Radiation-Driven Magnetic Fields in Sub-Keplerian Accretion Flows: An Alternative to MRI
Abstract
Large scale magnetic fields play a crucial role in shaping the dynamics and structure of the inner parts of accretion disks and the resulting jets from the vicinity of black holes and neutron stars. Currently, the primary mechanism considered for generating and amplifying large scale magnetic fields in accretion disks is the magneto-rotational instability (MRI). Here we show that non-conservative radiation fields provide a rapid and independent mechanism for generating and amplifying magnetic fields in accretion flows. A luminous, compact corona generates a radiation-driven poloidal field that is subsequently amplified by differential rotation, yielding quadratic magnetic-field growth and, over a broad range of coronal luminosities and sizes and MRI amplification locations, magnetization on timescales comparable to or shorter than those of the MRI. The mechanism therefore provides not merely an alternative to MRI, but an additional and, over a substantial region of parameter space, dominant channel for magnetic-field generation from initial conditions with zero magnetic field. Since the radiation-driven source arises directly from the non-conservative nature of the radiation field, such magnetic-field generation is an inevitable consequence of sufficiently strong and anisotropic radiation sources in black-hole accretion flows. More generally, the mechanism requires only a non-conservative radiation field and differential plasma motion, and is therefore expected to operate in a broad range of luminous astrophysical systems, including active galactic nuclei, gamma-ray bursts, and tidal disruption events.
Related
- Thermal Stability of Radiation-pressure-dominated Accretion Disks Threaded by Net Vertical Magnetic Flux
- Radiation-Regulated Spherical Accretion with an Inner Accretion Disk
- Radiation Hydrodynamics of Self-gravitating Protoplanetary Disks II. Accretion, Migration, Spin, and Internal Structure of GI Fragments
- Dynamics, ringdown, and accretion-driven multiple quasi-periodic oscillations of Kerr–Bertotti–Robinson black holes
- Multi-wavelength Emission Modeling from Accretion Flows around Isolated Black Holes Including Magnetic Flux Transport
BibTeX
@misc{vyas2026radiationdriven,
title = {{Radiation-Driven Magnetic Fields in Sub-Keplerian Accretion Flows: An Alternative to MRI}},
author = {Mukesh Kumar Vyas and Asaf Pe'er},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.19108},
eprint = {2609.19108},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19108},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Radiation-Driven Magnetic Fields in Sub-Keplerian Accretion Flows: An Alternative to MRI
AU - Mukesh Kumar Vyas
AU - Asaf Pe'er
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.19108
UR - https://arxiv.org/abs/2609.19108
AB - Large scale magnetic fields play a crucial role in shaping the dynamics and structure of the inner parts of accretion disks and the resulting jets from the vicinity of black holes and neutron stars. Currently, the primary mechanism considered for generating and amplifying large scale magnetic fields in accretion disks is the magneto-rotational instability (MRI). Here we show that non-conservative radiation fields provide a rapid and independent mechanism for generating and amplifying magnetic fields in accretion flows. A luminous, compact corona generates a radiation-driven poloidal field that is subsequently amplified by differential rotation, yielding quadratic magnetic-field growth and, over a broad range of coronal luminosities and sizes and MRI amplification locations, magnetization on timescales comparable to or shorter than those of the MRI. The mechanism therefore provides not merely an alternative to MRI, but an additional and, over a substantial region of parameter space, dominant channel for magnetic-field generation from initial conditions with zero magnetic field. Since the radiation-driven source arises directly from the non-conservative nature of the radiation field, such magnetic-field generation is an inevitable consequence of sufficiently strong and anisotropic radiation sources in black-hole accretion flows. More generally, the mechanism requires only a non-conservative radiation field and differential plasma motion, and is therefore expected to operate in a broad range of luminous astrophysical systems, including active galactic nuclei, gamma-ray bursts, and tidal disruption events.
ER -