Signals from a dead star offer the strongest evidence yet that extreme magnetic fields alter the properties of a vacuum, causing empty space to act like a prism that changes how light travels through it, according to a study published Aug. 5 in the journal Nature. Led by Rachael Stewart, a graduate student in physics at the George Washington University, the findings confirm a 90-year-old quantum mechanics prediction known as vacuum birefringence.
Magnetars as Cosmic Laboratories for Quantum Physics
Subatomic froth is an invisible consequence of quantum mechanics under ordinary conditions. However, extreme magnetic fields can force light waves to align strongly in a specific direction. “Detecting vacuum birefringence requires a magnetic field that is over 100 million times stronger than any we’ve ever made on Earth,” study co-author Marcus Lower, an astrophysicist at the Swinburne University in Australia, said in a statement. “Thankfully, nature has provided us with magnetars, which are the perfect cosmic laboratories to go looking for this effect.”
Magnetars form as dense, city-size remnants of exploded massive stars, hosting the most powerful magnetic fields in the universe. “We’re not just studying astronomical objects anymore; we’re using them to test the laws of nature,” study co-author Michela Negro, an astrophysicist at the Louisiana State University, stated.
Did you know? Magnetars generate magnetic fields so powerful that they provide the rare celestial objects capable of revealing vacuum birefringence, testing physics under conditions impossible to replicate in terrestrial laboratories.
Overcoming Past Observational Hurdles
Astronomers previously caught glimpses of this phenomenon without definitive proof. Researchers using the Very Large Telescope in Chile observed polarization hints in 2017 around a faint neutron star named RX J1856.5-3754, located about 400 light-years from Earth. Those optical measurements remained open to interpretation because isolating the optical signal proved challenging.
Scientists noted at the time that definitive proof required space-based X-ray observatories, specifically NASA’s Imaging X-ray Polarimetry Explorer (IXPE). Launched in 2021, IXPE carries three identical telescopes built to measure high-energy X-ray polarization. “It’s only in the last six or so years that we’ve actually had a telescope capable of detecting this effect around magnetars,” Lower told Michael West Media, an independent news website in Australia.
Multi-Telescope Observations of Magnetar 1E 1547-5408
In March and April 2025, researchers pointed IXPE at 1E 1547-5408, a magnetar that spins once every two seconds and steadily emits radio waves. The team supplemented IXPE data with observations from an X-ray telescope on the International Space Station, Australia’s Murriyang radio telescope, and the South African Radio Astronomy Observatory.
Two distinct findings pointed to vacuum birefringence. First, X-rays picked up by IXPE were nearly three times more polarized than in similar sources, exceeding standard models of neutron star surface emissions. Second, the polarization aligned with the star’s magnetic field, matching patterns seen in its radio waves. The team concluded that vacuum birefringence remains the only explanation fitting the data. “It’s a bit of a relief because it means that our theories still work and there’s nothing broken with physics,” Lower told Michael West Media.
A Decades-Long Journey for Researchers
For the South African Radio Astronomy Observatory’s chief scientist and co-author of the new study, Fernando Camilo, this breakthrough represents the culmination of an extended endeavor. Camilo has studied 1E 1547-5408 since 2007, when he first detected its radio waves using the Murriyang dish. Back then, 1E 1547 stood out as merely the second known Milky Way magnetar to put out radio emissions. “However we could never have imagined that 20 years later it would contribute to investigating a fundamental, and particularly quirky, prediction of quantum mechanics,” Camilo said in a statement.
Pro Tip: Keep track of upcoming X-ray polarimetry missions like GoSOX, which aim to refine these measurements and further separate vacuum birefringence signals from surrounding magnetar processes.
Frequently Asked Questions
What is vacuum birefringence?
Vacuum birefringence is a quantum mechanical effect where an extremely strong magnetic field alters the properties of a vacuum, causing it to act like a prism that forces light waves to align in a specific direction.
Why are magnetars used to study this effect?
Magnetars possess the most powerful magnetic fields in the universe—over 100 million times stronger than any magnetic field created on Earth—providing the extreme environments necessary to observe vacuum birefringence.
What telescope captured the definitive data?
NASA’s Imaging X-ray Polarimetry Explorer (IXPE), launched in 2021, provided critical high-energy X-ray polarization data during observations in March and April 2025.
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