Relativistic hybrid stars with super-strong toroidal magnetic fields: An evolutionary track with QCD phase transition

TL;DR

This study models hybrid stars with super-strong toroidal magnetic fields, revealing how a QCD phase transition influences their structure, magnetic field distribution, and potential gravitational wave signals.

Contribution

It introduces a full general relativity model of hybrid stars with a QCD phase transition and explores their evolutionary paths and observable signatures.

Findings

Maximum magnetic field strength increases by up to 30% due to quark phase.

Energy release from phase transition can reach up to 10^52 erg.

Potential gravitational wave signals could be detectable out to Megaparsec distances.

Abstract

We investigate structures of hybrid stars, which feature quark core surrounded by a hadronic matter mantle, with super-strong toroidal magnetic fields in full general relativity. Modeling the equation of state (EOS) with a first order transition by bridging the MIT bag model for the description of quark matter and the nuclear EOS by Shen et al., we numerically construct thousands of the equilibrium configurations to study the effects of the phase transition. It is found that the appearance of the quark phase can affect distributions of the magnetic fields inside the hybrid stars, making the maximum field strength about up to 30 % larger than for the normal neutron stars. Using the equilibrium configurations, we explore the possible evolutionary paths to the formation of hybrid stars due to the spin-down of magnetized rotating neutron stars. We find that the energy release by the phase transition to the hybrid stars is quite large ($\la 10^{52} \rm erg$) even for super strongly magnetized compact stars. Our results suggest that the strong gravitational-wave emission and the sudden spin-up signature could be observable signals of the QCD phase transition, possibly for a source out to Megaparsec distances.