Accretion of magnetic neutron stars. II. Plasma entry into the magnetosphere via diffusion. Polar cusps, and magnetic field reconnection
We investigate whether plsma can enter the magnetosphere of a radically accreting neutron star by diffusion across the magnetopause, loss-cone entry through the polar cusps, descent of the cusps to the stellar surface, or magnetic field reconnection, sufficiently readily to prevent the magnetosphere from becoming hydromagnetically unstable. We find that diffusion is never important under the conditions of interest, nor is loss-cone entry through the polar cusps when the plasma there is collisionless. If the plasma in the cusps were to cool and become collisional, the loss-cone entry rate would increase by a large factor, but this could not stabilize the magnetosphere because the density in the cusps would increase by a similar factor. We show that descent of the cusps cannot be the dominant entry process if the star has a persistent luminosity greater than a certain critical value approx.10/sup 36/ ergs s/sup -1/ and a substantial fraction of the magnetosphere is illuminated, but may be significant for much lower luminosities or anisotropic illumination. Assuming that current theoretical models of magnetic flux reconnection are qualitatively correct, plasma entry via reconnection cannot stabilize the magnetosphere unless the magnetic field in the accreting plasma is comparable in scale and strength to the magnetospheric field. We argue that this is unlikely, given the magnetic fields and plamsa flow patterns expected in neutron star binaries. We discuss the implications of these results for persistant X-ray sources and X-ray and ..gamma..-ray burst sources.
- Research Organization:
- Astrophysics Branch, Space Science Laboratory, NASA Marshall Space Flight Center
- OSTI ID:
- 6675313
- Journal Information:
- Astrophys. J.; (United States), Vol. 278:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
MAGNETIC STARS
STAR ACCRETION
STELLAR MAGNETOSPHERES
NEUTRON STARS
BINARY STARS
COSMIC X-RAY BURSTS
COSMIC X-RAY SOURCES
DIFFUSION
ELECTRIC FIELDS
FLUID FLOW
LOSS CONE
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
PLASMA
PLASMA INSTABILITY
STELLAR WINDS
ATMOSPHERES
COSMIC RAY SOURCES
FLUID MECHANICS
HYDRODYNAMICS
INSTABILITY
MECHANICS
STAR EVOLUTION
STARS
STELLAR ATMOSPHERES
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources