New Theory on Rays’ Sprint Across Space

oops1

http://www.nytimes.com/2007/11/09/science/space/09cosmic.html

By DENNIS OVERBYE
Published: November 9, 2007

They are the zestiest bits of matter in the universe. They can zing through space for millions of years at essentially the speed of light and with 100 million times the energy produced by the biggest particle accelerators on the earth, before crashing occasionally into Earth’s atmosphere and dying in a spray of microscopic fluff.

Since these ultrahigh-energy cosmic rays, as they are known, were first glimpsed in 1963, physicists and astronomers have scratched their heads wondering where they came from and what gargantuan process could produce such energies — wondering, even, if they were real.

Now 370 scientists and engineers from 17 countries in a group known as the Pierre Auger Collaboration say they finally have evidence of a fitting answer: supermassive black holes that rumble at the hearts of many galaxies, crushing stars and gas out of existence and spewing jets of radiation and subatomic particles into intergalactic space.

Using a new array of cosmic ray detectors known as the Pierre Auger Observatory, which is spread over an area the size of Rhode Island near Malargüe, in the pampas of Argentina, the scientists traced some of the highest-energy cosmic rays back to the vicinities of nearby galaxies bubbling with black hole fireworks, so-called active galaxies.

The work is reported today in the journal Science.

“The age of cosmic-ray astronomy has arrived,” said James Cronin, a Nobel-prize winning physicist at the University of Chicago and the co-founder of the Auger observatory.

“We’re really just getting started,” he added in an interview.

Each of the cosmic rays studied had energy in excess of 57 billion billion electron volts, about the energy of a nicely hit tennis ball. By comparison, the Large Hadron Collider at the European Organization for Nuclear Research, or CERN, near Geneva, will accelerate protons to a mere 7 trillion electron bolts when it turns on next summer.

“Such energies are so extreme that they could arise in only the most violent places in the universe,” the authors of the report wrote.

Because such active galaxies trace the general distribution of matter in the local universe, Dr. Cronin and others cautioned, the cosmic rays could originate with other objects, but the black holes’ known tendency toward violence makes them prime suspects. The important thing, Dr. Cronin said, is that for the first time researchers have shown that the high-energy rays do not come uniformly from all directions in the sky.

Until now, cosmic rays, which are often electrically charged particles like protons or atomic nuclei, have seemed to come from everywhere. Because magnetic fields bend the paths of charged particles after the particles are spit from the sun or some distant exploding star, they wander in curved, meandering paths, erasing the direction of their origins. They move under the influence of galactic and even intergalactic magnetic fields before smashing into our atmosphere and causing a cascade of other particles that eventually trigger detectors on the ground.

But ultrahigh-energy cosmic rays have so much energy that magnetic fields can barely nudge them. The galaxy cannot contain them. As a result, when they hit Earth they should point to within a few degrees like bullets back to their origins.

Study of these rays has been hampered by the fact that they are so rare; only an estimated one per century falls on a half square mile of Earth.

The observatory began collecting data in 2004 and since then has recorded a million cosmic rays, including 80 of the high-energy kind. The collaboration hopes to build a twin array in Colorado to begin doing cosmic ray astronomy in the northern sky.