Funding for UK participation in the OMEGA-QSO Consortium experiments: re-creating the physics of quasars in the laboratory

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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 neutron star or black hole. Potential energy is converted into kinetic and radiant energy, and since the radiation is generated in a compact region, its effective temperature can be as high as several million degrees, thereby leading to strong X-ray emission. This general scenario describes the class of astronomical objects known as accretion-powered X-ray sources. The most intense accretion-powered sources known are the active galactic nuclei (AGN), which are powered by the accretion of material onto a supermassive black hole. In particular, quasars (QSOs) - very high luminosity AGN which appear as point sources due to their large distances - may have black holes with masses of a billion times that of the Sun.Surprisingly, in spite of decades of research, the mechanism of AGN accretion is still poorly understood, and remains one of the outstanding problems in astrophysics today. However this is being addressed by two recently launched satellite missions, Chandra and XMM-Newton, which are obtaining high spectral resolution X-ray observations of AGN. Given adequate interpretive tools, these satellites will finally begin to shed light on this important class of objects. Quasars are of particular importance, as the most distant of these are around 10 billion light-years away, and as a result are observed as they were when the Universe was less than a billion years old. Hence the analysis of these objects provides vital information about the early Universe, such as its chemical composition.Highly sophisticated modelling codes are used by the astrophysics community to analyse the X-ray spectra of AGN, the most popular probably being CLOUDY, which is employed in over 100 papers per year. 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.Unfortunately, until recently it has not been possible to mimic an accretion-powered astronomical source in the laboratory, where one requires a plasma in which the excitation and ionization are dominated by the ambient radiation field (the so-called photoionization-dominated regime). However, we are part of a major international consortium - the OMEGA-QSO Consortium - comprised of scientists from Queen's University Belfast, Lawrence Livermore National Laboratory (LLNL), Laboratory for Laser Energetics (LLE) and the University of Kentucky. This Consortium has designed experiments on the OMEGA laser at the LLE, due to start in late 2006, which will re-create the physics of an AGN, specifically the effect of a high ambient radiation field on the excitation and ionization of a plasma. The experiments will hence allow, for the first time, the benchmarking of the CLOUDY code under the extreme conditions found in AGN, including quasars. Just as importantly, we will be able to benchmark the FLYCHK and GALAXY modelling codes, which are widely employed by the laboratory plasma physics community in situations where the radiation field is intense.In this proposal we seek funds from EPSRC to fulfil our responsibilities to the OMEGA-QSO Consortium project, including the provision of high quality atomic physics calculations required for input to the modelling codes. Support from EPSRC will be vital for full and continuing UK participation in this exciting, unique project.