Black Hole Grand Unification

活跃星系是宇宙中最强大的现象之一，能够塑造宇宙的演化。我们现在知道，每个活动星系最终都是由超大质量黑洞提供动力的，这些黑洞的质量是我们太阳的10亿倍，它们位于每个星系的中心。但在活跃星系的情况下，常驻的超大质量黑洞正受到来自“宿主”星系的气体的喂养，从而从其核心发出各种波长的强大光。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，它们可以比整个宿主星系发出的星光更亮。此外，一些AGN显示出从黑洞附近发出的强大物质喷流，这导致强烈的无线电发射，因此天文学家称这些AGN为“无线电响亮”。尽管经过多年的研究，这些强大喷流的起源，以及为什么一些AGN显示出它们，而其他“无线电安静”的AGN有更弱的喷流，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正在成长的宿主星系周围的环境相互作用，改变它的形成，甚至完全阻止它的增长。了解AGN喷流的起源以及为什么AGN表现出如此多样性，可能对理解每个星系和宇宙本身如何呈现今天的样子至关重要。最近出现了一种新的范式，它对AGN的多样性和喷气机的起源有了新的认识。这种范式，我们称之为“黑洞大统一”，将AGN的行为与“黑洞x射线双星系统”（BHXRBs）的行为进行了比较——BHXRBs是一颗正常恒星绕轨道运行并为一个相对较小的黑洞提供食物的恒星系统，黑洞的质量仅为太阳的十倍。这些BHXRBs似乎是AGN行为的一个缩影。例如，我所参与的广泛研究表明，AGN的x射线光输出的变化与BHXRBs相同，除了减慢了一百万或更多的因素，正如人们所期望的那样，如果AGN黑洞和伴随的“吸积盘”比BHXRBs大一百万或更多倍。此外，将BHXRBs和AGN的射电发射量与x射线发射量进行比较，也显示出同样简单的比例关系，这也意味着质量越大的黑洞显示出更多的射电发射，并以一种基本的方式将x射线和喷流行为联系起来，适用于所有质量范围很大的黑洞。至关重要的是，BHXRBs和AGN之间的这些深刻的相似性为这些黑洞系统之间的另一个基本联系指明了道路，这可以解释为什么一些AGN显示出强大的喷流，而另一些则没有。BHXRBs也显示出强烈的喷流，但只有在特定的“状态”下，这与气体被吸入黑洞的速度相对应。在低速率下，只有“低/硬”状态显示出强喷流。在较高的吸积速率下，BHXRBs可以存在两种状态：“中间”状态，可能对应于吸积速率的快速变化和强大的喷流，以及更稳定的高/软状态，没有强烈的喷流发射。因此，黑洞大统一范式表明，具有强喷流的无线电大声AGN是处于低/硬或中间状态的BHXRBs的超大质量类似物，而无线电安静AGN是高/软状态BHXRBs的类似物。换句话说，AGN是否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BHXRBs在不同状态下的特性，然后将它们扩展到我们期望在更大规模的AGN中看到的，并根据对许多AGN的大型调查的数据测试这些预测，看看无线电安静/无线电嘈杂的两分法是否真的可以在黑洞大统一范式中得到解释。

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.