Scientists at the Tibet Air-Shower Array high atop the Tibetan plateau recently observed the most powerful photons ever recorded from an astrophysical source hitting Earth. The photon was part of a barrage of light coming from the Crab Nebula, a giant cloud of gas some 6,500 light-years away with a pulsar—a neutron star spinning at 30 revolutions per second, emitting high-frequency radiation as a tight beam of energy—at its heart, which is all that remains of a powerful supernova that occurred, from our perspective, in 1054 A.D.
Although the Air Shower Array is used to recording extremely high powered photons, they say the photons they recently detected coming from the Crab Nebula are off the charts. According to the MIT Technology Review, the highest powered photons that can be created on Earth, such as those in the Large Hadron Collider, have an energy of roughly 14 terraelectronvolts (TeV), and scientists at the Air Shower Array routinely detect photons of that power. The photons they just saw coming from the Crab Nebula are over 100 TeV, including one single photon with an energy of 500 TeV. That’s the energetic equivalent of a falling ping-pong ball.
The Crab Nebula
What’s that? A falling ping-pong ball isn’t impressive enough for you? Consider this: a single photon is a weird subatomic particle/wave that operates on the quantum scale and has no mass, whereas ping-pong balls are large enough to play an Olympic sport with. That’s like throwing a ping-pong ball with the energetic equivalent of a nuclear bomb. That comparison may not be even close to correct, but you get the idea. It was a shockingly powerful photon.
As to how these high-energy photons are created, scientists have a working theory. According to the MIT Technology review:
Photons of this energy are thought to be created by a process known as inverse Compton scattering. This occurs when a high-energy particle transfers its energy to a photon. In the case of the Crab Nebula, the high-energy particles are probably electrons and protons accelerated by shock waves in the powerful magnetic fields that surround the pulsar.
Artist’s depiction of a pulsar. Credit: NASA’s Goddard Space Flight Center
According to the paper about these observations, this discovery opens up a whole new range of possible energy levels for photons and sheds some light on the conditions near pulsars, some of of the most extreme and mysterious objects in the known universe. Now that they have a record of an off-the-charts photon and exactly where it came from, the researchers can work backwards to figure out the sort of physical processes that are happening in and around the Crab Nebula pulsar. But as with all things spacey, the data will have to be checked and rechecked with further observations until scientists can make any definitive headway to understanding pulsars. Even then, there’s always a good chance that it all turns out to be nonsense.
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