Vacuum birefringence is a very unusual quantum phenomenon that has only been observed at the atomic level. In theory, it can occur, for example, near neutron stars. Due to the presence of very powerful magnetic fields, regions with appearing and disappearing matter can appear in a chaotic manner near such stars.
In the 1930s, German physicists Werner Heisenberg and Hans Heinrich Ouler developed the theory that a magnetized vacuum could behave like a prism with respect to light passing through it.
More recently, scientists from the Italian National Institute of Astrophysics and Zelenogur University (Poland) have witnessed this unusual vacuum property. Using the Very Large Telescope (VLT) of the European Southern Observatory, scientists led by Roberto Mignani observed the star RX J1856.5-3754, located 400 light years away.
Neutron stars are usually very compact, but dozens of times more massive than our Sun. Because of this, they have very powerful magnetic fields. A vacuum in its normal state (at least according to Einstein and Newton) does not manifest itself in any way, and light can propagate through it without any changes. However, according to quantum electrodynamics (QED), space is filled with endlessly appearing and disappearing virtual particles. Very powerful magnetic fields, such as those commonly found near neutron stars, can modify the properties of space.
Using new equipment from Chile's Very Large Telescope, researchers were able to observe a neutron star in the visible spectrum, effectively pushing the boundaries of existing observing technology.
A study of the star RX J1856.5-375 showed a significant level of linear polarization (16 percent), which scientists interpreted as a consequence of the effect of vacuum birefringence.
“The high level of polarization that we observed with the VLT is very difficult to explain with our current models, unless we are talking about the effect of vacuum birefringence predicted 80 years ago by quantum electrodynamics,” says Mignani.
Thanks to future and more powerful telescopes, Mignani said, scientists will be able to learn more about this unusual quantum effect by observing other neutron stars.
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"Measurements of polarization levels using new generation telescopes, for example, the same ESO's European Extreme Large Telescope (EELT), will be able to play a key role in testing the predictions of quantum electrodynamics regarding the effects of vacuum birefringence near most neutron stars," the scientist notes.
“This is the first time this research has been done in the visible spectrum. Further observations can also be carried out in the X-ray wavelength range,”adds researcher Kinwa Wu.
NIKOLAY KHIZHNYAK