I'm a reseearch fellow studying pulsar astrophysics jointly appointed at CSIRO Astronomy and Space Science (CASS)
and the International Centre for Radio Astronomy Research (ICRAR). I'm based in Sydney, Australia
but spend time in Perth at the Curtin University node of ICRAR.

Pulsars and gravitational waves: Pulsars are really good clocks. In many ways, they are the
best clocks in the Universe ! As a result, pulsars can be used to perform the best tests of gravitational
theories like general relativity. The most famous example of this is the study of pulsars in binary systems.
These systems have been used to put the greatest constraint on how gravity works in the "strong field",
i.e., with massive bodies closely orbiting one another.

General relativity predicts that any accelerating mass will produce gravitational radiation, analogous to
the way accelerating charges produce "normal" electromagnetic radiation. The effect of this radiation
is very small, and it has never been directly detected. There are a few of ground based experiments attempting
to detect it, the most famous being the laser interferometer LIGO. However, pulsars can also be used to
detect this radiation. I am involved in the Parkes Pulsar Timing Array (PPTA) collaboration, which is setting up a "pulsar observatory"
that will try to detect the very weak signal gravitational waves impart on the arrival time of pulses.

As part of this collaboration I am leading the effort to place limits on the place limits on the strength of level of
gravitational waves and understand the important astrophysical consequences.

I am also interested in astrophysical sources of noise can affect the stability of pulsars and the sensitivity
of a pulsar timing array. I am involved in examining the stability limits of the pulsars. I have undertaken
observational programs (particularly at the Arecibo observatory) to examine the effects of the interstellar
medium (ISM) on pulsar timing. The radio emission of the pulsars is refracted off of the electrons in the ISM.
This makes looking at pulsars similar to looking through warped glass. As a result, the path the light
takes to get from the pulsar to the earth is not a perfectly straight line, and will change lengths as the
conditions in the interstellar medium change. I have also analyzed rotational instabilities in the pulsar population
to assess what levels might exist in millisecond pulsars.

The pulsar emission mechanism: While there is a general picture of how pulsars work,
the specific details aren't that well known. In the next two years I (along with collaborators, making us "we")
hope to address two questions:

1) How is radio emission modulated? The intensity of the "pulses" that a pulsar emits varies for a
number of reasons. Some of the characteristics are well understood, like interstellar scintillation,
as discussed below. However, most aren't as well understood, and appear to be associated with
the neutron star and its surrounding magnetophere. We think that asteroids orbitting the pulsar may
play a role. I am currently exploring this idea further and also considering the question more
phenomenalogically.

2) Where is the radio emission region located? Over long time scales, pulsar "pulse" intensity
varies in a similar way to the twinkling of normal stars. While regular stars twinkle because their light is
refracted in the Earth's atmosphere, pulsars scintillate because of scattering in the interstellar medium (ISM).
The scattering is concentrated in a small region, and acts somewhat like a conventional interferometer
(like the VLA, for example), except that the baselines are really, really long.
By analyzing the intensity variations due to this effect, we can map the pulsar emission region.
We reported the results at a recent meeting, and are preparing to submit a paper very soon.

The pulsar environment: While we have ideas (see above) on how the environment might affect
pulsar emission, the evidence for any debris around pulsars is circumstantial. Pulsars may gain debris
disks from a couple of interesting sources. For normal pulsars, debris may form from material that has
fallen back from the supernova explosion. A couple of years ago, there was a claim of a detection of a
debris disk around a young anomalous X-ray pulsar. More recent work (by some of the same people)
has cast doubt on this detection. For recycled (millisecond) pulsars debris may be formed from material
evaporated from a companion star. Indeed, this is likely how the planets around pulsars were formed.

Debris disks need not be that large nor bright to cause the effects we are interested in, but we will
continue to study how these disks can be detected, and of course, search for them!