This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/25660
Description
Title
The magnetospheres of accreting neutron stars
Author(s)
Elsner, Ronald Fred
Issue Date
1976
Doctoral Committee Chair(s)
Lamb, Frederick K.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
magnetospheres
accreting neutron stars
star formation
accretion onto compact objects
Language
en
Abstract
Accretion onto compact objects may power some compact X-ray sources. In the present study, we develop further the theory of accretion onto magnetic neutron stars in the particular case when the accretion flow is radial and the neutron star is slowly rotating. We examine in detail the formation and structure of the star's magnetosphere, the physical processes that occur in the neighborhood of the magnetospheric boundary, and the manner in which accreting plasma.enters the magnetosphere. When plasma doe$ not enter and the boundary is in static equilibrium, the boundary shape is determined by the balance between the confining pressure outside and the pressure of the stellar field inside. We illustrate the way the shape differs for different scalings of confining pressure with radius, and show that cusps form in the polar magnetosphere if the scale of the magnetosphere is much larger than the star's radius. When plasma flows across the boundary, the structure of the magnetosphere is more
complex than in static eqilibrium, but in some limiting cases the
boundary shape resembles that of static magnetospheres. Plasma entry when the boundary is Rayleigh-Taylor stable is examined, and, under
conditions typical of bright binary X-ray sources, cusp losses and
diffusion across stellar magnetic field lines are eliminated as likely
ways that most of the accreting plasma might enter the magnetosphere.
Reconnection of strong, large-scale magnetic fields embedded in the
accreting plasma to the stellar field can keep pace with the inflow
towards the magnetosphere if reconnection proceeds at its maximum theoretical rate. However, for a wide range of conditions, Rayleigh-Taylor instability of the magnetospheric boundary is likely to be the most important plasma entry process. The condition for the onset of
this instability is investigated using MHD stability theory, and the nature of the unstable modes in the linear regime is studied using a linear perturbation analysis. We show that the weight of plasma on the boundary is sufficient to drive it unstable only if the ions cool to a temperature
Tcrit -0.3 of their local free-fall temperature. We show that Compton scattering cools plasma bathed by X-rays from the stellar surface and that if the magnetosphere is uniformly illuminated, plasma is likely to enter via this instability over most of the boundary. Two extreme examples of possible flows within the magnetosphere, and their effects on X-ray emission from the stellar surface, are described in a qualitative way. Analytical and numerical solutions for the flow and cooling of plasma in the region between The standoff shock wave outside the magnetosphere and the magnetospheric boundary are presented for the case when the plasma there is exposed to X-rays. The applicability of the present calculations to observed compact X-ray sources and some implications for X-ray burst sources are discussed.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
