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THE source of cosmic rays, particles which bombard the Earth鈥檚 atmosphere
with astronomical amounts of energy, has eluded physicists. But perhaps that鈥檚
because they鈥檝e been looking in the wrong place.

The highest-energy cosmic rays pack a multi-trillion electronvolt punch when
they hit the atmosphere. Physicists assumed these rays follow a direct path to
Earth because they thought the magnetic fields between galaxies were too weak to
deflect them. But no known particle has enough energy to travel from the nearest
potential line-of-sight source and still smash into our atmosphere with such
force. Researchers have proposed numerous solutions to this puzzle, even
suggesting that higher energy particles so far unknown to science might fit the
bill.

But Glennys Farrar of New York University and Tsvi Piran of Hebrew University
in Jerusalem have come up with a simpler solution. They say that the evidence
for weak magnetic fields is out of date. Their calculations, which expand on
similar results from other researchers, show that the fields are about 100 times
stronger than people supposed. That鈥檚 enough to alter the path of cosmic rays,
so they could in fact start off inside our own cosmic neighbourhood.

鈥淚 like this paper,鈥� says Todor Stanev of the University of Delaware in
Newark. 鈥淭hey have put these different ideas together in a convincing way so one
can see the big picture,鈥� he says.