Magnetic fields exist everywhere in the universe, from planets and stars to entire galaxies. These invisible forces influence major cosmic events and processes, such as solar storms, the movement of high-energy particles, and even the formation of galaxies. Small magnetic fields are often chaotic and turbulent, but much larger magnetic structures appear surprisingly organized. For decades, scientists have struggled to explain how the disorder in the universe creates such large-scale order.
Now, researchers led by scientists at the University of Wisconsin-Madison think they may have found the missing piece of the puzzle.
In a new study published in naturethe team used highly detailed computer simulations to study plasma flow. Their results suggest that large magnetic fields can be generated when turbulent plasmas develop organized jet-like flows. The discovery provides a new explanation for how cosmic magnetic fields are formed and could help scientists better understand everything from black hole formation to near-Earth space weather.
“Magnetic fields throughout the universe are large-scale and ordered, but our understanding of how these fields are generated is that they result from some kind of turbulent motion,” says the study’s lead author Bindesh Tripathi, a former physics graduate student at the University of Wisconsin-Madison and now a postdoctoral fellow at Columbia University. “Given that turbulence is known to be a destructive factor, the question remains how does it create a constructive large-scale field?”
Searching for order in the turbulence of space
Before focusing on three-dimensional (3D) magnetic fields, Tripathi studied systems involving fluid flows and two-dimensional (2D) magnetic fields. While studying 3D magnetic turbulence images and videos, he noticed that large-scale magnetic structures resembled the shapes of large-scale flows.
However, applying fluid mechanics directly to magnetic fields has not been easy. While fluid flow problems can often be simplified to two dimensions, magnetic field generation must be solved in full 3D space, making it much more computationally difficult.
To address this challenge, the researchers changed two important aspects of previous research.
The first is to add a constantly updated velocity gradient to the simulation. Velocity gradients occur when different parts of a system move at different speeds. For example, a bicycle rider who suddenly hits a curb will experience a steep velocity gradient as the rider’s momentum continues to move forward even though the bicycle has stopped. Similar effects occur throughout the universe, including inside the Sun and during neutron star mergers. The research team suspected that these gradients may play a major role in shaping the magnetic field.
Large-scale supercomputer simulation reveals patterns
The second big step is computational power. The researchers performed what is believed to be the most detailed simulation yet of a magnetic field interacting with an unstable velocity gradient. Their model used 137 billion grid points in 3D space.
In total, the team ran about 90 simulations, generating 0.25 petabytes of data and consuming nearly 100 million CPU hours on Purdue University’s Anvil supercomputer.
“We start the simulation with a flow with a velocity gradient, then add some small perturbations, such as moving one fluid particle to an infinitesimal size, propagate and grow the perturbations throughout the system, and then analyze the data over time,” Tripathi says. “Initially, these perturbations cause turbulence and magnetic fields within small-scale structures, but over time, larger, more ordered structures emerge.”
When the researchers repeated the simulation without maintaining large-scale velocity gradients, organized magnetic structures never formed. Instead, the system remained chaotic and disorganized.
“So that’s really the key: to have a stable large-scale gradient in velocity,” he emphasizes.
Solving the long-standing magnetic field problem
Scientists have been studying magnetic dynamos, the process that generates magnetic fields, for about 70 years. But most theoretical models struggle to produce the large, ordered magnetic structures that astronomers actually observe in space.
Paul Terry, a professor of physics at the University of Wisconsin-Madison and lead author of the study, added: “The generation of magnetic fields by dynamos has been extensively studied for 70 years, with the frustrating result that the fields produced differ from observations and are almost always small-scale and highly disordered. This study therefore has the potential to solve a long-standing problem.”
Although the new theory cannot be directly tested in the remote space environment, previous laboratory experiments appear to support this finding. In 2012, researchers at the Wisconsin Plasma Physics Laboratory observed behavior in magnetic fields that could not be explained by existing theories. A new model developed by Tripathi and his colleagues more closely matches these puzzling experimental results.
Black holes, neutron stars, and their impact on space weather
This discovery could have important implications for astrophysics as a whole.
“This research has the potential to explain the magnetodynamics associated with things like neutron star mergers and black hole formation, with direct applications to multimessenger astronomy,” Tripathi said. “It may also help us better understand the star’s magnetic field and predict gas eruptions from the Sun toward Earth.”
This research was supported by the National Science Foundation (2409206) and the U.S. Department of Energy (DE-SC0022257) through the DOE/NSF Partnership in Basic Plasma Science and Engineering. Purdue University’s Anvil supercomputer was used through assignment TG-PHY130027 from the Advanced Cyberinfra Structure Coordination Ecosystem: Services & Support (ACCESS) program, supported by the National Science Foundation (2138259, 2138286, 2138307, 2137603, and 2138296).
