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Efficiency of Angular Momentum Transport Essay examples

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Observations indicate that at present time stars born in magnetized rotating cores of molecular clouds~\citep{shu87, dudorov91, dudorov95, mckee07}. Centrifugal and electromagnetic forces lead to the formation of a disk-like structure during the gravitational collapse of the molecular cloud. Evolution of accretion disks depends on efficiency of angular momentum escape. Turbulence \citep{ss73}, magnetic braking and outflows are the most important mechanisms of angular momentum transport in accretion disks of young stars. Turbulence in accretion disks comes probably from magnetorotational instability \citep[MRI, ][]{balbus91}. Magnetic braking mechanism is based on the process of transfer of angular momentum by torsional Alfven waves…show more content…
\cite{chapman13} detected a correlation between core magnetic field direction and protostellar disk symmetry axis in a few low-mass protostellar cores using the SHARP polarimeter at Caltech Submillimeter Observatory at 350 $\mu$m dust continuum emission. \cite{donati05} probably detected magnetic field with azimuthal component of order of 1 kGs in the FU Orionis accretion disk. In absence of sufficient number of observational data, theoretical calculations of magnetic field of accretion disks of young stars become an important task.

Dragging of an external magnetic field in the accretion disks has been investigated in several works. \cite{lubow94} and \cite{agapitou96} considered bending of an initially vertical weak magnetic field in the infinitesimally thin viscous disk. They pointed out that inclination of poloidal magnetic fields lines and wind launching possibility depend on magnetic diffusion efficiency which is characterized by the magnetic Prandtl number $\mathcal{P}$. \cite{RRS96} investigate analogous problem in two-dimensional approach and showed that, in addition to radial magnetic field component, strong toroidal component of the magnetic field is also generated in the case of weak magnetic diffusion, $\mathcal{P}\gg 1$. \cite{shalybkov00} considered steady-state structure of the accretion disk in the presence of dynamically important magnetic field. They found that sufficient
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