The Double Pulsar

Abstract

A new eaa in fundamental physics began with the discovery of pulsars 1967, the discovery of the first binary pulsar in 1974 and the first millisecond pulsar in 1982. Ever since, pulsars have been used as precise cosmic clocks, taking us beyond the weak-field regime of the solar-system in the study of theories of gravity. Their contribution is crucial as no test can be considered to be complete without probing the strong-field realm of gravitational physics by finding and timing pulsars. This is particularly highlighted by the discovery of the first double pulsar system which was discovered by our team in 2003. The double pulsar is unique in that both neutron stars are detectable as radio pulsars. This, combined with significantly higher mean orbital velocities and accelerations when compared to other binary pulsars, suggested that the system would become the best available testbed for general relativity and alternative theories of gravity in the strong-field regime. Indeed, this has been achieved only three years after its discovery with four independent strong-field tests of GR, more than has been obtained for any other system. Use of the theory-independent mass ratio of the two stars makes these tests uniquely different from all preceding studies. Ourresults confirm the validity of GR at the 0.05% level, which is by far the best precision yet achieved for the strong-field regime. Remarkably, the transverse velocity of the systems center of mass is extremely small, a result which is important for future GR. tests and evolutinary studies.