SEMINAR: Pulsars and Gravity

Pulsars are extraordinarily good clocks. This property has been exploited in a wide range of applications ranging from studying the interiors of neutron stars to testing theories of gravitation. Many pulsars, especially millisecond pulsars, are in orbit around another star, providing a near-ideal gravitational laboratory. The original binary pulsar, PSR B1913+16, discovered by Hulse and Taylor in 1974, has provided the first observational evidence for the existence of gravitational waves (GWs) and has verified that Einstein’s general theory of relativity is an accurate theory of gravitation. The Double Pulsar (PSR J0737-3039A/B), discovered at Parkes, is an extraordinary system that not only gives new insight into magnetospheric and pulse emission physics, it also an unrivalled system for testing gravitational theories. Direct detection of gravitational waves is a major goal of current astrophysics. A Pulsar Timing Array (PTA) can in principle give a direct detection of GWs at nanohertz frequencies. A secondary goal of PTA projects is the establishment of a “pulsar timescale” which, over long time intervals, may be more accurate than the best available timescales based on atomic clocks. Since mid-2004, the Parkes Pulsar Timing Array (PPTA) project has been making regular timing measurements of 20 millisecond pulsars with steadily improving precision. While we do not yet have a significant GW detection, our current upper limit seriously constrains standard models for galaxy evolution and formation of super-massive black holes in galaxy cores. In collaboration with the European and North American PTAs we have formed the International Pulsar Timing Array (IPTA) to enhance progress toward PTA goals.

Richard N. Manchester CSIRO Fellow CSIRO Astronomy and Space Science Epping NSW Australia