Mixed phase effects on high-mass twin stars

TL;DR

This paper examines how the high-mass twin star phenomenon, predicted by hybrid star equations of state with strong first-order phase transitions, is affected by smoothing effects such as pasta structures, and relates these findings to lattice QCD results.

Contribution

It introduces a simple model for smoothing the phase transition in hybrid stars and analyzes its impact on the high-mass twin phenomenon, connecting astrophysical and lattice QCD data.

Findings

High-mass twin stars are sensitive to the nature of the phase transition.

Smoothing the transition affects the stability and appearance of twin stars.

The transition parameters align with lattice QCD results at the pseudocritical temperature.

Abstract

Recently it has been found that a certain class of hybrid star equations of state with a large latent heat (strong first order phase transition obtained by a Maxwell construction) between stiff hadronic hadronic and stiff quark matter phases allows for the appearance of a third family of compact stars (including "twins") at high mass of $\sim 2 M_\odot$. We investigate how robust this high-mass twin phenomenon is against a smoothing of the transition which would occur, e.g., due to pasta structures in the mixed phase. To this end we propose a simple construction of a pasta-like equation of state with a parameter that quantifies the degree of smoothing of the transition and could eventually be related to the surface tension of the pasta structures. It is interesting to note that the range of energy densities for the transition as well as the pressure at the onset of the transition of this class of hybrid star matter at zero temperature corresponds well to values of the same quantities found in finite temperature lattice QCD simulations for the 1 $\sigma$ region at the pseudocritical temperature $T_c=154 \pm 9$ MeV. The pattern of the speed of sound as a function of energy density is very different.