Accreting black holes are known to launch powerful, relativistic jets that move away from the black hole at close to the speed of light. These jets provide a key source of feedback of energy and momentum to the surrounding environment. When a black hole is feeding sedately the jets are fairly steady, but when it accretes at higher rates the jets become more powerful but episodic, appearing as individual clouds of radio emission moving away from the black hole.
Using the technique of very long baseline interferometry (VLBI) we can zoom in on these powerful jets, tracking their motion in real time as they move outwards. This technique involves combining the signals from multiple different telescopes separated by thousands of kilometres, and assembling an image from the combined data. This is the same technique recently used by the Event Horizon Telescope (EHT) Consortium to take the first image of a black hole shadow, and can provide sufficient resolution for an observer in Perth to make out a coin located in Sydney.
At such high angular resolution, the jets from nearby stellar-mass black holes can move significantly over the course of a typical few-hour observation, as well as brightening or fading over that time. This violates the fundamental assumptions that go into imaging radio astronomical data (which assume a source that is constant over the timescale of the observation), and therefore requires new approaches. In one recent case, we split a four-hour observation up into two-minute chunks to observe the jets evolving in real time. While this highly manual approach yielded new insights into the dynamics of the black hole jets, new imaging algorithms have recently been developed that could both automate the process and use all available information to get a more complete view of the jets.
In this project, you will investigate the application of some of these alternative imaging algorithms to VLBI data on black hole X-ray binaries, aiming to provide higher-fidelity imaging of time-variable structures. This will allow you to extract new science from existing data sets, probing how jets evolve and propagate in real time. In cases where we can couple the time-variable jet behaviour to the changes observed in the inflowing gas around the black hole (as seen in the X-rays), we can aim to probe the universal link between accretion and ejection phenomena around black holes.
The lead supervisor heads an international collaboration using high angular resolution radio observations to understand how jets are launched from accreting black holes. The successful applicant will work as part of this collaboration, using data from some of the leading radio telescope arrays around the world