The “Impossible” Particles Striking Earth Might Be Dark Matter

Highly energetic particles recently found to impact Earth have existed since science began. While many experts believe these particles are rare neutrinos, some now propose they could be even more extraordinary: dark matter particles traversing the cosmos.

In 2023, a KM3Net detector off Italy’s coast identified this “impossible” neutrino, which remains under construction. These particles exhibited an unprecedented energy level, 35 times greater than previously observed. The origin of these particles is shrouded in mystery, potentially linked to a galaxy hosting an active central black hole, known as a blazar, which serves as a backdrop for high-energy neutrinos permeating the universe.

Bhupal Dev from Washington University in St. Louis and his team present alternative hypotheses. They propose that the event may not have involved neutrinos at all, but rather dark matter particles originating from the blazar impacting Earth. “This opens a fresh avenue for testing dark matter,” he explains. “We can repurpose these neutrino telescopes into detectors for dark matter.”

Neutrino detectors already face a challenging task. These particles are incredibly small, have minimal mass, and seldom interact with matter on their travels across the universe. When they finally reach Earth, they sometimes collide with atoms, generating particles called muons that can be detected by neutrino observatories like the Antarctic KM3NET and IceCube.

Since 2011, IceCube has recorded hundreds of space neutrino sightings but has yet to detect anything as energetic as the recent KM3Net discovery. The fact that IceCube did not observe the source of KM3Net adds to the confusion.

Dev contends that the situation could be rationalized if the incoming particles were dark matter rather than neutrinos. Their predicted trajectories could mean they would have to travel through more Earth to reach KM3Net compared to IceCube, increasing the likelihood of scattering. “Dark matter presents numerous challenges in detection,” says Dev. “IceCube’s data might clarify why it missed these signals.”

The particles may have been generated in the blazar and shot toward Earth in concentrated beams. This theory is bolstered by the notion that high-energy protons from the blazar can transfer energy to dark matter more effectively than neutrinos. Most of the other events recorded by KM3Net and IceCube were likely neutrinos.

Nevertheless, not all researchers are convinced. “From an Occam’s razor perspective, this is likely just an extraordinary neutrino,” says Dan Hooper at the University of Wisconsin-Madison. However, if proven accurate, it could pave the way for the discovery and examination of dark matter particles that have remained elusive until now. “If these instruments can investigate both neutrinos and dark matter, it would generate considerable excitement,” remarks Hooper.

Shirley Lee from the University of California, Irvine suggests that when dark matter particles collide with Earth, they should result in the production of two muons in the detector. Yet, she notes that current detectors lack the precision to differentiate between signals from two particles versus one. “It’s potentially verifiable, but reconstructing muons at these energy levels is extremely complex,” she adds.