Clue to cosmic rays discovered


Nov 8, 2007

Black holes are the most likely source of the mysterious ultra high-energy cosmic rays that bombard the planet, scientists have discovered.

Observations at the world's largest cosmic ray detector suggest the particles are emitted by huge black holes in the middle of nearby galaxies.

The findings, unveiled in Science, may solve a long-running puzzle.

The origins of the highest energy forms of cosmic rays have been a mystery since their discovery in 1912.

The observations were made by more than 370 scientists from 17 countries working at the Pierre Auger Observatory in Argentina.

Professor Alan Watson of the University of Leeds, who led the study, said it opened a new window to the nearby Universe.

"As we finish the construction of our observatory and collect more and more data, we may look at individual galaxies in a detailed and completely new way," he said.

"Our observatory is producing a new image of the Universe based on cosmic rays instead of light."

Violent processes

The scientists found that super high-energy cosmic rays do not arrive on Earth from directions evenly distributed across the sky.

The observatory has 24 telescopes and 1,600 detectors

Instead, they seem to hail from areas of the sky occupied by compact centres of galaxies that contain giant black holes.

The magnetic fields around the black holes may speed up the cosmic rays, which would help explain their super energies.

"We have taken a big step towards solving a century-old mystery," said James Cronin of the University of Chicago, who, in 1991, conceived the observatory together with Prof Watson.

"We now begin to understand the violent processes that take place in neighbouring galaxies."

The Nobel Prize winner said that further observations would give a better picture of exactly where these particles come from and how they are being accelerated.

"Ultimately, we may learn more about black holes and their role in the evolution of the Universe," he added.

The observatory has 24 telescopes and 1,600 detectors covering an area about the size of Lancashire.

It is designed to detect showers of billions of secondary particles created when cosmic ray particles rain down on the Earth.

Cosmic rays are fast moving subatomic particles and nuclei originating from space that crash into the atmosphere.

Lower energy forms are produced by a number of different sources, such as the Sun, other stars, and exploding stars.