Testing Gravitational Theories with Pulsar Timing at Arecibo

• Long-term timing of PSR B1534+12, and careful monitoring of the polarization characteristics of its pulse profile has now allowed a measurement of the geodetic precession for this pulsar (Stairs et al. 2004). The measured precession time scale is consistent with the predictions of general relativity (GR, see figure below).
• A set of wide millisecond pulsar - white dwarf binary systems discovered with the Arecibo and Parkes telescopes, and timed at the Arecibo telescope, has recently been used to derive the tightest constraints ever on violations of the strong equivalence principle (SEP, Stairs et al. 2005). This is qualitatively different than similar tests made in the Solar System, like Lunar Laser Ranging (LLR). Many alternative theories of gravitation are essentially untestable in the solar system, because their weak-field predictions are essentially identical to those of GR, so LLR tests can not descriminate between these theories and GR. Their behavior only becomes different from GR (and henceforth testable) when intense gravitational fields, like those found in neutron stars, are involved.