Speaker
Description
The origin of ultra-high-energy cosmic rays (UHECRs) remains a major open question in astrophysics. Observational data suggest that starburst galaxies and active galactic nuclei (AGNs) are the most promising sources. However, accelerating particles to energies above 1 EeV in these environments is complex due to the demanding requirements on energy, density, and metallicity imposed by observations. In this talk, we will explore the theoretical challenge of explaining the presence of intermediate and heavy nuclei within the context of AGNs. We will specifically focus on the contribution of supermassive stars in enhancing the metallicity within AGNs, particularly their expected role in increasing the presence of CNO elements, and discuss whether this stellar enrichment can account for the observed mass composition of UHECRs.
