Magnetic fields are everywhere in the universe - planets, stars, entire galaxies - and they're surprisingly well-organized for something that should, by all rights, be a chaotic mess. For decades, scientists have scratched their heads over how disorder in space manages to produce such large-scale order. Now, researchers at the University of Wisconsin-Madison think they've found the missing piece, and it involves some truly massive number-crunching.
In a new study published in Nature, the team ran supercomputer simulations so detailed they used 137 billion grid points in 3D space. That's not a typo. The simulations, which generated 0.25 petabytes of data and consumed nearly 100 million CPU hours on Purdue University's Anvil supercomputer, focused on how turbulent plasma flows can spontaneously develop organized jet-like structures - and, in turn, create large magnetic fields.
"Magnetic fields across the cosmos are large-scale and ordered, but our understanding of how these fields are generated is that they come from some kind of turbulent motion," said study lead author Bindesh Tripathi, a former UW-Madison physics grad student now at Columbia University. "Given that turbulence is known to be a destructive agent, the question remains, how does it create a constructive, large-scale field?"
The key, the team found, was adding a constantly renewed velocity gradient - basically, different parts of a system moving at different speeds, like a cyclist hitting a curb while the bike stops but the rider keeps going. The same thing happens inside the Sun and during neutron star mergers. When the researchers ran simulations without that steady large-scale gradient, the organized magnetic structures never formed. Chaos reigned. With the gradient? Order emerged.
"So that's really the main key: to have a steady, large-scale gradient in velocity," Tripathi emphasized.
This isn't just academic navel-gazing. The findings could help explain everything from black hole formation to neutron star mergers to why solar storms sometimes aim straight at Earth. And they may finally resolve a 70-year-old mystery about magnetic dynamos - the processes that generate magnetic fields - which have stubbornly refused to produce the large, ordered structures astronomers actually observe.
"Magnetic field generation via dynamos has been extensively studied for 70 years, with the frustrating result that the generated fields almost always end up at small scales and highly disordered, unlike observations," said Paul Terry, physics professor at UW-Madison and senior author. "This work, therefore, potentially resolves a long-standing issue."
While we can't exactly test this in distant cosmic environments, earlier lab experiments from 2012 at the Wisconsin Plasma Physics Laboratory - which baffled existing theories - now make a lot more sense. So, congratulations to the supercomputer: you've finally made space magnetism slightly less mysterious.