Angular momentum transport and magnetism in stars and planets

恒星和行星中的角动量传输和磁性

• 批准号: 2573723
• 金额: --
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2573723
• 关键词: Angular; momentum; transport; magnetism; stars

When motions occur inside a star or planet, they can transport both heat and angular momentum. Because these motions - whether convective, wave-like, or some mix of the two - are ubiquitous, so is angular momentum transport. As a consequence, different parts of planetary and stellar interiors often rotate at different rates, with profound consequences for the mixing of material, the generation of stellar and planetary magnetism, and the end-states of stellar evolution. The spin rates of massive stellar cores, for example, may influence the nature of the compact remnant that occurs after core collapse, and strongly affect the natal spin rates of black holes, now being probed by gravitational wave astronomy.Recent observations have revealed that our current theoretical understanding of the angular momentum transport - and hence of differential rotation - has some major shortcomings. For example, asteroseismic measurements of the rotation rates of stars have demonstrated that evolved stellar cores rotate much slower than simple theoretical models of the transport would predict. Major puzzles have come from observations of objects in our own Solar System, too: for example, the Juno mission has recently revealed that Jupiter's observed banded zonal flows persist only throughout the outermost few percent of the planet, with a transition to nearly solid-body rotation below this. This has been widely interpreted as arising from magnetic field feedbacks on the flow, with the observed transition to solid-body rotation occurring at roughly the depth where the conductivity becomes high enough for the field to couple to the motion. This is in sharp contrast to the Sun, where conductivity is high throughout and yet a substantial shear is maintained. The different outcomes likely reflect the different regimes of flow speed and rotation rate in the two objects -- but a consistent theory of angular momentum transport in magnetised convection zones that can explain both outcomes in any detail has not yet been forthcoming.In this project, you will use a combination of 3D numerical simulations, analytical theory, and 1D modeling to study the angular momentum transport achieved by flows in stellar and planetary interiors. Along the way, you will study the magnetic fields that are generated by the flows (and which in turn also affect the momentum transport). Your precise role will depend to some extent on your own background and interests. Between us (i.e., you, me, and various collaborators), we will aim to conduct a set of 3D simulations in both local (Cartesian) and global (spherical) geometries, and compare the resulting transport to that envisioned in recently-developed semi-analytical theories. This will involve using massively parallel computers based here in Exeter, and elsewhere. We will use the simulations to test and calibrate the semi-analytical prescriptions, and ultimately attempt to incorporate these into a 1D evolutionary model of structure and evolution. We may also, more speculatively, explore the possibility that the heat and angular momentum transport, and field generation, can be solved for self-consistently, in parallel with the evolutionary calculation, essentially by solving a highly simplified set of fluid equations for a finite number of spatial modes.This project would be most suitable for someone with an interest in astrophysical fluid dynamics, as applied to stars or planets. It will require some level of proficiency with computation, so at least a modest amount of programming experience (and a basic familiarity with Unix-based environments) would be helpful. Some prior familiarity with fluid dynamics/MHD would be great, but is not essential.

当运动发生在恒星或行星内时，它们可以同时运输热量和角动量。因为这些运动 - 无论对流，波浪状还是两者的某种混合物 - 无处不在，所以角动量转运也是如此。结果，行星和恒星内部的不同部分通常以不同的速度旋转，对材料的混合，恒星和行星磁性的产生以及恒星进化的末端状态产生了深远的影响。例如，巨大恒星核的自旋速率可能会影响核心崩溃后发生的紧凑型残留物的性质，并强烈影响黑洞的自然自旋速率，现在被引力波天文学所探测。当前的观察结果表明，我们目前对近距离运输的理论理解 - 和差异的差异 - 有一些主要的旋转。例如，恒星旋转速率的星号测量结果表明，进化的恒星芯的旋转速度比传输的简单理论模型慢得多。主要难题也来自对我们自己的太阳系中的物体的观察结果：例如，朱诺的任务最近透露，木星观察到的带状层流仅在地球的最外层百分比中持续存在，并且在此下方的几乎固体旋转过渡。这已被广泛解释为是由于流动的磁场反馈而产生的，观察到的向实体旋转的过渡大致在电导率变得足够高的深度上发生，以使该场将其与运动搭配。这与太阳形成了鲜明的对比，在阳光下，电导率在整个过程中都很高，但保持了大量的剪切。不同的结果可能反映了两个物体中流速和旋转速度的不同条件 - 但是在磁性对流区域中，角动量传输的一致理论尚未在任何详细信息中解释这两种结果。在该项目中，您将使用3D数值模拟，分析理论以及1D模型的旋转效果来实现3D数值模拟的组合，以实现Angear flude and teelder teelder starter start art start art start start start start start start start start start。一路上，您将研究流量产生的磁场（进而影响动量传输）。您的确切角色将在某种程度上取决于您自己的背景和兴趣。在我们之间（即您，我和各种合作者）之间，我们的目标是在本地（笛卡尔）和全球（球形）几何形状中进行一系列3D模拟，并将所得的运输与最近开发的半分析理论所设想的运输。这将涉及使用基于埃克塞特和其他地方的大规模并行计算机。我们将使用模拟测试和校准半分析处方，并最终尝试将它们纳入结构和进化的一维进化模型。我们还可以更猜测，探索热量和角动量传输和田间产生的可能性，可以与进化计算平行地求解，从本质上讲，通过解决有限数量的空间模式的高度简化流体方程。这些项目最适合于对人体流体动态的感兴趣，或者适合于人体流体动力学的人。它将需要一定程度的熟练程度，因此至少有一定数量的编程体验（以及对基于UNIX的环境的基本熟悉）将很有帮助。对流体动力/MHD的一些事先熟悉会很棒，但不是必需的。