This movie taken by NASA'S Galaxy Evolution Explorer shows one of the
largest flares, or star eruptions, ever recorded at ultraviolet
wavelengths. The star, called GJ 3685A, just happened to be in the Galaxy
Evolution Explorer's field of view while the telescope was busy observing
galaxies. As the movie demonstrates, the seemingly serene star suddenly
exploded once, then even more intensely a second time, pouring out in
total about one million times more energy than a typical flare from our
Sun. The second blast of light constituted an increase in brightness by a
factor of at least 10,000.
Flares are huge explosions of energy stemming from a single location on a
star's surface. They are caused by the brief destruction of a star's
magnetic fields. Many types of stars experience them, though old, small,
rapidly rotating "red dwarfs" like GJ 3685A tend to flare more frequently
and dramatically. These stars, called flare stars, can experience powerful
eruptions as often as every few hours. Younger stars, in general, also
erupt more often. One of the reasons astronomers study flare stars is to
gain a better picture and history of flare events taking place on the Sun.
A preliminary analysis of the GJ 3685A flare shows that the mechanisms
underlying stellar eruptions may be more complex than previously believed.
Evidence for the two most popular flare theories was found.
Though this movie has been sped up (the actual flare lasted about 20
minutes), time-resolved data exist for each one-hundredth of a second.
These observations were taken at 2 p.m. Pacific time, April 24, 2004. In
the still image, the time sequence starts in the upper left panel,
continues in the upper right, then moves to the lower left and ends in
the lower right.
The circular and linear features that appear below and to the right of GJ
3685A during the flare event are detector artifacts caused by the extreme
brightness of the flare.