Type of project: laboratory astrophysics
Accretion is the dominant energy conversion process in the Universe, and involves the flow of material down the deep gravitational potential well of a massive compact object, such as a black hole, leading to strong X-ray emission. Perhaps the best-known example of accretion-powered X-ray sources is a quasar, which is powered by the accretion of material onto a supermassive black hole at the centre of a galaxy. There is a vast range of phenomenology associated with accretion-powered X-ray sources, including e.g. X-ray pulsars, X-ray bursts, black hole transients, dwarf novae, relativistic jets and quasars. Surprisingly however, in spite of decades of research, the mechanism of accretion is still poorly understood, and remains one of the outstanding problems in astrophysics.
Highly sophisticated modelling codes are employed to analyse the spectra of accretion-powered X-ray sources. However, how can one ensure that the modelling code employed to analyse astronomical observations is providing accurate results? This is only possible by ‘benchmarking’ the code against well-diagnosed laboratory experimental data. Over the last few years there have been several attempts to recreate, within a laboratory plasma, the extreme conditions found in accretion-powered astronomical X-ray sources such as quasars, but without success. However, we have developed a truly novel experimental technique that should allow us to recreate such extreme conditions, and hence properly mimic astrophysical sources. We have already undertaken preliminary experiments on the VULCAN laser at the Central Laser Facilty in Oxfordshire, and further experiments are planned on this and other laser facilities, such as the SG-II in China.
Initial experiments to assess the viability of the project were undertaken on the VULCAN laser in August 2016. An analysis of some of the data obtained indicate that our experiments were successful, and have the potential to truly recreate extreme astrophysical conditions when employed on more powerful laser systems. The PhD student will initially work on the more detailed analysis of the VULCAN experiments (alongside a postdoctoral researcher, recently funded by the Science and Technology Facilities Council). They will also help plan and undertaken further experimental campaigns on VULCAN, the SG-II laser in China, and other facilities as appropriate, as well as analyse the resultant observational data.
The student will compare the experimental data with theoretical spectra generated using highly sophisticated modelling codes, in particular the CLOUDY code developed by our collaborator Prof Gary Ferland at the University of Kentucky. This comparison with allow the ‘benchmarking’ of the CLOUDY code, and the student will modify the code as appropriate to improve agreement between theory and experiment. Training in the use of CLOUDY will be provided at one of the annual CLOUDY Summer Schools (one will be held in QUB in August 2017), and the student may also spend time in Kentucky working with Prof ferland on modelling aspects of the project.
The student will develop a range of skills that are highly valued in astrophysics, plasma physics and industry. These will include skills in astrophysical modelling, experimental and theoretical plasma physics, atomic processes, and computational physics.
For more information on the project, please contact Prof. Francis Keenan