  Disk accretion may be the fundamental astrophysical process. Stars and
planets form through the accretion of gas in a disk. Black holes and galaxies
co-evolve through efficient disk accretion onto the central supermassive black
hole. Indeed, approximately 20 percent of the ionizing radiation in the
universe is supplied by disk accretion onto black holes. And large-scale
structures - galaxy clusters - are dramatically affected by the relativistic
jets that result from accretion onto black holes. Yet, we are still searching
for observational answers to some very basic questions that underlie all
aspects of the feedback between black holes and their host galaxies: How do
disks transfer angular momentum to deliver gas onto compact objects? How do
accretion disks launch winds and jets?
