A Record-Breaking ‘Ghost Particle’ From Outer Space Made a Splash of Light in the Mediterranean

Astronomers have detected the highest-energy cosmic “ghost particle” on record, deep under the Mediterranean Sea.

The neutrino, as the subatomic particle is called, was found by researchers at the Cubic Kilometer Neutrino Telescope, or KM3NeT collaboration, a global team of more than 360 scientists. Their record-breaking finding was announced in the journal Nature on Wednesday.

“What we have discovered is, we think, the most energetic neutrino ever recorded on Earth,” says Paul de Jong, a physicist at the University of Amsterdam and current spokesperson for the KM3NeT collaboration, to Katrina Miller at the New York Times.

Neutrinos are known as “ghost particles” because they’re notoriously difficult to detect and often pass through matter without interacting with it. The abundant-yet-elusive particles also have no electric charge, so scientists can’t capture them by using electric or magnetic forces. Because virtually no material changes their course, however, the direction of neutrinos’ travel should point reliably back to the mysterious and incredibly powerful cosmic accelerators that launched them, such as a gamma-ray burst.

This neutrino, named KM3-230213A, was found using KM3NeT, a giant network of sensors forming a submerged telescope in the Mediterranean. The system is currently operating but still under construction. Though the research team detected the particle in February 2023, they’ve been working to gain confidence in the finding since then.

Identifying a neutrino with a new telescope is surprisingly rare. One of its two detectors, named ARCA, was only operating at about 10 percent capacity when its sensors picked up the particle. The detector didn’t catch the neutrino itself, but it saw the splash of particles left when it hit the water. Specifically, the neutrino bumped into some matter and created another type of tiny particle called a muon, which in turn set off a glowing wave of blue photons that the detector could see.

“These things have so much energy—they hit so hard—that you get this really enormous spray of particles,” explains Kate Scholberg, a physicist at Duke University was not involved in the research, to Meghan Bartels at Scientific American. “It doesn’t interact much, but when it does, it makes a gigantic, spectacular splash of all kinds of particles spraying everywhere. And it’s the light from those particles that you see.”

KM3-230213A was measured to have an energy of about 120 quadrillion electronvolts—30 times higher than any neutrino detected before. “It’s in a completely unexplored region of energy,” said Paschal Coyle, a neutrino physicist and a member of the KM3NeT team, during a press conference on February 11, per Reuters’ Will Dunham.

“This is about 1,000 times more energetic than anything we could produce on Earth,” adds Bryan Ramson, a neutrino physicist at the Fermi National Accelerator Laboratory in Illinois who was not involved in the study, to Scientific American.

When described in terms of everyday objects, that amount of energy might not sound like a lot. It’s roughly equivalent to the energy of a ping pong ball falling just over three feet in Earth’s gravity, or the energy required to run a small LED light for one second, per CNN’s Ashley Strickland. But put all of that energy into a single, subatomic particle, and it becomes enormous.

“One way I like to think about it is that the energy of this single neutrino is equivalent to the energy released by splitting not one uranium atom, or ten such atoms, or even a million of them,” explains Brad K. Gibson, a KM3NeT collaboration member, in an email to CNN. “This one little neutrino had as much energy as the energy released by splitting one billion uranium atoms … a mind-boggling number when we compare the energies of our nuclear fission reactors with this one single ethereal neutrino.”

Scientists haven’t been able to determine the precise source of the neutrino, but the research team believes it originated beyond the Milky Way.

The incredibly high energy of this neutrino has been met with some skepticism. Another neutrino telescope called IceCube has been looking for the particles in Antarctica for more than a decade and has not found anything as powerful. “My first impression is that this is very unexpected. And how can this be possible without IceCube having seen something [similar] before?” says Ignacio Taboada, a physicist at the Georgia Institute of Technology and spokesperson for the IceCube collaboration, to Scientific American.

While there are still questions to be answered, the detection starts a potential new phase in understanding the cosmos. And it means that more neutrinos than scientists previously thought might be flying through space. “It’s a sign that we’re on the right track, and it’s also a hint that maybe there might be a surprise,” says Denver Whittington, a physicist at Syracuse University who was not involved with the research, to Adithi Ramakrishnan at the Associated Press.

Sara Hashemi | READ MORE

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.