arXiv subjects

Zoey Zhiyuan Dong

Publications and source records attributed to Zoey Zhiyuan Dong.

3 recordsLinked to original sources

arXiv2026

Hybrid-star asteroseismology across sharp phase interfaces: Slow and rapid conversion in the $f$- and $p_1$-mode spectra

First-order phase transitions in neutron-star interiors can leave signatures in the polar quasi-normal-mode spectrum. We compute the complex quadrupolar $f$- and $p_1$-mode spectra in full general relativity for cold, nonrotating hybrid stars with a sharp hadron--quark interface. We model the equation of state by matching a hadronic SLy4 phase to a constant-sound-speed quark-phase. We compare slow phase conversion, in which fluid elements retain their phase and the interface moves with the fluid, with rapid phase conversion, in which matter changes phase as it crosses the boundary and the interface follows phase equilibrium rather than the fluid, together with an algebraic interpolation between these limits. On identical equilibrium backgrounds, the two physical limits produce a sizable separation in the real part of the $p_1$-mode frequency. This $p_1$ frequency separation is largest when the local tangential-displacement fraction of the eigenfunction changes rapidly across the interface. Across the surveyed EOS parameter space, rapid conversion generally lowers the $p_1$-mode frequency relative to slow conversion, with compactness-averaged separations reaching $\sim3.5\,{\rm kHz}$ on disconnected twin-star branches. The largest separations occur at relatively low transition pressures and large density discontinuities. By contrast, the $f$-mode is only weakly affected by the interface condition for individual stellar models. Across the sampled constant-sound-speed parameter space, departures exceeding the hadronic SLy4 reference residual occur mainly at low transition pressure, large density discontinuity, or both, with different boundaries for the real- and imaginary-part fitting variables. Thus, the $p_1$-mode probes the local interface response, whereas the tracked $f$-mode reflects the global departure of the hybrid sequence from the hadronic calibration.

gr-qc↗

arXiv2025

New modeling for hybrid stars with an elastic quark core

Heavy neutron stars may contain solid quark cores as motivated by, e.g. the crystalline color superconducting phase, forming elastic hybrid stars (HSs). Many previous studies assumed an elastic core to be unsheared for the background, static and spherically symmetric configuration, and introduced shear deformation only at a perturbative level. This study relaxes this assumption and explores the influence of non-linear elasticity on the static, spherically symmetric structure of elastic HSs within a fully relativistic elasticity framework. Such a framework effectively introduces anisotropic pressure within the quark matter core due to elasticity. The quark core is modeled using a quasi-Hookean equation of state (EOS) with shear contributions, while the nuclear matter envelope is treated as a perfect fluid. We find that including elasticity increases the maximum mass of HSs by several percent. This enhancement allows some soft EOSs to satisfy current observational constraints. However, since the effects of elasticity are primarily concentrated in the high-mass regime, the current observational constraints are insufficient to distinguish whether an elastic anisotropic quark core exists within these stars. Additionally, we show that the compactness of stable stars can exceed the critical value of 1/3 due to the inclusion of elasticity, making them potential candidates for black hole mimickers. Furthermore, we found that common phenomenological models fail to describe the anisotropy of the elastic core and propose a new parametrized anisotropy model that can accurately capture physically-motivated profiles with an error of 10% across a wide parameter space. This work not only bridges the gap between elastic EOSs and parametrized anisotropic models but also provides a foundation for applications such as studying nonradial perturbations, tidal deformability, and pulsation modes for elastic HSs.

gr-qc↗

arXiv2024

Love-C relations for elastic hybrid stars

Neutron stars (NSs) provide a unique laboratory to study matter under extreme densities. Recent observations from gravitational and electromagnetic waves have enabled constraints on NS properties, such as tidal deformability (related to the tidal Love number) and stellar compactness. Although each of these two NS observables depends strongly on the stellar internal structure, the relation between them (called the Love-C relation) is known to be equation-of-state insensitive. In this study, we investigate the effects of a possible crystalline phase in the core of hybrid stars (HSs) on the mass-radius and Love-C relations, where HSs are a subclass of NS models with a quark matter core and a nuclear matter envelope with a sharp phase transition in between. We find that both the maximum mass and the corresponding radius increase as one increases the stiffness of the quark matter core controlled by the speed of sound, while the density discontinuity at the nuclear-quark matter transition effectively softens the equations of state. Deviations of the Love-C relation for elastic HSs from that of fluid NSs become more pronounced with a larger shear modulus, lower transition pressure, and larger density gap and can be as large as 60%. These findings suggest a potential method for testing the existence of distinct phases within HSs, though deviations are not large enough to be detected with current measurements of the tidal deformability and compactness.

gr-qc↗