Ordinary baryons (composite fermions) contain three valence quarks or three valence antiquarks each. Collisions between particles were too energetic to allow quarks to combine into mesons or baryons. Particles are sorted into groups as mesons or baryons. The nuclear force acts between hadrons, known as mesons and baryons. D mesons (), charmed Sigma baryons (), and other charmed particles. Like all conventional baryons, they contain three quarks. Protons and neutrons are examples of baryons; pions are an example of a meson. As in the case of mesons and baryons, glueballs would be QCD color charge neutral. Being baryons, all hyperons are fermions. Baryons (protons and neutrons) make up ordinary stars and planets. In short, matter, as defined in physics, refers to baryons and leptons. The relative abundances depend on a single parameter, the ratio of photons to baryons. This overdense region contains dark matter, baryons and photons. The lightest baryons are the proton and the neutron. Before recombination, the Universe consisted of a hot, dense plasma of electrons and baryons.