Scientists have detected the most energetic neutrino ever recorded. Whilst tiny, this powerful particle has helped reshape our understanding of the universe’s extremes. These astounding findings were recently announced in the science journal Nature.
The basics - what is a Neutrino?
A neutrino is an incredibly small, near massless particle, way tinier than an atom, a proton or even an electron. As it zips across space it travels almost as fast as light, without ever slowing down. That’s why neutrinos can traverse galaxies and still crash into Earth with immense energy.
But what is central to neutrinos and makes this find so exciting is that they are so hard to detect. As one ‘zips’ across space, it zips ‘clean through’ almost everything. A neutrino will pass through walls, mountainsides, people, very rarely interacting with any of the other incredibly small particles that make up these things. A neutrino can pass through entire planets without leaving a trace!
Does this cute little guy have a name?
How did we see something so small, moving so fast? Well. given how rarely we ever detect neutrinos, and this one’s super-energy content, its name, KM3-230213A, really undersells it.
It is named after the KM3NeT (Cubic Kilometre Neutrino Telescope), a grid of thousands of high-tech detectors spread across a cubic kilometre of ocean 3,500 metres beneath the Mediterranean Sea off Sicily.
How did we see something so small, moving so fast?
Strictly speaking we never see neutrinos, but we see tell-tale signs they have passed through. Thankfully this one collided with something in the water — most likely one of the tiny particles in the nucleus of an atom of hydrogen or oxygen.
This collision produced a heavier particle called a muon that streaked through the water at near-light speed. As it moved, it emitted Cherenkov radiation, a faint blue glow that was picked up by over a third of the KM3NeT’s light-sensitive sensors.
As I’m sure you could imagine, this sort of experiment doesn’t result in a glossy 5” x 7” photo of a neutrino waving and saying, ‘Hi guys, just passing through’. The data from an event like this is extremely complex to analyse, with the findings announced on 12 February, 2025, in the science journal Nature, two years after detection.
So how much energy are we talking about?
Now I’ve called it incredibly ‘energetic’, so let’s put some numbers on that. The neutrino carried an estimated energy of 220 peta-electronvolts (PeV). That is about 1,000 times more energetic than any single particle we've managed to produce in our most powerful accelerators. At the time, the KM3NeT was only partially built, with just 21 of its planned 230 detection lines operational, making the catch even more remarkable.
220 PeV in lay terms is the energy equivalent of a mosquito flying at top speed, a gently flicked paperclip sliding along a desk, or the potential energy of a ping pong ball about to be dropped from a one-metre height.
None of this may seem that much — I mean it’s only a mosquito! — but the neutrino is fantastically smaller. For the same energy to reside in a particle billions of billions of billions of times smaller than a pesky mozzie is mindboggling.
Where did it come from?
The neutrino’s near-horizontal path suggests it came from beyond our galaxy, not from cosmic rays hitting Earth’s atmosphere, which typically send particles downward. And the neutrino’s energy — about 20 to 30 times higher than any previous detection — also hints at extraordinary intergalactic origins.
Scientists suspect it could have been launched by a supermassive black hole in an active galaxy, a gamma-ray burst, or a supernova remnant.
Another theory is that it’s a “cosmogenic” neutrino, born when ultra-high-energy cosmic rays smash into the oldest light particles in the universe, cosmic microwave background photons, which themselves have been zipping across the universe since light first began to travel freely, over 13 billion years ago!
Why the buzz?
Dr. Elisa Resconi, Professor of Astroparticle Physics at the Technical University of Munich and a leading KM3NeT collaborator, described the find as: “[A] milestone in neutrino astronomy. It shows we’re on the cusp of unlocking the universe’s most extreme processes, even with a detector still under construction.”
Her words underscore the potential of KM3NeT, which will grow more sensitive as it expands, possibly detecting many more such particles and improving our understanding of some of the most violent and extreme forces and events in the universe that serve as such super-powered engines.
Sometimes you just have to pinch yourself when you realise the scientific age in which we live.
3 things to know when neutrino dinner party chat breaks out
1. There’s a lot of them
Neutrinos are thought to be the second-most common particles in the universe after photons, and the most plentiful ones with mass. It is estimated that for any given square centimetre of the Earth’s surface, 65 billion neutrinos per second pass through this small patch of space! Despite this incredible amount of neutrinos, the overwhelming bulk of them do not interact with any other particles and only a handful that are this energetic would reach Earth in any given year.
2. One barely weighs anything
Neutrinos have almost no mass; you’d need billions of them to hit the mass of a proton. Scientists have placed a limit on how heavy they are, and know their mass is non-zero, but they still argue about exactly how much they weigh. Suffice to say to us non-physics nerds, it’s next to nothing.
3. It’s probably come from some crazy place
The vast bulk of neutrinos that reach Earth are solar neutrinos, created in our sun’s core. But as described above, these particles can pop out of wild cosmic events — like the exploding of stars or the formation of black holes. While we are yet to spot any, we know that some must have even come from the Big Bang itself.
Have a super-energetic day!
That’s all from me for now. If you'd like more geeky fun, please check out my other newsletters below, or connect with me on LinkedIn and/or X.
Yours in nerdiness,
Adam
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