Crustal magnetic fields do not lead to magnetar-strength amplifications in binary neutron-star mergers by Michail Chabanov et al. on Monday 28 November

The amplification of magnetic fields plays an important role in explaining

numerous astrophysical phenomena associated with binary neutron-star mergers,

such as mass ejection and the powering of short gamma-ray bursts. Magnetic

fields in isolated neutron stars are often assumed to be confined to a small

region near the stellar surface, while they are normally taken to fill the

whole stars in the numerical modelling. By performing high-resolution, global,

and high-order general-relativistic magnetohydrodynamic simulations we

investigate the impact of a purely crustal magnetic field and contrast it with

the standard configuration consisting of a dipolar magnetic field with the same

magnetic energy but filling the whole star. While the crust-configurations are

very effective in generating strong magnetic fields during the

Kelvin-Helmholtz-instability stage, they fail to achieve the same level of

magnetic-field amplification of the full-star configurations. This is due to

the lack of magnetized material in the neutron-star interiors to be used for

further turbulent amplification and to the surface losses of highly magnetized

matter in the crust-configurations. Hence, the final magnetic energies in the

two configurations differ by more than one order of magnitude. We briefly

discuss the impact of these results on astrophysical observables and how they

can be employed to deduce the magnetic topology in merging binaries.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.13661v1