This image of the Sun captured by the Solar and Heliospheric Observatory's MDI instrument shows two large sunspot groups on either side of the Sun's central meridian. Labeled 8882 and 8891 by the NOAA Space Environment Center, these two active regions cover 950 and 990 millionths of the solar disk, respectively. A typical eruption can release the same amount of energy as millions of 100-megaton hydrogen bombs all exploding at the same time. The energy source for solar flares is the Sun's magnetic field. Whenever the magnetic field around a sunspot group becomes twisted and sheared, like a stretched and twisted rubber band, an explosive release of energy could be just around the corner.
Most sunspots come in pairs with a magnetic field that looks somewhat like that of a bar magnet.
The energy stored in the twisted magnetic field lines serves as fuel for solar flares and CMEs. Eruptions occur when the fields rearrange to form a simpler, lower-energy configuration. Anatomy of a solar flare observed by the Yohkoh Soft X-ray Telescope. The explosive release of energy occurs where the magnetic field is twisted above the sunspot. Click for a larger image .