Cosmic rays are high-energy atomic particles continually bombarding the Earth’s surface at almost the speed of light. The magnetic field of our planet shields the surface from most of the radiation generated by these particles. Yet cosmic rays can cause electronic malfunctions and are the primary concern in the planning of space missions.
Researchers know that cosmic rays originate from the multitude of stars in the Milky Way, including our sun and other galaxies. The difficulty is in tracing the particles to specific sources, as the turbulence of interstellar gas, plasma, and dust causes them to disperse and re-diffuse in different directions.
In AIP Advances, by AIP Publishing, researchers at the University of Notre Dame have developed a simulation model to better understand these and other characteristics of cosmic ray transport, with the aim of developing algorithms to improve existing detection techniques .
Brownian motion theory is generally used to study the trajectories of cosmic rays. Much like the random movement of pollen particles in a pond, collisions between cosmic rays in fluctuating magnetic fields cause particles to propel in different directions.
But this classical diffusion approach does not sufficiently take into account the different propagation speeds affected by various interstellar environments and long periods of cosmic voids. Particles can be trapped for a time in magnetic fields, slowing them down, while others are pushed to higher speeds by star explosions.
To address the complex nature of cosmic ray travel, researchers use a stochastic scattering model, a set of random variables that change over time. The model is based on geometric Brownian motion, a classical diffusion theory combined with a slight trajectory drift in one direction.
In their first experiment, they simulated cosmic rays moving through interstellar space and interacting with localized magnetized clouds, represented as tubes. The rays travel undisturbed for a long period of time. They are interrupted by a chaotic interaction with the magnetized clouds, causing some rays to re-emit in random directions and others to remain trapped.
Numerical Monte Carlo analysis, based on repeated random sampling, revealed ranges of density and re-emission strength of interstellar magnetic clouds, leading to asymmetric or heavy tailed distributions of propagating cosmic rays.
The analysis indicates a marked superdiffusive behavior. The model’s predictions agree well with known transport properties in complex interstellar media.
“Our model provides valuable information on the nature of the complex environments traversed by cosmic rays and could help advance current detection techniques,” said author Salvatore Buonocore.
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