Atomic nuclei are home to protons and neutrons. But sometimes a guest flies in — a particle called the lambda. It's like a neutron, but heavier and with a special property physicists call strangeness. A nucleus with such a guest is called a hypernucleus.
At the MAMI accelerator in Mainz, researchers created the lightest hypernucleus — a triton with a lambda inside. It's unstable and decays quickly: the lambda disappears, and in its place a pion, a light messenger particle, flies out. The physicists measured the pion's momentum with high precision, like a speedometer on a race car.
From the pion's momentum, they could calculate how tightly the lambda was held in the nucleus. It turned out the binding energy is 0.523 MeV, like a grain of sand sticking to a tennis ball with a force that was previously underestimated. Before, they thought the bond was weaker, but now they see that the lambda interacts more strongly with the deuteron (a nucleus made of a proton and a neutron).
This result is like a new, more precise dynamometer for nuclear forces. It forces a rethink of calculations of hyperon-nucleon interactions, which are important for understanding neutron stars, where such particles may be abundant.
Hypernuclei live for less than a billionth of a second, but in that time they manage to tell us about the forces acting inside the atomic nucleus.
In the series 'Star Trek,' 'strange' particles are mentioned as an energy source — hypernuclei with a lambda are indeed part of the strange particle family.