Abstract
At every scale they occupy, magnetic fields affect various phenomena, including star formation, cosmic-ray transport, charged-particle acceleration, space weather, transport in planetary atmospheres and laboratory plasmas. These fields are often generated and sustained by turbulent flows in a process called the dynamo. In 1955, E. N. Parker parameterized the effects of small-scale turbulence to propose a mean-field dynamo theory1. The widely used theory reproduces observed large-scale fields but suffers from difficulty in tuning parameters as they are not justified from first principles: studies of turbulent flows show tangl…
Abstract
At every scale they occupy, magnetic fields affect various phenomena, including star formation, cosmic-ray transport, charged-particle acceleration, space weather, transport in planetary atmospheres and laboratory plasmas. These fields are often generated and sustained by turbulent flows in a process called the dynamo. In 1955, E. N. Parker parameterized the effects of small-scale turbulence to propose a mean-field dynamo theory1. The widely used theory reproduces observed large-scale fields but suffers from difficulty in tuning parameters as they are not justified from first principles: studies of turbulent flows show tangled magnetic fields, which are folded and fragmented into small-scale structures owing to shear-flow straining2,3. Here, considering a shear flow that is unstable and driven, we develop analytic theory and perform three-dimensional, advanced computer simulations of turbulence with up to 4,096 × 4,096 × 8,192 grid points, showing ab initio generation of quasi-periodic, large-scale magnetic fields. The generation occurs via the mean-vorticity effect—an additional mean-field dynamo process postulated4 in 1990. Crucial to this dynamo is the prior generation of large-scale three-dimensional jets, robustly produced as topologically protected and exact nonlinear solutions of the magnetohydrodynamic equations. The jet-driven dynamo applies to shear-driven laboratory and astrophysical systems. These include binary neutron star mergers5,6, where the reported dynamo probably operates on microsecond timescales to produce in milliseconds some of the strongest magnetic fields in the Universe7, providing signals for multi-messenger astronomy8.
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Data availability
Any data needed to evaluate the conclusions of this article are present in the article or Methods or available via Zenodo at https://doi.org/10.5281/zenodo.17162239 (ref. 56). Simulation files, post-processing scripts, additional materials, data used to produce figures, and details of numerical implementation are available via Zenodo at https://doi.org/10.5281/zenodo.17162239 (ref. 56). Upon request, the corresponding author will share additional details on analysis methods.
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Acknowledgements
We thank J. R. Beattie, A. M. Beloborodov, A. Bhattacharjee, K. J. Burns, F. Ebrahimi, R. Habegger, D. Lecoanet, B. Miquel, E. R. Most, J. S. Oishi, S. Patil and B. Ripperda for discussions. This work used Anvil at Purdue University through allocation TG-PHY130027 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) programme, which is supported by National Science Foundation grants 2138259, 2138286, 2138307, 2137603 and 2138296. We acknowledge staff support from Anvil and additional computing resources from Bridges-2. This material is based on work funded by the National Science Foundation (NSF) under award 2409206 and Department of Energy (grant number DE-SC0022257) through the DOE/NSF Partnership in Basic Plasma Science and Engineering. A.E.F. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2402142.
Author information
Author notes
B. Tripathi
Present address: Columbia University, New York, NY, USA
Authors and Affiliations
University of Wisconsin–Madison, Madis