  We study aggregation driven by a localized source of monomers. The densities
become stationary and have algebraic tails far away from the source. We show
that in a model with mass-independent reaction rates and diffusion
coefficients, the density of monomers decays as $r^{-\beta(d)}$ in $d$
dimensions. The decay exponent has irrational values in physically relevant
dimensions: $\beta(3)=(\sqrt{17}+1)/2$ and $\beta(2)=\sqrt{8}$. We also study
Brownian coagulation with a localized source and establish the behavior of the
total cluster density and the total number of of clusters in the system. The
latter quantity exhibits a logarithmic growth with time.
