Astronomers May Have Detected Vacuum Birefringence, a 90-Year Quantum Prediction

Astronomers may have found the strongest evidence yet for vacuum birefringence, a quantum effect predicted nearly 90 years ago by physicist Werner Heisenberg, which suggests that even a perfect vacuum is not truly empty. The findings, published in the journal Nature, come from an international team that included Dr. Marcus Lower of Swinburne University of Technology.

According to quantum theory, empty space contains "virtual particles" that flicker in and out of existence. An extremely strong magnetic field can align these particles and change how light passing through the vacuum travels — an effect that requires a magnetic field over 100 million times stronger than any produced on Earth. Researchers used magnetars, neutron stars with the most powerful magnetic fields known in the universe, as natural laboratories to search for it.

The team studied the magnetar 1E 1547.0-5408 with NASA's Imaging X-ray Polarimetry Explorer (IXPE), backed by the NICER telescope aboard the International Space Station and CSIRO's Murriyang radio telescope in Australia. Radio observations, analyzed on Swinburne's Ngarrgu Tindebeek supercomputer, showed that the magnetar's magnetic and rotational axes are nearly aligned and viewed almost pole-on — a rare, favorable geometry for detecting the effect.

X-rays detected by IXPE showed extremely high polarization, and the direction of that polarization stayed locked to the magnetar's magnetic field in the same pattern seen in the radio data — two clues consistent with vacuum birefringence. Dr. Lower said the alignment of the star's magnetic and rotational poles made it an ideal target for the search.

If confirmed, the detection would mark the first direct evidence of vacuum birefringence since Heisenberg's prediction in the 1930s. Researchers say further observations and more advanced simulations are needed to rule out other physical processes around the magnetar before the result can be considered fully confirmed.