Astronomers may have found the strongest evidence yet for a strange quantum effect predicted nearly 90 years ago: even completely empty space can change the way light travels.
The phenomenon, known as vacuum birefringence, was predicted in the 1930s by Werner Heisenberg and other pioneers of quantum physics.
According to quantum theory, a vacuum is not truly empty. Instead, it contains fleeting “virtual particles” that constantly appear and disappear.
Normally, their effects are almost impossible to observe. But extremely powerful magnetic fields may influence these virtual particles, causing empty space to behave somewhat like a material that changes the properties of light passing through it.
Now, an international team of astronomers may have detected this effect around one of the most magnetic objects in the universe.
The researchers studied a magnetar called 1E 1547.0–5408, or 1E1547. Magnetars are a rare type of neutron star—the incredibly dense remains of massive stars that have exploded. Their magnetic fields can be more than 100 million times stronger than magnetic fields scientists can produce on Earth.
The team used NASA’s Imaging X-ray Polarimetry Explorer (IXPE), the NICER X-ray telescope aboard the International Space Station, and CSIRO’s Murriyang, the Parkes radio telescope in Australia.
Dr Marcus Lower from Swinburne University of Technology analyzed radio observations from Murriyang using Swinburne’s Ngarrgu Tindebeek supercomputer.
By studying the polarisation of radio waves—the direction in which the waves oscillate—the researchers determined the orientation of the magnetar. They found that its magnetic and rotational axes are almost aligned and that Earth has an unusually direct view toward its magnetic pole.
This makes 1E1547 an excellent natural laboratory for searching for vacuum birefringence.
The researchers then found two important clues. X-rays coming from the magnetar showed extremely strong polarisation, while the direction of that polarisation closely followed the magnetar’s magnetic field, much like its radio waves.
The enormous magnetic field could be causing virtual particles in the vacuum surrounding the star to align with the field. This would affect how light travels through the apparently empty space.
“Detecting vacuum birefringence requires a magnetic field that is over 100 million times stronger than any we’ve ever made on Earth,” Lower said.
The researchers say more observations and improved computer simulations are needed to rule out other possible explanations.
If the finding is confirmed, it could provide scientists with a rare opportunity to test quantum physics under conditions impossible to reproduce on Earth—and finally confirm a prediction that has remained largely theoretical since the 1930s.
The study was published in Nature.
