Ultrahigh energy cosmic rays come from outside the Milky Way
Huge experiment is trying to track the particles back to their sources
LYING IN WAIT Huge tubs of water (one shown) at the Pierre Auger Observatory in Argentina reveal the tracks left as cosmic particles zip through them.
Steven Saffi
The largest study yet of the most energetic particles to slam into Earth provides the first solid clues to where the particles come from. Using a giant array of tubs of water, scientists found that these ultrahigh energy cosmic rays mostly originate outside the Milky Way.
An international team analyzed about 12 years of data to show that particles with energies above 8 billion billion electron volts generally come from a particular direction in the sky, and it’s not the galaxy’s center. The researchers report their findings in the Sept. 22 Science.
“It’s the first clear experimental indication that the sources of these high-energy particles are located outside of our own galaxy, probably somewhere in the nearby universe,” says Karl-Heinz Kampert of the University of Wuppertal in Germany, a spokesperson for the Pierre
