Supermassive black hole growth - a small-scale solution to a large-scale problem

几乎每个星系的中心都有一个暗天体，其质量是太阳的一百万倍以上。虽然这些天体质量很大，但它们被自身引力压缩到了极高的密度，密度如此之高--事实上，光无法逃脱它们的表面；这些就是超大质量黑洞(SMBH)。这些奇异的天体是如何形成的，这是天文学家面临的一个突出的谜团，也是我发现的一个特别有趣的谜团。通过观察遥远的距离，我们能够瞥见宇宙生命的头几十亿年里发生了什么。虽然在这样的距离下进行研究非常困难，但一些SMBH可以被“称重”。令人惊讶的是，这表明它们在宇宙只有10亿年的时候就已经完全长大了。尽管科学家们认为增长应该需要很长时间，但这一发现要求它们以极高的速度落到黑洞上，以令人难以置信的速度增长--比辐射和重力平衡--即所谓的爱丁顿极限--所允许的速度更快。吸积如何以这样的速度运行尚不清楚，但这是天体物理学中的一个紧迫问题--我的目标是解决这个问题。尽管我们不能研究SMBH直接增长，但我们可以观察到物质如何坠落到附近星系的SMBH上，以及我们银河系内更小的黑洞(双星系统中有轨道恒星：BHBs)上。因此，我们知道物质不会直接落到黑洞上，而是形成一个吸积盘，释放出大量的辐射。在非常高的速度下，并不是所有的物质都落到黑洞上；相反，部分物质会被风或喷流喷出。风以相当慢的速度(约为光速的10%)将物质从圆盘表面带出，而喷流是以接近光速的速度从黑洞附近喷出的更强大的物质。顺理成章的是，类似的流出将伴随着SMBH的增长，物质从吸积流中取出并重新分配到周围--一种形式的反馈。了解爱丁顿吸积的性质和相关的流出对于理解SMBH的增长和反馈肯定对宿主星系产生的影响是必要的。在实践中，这需要观察吸积流在达到爱丁顿极限时如何变化，并与流出相耦合，即它们是如何相互作用的。在实践中，这已经被证明是极其困难的：来自吸积流到附近星系中的两个SMBH和银河系BHB的辐射被中间的物质所遮挡，从而阻止了对耦合的观察。我的提议以一种新的方式解决这个问题：通过观察附近星系中高速增长的BHBs，在这些星系中，介入物的数量要少得多，从而可以研究流入星系的辐射。这些河外黑洞有两种“味道”：一种是在银河系中常见的，显示出强大的喷流；另一种是更亮的，被认为是艾丁顿吸积的一种更极端的形式，具有强大的风。我正在领导第一次重大的寻找新的BHBs的工作，在附近的两个星系中有强大的喷流。通过使用多台仪器对一系列波长进行观测，包括世界上最先进的射电望远镜VLA和NASA的X射线卫星Swift，我将观察圆盘和喷流如何一起变化，从而限制流入的性质和喷流的发射方式。为了了解最明亮的强风来源，我将把新颖的分析技术与理论相结合，揭示流入和流出的性质。通过研究局部宇宙中SMBH的吸积，我将把我的发现外推到更大的黑洞质量，在那里流入和流出的耦合无法研究。最后，通过使用高红移SMBH增长的模拟，我将能够探索反馈对宿主星系的影响，否则将隐藏在一个看不见的时代。

In the centre of almost every galaxy sits a dark object, with a mass over a million times that of the Sun. Although massive, these objects have been compressed by their own gravity to extremely high densities, so dense in-fact that light cannot escape their surface; these are the supermassive black holes (SMBHs). How these exotic objects formed is one of the outstanding mysteries facing astronomers and one I find particularly intriguing.By looking to great distances we are able to glimpse what happened in the first few billion years of the Universe's life. Although very difficult to perform studies at these distances, a few SMBHs can be 'weighed'. Surprisingly this has shown that they were fully-grown when the Universe was only ~1 billion years old. Although scientists thought that growth should take a long time, this discovery demands that they instead grew incredibly quickly by material falling onto the black hole at extreme rates - faster than should be allowed by the balance of radiation and gravity, the so-called Eddington limit. How accretion operates at such rates is unclear but is a pressing issue in astrophysics - an issue I aim to address.Although we cannot study the SMBHs growing directly, we can observe how material falls onto SMBHs in nearby galaxies and onto much smaller black holes (with orbiting stars in binary systems: BHBs) within our own Galaxy. As a result, we know that material doesn't fall directly onto the black hole but forms an accretion disc, which emits large amounts of radiation. At very high rates, not all of the material falls onto the black hole; instead some fraction is expelled in 'winds' or 'jets'. Winds carry material from the surface of the disc at fairly 'slow' speeds (~10% of the speed of light) whereas jets are much more powerful ejections of matter from close to the black hole at almost the speed of light. It is logical that similar outflows will have accompanied the SMBH growth, with matter taken from the accretion flow and redistributed to the surroundings - a form of 'feedback'.Understanding the nature of Eddington accretion and the associated outflows is necessary for understanding the growth of SMBHs and the impact feedback must have had on the host galaxy. In practice this requires observing how the accretion flow changes as it reaches the Eddington limit and couples to the outflow, i.e. how they interact. In practice this has proven to be extremely difficult: emission from the accretion flow onto both SMBHs in nearby galaxies and onto Galactic BHBs is obscured by intervening material, preventing a view of the coupling. My proposal approaches this problem in a new way: by looking at BHBs accreting at high rates in nearby galaxies where the amount of intervening material is much lower, allowing the emission from the inflow to be studied. These extragalactic BHBs come in two 'flavours': those which are commonly seen in the Milky Way and show powerful jets, and those which are even brighter and thought to be a more extreme form of Eddington accretion with powerful winds. I am leading the first major search for new BHBs with powerful jets in two nearby galaxies. By observing with several instruments across a range of wavelengths, including the world's foremost radio telescope, the VLA, and NASA's X-ray satellite, Swift, I will observe how the disc and jets change together, thereby constraining both the nature of the inflow and how the jets are launched. In order to understand the brightest sources with powerful winds, I will combine novel analysis techniques with theory to reveal the nature of both inflow and outflow. By studying accretion onto SMBHs in the local Universe, I will extrapolate my findings to larger black hole masses where the coupling of inflow and outflow cannot be studied. Finally, by using simulations of high redshift SMBH growth I will be able to explore the impact of feedback on the host galaxies, in an epoch otherwise hidden from view.