Binary pulsars and relativistic gravitation

Radio pulsars, which are rapidly rotating, highly magnetized neutron stars, are known to be extraordinarily precise 'celestial clocks' with a variety of applications in astrophysics and fundamental physics. The pulsars found in close binary systems, especially those with massive () compact companions, have proved to be excellent tools of experimental gravitation. Moving in eccentric orbits at mildly relativistic speeds (), having surface potentials of the order of (compared to for the Sun), the high-mass binary pulsars are, in fact, the best known probes of relativistic gravity. Precise timing measurements of the first relativistic binary pulsar, SCR B1913+16, discovered by Hulse and Taylor in 1974, have led to establishing the most convincing evidence, so far, that the quadrupolar gravitational waves exist. This and several other, later discovered binary pulsars have defined a distinct class of celestial objects characterized by the presence of measurable relativistic effects in their orbital motion. Timing observations of binary pulsars provide a method to detect these effects and to apply them in the tests of general relativity and other gravity theories in strong-field conditions.