Dots in a murky sky.

A familiar joke in the astronomical world is that you can sleep through somebody's seminar or conference talk and still make the speaker sweat by nodding awake long enough to ask, "Have you considered the effects of dust?" The speaker likely will mutter, "Well, we realize of course that dust may well be important, but for now we have assumed that its effect on our observations is negligible." Ignoring dust, or the complexities of its effects, is a mistake astronomers have made many times. The field may be going through another cycle as it attempts to understand active galactic nuclei (AGN)-bright regions at the centers of galaxies that are thought to be powered by accretion of gas onto a supermassive black hole. By the time the cycle is complete, we may have a better understanding of the growth of black holes, the growth of galaxies, and the properties of dust itself.