We re-examine the Bardeen-Petterson effect in accretion discs subject to Lense-Thirring precession in the bending wave regime (where the disc viscosity is smaller than the disc aspect ratio) using three dimensional smoothed particle hydrodynamics (SPH) simulations. Below are some of our simulations, each using 10 million particles.
A cross section of an accretion disc that shows an oscillatory tilt profile. The disc settles into a steady state from the inner edge, moving outwards but remaining misaligned at large radii. This disc was initially inclined at 15 degrees.
An accretion disc initially inclined at 120 degrees to the plane of the black hole spin. As the disc evolves rings of material are torn off and precess effectively independently. This disc runs for almost 1600 orbits at the inner edge.
An accretion disc inclined at 30 degrees and not taking into account Einstein precession. This disc eventually tears into two distinct sections, showing Bardeen-Petterson alignment (but no smooth transition).