The Largest Map Yet of Magnetic Fields Across the Universe

Radio astronomers have created the biggest map of magnetic fields in the cosmic web ever made. Using Australia's ASKAP radio telescope and a new analysis method, researchers at CSIRO and international partners have mapped magnetic fields across galaxy clusters and the space between them—five times larger than all previous maps combined.

The method they used is called synchrotron intensity gradient mapping, or SIG. Devised by Alexandre Lazarian at the University of Wisconsin-Madison, it works by analyzing radio signals to figure out which way magnetic fields are pointing in different locations within galaxy clusters. The technique relies on studying how synchrotron radiation—light given off by charged particles spinning around magnetic field lines—changes in intensity from place to place.

How ASKAP Made This Possible

The Australian Square Kilometre Array Pathfinder (ASKAP) is a radio telescope in Western Australia that captures radio waves across a wide area. What makes it ideal for this work is its ability to detect polarized radio signals—waves that vibrate in specific directions. This sensitivity allowed the team to pick up the faint radio signals that fill galaxy clusters and the space between them.

Dr. Tessa Vernstrom, a researcher at CSIRO, has led much of this work studying the gas and magnetic fields that connect the universe. She focuses on the filament-like networks of gas and magnetism that form the cosmic web's backbone, linking galaxies across billions of light-years.

The team tested their method on the El Gordo cluster, a massive group of galaxies spanning 6 million light-years. This served as a proof of concept—showing that the SIG technique could map magnetic field directions at scales never attempted before.

Why This Method Works Better

Traditional ways of measuring cosmic magnetic fields relied mainly on something called Faraday rotation. But this technique has drawbacks: the gas between us and distant objects can muddy the signal, and it doesn't give a very detailed picture.

The SIG method takes a different approach. When charged particles spiral around magnetic field lines, they emit radio waves with varying brightness. By looking at how that brightness changes across space, astronomers can work out the 3D structure of the magnetic field itself. This avoids many of the complications that plague the older techniques.

The method's success depends on having very high-quality radio data across large areas of sky—exactly what ASKAP was designed to provide. Lazarian's published work in Nature Communications laid out the mathematical framework that makes this possible, showing how to convert radio observations into actual magnetic field maps.

What This Reveals About the Universe

These expanded maps show something striking: magnetic fields are everywhere in the cosmic web, far beyond just individual galaxies. The measurements provide direct evidence that magnetism threads through the filament-like structures that connect galaxies across cosmic distances—something theory predicted but observation hadn't firmly confirmed until now.

Magnetic fields in galaxy clusters and intergalactic space matter because they affect how plasma moves, how cosmic rays travel, and where new stars form. Understanding where these fields come from—whether they originated in the early universe or built up over time through other processes—is a fundamental question in cosmology. These new maps give astronomers data to work with.

Magnetism also creates pressure and tension forces, much like gravity does. These forces can shape how matter clumps together to form galaxies and how gas flows along the cosmic web's filaments. The SIG method can now detect and measure these magnetic signatures in ways we couldn't before.

Looking ahead, these magnetic field maps open new ways to study how cosmic structures formed and evolved. The detailed geometry of magnetic fields leaves clues about what shaped the universe at different points in its history.

What Comes Next

Alec Thomson leads the team building the Square Kilometre Array (SKA) Observatory, ASKAP's more powerful successor. The SKA will have far greater sensitivity and resolution, allowing even more detailed studies of cosmic magnetism across larger stretches of space.

The success of ASKAP's magnetic mapping work sets the stage for future large-scale surveys using newer radio telescopes. Those observations will push measurements back further in time, tracking how cosmic magnetic fields evolved from the early universe to today, and revealing how central they are to galaxy formation.

In my view, the transition from measuring isolated magnetic fields in nearby galaxies to systematically mapping magnetic structures across intergalactic space marks a genuine leap forward in observational astronomy. It's a shift comparable to radio astronomy's emergence as a discipline in the mid-20th century. For decades, cosmic magnetism remained largely theoretical—we had models but not much data to test them against. These measurements begin to change that, moving the field from educated guessing toward empirical evidence. As radio telescope capabilities continue to improve, magnetism should finally get the observational attention cosmology has long owed it.