Starship Asterisk*

Astrophysicists ponder whether ultrahigh-energy particles really do come from the centre of galaxies.

Astronomers using a giant array of detectors in Argentina had thought three years ago they were close to solving the mystery of the Universe's highest energy cosmic rays. But the same researchers have now had to backpedal in the face of new observations that threaten their earlier conclusions about the origins and composition of these intense particles.