(14) The positrons emitted in the first step of the cycle are annihilated by collisions with electrons. Where did these electrons come from?
The total charge of the sun is 0. Since the charge is balanced, if single protons exist, single electrons must exist as well. The temperature of the sun is so high that elemental hydrogen does not exist in the stellar core. Hydrogen exists in its ionized form, in which the electrons are separated from the atoms. The electrons usually escape in collisions with other high energy particles in the core. The annihilation of the positrons looks like:
