The Most Energetic Light Ever Seen Just Showered Down from the Skies Above Tibet

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Crab Nebula image
An image of the Crab Nebula taken by the Hubble Space Telescope. Scientists recently detected the most energetic photons ever seen, and they originate in this nebula. (Image credit: NASA, ESA, J. Hester, A. Loll (ASU))

High up on the Tibetan plateau, scientists just measured the most energetic light ever seen. These photons were gamma rays with energies exceeding 100 trillion electronvolts — one even had nearly 500 trillion electronvolts of energy. Previously, only photons with tens of trillions of electronvolts had been seen.

The scientists found the photons had originated in the Crab Nebula, a pulsar, or a powerful spinning supernova remnant 6,523 light-years away.

By studying showers of secondary particles called muons, the scientists were able to work backwards to figure out the energy and origin of the incoming gamma rays that caused the showers. In a new paper accepted June 13 to Physical Review Letters, astronomers studying these Crab Nebula showers reported 24 events caused by photons with energies higher than 100 trillion electronvolts. By comparison, particles of visible light from our sun only have an energy of a few electronvolts.

"It's a very, very important result," Felix Aharonian, professor at the Dublin Institute for Advanced Studies, who was not involved with the new work, told Live Science. "It agrees with expectation to a large extent and it could have a lot of implications because now it's experimental results, not just theoretical speculations."

The results specifically help scientists to understand how such high-energy photons are created, and if there is a limit to how much energy they can have. The scientists speculated that in this case, the gamma rays had been accelerated through a process known as Inverse Compton scattering. During this process, super high-energy electrons bounce off lower energy photons, giving the photons tremendous energy. These electrons in the Crab Nebula may have scattered off low-energy photons from the cosmic background radiation — some of the universe's first light.

"We knew that the Crab Nebula was a unique source in the universe," Aharonian told Live Science. "Now we see that yes, the electrons in the Crab Nebula are accelerated up to 1,000 trillion electronvolts."

Shock waves in the magnetic environment in the nebula are likely responsible for accelerating the electrons to such extreme energies. If confirmed, this would add the Crab Nebula to just a couple of other proposed pulsars at the center of the galaxy thought capable of accelerating electrons to this degree.

Originally published on Live Science.

Mara Johnson-Groh
Mara Johnson-Groh
Live Science Contributor

Mara Johnson-Groh is a contributing writer for Live Science. She writes about everything under the sun, and even things beyond it, for a variety of publications including Discover, Science News, Scientific American, Eos and more, and is also a science writer for NASA. Mara has a bachelor's degree in physics and Scandinavian studies from Gustavus Adolphus College in Minnesota and a master's degree in astronomy from the University of Victoria in Canada.