Nearby galaxies might be the source of cosmic rays

November 14th, 2007 - 10:19 am ICT by admin  
“With this fundamental discovery, the age of cosmic-ray astronomy has arrived. In the next few years, our data will permit us to identify the exact sources of these cosmic rays and how they accelerate these particles,” said Nobel laureate James Cronin.

Cosmic rays fly through the universe at nearly the speed of light. The most powerful cosmic rays contain more than one hundred million times more energy than the particles produced in the world’s most powerful particle accelerator. Fortunately, Earth’s atmosphere provides protection against their potentially harmful effects on humans.

Since the discovery of cosmic rays in 1938 by French physicist Pierre Auger, their origin has remained a mystery. But now, the Auger collaboration has tracked them to Active Galactic Nuclei (AGN). Likely powered by supermassive black holes, AGN shine far brighter than regular galaxies as a byproduct of their gravitationally destructive force.

“After decades of negative results from past experiments, Auger physicists finally find that cosmic rays do not come equally from every direction in space,” said Angela Olinto, Professor in Astronomy and Astrophysics, University of Chicago.

Scientists have long considered AGN to be possible sources of high-energy cosmic rays. And while they have now found a strong correlation between the two, exactly what accelerates cosmic rays to such extreme energies remains unknown.

“They are really spectacular objects,” said Maximo Ave, a Research Associate at the Kavli Institute for Cosmological Physics at Chicago. “They most likely can be produced only in a place where some very extreme physical process is happening,” he added.

The Auger collaboration has increased the odds of detection of cosmic rays by building an array of detectors that cover 1,200 square miles of the Pampa Amarilla, a vast plain in western Argentina. When complete, the array will consist of 1,600 detectors spaced at one-mile intervals. Ninety percent of the array is now operational.

Each detector consists of a plastic water tank measuring 5- feet tall and 12 feet in diameter. When a cosmic ray collides with an air molecule in Earth’s atmosphere, it triggers a shower that multiplies into billions of secondary particles before reaching the ground. When these particles cross from air into water, the speed changes, producing a shock. The shock creates a flash of light that is detected in the dark chamber of the water tank.

“With this we can estimate the energy, and we can estimate the direction it comes from, which are the two parameters that are important for this analysis,” said Joao de Mello Neto, a scholar from the University of Rio de Janeiro in Brazil.

Complementing the ground detectors are 24 telescopes that monitor the sky for signs of cosmic rays on clear, moonless nights. The telescopes detect the time emission of fluorescent light that results from the interaction of cosmic rays with nitrogen molecules in the atmosphere.

The detection of 27 highest-energy cosmic rays by the Auger Observatory from January 2004 to August 2007 is an significant feat.

“We have taken a big step forward in solving the mystery of the nature and origin of the highest-energy cosmic rays,” said Cronin. (ANI)

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