Anisotropic pressure in strange quark matter in the presence of a strong nonuniform magnetic field

TL;DR

This paper investigates the thermodynamic properties of strange quark matter in nonuniform magnetic fields within the MIT bag model, revealing how magnetic field strength influences stability and pressure anisotropy in strange quark stars.

Contribution

It introduces a model for the spatial dependence of magnetic fields in strange quark matter and analyzes the stability bounds related to magnetic field strength in quark stars.

Findings

Critical magnetic field bounds are identified for stability.

Magnetic field dependence form affects the critical field significantly.

Variation in bag pressure has minimal impact on the critical magnetic field.

Abstract

Thermodynamic properties of strange quark matter (SQM) in a nonuniform magnetic field are studied within the phenomenological MIT bag model under the charge neutrality and beta equilibrium conditions, relevant to the interior of strange quark stars. The spatial dependence of the magnetic field strength is modeled by the dependence on the baryon chemical potential in the exponential and power forms. The total energy density, longitudinal and transverse pressures in magnetized SQM are found as functions of the baryon chemical potential. It is clarified that the central magnetic field strength in a strange quark star is bound from above by the critical value at which the derivative of the longitudinal pressure with respect to the baryon chemical potential vanishes first somewhere in the interior of a star under varying the central field. Above this upper bound, the instability along the magnetic field is developed in magnetized SQM. The change in the form of the dependence of the magnetic field strength on the baryon chemical potential between the exponential and power ones has a nonnegligible effect on the critical magnetic field strength while the variation of the bag pressure within the absolute stability window for magnetized SQM has a little effect on the critical field.