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How does turbulence behave in the space between the stars of our galaxy? In a large-scale computer simulation, an international team of researchers, including Prof. Dr Ralf Klessen from the Centre for Astronomy of Heidelberg University (ZAH), has mapped the full range of turbulent energy in the so-called interstellar medium with unprecedented numerical resolution. This detailed quantitative mapping also takes into account the complex magnetic properties of this cosmic “disorder”. The results offer key insights into processes that shape the structure and evolution of galaxies, including star formation.
Press Release
Heidelberg, 16 May 2025
Cosmic Turbulence Shapes Structure and Evolution of Galaxies
Large-scale computer simulation maps magnetic “disorder” of the interstellar medium
Unlike the phenomenon observed on Earth – chaotic, seemingly random motion in air or water – turbulence in space occurs in a plasma, a hot, electrically charged gas permeated by and strongly affected by magnetic fields. This makes it particularly difficult to observe and model what might be going on in the interstellar medium. The international research team has now developed the world’s largest simulation designed to replicate the magnetic turbulence under galactic conditions. Their high-precision data reveal major deviations from canonical models, according to Prof. Klessen. The researchers were able to observe that fundamental principles of the turbulence theory apply in the case of magnetized plasma.
One central process of the turbulence theory is the so-called turbulent cascade, where energy injected into a fluid or plasma at large scales is transferred gradually into smaller and smaller scales until it is eventually dissipated as heat. “The turbulent cascade in the interstellar medium extends over many orders of magnitude, far greater than we were previously able to realistically model on a standard computer,” emphasizes Ralf Klessen, who runs the Star Formation group at the ZAH. The Heidelberg researcher points out that the transition between supersonic and subsonic turbulence is particularly significant since astrophysical plasmas often exhibit supersonic flows. “The so-called sonic scale is an important parameter in our theoretical models of star formation. In this new calculation, we have succeeded for the first time in resolving and describing in detail this important transition in the presence of magnetic fields on a high-performance supercomputer,” explains Prof. Klessen.
One important parameter of the major computer simulation is the so-called Reynolds number, a dimensionless quantity that measures the ratio of inertial forces to viscous forces in a fluid flow. The present calculations using Reynolds numbers of over one million took more than 80 million CPU hours distributed across 140,000 computer cores on a high-performance supercomputer at the Leibniz Supercomputing Centre. The researchers learned that magnetic fields considerably influence how energy cascades in the interstellar medium. They suppress small-scale movements and enhance certain wave-like disturbances that locally create the conditions for the birth of new stars. “Using our simulations, we were able to characterize how turbulent energy is distributed from the largest galactic scales down to the scales where star formation begins,” states Klessen. “Our galaxy is not static, but a dynamic, turbulent environment, and the new findings bring us a step closer to understanding the physical laws that govern this cosmic ‘disorder’.”
The results of the research of the international team of researchers from the USA, Canada, Australia, and Germany were published in the journal “Nature Astronomy”.
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J.R. Beattie, Ch. Federrath, R.S. Klessen, S. Cielo, A. Bhattacharjee: The spectrum of magnetized turbulence in the interstellar medium. Nature Astronomy (13 May 2025); DOI: 10.1038/s41550-025-02551-5
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