Study Of Bulk Viscosity Of Neutron Stars

The coupling among quarks due to strong interaction is very important for the research of quark gas. Strange quark matter (SQM) can be described as an ideal gas of quasi-particles with effective masses. The effective masses are generated by the interaction of the quarks within the system. Calculation shows that the effective masses are several times larger than the masses do not take the coupling effect into consideration. The effective mass increased very rapidly due to the increase of the coupling constant g. Because the bulk viscosity of the strange quark matter is very sensitive to the masses of strange quarks, the medium effect will affect the bulk viscosity of the strange quark matter greatly.Considering medium effect, calculation on the reaction rate of the weak reaction s + u→u + d was done. It shows that the medium effect has very slight effect on the reaction rate in low temperature (T<10-2MeV). The effect grows larger when the temperature rises. The reaction rate will be in direct proportion to the square of the temperature. The variance amplitude of the reaction rate will increase if coupling constant g increases. But the effect of the coupling constant g to the bulk viscosity will become notable only when the temperature is higher than 10-1MeV. This is due the fact that the medium effect only affect the temperature term. The bulk viscosity of strange quark stars or the neutron stars with quark cores was calculated in two different circumstances (considering the medium effect or do not consider it). Calculations show that the bulk viscosity of the stars remains constant when the relative amplitude is small. The bulk viscosity grows rapidly when the relative amplitude larger than 10-5. I found that the bulk viscosity increase 1-2 magnitudes due to the medium effect than the result calculated in [3] and about 6 times larger than the result calculated in [7] in which the medium effect was partly considered. The bulk viscosity will increase when the coupling constant g increases. The effect to the bulk viscosity of strange quark matter due to temperature rising is also discussed in this article. It shows that the higher temperature produced the larger increase of the bulk viscosity in the case of g≠0 than in the case of g=0.In the end I compare the damping time of the stars (consider the medium effect or do not consider it.). Calculation shows that the relative high amplitude oscillations are damped in fractions of a second. When temperature rises, the damping time of the stars will decrease very rapidly. The damping time of the stars will decrease due to the increase of the coupling constant g. This shows that the medium effect will shorten the damping time of the stars.