  Densities in compact stars may be such that quarks are no longer confined in
hadrons, but instead behave as weakly interacting particles. In this regime
perturbative calculations are possible. Yet, due to high pressures and an
attractive channel in the strong force, condensation of quarks in a superfluid
state is likely. This can have interesting consequences for magnetic fields,
especially in relation to the discovery of slow-period free precession in a
compact star. In this proceedings there will be a discussion of the mass-radius
relations of compact stars made from quark matter and magnetic field behaviour
in compact stars with a quark matter core.
