Auger Observatory closes in on long-standing mystery,
links highest-energy cosmic rays with violent black holes

MALARGÜE, Argentina, Nov. 8, 2007 — Scientists of the Pierre Auger Collaboration announced today (Nov. 8) that Active Galactic Nuclei are the most likely candidate for the source of the highest-energy cosmic rays that hit Earth. Using the Pierre Auger Observatory in Argentina, the largest cosmic-ray observatory in the world, a team of scientists from 17 countries found that the sources of the highest-energy particles are not distributed uniformly across the sky. Instead, the Auger results link the origins of these mysterious particles to the locations of nearby galaxies that have active nuclei in their centers. The results appear in the Nov. 9 issue of the journal Science. Colorado School of Mines physics professors, Lawrence Wiencke and Fred Sarazin are members of the Auger Collaboration.

Active Galactic Nuclei (AGN) are thought to be powered by supermassive black holes that are devouring large amounts of matter. They have long been considered sites where high-energy particle production might take place. They swallow gas, dust and other matter from their host galaxies and spew out particles and energy. While most galaxies have black holes at their center, only a fraction of all galaxies have an AGN. The exact mechanism of how AGNs can accelerate particles to energies 100 million times higher than the most powerful particle accelerator on Earth is still a mystery.

Cosmic rays are protons and atomic nuclei that travel across the universe at close to the speed of light. When these particles smash into the upper atmosphere of our planet, they create a cascade of secondary particles called an air shower that can spread across 15 or more square miles as they reach the Earth's surface. The ultra-high energy cosmic rays measured for this discovery strike the earth at a rate of only a few per square mile per century and each carries the equivalent energy of a tennis ball traveling 50 miles per hour.

The Pierre Auger Observatory records cosmic ray showers through an array of 1,600 particle detectors placed about one mile apart in a grid spread across 1,200 square miles. Specially designed telescopes also record the emission of fluorescence light from the air shower. Professor Wiencke, who recently joined the CSM physics department, is responsible for laser “test-beam” facilities at the array center that simulate the optical signature of high energy cosmic ray showers. The Auger collaboration is developing plans for a second, larger installation in South East Colorado to extend coverage to the entire sky while substantially increasing the number of high-energy events recorded.

“We have taken a big step forward in solving the mystery of the nature and origin of the highest-energy cosmic rays, first revealed by French physicist Pierre Auger in 1938,” said Nobel Prize winner James Cronin, of the University of Chicago, who conceived the Pierre Auger Observatory together with Alan Watson of the University of Leeds.

While the observatory has recorded almost a million cosmic-ray showers, only the rare, highest-energy cosmic rays can be linked to their sources with sufficient precision. Auger scientists so far have recorded 81 cosmic rays with energy above 4 x10 19 electron volts, or 40 EeV. This is the largest number of cosmic rays with energy above 40 EeV recorded by any observatory. At these ultra-high energies, the uncertainty in the direction from which the cosmic ray arrived is only a few degrees, allowing scientists to determine the location of the particle's cosmic source.

“The discovery is exciting and fundamental. Our instrument in Argentina has opened a new window on the extreme universe through charged particle astronomy,” said Wiencke. “Critical to our observations were the large scale of the instrument and understanding the conversion from the raw data on the ground to the energies of the air showers in the atmosphere.”

The Auger collaboration discovered that the 27 highest-energy events, with energy above 57 EeV, do not come equally from all directions. Comparing the clustering of these events with the known locations of 381Active Galactic Nuclei, the collaboration found that most of these events correlated well with the locations of AGNs in some nearby galaxies, such as Centaurus A.

Cosmic rays with energy higher than about 60 EeV lose energy in collisions with the cosmic microwave background, radiation left over from the Big Bang that fills all of space. But cosmic rays from nearby sources are less likely to lose energy in collisions on their relatively short trip to Earth. Auger scientists found that most of the 27 events with energy above 57 EeV came from locations in the sky that include the nearest AGNs, within a few hundred million light years of Earth.

Auger scientists are now developing the blue prints of a new larger array to be located in South East Colorado, in an area around Lamar. Auger members from CSM, Colorado State University (CSU) in Fort Collins and Pueblo, and affiliated members from the Lamar Community College (LCC) and the South East Colorado Enterprise Development (SECED), recently created the Colorado Coalition for Cosmic-Ray Research (C3R2) to promote the establishment of the northern hemisphere Pierre Auger Observatory. “Hosting such a world-class scientific experiment constitutes a fantastic opportunity for Colorado ”, said Fred Sarazin, assistant professor at CSM and chair of C3R2. “Strong support from the State will be essential to secure federal and international funding for the project”. When built, the northern Pierre Auger Observatory will be the largest detector array in the world.

The observatory is named for French scientist Pierre Victor Auger (1899-1993), who in 1938 was the first to observe the extensive air showers generated by the interaction of high-energy cosmic rays with the Earth's atmosphere.  

Contacts:
Lawrence Wiencke / 303-384-2234 / lwiencke@mines.edu / www.mines.edu/~lwiencke
Fred Sarazin / 303-273-3283 / fsarazin@mines.edu

Photos as well as press information from the countries participating in the Auger Project may be found at: http://www.auger.org/media .

Reporters can contact Science magazine at 202-326-6440 or scipak@aaas.org to receive an official version of the Auger publication.