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The radio/X-ray coupling in Aql X-1

The first parallax distance to a black hole

The speed of a black hole

Shock modelling of Cygnus X-3

Constraints on quiescent black hole jet sizes

Magnetic field alignment in SS 433

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NRAO Charlottesville,
520 Edgemont Road,
Charlottesville,
VA 22903,
USA

jmiller AT nrao DOT edu

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My research

X-ray binary jets

Relativistic jets are well-known in extragalactic radio astronomy. It is believed that such phenomena are powered by supermassive black holes in the centres of the host galaxies. Accretion onto the compact object results in the formation of an accretion disk and the ejection of relativistic plasma in a collimated outflow. Analogues of such systems have been found in our own galaxy, except that instead of the central source being a 107Mo black hole, it may be a stellar-mass black hole, or even a neutron star. Such X-ray binary systems have been nicknamed "Microquasars", indicating not only similar morphology to their massive namesakes, but also, it is believed, similar physics. While the ratios of typical black hole mass to distance in Active Galactic Nuclei and X-ray binaries imply that we can achieve higher spatial resolution when studying supermassive black holes in nearby galaxies, the smaller black hole masses in X-ray binaries imply that such systems evolve on a much faster timescale. Such systems are therefore the ideal laboratories for studying the evolution of accreting black holes through their duty cycles, and the universal connection between accretion and ejection that is seen throughout the visible Universe.

Doctoral research

My PhD thesis was a case study at radio wavelengths of the Galactic X-ray binary system, Cygnus X-3. This system is located in the galactic plane in or behind one of the spiral arms at a distance of approximately 10kpc. The nature of the compact object it harbours is still uncertain, although the infrared spectrum of the source indicates that its companion is a Wolf-Rayet star of the WN7 subclass. It has an orbital period of 4.8 hours, and periodically undergoes huge radio outbursts, reaching fluxes of up to 20Jy.

Recent research

I have recently worked on high-resolution data of the quiescent X-ray binary V404 Cyg, attempting to resolve the jets inferred to exist in this low-luminosity system, and performing astrometric observations to measure the proper motion and parallax of the system. I am leading a large project with the VLBA to investigate the formation and evolution of relativistic jets in different classes of X-ray binary systems, and am working on a large low-frequency mosaic of the region of the Galactic Plane surrounding the Galactic Center.

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Non-astronomical