
- It is not exceedingly young
Essentially such stars may be regarded as solar analogues. As of 2000[update], nine superflare stars have been found, some of them similar to the Sun. The energy released during such a flare is 100 times to 10 million times that of the sun's largest coronal mass ejections.
The original paper  identified nine candidate objects from a literature search:
- Groombridge 1830
- Kappa Ceti
- MT Tauri
- Pi1 Ursae Majoris
- S Fornacis
- BD +10°2783
- Omicron Aquilae
- 5 Serpentis
- UU Coronae Borealis
The observations vary for each object. Some are X-ray measurements, others are visual, photographic, spectroscopic or photometric. The energies for the events vary from 2 X 1033 to 2 X 1038 ergs.
Effects of a Hypothetical Superflare
Superflares increase the brightness of the star by up to 20 times its normal brightness and the luminosity by 1,000 times. They may last from a few hours to a week. If the Sun were to release a superflare, it would make a winter day as warm as a summer day. The ozone layer of the Earth might be destroyed by the intense flow of charged particles produced by such a flare, and surface ice would melt on the daylight side of moons as distant from the sun as those of Jupiter, freezing again after the flare faded away. There is no evidence of superflares ever having occurred in the Solar System.
In the film, Knowing (2009), the world was destroyed by a superflare in a story that was loosely based on parts of the Bible.
- Rubenstein, Eric P.; Schaefer, Bradley E. (2000/02). "Are Superflares on Solar Analogues Caused by Extrasolar Planets?". The Astrophysical Journal (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000ApJ...529.1031R&db_key=AST&high=38e0b7728728235: American Astronomical Society) 529 (2): 1031–1033. arXiv:astro-ph/9909187. Bibcode:2000ApJ...529.1031R. doi:10.1086/308326. Lay summary – Groombridge 1830.
- Schaefer, King and Deliyannis [arXiv:astro-ph/9909188 "Superflares on Ordinary Solar-Type Stars"]
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