  Matter at intermediate baryon densities and low temperatures is notoriously
hard to tackle theoretically. Whereas lattice methods cannot cover more than
rather small densities, perturbative methods are only applicable at much higher
densities. The regime of intermediate chemical potential at low temperatures in
the QCD-phase diagram is therefore out of reach of first-principle methods,
thus we have to rely on stellar objects to investigate dense nuclear and quark
matter at low temperatures. Compact stars can serve as an unique laboratory for
this regime. Due to their fast rotation and high magnetic field, phenomena like
hydrodynamic instabilities and the formation of vortices/flux tubes become of
phenomenological interest. In my thesis, I investigate these multicomponent
systems in a consistent multi-fluid treatment. By starting from a
fieldtheoretical, bosonic model, the phase structure of a two-fluid system,
e.g. consisting of superfluid neutrons and superconducting protons, is
explored. Consequently, hydrodynamic instabilities, which might serve as
trigger for pulsar glitches, are calculated for these two-fluid systems. By
incorporating a gauge field and taking into account the charge of one scalar
field, the influence of a superfluid on the magnetic phase structure of a
superconductor is studied. In the last part, color superconducting quark
matter, which can effectively be described as a multicomponent
(color-)supercondcutor, is investigated.
