Probing the neutron star interior and the Equation of State of cold dense matter with the SKA

With an average density higher than the nuclear density, neutron stars (NS) provide a unique testground for nuclear physics, quantum chromodynamics (QCD), and nuclear superfluidity. Determination of the fundamental interactions that govern matter under such extreme conditions is one of the major unsolved problems of modern physics, and - since it is impossible to replicate these conditions on Earth - a major scientific motivation for SKA. The most stringent observational
constraints come from measurements of NS bulk properties: each model for the microscopic behaviour of matter predicts a specific density-pressure relation (its ‘Equation of state’, EOS). This
generates a unique mass-radius relation which predicts a characteristic radius for a large range of
masses and a maximum mass above which NS collapse to black holes. It also uniquely predicts
other bulk quantities, like maximum spin frequency and moment of inertia. The SKA, in Phase
2 and particularly in Phase 2 will, thanks to the exquisite timing precision enabled by its raw
sensitivity, and surveys that dramatically increase the number of sources: 1) Provide many more
precise NS mass measurements (high mass NS measurements are particularly important for ruling
out EOS models); 2) Allow the measurement of the NS moment of inertia in highly relativistic
binaries such as the Double Pulsar; 3) Greatly increase the number of fast-spinning NS, with the
potential discovery of spin frequencies above those allowed by some EOS models; 4) Improve
our knowledge of new classes of binary pulsars such as black widows and redbacks (which may
be massive as a class) through sensitive broad-band radio observations; and 5) Improve our understanding of dense matter superfluidity and the state of matter in the interior through the study
of rotational glitches, provided that an ad-hoc campaign is developed.