Collaboration: Part of the research team that participated in the experiment. (Courtesy: G. Otto, GSI/FAIR) Signs of an exotic atom-like system made up of a neutral meson bound to an atomic nucleus via the strong interaction have emerged in experimental data from two international collaborations. If confirmed, this hitherto unobserved system could shed light on the origins of hadron masses and provide new insights into the fundamental symmetries of quantum chromodynamics in nuclear matter. The strong interaction is one of the four fundamental forces of nature, alongside gravity, electromagnetism and the weak interaction. It is responsible for binding quarks into hadrons, which are three-quark particles such as protons and neutrons, and for holding protons and neutrons together within atomic nuclei.…