MAGNETIC FIELD DECAY IN ISOLATED NEUTRON STARS 徐佩君

Why it is said that the magnetic fields of neutron stars decay ? The surface magnetic field strengths Young pulsars : ~10^12 gauss Older pulsars : ~10^10 gauss Millisecond pulsars : ~10^8 gauss

The governing equation for the magnetic field ohmic decay ambipolar diffusionHall drift

Ohmic Decay (Ostriker and Gunn 1969) They assumed σ to be electrical conductivity in the crust and L the radius of the neutron star. σ= 0.6*10^23 1/s τ= 4*10^6 yrs (Baym, Pethick, and Pines 1969) They argued that it is more correct to assume σ in the interior of a neutron star, which greatly exceeds the value in the crust, so that τ is larger than the Hubble time. (Geppert and Rheinhardt 2002) L=10^5 crust thickness σ= 5*10^28 1/s averaged electrical conductivity Ohmic decay may too slow to directly affect magnetic fields of stellar scale.

plasma kinetic theory Vlasov equation Fluid force equation for species s Continuity equation

including collisions Ks

one-fluid model magnetohydrodynamics (MHD)

MHD equations

diffusion time L : scale length

What is the origin of V & j ? Is it reasonable to discuss ambipolar term and Hall term independently? drift velocity for g × B drift F=mg Vi >>Ve V and j are comparable

following study ambipolar term and Hall term relaxation time electrical conductivity

Reference Nicholson, Dwight R. 1983, Introduction to plasma theory Goldreich, P., & Reisenegger, A. 1992, ApJ, 395, 250 Sang, Yeming & Chanmugam, G. 1987, ApJ, 323, 61 Ostriker, J. P. & Gunn, J. E. 1969, ApJ, 157 Geppert, U., & Rheinhardt, M. 2002, A&A, 392, 1015 Andrew G. Lyne & Francis Graham-Smith. 1998, Pulsar astronomy