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Sci Tech
Violent black holes linked to high-energy cosmic rays
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Cosmic rays comprise protons and atomic nuclei, which travel at close to the speed of light
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Using the Pierre Auger Observatory (the largest cosmic ray observatory in the world) in Argentina, a team of scientists found that the sources of highest-energy particles that reach the Earth are not distributed uniformly across the sky.
Active Galactic Nuclei
Instead, the Auger results link the origins of these mysterious particles to the locations of nearby galaxies that have active nuclei in their centres.
These nuclei, called Active Galactic Nuclei (AGN), have long been considered sites where high-energy particle production might take place. They swallow gas, dust and other matter from their host galaxies and spew out particles and energy.
In Science, the Pierre Auger Collaboration, comprising researchers from 17 countries, announced that Active Galactic Nuclei — thought to be powered by supermassive black holes that devour large amounts of matter — are the most likely candidate for the source of the highest-energy cosmic rays that hit Earth.
University of Adelaide scientists are among this leading international research group.
The scientists are from the University’s School of Chemistry & Physics. While most galaxies have black holes at their centre, only a fraction of all galaxies have an AGN, according to a University of Adelaide press release.
The exact mechanism of how AGNs can accelerate particles to energies 100 million times higher than the most powerful particle accelerator on Earth is still a mystery.
Solving the mystery
“We have taken a big step forward in solving the mystery of the nature and origin of the highest-energy cosmic rays, first revealed by French physicist Pierre Auger in 1938,” says Nobel Prize winner James Cronin, of the University of Chicago, who conceived the Pierre Auger Observatory together with Alan Watson of the University of Leeds.
Air shower
Cosmic rays are comprised of protons and atomic nuclei, which travel across the universe at close to the speed of light.
When these particles smash into the upper atmosphere of our planet, they create a cascade of secondary particles called an ‘air shower’ that can spread across 40 or more square kilometres as they reach the Earth’s surface.
“We find the southern hemisphere sky as observed in ultra-high-energy cosmic rays is non-uniform. This is a 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,” says Cronin.
“These enormously energetic particles are very rare, but they pack a real punch.
This discovery is a major step towards understanding some of the most extreme processes in the Universe,” says Associate Professor Bruce Dawson from the University of Adelaide. — Our Bureau
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