Nonlinear Damping of Tides in Stellar and Planetary Systems

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

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.