New plasma instability sheds light on the nature of cosmic rays

Scientists at the Leibniz Institute for Astrophysics in Potsdam (AIP) have discovered a new plasma instability that promises to revolutionize our understanding of the origin of cosmic rays and their dynamic impact on galaxies.

At the beginning of the last century, Victor Hess discovered a new phenomenon called cosmic rays which later earned him the Nobel Prize. He carried out high-altitude balloon flights to find that the Earth’s atmosphere is not ionized by radioactivity from the ground. Instead, it confirmed that the origin of the ionization was extraterrestrial. Subsequently, it was determined that cosmic “rays” consisted of charged particles originating from space and flying at a speed close to that of light rather than that of radiation. However, the name “cosmic rays” has survived these discoveries.

In the new study, Dr. Mohamad Shalaby, AIP scientist and lead author of this study, and his collaborators performed numerical simulations to track the trajectories of many cosmic ray particles and study how they interact with plasma surrounding environment made up of electrons and protons. The paper appears on the preprint server arXiv.

When the researchers studied cosmic rays flying from one side of the simulation to the other, they discovered a new phenomenon that excites electromagnetic waves in the background plasma. These waves exert a force on the cosmic rays, which modifies their sinuous trajectories.

More importantly, this new phenomenon can be better understood if we consider that cosmic rays do not act as individual particles but rather as supporting a collective electromagnetic wave. As this wave interacts with the fundamental waves in the background, these are strongly amplified and an energy transfer takes place.

“This idea allows us to view cosmic rays as behaving as radiation and not as individual particles in this context, just as Victor Hess originally thought,” remarks Professor Christoph Pfrommer, head of the Cosmology and high energy astrophysics at the AIP. . A good analogy for this behavior is that individual water molecules collectively form a wave that breaks on the shore.

“These advances have only been possible by considering smaller scales that have been neglected before and which challenge the use of effective hydrodynamic theories in the study of plasma processes,” explains Dr. Mohamad Shalaby.

There are many applications to this newly discovered plasma instability, including a first explanation of how electrons in interstellar thermal plasma can be accelerated to high energies at supernova remnants.

“This newly discovered plasma instability represents a significant advance in our understanding of the acceleration process and finally explains why these supernova remnants glow in radio and gamma rays,” reports Mohamad Shalaby. Furthermore, this groundbreaking discovery opens the door to a deeper understanding of the fundamental processes of cosmic ray transport in galaxies, which represent the greatest mystery in our understanding of the processes that shape galaxies during their cosmic evolution.