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

吸积是宇宙中主要的能量转换过程，涉及到物质沿着大质量致密物体（如中子星或黑洞）的深引力势井流动。势能转化为动能和辐射能，由于辐射产生于致密区域，其有效温度可高达几百万度，从而导致强烈的x射线发射。这个一般场景描述了一类被称为吸积动力x射线源的天体。已知的最强烈的吸积能量源是活动星系核（AGN），它是由物质吸积到超大质量黑洞上提供能量的。特别是，类星体（qso）——非常高亮度的AGN，由于它们的距离很远，看起来像点源——可能有质量是太阳10亿倍的黑洞。令人惊讶的是，尽管经过了几十年的研究，AGN吸积的机制仍然知之甚少，并且仍然是当今天体物理学中突出的问题之一。然而，最近发射的两个卫星任务，钱德拉和xmm -牛顿正在解决这个问题，它们正在获得AGN的高光谱分辨率x射线观测。如果有足够的解释工具，这些卫星将最终开始阐明这类重要的物体。类星体尤其重要，因为类星体中最远的距离约为100亿光年，因此我们观察到的类星体是宇宙诞生不到10亿年时的样子。因此，对这些天体的分析提供了关于早期宇宙的重要信息，比如它的化学成分。天体物理学团体使用高度复杂的建模代码来分析AGN的x射线光谱，其中最受欢迎的可能是CLOUDY，每年有100多篇论文使用它。然而，如何确保用于分析天文观测的建模代码提供准确的结果呢？这只能通过将代码与诊断良好的实验室实验数据进行“基准测试”来实现。不幸的是，直到最近，还不可能在实验室中模拟一个吸积动力的天文源，在实验室中，人们需要一个等离子体，在这个等离子体中，激发和电离是由环境辐射场主导的（所谓的光电离主导体制）。然而，我们是由贝尔法斯特女王大学、劳伦斯利弗莫尔国家实验室（LLNL）、激光能量学实验室（LLE）和肯塔基大学的科学家组成的一个主要国际联盟- OMEGA-QSO联盟的一部分。该联盟已经在LLE设计了OMEGA激光实验，预计将于2006年底开始，这将重现AGN的物理特性，特别是高环境辐射场对等离子体激发和电离的影响。因此，实验将首次允许在AGN中发现的极端条件下（包括类星体）对CLOUDY代码进行基准测试。同样重要的是，我们将能够对FLYCHK和GALAXY建模代码进行基准测试，它们被实验室等离子体物理界广泛应用于辐射场强烈的情况下。在本提案中，我们向EPSRC寻求资金，以履行我们对OMEGA-QSO联盟项目的责任，包括提供建模代码输入所需的高质量原子物理计算。EPSRC的支持对于英国全面和持续参与这个令人兴奋的、独特的项目至关重要。

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.