Gamma-ray astronomy allows the in-depth study of the violent Universe, from supernova explosions to Active Galactic Nuclei through dark matter.
The gamma-ray astronomy of the highest energies is one of the most recent branches of the relativistic astrophysics. Gamma rays are a much more energetic form of radiation than visible light and can never reach the ground. Once they penetrate the atmosphere, the gamma photons interact and produce a cascade of very energetic secondary particles that move at a speed higher than that of light in the air (although traveling at a speed lower than that of light in a vacuum). In 1934, the Russian physicist Pavel Cherenkov noticed that this phenomenon produced a bluish luminescence, conceptually similar to the sonic roar that accompanies the overcoming of the speed of sound. In fact it is a very short emission (a few billionths of a second) and very weak (less than a tenthousandth of the bottom of the night sky) that can only be revealed by large telescopes capable of collecting as much light as possible, equipped with instrumentation extraordinarily fast and sensitive. In fact, the current generation of gamma-ray telescopes began to produce important results when it was understood that the performance of the instruments increased greatly by using multiple telescopes operating in unison.
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