A plasma’s structure, with different colours representing varying charge and gas densities
James R. Beattie et al. 2024
The most detailed simulation of the chaotic supersonic plasma that floats across our universe has revealed an intricate map of swirling magnetic fields.
Clouds of charged particles, or plasmas, are ubiquitous in our universe and can exist at small scales, as with the solar wind, or cover vast distances, such as over entire galaxies. These clouds experience turbulence, similar to the air in Earth’s atmosphere, which dictates key characteristics of our universe, such as how magnetic fields vary over space or how quickly stars form.
However, the turbulence’s inherently chaotic nature, as well as the mix of very different plasma speeds, makes it impossible to predict the plasma’s behaviour in a mathematically exact way.
Now, James Beattie at the Australian National University in Canberra and his colleagues have run the largest chaotic plasma simulation of its kind, using the SuperMUC-NG supercomputer at the Leibniz Supercomputing Centre in Germany.
The researchers set up a plasma fixed over a 10,000-cube grid, which they artificially stirred to see how the turbulence rippled through it, similar to stirring a cup of coffee. The simulation would take 10,000 years to run on a standard single-core computer, says Beattie.
A plasma’s intricate structure can be seen above in one extraordinary slice from the simulation grid. The top half of the image shows its charge density, with regions of red representing high density and blue for low density. The bottom half of the image shows gas density, with yellow-orange colours representing high density and green showing low density. The white lines indicate the contours of the resulting magnetic field lines.
As well as teaching the researchers about how plasma typically move through our universe, the simulation also contained an unexpected result, says Beattie. The team learned that the movement of magnetic fields from enormous plasmas doesn’t trickle down to the very smallest scales, unlike the swirls in a cup of coffee, which should move from large-scale vortices right down to the atoms themselves.
“The mixing properties on the large scales and the small scales seem to be very different,” says Beattie. “In fact, it becomes much less turbulent on the small scales than you’d expect it to.”
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