A pulsar is a
neutron star which produces pulsating radio emission due to a strong
magnetic field. A neutron star is the ultra-compact remnant of a massive star which exploded as a
supernova. Neutron stars have a mass bigger than the
Sun, yet are only a few kilometers across. These extremely dense objects rotate on their
axes, producing focused
electromagnetic waves which sweep around the sky and briefly point toward Earth in a lighthouse effect at rates that can reach a few hundred pulses per second. Although double neutron star systems were known before its discovery, PSR J0737−3039 is the first and only known system () where both neutron stars are pulsars – hence, a "double pulsar" system. The object is similar to
PSR B1913+16, which was discovered in 1974 by Jocelyn Bell,
Taylor and
Hulse, and for which the two won the 1993
Nobel Prize in Physics. Objects of this kind enable precise testing of
Einstein's theory of
general relativity, because the precise and consistent timing of the pulsar pulses allows relativistic effects to be seen when they would otherwise be too small. While many known pulsars have a binary companion, and many of those are believed to be neutron stars, J0737−3039 is the first case where both components are known to be not just neutron stars but pulsars.
Discovery PSR J0737−3039A was discovered in 2003, along with its partner, at Australia's 64 m antenna of the
Parkes Radio Observatory; J0737−3039B was not identified as a pulsar until a second observation. The system was originally observed by an international team during a high-latitude multibeam survey organized in order to discover more pulsars in the night sky. Initially, this
star system was thought to be an ordinary pulsar detection. The first detection showed one pulsar with a period of 22.699 milliseconds in orbit around a neutron star. Only after follow up observations was a weaker second pulsar detected with a pulse of 2.7734 seconds from the companion star. == Physical characteristics ==