A gamma-ray pulsar is a compact neutron star that accelerates charged particles to relativistic speeds in its extremely strong magnetic field. This process produces gamma radiation (violet) far above the surface of the compact remains of the star, while radio waves (green) are emitted over the magnetic poles in the form of a cone. The rotation sweeps the emission regions across the terrestrial line of sight, making the pulsar light up periodically in the sky. б© NASA/Fermi/Cruz de Wilde