Nonlinear Damping of Tides in Stellar and Planetary Systems

菲利普·阿拉斯博士（弗吉尼亚大学）和合作者将研究双星通过潮汐损失的能量。在密近双星系统中，引力潮的耗散作用是使自转同步和轨道圆化。尽管几十年来进行了大量的观测和理论研究，流体物体中潮汐耗散的物理机制仍然是一个谜。基于物理动机的精确潮汐理论对于理解密近双星的起源、它们随后的轨道演化以及由于潮汐加热而引起的热演化至关重要。潮汐耗散的理论在广泛的系统中得到应用，从系外行星的生存，到包含类太阳星星的双星的圆化，再到作为强引力波源的致密双星的命运。以前对潮汐耗散的研究假设流动是层流的，大部分关注的是线性阻尼机制，如辐射扩散或对流区产生的湍流粘性。这样的研究在数量级上无法产生解释所观察到的系统所需的耗散水平。该研究小组最近对潮汐的研究发现，线性潮汐流是不稳定的，导致小尺度波浪和潮汐诱导湍流的增长。本质上，层流常常被假定为不存在的情况下，它被采用的类型。非线性阻尼从这个潮汐引起的湍流提供了一个很有前途的替代传统的线性阻尼mechanism.Authors将发展的非线性潮汐理论的研究，为每一种类型的恒星或行星结构的利益，稳定性的线性潮汐流，潮汐引起的湍流，同步和循环率，和深度相关的内部加热。他们的潮汐耗散计算主要应用于太阳系外气体巨行星、太阳型双星以及包含白色矮星或中子星的吸气双星。由于潮汐在近距离双星中的普遍重要性，计划中的研究将对天体物理学中的各种问题产生影响。它将阐明太阳系外行星系统和恒星双星演化中长期存在的难题，并将阐明潮汐加热对热彗星内部结构的影响。对近距离白色矮星和中子星星双星的研究将确定潮汐是否能改变这些系统的轨道演化，这对电磁波和引力波测量都有重要意义。该项目涉及一名博士后和一名研究生的培训。该小组将向天文学界和公众传播他们的研究成果。

Dr. Philip Arras (University of Virginia) and collaborators will investigate the energy lost by binary stars via tides. Dissipation of gravitational tides in close binary systems acts to synchronize the rotation and circularize the orbit. Despite decades of intense observational and theoretical study, the physical mechanism for tidal dissipation in fluid objects remains a mystery. Physically motivated, accurate theories of tides are crucial to understand the origin of close binaries, their subsequent orbital evolution, and thermal evolution due to tidal heating. Theories of tidal dissipation find application in a broad range of systems, from the survival of exoplanets, to the circularization of binaries containing a Sun-like star, to the fate of compact binaries which are strong gravitational wave sources.Previous investigations of tidal dissipation assumed the flow is laminar and much of the focus was on linear damping mechanisms, such as radiative diffusion or turbulent viscosity arising in convection zones. Such studies fail by orders of magnitude to produce the level of dissipation needed to explain the observed systems. In recent studies of tides by this research team, it was discovered that the linear tidal flow is unstable, leading to the growth of small scale waves and tidally-induced turbulence. In essence, the laminar flow often assumed does not exist for the types of situations in which it is employed. Nonlinear damping from this tidally-induced turbulence provides a promising alternative to conventional linear damping mechanisms.The authors will develop the theory of nonlinear tides by studying, for each type of stellar or planetary structure of interest, the stability of linear tidal flow, tidally induced turbulence, synchronization and circularization rates, and depth-dependent internal heating. The primary applications of their calculations on tidal dissipation are to close-in gas giant extrasolar planets, solar-type binaries, and inspiraling binaries containing white dwarfs or neutron stars.The planned research will have impact on a wide variety of problems in astrophysics, due to the ubiquitous importance of tides in close binaries. It will shed light on longstanding puzzles in the evolution of extrasolar planetary systems and stellar binaries, and will elucidate the impact of tidal heating on the internal structure of Hot Jupiters. The work on close white dwarf and neutron star binaries will determine if tides can alter the orbital evolution of these systems, which has important implications for both electromagnetic and gravitational wave measurements. This project involves training of a postdoc and a graduate student. The team will disseminate the results from their research to the astronomical community and to general public.