A now-closed Utah cosmic observatory has substantiated a prediction about the behavior of cosmic rays.

The new research also casts doubt on a famous discovery by University of Utah scientists, the 1991 finding of a cosmic ray that supposedly carried a billion-billion electron volts of energy. Now it seems it may have been an ordinary cosmic ray distorted by atmospheric conditions.

"Cosmic ray" is a misnomer. They're not rays like beams of light, but subatomic particles ejected into space. According to the U., lower-energy cosmic rays stream from stars like our sun, while more powerful ones are released by some cataclysm such as an exploding star or a black hole gobbling matter in its vicinity.

Cosmic rays continually rain onto Earth's atmosphere. Under good conditions they can be detected by the flashes they make when colliding with air, or they can be detected by ground units they hit.

The 1991 "record" was detected by the University of Utah Fly's Eye Observatory at Dugway Proving Ground. The new report by scientists at the U. and around the world was developed from work at its replacement, the High Resolution Fly's Eye, or HiRes, observatory also at Dugway.

From 1997 until April 2006, when HiRes closed, it made scores of observations of cosmic rays of many energy levels detecting flashes of light in the sky during moonless nights. Views from one observatory, then from two sites about eight miles apart, provided details about direction and intensity of showers of particles created when cosmic rays collided with the atmosphere.

The study, "First Observation of the Greisen-Zatsepin-Kuzmin Suppression," published Friday in the prestigious journal Physical Review Letters, supports a 1966 prediction about the upper limit of intensity for cosmic rays.

Interestingly, according to a university press release, the limit was predicted by Kenneth Greisen of Cornell University while he was visiting the U. It also was predicted independently by Soviet scientists Georgiy Zatsepin and Vadim Kuzmin.

The 1991 super-cosmic-ray seemed to be over the limit. So did a series of detections by a Japanese observatory called the Akeno Giant Air Shower Array.

But nine years of study by HiRes showed that the prediction was right. Cosmic rays from far reaches of the universe lose energy when they collide with the Cosmic Microwave Background, material left over from the Big Bang. The study shows the cutoff is real, although it may not be absolute.

"Everybody's been looking for this for 40 years," said Pierre Sokolsky, a physics professor and spokesman for the HiRes Collaboration and dean of science at the University of Utah. "This is the first real definitive observation."