Possible first signs in the empty space of a strange quantum property

                              

 
Using ESO's Very Large Telescope (VLT), a team of astronomers, who have studied the light emitted by an extraordinarily dense and strongly magnetized neutron star, may have found the first observational evidence of a strange quantum effect first predicted in The 1930s. The polarization of observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence. 

 
A team led by Roberto Mignani, INAF Milan (Italy) and the University of Zielona Gora (Poland), used ESO's VLT (Very Large Telescope), installed at the Paranal Observatory (Chile), to observe the neutron star RX J1856.5-3754, about 400 light years from Earth. 

 
Despite being among the closest neutron stars, its extreme darkness made it impossible for astronomers to observe it in visible light using the FORS2 instrument, installed in the VLT, within the limits of current telescope technology. 

 
Neutron stars are the dense remnant nuclei of massive stars (at least 10 times more massive than our Sun) that have burst like supernovae at the end of their lives. They also have very extreme magnetic fields, billions of times stronger than those of the Sun, which permeate its outer surface and its surroundings. 

 
These fields are so strong that they even affect the properties of the empty space around the star. It is believed that normally the vacuum is completely empty, and that light can travel through it without undergoing any change. But in quantum electrodynamics (QED), the quantum theory that describes the interaction between photons of light and charged particles, like electrons, space is filled with virtual particles that appear and disappear all the time. Very strong magnetic fields can modify this space, which affects the polarization of the light passing through it. 

    
Mignani explains: "According to QED, a highly magnetized vacuum behaves as a prism does with the propagation of light, an effect known as vacuum birefringence." 

  
However, up to now, among the many predictions of QED, vacuum birefringence lacked a direct experimental demonstration. Attempts to detect it in the laboratory have not been successful in the 1980s since it was predicted in an article by Werner Heisenberg (known to formulate the uncertainty principle) and Hans Heinrich Euler. 

 
"This effect can only be detected in the presence of extremely strong magnetic fields, such as those around neutron stars. This proves, once again, that neutron stars are laboratories of great value for the study of the fundamental laws of nature, "says Roberto Turolla (University of Padua, Italy). 

 
After a careful analysis of the VLT data, Mignani and his team detected linear polarization (to a significant degree of about 16%) probably due, according to the researchers, to the effect of vacuum birefringence in the surrounding empty space area To RX J1856.5-3754. 

 
Vincenzo Testa (INAF, Rome, Italy) comments: "It is the weakest object in which polarization has ever been measured. It requires one of the world's largest and most efficient telescopes, the VLT, and precise data analysis techniques to improve the signal of such a weak star. " 

 
"The high linear polarization that we measure with the VLT can not be easily explained with our models, unless we include the vacuum birefringence effects predicted by QED," Mignani adds. 

 
"This VLT study is the first observational support for predictions of this type of QED effects emanating from an extremely strong magnetic field," comments Silvia Zane (UCL / MSSL, UK). 

 
Mignani is thrilled by the improvements in this area of ​​study that you could give thanks to more advanced telescopes: "Measurements of polarization with next-generation telescopes such as ESO's European Extremely Large Telescope (E-ELT) can play a Crucial role in testing the predictions of the vacuum birefringence effects of the QED around many more neutron stars. " 

 
"This measurement, first realized now in visible light, also paves the way for similar measurements to be made on X-ray wavelengths," adds Kinwah Wu (UCL / MSSL, UK).