Alternative Paradigm to Resistive Accretion Disks: Magnetic Microstructures. (arXiv:2009.07215v1 [astro-ph.SR])

<a href="http://arxiv.org/find/astro-ph/1/au:+Montani_G/0/1/0/all/0/1">Giovanni Montani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carlevaro_N/0/1/0/all/0/1">Nakia Carlevaro</a>

We analyze the stationary configuration of a thin axisymmetric stellar

accretion disk, neglecting non-linear terms in the plasma poloidal velocity

components. We set up the Grad-Shafranov equation for the system, including the

plasma differential rotation. Then, we study the small scale backreaction of

the disk to the central body magnetic field and we calculate the resulting

radial infalling velocity. We show that the small scale radial oscillation of

the perturbed magnetic surface is associated to the emergence of relevant

toroidal current densities, able to balance the generalized Ohm law even in the

presence of quasi-ideal values of the plasma resistivity. We provide a possible

explanation for the puzzle of an anomalous resistivity, since the Ohm law

involves relevant values of the poloidal velocity which is averaged to zero on

the radial profile of the disk due to the microscopic rapid oscillations. The

contribution to the infalling velocity of the averaged backreaction contrasts

accretion, but it remains negligible as far as the induced magnetic field is

small compared to that of the central body.

We analyze the stationary configuration of a thin axisymmetric stellar

accretion disk, neglecting non-linear terms in the plasma poloidal velocity

components. We set up the Grad-Shafranov equation for the system, including the

plasma differential rotation. Then, we study the small scale backreaction of

the disk to the central body magnetic field and we calculate the resulting

radial infalling velocity. We show that the small scale radial oscillation of

the perturbed magnetic surface is associated to the emergence of relevant

toroidal current densities, able to balance the generalized Ohm law even in the

presence of quasi-ideal values of the plasma resistivity. We provide a possible

explanation for the puzzle of an anomalous resistivity, since the Ohm law

involves relevant values of the poloidal velocity which is averaged to zero on

the radial profile of the disk due to the microscopic rapid oscillations. The

contribution to the infalling velocity of the averaged backreaction contrasts

accretion, but it remains negligible as far as the induced magnetic field is

small compared to that of the central body.

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