Equations of State for Hadronic Matter and Mass-Radius Relations of Neutron Stars with Strong Magnetic Fields

Chinatsu Watanabe,Shuichiro Ebata,Naotaka Yoshinaga

doi:10.3390/universe8010048

Chinatsu Watanabe, Shuichiro Ebata + Show 1 more

Open Access

https://doi.org/10.3390/universe8010048

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Journal: Universe	Publication Date: Jan 12, 2022
Citations: 2	License type: CC BY 4.0

Affiliation: Saitama University

Abstract

Neutron star is an important object for us to verify the equation of state of hadronic matter. For a specific choice of equations of state, mass and radius of a neutron star are determined, for which there are constraints from observations. According to some previous studies, since the strong magnetic field acts as a repulsive force, there is a possibility that neutron stars with strong magnetic fields may have relatively heavier masses than other non-magnetized neutron stars. In this paper, the structure of a neutron star with a strong internal magnetic field is investigated by changing its internal functional form to see how much the neutron star can be massive and also how radius of a neutron star can be within a certain range.

Highlights

To study a neutron star (NS) is an interesting and important subject in nuclear physics as it is a unique object of superdense hadronic matter, where its central density might be several times larger than the nuclear saturation density
Equation of state (EoS) for the nuclear matter that depends on the energy density functional is often utilized to discuss various properties of NSs, for instance, the mass–radius (MR) relation
Each EoS curve must go through these areas if they satisfy the observational constraints

Summary

Introduction

To study a neutron star (NS) is an interesting and important subject in nuclear physics as it is a unique object of superdense hadronic matter, where its central density might be several times larger than the nuclear saturation density. This leads to a reduction in the Fermi pressure to soften the EoS and to a reduction in the predicted maximum mass less than 2 M. To obtain NS masses more than 2 M is one of the goals to be achieved for the optimal EoSs. There are some characteristic NSs: millisecond-pulsar, which has a short rotational period of less than 10 ms, and magnetar, which has a powerful magnetic field on its surface. These EoSs have similar saturation properties at nuclear saturation density This RMF includes a strong magnetic field, which has a functional form of baryon number density ρ.

Equation of State

Magnetic Fields

EoS of Hadronic Matter with Magnetic Fields

Comparison of the Case without Magnetic Fields

Changing α and γ Parameters of the Magnetic Field Function