High-energy & quantum cosmology
The GZK Limit
A theoretical ceiling on the energy of cosmic-ray protons that reach us from far away: above roughly 5×10¹⁹ electronvolts they collide with cosmic-microwave-background photons and lose energy, so the highest-energy cosmic rays must originate relatively nearby. Observatories studying the ultra-high-energy sky test this predicted cutoff.
Highlights
- ›A cosmic-ray energy ceiling set by the microwave background
Related physics & astronomy
Knowledge connections
- Associated withCosmic Rays
- Associated withThe Cosmic Microwave Background
- Associated withMass–Energy Equivalence
Sources
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.