The equation of state of nuclear material to explore in the neutron star

A neutron star is considered to be composed of the central region 'core' with the density of equivalent to or several times of nucleus density, and the low-density region called 'crust' surrounding the outside of the core. This paper starts from the basic knowledge of the state equation of uniform nuclear material, and discusses how the state equation of the material constituting neutron star is characterized. It also describes the state equation of the core of neutron star and the maximum mass of neutron star. The maximum mass of neutral star does not reach twice the mass of the sun when considering hyperon, which poses a question called 'hyperon puzzle.' Finally, this paper refers to the neutron star crust, and explains the shape and size of the aggregation formed by nucleons themselves that can be regarded as 'nuclei' in the region close to the inner core. (A.O.)