19:00 03 December 03
Are mini black holes raining down through the Earth's atmosphere? It is possible, says a team of physicists. They think this could explain mysterious observations from mountain-top experiments over the past 30 years.
Ordinary black holes form when stars explode at the end of their lives. The heavy stellar core can collapse into a superdense "singularity" whose gravity is so strong that nothing - not even light - can escape.
If some of physicists' favourite theories about extra dimensions are correct, it would also be possible for high-energy cosmic-ray particles from space to create black holes when they collide with molecules in the Earth's atmosphere (New Scientist print edition, 29 September 2001).
These black holes would be invisibly small, with a mass of only 10 micrograms or so. And they would be so unstable that they would explode in a burst of particles within around a billion-billion-billionth of a second.
Theodore Tomaras, a physicist at the University of Crete in Heraklion, Greece, and his Russian colleagues Andrei Mironov and Alexei Morozov wondered if these mini black holes might explain some strange observations made by cosmic-ray detectors in the Bolivian Andes and on a mountain in Tajikistan, central Asia.
The detectors record showers of particles that cascade through the atmosphere when a high-energy cosmic-ray particle smashes into molecules there.
In 1972, the Andean detector registered a mysterious signal. In contrast to a normal cosmic-ray collision, the cascade was unusually rich in charged, quark-based particles and far more particles turned up in the bottom part of the detector than in the top part. It was dubbed a "Centauro" event, because it looked like a little head on a surprisingly big body, like the half-man half-horse centaurs of mythology.
Since then, the detectors in Bolivia and Tajikistan have clocked up more than 40 Centauro-like events. Several explanations have been suggested: they might arise when hypothetical nuggets of strange-type quarks hit the detectors, or if the strong force between particles behaves unexpectedly when they have enormously high energies.
But exploding black holes also fit the bill. The team has worked out what signal a detector should see if a cosmic ray creates a mini black hole that explodes nearby. The researchers' prediction is consistent with the Centauro-like events.
"We might be wrong, but it looks to us more natural than all other existing explanations," says Tomaras. The team hopes that detailed analysis of future Centauro-like events, as well as computer simulations of mini black holes exploding, will help to resolve the issue.
If they are right, the consequences would be stunning. As well as proving that tiny black holes exist, it would unveil hidden dimensions in our universe.
It would also show that the CERN particle physics laboratory near
Geneva will soon be able to churn out black holes to order. Particle
collisions at the Large Hadron Collider, due to start in 2007,
would have enough energy to create thousands of black holes every