Russian scientists claim the existence of 4-neutron atoms.

Тетранейтрон

Тетранейтрон
© Андрей Широков, МГУ имени М.В. Ломоносова

In the event that these "atoms", deprived of protons, really exist, this would fully explain the mystery of the existence of neutron stars - clusters of matter consisting of neutral particles and mysteriously preserving their stability.

Scientists from the Research Institute of Nuclear Physics at Moscow State University assume that a hypothetical 4-neutron atom, or "tetetayutron," can exist at much lower energies than previously thought, and expect to find it in the course of further research.

 

 

Source: http://onlinelibrary.wiley.com/doi/10.1002/adma.201606034/full