OF THE MIND
TECH INSTRUMENT CENTER
TO BLACK MOUNTAIN
MAY UNLOCK MAD COW DISEASE
SPEECH WASN'T FREE
The thought of high-energy cosmic rays crashing into the Earth's atmosphere probably doesn't keep too many people up all night.
But that's not true for John Belz, a UM assistant professor of physics and astronomy, and a few of his more committed students, who hunker down for the night, twice a month, in a cluttered lab in the basement of the UM Science Complex. From there, in front of a bank of computer monitors stacked on metal shelves, they remotely operate cosmic ray detection equipment — called the High Resolution Fly's Eye — located on a faraway hilltop southwest of Salt Lake City.
They are not looking for garden-variety cosmic rays — a catchall term thatdescribes any type of extraterrestrial radiation that comes into the path of the Earth. Common cosmic rays are continuously zooming at the Earth, and Belz says these particles pelt us all the time. (It's not worth becoming alarmed since there are no known ill effects.)
Humankind has had a tangible relationship with this space-born energy for some time. Cosmic rays are responsible for the northern lights, which are created when cosmic radiation is trapped in the Earth's magnetic field. And the carbon dating technique used by archaeologists depends on the ratio of "normal" carbon compared to the radioactive isotope carbon-14, which is the product of cosmic ray collisions in the atmosphere.
Belz is interested in recording a less ubiquitous kind of cosmic ray — those with the highest energy. One of these rare, energetic particles, usually a proton or the nucleus of an atom, might enter a given square mile of the sky once in a decade. And despite their tiny, subatomic size, they pack quite a wallop. Belz compares the energy in the subatomic particle to that of a major league fast ball — an astonishing amount of energy given the size of the particle. But you won't find any terrestrial impact craters — the particle's journey ends in the planet's atmosphere where it collides with other particles and sets off a chain reaction that astrophysicists call an "air shower."
The particle's near-light-speed entry sets off a cascading series of collisions of atmospheric atoms. The collisions set off by the super-energetic catalyst emit a glow of ultraviolet energy not visible to the naked eye — but strong enough to be detected by the array of devices in the clear Utah sky.
To document these brief showers of non-visible light, the equipment records ultraviolet light signals at a rate of millions of times per second. A relevant event might occur once an hour. Belz and his students constantly measure the atmosphere, so they have a strong idea of the conditions at the precise time the particle creates the shower. The researchers, in effect, subtract out the atmosphere and are left with a detailed map of the air shower.
The research measures the invisible to learn about the tiny — but the results could help answer a huge question.
"We hope to add to our model of the structure of the universe by understanding the violent processes that give rise to the highest energy cosmic rays," Belz says. "What is accelerating these particles to this enormous energy? Nobody really knows."
tremendously violent natural processes must be behind the acceleration
of ultra-high-energy cosmic rays, and
big is happening right under our astrophysical noses," Belz
says. "The solution could be mundane, like we've