New study questions nearby galaxies being source of cosmic rays

November 20th, 2007 - 2:44 pm ICT by admin  

London, Nov 20 (ANI): A new research by scientists has discounted an earlier theory attributing the source of cosmic rays as being nearby galaxies.
Though the origin of cosmic rays has remained a mystery since their discovery in 1938, a n international collaboration of more than 370 scientists working at the Pierre Auger Observatory in Argentina, reported last week that the rare ultra-high-energy cosmic rays come from active galactic nuclei (AGN), which shine far brighter than regular galaxies.
These violent galaxies that host the AGN have supermassive black holes at their centre, and had been touted as, but never proven to be, the source of cosmic rays. They are also 100 million times more energetic than those produced by Earth’s best particle accelerators.
But lack of evidence has failed to support the theory pointing towards the AGN being the source of cosmic rays.
A group of scientists had even cautioned the Auger Collaboration that what they were seeing was only a correlation rather than absolute proof.
Now, the High Resolution Fly’s Eye (HiRes) collaboration, a smaller operation based at the University of Utah in Salt Lake City, has tried to check this conclusion against data from ultra-high-energy cosmic-ray events they detected in the northern sky.
The researchers used the Auger team’s parameters for factors such as the maximum distance of the active galactic nuclei from Earth and the maximum angle the ray will be bent by interactions with magnetic fields, and looked to see whether the active galactic nuclei could also explain their events.
Their results suggest that they don’t, as only 2 of the 13 events looked at by the HiRes team correlated with active galactic nuclei.
“They see correlations, we do not see correlations,” Nature News quoted Gordon Thomson, one of the HiRes collaborators, as saying.
But according to Paul Mantsch, a member of the Auger team, the two teams have different estimates for the energy of the rays, which might cause problem in comparing the results.
“The Auger team saw correlations with active galactic nuclei only for very-high-energy rays,” said Mantsch. “If HiRes looks only at their own highest-energy rays, there could be so few events as to make statistical conclusions even more difficult,” he added.
Andrea Santangelo, who is a member of the Extreme Universe Space Observatory mission team, which aims to look at high energy cosmic rays from space, says that more data will help to settle the issue. (ANI)

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