Gamma-rays are the hardest radiation of the entire electromagnetic spectrum. Luckily, our atmosphere protects us against this radiation, which would otherwise destroy all life on Earth. Gamma-ray observatories on the ground measure secondary or tertiary radiation species, not the primary radiation. To mention just one example, one such experiment is the Milagro detector (external link). In order to gain access to primary gamma-ray photons one needs to launch observatories into space, onboard satellites.
Examples of such observatories operating at energies of tens of keV (kilo electron Volt; for comparison, an optical photon carries an energy of about 1 eV) or higher (up to tens of GeV) were/are:
- Compton Gamma Ray Observatory, CGRO (external link)
- High Energy Transient Explorer, HETE-2 (external link)
- International Gamma-ray Astrophysics Laboratory,
Gamma-ray observatories give us access to high-energy processes involving massive particles, like for example protons, electrons or whole cores of atoms that were stripped of their electrons, called "cosmic rays". To say it shortly: environments that we would not want to find ourselves in. And to close the circle (if you've been reading these pages starting with radio observatories, at the low energy end of the electomagnetic spectrum), cosmic rays are the massive particle component that is created in the same processes as electrons emitting nonthermal radio continuum emission.