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Peer-reviewedCC BY 4.0The Astrophysical Journal

No Evidence of Vorticity Production from Irrotational Turbulent Gravitational Collapse Yet

  • Axel Brandenburg1,2,3,4
  • Evangelia Ntormousi5
  • Jennifer Schober6
6 affiliations
  1. 1KTH Royal Institute of Technology and Stockholm University
  2. 2Stockholm University
  3. 3Carnegie Mellon University
  4. 4Ilia State University
  5. 5Scuola Normale Superiore
  6. 6Universität Bonn
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Abstract

Gravitational collapse creates large amounts of kinetic energy that could potentially seed turbulence. If such turbulence were also suitable to initiate dynamo action, the resulting magnetic field would further modify the dynamics, especially on small length scales. However, a small-scale dynamo is believed to require vortical turbulence, whereas the collapse produces mainly irrotational motions, which may not be efficient for dynamo action. Here, we study the efficiency of vorticity production during a turbulent collapse. We adopt a barotropic equation of state, where pressure and density gradients are parallel, and no magnetic field, so that vorticity can only be produced by viscosity and by vortex dynamo-type amplification. Using direct numerical simulations of gravitational collapse, we show that, for the parameter space accessible to our numerical resolution, these effects are related to the initial irrotational turbulence and are not induced by the collapse. Vorticity production along with the associated small-scale dynamo action are still expected to occur for sufficiently large Reynolds numbers, especially when baroclinic effects are allowed for, but some of the earlier numerical evidence in the literature using a barotropic equation of state is now found to be the result of subgrid-scale modeling and not reproduced in direct numerical simulations.

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Cite

BibTeXRIS
BibTeX
@article{brandenburg2026evidence,
  title = {{No Evidence of Vorticity Production from Irrotational Turbulent Gravitational Collapse Yet}},
  author = {Axel Brandenburg and Evangelia Ntormousi and Jennifer Schober},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = oct,
  doi = {10.3847/1538-4357/aea846},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea846},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - No Evidence of Vorticity Production from Irrotational Turbulent Gravitational Collapse Yet
AU  - Axel Brandenburg
AU  - Evangelia Ntormousi
AU  - Jennifer Schober
PY  - 2026
DA  - 2026/10/16
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea846
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea846
AB  - Gravitational collapse creates large amounts of kinetic energy that could potentially seed turbulence. If such turbulence were also suitable to initiate dynamo action, the resulting magnetic field would further modify the dynamics, especially on small length scales. However, a small-scale dynamo is believed to require vortical turbulence, whereas the collapse produces mainly irrotational motions, which may not be efficient for dynamo action. Here, we study the efficiency of vorticity production during a turbulent collapse. We adopt a barotropic equation of state, where pressure and density gradients are parallel, and no magnetic field, so that vorticity can only be produced by viscosity and by vortex dynamo-type amplification. Using direct numerical simulations of gravitational collapse, we show that, for the parameter space accessible to our numerical resolution, these effects are related to the initial irrotational turbulence and are not induced by the collapse. Vorticity production along with the associated small-scale dynamo action are still expected to occur for sufficiently large Reynolds numbers, especially when baroclinic effects are allowed for, but some of the earlier numerical evidence in the literature using a barotropic equation of state is now found to be the result of subgrid-scale modeling and not reproduced in direct numerical simulations.
SN  - 0004-637X
SN  - 1538-4357
ER  -