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The San Diego Union-Tribune

Scientists set to grab cosmic fastballs


November 23, 2005

Cosmic rays, the highest-energy particles in the universe, are being pitched at Earth from someplace beyond our galaxy and for more than seven decades no one has been able to figure out where they are coming from.

Now, armed with a cosmic ray catcher's mitt that is being inaugurated in Argentina on a site half the size of Rhode Island, scientists from the University of Chicago and Fermilab, along with more than 250 other scientists from 16 countries, hope to solve one of astronomy's biggest mysteries.

In addition to searching for the source of cosmic rays, researchers will use the observatory, which consists of hundreds of small detectors spread over 1,200 square miles of ranch and farm land, to explore the universe in ways they couldn't before.

The $50 million observatory is named after Pierre Auger, who in 1938 discovered particle showers on Earth caused by cosmic rays. He later studied cosmic rays at the University of Chicago using a hot-air balloon.

Cosmic rays are so powerful that when they collide with air molecules in Earth's atmosphere, they can temporarily produce energies similar to those that existed right after the Big Bang, the explosive beginning of the universe some 13 billion years ago.

"We want to understand how nature reaches these energies," said University of Chicago astrophysicist Angela Olinto. "The energies of the particles that we'll be observing with this detector are millions of times more powerful than we can produce with particle accelerators on Earth.

Genetic mutations

In principle these particles will give us the possibility of testing physics that we can't test in our laboratories. What happened at the beginning of the universe is the same that you could try to probe by reaching higher and higher energies."

Cosmic rays are protons that have been accelerated to speeds approaching the speed of light, or 186,000 miles per second. Among the contenders as their source are super massive black holes, gigantic exploding stars, decay of mysterious dark matter or the hyper magnetic fields of neutron stars spinning at 3,000 revolutions a second.

Cosmic rays come in all types of energies and constantly bombard the Earth. An ultrahigh-energy cosmic ray slams into oxygen, nitrogen or other atoms in the Earth's atmosphere with the power of a billiard ball traveling at more than 100 mph, but with its mass condensed into the size of an elementary particle.

The energy of the collision creates showers of other particles that, when they hit other atmospheric atoms, break up into even more particles, eventually producing a cascade of hundreds of billions of particles.

Sometimes, theorists believe, such powerful collisions might create miniature black holes. The black holes would pose no danger because they quickly evaporate, but they may leave behind subatomic debris that scientists plan to study to learn more about these puzzling gravitational mighty-mites.

For the most part, cosmic rays are harmless because they are slowed down while passing through the atmosphere, and even the strongest of them are greatly weakened. Cosmic rays also are thought to cause some cancers because of the damage they can do to DNA.

To solve the riddle of their origin, scientists built the large observatory at Malargue in western Argentina to capture the most energetic cosmic rays. These rays are so powerful that they are not affected by magnetic fields and follow a straight line from their source to the Earth.

A large observatory is needed because that kind of cosmic ray is rare, hitting an area slightly larger than half a square mile once a century. An even bigger cosmic ray observatory, which would be 10 times bigger than the one in Argentina, is in preliminary planning stages for Colorado.

The Argentine observatory has two types of detectors, one that picks up the last stages of a cosmic ray breakup as it hits the ground and another that can detect the rays when they first hit the atmosphere. By using both together for the first time, scientists believe they will be able to track the direction of the most powerful cosmic rays back to their source.

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