g-mode Oscillations in Neutron Stars

by Constantinos Constantinou (Istituto Nazionale di Fisica Nucleare)

Monday May 8, 2023, 2:30 PM → 4:00 PM Europe/Rome

We examine the principal core g-mode oscillation in hybrid stars containing quark matter, implementing both a first-order phase change (in a novel framework that mimics arbitrary surface tension) as well as a crossover (using a recent model inspired by lattice QCD) for the emergence of quarks. 
We compute the properties of the composition-dependent g-mode, employing the Cowling approximation and also linearized perturbative equations of general relativity. We find that stars with a Gibbs mixed phase yield g-mode amplitudes and the associated gravitational energy radiated that dominate over those of crossover stars owing to the distinct behaviors of the equilibrium and adiabatic sound speeds in the two frameworks. Moreover, the Cowling approximation underestimates the g-mode frequency by up to 10% for higher mass stars, depending on the parameters of the nuclear equation of state and how the mixed phase is constructed. We also find that the g-mode frequencies are well described by a linear scaling with the combined lepton and quark fraction in the center of stars. We conclude that should the principal g-mode be excited to sufficient amplitude for detection in a binary merger, its frequency would be a possible indication for the existence of nonnucleonic matter in neutron stars. Finally, we demonstrate that the compositional 
g-mode in a hybrid NS reduces to a discontinuity g-mode at the Maxwell limit.

Constantinou_talk2_cc.pdf