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).