Alexander Tchekhovskoy, Jonathan C. McKinney
We study prograde and retrograde disc accretion on rapidly spinning black
holes (BHs) via global 3D time-dependent non-radiative general relativistic
magnetohydrodynamic simulations. Our discs contain more large-scale vertical
magnetic flux than the accreting gas can push into the BH. As a result, the BH
becomes saturated with flux, and strong centrally concentrated large-scale
magnetic fields form that obstruct the accretion and lead to a magnetically
arrested disc. We show that the efficiency with which such accretion systems
generate steady outflows depends only on the dimensionless BH spin, a, and
accretion disc angular thickness, h/r. Prograde BHs with thick discs (h/r ~
0.3-0.6) generate jets and outflows several times more efficiently than
retrograde BHs, for the same absolute value of spin. Both orientations can
reach high values of outflow efficiency, eta ~ 100%, with higher efficiency
values for thicker discs.
View original:
http://arxiv.org/abs/1201.4385
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