  We have examined the effect of slow growth of a central black hole on
spherical galaxies that obey S\'ersic or $R^{1/m}$ surface-brightness profiles.
During such growth the actions of each stellar orbit are conserved, which
allows us to compute the final distribution function if we assume that the
initial distribution function is isotropic. We find that black-hole growth
leads to a central cusp or ``excess light', in which the surface brightness
varies with radius as $R^{-1.3}$ (with a weak dependence on S\'ersic index
$m$), the line-of-sight velocity dispersion varies as $R^{-1/2}$, and the
velocity anisotropy is $\beta\simeq -0.24$ to $-0.28$ depending on $m$. The
excess stellar mass in the cusp scales approximately linearly with the
black-hole mass, and is typically 0.5--0.85 times the black-hole mass. This
process may strongly influence the structure of nuclear star clusters if they
contain black holes.
