Magnetic effects on the viscous boundary layer damping of the r-modes in neutron stars - art. no. 044009

This paper explores the effects that magnetic fields have on the viscous bo undary layers (VBLs) that can form in neutron stars at the crust-core inter face, and it investigates the VBL damping of the gravitational-radiation dr iven r-mode instability. Approximate solutions to the magnetohydrodynamic e quations valid in the VBL are found for ordinary-fluid neutron stars. It is shown that magnetic fields above 10(9)( 10(10) K/T)G significantly change the structure of the VBL, and that magnetic fields decrease the VBL damping time. Furthermore, VBL damping completely suppresses the r-mode instabilit y for B greater than or similar to 10(12) G (independent of the temperature ). These bounds refer to the strength of the radial component of the equili brium field at the location of the core radius. Magnetic effects on the VBL vanish wherever the radial component of the equilibrium field vanishes. Th us, magnetic fields will profoundly affect the VBL damping of the r-mode in stability 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 low-mass x-ray binary systems and other cold old pul sars (if they have sufficiently large internal fields).