We've never seen photons like these before.
The Tibet Air Shower Array is located about five kilometers (3.1 miles) above sea level, and this high altitude makes it an ideal spot to gather data on the subatomic particles that shower the Earth after high-energy cosmic rays blast the planet's atmosphere.
Now, researchers are reporting that the array has detected the highest-energy photon ever seen on Earth — and they think they know exactly where it came from.
According to a paper published by the Tibet Air Shower Gamma Collaboration on the preprint server arXiv, the array recently spotted several photons with energies above 100 teraelectronvolts (TeV), whereas they'd never seen one break the 100 TeV mark before.
As if that weren't remarkable enough, the array also spotted one photon with an energy of nearly 500 TeV.
The team tracked the source of the photons to the Crab Nebula, the remains of a star that went supernova around the year 1054.
They suspect that shock waves in the magnetic fields surrounding the nebula's pulsar likely accelerated electrons and protons. Those subatomic particles then transferred their energy to photons in the cosmic microwave background.
Those are the light particles the Tibet Air Shower Array detected some 6,500 light-years away from their source — and now that they've reached Earth, the unusual photons could yield new insights into nebulas and the shock waves passing through their magnetic fields.
READ MORE: The Crab Nebula just blasted Earth with the highest-energy photons ever recorded [MIT Tech Review]
More on nebulas: See What Astronomers Are Calling "the Last Breath of a Dying Star"