Stellar Dynamics Near Black Holes

特里梅因博士将开发新的方法来研究星系中心黑洞周围的恒星系统，这些星系的质量比任何一颗恒星都要大得多。恒星轨道的变化会导致x射线耀斑，因为被潮汐破坏的恒星会落入黑洞，并导致紧凑的物体，如恒星或较小的黑洞，缓慢地螺旋进入黑洞。如果一颗双星离黑洞太近，它的一个成员可能会被射出星系，成为超高速恒星，而另一个则被紧紧地束缚在黑洞上。新方法将平均每颗恒星在其轨道上的快速运动，并通过长期哈密顿量的基函数展开来表示所有其他恒星对每颗恒星的引力，用轨道元素或作用角变量来表示每颗恒星。在进一步的简化中，每颗恒星的角动量通常比它的能量变化快得多；因此，在轨道能量冻结的约束下，可以探索恒星盘的热力学平衡。初步研究表明，黑洞周围的恒星盘可能会经历“相变”，变得不平衡。这种新方法将比竞争对手的方法快得多，并提供更深入的物理洞察。研究生将通过参与研究而得到训练。这项工作将使人们更深入地了解星系核围绕其中心黑洞的发展方式，这是星系形成的基本问题之一。特里梅因博士是被大量引用的研究生论文《银河动力学》（Galactic Dynamics）的合著者；第二版刚刚出版。这项工作是由美国国家科学基金会天文科学部和美国国家航空航天局天体物理理论计划共同资助的。

Dr. Tremaine will develop new methods to study stellar systems around black holes at the centers of galaxies, which are much more massive than any individual star. Changes in the stellar orbits can result in X-ray flares as tidally-disrupted stars fall into the black hole, and cause compact objects such as stars or smaller black holes to spiral slowly into the black hole. If a binary star gets too near the black hole, one of its members can be shot out of the galaxy as a hypervelocity star while the other becomes tightly bound to the black hole. The new method will average over the fast motion of each star in its orbit, and represent the tug on each star of all the others with a basis-function expansion of the secular Hamiltonian, representing each star by its orbital elements or action-angle variables. In a further simplification, the angular momentum of each star usually changes much faster than its energy; so the thermodynamic equilibrium of a disk of stars can be explored under the constraint that the orbital energies are frozen. Preliminary work suggests that a disk of stars around a black hole may undergo a 'phase transition' to become lopsided. This new method will be significantly faster than competing approaches, and offer deeper physical insight.A graduate student will be trained by participating in the research. This work will give deeper insight into the way that the nuclei of galaxies develop around their central black holes, which is one of the fundamental problems of galaxy formation. Dr. Tremaine is co-author of the heavily-cited graduate-level text 'Galactic Dynamics'; a second edition has just been published. This work is jointly funded by the NSF Division of Astronomical Sciences and NASA's Astrophysics Theory Program.