A neutrino telescope sees the signs of something cataclysmic

KM3Net is not a conventional telescope. It is not dependent on visible light, as astronomers have long, nor on other pieces of the electromagnetic spectrum, such as radio waves or gamma rays that were added to their arsenal in the 20th century. Instead, it investigates the universe with neutrinos, ghostly but omnipresent subatomary particles that are produced in nuclear reactions. Scientists had theoretized that neutrinos should exist with very high energy, produced by violent astronomical processes such as Gamma-Ray outbursts or matter that fall into gigantic black holes. Now they have proof that they were right.

Detecting neutrinos is difficult. They are distant particles that rarely devote to communicate with the rest of the universe. They only feel two of the four fundamental forces: the weak nuclear force, which works over very small distances and gravity; They are immune to electromagnetism and the strong nuclear force. Trillions of neutrinos, usually produced by the sun, rain on every square meter of the earth's surface every second. The vast majority sails through the planet.

Occasionally, however, one will be directly in another subatomical particle in an atom. That will produce a shower of secondary particles that are much easier to recognize. A neutrino telescope is therefore a huge exercise in statistics. View a lot of atoms for a long time and sooner or later you will see a collision. Detectors such as Super Kamiokande, in Japan or Ice Cube, in Antarctica, use huge amounts of ultra -purple water and ice respectively. The secondary particles produced by Neutrino collisions produce characteristic flashes of light when they pass through the detector. KM3Net uses the Mediterranean Sea instead. Two groups of detectors are a few kilometers deep in the waters of Sicily and Toulon in France. (A third is planned near Pylos, in Greece.)

The Neutrino from 2023 came in from the west and almost traveled horizontally. It went through more than 100 km of rock before it bumped into something and generated a very energetic muon – a heavier cousin of the electrons that surround atomic nuclei. It was that muon, instead of the neutrino itself, who flashed through the detector. But by working backwards, the researchers were able to conclude for the time being that the neutrino that generated it packed something as 220 Petaelectron-Voltt of energy-in the terms of the layman, about the same as a ping-pongball that dropped from a height of a meter.

The big question is what it could have produced. Fortunately, the reluctance of the neutrinos means to communicate with everything, they map straight paths through space, not influenced by magnetic fields or gas clouds. When the researchers of KM3Net started searching through archived observations of the piece of space from which the neutrino had come, they saw a dozen “blazars”, energy produced by matter that fell into black holes, which point straight to the earth. Each of these could have been the source.

But they don't know for sure: the detection was made while KM3Net was about 10% complete, and there are other, less exciting, possible explanations. Scientists will be better prepared in the future. An automated system, designed to warn other telescopes of remarkable neutrino detections, did not work in 2023. If it had been, scientists could quickly train all kinds of other instruments on the relevant patch of the air, in the hope of spotting extra indications. That system must be active soon. All that can be done now is waiting and hope that something similar happens again.

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