Equilibrium sequences of non rotating and rapidly rotating crystalline color superconducting hybrid stars

TL;DR

This paper models equilibrium configurations of hybrid stars with crystalline color-superconducting quark matter cores, revealing new stable branches and implications for maximum mass and rotational properties.

Contribution

It introduces the first stable hybrid star sequences with crystalline color-superconducting cores, expanding understanding of their structure and stability.

Findings

Identification of a new stable branch of CCS hybrid stars.

Maximum masses align with current astronomical observations.

Rotating hybrid stars can support larger spins than nuclear stars.

Abstract

The three-flavor crystalline color-superconducting (CCS) phase of quantum chromodynamics (QCD) is a candidate phase for the ground state of cold matter at moderate densities above the density of the deconfinement phase transition. Apart from being a superfluid, the CCS phase has properties of a solid, such as a lattice structure and a shear modulus, and hence the ability to sustain multipolar deformations in gravitational equilibrium. We construct equilibrium configurations of hybrid stars composed of nuclear matter at low, and CCS quark matter at high, densities. Phase equilibrium between these phases is possible only for rather stiff equations of state of nuclear matter and large couplings in the effective Nambu--Jona-Lasinio Lagrangian describing the CCS state. We identify a new branch of stable CCS hybrid stars within a broad range of central densities which, depending on the details of the equations of state, either bifurcate from the nuclear sequence of stars when the central density exceeds that of the deconfinement phase transition or form a new family of configurations separated from the purely nuclear sequence by an instability region. The maximum masses of our non-rotating hybrid configurations are consistent with the presently available astronomical bounds. The sequences of hybrid configurations that rotate near the mass-shedding limit are found to be more compact and thus support substantially larger spins than their same mass nuclear counterparts.