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Don't Blink!
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by Jana Jones, student writer
DECEMBER 23, 2003 -- The romance and mystery of a shooting star has long caught the attention of the human race. Researchers at Michigan Tech have been looking to the sky lately to study falling lights as well. However, these particles aren't slow and dreamy like stars.
As Associate Professor David Nitz (Physics) said, "These are the most accelerated particles anywhere in the universe."
Michigan Tech is one of the institutions involved in the Pierre Auger Observatory, a collaboration involving 215 scientists and 14 countries devoted to examining highest energy cosmic rays. These rays are space particles--usually protons or heavier ions--that hit the atmosphere and create showers of secondary particles. Though they are invisible to the naked eye, the Pierre Auger Observatory, located in Argentina, can detect these particles through two methods: surface detectors, which are large water tanks, and fluorescence telescopes, which can see the ultraviolet glow emitted by the showers in mid-air.
These high-energy cosmic rays defy previous scientific theories. Scientists used to think that cosmic rays could not approach the Earth with energy greater than 1020 electron volts; however, recent experiments in Utah and Japan have detected these ultra fast particles. For reference, 1020 electron volts is 100 million times more powerful than the proton energy attainable in the most powerful particle accelerator in the world, faster than even supernovas can accelerate particles.
Michigan Tech is providing and certifying electronic components called front end boards, which collect the data in the water tanks at the Auger Observatory, as well as supplying a specialized telescope system that helps to calibrate the fluorescence telescopes used to observe the showers of particles on moonless nights.
To measure the intensity of the ultraviolet light emitted by the particles, researchers also need to know how clear the atmosphere is at any given time. By measuring the light of stars with a known brightness, scientists can compensate for the clarity of the atmosphere and figure out how bright the particle showers are.
The highest energy cosmic rays are extremely rare. They hit the Earth's atmosphere at a rate of approximately once per year per square mile. That means that ground arrays need to cover a large area.
The Pierre Auger Observatory installed its 100th surface detector this October.
"The 100th surface detector puts us past a milestone," Nitz said. "That makes us the largest ground array ever built." However, the observatory is still only at six percent of its planned final size.
The Pierre Auger Project thus far covers 70 square miles of ground. Ultimately the array will have 1,600 detectors and cover an area the size of Rhode Island. However, there are plans to expand the project beyond that. Scientists are looking at establishing a site in the Northern Hemisphere.
According to Nitz, there are two sites under consideration, one in Utah and one in Colorado. The ideal location for an array is a flat and dry area with clear skies, with a supportive local population. Nitz hopes that the location of the northern site will be decided within the year. Until then, scientists will keep observing showers in Argentina.
"It's basic science," Nitz said. "When there's a problem you don't understand, you want to examine it. When you understand the science there are often applications that you can use."
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