Numerical evidence for a small-scale dynamo approaching solar magnetic Prandtl numbers

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Nature Astronomy, Volume 2023
Magnetic fields on small scales are ubiquitous in the Universe. Although they can often be observed in detail, their generation mechanisms are not fully understood. One possibility is the so-called small-scale dynamo (SSD). Prevailing numerical evidence, however, appears to indicate that an SSD is unlikely to exist at very low magnetic Prandtl numbers (PrM) such as those that are present in the Sun and other cool stars. Here we have performed high-resolution simulations of isothermal forced turbulence using the lowest PrM values achieved so far. Contrary to earlier findings, the SSD not only turns out to be possible for PrM down to 0.0031 but also becomes increasingly easier to excite for PrM below about 0.05. We relate this behaviour to the known hydrodynamic phenomenon referred to as the bottleneck effect. Extrapolating our results to solar values of PrM indicates that an SSD would be possible under such conditions.
Funding Information: We acknowledge fruitful discussions with A. Brandenburg, I. Rogachevskii, A. Schekochihin and J. Schober during the Nordita programme on ‘Magnetic field evolution in low density or strongly stratified plasmas’. Computing resources from CSC during the Mahti pilot project and from Max Planck Computing and Data Facility (MPCDF) are gratefully acknowledged. This project, including all authors, has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Project UniSDyn, grant agreement number 818665). This work was done in collaboration with the COFFIES DRIVE Science Center. | openaire: EC/H2020/818665/EU//UniSDyn
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Warnecke, J, Korpi-Lagg, M J, Gent, F A & Rheinhardt, M 2023, ' Numerical evidence for a small-scale dynamo approaching solar magnetic Prandtl numbers ', Nature Astronomy, vol. 7, no. 6, pp. 662-668 .