Determinations of neutron star masses, radii and quadrupole moments allow a good determination of the equation of state (EOS) for low temperature high baryon density baryonic matter.
The degrees of freedom become relativistic at a few times nuclear matter density. This suggests that quarks are the important degrees of freedom. I argue that such a very rapid transition to a relativistic system of quarks is expected for Quarkyonic matter. Quarkyonic matter may be thought of as confined degrees of freedom near a Fermi surface surrounding a filled Fermi sea of quarks. I motivate and explain this.