Eric Poisson Department of Physics University of Guelph Guelph, Ontario, N1G 2W1 (519) 824-4120 x53991
	Eric Poisson Department of Physics University of Guelph

Tidal heating of black holes

It is well known that Io's spectacular volcanic activity is caused by gravitational tidal heating: The tidal forces supplied by Jupiter's gravity do work on Io and increase its internal energy, leading to a hot interior and volcanism. It is perhaps less well known that a black hole also can be heated by an external tidal field...

In the first part of this talk I describe, within the context of Newtonian physics, how an external tidal field does work on an idealized astronomical body. And I explain how the acquired internal energy is dissipated as heat by the body's viscosity. In the case of Io, it is this heat which is ultimately responsible for the volcanic activity. In the second part of this talk I turn to the relativistic physics of a tidally-distorted black hole. Introducing the laws of black-hole thermodynamics I show that a black hole subjected to an external tidal field (supplied, for example, by a companion body) increases its mass (internal energy) and surface area (entropy). The growth of the black hole is produced entirely by the tidal interaction, and it occurs even in the complete absence of matter crossing the event horizon. In the third part of this talk I explain how the tidal heating of black holes can have measurable effects in the context of gravitational-wave astronomy.

This talk is intended for a general physics audience.

Tidal distortion of nonrotating black holes

In this talk I describe my recent work on the tidal distortion of a nonrotating black hole. In the first part of the talk I present the metric of such a black hole, which is expressed in a light-cone coordinate system that penetrates the event horizon and possesses a clear geometrical meaning. The metric is written as an expansion in powers of r/R << 1, where r is a measure of distance from the black hole and R is the local radius of curvature of the external spacetime; this is assumed to be much larger than M, the mass of the black hole. The metric is calculated up to a remainder of order (r/R)^4, and it depends on a family of tidal gravitational fields which characterize the hole's local environment.

In the second part of the talk I discuss the induced quadrupole moment of a tidally distorted black hole. I show that an operational definition of this quantity in terms of the tidal heating of the event horizon leads to an ambiguous result. This conclusion agrees with arguments presented recently by Fang and Lovelace. I further show that this conclusion emerges also in the context of a tidally distorted viscous sphere in Newtonian gravity.

This talk is fairly technical and is intended for an expert audience.

The gravitational self-force

The gravitational self-force describes the effect of a particle's own field on its motion; while the motion is geodesic in the test-mass limit, it is accelerated to first-order in the particle's mass. I will review the foundations of the self-force, and show how an infinite field can be unambiguously decomposed into a singular piece that exerts no force, and a smooth remainder that is responsible for the acceleration. I will also describe the recent effort, by a number of workers, to compute the self-force in the case of a small mass moving in the field of a much more massive black hole.

The context of this work is provided by the Laser Interferometer Space Antenna, which will be sensitive to low-frequency gravitational waves. Among the sources for this detector is the motion of small compact objects around massive (galactic) black holes. To calculate the waves emitted by such systems requires a detailed understanding of the motion, beyond the test-mass approximation.

This talk is fairly technical and is intended for an expert audience.

Wave propagation in curved spacetime: Hearing the shape of a black hole and the geometry of the Universe

In this talk I discuss some aspects of the propagation of gravitational waves in curved spacetime, in the context of the near-future detection of these waves by interferometric detectors such as LIGO and LISA. I first introduce a specific source of gravitational radiation: the inspiral, and ultimate capture, of a small body moving around a much larger black hole. I then explain how a precise measurement of the waves emitted by this system can reveal the detailed shape of the black hole, and how it might be possible (at least in principle) to also determine the geometry of the Universe.

This talk is intended for a general physics audience.