Physicists suggest they might have pinpointed the origin of an extremely potent, virtually undetectable particle that struck Earth, linking it to the terminal explosion of a very small black hole. The findings of this research are detailed in the journal Physical Review Letters.
If their hypothesis holds true, this single event could illuminate what forged the Universe in its earliest moments following the Big Bang.
In 2023, the KM3NeT observatory detected a particle with an energy of approximately 220 PeV—equivalent to a quadrillion electron volts—beneath the Mediterranean Sea. To account for this surge, physicist Michael J. Baker correlated the record-breaking particle with a vanishing black hole that emerged in the initial stages of cosmic existence.
At the University of Massachusetts Amherst (UMass Amherst), a novel concept has arisen, suggesting the presence of black holes that can remain dormant before rapidly exploding. Should this framework prove accurate, the same explanation should apply to other phantom particles arriving with significantly lower energies.
The flare originated from a neutrino—a virtually massless particle that almost never interacts with matter—and carried more energy than any neutrino previously observed.
To achieve such extreme energy, an accelerator far surpassing the capabilities of any current laboratory is required, as only immense gravity or powerful shockwaves can propel particles with such force.
At the Large Hadron Collider, the FASER experiment measured neutrinos in the trillion-electron-volt range, which is nearly 100,000 times less energetic than this event.
Few known cosmic phenomena can emit neutrinos in such quantities, which leaves room for explanations originating from the first seconds of the Universe’s history.
The deep water provided KM3NeT with a dark backdrop, enabling its sensors to capture the fleeting light emitted by the passing neutrino.
When a neutrino strikes a water molecule, it releases a charged particle that generates Cherenkov radiation—a blue light in pure water.
This charged particle left a faint blue glow along its trajectory, allowing scientists to reconstruct the neutrino’s direction and energy.
Since neutrinos pass through nearly everything, every detection relies on chance, and a single event cannot characterize the entire population.
Some physicists view primordial black holes—those formed shortly after the Big Bang—as relict objects surviving from the Universe’s initial moments.
Unlike black holes stemming from dead stars, these may have been minuscule initially, and in the current Universe, their mass could lead to their evaporation.
An exploding primordial black hole within our galaxy could eject particles, including neutrinos energetic enough to reach detectors.
However, the existence of such early black holes remains unconfirmed, meaning any single candidate must undergo rigorous cross-verification.
Back in the 1970s, physicists identified Hawking radiation—particles emitted from a black hole’s edge—as one mechanism by which black holes “fade away.”
Calculations indicate that smaller black holes heat up as they lose mass, accelerating this process. Near the end, the process goes runaway, and the final moments might resemble an explosion releasing high-energy neutrinos.
Connecting the neutrino burst to this evaporation would offer empirical evidence for this effect beyond theoretical math.
In their work, they notably proposed endowing black holes with a “hidden charge” that behaves differently from electricity.
With a sufficient charge, a black hole would become “quasi-extremal,” nearly fully charged and significantly colder, thus slowing Hawking radiation.
Instead of normal electricity, this hidden charge would remain trapped for millennia because the black hole could not easily shed it.
Ultimately, the accumulated field might trigger the Schwinger effect—pair production in intense fields—leading to charge discharge and an explosion.
Years before the KM3NeT detection, IceCube had already recorded extremely high-energy neutrinos within the Antarctic ice, each carrying over one quadrillion electron volts of energy—a magnitude far exceeding the reach of human-made particle accelerators.
Because the quasi-extremal black holes remain cool for most of their lifespan, they emit fewer medium-range neutrinos prior to their final flare.
This noise suppression technique allowed the UMass Amherst team to link both detectors simultaneously without requiring an infeasible number of explosions.
Nevertheless, this idea predicts that bursts should be rare and occur in proximity, meaning future detections should align in both time and direction.
High-energy explosions should emit gamma rays, the most energetic form of light, alongside neutrinos.
From China, the LHAASO (Large High Altitude Air Shower Observatory) telescope scanned the sky hours before the event and detected no unusual flares.
According to this charged black hole concept, the final energy release would be extremely swift, meaning any flash of light would appear only minutes before the particle arrives.
If a similar event occurs in the future, accompanied by a flare within this narrow time window, it would validate the theory, while another calm sky would make defense of the theory more difficult.
Beyond the neutrino puzzle, the model aims to investigate dark matter—the invisible mass holding galaxies together, hidden within black holes.
This population, spread throughout the Milky Way Galaxy, would be located close enough for periodic bursts of activity while remaining concealed from most telescopes.
“Furthermore, these black holes could constitute all the observable dark matter in the Universe,” Baker notes.
Numerous measurements already constrain the abundance of primordial black holes, thereby narrowing the permissible range considerably.
Additional data gathered by KM3NeT and IceCube will provide a test to see if the rare, nearby bursts continue to exhibit the same energy signature.
More precise correlation between neutrino track tracing and gamma-ray searches in LHAASO data will determine how far this black hole hypothesis can advance.
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