An important phenomenon in quantum hadrodynamics is the nuclear force, or residual strong force. It is the force operating between those hadrons which are nucleons – protons and neutrons – as it binds them together to form the atomic nucleus. The bosons which mediate the nuclear force are three types of mesons : pions, rho mesons and omega mesons. Since mesons are themselves hadrons, quantum hadrodynamics also deals with the interaction between the carriers of the nuclear force itself, alongside the nucleons bound by it. The hadrodynamic force keeps nuclei bound, against the electrodynamic force which operates to break them apart (due to the mutual repulsion between protons in the nucleus).