Neutron stars apparently have an outer shell of iron, but it is iron like no Earth iron, an iron of 4 orders of magnitude greater density. During the catastrophic collapse of stellar material in the core of a star destined to become a neutron star, gaseous nuclear matter is believed to condense to the liquid phase. A giant nucleus, or neutron star, is formed in this nuclear phase transition. In order to understand the formation of neutron stars and black holes, it is essential to know the conditions under which nuclear matter changes from the gas phase to the liquid phase. In the case of the neutron star, the only accessible approach is to study the reverse process, the expansion and vaporization of heavy atomic nuclei, which approach a neutron star's density and, in the intranuclear domain, share many of its fluid properties.
Various tests distinguish between the extremes of boiling and shattering.
The major task is now to make a quantitative connection between the data and nuclear compressibility, in particular the nuclear compressibility of the core of neutron stars and black holes.