A Centauro event is a kind of anomalous event observed in cosmic-ray detectors since 1972. They are so named because their shape resembles that of a

centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as being ...

: i.e., highly asymmetric. If some versions of

string theory In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interac ...

are correct, then high-energy cosmic rays could create

black holes A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can def ...

when they collide with molecules in the Earth's atmosphere. These black holes would be tiny, with a mass of around 10 micrograms. They would also be unstable enough to explode in a burst of particles within around 10⁻²⁷

second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...

Theodore Tomaras Theodore may refer to: Places * Theodore, Alabama, United States * Theodore, Australian Capital Territory * Theodore, Queensland, a town in the Shire of Banana, Australia * Theodore, Saskatchewan, Canada * Theodore Reservoir, a lake in Saskatche ...

, a physicist at the University of Crete in Heraklion, Greece, and his Russian collaborators hypothesize that these miniature black holes could explain certain anomalous observations made by

cosmic-ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

detectors in the

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

n Andes and on a mountain in Tajikistan. In 1972, the Andean detector registered a cascade that was strangely rich in charged,

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly o ...

-based particles; far more particles were detected in the bottom portion of the detector than in the top portion. In years since, the detectors in Bolivia and Tajikistan have detected more than 40 Centauro events. Various explanations have been suggested. One possible explanation might be if the strong force between particles behaves unusually when they have extremely high energies. Exploding black holes are also a possibility. The team calculated what signal a detector would register if a cosmic ray creates a miniature black hole that explodes nearby. The researchers' prediction is consistent with the observed Centauro events. The Tomaras team hopes that computer simulations of mini-black holes exploding, and further observations, will solve the puzzle.

Solution to the Centauro puzzle

In 2003 an international team of researches from Russia and

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

found out that the mysterious observation from mountain-top cosmic ray experiments can be explained with conventional physics. The new analysis of Centauro I reveals that there is a difference in the arrival angle between the upper block and lower block events, so the two are not products of the same interaction. That leaves only the lower chamber data connected to the Centauro I event. In other words, the man-horse analogy becomes redundant. There is only an obvious "tail", and no "head". The original detector setup had gaps between neighboring blocks in the upper chamber. Linear dimensions of gaps were comparable to the geometrical size of the event. The signal observed in the lower detector was similar to an ordinary interaction occurred at low altitude above the chamber, thus providing a natural solution: passing of a cascade of particles through a gap between the upper blocks. In 2005 it was shown that "other Centauro events" can be explained by peculiarities of the Chacaltaya detector. So-called "exotic signal" observed so far in cosmic ray experiments using a traditional X-ray emulsion chamber detector can be consistently explained within the framework of standard physics.

Solution to the Centauro puzzle

Further reading