The Oort Cloud in the Galactic Context

由于奥尔特彗星云延伸到距离最近的恒星三分之一的距离，因此银河系环境和这颗彗星云的演化之间有很强的联系。事实上，观测到的新彗星的半长轴分布的尖峰是由于经过的恒星和整个银河潮汐对更远的彗星产生了更大的扭矩。鉴于这种联系，由于太阳在银河系中的轨道和太阳从形成环境中漂移而导致的银河系环境的变化，将对奥尔特云中彗星的分布和随后这些彗星向内太阳系的输送产生重大影响。在这个研究计划中，Thomas Quinn博士和他的同事将首先在假设一些不同的恒星形成环境的情况下，研究太阳系45亿年历史上奥尔特云的形成和演化。太阳很可能是在一个密集的星团中形成的，但离开星团的实际密度和时间尺度尚不确定。这项工作将考虑一些恒星密度和星团消散时间，并将产生的奥尔特云和随后的彗星簇射强度与没有星团环境的对照情况进行比较。然而，太阳系并不在银河系中占有一席之地。因此，随着太阳在银河系中的轨道演变，这项研究将继续纳入银河系扰动的变化。这将在冷暗物质(CDM)宇宙中通过分级合并形成的宇宙学激励的银河系模型的背景下完成。这个模型已经使用研究小组的大规模并行宇宙学程序TRANSE进行了计算，并且该模型已经被证明产生了许多螺旋星系的观测特征。奥尔特云的演化将被计算出来，因为它感受到了存在于星系模型中的盘、旋臂和其他子结构中的气体、恒星和暗物质的扰动。这项研究将特别关注随后进入内太阳系的彗星流量的变化以及对地球冲击率的可能后果。自从白垩纪末的灭绝事件与彗星撞击之间建立了联系以来，彗星与古生物学和地质学学科之间已经建立了强有力的联系。奎恩博士和获得该奖项资助的研究生都是华盛顿大学天体生物学项目的一部分，因此，他们将把他们的研究与该项目中生物学家和地质学家所做的工作联系起来。轨道动力学和彗星之间的联系也吸引了广大公众。我们的行星系统的起源，它如何融入整个银河系，以及它对生命的影响等问题，都是吸引公众进入动力学研究结果的问题。奎恩博士和这位研究生将把他们的研究成果纳入他们的本科课程和公开讲座中。

AST 0709191QuinnSince the Oort comet cloud extends to 1/3 the distance to the nearest stars, there is a strong connection between the galactic environment and the evolution of this cloud. Indeed the spike in semi-major axis distribution of observed new comets is due to the more significant torquing of more distant comets by passing stars and the Galactic tide as a whole. Given this connection, changes in the Galactic environment due to the orbit of the Sun in the Galaxy and drifting of the Sun from its formation environment will have significant effect on the distribution of comets in the Oort cloud and the subsequent delivery of those comets to the inner Solar System.In this research program, Dr. Thomas Quinn and colleagues will first study the formation and evolution of the Oort Cloud over the 4.5 billion years of the Solar System's history assuming a number of different star forming environments. It is quite likely that the Sun formed in a dense stellar cluster, but the actual densities and timescale for leaving the cluster are uncertain. The work will consider a number of stellar densities and cluster dissipation timescales and compare the resulting Oort Cloud and subsequent comet shower strength with a control case with no cluster environment. The Solar System, however, does not occupy a static place within the Galaxy. The research will therefore go on to incorporate changes in Galactic perturbations as the orbit of the Sun in the Galaxy evolves. This will be accomplished in the context of a cosmologically motivated model of the Galaxy formed via hierarchical merging in a Cold Dark Matter (CDM) Universe. This model has been calculated using the research group's massively parallel cosmological code, GASOLINE, and the model has been shown to produce many observed characteristics of spiral galaxies. The evolution of the Oort Cloud will be calculated as it feels the perturbations of the gas, stars, and dark matter from the disk, spiral arms and other substructure that exists in the galaxy model. The study will pay particular attention to the subsequent changes to the comet flux into the inner Solar System and possible consequences for impact rates on the Earth.Ever since the connection was made between the extinction event at the end of the Cretaceous and a comet impact, a strong connection has been made between comets and the disciplines of Paleontology and Geology. Both Dr. Quinn and the graduate student supported on this award are part of the University of Washington's Astrobiology program and therefore, will be connecting their research to work done by biologists and geologists in that program. The connection between orbital dynamics and comets also engages the public at large. The issues of the origin of our planetary system, how it fits into the galaxy as a whole and the implications for life are issues that draw the public into the results of dynamical research. Dr. Quinn and the graduate student will incorporate their results into their undergraduate classes and public lectures.***