Connecting the lifecycles of galaxies and their central black holes

理解为什么星系--包括我们自己的星系，银河系--看起来是这样的，这是我们理解我们周围的宇宙使命的重要组成部分。在大多数(如果不是全部)星系(包括银河系)的中心，有一个超大质量黑洞，质量是太阳的数百万到数十亿倍。这些黑洞似乎是星系的关键组成部分，决定了它们的大部分结构和演化，尽管如何和为什么仍不清楚。作为未来领导者的成员，我和我的团队正在确定这些黑洞是如何增长的，这种增长何时发生在星系的生命周期内，以及这些黑洞如何影响它们所在的星系。星系有很长的寿命。随着它们内部的气体形成恒星，它们进化得很慢，这些恒星的年龄超过数十亿年，星系的整体形状和结构逐渐改变。相比之下，黑洞中心的大质量黑洞似乎增长得相对较快，只有几百万年的短暂“增长爆发”。在这些生长爆发期间，物质落向黑洞，加热，并可以产生跨越整个电磁频谱的巨大辐射。拥有这样一个不断增长的黑洞的星系被描述为具有“活动星系核”或AGN。近年来，天文学家已经开始了解形成活动星系核的黑洞附近物质的结构，以及这些结构如何产生不同波长的辐射--包括X射线、光学和红外光以及射电发射。这些结构导致了在不同星系中观察到的各种现象，所有这些现象都与由不断增长的超大质量黑洞提供动力的活动星系核有关。然而，我们不知道对于单个活动星系核来说，这些结构在数百万年或更长时间内是如何变化的，在与星系演化相关的时间尺度上是如何变化的。我的团队和我正在开发新的技术来连接星系及其中心黑洞的生命周期，探测数百万到数十亿年的时间尺度。我们的研究揭示了物质是如何进入星系中心的，这种物质是如何形成活动星系核的，活动星系核在数百万年的过程中是如何变化并最终消失的，活动星系核在这段时间内对星系有什么影响，以及这个整个过程在星系的整个生命周期中重复的频率。研究如此长的时间尺度的过程是极其具有挑战性的。我们不能在这段时间内观测一个星系，因此，我们正在使用新的天空观测，提供数百万个星系及其活动星系核的“快照”，每个星系处于不同的生命阶段。我们已经开发了从这些静态快照中提取信息的新方法，并正在建立新的模型来描述单个AGN的生命周期，并解释我们在这些快照中看到的内容。我们还在研究有或没有活动星系核的星系的性质，以确定某些类型的星系是否更有可能有活动星系核。通过这样做，我们可以确定星系内部的哪些物理机制负责将物质驱动到其中心区域，并为活动星系核的活动周期提供燃料。我们的工作结合了一系列新的天文调查的数据。我们正在使用主要的地面望远镜正在进行的新调查，测量印有关于其生命周期的重要信息的星系大样本的光谱图，结合最近发射的eROSITA望远镜提供的新的天空X射线成像，以及现有的红外数据和新的射电波长调查，可以结合起来追踪这些星系内活动星系核结构的变化。

Understanding why galaxies - including our own galaxy, the Milky Way - look the way they do is a vital part of our mission to understand the Universe around us. At the centre of most, if not all, galaxies (including the Milky Way) lies a supermassive black hole, with a mass that is millions to billions of times the mass of the Sun. These black holes appear to be crucial component of galaxies, determining much of their structure and evolution, although how and why is still unclear. As a Future Leaders Fellow, my team and I are determining how these black holes grow, when this growth occurs within the lifecycle of a galaxy, and how these black holes affect the galaxies they lie in.Galaxies have long lives. They evolve slowly as the gas within them forms stars, these stars age over billions of years, and the overall shape and structure of a galaxy gradually changes. By comparison, the massive black holes at their centres appear to grow relatively rapidly, in short-lived "growth spurts" lasting at most a few million years. During these growth spurts, material falls towards the black hole, heats up and can produce huge amounts of radiation spanning the entire electromagnetic spectrum. A galaxy with such a growing black hole is described as having an "active galactic nucleus" or AGN. Over recent years, astronomers have started to understand the structure of the material close to a black hole that forms an AGN and how these structures produce radiation at different wavelengths - including X-rays, optical and infrared light and radio emission. These structures result in a wide range of observed phenomena in different galaxies, all of which can be associated with an AGN powered by a growing supermassive black hole. However, we do not know how these structures change over millions of years or longer for an individual AGN, over timescales relevant for galaxy evolution.My team and I are developing new techniques to connect the lifecycles of galaxies and their central black holes, probing timescales of millions to billions of years. Our studies reveal how material is brought into the centre of a galaxy, how this material forms an AGN, how the AGN changes and eventually fades over the course of many millions of years, what impact the AGN has on the galaxy during this time, and how often this whole process repeats throughout the lifetime of a galaxy.Studying processes on such long timescales is extremely challenging. We cannot watch a single galaxy over this time, so instead, we are using new surveys of the sky that provide "snapshots" of many millions of galaxies and their AGN, each at a different life stage. We have developed new methods to extract information from these static snapshots and are building new models to describe the lifecycles of individual AGN and explain what we see in these snapshots. We are also studying the properties of galaxies with (and without) AGN to determine whether certain types of galaxies are more likely to have an AGN. In doing so, we can determine which physical mechanisms within galaxies are responsible for driving material into their central regions and fuelling the periods of AGN activity. Our work combines data from an array of new astronomical surveys. We are using new surveys that are underway with the premier ground-based telescopes, measuring the spectrum of light from large samples of galaxies that is imprinted with vital information on their lifecycles, combined with new X-ray imaging of the sky provided by the recently launched eROSITA telescope as well as existing infrared data and new surveys at radio wavelengths that can be combined to track the variation in AGN structure within these galaxies.