Primordial black holes could rewrite our understanding of dark matter and the early universe. A record-breaking detection at the bottom of the Mediterranean Sea has some physicists wondering if we just spotted one.

Nearly three years ago, a particle from space slammed into the Mediterranean Sea and lit up the partially complete Cubic Kilometer Neutrino Telescope (KM3NET) detector off the coast of Sicily. The particle was a neutrino, a fundamental component of matter commonly known for its ability to slip through other matter unnoticed.

The IceCube observatory in Antarctica, a comparable detector that has been running for more than a decade, has found hundreds of cosmic neutrinos — but none quite like this one. Some 35 times more energetic than any neutrino seen before, the particle might have shot out from a highly active galaxy — a blazar — or a background source(opens a new tab) of cosmogenic high-energy particles that scientists suspect pervade the cosmos.

But those aren’t the only possibilities. The day after the KM3NET collaboration announced the detection(opens a new tab), the physicist David Kaiser(opens a new tab) walked into a room full of his colleagues at the Massachusetts Institute of Technology with a bold proposition: What if the monster neutrino came from an exploding primordial black hole?

...