Metallic hydrogen

If hydrogen is sufficiently compressed then it will undergo a phase change and Metallic Hydrogen will result. Metallic hydrogen is an example of degenerate matter. It consists of a lattice of atomic nuclei (namely protons) with a spacing that is significantly smaller than a Bohr radius, indeed more comparable with an electron wavelength. The electrons are unbound and behave like the conduction electrons in a metal.

Popular models of the planet Jupiter hold that its core is rich in metallic hydrogen.