Comprehensive Model for the Formation-Evolution of Massive Cosmic Systems: The Answer is Blowing in the Wind

大质量的宇宙晕，包括宇宙中最大的星系以及星系群和星系团，是一个非凡的系统。这些光晕的质量从相当于1万亿个太阳到令人难以置信的亿亿个太阳，是宇宙中最大、质量最大的引力束缚物体。它们的大部分质量是暗物质。在构成这些系统的可见物质中，大部分是以百万度（或更高）热的x射线气体的形式存在的。这些光晕中存在着巨大的黑洞，它们以周围的气体为食，并推动强大的喷流，向外延伸10万光年或更远。我们今天观察到的这些系统是如何形成的？是什么过程塑造了他们？这些问题之所以如此紧迫，其中一个原因是，这些巨大的光晕共同拥有宇宙中50%的星系，如果不知道它们所处的极端环境如何影响它们的进化，就不可能解释为什么观察到的星系表现出它们所具有的特性。另一个原因是，这些巨大的光晕是形成的宇宙结构中最年轻的。事实上，质量最大的黑洞仍然带有导致它们形成的条件的印记，因此，它们被认为是研究宇宙几何和膨胀的重要探测器。然而，星系团作为宇宙探测器的使用，关键取决于我们对当地宇宙中的星系团为什么是这样的以及它们在早期是什么样子的理解程度。我的研究重点是开发现实模型，寻求解决上述问题。这种模型包括在强大的超级计算机上进行最先进的计算机模拟，以“虚拟地”复制宇宙137亿年的历史，并试图在模型框架内尽可能彻底地描述影响大质量光晕特征的相互关联的物理过程的令人难以置信的复杂网络。这些过程包括：(a)形成汇聚暗物质流的流动，并随着时间的推移产生越来越大的宇宙结构；(b)支配星系的形成，以及其中恒星的诞生、生命和死亡；(c)描述热气体对星系的作用，当后者通过前者时；对于那些(d)负责将恒星碎屑以及垂死恒星释放的爆炸能量从星系中传送到更广阔环境中的风的人；(e)调节超大质量黑洞在捕获和吸收周围气体时的反应；和更多。数值模拟是解开这张网的唯一方法。挑战在于确保模拟正确地捕获所涉及的物理，并且在当今计算限制所施加的约束下做到这一点需要独创性，创造力和洞察力。

Massive cosmic halos, a category that includes the most massive galaxies in the universe as well as galaxy groups and clusters, are remarkable systems. With masses ranging from an equivalent of 10,000 billion to a mind-boggling million billion suns, these halos are the largest, most massive gravitationally bound objects in the cosmos. The majority of their mass is dark matter. Of the visible matter that comprises these systems, the bulk is in the form of million degrees (or more) hot, X-ray emitting gas. The halos host gargantuan black holes that feed off the ambient gas and propel powerful jets that extend out a hundred thousand light-years or more. How did these systems we observe today form? What processes have shaped them? One reason why these are pressing questions is that the massive halos collectively host >50% of the galaxies in the universe and it is just not possible to explain why the observed galaxies exhibit the properties they do without knowing how a significant fraction's evolution is impacted by the extreme environment they reside in. Another reason is that the massive halos are the youngest of the cosmic structures to have formed. In fact, the most massive still bear the imprints of the conditions that led to their formation and therefore, have been identified as important probes of the geometry and the expansion of the universe. The use of galaxy clusters as cosmological probes, however, depends critically on how well we understand why clusters in the local universe look the way they do, and what they looked like at an earlier epoch. My research focuses on developing realistic model that seeks to address the above issues. This modeling involves carrying out state-of-the-art computer simulations on powerful supercomputers to replicate "virtually" the universe's 13.7 billion year history and attempt to describe, as thoroughly as possible within the framework of the model, the incredibly complex web of inter-related physical processes that influence the characteristics of the massive halos. These processes range from those that (a) shape the flow of convergent dark matter flows and give rise to increasingly larger cosmic structures with time; (b) govern the formation of galaxies, and the birth, life and death of stars therein; and (c) describe the action of the hot gas on the galaxies as the latter speed through the former; to those that (d) are responsible for winds that transport stellar detritus as well as the explosive energy released by dying stars out of the galaxies and into the wider environment; (e) regulate the response of supermassive black holes as they capture and draw in gas from their surroundings; and more. Numerical simulations are the only way of unraveling this web. The challenge lies in ensuring that the simulations correctly capture the physics involved, and doing so within the constraints imposed by today's computational limitations requires ingenuity, creativity and insight.