An extremely magnetized neutron star has demonstrated an effect predicted by quantum electrodynamics but never seen before. The authors of a new study found that the X-rays emitted by the object were polarized in a very different way, forming a 90° angle to each other.
Located 13,000 light-years away in the constellation of Cassiopeia, a magnetar (neutron star with a powerful magnetic field) called 4U 0142+61 has been observed to emit highly polarized X-rays. That is, the photons carrying this radiation had the same orientation.
However, what really surprised the scientists is that the polarization of the high-energy X-rays was at a 90-degree angle to the polarization of the low-energy X-rays. The phenomenon is a result of the “photon metamorphosis”, theorized for some time by quantum electrodynamics.
Neutron stars are the dense, hot remnants of massive stars that have exploded in supernovae. Some of them, the so-called magnetars, have a magnetic field 100 trillion times stronger than Earth’s. When electrons and photons interact in the magnetized atmosphere of these objects, something known as a vacuum resonance occurs.
In this state, photons can temporarily convert into “virtual” pairs of electrons and positrons (the antiparticle of electrons) that are influenced by the magnetic field of the magnetar. This process is called vacuum birefringence, and when combined with another process called plasma birefringence, the polarity of high-energy X-rays is 90 degrees to low-energy X-rays.
Previous attempts to detect this type of phenomenon in laboratories have failed, as a magnetic field that does not exist on our planet is needed. The new study is yet another example of the importance of neutron stars and magnetars as cosmic laboratories for research into the physics of the universe’s extreme environments.
The magnetar data used for this study was collected by NASA’s Imaging X-ray Polarimetry Explorer (IXPE). The article describing the results was published in the Proceedings of the National Academy of Sciences.
Source: PNAS; via: Space Daily
