The sky in gamma rays (seen by EGRET)

Gamma ray astronomy

Where are ultra-high-energy gamma rays coming from? Ordinary telescopes collect photons, in the same sense that AMS collects charged cosmic rays. Photons can have various energies; a red photon has a very low energy; a blue photon has two or three times as much; ultra-violet photons are higher still; next are X-rays; and the highest-energy photons are called gamma rays. Astronomers need to look at the sky at all energies, but ordinary telescopes only work for IR, visible, UV, and (with great effort) X-rays.

AMS can help on the high-energy end. AMS can detect high-energy gamma rays - these are photons so energetic that they can actually "manufacture" mass when they crash into something. A gamma ray crashing into AMS can produce an electron and a positron, which are charged particles, so AMS measures them normally. AMS can actually take images of the sky and see where the gamma rays are coming from - just like a telescope. The "flux" of these particles is very low, but even a single ultra-high-energy gamma ray can identify an interesting astrophysical source.

AMS's calorimeter also can identify gamma rays, although its direction sensitivity is not so good.
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