This is a neutron star. It's core is hypothesized to be made of neutron degenerate matter, also known as neutronium.

Neutronium (n) (also called element zero or neutron degenerate matter) is the name for the element with an atomic number of zero. It's average atomic mass is 1, because it is only ever found naturally, outside of neutron stars, as a lone neutron.

Neutronium and The Periodic Table[]

Neutronium would be the head of the periodic table, as it would be placed in group zero and in period zero. It would be placed in period zero, because it has no electron shells (as it has no electrons). And since it has no electrons or shells , it would have no electrons in its outermost shell.


Neutronium has 2 confirmed isotopes and three unconfirmed isotopes that all have very short half-lives.

Confirmed Isotopes[]

A mononeutron, or 1n is simply a neutron. It has a lifetime of 15 minutes, with a half life of 610 seconds. It undergoes beta decay, and turns into a proton, emitting an electron and an electron neutrino.

A dineutron, or 2n is two unbound neutrons. It was observed during beta decay of beryllium-16. They may not be bound, bur there attraction nearly makes them so.

A tetraneutron, or 4n is four unbound neutrons.

Group Number[]

Neutronium is a noble gas. So it would make sense to put it in the noble gas section above Helium. It would be placed in group 18 period 0.

Unconfirmed Isotopes[]

Unconfirmed isotopes include the trineutron and the pentaneutron. The existence of the trineutron for even a short period of time is doubted.