New evidence may now rule out gamma-ray bursts as sources of these ultra-high-energy cosmic rays.
Researchers employed the IceCube neutrino detector, an array of thousands of detectors encompassing a cubic kilometer of clear Antarctic ice at the South Pole. Neutrinos are ghostly particles that often pass right through matter, only rarely striking atoms.
"This is a coming-of-age for neutrino astronomy — the first time we're able to use neutrino data as a new way of looking at astrophysical objects and say something substantive about them," said study co-author Nathan Whitehorn, a physicist at the University of Wisconsin-Madison, who led the recent gamma-ray burst research with Peter Redl of the University of Maryland.
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.
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.