As we all know, stars are run by the process of nuclear fusion at the core of the star, but this is not all simple as it sounds. The nuclear reaction which takes place at the stars is known as a Proton-Proton Chain (PP Chain). The steps are as follows:

1. Two protons fuse, in this process a proton changes into a neutron, thus forming a deuteron. A neutrino (a very small mass particle) and a positron (antimatter particle pair for an electron) are formed as a by-product in this step.

2. Then, two deuterons fuse to form Helium - 3 nuclei (two protons and one neutron). Gamma rays are released as a by-product.

3. Finally, two helium - 3 nuclei fuse to form a stable helium - 4 nucleus (two protons and two neutrons). In this process, two protons are released.

These are the steps in a PP Chain nuclear fusion reaction that takes place at the cores of stars. Energy is released in the form of photons and electromagnetic radiation is based on the difference between the binding energy of the products and reactants.