Is empty space really empty? This magnetic star may finally solve a 90-year-old mystery

The idea dates to 1936, when the German physicist Werner Heisenberg and his student Hans Euler proposed that space is never truly void. Instead, they argued, it is a simmering sea of "virtual particles" — electrons and their antimatter counterparts, positrons — that flicker in and out of existence, briefly interacting with their surroundings before vanishing. This subatomic froth is a consequence of quantum mechanics, and it remains invisible under ordinary conditions. They are among the rare celestial objects capable of generating fields strong enough to reveal vacuum birefringence, offering scientists an extreme environment to test physics under conditions impossible to replicate on Earth. "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, said in a statement. Astronomers have caught glimpses of this elusive phenomenon before, but not conclusively. In 2017, researchers using the Very Large Telescope in Chile observed polarization hints around a faint neutron star called RX J1856.5-3754, located about 400 light-years from Earth. However, those optical measurements remained open to interpretation, partly due to the challenges of isolating the optical signal. An illustration of a magnetar. ()At the time, scientists noted that definitive proof would require space-based X-ray observatories, specifically NASA's then-forthcoming Imaging X-ray Polarimetry Explorer (IXPE). Launched in 2021, IXPE carries three identical telescopes designed to measure the polarization of high-energy X-rays. "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. In March and April 2025, the researchers pointed IXPE at 1E 1547-5408, a magnetar that spins once every two seconds and is unusual among its kind for steadily emitting radio waves. The team supplemented that data with observations from an X-ray telescope aboard the International Space Station, as well as Australia's Murriyang radio telescope and the South African Radio Astronomy Observatory. According to the study, two findings pointed to vacuum birefringence at work. First, the X-rays picked up , far higher than standard models of a neutron star's surface emission could explain on their own. Second, the polarization pointed the same way as the star's magnetic field, matching the pattern already observed in its radio waves. The researchers concluded that this combination leaves vacuum birefringence as the only explanation that fits 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 the Michael West Media news site.