My research career has focused on developing new and improved instrumentation and data reduction techniques for radio interferometry, and applying these developments to the study of compact objects such as neutron stars and black holes.
I recently completed an ARC Future Fellowship, during which I localised the sources of Fast Radio Bursts (FRBs) for the first time. FRBs are millisecond-duration flashes of radio emission that appear to originate from well outside our Milky Way galaxy, and potentially from billions of light-years away. The mechanism responsible remains unknown, and could range from tremendously magnetised isolated neutron stars, to mergers of compact objects, or even more exotic possibilities. A key requirement for understanding their origin is to pinpoint their host galaxy, but most existing FRB searches do not obtain a sufficiently precise position upon detection of an FRB. In my Fellowship, I commissioned new capabilities on the UTMOST and ASKAP instruments, allowing them to localise an FRB to a host galaxy upon discovery. Since the completion of my Future Fellowship in 2021, I am continuing this work via a collaborative ARC Discovery Project.
Using Very Long Baseline Interferometry (VLBI), I have measured the distance to dozens of radio pulsars by observing their annual geometric parallax. VLBI allows milliarcsecond angular resolution, the highest of any direct imaging approach in astronomy: taking an image of the full moon at this resolution would require well over 1 million megapixels. By carefully calibrating the images, even smaller changes in position can be discerned. For a typical radio pulsar at a distance of 10,000 light years, this “parallax” wobble amounts to 0.3 milli-arcseconds, or the angle subtended by a human hair at a distance of 60 km. By directly measuring radio pulsar distances, we can determine their luminosity across the electromagnetic spectrum, assist in the search for low-frequency gravitational waves, and build better models of the ionised interstellar medium. I am the PI of the PSRPI and MSPSRPI projects, which together are quadrupling the number of radio pulsars with an accurate parallax-based distance.
VLBI can also be used to study the cataclysmic “afterglows” generated by merging neutron stars (which can also be seen by gravitational wave detectors such as LIGO and Virgo). I am a member of the OzGrav ARC Centre of Excellence, and have an ARC Discovery Project focused on detecting and characterising milliarcsecond-scale radio afterglows from upcoming LIGO/Virgo GW detections.
VLBI can also be used to study Active Galactic Nuclei (AGN) with great detail, zooming in close to the supermassive black holes that power the AGN and the launching of the powerful jets that help sculpt galactic growth over cosmic time. However, the tremendous angular resolution comes at a disadvantage: making images of large areas of the sky is computationally formidable. The “multi-field” VLBI approach I helped pioneer (see next paragraph) can be used to make postage-stamp images around areas of interest, such as radio sources identified in previous, lower-resolution surveys. I have participated in a number of radio AGN surveys using VLBI of varying breadth and depth, including the mJIVE-20 project, which is the largest cache of moderately faint radio AGN ever assembled.
Modern radio interferometry is largely enabled by high speed digital electronics for both real-time and offline processing. I have led the development of the DiFX software correlator, a flexible software package for realtime processing which is deployed on commodity hardware. DiFX is used by several major VLBI facilities world-wide. I also have a keen interest in the development of improved algorithms for the calibration of interferometer data.