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arXiv · 2611.01827

Angular Momentum Transport across Accretion States around a rapidly spinning black hole

Rohan Raha·Koushik Chatterjee
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Abstract

Accretion requires the outward transport of angular momentum, but the relative contributions of matter advection, turbulent stresses, ordered magnetic fields, winds, and black-hole spin remain uncertain in strongly magnetized flows. We use high-resolution three-dimensional GRMHD simulations around a rapidly rotating black hole ($a=0.998$) to compare SANE, intermediate-flux, and magnetically arrested disk states. In SANE and intermediate states, outward stresses are insufficient to overcome inward angular-momentum advection, and the net flux remains inward. In MAD, ordered Maxwell stresses regulate the disk and drive winds, while the Blandford-Znajek jet carries a distinct, near-constant flux extracted from the black hole, making the total angular-momentum flux outward. Magnetic-flux eruptions modulate both channels. During an eruption, an equatorial current sheet extends beyond the ergosphere, and low-density, magnetically dominated bubbles of expelled flux enter the polar region. The jet becomes asymmetric, its tilt more than doubles, and its opening angle first widens and then contracts below its pre-eruption value. Eruptions suppress the horizon accretion rate and briefly reverse the angular-momentum flux through the jet surface, while reorganizing the Maxwell stresses in the disk. As horizon-threading flux re-accumulates, the turbulent stress recovers toward its saturated MAD level. Eruption durations and lags among horizon flux, accretion rate, and jet tilt of ~40-90 $r_g/c$ correspond to milliseconds for stellar-mass black holes and tens of minutes for Sgr A*. These results distinguish disk-regulating magnetic torques from black-hole-sourced jet transport and show how flux eruptions couple disk accretion, winds, and jet morphology.

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Rohan Raha, Koushik Chatterjee. 2026-11-01. Angular Momentum Transport across Accretion States around a rapidly spinning black hole. https://arxiv.org/abs/2611.01827

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