Space and Physics

Highest-Energy Neutrino Spotted Outside Our Galaxy


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockApr 25 2016, 23:02 UTC
1226 Highest-Energy Neutrino Spotted Outside Our Galaxy
An artist's impression of IceCube detectors buried in the Antarctic ice. Jamie Yang/IceCube Collaboration

Neutrinos are the honey badgers of particle physics, moving through the universe unimpeded and careless. The most energetic of them are produced in the most dramatic events in the universe, and studying them gives us a unique view of these phenomena.


The IceCube Neutrino Observatory was built with this purpose in mind, and now new research reports on the detection of the highest-energy neutrino yet, which comes from a galaxy 9.1 billion light-years away.

The IceCube Neutrino Observatory was designed to detect high-energy neutrinos, which is a very difficult job. The observatory uses detectors encased in the Antarctic ice that can register flashes of light and "see" these elusive particles. What the detectors actually see is the energy released by a neutrino occasionally colliding with a water molecule. Since 2010, only 40 events have been detected.

Out of these 40 events, one stood out. It had an energy of 2 PetaElectronvolts, or 3.2x10-4 Joules, about the energy of a penny falling 1 meter (3.3 feet). This might seem like a small amount of energy, but packed into a tiny neutrino, it is enormous. Whatever produced that neutrino must be incredibly powerful, so researchers followed up the IceCube detection with a series of radio telescopes.

They found that the most likely astrophysical object to cause this neutrino was galaxy PKS B1424-418. The galaxy has been regularly observed for decades, but astronomers noticed a sudden brightening between 2011 and 2014. This indicated to the researchers that the supermassive black hole that powers this far away galaxy had suddenly become more active.


The researchers calculated that this, with a 5 percent margin of error, is the source of the 2 PetaElectronvolt neutrino. The findings are published in Nature.

Neutrinos are one of the most abundant types of particles in the universe. They are 500,000 times less massive than electrons and they carry no electric charge, a factor that allows them to move through solid matter without any problems. Trillions of neutrinos are currently going through your body at the speed of light.

The neutrinos that flow through Earth are mostly produced in nuclear reactions inside the Sun. There are other more energetic neutrinos zipping through the cosmos, and while we know they are produced by supermassive black holes, the exact mechanism that forms them is still mysterious. 


[H/T: Cosmos Magazine]

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