Scientists detect a mysterious messenger from the cosmosWith a deep-sea detector off the coast of Sicily, scientists have captured evidence of an exceptional ultra-high-energy neutrino.
https://www.washingtonpost.com/science/2025/02/12/neutrino-cosmos-universe-astonomers/
Scientists detected the highest-energy neutrino ever measured using the ARCA telescope, built out of spherical digital optical modules like this one that sense light and are anchored two miles under the Mediterranean Sea. (N. Busser)
An international team of scientists announced Wednesday the detection of an extraordinary, elusive neutrino — a tiny, subatomic particle that flitted at close to the speed of light toward an undersea detector off the coast of Sicily carrying about 30,000 times the energy generated by the largest particle accelerator on the planet.
The observation, unveiled in the journal Nature, revealed the highest-energy neutrino ever detected, sparking speculation about the astrophysical cataclysm that may have shot it across Earth’s bow.
Just as astronomers use telescopes that observe the light from stars to explore and explain the universe, scientists have set up massive telescopes deep in water and ice to measure neutrinos. These cosmic messengers can travel undisturbed over vast distances, carrying information about mysterious high-energy events that generate them.
A detection unit that will be used to search for neutrinos is brought to its deployment winch. (Paschal Coyle)
From the deep cosmos to the deep sea: new results from the KM3NeT neutrino telescope
“It’s incredible, right?” neutrino physicist Paschal Coyle, a member of the KM3Net team that did the research, said at a news conference. “There are these objects in the universe that can accelerate particles to such extreme energies. How that’s done, we don’t completely understand yet. So every piece of information that gives us a clue of the processes involved in achieving such high energy — this is one of the main goals of astronomy.”
Neutrinos weigh almost nothing and have no charge. Far from exotic, they are generated by nuclear fusion reactions inside the sun. Trillions stream through our bodies constantly, without anyone noticing.
But they are also generated outside our galaxy, and because they rarely interact with matter, they travel in straight lines from their origins to us — like arrows that pinpoint exactly where they came from. That can help scientists searching the universe for astrophysical phenomena.
Detectors are prepared for installation in the sea. (Patrick Dumas)
In this case, one possibility is that a very energetic cosmic ray interacted with the cosmic microwave background, the leftover radiation from the Big Bang, and produced this neutrino. Another is that the particle was created when a “blazar,” a galaxy with a supermassive black hole at its center, gobbled up stars. But the debate is only beginning.
Stephanie Wissel, a neutrino physicist at Penn State, who was not involved in the research, called the discovery a “knock your socks off” observation and a remarkable stroke of luck. The neutrino left its trail while the observatory, ARCA, anchored deep in the Mediterranean Sea, was still under construction.
“We’ve never seen a neutrino this energetic, and we have been looking for them for a few decades now,” Wissel said. “We’re trying to understand what the universe is capable of and how it does it — and this one neutrino is exciting.”
Invisible messengers
To catch a neutrino, scientists have to look for footprints. These elusive particles occasionally interact with the protons or neutrons inside atoms and convert into another kind of particle called a muon. That muon speeds through water, creating a phenomenon called Cherenkov radiation — a blue glow — that can be detected.
The undersea observatory that tracked this remarkable neutrino is made up of cables anchored to the seafloor and strung with ball-shaped light detectors. The final version will contain several thousand modules spread over a cube that stretches 10 city blocks in each direction. It is just one of the telescopes of the KM3Net Collaboration, backed by a team of 360 scientists from 21 countries. But the observatory was still being built in February 2023, with just 10 percent of its lines operational, when a third of them lit up as a very energetic muon shot through their detector.
Because the equipment was still getting up and running, there was no automated email alert.
Installing a KM3NeT detection unit on the seabed
KM3NeT Underwater Telescope Opens A New Window On Our Universe
“The first reaction was: ‘Yeah, probably something funny going on,’” said Aart Heijboer, a neutrino physicist at the University of Amsterdam. “Even when we thought it was real, it took us a few weeks before we realized this is a higher-energy neutrino than anyone had ever seen.”
Coyle, director of research at the Center for Particle Physics in Marseille, recalled that when he first tried to run a computer program to help visualize the data, it crashed because he had not foreseen such an ultra-high-energy particle and had not designed his code to handle it.
Ignacio Taboada, a spokesperson for the National Science Foundation-funded IceCube Neutrino Observatory at the South Pole, which has been searching for high-energy neutrinos since 2011, said he is confident the new work was done correctly. But the event is such an outlier that it is difficult to know what to make of it without more data on similar neutrinos.
“This event is really weird. It’s really strange. It’s something that’s hard to explain,” Taboada said. “We will be looking into the direction of this event, and see what is it we can find there.”
Modules used to detect evidence of neutrinos. (Vincent Moncorge)
Signs of faraway cataclysms
The biggest puzzle is what could have generated this neutrino. Even the explosive death of a star in a supernova, for example, could not create a neutrino this energetic, Wissel said. To generate this energy, humans would have to build a particle accelerator that circled the Earth itself, Coyle said.
The scientists behind the collaboration scoured possible astronomical phenomena and did not come up with a clear answer. IceCube, the Antarctica experiment, has found evidence of high-energy neutrinos — though much less energetic than the newly discovered one. By analyzing many of these particles over years, that team has found evidence of neutrino sources in our own galaxy and in other star-forming galaxies.
But many cosmic neutrino sightings don’t line up with any known source, “perhaps indicating source populations that are very distant from Earth, or hinting at an as-yet-undiscovered type of astrophysical object,” Erik Blaufuss, a neutrino physicist at the University of Maryland who was not involved in the research, wrote in a perspective article in Nature.
Puzzling out the story of this neutrino, and trying to find others, will help open a new window on the universe.
“It’s the same reason you look up at the stars and wonder what’s going on up there,” Blaufuss said in an interview. “It’s really trying to understand the universe we live in.”
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