Electrons (blue) and positrons (red) from a computer-simulated pulsar. These particles become accerlated to extreme energies in a pulsar's powerful magnetic and electric fields; lighter tracks show particles with higher energies. Each particle seen here actually represents trillions of electrons or positrons. Better knowledge of the particle environment around neutron stars will help astronomers understand how they behave like cosmic lighthouses, producing precisely timed radio and gamma-ray pulses. Credit: NASA's Goddard Space Flight Center.