At this and other PF forums people have several times been referring to the very precise test of General Relativity being made with this binary pulsar thirty years of testing the prediction of GR are summarized in this paper http://arxiv.org/abs/astro-ph/0407149 Relativistic Binary Pulsar B1913+16: Thirty Years of Observations and Analysis J.M. Weisberg, J.H. Taylor it is like having two very accurate clocks orbiting each other there are two neutron stars, each of them a pulsar, in close fast orbit around each other Any pair of objects in a binary orbit must stir up ripples in the graviational field as they go around each other---and must radiate away energy but only if they are close and fast and massive will the radiation amount to much these two neutron stars radiate away energy (GR predicts) fast enough that they gradually come closer and closer to each other, spiralling in, go noticeably faster over 30 years the change has been measured and the rate of energy loss agrees to within observational error (to within 0.02 percent) with what the theory of gravity predicts. BTW some other binary pulsar pairs have been found---I remember posting about one of the finds not so long ago. These pairs of neutron stars are very nice objects. The pair actually loses mass as it radiates gravitationally.