Simulate the regurgitation of cosmic rays on the background plasma and excite plasma instability. The figure shows the distribution of background particles in phase space in response to flowing cosmic rays, which is spanned by particle position (horizontal axis) and velocity (vertical axis). The color visualizes the number density, and phase space holes are a manifestation of the highly dynamic nature of instability, which dissipates in a random motion. **shalaby/aip
Scientists at the Leibniz Institute for Astrophysics (AIP) in Potsdam have discovered a new plasma instability that promises to revolutionize our understanding of the origin of cosmic rays and their dynamic effects on galaxies.
At the beginning of the last century, Victor Hess discovered a new phenomenon called cosmic rays, which later won him the Nobel Prize. He made a high-altitude balloon flight and found that the Earth's atmosphere was not ionized by radioactivity from the ground. Instead, he confirmed that the origin of ionization was extraterrestrial. Subsequently, it was determined that cosmic "rays" consist of charged particles from outer space that fly at speeds close to the speed of light rather than radiation. However, the name "cosmic rays" outlasted these discoveries.
In the new study, Dr. Mohamad Shalaby, a scientist at AIP and lead author of the study, and his collaborators performed numerical simulations to track the trajectories of many cosmic ray particles and study how they interact with the surrounding plasma, which is made up of electrons and protons. **Appears on 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 could excite electromagnetic waves in the background plasma. These waves exert a force on cosmic rays, which alters their sinuous path.
Momentum distribution of protons (dotted line) and electrons (solid line). The figure shows the appearance of the energetic tail of the electron under a slower-moving shock wave. **shalaby/aip
Above all, this new phenomenon is best understood if we consider that cosmic rays do not act as individual particles, but support collective electromagnetic waves. When this wave interacts with the fundamental waves in the background, these waves are strongly amplified and energy transfer occurs.
This insight allows us to treat cosmic rays as radiation rather than individual particles in this context, as Victor Hess originally thought," commented Professor Christoph Pfrommer, Head of the Department of Cosmology and High Energy Astrophysics at AIP. A good analogy for this behavior is that individual water molecules work together to form a wave that breaks on the shore.
Dr. Mohamad Shalaby explains: "This progress has only been achieved by considering previously overlooked smaller scales that call into question the use of effective hydrodynamic theories when studying plasma processes.
This newly discovered plasma instability has many applications, including the first explanation of how electrons from a hot interstellar plasma accelerate to high energies at supernova remnants.
This newly discovered plasma instability represents a major leap forward in our understanding of the acceleration process and ultimately explains why these supernova remnants glow in radio and gamma rays," Mohamad Shalaby reported. In addition, this groundbreaking discovery opens the door to a deeper understanding of the fundamental processes of cosmic ray transmission in galaxies, which represents the greatest mystery in our understanding of the shaping process during the evolution of galaxies in the universe.
More information: Mohamad Shalaby et al., Deciphering the Physical Basis of Mesoscale Instability, Arxiv (2023). doi： 10.48550/arxiv.2305.18050