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

**Authors:** Nicholas Kaaz, Matthew T. P. Liska, Jonatan Jacquemin-Ide, Zachary L. Andalman, Gibwa Musoke, Alexander Tchekhovskoy, Oliver Porth  
**arXiv:** [2210.10053](https://arxiv.org/abs/2210.10053)  
**Date:** 2022-10-18  
**Summary page:** https://www.summarizepaper.com/en/paper/2210.10053v1/

## Key points

- Investigation of gas feeding a black hole (BH) and its interaction with BH's spin
- Focus on accretion disk precession and warping caused by misalignment of gas angular momentum with BH spin
- High-resolution simulations using general-relativistic magnetohydrodynamic code
- Highly tilted accretion disk around rapidly rotating BH with thin height-to-radius ratio and tilt angle
- Lense-Thirring torques from BH rotation cause disk to precess and become warped
- Warped disk tears into two sub-disks that individually precess, leading to high mass accretion rates
- Two novel dissipation mechanisms in warped disks: extreme scale height oscillations and tear-induced low-angular momentum "streamers"
- Findings challenge traditional understanding of accretion processes driven by local turbulent stresses in disks
- Alternative drivers for mass accretion onto BHs identified, modifying standard accretion paradigm
- Implications for active galactic nuclei and potential explanation for extreme variability observed in these objects
- Study sheds light on dynamics of accretion disks around rapidly rotating black holes, calls for further exploration

## Summary

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The authors investigate the dynamics of gas feeding a black hole (BH) and its interaction with the BH's spin in this study. They focus on the phenomenon of accretion disk precession and warping, which occurs when the angular momentum of the gas is misaligned with respect to the BH spin. To explore these processes, they perform high-resolution simulations using a general-relativistic magnetohydrodynamic code. The researchers simulate a highly tilted accretion disk around a rapidly rotating BH with a thin height-to-radius ratio of 0.02 and a tilt angle of 65 degrees. They find that as the BH rotates, it drags the surrounding space-time, resulting in Lense-Thirring torques that cause the disk to precess and become significantly warped. Interestingly, the authors observe that the warped disk continuously tears into two sub-disks that individually precess. This tearing process leads to mass accretion rates that far exceed expectations based on standard $\alpha$-viscosity models. The researchers identify two novel dissipation mechanisms specific to warped disks responsible for driving accretion. Firstly, they discover extreme scale height oscillations occurring twice per orbit throughout the disk. When these oscillations compress, "nozzle" shocks form, dissipating orbital energy and driving accretion. Secondly, there is extreme dissipation at the location of the tear in the disk. This results in low-angular momentum "streamers" forming and raining down onto the inner sub-disk, causing it to rapidly accrete even when it is momentarily aligned with the BH spin and unwarped. These findings challenge traditional understanding of accretion processes driven by local turbulent stresses in disks. The identified mechanisms significantly modify the standard accretion paradigm by providing alternative drivers for mass accretion onto BHs. Furthermore, these mechanisms may have important implications for active galactic nuclei, as they can lead to structural changes on much shorter timescales than expected in $\alpha$-disks. This could potentially explain some of the extreme variability observed in these astrophysical objects. Overall, this study sheds light on the complex dynamics of accretion disks around rapidly rotating black holes and highlights the need for further exploration of these processes to fully understand the physics involved.