Bizarre cosmic ray mystery deepens (+video)
Humongous space explosions known as gamma ray bursts have been ruled out as a source of the universe's most intense cosmic rays, a new study has found.
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Evidence points elsewhere
The investigators focused on neutrinos whose energy levels suggest they are linked with gamma-ray bursts. The fireballs that give rise to the gamma rays seen in gamma-ray bursts were thought to potentially hurl particles at very high energies, generating both cosmic rays and energetic neutrinos.Skip to next paragraph
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After analyzing data on 307 gamma-ray bursts in 2008 and 2009, the scientists discovered the levels of these neutrinos were at least 3.7 times lower than expected. This suggests gamma-ray bursts are probably not the sources of the most powerful cosmic rays.
"After observing gamma-ray bursts for two years, we have not detected the telltale neutrinos for cosmic-ray acceleration," Halzen said.
Still, it could be that current models of neutrino production from these events might be off.
"We're not entirely clear yet as to what this neutrino flux we're not seeing might mean," Whitehorn told SPACE.com. "Our understanding of gamma-ray bursts is not complete — there's a lot of theoretical uncertainty. I suspect what will happen now is that there'll be a lot of efforts in the theory community of how to get neutrino fluxes compatible with the results."
Instead of gamma-ray bursts, researchers note that black holes at the centers or nuclei of active galaxies may be responsible for these ultra-high-energy cosmic rays, sucking in matter and spitting out enormous particle jets as they gorge.
"Active galactic nuclei are big — great big accelerators that may be able to accelerate particles to very high energies," said Klein, a long-time member of the IceCube Collaboration.
IceCube has looked for neutrinos from active galactic nuclei, but as yet the data is inconclusive.
The scientists detailed their findings in tomorrow's (April 19) issue of the journal Nature.
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