Schiminovich and I hope to detect intergalactic scattering with our quasar–photon cross-correlations. In order to make this detection, which will require precision, we need to create a differential experiment. The first difference is between mean quasars and mean white dwarfs. The white dwarfs are so close, they should have essentially no scattering (or scattering local to the observatory that is shared with the quasars). I made the white-dwarf–photon cross-correlations this weekend.
The mean white-dwarf image is probably interesting in its own right, if I broke down the white dwarfs by type and temperature, because they would provide extremely high signal-to-noise GALEX information. Does anyone want that?