Issue |
A&A
Volume 641, September 2020
|
|
---|---|---|
Article Number | A165 | |
Number of page(s) | 11 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202037835 | |
Published online | 25 September 2020 |
A dynamo amplifying the magnetic field of a Milky-Way-like galaxy
1
Foundation for Research and Technology (FORTH), Nikolaou Plastira 100,
Vassilika Vouton GR - 711 10,
Heraklion,
Crete,
Greece
2
Department of Physics and ITCP, University of Crete,
71003
Heraklion,
Greece
e-mail: entorm@physics.uoc.gr
3
Scuola Normale Superiore,
Piazza dei Cavalieri 7,
56126
Pisa,
Italy
4
Max-Planck Institute for Astrophysics,
Karl-Schwarzschild-Strae 1,
85748
Garching,
Germany
Received:
27
February
2020
Accepted:
22
June
2020
Context. The magnetic fields of spiral galaxies are so strong that they cannot qualify as primordial. Their typical values are over one billion times higher than any value predicted for the early Universe. Explaining this immense growth and incorporating it in galaxy evolution theories is one of the long-standing challenges in astrophysics.
Aims. So far, the most successful theory for the sustained growth of the galactic magnetic field is the alpha-omega dynamo. This theory predicts a characteristic dipolar or quadrupolar morphology for the galactic magnetic field, which has been observed in external galaxies. So far, however, there has been no direct demonstration of a mean-field dynamo operating in direct, multi-physics simulations of spiral galaxies. We carry out such a demonstration in this work.
Methods. We employed numerical models of isolated, star-forming spiral galaxies that include a magnetized gaseous disk, a dark matter halo, stars, and stellar feedback. Naturally, the resulting magnetic field has a complex morphology that includes a strong random component. Using a smoothing of the magnetic field on small scales, we were able to separate the mean from the turbulent component and analyze them individually.
Results. We find that a mean-field dynamo naturally occurs as a result of the dynamical evolution of the galaxy and amplifies the magnetic field by an order of magnitude over half a Gyr. Despite the highly dynamical nature of these models, the morphology of the mean component of the field is identical to analytical predictions.
Conclusions. This result underlines the importance of the mean-field dynamo in galactic evolution. Moreover, by demonstrating the natural growth of the magnetic field in a complex galactic environment, it brings us a step closer to understanding the cosmic origin of magnetic fields.
Key words: magnetic fields / dynamo / ISM: magnetic fields / galaxies: magnetic fields
© ESO 2020
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