Testing Gravitational Theories with Pulsar Timing at Arecibo

Binary pulsars can be used to test gravitation, and application for which they remain unsurpassed (check here for a good reviewe on this issue). Russel Hulse and Joe Taylor earned the Nobel Prize in Physics in 1993 for discovering at the Arecibo Observatory, in 1974, the first binary pulsar, PSR B1916+13. The precise tracking of the motion of this object led to the confirmation of the existence of gravitational waves, a fundamental prediction of general relativity (GR). Pulsar binaries give us the only tests of gravitational theories for strong gravitational fields. Understanding the nature of gravitation is one of the priorities for research in astrophysics outlined in the report of the National Academies entitled From Quarks to the Cosmos: Eleven Science Questions for the New Century (Board on Physics and Astronomy, 2003, National Academies Press). The following two experiments, carried out recently at the Arecibo Observatory, have introduced further constraints on alternative theories of gravitation:

Measurement of rate of precession for PSR B1534+12

Top panel: the position angle of linear polarization in 2001 June, with the best fit rotating vector model (RVM) overlaid. Middle panel: total intensity (black) and linear polarization (red) profiles in 2001 June. Inset: evolution of impact angle beta with time, indicating that the pulsar's spin axis is precessing away from our line of sight. Bottom panel: ``Difference'' profile, representing essentially the time-derivative of the observed profile. Changes corresponding to this difference profile are observed on both long-term (precession) and orbital (aberration) timescales. Together these allow an estimate of the geodetic precession rate, which agrees very well with the predictions of General Relativity. From Stairs, Thorsett & Arzoumanian (2004).