2023-06-13 14:15:01
High-energy gamma-ray radiation, especially above 1 gigaelectronvolt (GeV) to 1 teraelectronvolt (TeV), is a phenomenon that has been the subject of study in the field of astrophysics for years. There is a diffuse distribution of high energy gamma rays that can be observed coming from all directions in the sky. While many sources that can generate this radiation are known, there is still an unknown party whose sources have not been identified. One of the possible explanations for this unknown radiation could be dark matter, the nature of which is not yet fully understood. However, it is unknown what other sources could contribute to this emission.
This is where galaxy clusters come into play. These clusters are the key study object to understand their contribution to the emission of high energy gamma rays. Galaxy clusters are structures that often contain hundreds of individual galaxies and are gravitationally bound together.
These structures also contain gas, and particle acceleration processes occur within them. Cosmic rays are accelerated both by astronomical objects present in clusters and by the intracluster medium itself. Well, the interactions of these cosmic rays could be responsible for much of the production of gamma rays, neutrinos and other particles.
This has been determined in a study, based on a simulation, carried out by a team made up of, among others, Saqib Hussain, from the University of Sao Paulo in Brazil, and Rafael Alves Batista, from the Institute of Theoretical Physics (IFT), center mixed from the Autonomous University of Madrid (UAM) in Spain and the Higher Council for Scientific Research (CSIC) of Spain.
Artist’s impression of the generation of a gamma-ray flash. (Image: Aurore Simonnet/Sonoma State University/NASA Education & Public Outreach)
This simulation is one of the largest and most detailed available, ranging from archaic galaxies of about ten billion years ago to the most recently formed structures today. Properties obtained from these simulations, such as gas distribution, magnetic fields and radiation, were used to study the propagation of cosmic rays and their interaction with the gas present in the clusters.
Alves Batista, one of the lead authors of the study, also contributed a key tool in developing the simulation. This is a particle propagation code known as CRPropa. This code makes it possible to calculate not only the probability of interaction of particles such as protons with the background present in clusters of galaxies, but also the trajectories of these particles. In addition, the code also calculates the properties of the particles produced in these interactions, including the formation of pions and the subsequent generation of gamma rays. Alves Batista and other colleagues started the development of CRPropa years ago and this tool has multiple uses in theories of astroparticle transport in astrophysical settings and at cosmological distances.
The computer simulation carried out in the recent study covers a large region of the universe, with a size of about 9000 megaparsecs, about 30 billion light-years, while the region simulated in detail is about 200 megaparsecs. According to Alves Batista: “The simulated sample is quite representative and, in fact, the rest of the universe is expected to have similar characteristics.”
The research concludes that galaxy clusters may be an important source of high energy gamma ray emission. If this is true, there could be a significant contribution from clusters to the observed flow from Earth, limiting the contribution from other astrophysical objects.
However, it should be noted that these results are theoretical and have not yet been verified experimentally. In the future, data from the telescopes is expected to confirm these approximations. For example, some existing telescopes like the Fermi-LAT and future ones like the CTA (Cherenkov Telescope Array), with which the IFT is involved.
In short, the results help to better understand the diffuse flow of gamma rays, which is not yet fully understood.
The study is titled “The diffuse gamma-ray flux from clusters of galaxies”. And it has been published in the academic journal Nature Communications. (Source: Institute of Theoretical Physics (IFT) / UAM / CSIC)
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