Astrophysics (index)

GZK Limit

(Greisen-Zatsepin-Kuzmin Limit)
(limit on energy of cosmic rays)

The GZK Limit (for Greisen-Zatsepin-Kuzmin Limit) is a theoretical limit on the energy of Cosmic Rays (high velocity protons and other atomic nuclei), i.e., 5x1019 eV or about 8 Joules. The limit was calculated by the three developers based upon the expected interaction of the particles with the Cosmic Microwave Background (CMB) over long distances.

Cosmic Rays are observed above this limit, are called Extreme-Energy Cosmic Rays or EECRs, and have no well-accepted explanation.