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Magnetic Field Amplification during a Turbulent Collapse
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Carnegie Mellon University, USA; Ilia State University, Georgia.ORCID-id: 0000-0002-7304-021X
Antal upphovsmän: 22025 (Engelska)Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 990, nr 2, artikel-id 223Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The question of whether a dynamo can be triggered by gravitational collapse is of great interest, especially for the early Universe. Here, we employ supercomoving coordinates to study the magnetic field amplification from decaying turbulence during gravitational collapse. We perform 3D simulations and show that for large magnetic Reynolds numbers, there can be exponential growth of the comoving magnetic field with conformal time before the decay of turbulence impedes further amplification. The collapse dynamics only affect the nonlinear feedback from the Lorentz force, which diminishes more rapidly for shorter collapse times, allowing nearly kinematic continued growth. We confirm that helical turbulence is more efficient in driving dynamo action than nonhelical turbulence, but this difference decreases for larger collapse times. We also show that for nearly irrotational flows, dynamo amplification is still possible, but it is always associated with a growth of vorticity—even if it still remains very small. In nonmagnetic runs, the growth of vorticity is associated with viscosity and grows with the Mach number. In the presence of magnetic fields, vorticity emerges from the curl of the Lorentz force. During a limited time interval, an exponential growth of the comoving magnetic field with conformal time is interpreted as clear evidence of dynamo action.

Ort, förlag, år, upplaga, sidor
2025. Vol. 990, nr 2, artikel-id 223
Nyckelord [en]
Magnetic fields
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
URN: urn:nbn:se:su:diva-247298DOI: 10.3847/1538-4357/adf725ISI: 001568029600001Scopus ID: 2-s2.0-105015866670OAI: oai:DiVA.org:su-247298DiVA, id: diva2:2000041
Tillgänglig från: 2025-09-23 Skapad: 2025-09-23 Senast uppdaterad: 2025-09-23Bibliografiskt granskad

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Brandenburg, Axel

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Nordiska institutet för teoretisk fysik (Nordita)Institutionen för astronomiOskar Klein-centrum för kosmopartikelfysik (OKC)
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Astrophysical Journal
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