Radial Oscillations in Hybrid Stars with Slow Quark Phase Transition

TL;DR

This paper explores how slow phase transitions at the hadron-quark interface affect the stability and oscillation frequencies of hybrid neutron stars, revealing the existence of stable configurations beyond the maximum mass.

Contribution

It introduces the concept of Slow Stable Hybrid Stars (SSHSs) and analyzes their stability considering slow phase transitions and different equations-of-state models.

Findings

Maximum mass occurs before the fundamental mode's frequency decreases.

Stable hybrid star configurations can exist beyond the maximum mass.

The length of the SSHS branch depends on energy density jump and quark EoS stiffness.

Abstract

This study investigates the radial oscillations of hybrid neutron stars, characterized by a composition of hadronic external layers and a quark matter core. Utilizing a density-dependent relativistic mean-field model that incorporates hyperons and baryons for describing hadronic matter, and a density-dependent quark model for quark matter, we analyze the ten lowest eigenfrequencies and their corresponding oscillation functions. Our focus lies on neutron stars with equations-of-state involving N, N + $\Delta$, N + H, and N + H + $\Delta$, featuring a phase transition to quark matter. Emphasizing the effects of a slow phase transition at the hadron-quark interface, we observe that the maximum mass is attained before the fundamental mode's frequency decreases for slow phase transitions. This observation implies the stability of stellar configurations with higher central densities than the maximum mass, called Slow Stable Hybrid Stars (SSHSs), even under small radial perturbations. The length of these SSHS branch depends upon the energy density jump between two phases and the stiffness of the quark EoS.