Magnetically Driven Retrograde Precession in Misaligned Black Hole Accretion Flows

TL;DR

This paper demonstrates through simulations that strong magnetic fields can induce a novel retrograde precession in black hole accretion disks, challenging the traditional Lense-Thirring explanation for jet precession.

Contribution

The study introduces a new magnetic torque mechanism causing retrograde precession in tilted accretion flows, expanding understanding of jet precession phenomena.

Findings

Discovery of a magnetic torque-induced retrograde precession.

Magnetic fields can oppose Lense-Thirring precession.

Implications for interpreting jet precession in black hole systems.

Abstract

Observations of accreting black hole (BH) systems, such as microquasars and supermassive black holes, often reveal a precessing jet with changing directions, indicating a misaligned accretion flow relative to the BH spin. The precession is commonly attributed to the Lense-Thirring (LT) effect, which arises from the BH's rotation twisting the surrounding spacetime and accretion flow. In the strongly magnetized regime, which is preferred accretion flow conditions for M~87$^*$ and likely other jet-producing systems, the large-scale magnetic field can significantly influence the flow dynamics. Here, we perform large-scale three-dimensional general relativistic magnetohydrodynamic simulations of tilted accretion onto a rotating BH, and find a never-seen-before new retrograde precession. This precession arises from a magnetic torque on the disk generated by the poloidal magnetic field aligned with the BH's rotation, opposing the LT torque. This finding highlights the unique property of highly magnetized accretion flows around BHs and provides a new interpretation of jet precession observed in many systems.