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The remaining frontier in understanding the early Universe is the formation of the first stars, galaxies and massive black holes. The interplay of theory and upcoming observations promises to answer key open questions in this emerging field.
Cosmic rays are charged particles arriving at Earth from space. Those at the highest energies are particularly interesting because the physical processes that could create or accelerate them are at the limit of our present knowledge. The Pierre Auger Observatory is the largest cosmic-ray detector on Earth, and as such is beginning to resolve past observational disagreements regarding the origin and propagation of these particles.