Resistive Magnetohydrodynamics of Jet Formation and Magnetically Driven Accretion

We carried out 2.5-dimensional resistive magnetohydrodynamic simulations to study the effects of magnetic diffusivity on magnetically driven mass accretion and jet formation. The initial state is a constant angular-momentum torus threaded by large-scale vertical magnetic fields. Since the angular momentum of the torus is extracted due to magnetic braking, the torus medium falls toward the central region. The infalling matter twists the large-scale magnetic fields and drives bipolar jets. We found that (1) when the normalized magnetic diffusivity,$\bar \eta \equiv \eta/(r_0 V_{\textrm {Ko}})$, where VK0 is the Keplerian rotation speed at a reference radius $r=r_0$, is small $(\bar \eta \leq 10^{-3})$, mass accretion and jet formation take place intermittently; (2) when $10^{-3}\leq \bar \eta \leq 10^{-2}$, the system evolves toward a quasi-steady state; and (3) when $\bar \eta \geq 10^{-2}$ the accretion/mass outflow rate decreases with bar $\bar \eta$ and approaches 0. The results of these simulations indicate that in the center of a galaxy which has a super-massive ( ∼ 10⁹M⊙) black hole, a massive (∼ 10⁸M⊙) gas torus and magnetic braking provide a mass accretion rate which is sufficient to explain the activity of AGNs when $\bar \eta \leq 5 \times10^{-2}$