Formation of Precessing Jets by Tilted Black-hole Discs in 3D General
  Relativistic MHD Simulations
  Gas falling into a black hole (BH) from large distances is unaware of BH spin
direction, and misalignment between the accretion disc and BH spin is expected
to be common. However, the physics of tilted discs (e.g., angular momentum
transport and jet formation) is poorly understood. Using our new
GPU-accelerated code H-AMR, we performed 3D general relativistic
magnetohydrodynamic simulations of tilted thick accretion discs around rapidly
spinning BHs, at the highest resolution to date. We explored the limit where
disc thermal pressure dominates magnetic pressure, and showed for the first
time that, for different magnetic field strengths on the BH, these flows launch
magnetized relativistic jets propagating along the rotation axis of the tilted
disc (rather than of the BH). If strong large-scale magnetic flux reaches the
BH, it bends the inner few gravitational radii of the disc and jets into
partial alignment with the BH spin. On longer time scales, the simulated
disc-jet system as a whole undergoes Lense-Thirring precession and approaches
alignment, demonstrating for the first time that jets can be used as probes of
disc precession. When the disc turbulence is well-resolved, our isolated discs
spread out, causing both the alignment and precession to slow down.
