Warped Geometrically Thin Accretion Disks

When a geometrically thin disk is tilted relative to a spinning black hole, frame dragging can cause the disk to warp and tear it into independently precessing inner and outer disks. Gas streams through the tear, while collisions and nozzle shocks redistribute angular momentum and drive rapid accretion. This challenges the current accretion paradigm which states accretion is driven by magneto-rotational instability (MRI) induced turbulence. Below you can see this tearing process at play in the largest published GRMHD simulations to date that used 5,400 V100 GPUs on OLCF Frontier.

Our follow-up 2023 GRMHD simulation followed a 65°-tilted disk as it tore and precessed but include radiative and two-temperature effects. It produced luminosity swings from a few percent to about 50% of Eddington, remained thermally stable for more than 21,000 r_g/c, and formed nozzle shocks that compressed the disk tenfold and heated electrons to 10⁸–10⁹ K. These hot regions can potentially generate Comptonized emission and rapid variability beyond standard flat-disk models. Kaaz et al. (2026) showed that the same mechanism can power changing-look AGN. Ray-traced torn-disk simulations produce order-of-magnitude continuum and broad-line changes on month-to-year timescales, week-scale variability from inner-disk precession, and intraday quasi-periodic oscillations from radial breathing. The precessing inner disk also drives evolving red-to-blue broad-line asymmetries, which is a distinctive observational signature of disk tearing.

Warped Geometrically Thin Accretion Disks with Jets

Here we perform a similar simulation to the one above, but include a strong poloidal magnetic field, which is a necessary ingredient to form a jet. As can be seen, the black hole drags the space-time around the disk, shredding this thin disk (H/R=0.03) totally apart. The jet, in red, gets disrupted due to differential precession between inner and outer disk. Jet precession has been invoked some types of quasi-periodic oscillations (QPOs) and has been recently confirmed (see my previous paper). As can be read in this paper, the violent collisions between disk and jets might lead to extra dissipation and transfer energy and angular momentum between the disk and jet.

Moderately Thick Accretion Disks with Poloidal Magnetic Fields

Here we perform a simulation of a tilted accretion disks threaded with a poloidal magnetic fields which is thicker (H/R=0.1) than the two examples (H/R=0.02-0.03) shown above. As can be seen, the disk almost stops precessing while it slowly aligns with the black hole. This demonstrates that disk tearing is necessary to produce a disk which precesses for the many periods necessary to explain quasi-periodic oscillations and justifies the order(s) of magnitude more expensive simulations described above. Details of this work are described in my paper.

Geometrically Thick Accretion Disks with Poloidal Magnetic Fields

The animation below shows a GRMHD simulation of a geometrically thick (H/R=0.3) accretion disk tilted by 30 degrees at low (model W-U) and high (model W-R) resolution. As can be seen, the disk barely shows any precession due to the torque of the spinning black hole (a=0.9375). The reason for this is that the disk is expanding in radius, which reduces the amount of torque the spinning black hole can exert on the accretion disk. Expansion in radius is only correctly captured at high resolutions. Details can be found in this paper.

Publications

1) Formation of Precessing Jets by Tilted Black-hole Discs in 3D General Relativistic MHD Simulations

2) A Phase Lag between Disk and Corona in GRMHD Simulations of Precessing Tilted Accretion Disks

3) Bardeen-Petterson Alignment, Jets and Magnetic Truncation in GRMHD Simulations of Tilted Thin Accretion Discs

4) Disc Tearing and Bardeen-Petterson Alignment in GRMHD Simulations of Highly Tilted Thin Accretion Discs

5) Disc tearing leads to low and high frequency quasi-periodic oscillations in a GRMHD simulation of a thin accretion disc

6) Formation of Magnetically Truncated Accretion Disks in 3D Radiation-transport Two-temperature GRMHD Simulations

7) Radiation Transport Two-Temperature GRMHD Simulations of Warped Accretion Disks

8) Nozzle Shocks, Disk Tearing and Streamers Drive Rapid Accretion in 3D GRMHD Simulations of Warped Thin Disks

9) Extreme Scale Height Variations and Nozzle Shocks in Warped Disks

10) Changing-Look AGN Powered by Disk Tearing