Open AccessAngular momentum transport in protostellar discs
Author(s) -
Salmeron Raquel,
Königl Arieh,
Wardle Mark
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.11277.x
Subject(s) - physics , angular momentum , magnetorotational instability , ambipolar diffusion , accretion (finance) , magnetic field , turbulence , magnetohydrodynamics , mechanics , astrophysics , classical mechanics , plasma , quantum mechanics
Angular momentum transport in protostellar discs can take place either radially, through turbulence induced by the magnetorotational instability (MRI), or vertically, through the torque exerted by a large‐scale magnetic field that threads the disc. Using semi‐analytic and numerical results, we construct a model of steady‐state discs that includes vertical transport by a centrifugally driven wind as well as MRI‐induced turbulence. We present approximate criteria for the occurrence of either one of these mechanisms in an ambipolar diffusion‐dominated disc. We derive ‘strong field’ solutions in which the angular momentum transport is purely vertical and ‘weak field’ solutions that are the stratified‐disc analogues of the previously studied MRI channel modes; the latter are transformed into accretion solutions with predominantly radial angular momentum transport when we implement a turbulent‐stress prescription based on published results of numerical simulations. We also analyse ‘intermediate field strength’ solutions in which both modes of transport operate at the same radial location; we conclude, however, that significant spatial overlap of these two mechanisms is unlikely to occur in practice. To further advance this study, we have developed a general scheme that incorporates also the Hall and Ohm conductivity regimes in discs with a realistic ionization structure.