Science and Technology

Researchers from Instituto Superior Técnico unveil a new mechanism that converts X-rays into radio waves

This mechanism can operate in astrophysical scenarios and could be associated to the mysterious fast radio bursts

In a recent article published in the prestigious journal Physical Review Letters, which stems from a recent work of a graduated Ph.D student of IST Fabrizio Del Gaudio, researchers from the Group of Lasers and Plasmas of the Institute for Plasmas and Nuclear Fusion (GoLP/IPFN) unveiled a new mechanism that explains how a dense flux of x-rays could generate radio waves in a plasma. Professor Luís Oliveira e Silva, (Department of Physics – DF/IST), professor Ricardo A. Fonseca (University Institute of Lisbon (ISCTE) and researcher Thomas Grismayer co-authored this article.

While propagating in a magnetized plasma, energetic photons can set up a plasma wake, in the same way as a boat on a lake creates a wake behind it. Up to know, it was thought that only photons of low energy, like the ones composing a laser pulse in the laboratory, could generate such waves in plasmas. The work of the researchers of IST demonstrates that via a quantum process called Compton scattering, energetic photons knock the electrons. This sudden kick moves the electrons away from their equilibrium position leading to the formation of a plasma wake.

When the wake moves away from the magnetized environment, it can be converted into pure electromagnetic waves. The researchers of Técnico conjecture that this mechanism can be present in astrophysical objects where ultra intense sources of x-rays can be present such as neutron stars. Recent astronomical observations indicate that the puzzling radio bursts that have been detected since the 1960’s are associated to neutron stars, thereby consolidating the plausible explanation suggested by the researchers.

According to Thomas Grismayer, one of the co-authors of the article: “The emission of energetic photons such as x-rays is usual in astrophysics, nonetheless the conversion of these into radio waves is a discovery”. Luís Oliveira e Silva reinforces this message: “This is a plasma process truly fundamental but we do think that it has many implications”. The conditions in which this process can occur require high flux of x-rays as it could exist in neutron stars. The researchers of Tecnico are already thinking about the possible observation of this mechanism in the laboratory and are generalizing this work to conditions less extreme than those associated with extreme astrophysical environments.

The work was done in the context of the InPairs project, a European Research Council grant, and the simulations were performed on the supercomputer MareNostrum 4 based in Barcelona.