Messenger - Vol. 3, No. 3, Page 6
Spring 1994
On Research
Cosmic particles shed new light on ancient mysteries

     When a star dies, it collapses catastrophically, hurling debris
into space and generating a shock wave similar to a massive sonic
boom. As the blast gains momentum, it accelerates electrons and
interstellar nuclei in its path, pushing them forward in a frenzied
state of hyperactivity. If they happen to enter our atmosphere, these
"souped-up" projectiles collide with nitrogen and oxygen, showering
the Earth with "secondary" cosmic particles.
     The exact origins of these cosmic particles must be determined
before scientists can fully explain the chemical evolution of
     "All the matter we see around us is cooked inside stars and
distributed during supernova explosions," says Thomas K. Gaisser, a
physics professor in the Bartol Research Institute at the University.
"Previous generations of stars collapsed and exploded, forming the sun
and our solar system. We need to know what happens when stars 'die' to
explain how our world was formed. Cosmic particles provide us with
some of the clues we need to solve this mystery."
     Bartol's South Pole array is among the detectors used to study
such high-energy particles, he says.
     Gaisser is particularly interested in rare particles
demonstrating energies as high as 1020 electronvolts-roughly the
energy of a tennis ball traveling 50 miles per hour, but carried by a
single atomic nucleus.
     How can researchers learn more about these supercharged
particles? Measurements support computer simulations that show how
ionized nuclei from space interact and cascade to Earth as secondary
cosmic particles. Using such techniques, Gaisser and others recently
determined that very-high-energy particles may be generated outside
our galaxy. Since our galaxy is believed to be the source of virtually
all other cosmic particles, the apparent discovery of rare extra-
galactic particles generated excitement among scientists.
     "We found that lower-energy particles consisted mainly of heavy
nuclei, such as iron or oxygen," Gaisser says. "But higher-energy
particles were mostly protons, which may have been propelled into
space on a very strong extra-galactic shock."
     Gaisser continued his investigation of cosmic mysteries during
March as a resident fellow at the Bellagio Conference and Study Center
in Italy. The center hosts scholars and authors pursuing research
projects in a variety of fields.
                                                    -Ginger Pinholster