Ambipolar diffusion in interstellar clouds: one-dimensional, isothermal collapse

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1983

OSTI ID:5073071

Paleologou, E

The formulation of a theory of star formation faces two fundamental problems: (i) the angular momentum problem, and (ii) the magnetic flux problem. It has been demonstrated previously by detailed calculation that magnetic braking by itself can resolve the angular momentum problem (at least for binary stars and, most likely, for single stars as well) during the early, relatively diffuse stages of cloud contraction. The magnetic flux problem lies in the observation that fluxes of typical stars are between 2 and 5 orders of magnitude smaller than fluxes of corresponding masses at interstellar densities. The detailed calculations of collapsing model clouds described in this paper show that the flux-to-mass ratio in cloud cores can decrease by more than 4 orders of magnitude at neutral densities n/sub n/ < 10/sup 9/ cm/sup -3/ due to ambipolar diffusion alone. Ambipolar diffusion sets in at gas densities larger than those by which the bulk of the angular momentum problem is resolved by magnetic braking. The evolution in time of model self-gravitating clouds which would have been in an exact equilibrium state with spatially nonuniform density and magnetic field if ambipolar diffusion had been ignored is followed numerically sometimes for twenty-eight initial central free-fall times. Thus any evolution at all is entirely the result of ambipolar diffusion. A cloud is in pressure equilibrium with a magnetic, hot and tenuous external medium. In a typical case, appreciable drift velocities between ions and neutrals develop in the core where a combination of steep magnetic-field gradients and a small degree of ionization exist. Soon thereafter the core contracts dynamically under self-gravity, with ever-decreasing flux-to-mass ratio.

• Research Organization: Illinois Univ., Urbana (USA)
• OSTI ID: 5073071
• Country of Publication: United States
• Language: English

Related Subjects

640102 -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMBIPOLAR DIFFUSION
ANGULAR MOMENTUM
COSMIC GASES
DIFFUSION
FLUIDS
GASES
GRAVITATIONAL COLLAPSE
HYDROMAGNETIC WAVES
INTERSTELLAR SPACE
MAGNETIC FLUX
MASS
MATHEMATICAL MODELS
SHOCK WAVES
SPACE
STAR EVOLUTION