Adiabatic index of dense matter and damping of neutron star pulsations

The adiabatic index Gamma(1) for perturbations of dense matter is studied under various physical conditions which can prevail in neutron star cores. The dependence of Gamma(1) on the composition of matter (in particular, on the presence of hyperons), on the stellar pulsation amplitude, and on the baryon superfluidity is analyzed. Timescales of damping of stellar pulsations are estimated at different compositions, temperatures, and pulsation amplitudes. Damping of pulsations by bulk viscosity in the neutron-star cores can prevent the stars to pulsate with relative amplitudes greater than or similar to (1-15)% (depending on the composition of matter).