Universe
Today: High-energy particles called cosmic rays are
constantly bombarding Earth from all directions, and have been
thought to come from the blast waves of supernova remnants,
writes Nancy Atkinson for
Universe Today. But new observations from the
PAMELA cosmic-ray detector show an unexpected
difference in the momenta (per unit charge) of protons and
helium nuclei, the most abundant components of cosmic rays. The
difference is extremely small, but if they both come from the
same kinds of accelerators, their spectra should be very
similar. Oscar Adriani and his colleagues, who used data from
the
PAMELA instrument, say their new findings are a
challenge to our current understanding of the acceleration and
propagation of cosmic rays, which may be controlled by unknown
and more complex processes. Their
results
were published in
Science.
