Lighting the Way: Project Studies Cosmic Rays
Thursday, September 27, 2001
An artist's rendition of the seven telescope-dishes planned in an Arizona desert south of Tucson to study cosmic rays. BY GREG LAVINE
THE SALT LAKE TRIBUNE

    For three decades, Utah researchers have probed the cosmos in hopes of learning more about the mysterious cosmic rays bombarding the earth's atmosphere.
    Utah has a rich history in studying cosmic rays, starting in the 1960s with experiments in the Park City Silver King Mine to today's High Resolution Fly's Eye Detector at Dugway Proving Grounds.
    Learning about cosmic rays can lead to a better understanding of our universe. Distant objects, such as supernovae, produce the cosmic rays. By the time these rays reach Earth, some are more than 150 million years old.
    David Kieda, a University of Utah physics professor and head of the Utah High Energy Astrophysics Institute, said the U. is now involved in the next-generation of cosmic ray detectors. VERITAS -- Very Energetic Radiation Imaging Telescope Array System -- will be built in an Arizona desert south of Tucson.
    The U. will be a partner in operating the seven-telescope network, Kieda said during last week's Science at Breakfast lecture.
    "[Utah] is becoming a world-renowned leader in high energy astrophysics research," he said.
    VERITAS, which will be complementary to the HiRes Fly's Eye program, will study very-high energy gamma rays as they hit the atmosphere. The Fly's Eye apparatus studies ultra-high energy cosmic rays. Since each system gathers different kinds of information, together they can provide an array of data on various cosmic objects.
    Trevor Weekes, VERITAS spokesman and researcher on the program, said the atmosphere acts like a 3-foot-thick lead wall against incoming cosmic rays. The VERITAS equipment will be 20 times more sensitive than the the project Weekes now works on, the Whipple Telescope at Mt. Hopkins in Arizona.
    Since scientists cannot see cosmic rays, they rely on other evidence to learn about the rays. A cosmic or gamma ray hitting the upper atmosphere triggers a particle shower, which falls to the earth. It is the light from these resulting particle showers that the equipment tries to record.
    VERITAS looks for clues that gamma rays are hitting the atmosphere. Gamma rays come from distant spots inside and outside our galaxy, such as the Crab Nebula and supernovae.
    Kieda said some gamma rays hurtle directly toward Earth. Spotting a resulting particle storm allows researchers to trace a line back to the gamma ray's source.
    One of the VERITAS project's goals is to identify how many gamma ray sources exist. Scientists in the 1990s discovered about a dozen sources of these rays.
    "There are not expected to be many sources for very-high energy gamma rays," Weekes said.
    The VERITAS telescopes will detect what is known as Cerenkov light. These brief flashes of blue light are from particles that have been propelled beyond the speed of light.
    Though cosmic rays cannot enter the earth's atmosphere, astronauts orbiting the planet notice the rays. When astronauts close their eyes and try to sleep, they report seeing tiny flashes of light, Kieda said. Cosmic rays strike charged particles, which in turn move and emit Cerenkov light.
    A telescope must be looking headon into the shower in order to record the data. Each telescope will be armed with a sophisticated camera to capture the bluish Cerenkov light.
    In contrast, the HiRes Fly's Eye detectors seek out fluorescence. When certain cosmic rays hit the atmosphere and trigger particle showers, some of the molecules rattle around giving off fluorescence.
    The HiRes Fly's Eye equipment does not have to be looking directly at the shower and can capture a cross section. Special cameras record this fluorescent light.
    VERITAS should help locate quasars, or active galactic nuclei, which are known sources of gamma rays. Quasars are black holes with the mass of a million suns, which are surrounded by spiralling discs containing material such as protons and iron. This spinning material falls into the black hole, Kieda said.
    Similar to 1980s video game icon Pac Man, who chomped dots and ghosts, quasars consume stars, planets and iron.
    "It's one of the most energetic things in the whole universe," Kieda said.
    Some of the material that the black hole does not swallow is released as shock waves, which creates radiation. If someone dropped a rock in a pool, the resulting splash could be thought of as the shockwave. Electrons, or other particles, can be propelled into space as they ride the shock waves like surfers on the ocean.
    VERITAS also will probe how gamma rays are accelerated to such high speeds, as well as how fields and other forces in space affect the rays.
    Each of the seven reflective dishes to be built at the base of Mt. Hopkins will cover a part of the sky equivalent to five or six times the moon's diameter. Together, the collection of 33-foot dishes can cover a good chunk of the night sky visible from Montosa Canyon.
    Scientists operating the telescope array can also aim all the dishes at a single point to mine any given object for information with increased sensitivity.
    The first telescope-dish of VERITAS is expected to come online in late 2002, with the other six units being built by early 2005. While VERITAS is being built, several other similar projects will be setting up shop in various spots around the world.
    "We can actually get continuous coverage around the world," Kieda said, between VERITAS and the other planned gamma ray observatories.
    The Department of Energy, the National Science Foundation and Harvard-Smithsonian are funding the $22 million project. Schools joining the U. on this undertaking include the University of Chicago, Iowa State University, the University of California at Los Angeles, Purdue University and Washington University in St. Louis.
    Weekes said VERITAS has secured enough money to build the first dish, but that the Bush administration was reviewing the rest of the project.