Astronomers studying one of the most magnetic objects in the universe have found some of the strongest evidence yet for a bizarre effect predicted by quantum physics nearly 90 years ago. The finding suggests that a powerful magnetic field can change the way light travels through a vacuum, even when no ordinary matter is present.
The phenomenon is known as ‘vacuum birefringence.’ It emerges from quantum electrodynamics (QED), the theory describing how light and charged particles interact. Werner Heisenberg and Hans Euler predicted the underlying effect in 1936, proposing that what appears to be empty space can behave differently when exposed to an extraordinarily strong magnetic field.
Magnetars Turn Space Into a Quantum Laboratory
In quantum physics, a vacuum is not simply an inert void. It can be described as a fluctuating environment associated with ‘virtual particles’ that briefly appear and disappear. Under sufficiently intense magnetic fields, these quantum fluctuations are expected to influence light depending on its polarization, effectively giving the vacuum optical properties that ordinary empty space does not have.
Finding an environment extreme enough to reveal that effect has been the problem.
The new study turned to a magnetar called 1E 1547.0–5408 (or 1E1547 for short). Magnetars are neutron stars, the extraordinarily dense remnants left behind after some massive stars explode. They pack enormous amounts of matter into an object only about the size of a city and possess magnetic fields far beyond anything that can be sustained in a laboratory. Magnetar surface fields can exceed 10^14 gauss.
A Powerful Test of Vacuum Birefringence
That makes them natural laboratories for physics that is almost impossible to reproduce on Earth.
An international team, including Dr. Marcus Lower of Swinburne University of Technology, examined 1E1547 using NASA’s Imaging X-ray Polarimetry Explorer (IXPE). They combined those measurements with observations from the NICER X-ray telescope aboard the International Space Station and Murriyang, CSIRO’s Parkes radio telescope, which is owned and operated by Australia’s national science agency.
The results, published in Nature, provide a major new test of vacuum birefringence.
Magnetar Geometry Reveals a Crucial Clue
Rather than simply measuring how bright the magnetar appeared, the researchers examined the polarization of its radiation. Polarization describes the orientation in which a light wave oscillates. If vacuum birefringence is occurring, the magnetar’s immense magnetic field should influence that orientation in a predictable way as the radiation moves outward.
Radio measurements played a crucial role in establishing the magnetar’s geometry.
By tracking how the direction of the radio waves oscillated (their ‘polarisation state’) as 1E1547 rotated, the researchers concluded that its magnetic axis and rotational axis are almost aligned. Earth also appears to view the star nearly pole-on.
X-Ray Polarization Provides Striking Evidence
That unusually favorable geometry gave scientists a comparatively clean view along the magnetar’s magnetic field and made 1E1547 an especially useful target for testing the quantum prediction.
The X-rays then provided the striking part of the result.
IXPE detected exceptionally strong polarization in the magnetar’s softer X-rays. The study reports an average polarization of about 65% at 2 keV, while at some points during the magnetar’s rotation the polarization between 2 and 3 keV approached 80%.
Just as importantly, the orientation of the X-ray polarization followed the magnetar’s large-scale magnetic field in a way consistent with the radio measurements. Taken together, the observations are difficult to explain with conventional models in which radiation simply leaves the neutron star and travels through an unaffected vacuum. Models that include vacuum birefringence can naturally reproduce the behavior.
Closing In on a 90-Year-Old Quantum Prediction
Dr. Lower’s observations with Murriyang and subsequent analysis using Swinburne’s Ngarrgu Tindebeek supercomputer therefore contribute to what may be the first direct detection of this long-predicted quantum effect.
“Because of the magnetic field’s strength, Heisenberg’s virtual particles become aligned with the direction the field is pointing,” Dr. Lower said.
“By carefully tracking the direction the radio waves and X-rays oscillate as the magnetar rotates, the team found that the alignment of 1E1547’s magnetic and rotational poles were ideal for detecting vacuum birefringence.”
What It Will Take to Confirm the Discovery
Scientists have chased the effect for decades. Previous astronomical observations have produced evidence consistent with vacuum birefringence, including measurements of another neutron star and earlier polarized X-ray observations of magnetars, while laboratory experiments have also attempted to detect magnetic vacuum birefringence directly. A definitive measurement has remained elusive.
The new observations significantly narrow that gap, but the researchers say the case is not yet closed. Other processes around magnetars can also affect polarization, making additional observations and more detailed simulations essential for separating those effects from the signature of vacuum birefringence.
If that work strengthens the current interpretation, 1E1547 could provide compelling astrophysical evidence that even seemingly empty space has measurable quantum properties.
“With these future data on hand and our updated simulations, we may finally be able to complete the quest started by Heisenberg nearly 90 years ago.”
Reference: “Vacuum birefringence and the polarized X-ray emission from a radio magnetar” by Rachael E. Stewart, Hoa Dinh Thi, George Younes, Marcus E. Lower, Matthew G. Baring, Michela Negro, Fernando Camilo, Joel B. Coley, Teruaki Enoto, Alice K. Harding, Wynn C. G. Ho, Chin-Ping Hu, Philip Kaaret, Paul Scholz, Alex Van Kooten and Zorawar Wadiasingh, 5 August 2026, Nature.
DOI: 10.1038/s41586-026-10859-z
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