Rapid Black Hole Spin-down by Thick Magnetically Arrested Disks

Understand

Black hole (BH) spin can play an important role in galaxy evolution by controlling the amount of energy and momentum ejected from near the BH into the surroundings.

• We focus on radiatively-inefficient and geometrically-thick magnetically-arrested disks (MADs) that can launch strong BH-powered jets.
• With an appropriately chosen adiabatic index, these systems can describe either the low-luminosity or highly super-Eddington BH accretion regimes.
• Using a suite of 3D general relativistic magnetohydrodynamic (GRMHD) simulations, we find that for any initial spin, a MAD rapidly spins down the BH to the equilibrium spin of $0< a_{\rm eq} \lesssim 0.1$, very low compared to $a_{\rm eq} = 1$ for the standard thin luminous (Novikov-Thorne) disks.