APS/Alan Stonebraker

Figure 1: Excitations of the Hoyle state in carbon-$12$ are thought to exist as so-called cluster states in which the six protons and six neutrons aggregate into three alpha particles. Recent experiments provide new evidence for the existence of these states, and may shed light on whether the alpha particles arrange themselves in a triangle, a chain, or other structure, or move more or less freely around each other.