Constraining equation of state groups from $g$-mode asteroseismology

Abstract

Buoyancy-restored modes inside neutron stars depend sensitively on both the microphysical (e.g., composition and entropy gradients) and macrophysical (e.g., stellar mass and radius) properties of the star. Asteroseismology efforts for g-modes are therefore particularly promising avenues for recovering information concerning the nuclear equation of state. In this work it is shown that the overall low-temperature g-space consists of multiple groups corresponding to different classes of equation of state (e.g., hadronic vs. hybrid). This is in contrast to the case of pressure-driven modes, for example, which tend to follow a universal relation regardless of microphysical considerations. Using a wide library of currently-viable equations of state, perturbations of static, stratified stars are calculated in general relativity to demonstrate in particular how g-space groupings can be classified according to the mean mass density, temperature, central speed of sound, and tidal deformability. Considering present and future observations regarding gravitational waves, accretion outbursts, quasi-periodic oscillations, and precursor flashes from gamma-ray bursts, it is shown how one might determine which group the g-modes belong to.

Impact of the equation of state on $f$- and $p$- mode oscillations of neutron stars

“…In this work, we approximate this speed of sound with the equilibrium sound speed c 2 eq = dp/dε. Generally, c 2 ad is usually slightly larger than the equilibrium sound speed c 2 eq due to lag in weak equilibrium [38,39], and temperature equilibrium [40,41].…”