Binary pulsars. Artwork of a binary star system of two pulsars. One (lower centre) is seen emitting a pulse (pale beam) of energy. Pulsars are rapidly- rotating neutron stars that cast out narrow beams of energy as they rotate. The beams are confined by extremely strong magnetic fields. The dark pink ellipses are the mutual orbits of these pulsars around the blue dot. The double ellipses show the orbits decaying as the pulsars emit gravitational waves (purple, lower right). This is a confirmed prediction of the General Theory of Relativity. Pulsars are stellar cores, compressed to nuclear densities, that have rotation periods ranging from a few seconds to hundredths of a second.