Tidal Love Numbers of Kerr Black Holes
Résumé
The open question of whether a Kerr black hole can become tidally deformed or not has profound implications for fundamental physics and gravitational-wave astronomy. We consider a Kerr black hole embedded in a weak and slowly varying, but otherwise arbitrary, multipolar tidal environment. By solving the static Teukolsky equation for the gauge-invariant Weyl scalar ψ0 and by reconstructing the corresponding metric perturbation in an ingoing radiation gauge, for a general harmonic index ℓ, we compute the linear response of a Kerr black hole to the tidal field. This linear response vanishes identically for a Schwarzschild black hole and for an axisymmetric perturbation of a spinning black hole. For a nonaxisymmetric perturbation of a spinning black hole, however, the linear response does not vanish, and it contributes to the Geroch-Hansen multipole moments of the perturbed Kerr geometry. As an application, we compute explicitly the rotational black hole tidal Love numbers that couple the induced quadrupole moments to the quadrupolar tidal fields, to linear order in the black hole spin, and we introduce the corresponding notion of a tidal Love tensor. Finally, we show that those induced quadrupole moments are closely related to the well-known physical phenomenon of tidal torquing of a spinning body interacting with a tidal gravitational environment.
Mots clés
General relativity
alternative theories of gravity
black hole: Kerr
black hole: Schwarzschild
black hole: rotation
black hole: spin
metric: perturbation
space-time: perturbation
radiation: gauge
scalar: Weyl
invariance: gauge
symmetry: axial
gravitational radiation
Teukolsky equation
gravitation
black hole: deformation
moment: multipole
space-time: geometry
gravitation: potential
star: compact
curvature: scalar
boundary condition
transformation: conformal