Sun structure. Cutaway illustration showing the inside of the Sun. At the centre is the core, the site of the Sun's nuclear reactions, which fuse hydrogen to form helium. The core is at a temperature of around 15 million Kelvin. Around the core is the radiative zone, where the photons produced in the core collide with charged particles, re-radiating heat and light. Above this is the conductive zone, where hot gas rises to the surface (photosphere) to release energy before falling back to be reheated, forming convection currents. magnetic fields on the surface of the sun inhibit convection, causing some areas to have lower temperatures than others (sunspots). These also cause solar prominences (loops), where charged gas is drawn across areas of opposite polarity. Flares take place in active regions and provoke a sudden increase of the radiative flux emitted from the corona, an aura of plasma that surrounds the sun.