Mass--radius relations, surface redshift, and echo time of neutron-star--wormhole system with chaotic magnetic field and anisotropic matter

Abstract

In this paper, we formulate neutron-star--wormhole (NSWH) systems supported by two scalar fields, allowing for both chaotic magnetic field and pressure anisotropy of the neutron fluid. The wormhole is traversable regardless of whether anisotropy of the neutron fluid and/or magnetic fields are included. In particular, the null energy condition (NEC) remains violated in the vicinity of the wormhole throat, ensuring the traversable nature of the geometry. For magnetized configurations, the resulting NSWH systems can become extremely massive, with ADM masses exceeding $8\,M_\odot$, and can exhibit large surface redshifts exceeding $z \simeq 1.5$. The system can also reach the ultracompact regime, which allows us to calculate echo time that might be produced the systems. Our calculations of the echo time indicate that it can vary depending on the chaotic magnetic field configuration and fluid anisotropy. For non-magnetized configurations, the gravitational-wave echo time is of the order of $10^{-2}-10^{-1}$ ms. For the magnetized configurations, however, it ranges from the order of $10^{-1}$ $μ$s $-10^{-1}$ ms, suggesting that magnetic fields broaden the range of echo time. Moreover, to investigate the direct impact of the magnetic field on the echo time, we derive an explicit expression for the echo time as a function of uniform magnetic field. The resulting relation shows that the echo time decreases as the magnetic field strength increases.