Cosmic web reveals tiny magnetic fields from the dawn of time

Long before galaxies sparkled in the sky or stars took shape, invisible forces stirred in the early Universe. One of those forces—magnetism—emerged in ways scientists are only now beginning to understand. Though these magnetic fields were astonishingly weak—billions of times less powerful than a fridge magnet—their fingerprints still linger in the vast cosmic web that stretches across space.

This delicate but vital finding comes from a large-scale study led by researchers at SISSA, the International School for Advanced Studies in Trieste, Italy. Collaborating with scientists from the Universities of Hertfordshire, Cambridge, Nottingham, Stanford, and Potsdam, the team ran over 250,000 computer simulations to probe how these early magnetic fields may have shaped the very structure of the Universe.

Their paper, published in Physical Review Letters, may reshape our understanding of the first moments after the Big Bang and how the earliest stars and galaxies formed.

In the vast emptiness between galaxies lies a faint network called the cosmic web. This structure resembles a spider’s web, linking galaxies together in threadlike filaments of gas and dark matter. Though most people imagine space as empty, these filaments are teeming with material—some visible, some hidden.

What puzzled scientists for years was the presence of magnetism in this web, not just near galaxies but in distant, quiet regions far from any stars. According to Mak Pavičević, a PhD student at SISSA and the lead author of the study, this magnetism seemed out of place.

“The cosmic web, of which much remains to be discovered, is a filamentary structure connecting the galaxies that permeates the Universe,” said Pavičević. “One of its many unsolved mysteries is why it is magnetised… even in distant regions that are sparsely populated.”

His advisor and co-author, Matteo Viel, explained further: “Our hypothesis was that this could be a legacy of events occurring in cosmic epochs during the birth of the Universe… through events in later epochs, called phase transitions.”

These “phase transitions” refer to brief periods after the Big Bang when the Universe rapidly changed states, like water freezing into ice. During such transitions, it’s believed magnetic fields may have been born. Alternatively, these fields might have formed during the “inflationary” period—an unimaginably brief moment of rapid expansion that occurred even before the Big Bang itself.

Either way, the team wanted to know: how strong were those magnetic fields? And could they really still influence the shape of the Universe today?

To answer these questions, the team turned to advanced computer simulations. Working with over a quarter of a million of them, they tested how primordial magnetic fields might affect the cosmic web over billions of years.

“These are the most realistic and largest suite state-of-the-art simulations of the influence of primordial magnetic field on the intergalactic cosmic web,” said Vid Iršič from the University of Hertfordshire, a co-author of the paper.

These simulations recreated the early conditions of the Universe and tracked how particles, gases, and magnetic forces evolved over time. By comparing the results with real data gathered by telescopes, the scientists could see which models best matched reality.

One major finding stood out. Including even a weak magnetic field in the early Universe helped the simulation better match what astronomers observe today. A tiny magnetic field of just 0.2 nano-gauss—comparable to the magnetism produced by neurons in your brain—seemed to fit the observed data more closely than models without it.

The magnetic influence, though minuscule, appeared to amplify the density of matter in some parts of the cosmic web. This increased density could have made it easier for stars and galaxies to form, speeding up the birth of complex structures in space.

“We can say that a standard model of the Universe with a very weak magnetic field of around 0.2 nano-gauss actually fits experimental data much better,” said Viel.

Another breakthrough came when the researchers calculated just how strong these ancient magnetic fields could have been. Their study set a new upper limit, significantly lower than what previous studies had estimated. This narrows down the possible range and supports independent research using different tools, such as data from the cosmic microwave background (CMB)—the faint afterglow of the Big Bang.

“Our research places strict limits on the intensity of magnetic fields formed in the very early moments of the Universe,” said Pavičević.

Iršič added that these new limits could reshape several areas of cosmology. “Not only will these new limits help us understand the impact of the primordial magnetic fields on the evolution of the cosmos, but they also hold important implications for other theoretical models that enhance structure formation.”

The team hopes their work will inspire further study using new instruments like the James Webb Space Telescope, which may soon be able to spot more direct evidence of these fields by observing early galaxies in finer detail.

One key tool in this study is something called the Lyman-alpha forest. This “forest” isn’t made of trees, but of light—specifically, light from distant quasars passing through hydrogen gas in the Universe.

As light travels from a quasar (a bright, active galaxy) toward Earth, it passes through clouds of hydrogen gas that absorb some of the light at specific wavelengths. These absorption patterns create a series of dark lines in the quasar’s spectrum, known as the Lyman-alpha forest.

Scientists can study these lines to learn about the distribution of matter in the Universe. The forest is particularly good at revealing small-scale structures, including those in the cosmic web far from any galaxies—exactly the regions where ancient magnetic fields are hardest to explain.

By analyzing how these absorption lines change across different scales, scientists can infer how much “power” exists in the density of matter at those scales. If primordial magnetic fields are present, they increase this power, especially at smaller scales. That leaves a measurable imprint on the Lyman-alpha forest.

This technique gave the researchers a precise way to test their simulations and rule out models with overly strong magnetic fields.

“We argue that the Lyman-alpha forest could be the ideal way to constrain cosmological PMFs,” the team wrote. “It probes the filamentary cosmic web in environments far from galaxies, where the impact of magnetic fields generated by astrophysical sources should be minimal.”

While the math and simulations are complex, the broader message is clear. Even the weakest forces, born in the first moments of time, may have left lasting marks on the largest structures in the Universe.

Magnetic fields, long overlooked in cosmological models, could be a key player in shaping how matter clumped together to form stars, galaxies, and eventually planets.

The study also adds weight to the idea that new physics—beyond what we currently understand—may be hidden in the fine details of cosmic structure. These findings don’t just limit how strong early magnetic fields could have been. They also challenge scientists to think about how such tiny forces can influence the evolution of everything we see in the sky today.

And with powerful tools like the James Webb Space Telescope now active, researchers are excited to push these findings even further. The mysteries of the early Universe are far from solved—but thanks to studies like this, we’re getting closer.

Note: The article above provided above by The Brighter Side of News.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.