Accretion disc physics: breaking the symmetries

我的研究与被称为吸积盘的天文系统有关。在这些系统中，一个气体盘在中心恒星或黑洞的重力场中绕轨道运行，通过其旋转的离心效应来平衡恒星的引力。我们的太阳系是由这样一个圆盘形成的：首先，中心附近的一些旋转气体形成了太阳本身，然后，一些气体进一步形成了行星，这些行星今天仍在以相同的轨道旋转。吸积盘也是大量其他天体物理现象的基本组成部分。在黑洞的引力作用下，气体会形成圆盘，其原因与行星围绕太阳运行的原因相同。盘内的气体从盘内螺旋状缓慢地进入黑洞，在此过程中被加热并发光。当它落在（或“吸积”）黑洞上时，它会以光的形式释放出高达40%的静止质量能量，我们可以观察到。这使得吸积黑洞成为宇宙中最明亮的物体。我们可以在接近整个宇宙的距离上观察到它们的吸积盘。它们发出的光几乎经历了整个宇宙的年龄才到达我们这里，所以它们向我们展示了第一批恒星和星系形成时的情况。理解吸积盘对于理解整个宇宙至关重要。但我们目前试图描绘它们的方式太简单了。即使在今天，几乎所有关于圆盘的讨论都假设——本质上是为了方便——它们具有尽可能简单的几何形状，气体在一个平面上围绕中心物体旋转，并在光滑的圆形轨道上运行。这种方法使我们无法考虑观察到的现象背后的实际物理效应。我的研究旨在通过放松对初始条件和输入物理的假设来消除这些对称性。在过去的几年里，这种方法已经揭示了新的圆盘过程，这些过程为以前观察到的神秘现象提供了令人信服的解释。我建议用这种第一原理方法来模拟更完整的系统。使用最先进的数值方法，这项工作将产生广泛的影响，并对该领域的标准图景构成重大改变。它将连接来自大量新观测设施的数据，包括空间和地面。我预计它将极大地改变我们理解各种紧迫问题的方式，比如恒星和行星是如何形成的，以及黑洞是如何增长到比太阳大数百万倍的质量的。

My research is concerned with astronomical systems called accretion discs. In these systems, a disc of gas orbits in the gravity field of a central star or black hole, balancing the gravitational pull of the star by the centrifugal effect of its rotation. Our Solar System formed out of a disc like this: first some of the rotating gas near the centre made the Sun itself, and then some of the gas further out formed planets, and these continue to revolve in the same orbits today.Accretion discs are the essential ingredient for a vast range of other astrophysical phenomena as well. Gas falling in the gravity of a black hole forms a disc for the same reason that planets orbit our Sun. The gas in the disc spirals slowly on to a black hole from a disc, heating up and emitting light as it does. As it falls (or "accretes") on to the black hole it emits up to 40% of its rest mass energy as light which we can observe. This makes accreting black holes the most luminous objects in the Universe. We can observe their accretion discs at distances approaching the entire extent of the Universe. Their light has taken almost the entire age of the Universe to reach us, so they show us how things were when the first stars and galaxies were forming. Understanding accretion discs is essential to understanding the Universe as a whole. But the way we currently try to picture them is too simple.Even today almost every discussion of discs assumes - essentially for convenience - that they have the simplest possible geometry, with gas orbiting the central object in a single plane, and on smooth circular orbits. This approach prevents us considering real physical effects which underly observed phenomena.My research aims to remove these symmetries by relaxing assumptions made about initial conditions and input physics. This approach has already revealed new disc processes in the last couple of years, and these offer cogent explanations of previously mysterious observed phenomena. I propose to simulate more complete systems with this first principles approach. Using state-of-the-art numerical methods, this work will have a wide impact, and constitute a big change to the standard picture of the field. It will connect to data from a vast range of new observing facilities, both space and ground based. I anticipate that it will significantly change the way we understand various pressing problems, such has how stars and planets form, and how black holes can grow to masses many millions of times greater than the Sun.