Could the end be in sight for ultrahigh-energy cosmic rays?

Physicists have known since 1912 that the Earth is constantly bombarded by a cosmic rain of high-energy particles – mostly protons and heavier nuclei – but until recently little progress had been made in understanding where these particles might come from. The reason we cannot do astronomy with cosmic rays is simple: they are charged particles that are deflected by magnetic fields, which means that we cannot determine where they originate from. Even the galactic magnetic field, which is only a few microgauss, can redirect cosmic rays that have energies up to 109 gigaelectron-volts (1018eV) so that they appear to come uniformly from all directions.