But the extreme altitude makes it a useful place for scientists. In 1990, they built an observatory here to study the showers of subatomic particles that rain down from the upper atmosphere whenever it is hit by a high-energy cosmic ray. This work is better done at high altitude because there is less atmosphere to absorb the particles.
Since then, the so-called Tibet Air Shower Array has recorded vast numbers of high-energy cosmic rays, particles accelerated to huge energies by astrophysical phenomena such as supernovas, active galactic nuclei, and mysterious as-yet-unidentified sources.
But the array also picks up air showers caused by a different source - high-energy photons. These mysterious photons are also created by astrophysical phenomena such as the interaction between high-energy particles and the cosmic microwave background. Consequently, they can provide a unique insight into these processes and the environments in which they occur.
Over the years, the Tibet Air Shower Array has spotted plenty of these photons with energies up to dozens of teraelectronvolts (TeV 1012). That's roughly equivalent to the highest-energy photons that can be created on Earth. But nobody has ever observed more powerful photons.
Until now. Today, researchers from the Tibet Air Shower Gamma Collaboration say they have observed photons with energies above 100 TeV for the first time, including a remarkable photon with an energy of almost 500 TeV. This single photon has about the same energy as a falling Ping-Pong ball and is the highest-energy photon ever recorded.
The collaboration has also worked out where these photons are coming from: the Crab Nebula, the remnants of a supernova that occurred in 1054 AD in the Perseus Arm of the Milky Way, some 6,500 light-years from Earth.
.... read more at https://www.sott.net/article/415559-Earth-hit-by-highest-energy-photons-ever-recorded-from-the-Crab-Nebula