Grad Talk: The fate of twin stars on the unstable branch: implications for the formation of twin stars

Pedro Espino, University of Arizona

When

2:10 to 3:20 p.m., Oct. 23, 2020

Where

Abstract: Hybrid hadron-quark equations of state have been shown to be compatible with the LIGO-Virgo event GW170817. When the surface tension between the hadronic and quark phase is sufficiently strong, a first-order phase transition can be sustained over a large range of energy densities, leading to the emergence of a third family of stable compact stars. These stars are hybrid hadron-quark stars. The equilibrium stable hybrid hadron-quark star branch is separated by the stable neutron star branch with a branch of unstable hybrid hadron-quark stars. The end-state of these unstable configurations has not been studied, yet, and it can have implications for the formation and existence of these stars. Of particular interest are hybrid stars with the same mass as neutron stars but different radii (twin stars). To study the dynamics of unstable hybrid hadron-quark twin stars we perform 3-dimensional general relativistic hydrodynamic simulations of non-rotating and rotating unstable-branch twin stars. We find that unstable hybrid hadron-quark stars naturally migrate toward the hadronic regime. The unstable configurations can be temporarily driven away from the stable hadronic regime by depleting the pressure, but ultimately settle into hadronic configurations. Before settling into the hadronic regime, these stars undergo (quasi)radial oscillations on a dynamical timescale while the central region bounces between the two phases. We detail the dynamics of the migration toward the stable hadronic branch and point out important stellar properties which affect the evolution. Our study suggests that it may be difficult to form stable twin stars, and hence it may be more likely that astrophysical hybrid hadron-quark stars have masses above the twin star regime. Additionally, our results suggest that oscillations between the two phases could provide a unique gravitational wave signature for a Quantum Chromodynamics (QCD) deconfinement in core-collapse supernovae.

Zoom Link:  https://arizona.zoom.us/j/93847461477?pwd=V01rSkxOYm83NmNmVjFHQUptcGRNdz09