  The exponential blueshift associated with the event horizon of a black hole
makes conformal symmetry play a fundamental role in accounting for its thermal
properties. Using a derivation based on two-point functions, we show that the
spectrum of thermal radiation of scalar particles by Kerr (and Schwarzschild)
black holes can be explicitly derived on the basis of a $2$-dimensional
conformal symmetry arising in the wave equation near the horizon. This result
reinforces the recently conjectured relation between Kerr geometry and a
$2$-dimensional conformal field theory.
