The Observer, December 7, 2007
Volume XL, Issue 13
Covault presents colloquium on high energy cosmic rays
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On Nov. 29, physics faculty, students, and other interested community members filed into Rockefeller 301 to hear Corbin Covault's colloquium on high energy cosmic rays.
Covault and his research group have been collaborating with over 300 international scientists at the Pierre Auger Observatory in Argentina. They are mainly researching the source of cosmic rays, which are about one billion times more energetic than light.
Their work is slightly complicated by the fact that, unlike astronomers studying stars, they cannot train telescopes to the sky and collect data that way. Instead, they must wait until the particles pass through earth's atmosphere and into their detectors.
Figuring out where the particles come from is complicated. Cosmic rays are charged particles that interact with magnetic fields in space, undergoing many changes in direction before arrival at the earth's atmosphere. When the particles hit the atmosphere, they split into smaller particles, which in turn split into smaller particles, until the final product reaches the earth's surface.
In order to be certain that they are not studying particles that have been altered by their passage through the atmosphere, scientists look at either neutral particles or those with the highest energy. The scientists in Covault's research group are studying the latter. However, these particles are also quite rare: about one strikes each square kilometer per century. Thus, there is a need for a sizeable observatory to detect these particles.
The Pierre Auger observatory, the largest cosmic ray observatory in the world, consists of 1600 cosmic ray particle detection stations spread out over 3000 square kilometers. Each station has a black bag of water through which the particles pass, creating a tiny flash of light. The light is then detected with a sensitive phototube, and the arrival of the particle is timed exactly by a GPS unit.
The deployment of these stations was a job shared by members of the institutions involved. The Case research group, which consists of several undergraduate students, one graduate student, and Covault, calibrated, tested, and deployed over 1600 of the GPS units involved in the experiment. Covault gratefully acknowledged the help, good-naturedly adding, "Anytime you have to do 1600 of anything, it's good to have some undergraduate help."
Between January 2004 and the summer of 2007, the observatory recorded 27 high-energy cosmic waves. The research team gathered information with the hopes of discovering where the rays come from, their energy levels, and what they are made of.
The international team was surprised to discover that when they put the map of where the cosmic rays were expected to have originated from on top of a map of Active Galactic Nuclei (AGN), 20 of the recorded waves overlapped with AGNs.
While Covault says the collaboration is not yet ready to proclaim that AGNs are the source of cosmic rays, there is a statistically significant correlation between them. AGNs, if not the source of cosmic rays, are still good tracers for whatever is the source of cosmic rays. The international research group is now looking ahead – their next step is to build another, larger cosmic ray observatory in Colorado.
