Studies On Properties Of Strange Stars

The conjecture that strange quark matter (SQM) may be the true groundstate of the quantum chromodynamics (QCD) vacuum was proposed nearly threedecades ago. The possible existence of strange stars has attracted manyauthors. It was assumed that all pulsars are strange stars which arecomposed of strange quark matter. If this assumption is proven, bulkquarks are found naturely. In this thesis, the following aspects ofstrange stars have been studied.Firstly, we have discussed the bulk viscosity of strange stars. Thebulk viscosity of interacting strange quark matter is calculated in thelight of strange quark mass dependent on the reaction rate of u + s <->d + u. Based on this, we rederive the bulk viscosity of interacting strangequark matter. The extra pressure terms comes from the interaction betweenquarks are included. If the temperature is lower than 0.01MeV, our resultsare 50% smaller than the un-consistent one and one order of magnitude morethan the results which do not consider the medium effects. If thetemperature is higher or equal to 0.01 MeV, our results are 30% smallerthe un-consistent one and twice more than the results which do not considerthe medium effects.Secondly, we have studied the thermodynamics of strange quark matterwith density dependent bag constant self-consistently in the frameworkof the general ensemble theory and the MIT bag model. In our treatment,an extra pressure term is derived in the expression of pressure. With theadditional term, the zero pressure locates exactly at the lowest energystate, indicating that our treatment is a self-consistently thermodynamictreatment. The self-consistently thermodynamic equations of state (EOS)of strange quark matter in both the normal and color-flavor-locked (CFL) phase are derived. They are both softer than the inconsistent ones.Strange stars in both of the normal and CFL phase have smaller masses andradii in our treatment. It is interesting to find that the energy densityat a star surface in our treatment is much higher than that in theinconsistent treatment for both phases. Consequently, the surfaceproperties and the corresponding observational properties of strangestars in our treatment are different from those in the inconsistenttreatment.Finally, we have compared the effects of self-consistent with theunself-consistent results on the electrosphere of a bare strange star indensity denpendent bag model. It is found that the electric field obtainedby the self-consistent EOS is larger than the electric field obtained bythe unself-consistent EOS about 12-20%. The corresponding electron numberdensity increases about 17-20%. Then we discuss the effects of densitydependent parameters on the structure of the electrosphere of a barestrange star. It is found that the main differences in the structures ofthe electroshpere for different parameters lie in 200 fm from the surface.The largest deviations in the electric field between those models areabout 30-50% on the star surface.