Supernovae are the primary source of high-energy cosmic rays, as they produce shock waves that accelerate particles to extremely high energies.

The highest energy cosmic ray ever detected had an energy of approximately 10^20 eV, which is equivalent to the energy of a baseball traveling at 99.99999999999999% the speed of light.

High-energy cosmic rays are mostly composed of protons, with a small fraction of heavier nuclei and electrons.

High-energy cosmic rays primarily interact with matter through inelastic scattering, where the cosmic ray particle transfers energy to the target particle.

High-energy cosmic rays produce extensive air showers that consist of muons, electrons, and hadrons.

The Pierre Auger Observatory is a large-scale cosmic ray detector array located in Argentina, designed to study the highest energy cosmic rays.

The Telescope Array is a large-scale cosmic ray detector array located in Utah, United States, designed to study the highest energy cosmic rays.

Studying high-energy cosmic rays is challenging due to their low flux, high energies, and interactions with the atmosphere.

Potential sources of ultra-high-energy cosmic rays include Active Galactic Nuclei, Gamma-ray bursts, and Topological defects.

The GZK cutoff is the maximum energy that cosmic rays can reach due to their interactions with the cosmic microwave background.

The GZK cutoff implies that cosmic rays cannot reach Earth from distant sources, as they would lose energy through interactions with the cosmic microwave background.

Cosmic ray observatories include underground detectors, space-based detectors, and balloon-borne detectors.

The Auger Engineering Radio Array is a radio telescope array used to study cosmic rays.

The Cosmic Ray Energy Spectrum is a plot of the flux of cosmic rays as a function of their energy.

The knee in the Cosmic Ray Energy Spectrum is the point at which the spectrum changes from a power law to an exponential.