Simulation helps in the search for the origin of cosmic radiation

The colorful lines show how cosmic radiation is deflected in magnetic fields. The white straight lines represent a large-scale magnetic field. In addition, small-scale magnetic fields not shown here act on the orbits of the particles (colorful lines).
Credit: RUB, Dr. Lukas Merten

The cosmic radiation seems to be all around us. That is exactly what makes it difficult to find their sources. It would be helpful if you could trace your way back through space. A new program helps with this.

An international research team has developed a computer program that can be used to simulate the transport of cosmic radiation through space. The scientists hope to be able to solve the puzzle about the sources of cosmic radiation. So far it is unknown which celestial objects emit the high-energy radiation that patterns the earth from space. In order to be able to explain experimental data, theoretical models are required; the new computer simulation can deliver this. A team of researchers from the Ruhr University Bochum (RUB) describes the software in the journal of Cosmology and Astroparticle Physics, published online on September 12, 2022.

Like a uniformly illuminated sky during the day

Since their discovery of 100 years, researchers have been trying to decipher where the cosmic radiation comes from. The problem: viewed from Earth, it looks like heaven by day with the naked eye: it is illuminated almost everywhere where you look. Because the light of the sun is scattered in the earth's atmosphere and is distributed evenly over the entire sky. Cosmic radiation is also scattered on its way to earth - through interactions with cosmic magnetic fields. Only a uniformly illuminated picture can be seen from the earth; the origin of the radiation remains hidden.

Particle paths simulated from start to finish

Members of the Bochum research team: Patrick Reichherzer (left) and Julien Dörner
Credit: RUB, Marquard

“It is possible with our CRPropa program, track the orbits of the particles from their formation to their arrival on earth - for all energies, that we can observe from Earth”, says Julien Dörner, PhD student at the RUB. “We can also fully take into account the interaction of particles with matter and photon fields in the universe."

The program can not only simulate cosmic radiation, but also neutrino particles or gamma radiation, which arise in the interactions of cosmic radiation. "Unlike cosmic rays, these messenger particles can be observed directly from their sources, so they come directly to Earth," explains Dr. Patrick Reichherzer, postdoctoral student at the RUB. “With the software, we can also predict such radiation from neutrinos and gamma radiation from foreign galaxies such as Starbursts or active galaxies."

The simulation program presented is the most comprehensive simulation software currently available and enables new research paths. "We can open up new energy areas in the simulation that could not be fully recorded with previous programs," says Prof. Dr. Karl-Heinz Kampert from the Bergische Universität Wuppertal. “In particular, the transition from cosmic radiation from our own galaxy to a portion that comes from foreign galaxies can be described theoretically and compared with observations."

Experimental data can only be interpreted with theoretical help

The simulation program was developed in an international collaboration between 17 scientists who conduct research in Germany, Spain, the Netherlands, Italy, Croatia, England and Austria. The RUB is responsible for the project with eight researchers. The work was created as part of the Collaborative Research Center (SFB) 1491 "The Interplay of Cosmic Matter", funded by the German Research Foundation. SFB spokeswoman Prof. Dr. Julia Tjus from the RUB emphasizes: “The publication is a big step to quantitatively describe the transport and interaction of cosmic rays in three dimensions. CRPropa will make a significant contribution to understanding where the cosmic radiation comes from. Because we need theoretical calculations that help us to interpret the variety of data that we have from the cosmos."

The work was funded by the “la Caixa” Foundation (ID 100010434) the EU's Horizon 2020 program (Funding code 847648 and 646623) the Radboud Excellence Initiative, the Austrian Fund for the Promotion of Scientific Research (Grant number I 4144-N27) the German Research Foundation (Collaborative Research Center 1491, Projects TJ 62 / 8-1 and KA710 / 5-1 as well as Cluster of Excellence 2121 Quantum Universe - 390833306) the Russian Science Foundation (Grant number 22-11-00063) the Federal Ministry of Education and Research (Funding code 05A20PX1 and 05A20GU2) as well as the German Academic Exchange Service and the RUB Research School.

Open-source repository CRPropa 3.2

Source/Credit: Ruhr University Bochum

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