2013 marks the peak of the Sun's 11-year solar activity cycle. The Sun put out several X-class solar flares in October, including this one on October 25. The images for this photo were taken by the Solar Dynamics Observatory at 15:00 UTC through several ultraviolet filters.
The image is composed of an RGB stack of images taken through filters with wavelengths of 211, 193, and 131 nanometers. A fourth image, taken through a 304-nanometer filter, was dropped on top as a transparent overlay to add the granular texture of the solar photosphere.