Cosmic Rays Create Dazzling Mystery
Two stunning 'events' whose origin cannot be explained lead physicists to design project for northern, southern hemispheres
SALT LAKE CITY
Imagine you are a scientist and in the course of your work you suddenly observe something that defies everything you know about the laws of physics. That is where cosmic ray researcher Eugene Lowe found himself four years ago. ''It was like coming across an ice cube near the equator on a deserted island,'' recalls Dr. Lowe of the University of Utah. ''It didn't seem quite possible.''
His research team, observing through optical cosmic ray detectors in Utah's west desert, saw something that left them absolutely stunned and has since set the world of cosmic ray physics to solve the mystery.
Out of nowhere, the most powerful cosmic ray ever detected slammed into the atmosphere, made a brief flash, and then rained down onto the earth in a cascade of billions of microscopic particles. As scientists later recalled, it was if they had reached out to net a butterfly and had snagged an F-16 instead. The energy of this ray was millions of electron volts higher than most accepted theories allowed, and they were at a complete loss to explain it. What could have caused it?
It might have been written off as some sort of interstellar Bigfoot sighting, but two years later, a similar ray was observed over Japan.
''They do exist. They are beautifully documented events,'' says James Cronin, a leading cosmic-ray researcher with the University of Chicago and a Nobel Prize winner for his work in particle physics. ''And there is no object that one can imagine anywhere in the Universe that has the capability of making such an acceleration.''
Dr. Cronin will head a proposed $100 million project to look for more events like the ones that occurred over Utah and Japan. The project, dubbed ''Pierre Auger'' after a French pioneer in cosmic-ray research, would involve more than 100 scientists from around the world and working at two sites - one in the Northern and one in the Southern Hemisphere - each as large as the state of Delaware.
It's the most recent chapter in a story that goes back to the early part of the century. Cosmic rays - actually tiny charged particles such as protons or electrons that travel through space near the speed of light - were first discovered by pioneer researcher Victor Hess who detected them in high-altitude balloon trips in 1912. Since that time, cosmic rays have led to the discovery of phenomena such as anti-matter and helped launch the first studies of particle physics. They are also constantly bombardi ng the earth and are imperceptibly passing through us all every moment.
Lower energy rays are thought to be produced by the sun or sometimes giant exploding stars called supernovae. But no one knows what could have produced the powerful rays like those discovered over Utah and Japan.
Ever since cosmic background radiation was discovered in the early 1960s, cosmic rays were thought to have an energy ceiling. Most cosmic rays encounter resistance from this magnetic force much as a runner feels wind resistance. This resistance causes cosmic rays to careen wildly across the galaxy, losing energy along the way. But the rays that hit above the Utah desert and Japan flew straight in like Nolan Ryan fastballs, seemingly unimpeded by the massive universal force. This puzzles scientists, but
may also offer a clue: Because these rays fly straight, scientists hope to use a detector to point back to their origins.
When completed, the detector might look something like a massive hexagon made up of 3,000 detector stations 1.5 miles apart. The stations will communicate with one another to determine the direction of a ray's origin and whether it is part of a shower of cosmic rays.
In the center of the hexagon, a large telescope would scan the horizon for brief flashes of light that occur when cosmic rays strike the atmosphere and explode. The shards from these explosions, cascades of billions of secondary particles, then rain down onto the earth. They would be captured by the large triangular detectors on the ground.
Scientists need such large detectors because cosmic rays of the highest energies are scarce, failing at the estimated rate of about one per 100 square kilometers per year. ''So what we propose to do is build a detector that physically covers a lot of ground,'' Cronin says. ''About 5,000 square kilometers, or 50 miles on a side. If we build a big enough detector, we will get something like 50 [sightings of powerful rays] a year.''
With so many sightings, scientists hope to map the rays' origins and point other types of telescopes in those directions, looking for a source that could have generated so much energy.
''Here you have the elements of a mystery whose solution could be many different things,'' Cronin says. ''It could be, in the end, a fairly conventional explanation - things we haven't thought of. It could be a brand-new particle that we don't understand. It could be a brand-new astrophysical mechanism that we had never conceived of before. But for scientists to be presented with a problem such as this is just extremely exciting. You know that whatever you find is going to be new knowledge, and it might
be sensational knowledge.''
Scientists expect to have a blueprint of the project prepared by the end of this month and will then begin the process of raising funds and choosing sites. Choices for sites are located all over the world, but include the American Southwest. If all goes well, according to scientists, the project may be up and working by the turn of the century.