In addition to bonding quarks together to form hadron particles, gluons also provide the force that holds the hadrons themselves together. Specifically, gluons are what cause the protons and neutrons together within an atomic nucleus, overcoming the intensity of the electric repulsion between the positive charges within the nucleus of an atom. Because the electrical repulsion is governed by the inverse-square law, it is incredibly powerful at short distances ... which means that the strong nuclear force has to be even more powerful at these short distances within the nucleus (thus the name "strong nuclear force").
Properties of a Gluon
A gluon has a spin of 1, which makes it a boson. According to the theory of quantum chromodynamics, a gluon has 0 mass and electrical charge, which is consistent with the limits of experimental evidence observed thus far.
Gluons are represented in Feynman diagrams by spirals.
History of the Gluon
In 1965, physicists suggested that quarks (the parts that made up hadrons) could interact through gauge bosons, called gluons. However, there was no direct experimental evidence of this until a 1979 result at the Positron-Electron Tandem Ring Accelerator (PETRA) particle accelerator in Hamburg, Germany. Further evidence over the years since has supported this interpretation of quantum chromodynamics.