Constraining the Neutron Star Equation of State

Abstract: Neutron stars are stellar objects of extreme properties. The dense core enables usto study nuclear matter beyond saturation density. The exact composition of matterat such densities is not yet established, but the thermodynamic states of the matteris theoreticized by the Equation of State (EOS). The EOS cannot be derived analyt-ically and is dependent on constraints from neutron stars and nuclear experiments inlaboratories on earth. Recent advances in astrophysical experiments have probed newconstraints on the EOS by studying properties such as mass, radius and tidal deformabil-ity of neutron stars. Especially the possibility to detect gravitational waves from mergingbinary systems by the LIGO/VIRGO collaboration and the mass-radius measurementsby NICER have contributed a great deal. Constraints from terrestrial experiments havebeen derived by studying matter at supra saturation density in Heavy Ion Collisions andby determining the neutron skin thickness. In this work, an overview of neutron stars,dense matter and the EOS is presented. Further, results of studies aiming to determineand constrain the EOS are reviewed. Even though there is consensus about some neutronstar properties among different research groups, there are still major uncertainties as allresult depend on a relatively small set of observational data. Therefore, the EOS can stillbe considered to be far from precise and the knowledge of the true neutron star matterremains undisclosed.