Accretion by rotating magnetic neutron stars
It is generally accepted that many pulsating X-ray sources are rotating magnetic neutron stars undergoing accretion. The text of this thesis provides a historical introduction to four studies, contained herein as appendices, in which a theory of accretion by such stars is developed. In these studies, a detailed magnetohydrodynamic description is given of the accretion flow and the magnetic field configuration within the magnetosphere of the neutron star. It is shown that the accreting matter moves along the stellar field lines when viewed in the frame corotating with the star, and that the stellar field is azimuthally distorted by the matter. In the case of slow rotators, matter rotates in a sense opposite that of the net angular momentum flux toward the star. Then it is shown that bounds on the accretion torque exerted on the star can be obtained by applying general conservation laws to the flow in the transition zone between the magnetospheric flow and the exterior flow, even in the absence of detailed knowledge of the flow in this zone. Next, the location, the size, and the structure of the transition zone are determined in the case of accretion from a Keplerian disk. The stellar magnetic field penetrates the inner part of the disk via the Kelvin-Helmholtz instability, turbulent diffusion, and reconnection, producing a broad transition zone composed of two regions, a broad outer zone where viscous stresses dominate magnetic stresses, and a narrow inner zone or boundary layer where magnetic stresses dominate. The accretion torque on the star is calculated. It is shown that the magnetic coupling between the star and the plasma outside the inner edge of the disk makes an appreciable contribution to the accretion torque, and that the spin-up torque on fast rotators is substantialy less than that on slow rotators as a result.
- Research Organization:
- Illinois Univ., Urbana (USA)
- OSTI ID:
- 6337399
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
FLUID FLOW
FLUID MECHANICS
HELMHOLTZ INSTABILITY
HYDRODYNAMICS
INSTABILITY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MATHEMATICAL MODELS
MECHANICS
MOTION
NEUTRON STARS
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PULSATIONS
ROTATION
STAR ACCRETION
STAR EVOLUTION
STAR MODELS
STARS
STELLAR ATMOSPHERES
STELLAR MAGNETOSPHERES
VELOCITY