A normally dull star in Ursa Major, the Great Bear constellation, give off an incredible flare while scientists watched, increasing its brightness 15-fold in just three minutes, before returning to normal.
Dubbed WX UMa, the stellar body belongs to a rare class of variable stars known as flare stars, which suddenly and unpredictably boost their brightness in a matter of moments. But the flares are fleeting; these stars revert to their dimmer state in tens of minutes, researchers say.
WX UMa lies in a binary system in Ursa Major roughly 15.6 light years from Earth. It's outshined by a companion star that's 100 times brighter, except during the few times a year when WX UMa gives off luminous flares.
http://www.space.com/21567-flare-star-brighter.html