The largest solar flare recorded in nearly five years was triggered by interactions between five rotating sunspots, say researchers who studied observations of the flaring region of the Sun taken by the Solar Dynamics Observatory over a period of five days. The flare occurred at 1.44am on February 15,2011, when the Sun released the largest recorded solar flare since December 2006 and the first flare of the current solar cycle to be classified as the most powerful “X-class”.
“Sunspots are features where magnetic field generated in the Sun’s interior pushes through the surface and into the atmosphere,” said Dr. Daniel Brown from the University of Central Lancashire who presented his team’s the findings at the RAS National Astronomy Meeting in Llandudno, Wales, on Wednesday. “Twisting the Sun’s magnetic field is like twisting an elastic band. At first you store energy in the elastic, but if you twist too much the elastic band snaps, releasing the stored energy. Similarly, rotating sunspots store energy in the Sun’s atmospheric magnetic field. If they twist too much, the magnetic field breaks releasing energy in a flash of light and heat which makes up the solar flare.”
The movie above shows the dynamics of the Sun’s atmosphere over 6 days as seen by SDO, using composite data from two instruments; the surface data is from SDO/HMI, and the atmospheric data (at around 1,000,000 degrees) is from SDO/AIA. The right-hand inset shows a close up of active region 11158 from both of these instruments. The sunspots are seen to emerge and undergo a twisting motion in the solar surface. The response fo the coronal loops in the atmosphere shows rapid brightenings throughout the movie which are the solar flares being released.
Looking at these days of SDO observations that included this flare, Brown found that the active region that flared contained five newly emerged sunspots. All five of the sunspots rotated between 50 and 130 degrees, some in a clockwise and some in an anticlockwise direction, over the five days of observations.
“Rotating sunspots are an extremely efficient way to inject energy into the magnetic field of the Sun’s atmosphere,” said Brown. “With five sunspots rotating at the same time enough energy has been injected into the atmospheric magnetic field to produce the largest solar flare seen for almost 5 years.”
In addition to the large X-class flare, the same region also released over 40 smaller flares during the five days studied.