The effects of ambipolar diffusion, dust, and ultraviolet radiation in the formation of cores and protostars in interstellar molecular clouds
Ciolek, Glenn Eugene
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https://hdl.handle.net/2142/18869
Description
Title
The effects of ambipolar diffusion, dust, and ultraviolet radiation in the formation of cores and protostars in interstellar molecular clouds
Author(s)
Ciolek, Glenn Eugene
Issue Date
1993-10
Doctoral Committee Chair(s)
Mouschovias, T. Ch.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
star formation
astrophysics
ambipolar diffusion
ultraviolet radiation
prostars
interstellar molecular clouds
Language
en
Abstract
"Star formation, a central problem in astrophysics, takes place within magnetically supported
interstellar molecular clouds. The observed inefficiency of star formation in molecular
clouds, in which only a small fraction of a cloud's mass is converted into stars, is
explained naturally by magnetic support of the envelope and slow, inward drift of neutral
matter with respect to plasma and magnetic field (ambipolar diffusion), which allows a
cloud to gradually increase its central mass-to-flux ratio until it reaches the critical value
for gravitational collapse. Beyond this stage, the magnetically supercritical core contracts
dynamically, while the envelope remains magnetically supported. Interstellar grains, a
significant component of the interstellar medium, can become charged, couple to the
magnetic field, and decrease the rate of ambipolar diffusion in a cloud.
In this thesis we model the self-initiated formation and contraction of cloud cores due
to ambipolar diffusion in axisymmetric, self-gravitating, isothermal, magnetic molecular
clouds, accounting for a cosmic abundance of interstellar grains (both charged and neutral),
and an external (stellar) ultraviolet radiation field. The basic microscopic and
macroscopic effects of grains are discussed. The magnetohydrodynamic equations for a
multicomponent plasma are derived, the dimensionless free parameters are obtained, and
their meaning is explained physically. The ion and electron fluids combine to form a
system of ""quasiparticles"", each having an effective charge Zetr = e(ni- ne)/ni (where ni
and ne are the number densities of ions and electrons, and e the electronic charge). Electrostatic
attraction between quasiparticles, which are attached to the magnetic field, and
negatively charged grains couples the grains to the field even at densities at which grainneutral
collisions would normally detach them from the field. Also, neutral grains can
couple to the magnetic field through (inelastic) charge capture. Interstellar UV radiation
increases the degree of ionization in a cloud's envelope, with a corresponding decrease in
the rate of ambipolar diffusion in the envelope. The results and their application to the
formation of cores and protostars in molecular clouds are discussed."
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