Constraints on Pasta Structure of Neutron Stars from Oscillations in Giant Flares

Abstract

We show that the shear modes in the neutron star crust are quite sensitive to the existence of nonuniform nuclear structures, so-called "pasta". Due to the existence of pasta phase, the frequencies of shear modes are reduced, where the dependence of fundamental frequency is different from that of overtones. Since the torsional shear frequencies depend strongly on the structure of pasta phase, through the observations of stellar oscillations, one can probe the pasta structure in the crust, although that is quite difficult via the other observations. Additionally, considering the effect of pasta phase, we show the possibility to explain the all observed frequencies in the SGR 1806-20 with using only crust torsional shear modes.