Astrophysical fluid bodies that orbit close to one another induce tidal distortions and flows that are subject to dissipative processes. The spin and orbital motions undergo a coupled evolution over astronomical timescales, which is relevant for many types of binary star, short-period extrasolar planetary systems, and the satellites of the giant planets in the Solar System. I review the principal mechanisms that have been discussed for tidal dissipation in stars and giant planets in both linear and nonlinear regimes. I also compare the expectations based on theoretical models with recent observational findings.

We critically assess the role of the Blandford-Znajek mechanism in the powering of outflows from accretion disk-fed black holes. We argue that there is no reason to suppose that the magnetic field threading the central spinning black hole differs significantly in strength from that threading the central regions of the disk. In this case, we show that the electromagnetic output from the inner disk regions is expected in general to dominate over that from the hole. Thus the spin (or not) of the hole is probably irrelevant to the expected electromagnetic power output from the system. We also point out that the strength of the poloidal field in the center of a standard accretion disk has been generally overestimated, and discuss scenarios which might give rise to more significant central poloidal fields.Comment: 5 pages, to be published in the Astrophysical Journa

Tidal friction is thought to be important in determining the long-term spin-orbit evolution of short-period extrasolar planetary systems. Using a sim

We study the radiation-driven warping of accretion discs in the context of X-ray binaries. The latest evolutionary equations are adopted, which exten

We discuss the linear response to low-frequency tidal forcing of fluid bodies that are slowly and uniformly rotating, are neutrally stratified and may contain a solid or fluid core. This problem may be regarded as a simplified model of astrophysical tides in convective regions of stars and giant planets. The response can be separated into non-wavelike and wavelike parts, where the former is related instantaneously to the tidal potential and the latter may involve resonances or other singularities. The imaginary part of the potential Love number of the body, which is directly related to the rates of energy and angular momentum exchange in the tidal interaction and to the rate of dissipation of energy, may have a complicated dependence on the tidal frequency. However, a certain frequency average of this quantity is independent of the dissipative properties of the fluid and can be determined by means of an impulse calculation. The result is a strongly increasing function of the size of the core when the tidal potential is a sectoral harmonic, especially when the body is not strongly centrally condensed. However, the same is not true for tesseral harmonics, which receive a richer response and may therefore be important in determining tidal evolution even though they are usually subdominant in the expansion of the tidal potential. We also discuss analytically the low-frequency response of a slowly rotating homogeneous fluid body to tidal potentials proportional to spherical harmonics of degrees less than five. Tesseral harmonics of degrees greater than two, such as are present in the case of a spin–orbit misalignment, can resonate with inertial modes of the full sphere, leading to an enhanced tidal interaction.

A planet of low mass orbiting in a two-dimensional gaseous disc generates a one-armed spiral wake. We explain this phenomenon as the result of constr