Magnetic effects on the viscous boundary layer damping of the r-modes in neutron stars

TL;DR

This study investigates how magnetic fields influence viscous boundary layer damping of r-mode instabilities in neutron stars, revealing that strong magnetic fields significantly alter damping times and can suppress the instability.

Contribution

It provides approximate solutions to magnetohydrodynamic equations in neutron star boundary layers, showing magnetic fields above 10^9 Gauss impact damping and can suppress r-mode instabilities.

Findings

Magnetic fields above 10^9 Gauss alter VBL structure.

Magnetic fields decrease VBL damping time.

Fields >= 10^{12} Gauss suppress r-mode instability.

Abstract

This paper explores the effects that magnetic fields have on the viscous boundary layers (VBLs) that can form in neutron stars at the crust-core interface, and it investigates the VBL damping of the gravitational-radiation driven r-mode instability. Approximate solutions to the magnetohydrodynamic equations valid in the VBL are found for ordinary-fluid neutron stars. It is shown that magnetic fields above 10^9 Gauss significantly change the structure of the VBL, and that magnetic fields decrease the VBL damping time. Furthermore, VBL damping completely suppresses the r-mode instability for B >= 10^{12} Gauss. Thus, magnetic fields will profoundly affect the VBL damping of the r-mode instability in hot young pulsars (that are cool enough to have formed a solid crust). One can speculate that magnetic fields can affect the VBL damping of this instability in LMXBs and other cold old pulsars (if they have sufficiently large internal fields).