what is a gamma ray?
Gamma ray (also called gamma radiation), denoted by the lower-case Greek letter gamma (Î³ or Î³ {\displaystyle \gamma } ), is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei and consists of high-energy photons.
Gamma ray astronomy is the study of astronomical objects at the shortest wavelengths of the electromagnetic spectrum. Gamma rays may be observed directly by satellites such as the Compton Gamma Ray Observatory or by specialized telescopes called atmospheric Cherenkov telescopes.