Black Hole Grand Unification

活动星系是宇宙中最强大的现象之一，能够塑造其演变。我们现在知道，每个活跃的星系最终都是由超大质量黑洞提供动力的，这些黑洞的质量比我们的太阳大10亿倍，它们位于每个星系的中心。但在活动星系的情况下，居住的超大质量黑洞由“宿主”星系的气体提供能量，从其核心产生所有波长的强大光发射。活动星系核（AGN）的类型是多种多样的：它们的能量范围从相对微弱的低光度AGN到强大的“类星体”，这些类星体可以胜过整个宿主星系的星光。此外，一些活动星系核显示出从黑洞附近发出的强大的物质喷流，这些喷流会引起强烈的无线电发射，因此天文学家称这些活动星系核为“射电暴”。尽管多年的研究，这些强大的喷流的起源，以及为什么一些活动星系核显示他们和其他“无线电安静”活动星系核有弱得多的喷流，仍然是一个谜。但这是一个需要解决的重要谜团，因为这些喷流可以与生长中的宿主星系周围的环境相互作用，改变其形成，甚至完全停止其生长。了解活动星系核喷流的起源以及活动星系核为何表现出如此多样性，对于了解每个星系和宇宙本身如何呈现出今天的样子可能至关重要。最近，一种新的范式出现了，它对活动星系核的多样性和喷流的起源有了新的认识。我们称之为“黑洞大统一”的这一范例将活动星系核的行为与“黑洞X射线双星系统”（BHXRBs）-星星系统-的行为进行了比较，在这些系统中，一颗正常的星星围绕一个相对较小的黑洞运行，并为一个质量仅比我们的太阳大10倍的黑洞提供能量。这些BHXRB似乎是活动星系核行为的缩影。例如，我参与的广泛研究表明，活动星系核的X射线输出变化与BHXRB中的X射线输出变化相同，只是速度减慢了一百万倍或更多，如果活动星系核黑洞以及伴随的“吸积盘”比BHXRB大一百万倍或更多倍，人们就会预料到这一点。此外，与BHXRB和AGN中的X射线发射相比，无线电发射量的比较显示了相同的简单标度关系，这也意味着质量更大的黑洞显示出更多的无线电发射，并且在质量范围很大的所有黑洞中，X射线和喷流行为以基本的方式联系在一起。至关重要的是，BHXRB和AGN之间的这些深刻相似之处为这些黑洞系统之间的另一种基本联系指明了方向，这可以解释为什么有些AGN显示出强大的喷流，而另一些则没有。BHXRB也显示出强烈的喷流，但仅在某些“状态”下，这对应于气体被馈送（吸积）到黑洞的速率。在低速率下，只有“低/硬”状态显示出强烈的喷流。在较高的吸积率的BHXRB可以存在于两种状态，“中间”状态，这可能对应于吸积率的快速变化，并具有强大的喷流，和更稳定的高/软状态，这表明没有强喷流排放。因此，黑洞大一统范式表明，具有强喷流的射电大声活动星系核是低/硬或中间状态的BHXRB的超大质量类似物，而射电安静活动星系核则是高/软状态BHXRB的类似物。换句话说，活动星系核是否具有强喷流取决于它的吸积速率和吸积变化的历史。我的新研究的主要目的是测试这个想法，通过系统地测量BHXRB在不同状态下的属性，然后将它们放大到我们期望在更大质量的AGN中看到的，并根据对许多AGN的大型调查数据测试这些预测，看看无线电安静/无线电大声二分法是否真的可以在黑洞大一统范式中解释。

Active galaxies are one of the most powerful phenomena in the Universe, capable of shaping its evolution. We now know that each active galaxy is ultimately powered by the supermassive black holes, up to a billion times more massive than our Sun, which reside at the heart of every galaxy. But in the case of active galaxies the resident supermassive black hole is being fed by gas from the `host' galaxy to produce powerful emission of light in all wavelengths from its nucleus. The types of Active Galactic Nuclei (AGN) are diverse: they range in power from the relatively faint low-luminosity AGN, to the mighty `quasars' which can outshine the starlight from their entire host galaxy. Also, some AGN show powerful jets of matter emanating from close to the black hole, which cause intense radio emission so that astronomers call these AGN `radio-loud'. Despite many years of study, the origin of these powerful jets and why some AGN show them and other, `radio-quiet' AGN have much weaker jets, remains a mystery. But it is an important mystery to solve, because these jets can interact with the environment surrounding the growing host galaxy to alter its formation, and even stop its growth altogether. Understanding the origin of the AGN jets and why AGN show such diversity, may be crucial to understanding how each galaxy, and the Universe itself, appears the way it does today. Recently, a new paradigm has emerged which throws new light on the diversity of AGN and the origin of jets. This paradigm, which we call `black hole Grand Unification', compares the behaviour of AGN with that of `black hole X-ray binary systems' (BHXRBs) - star systems where a normal star orbits and feeds a relatively small black hole only ten times more massive than our sun. These BHXRBs appear to be a microcosm of AGN behaviour. For example, extensive research I have been involved in has shown that the variations in X-ray light output from AGN are the same as in BHXRBs, except slowed down by a factor of a million or more, as one would expect if the AGN black holes, and the accompanying `accretion disks' which feed them are a million or more times larger than in BHXRBs. Also, comparisons of the amount of radio emission compared to X-ray emission in BHXRBs and AGN shows the same simple scaling relation, which also implies that more massive black holes show more radio emission, and links the X-ray and jet behaviour in a fundamental way for all black holes over a huge range in mass. Crucially, these deep similarities between BHXRBs and AGN point the way to another fundamental connection between these black hole systems, which could explain why some AGN show powerful jets and others don't. BHXRBs also show strong jets, but only in certain `states', which correspond to the rate at which gas is being fed (accreted) to the black hole. At low rates, only the `low/hard' state shows strong jets, is seen. At higher accretion rates the BHXRBs can exist in two states, the `intermediate' state, which probably correspond to rapid changes in accretion rate and has powerful jets, and the more stable high/soft state, which shows no strong jet emission. The black hole Grand Unification paradigm therefore suggests that the radio-loud AGN with strong jets are the supermassive analogues of BHXRBs in the low/hard or intermediate states, while the radio-quiet AGN are the analogues of the high/soft state BHXRBs. In other words, whether an AGN has strong jets or not depends on its accretion rate and the history of changes in accretion. The main aim of my new research is to test this idea, by systematically measuring the properties of BHXRBs in the different states, then scaling them up to what we would expect to see in the much more massive AGN, and testing these predictions against data from large surveys of many AGN, to see if the radio-quiet/radio-loud dichotomy really can be explained within the black hole Grand Unification paradigm.