The photon that they detected had an energy of 1.1 petaelectronvolts (PeV) – that is, 1.1 million billion electronvolts. The highest was 1.4 PeV, but researchers aren’t exactly sure of its origin. The Crab nebula photon probably came from a high-energy electron in the nebula smashing into a background photon and blasting it to its extreme energy level.
“The gamma rays are nothing special on their own – they are messengers carrying information about the parent electrons that are accelerated,” says Felix Aharonian at the Max Planck Institute for Nuclear Physics, Germany. “We can make so many important conclusions from just one gamma ray.”
One of those conclusions is that the original electron had an energy around 2.3 PeV. That is more than 15 per cent above the theoretical limit of how much energy the electromagnetic fields in the Crab nebula could possibly impart to an electron. It is also more than 20,000 times higher-energy than any human-made electron accelerator has been able to reach.
“Particle accelerators are the most sophisticated, complex machines we have ever made. But here, in this chaotic environment, somehow it is an ideal machine reaching the edge of what fundamental physics allows,” says Aharonian.
In combination with other gamma rays with slightly lower energies, this finding indicates that the Crab nebula – the remnants of a supernova which contains a neutron star – may be accelerating more particles to ultra-high energies than our current ideas can explain. If we find more gamma rays like this, it may challenge our ideas of how these objects accelerate particles.
Journal reference: Science, DOI: 10.1126/science.abg5137
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