This phenomenon, called 'vacuum birefringence', was first predicted nearly 90 years ago by Werner Heisenberg, one of the founding fathers of quantum mechanics. He suggested that even a perfect vacuum should be teeming with 'virtual particles' that rapidly pop in and out of existence.
The astronomers, including Dr Marcus Lower from Swinburne University of Technology, used the properties of a magnetar – a rare type of neutron star with the strongest magnetic fields in the universe – to study this quantum cold case.
Their observations uncovered what could be the first detection of vacuum birefringence taking place in the magnetar's ultra-strong magnetic field and could open new pathways to exploring the quantum universe. The results were published today in Nature.
In the presence of an extremely powerful magnetic field, a sea of Heisenberg's virtual particles is expected to refract light in specific ways, producing vacuum birefringence. Only the rare magnetar has magnetic fields strong enough to make this quantum effect visible.
Dr Lower is part of the international team who observed a magnetar known as 1E 1547.0–5408 (or 1E1547 for short) using NASA's Imaging X-ray Polarimetry Explorer (IXPE), supported by the NICER X-ray telescope on the International Space Station and Murriyang, CSIRO's Parkes radio telescope, owned and operated by Australia's national science agency.
Dr Lower's observations made with Murriyang and subsequent analysis using Swinburne's Ngarrgu Tindebeek supercomputer could be the first direct detection of this once-theoretical quantum effect.
Dr Lower said that despite being predicted back in the 1930s, a concrete detection of vacuum birefringence has so far remained elusive.
"Detecting vacuum birefringence requires a magnetic field that is over 100 million times stronger than any we've ever made on Earth. Thankfully, nature has provided us with magnetars, which are the perfect cosmic laboratories to go looking for this effect," Dr Lower said
By carefully tracking how the direction the radio waves emitted by the magnetar oscillate (their 'polarisation state') as it rotates, the team found the magnetic and rotational axes of 1E 1547 are nearly aligned and are viewed almost pole-on. This combination of magnetic and viewing geometry makes 1E 1547 ideal to look for vacuum birefringence.
The team then identified two telltale signs that vacuum birefringence is acting around the magnetar; they found that X-rays produced by the magnetar and picked up by IXPE had extremely high levels of polarisation and that the polarisation direction was locked to 1E1547's magnetic field in the same way as the radio waves.
"Because of the magnetic field's strength, Heisenberg's virtual particles become aligned with the direction the field is pointing," Dr Lower said.
"By carefully tracking the direction the radio waves and X-rays oscillate as the magnetar rotates, the team found that the alignment of 1E1547's magnetic and rotational poles were ideal for detecting vacuum birefringence."
If confirmed, this discovery paves the way for understanding how our theories of quantum physics work in one of the most extreme environments in our universe.
Dr Lower says this significant finding could soon be confirmed, with additional data and improved computer simulations to better differentiate the vacuum birefringence signal from other processes occurring around magnetars.
"With these future data on hand and our updated simulations, we may finally be able to complete the quest started by Heisenberg nearly 90 years ago."
The paper Vacuum birefringence and the polarized X-ray emission of a radio magnetar has been published in Nature .
This media release was also published at the Swinburne University of Technology's website .
