This is an X-ray image of the sun, taken by the soft X-ray telescope onbard the Yohkoh spacecraft. X-rays are produced in the corona of the sun, not at it's surface, so X-ray images of the sun reveal what's happening in the solar atmosphere.

The Yohkoh satellite is an observatory for studying X-rays and gamma-rays from the Sun. Yohkoh is a project of the Institute for Space and Astronautical Sciences, Japan; Yohkoh (the spacecraft) was built in Japan, but the observing instruments have contributions from the U.S. and from Great Britain.