Exotic phases of matter in compact stars

Sammanfattning: Astrophysical observations constitute an increasingly important source of information, thanks to the high resolution of present and near-future terrestrial and orbiting observatories. Especially, the properties of matter at low temperatures and extremely high densities can only be studied by observations of compact stellar objects. Traditionally, astrophysicists distinguish between three different types of compact objects. These are white dwarfs, neutron stars, and black holes. Neutron stars are presumably unique astrophysical laboratories for a broad range of physical phenomena. Examples are exotic phases of matter at super-nuclear densities and hypothetical new states of matter, e.g., superconducting quark matter. This Licentiate thesis treats a subset of the exotic phases of matter that could exist in compact stellar objects. In particular, a model of three-flavour colour superconducting quark matter is derived and a signature for a new state of matter is suggested. The former is an effective so-called Nambu-Jona-Lasinio model of quark matter at high densities, which incorporates local colour and electric charge neutrality, as well as self consistently determined quark masses and superconducting condensates. The phase diagram of three-flavour colour superconducting quark matter is presented and the effect of superconducting condensates on the possible configurations of compact stars is discussed. In the second part of the thesis, it is shown that a hypothetical class of particles, so-called preons, which might be the building blocks of quarks and leptons, could allow for a new class of compact objects, preon stars. The properties of preon stars are estimated and potential methods to observe them are discussed.