Dense Matter and Compact Stars in Strong Magnetic Fields

TL;DR

This review explores how ultra-strong magnetic fields in magnetars influence dense matter properties, affecting neutron star structure and potential observable phenomena.

Contribution

It systematically analyzes the impact of intense magnetic fields on fermionic matter, including various particle interactions and phases relevant to neutron stars.

Findings

Magnetic fields cause Landau quantization affecting particle energy levels.

Strong magnetic fields may induce phase transitions to exotic matter.

Impacts on neutron star mass-radius relations and observational signatures.

Abstract

Compact stars serve as natural systems where matter exists at densities far beyond those achievable in laboratory experiments. Among them, magnetars are expected to possess interior magnetic fields that may reach values of the order of $10^{17}-10^{18}$ G. These extreme conditions are expected to alter the microscopic and macroscopic properties of dense matter. In this review, we examine how strong magnetic fields affect fermionic matter through mechanisms such as Landau quantization and anomalous magnetic moment interactions. We further discuss the behaviour of magnetized hadronic matter within relativistic mean-field approaches and consider the possible emergence of additional degrees of freedom, including hyperons, $\Delta$ resonances, meson condensates and quark matter. The consequences of these effects for neutron-star structure and observational constraints are also briefly outlined.