NASA’s IXPE May Have Proven 90-Year-Old Theory

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NASA’s IXPE May Have Proven 90-Year-Old Theory

A first of its kind measurement of a magnetar may have captured empty space behaving in a way physicists have predicted for 90 years, but never directly observed. The results published Wednesday in Nature.

An illustration of a bright blue, glowing neutron star against a black, starry background. Thin blue rings representing magnetic field lines loop around the star. A bright blue beam shoots diagonally downward to the left. On the right side, two semi-transparent cones emerge from the star, containing wavy lines representing radiation. The upper cone aligns with the magnetic field and shoots a bright white beam diagonally upward, while the lower, darker blue cone is offset and shoots a purple-blue beam straight out to the right.

This artist’s concept depicts magnetar 1E 1547.0-5408, a rapidly rotating neutron star with magnetic fields over a trillion times stronger than Earth’s. Blue curves emanating from the star’s two magnetic poles represent the magnetic field lines. The magnetar is a significant emitter of radio and X-ray radiation, with their peaks offset during its 2.1-second rotation period. This indicates the primary X-ray emitter is a secondary “hot spot” offset from the magnetic axis. These emitters are depicted as conical sections: the lighter blue radio emission peaks at the magnetic field’s symmetry axis, while the darker blue X-ray emission peaks below. The upper and lower emission cones show X-ray polarization degrees of 40% and 80%, respectively. These high values, along with smooth, coherent variations in polarization across the rotation period, provide the most definitive signal to date of vacuum birefringence a long-sought prediction of quantum electrodynamics.

NASA/Pablo Garcia

Fast facts

Magnetars are a special class of neutron stars with ultra-strong magnetic fields, the strongest of any object in the observable universe, around a trillion times stronger than the strongest permanent magnets ever built on Earth. These super magnetic neutron stars offer glimpses into the physics of intense environments that cannot be found anywhere else.
Neutron stars are the leftover cores of massive stars, formed at the end of their life cycles, that possess more mass than the Sun, condensed down to the size of a city, making them natural laboratories for studying extreme physics.

Scientists using NASA’s IXPE (Imaging X-ray Polarimetry Explorer) conducted more than 140 hours of observations of the magnetar 1E 1547-5408, between March and April 2025, alongside NASA’s NICER (Neutron Star Interior Composition Explorer) and Murriyang, CSIRO’s Parkes radio telescope, owned and operated by Australia’s national science agency. This was the first-ever coordinated radio and X-ray polarization measurement of a magnetar.

1E 1547-5408, spinning in a full rotation every 2 seconds, is a unique magnetar that consistently emits bright radio energy and X-ray light, for reasons scientists are still trying to understand.

Observations showed the polarization, or the orientation and level of alignment of the incoming photons, is nearly three times greater than seen in similar sources. This high level of polarization was surprising, since the geometry of the magnetar’s magnetic fields suggest that the measurements we see should be close to zero at certain points in the star. Standard surface emission models do not explain this large value either, indicating that another effect must be boosting the polarization.

Enter vacuum birefringence, a 90-year-old theory in the realm of quantum electrodynamics. First proposed in 1936, the theory suggests that the vacuum of space can be altered by extreme magnetic fields, far higher than those humans can create on Earth. Under such conditions, the vacuum acts like a lens or a prism, filtering light based on the direction it is traveling, therefore enhancing its total polarization. The IXPE mission’s ability to measure X-ray polarization was essential to test this theory.

Simulations performed by the research team support the possibility of vacuum birefringence causing the distinct signal. Hoa Dinh Thi, a postdoctoral associate at Rice University in Houston and co-lead author of the publication highlighting the results, said, “Our model suggests that reproducing the observed X-ray polarization signatures, while also satisfying the constraints set by radio observations, requires the presence of vacuum birefringence in the neutron star’s environment. This finding exemplifies how neutron stars enable us to test fundamental physics in environments not replicable in labs on Earth.”

The large polarization measurements from the magnetar give strong support to the theoretical prediction, and could be the first time this effect has been directly observed anywhere.

“This result truly highlights the interdisciplinary power of the field of astrophysics,” said Rachael Stewart, a Ph.D. candidate at George Washington University and lead author of the paper published in Nature. “The information we obtained from looking at this distant star core also gives us clues about the nature of the fabric of reality as we know it, and I find that to be incredible.”

Further IXPE observations of this source and other magnetars will confirm this signal and potentially reveal other exotic effects of quantum electrodynamics.

More about IXPE

The IXPE mission, which continues to provide unprecedented data enabling groundbreaking discoveries about celestial objects across the universe, is a joint NASA and Italian Space Agency mission with partners and science collaborators in 12 countries. It is led by NASA’s Marshall Space Flight Center in Huntsville, Alabama. Headquartered in Falls Church, Virginia, BAE Systems, Inc., manages spacecraft operations together with the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder. Learn more about IXPE’s ongoing mission here:

https://nasa.gov/ixpe