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Saturday, December 31, 2005

UNM Scientists Hunt Cosmic Rays

By John Fleck
Journal Staff Writer
    John Matthews and his colleagues are hunting "the extreme universe." As if the pieces of the universe we already know about aren't extreme enough.
    On a high plain in Argentina, at the foot of the Andes, the University of New Mexico physicist is helping build what, for lack of a better word, you might call an "observatory."
    But the Pierre Auger Cosmic Ray Observatory bears only a passing resemblance to the sort of mountaintop cluster of telescopes the word "observatory" implies. The typical observatory doesn't have 1,012 tanks of water spread across a desert plain.
    Or goats.
    Hovering over a computer screen recently showing pictures of one of their latest trips to Argentina, Matthews and UNM colleague Bill Miller stopped on pictures of the goats- managed by gauchos with a team of what both agreed were the most remarkably talented herding dogs.
    It became a ritual every day as the two made a two-hour drive to the site where they were installing instruments- a trip delayed by the vast herds.
    "You'd just stop and it was just an ocean of goats," Matthews said.
    But the agricultural lifestyle has been a bonus for the project, Matthews said. The skills learned in rural life, maintaining farms and ranches, have made for a talented work force to help the visiting scientists build their observatory.
    Such is a conversation about the Auger project- half high-tech wizardy and half Argentinian travelogue.
    Spread across a New Mexico-like semiarid plain near the town of Malargüe on the Pampa Amarilla, the "yellow prairie" of western Argentina, Auger is a $50 million international collaboration to hunt some of the universe's most exotic prey.
    You'll never see the prey yourself, but UNM graduate student Doug Hague can offer a glimpse in his cluttered office in the university's aging Physics and Astronomy building.
    Typing a couple of commands on his laptop, Hague conjured up a map of the sky with what looks like random blue dots.
    Each dot represents a "cosmic ray" detected by Auger. Hague is trying to figure out where they're coming from. Something in the distant universe is spitting them out with almost unimaginable force.
    Cosmic rays are one of the great frontiers of astrophysics.
    "Ray" is really a misnomer. Cosmic rays are really subatomic particles- pieces of the building blocks of matter, things like protons and neutrons flying through space at nearly the speed of light.
    They don't penetrate Earth's atmosphere, but scientists can "see" them anyway by watching for the cascading chaos created when one slams into air molecules high above the planet's surface.
    The fallout from the collision rains down on Earth like billiard balls scattering across a table. Some of those "billiard balls"- actually subatomic particles- pass through Auger's tanks of water, creating a brief glow that can be detected.
    A bit larger than a stock tank, they contain ultra-pure water. And when the Auger Observatory is completed, there will be 1,600 of them.
    Auger also has telescopes that look up for a faint glow of ultraviolet light created when a cosmic ray hits the atmosphere.
    The question Hague and fellow grad student Julie Smith are trying to answer is: What could spit out such incredibly high-energy particles?
    To get a sense of how high their energy is, it's useful to consider similar high-energy particles created in physicists' giant particle accelerators here on Earth.
    The Tevatron, at Fermilab outside Chicago, holds the title for creating the world's highest-energy particles, accelerating protons and slamming them into targets to study their fundamental properties. The particles Auger is tracking come flying in from outer space with 100 million times the energy of the Tevatron.
    "Somehow nature is 100 million times smarter, better than we are," Matthews said. "How and where nature does it is indeed one of the main questions."
    Water tank detectors and the sort of telescopes being used at Auger have been used before. In fact, the water tanks were pioneered in the 1960s at a project on Albuquerque's West Mesa called "Volcano Ranch."
    But nobody has ever tried it on this scale. Because the cosmic rays the scientists are looking for- the extremely high energy ones- are rare, they need a lot of water tanks to do the job.
    Even with the observatory uncompleted, the scientists are already seeing results.
    On his computer, Hague has done rough calculations plotting the arrival of some 700 cosmic rays, trying to figure out where they are coming from. And that is the dilemma. What sort of cosmic force could fire out a particle with that kind of energy?
    Supermassive black holes are one candidate, but no one knows for sure.
    "If it was easy," Matthews said, "someone would have already discovered it."

E-MAIL Journal Staff Writer John Fleck