  The origin of Galactic cosmic rays (with energies up to 10^15 eV) remains
unclear, though it is widely believed that they originate in the shock waves of
expanding supernova remnants. Currently the best way to investigate their
acceleration and propagation is by observing the gamma-rays produced when
cosmic rays interact with interstellar gas. Here we report observations of an
extended region of very high energy (VHE, >100 GeV) gamma-ray emission
correlated spatially with a complex of giant molecular clouds in the central
200 pc of the Milky Way. The hardness of the gamma-ray spectrum and the
conditions in those molecular clouds indicate that the cosmic rays giving rise
to the gamma-rays are likely to be protons and nuclei rather than electrons.
The energy associated with the cosmic rays could have come from a single
supernova explosion around 10,000 years ago.
