Scientists at the National Astronomical Observatory of the Chinese Academy of Sciences (NAOC) have discovered for the first time the circular polarization of electromagnetic radiation, the source of which is fast, repetitive radio bursts. The results of the study, published in the journal Science Bulletin, point to the magnetic field of neutron stars as the most likely source of explosions.

Fast radio bursts (FRBs) occur within a few milliseconds and are accompanied by the release of large amounts of energy into space, such as the Sun emits over tens of thousands of years. Researchers associate this phenomenon with supernovas, neutron star collisions, active black holes or magnetars, but the exact nature of the phenomenon remains a mystery.

Since 2007, when the first FRBs were discovered, more than 600 burst sources, mostly singular, have been identified. Less than five percent of all FRBs are recurrent, and about 10 of these are persistently active. Single FRBs have already introduced two types of radio wave polarization – circular and linear. With linear polarization, the electric field vector of electromagnetic radiation oscillates in a plane and defines a circle with circular polarization. Only one repeating FRB was found to be circularly polarized, but not active.

Through a systematic analysis of data obtained with the FAST telescope, the researchers found circular polarization in less than five percent of bursts from repetitive sources FRB20121102A and FRB20190520B, which are a constantly active source. Circular polarization generation conditions are expected to be rarer in repetitive FRBs, but observational results indicate that circular polarization may be a common feature of periodically occurring fast radio bursts.

Polarization is a key feature of FRBs and carries important information about emission mechanisms and the environment of the flare source. The observed circular polarization may originate from the magnetosphere of magnetars, neutron stars with extremely strong magnetic fields, and many studies indicate FRBs to be the most likely source.