Primordial black hole: an explosion that could explain almost everything

In 2023, a subatomic particle called a neutrino crashed into Earth with an energy so high that it should have been impossible.

In fact, there are no known sources in the Universe capable of producing such energy – 100,000 times more than the most energetic particle ever produced by the LHC (Large Hadron Collider), the most powerful particle accelerator in the world. However, a team of physicists at the University of Massachusetts Amherst recently hypothesized that something like this could happen when a special type of black hole, called “quasi-extreme primordial black hole”explodisse.

In a new paper published in the journal Physical Review Letters, the team not only explains the otherwise impossible neutrino, but shows that the elementary particle can reveal the fundamental nature of the Universe.

Black holes exist, and we understand their life cycle well: a large, old star runs out of fuel, implodes into a powerful, massive supernova, and leaves behind an area of ​​space-time with gravity so intense that nothing, not even light, can escape. These black holes are incredibly heavy and are essentially stable.

But, as physicist Stephen Hawking noted in 1970, another type of black hole – a primordial black hole (BNP) – could be created not by the collapse of a star, but from the primordial conditions of the Universe, shortly after the Big Bang. So far, BNPs only exist in theory and, like normal black holes, they are so dense that almost nothing can escape them – which makes them “black”. However, despite their density, BNPs can be much lighter than the black holes we have observed so far. Furthermore, Hawking showed that primordial black holes could slowly emit particles, through what is now known as “Hawking radiation”, if they were hot enough.

“The lighter a black hole is, the hotter it must be and the more particles it will emit,” Andrea Thamm, co-author of the new research and assistant professor of physics at UMass Amherst. “As BNPs evaporate, they become increasingly lighter and therefore hotter, emitting even more radiation in an uncontrolled process until they explode. It is this Hawking radiation that our telescopes can detect.”

If such an explosion were observed, it would give us a definitive catalog of all existing subatomic particles, including those we have already observed, such as electrons, quarks and Higgs bosons, those we have only theorized, such as dark matter particles, as well as everything else that is, until now, entirely unknown to science. The UMass Amherst team previously demonstrated that such explosions could occur with surprising frequency – every decade or so – and if we paid attention, our current instruments for observing the cosmos could record these explosions.

So far, everything is theoretical.

Then, in 2023, an experiment called the KM3NeT Collaboration (Cubic Kilometer Neutrino Telescope) captured this so-called impossible neutrino – exactly the kind of evidence the UMass Amherst team assumed we might soon see.

But there was a setback: a similar experiment, called IceCube, also created to capture highly energetic cosmic neutrinos, not only did not record the event, but had never recorded anything with a hundredth of its power. If the Universe is relatively dense in BNPs, and they explode frequently, shouldn’t we be flooded with high-energy neutrinos? What can explain this discrepancy?

“We think that the BNPs with a ‘dark charge’ – which we call quasi-extreme primordial black holes – are the what is missing“, says Joaquim Iguaz Juan, postdoctoral researcher in physics at UMass Amherst and one of the co-authors of the scientific article. The dark charge is essentially a copy of the usual electrical force as we know it, but which includes a very heavy and theoretical version of the electron, which the team calls the “dark electron”.

“There are other, simpler models of BNPs,” he says Michael Baker, co-author and assistant professor of physics at UMass Amherst; “Our dark charge model is more complex, which means it can provide a more accurate model of reality. What’s so great is seeing that our model can explain this otherwise inexplicable phenomenon.”

“A BNP with a dark charge,” adds Thamm, “has unique properties and behaves differently than other simpler BNP models. We have shown that this can provide an explanation for all the apparently inconsistent experimental data.”

The team is confident that their model of darkly charged BNPs can not only explain the neutrino, but can also answer the mystery of dark matter. “Observations of galaxies and the cosmic microwave background suggest that some type of dark matter exists,” says Baker.

“If our dark charge hypothesis is true,” adds Iguaz Juan, “then we think that there may be a significant population of BNPswhich would be consistent with other astrophysical observations and explain all the dark matter missing in the Universe.”

“The observation of the high-energy neutrino was an incredible event“, concludes Baker. “It gave us a new window to the Universe. But we may now be on the verge of experimentally verifying Hawking radiation, obtaining evidence for the existence of primordial black holes and new particles beyond the Standard Model, and explaining the mystery of dark matter.”