Pulsar. Diagram showing the physical phenomena associated with a pulsar (rapidly-rotating neutron star). Neutron stars have powerful magnetic fields (lines at upper left and lower right) and rotate very fast (less than a second). This leads to the acceleration of charged particles by the magnetic field and the release of radiation from the poles (photons, upper right and lower left). The axis of rotation (blue arrows) does not coincide with the magnetic axis (blue line), and the rotation sends the two photon beams sweeping across the sky to be detected as pulses on Earth. Neutron stars are remnant stellar cores, having a mass greater than the Sun in a volume less than 20 kilometres wide.