Almost three years ago, a particle from space hit the Mediterranean Sea and lit up the partially complete Cubic Kilometer Neutrino Detector (KM3NET) 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 operating for more than a decade, has found hundreds of cosmic neutrinos — but none quite like this one. The particle, which is about 35 times more energetic than any neutrino seen before, may have shot out of a highly active galaxy – a blazar – or background source cosmogenic high-energy particles that scientists believe permeate the universe.
But these are not the only options. The day after the KM3NET collaboration was announced detectionphysicist David Kaiser 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?
Such black holes “could have formed before there were atoms, let alone stars,” said Kaiser, who has been heavily involved in the hunt for these hypothetical objects.
The idea that the neutrino comes from a primordial black hole is a long shot; Kaiser said he was “half joking” when he suggested it. But in the absence of a definitive explanation, it remains intriguing, not least because the existence of primordial black holes could mean they play a role in dark matter.
So the question is, have we found just one?
In a split second
The idea of primordial black holes was first proposed in 1966 by Soviet physicists Yakov Zel’dovich and Igor Novikov and solidified by British astrophysicist Stephen Hawking. in 1971. Hawking and his student Bernard Carrfrom Queen Mary University of London in the UK, then elaborated the concept of primordial black holes in 1974.
A primordial black hole, or PBH, is loosely defined as a black hole that formed in the first fraction of a second of the universe. The hypothesis states that during the rapid expansion of the universe, there could have been spikes in the density of space-time that were so high they would have collapsed into black holes. These black holes would span a range of masses depending on the size of the spikes. Some may have been as small as an atomic nucleus.
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