Have you ever wondered what holds matter together? The atomic nucleus hosts protons and neutrons, but they are not its most fundamental constituents. In fact, they consist of elementary particles called quarks, which constantly appear, recombine and disappear. The gluon is yet another elementary particle that plays a key role inside the nucleus: it holds quarks together by mediating the strong interaction. Gluons stabilize the nuclei and form matter as we know it.