An international research team has created a computer program that can simulate cosmic ray transport through space. The researchers hope it will help them solve the mystery of cosmic ray sources.
So far, we don’t know which celestial objects are responsible for the high-energy radiation that bombards the Earth from space. To explain experimental data, theoretical models are required; the new computer simulation can provide these. The software is described in the Journal of Cosmology and Astroparticle Physics by a team of researchers from Ruhr-Universität Bochum (RUB).
Like a brightly lit sky during the day
Researchers have been trying to figure out where cosmic rays come from since their discovery 100 years ago. The problem is that, when viewed from Earth, they appear to the naked eye to be identically brightly illuminated almost everywhere we look.
This is due to the sun’s light being scattered in the Earth’s atmosphere and spreading evenly across the entire sky. Interactions with cosmic magnetic fields scatter cosmic rays on their way to Earth. From Earth, all we can see is a uniformly illuminated image; the source of the radiation remains unknown.
Particle trajectories were simulated from production to detection
“Our programme CRPropa allows us to trace particle trajectories from formation to arrival on Earth—and this for all energies that we can observe from Earth,” explains Julien Dörner, a Ph.D. student at RUB. “We can also fully account for the interaction of particles in the universe with matter and photon fields.”
Not only can the programme simulate cosmic ray propagation, but it can also simulate the signatures of neutrinos and gamma rays produced in cosmic ray interactions. “Unlike cosmic rays, these messenger particles can be observed directly from their sources because they follow a straight path to Earth,” explains Dr. Patrick Reichherzer, a postdoctoral researcher at RUB.”We can also use the software to predict such signatures from distant galaxies, such as starbursts or active galaxies.”
The simulation programme presented here is currently the most comprehensive software available, and it opens up new doors to the universe. “We can explore new energy ranges in the simulation that could not be fully captured in such detail with the programmes available to date,” says University of Wuppertal Professor Karl-Heinz Kampert. “Most importantly, we can develop and compare a theoretical model that describes the transition from cosmic rays from our own Galaxy to a fraction from distant galaxies.”
Theoretical calculations are required in order to interpret experimental data
An international collaboration of 17 researchers from Germany, Spain, the Netherlands, Italy, Croatia, England, and Austria resulted in the development of the simulation programme. The RUB is the project’s lead partner, with eight researchers. The project was carried out as part of the German Research Foundation-funded Collaborative Research Centre (CRC) 1491 The Interplay of Cosmic Matter.
According to CRC spokesperson Professor Julia Tjus of RUB, “the publication is a significant step toward a quantitative description of the transport and interaction of cosmic rays in three dimensions.” CRPropa will help scientists understand where cosmic rays come from.After all, we need theoretical calculations to help us interpret the vast amounts of data we receive from the various instruments that monitor the universe.”