Astronomy magazine Contributing Editor Martin Ratcliffe filed this report from the inauguration of the Pierre Auger Cosmic Ray Observatory in Malargue, Argentina. Ratcliffe sent us this update and images while the event was underway! Thanks, Martin!
November 14 is an exciting day for cosmic-ray astronomy. The inauguration of the Pierre Auger Cosmic Ray Observatory’s (PACRO) southern site took place this afternoon in Malargue, Argentina. Nestled beneath the majestic snow-capped Andes Mountains, the small skiing town Malargue has become the Mecca for astroparticle physicists in search of the holy grail of cosmic ray astronomy: the source of ultra-high-energy cosmic rays (UHECRs). Cosmic rays continually fall toward the 1,600 detectors arranged across 1,150 square miles of Argentina’s Pampa Amarilla (yellow prairie). PACRO is the culmination of a dream of James Cronin and Alan Watson (pictured at right with Paul Paul Mantsch, the Auger Project Manager), who inspired the construction of the large area cosmic-ray detector. These two men developed the idea for the observatory back in 1992. Cronin, a Nobel-prize winner, is a physics professor at the University of Chicago, and Watson is a physics professor at University of Leeds, England.
Cosmic rays strike Earth’s upper atmosphere, creating a cascade of millions of secondary particles — a particle shower — that can be detected on the ground. On very dark, clear nights, PACRO’s 24 large-area telescopes detect faint ultraviolet flashes caused by the cascading shower.
One UHECR makes the Large Hadron Collider (LHC) appear puny. LHC will reach energies of a few trillion electron volts. UHECRs have 100 million times more energy than the subatomic particles accelerated by the LHC. When such particles hit our atmosphere, they generate a cascade of secondary particles, many of which reach the ground. The highest energy UHECRs are rare. Only one strikes a square kilometer of Earth every millennium, hence the need for very large detectors to offer the chance to catch a few per year.
In November 2007, scientists announced the first results from the almost completed Auger array: a correlation between the highest energy cosmic rays and the location of active galactic nuclei. Tentative results like these generated as much a wave of excitement across the community as prospects of greater discoveries lie in wait to the now completed array.
Pierre Auger South cannot see the Northern Hemisphere sky, however. A detailed proposal for a much larger Pierre Auger North (3,100 square miles) is underway. The preferred site is southeastern Colorado in the United States, centered on the town of Lamar. Funding for the northern site remains to be secured.
Why am I here? Aside from the dramatic scenery, wonderful people, and amazing science, the company I work for, Sky-Skan, installed the first digital planetarium in Argentina. It opened officially in August 2008.
On Friday and Saturday we displayed real-time scientific visualizations in Digital Sky of cosmic-ray particle showers in Earth's atmosphere, part of a long-term collaboration with the University of Chicago and Adler Planetarium (thanks to Dr. Mark SubbaRao) and the Kavli Institute for Cosmological Physics (thanks to Randy Landsberg) both of whom will be here in Malargue this weekend.