High mass pulsars as hybrid stars: Phase transitions and oscillation modes

Abstract

Recent observations of high-mass pulsars justify the investigation of the internal composition of neutron stars. At the extreme densities relevant to such objects, quantum chromodynamics predicts a phase transition in neutron star matter to deconfined quark matter. However, the nature of this phase transition remains uncertain due to the absence of direct observational evidence. In this work, we investigate the possibility of such a transition inside neutron stars, focusing on the scenario of a first-order phase transition. In particular, we consider the slow conversion of the hadronic phase into the deconfined quark phase. For comparison, we also construct hybrid stars using a continuous Gibbs phase transition description. Our findings indicate that the neutron star structure is significantly influenced by the adopted phase transition model. In the context of gravitational wave observations, we analyze the non-radial f-mode oscillations in high-mass pulsars. We find that these oscillations are sensitive to both the nature of the phase transition and the underlying neutron star structure. Consequently, we explore neutron star oscillations as a potential probe of the internal composition of high-mass pulsars, as these oscillation modes can provide signatures of phase transitions.