Evolution of dust grain size distribution and grain porosity in galaxies

The radiative properties of interstellar dust are affected not only by the grain size distribution but also porosity. We develop a model for evolution size-dependent porosity and over entire history galaxy evolution. include stellar production, supernova destruction, shattering, coagulation, accretion. Coagulation is {assumed to be} source use one-zone with constant dense gas fraction ($\eta_\mathrm{dense}$), which regulates balance between shattering coagulation. find that develops after small grains sufficiently created interplay accretion (at age $t\sim 1$ Gyr star formation time-scale $\tau_\mathrm{SF}=5$ Gyr) coagulated. filling factor drops down 0.3 at radii $\sim 0.03~\mu$m $\eta_\mathrm{dense}=0.5$. more porous smaller $\eta_\mathrm{dense}$ because grains, from coagulated form, abundant. calculate extinction curves based on above results. steepens curve significantly silicate, much amorphous carbon. increases collisional cross-sections produces slightly large through enhanced coagulation; however, does necessarily become flatter steepening effect discuss implication our results Milky Way curve.